Field emission—the quantum-mechanical tunneling of electrons from the surface of a material into vacuum by means of a strong electric field—has been studied for over a century. However, the usage of devices based on this mechanism has been limited to a handful of niche applications such as high-power RF systems and field emission displays. The preference for solid-state devices relies on their low cost, long lifetimes, reduced power consumption, ease of integrability, and simple and scalable fabrication. Nonetheless, with the advent of modern fabrication techniques, it has been possible to build field emission devices with nanoscale dimensions that offer several advantages over traditional semiconductor devices. The use of vacuum allows ballistic transport with no lattice scattering. As device capacitance can be engineered by tuning the geometry, these devices are appealing for high-frequency operation. Vacuum is also inherently immune to harsh operating conditions such as high temperature and radiation, which is desirable for aerospace, nuclear, and military applications. In addition, even though field emission requires substantial electric fields, by exploiting the nanoscale gaps that can be easily fabricated with state-of-the-art lithographic capabilities, we can expect operating voltages comparable to CMOS. Thus, vacuum emission devices have the potential to greatly improve upon the limitations of current technologies.
In this work, we experimentally demonstrate various design paradigms to develop nanoscale field emission devices for high-temperature environments and high-frequency operation. First, we propose suspended lateral two- and four-terminal devices. By removing the underlying solid substrate, we aim to increase the resistance of the leakage current pathways that emerge at elevated temperatures. Tungsten is the chosen electrode material due to its low work function and ability to withstand high temperatures. Our next architecture consists of a multi-tip two-terminal array, which exclusively relies on the inherent fast response of field emission. Due to the strong non-linearity in the emission characteristic, frequency mixing is measured. Lastly, we combine field emission with plasmonics to conceive devices that can be modulated both electrically and optically at telecommunication wavelength. By taking advantage of the strong confinement and significant optical field enhancement of surface plasmon polaritons, we seek to minimize the applied voltages required for field emission as well as the necessary laser powers for photoemission towards the development of high-speed, low-power, nanoscale optoelectronic systems.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/7GHS-NX49, author = {Adalian, Dvin Artashes-Boghos}, title = {Development and Dynamics of Microfabricated Enzymatic Biosensors}, school = {California Institute of Technology}, year = {2019}, doi = {10.7907/7GHS-NX49}, url = {https://resolver.caltech.edu/CaltechTHESIS:06102019-031412552}, abstract = {We have extended the application of microfabrication techniques to all parts of electrochemical enzymatic sensor processing and characterized the behavior of the resulting new sensor geometries. Improved and parallelized enzyme immobilization techniques utilizing spin coating along with porous sputtered platinum barrier layers are implemented on microfabricated platinum electrodes on silicon wafer substrates as well as on millimeter-scale wireless CMOS potentiostats. Functional biosensor sensitivities and linear ranges were observed with multi-month lifetimes, demonstrating that the enzyme layer fabrication process is compatible with precise and massively parallelized CMOS fabrication, making further progress toward the production of low cost and low-tissue impact fully implantable miniaturized biosensors.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/Z94B2ZHZ, author = {Jones, William Maxwell}, title = {Nanoscale Field Emission Devices}, school = {California Institute of Technology}, year = {2018}, doi = {10.7907/Z94B2ZHZ}, url = {https://resolver.caltech.edu/CaltechTHESIS:12132017-132404589}, abstract = {This thesis outlines work done to produce in-plane nanoscale field emission devices. Field emission, the process of quantum tunneling electrons from a conductor into a vacuum, has been theorized as a device concept for almost as long as integrated circuits have existed. This is because the micro- and nanoscale dimensions of integrated circuits make field emission possible at modest voltages, and because the physics of field emission and conduction in a vacuum channel suggest that field emission devices can operate at extremely high frequencies and in harsh environments where CMOS devices face challenges. Yet despite many attempts to make practical field emission devices none have risen to the level of commercial products. These attempts were stymied by short lifetimes, high operating voltages, and the necessity for vacuum enclosure. In this thesis work, I outline how new fabrication technologies like high resolution electron beam lithography, atomic layer deposition, and refinement in reactive ion etching make lateral field emission devices with extremely short vacuum channels practical. The demonstrated devices can operate at near CMOS voltages and at atmospheric pressures, and are robust to emitting tip destruction. These devices are prime candidates for integration into demonstration circuits.
The second part of this thesis outlines work done in an emerging field to combine field emission with plasmonics for practical devices. The tunneling process in field emission depends exponentially on the magnitude of the instantaneous electric field, either static or time-varying, at the emitting surface. While it has long been known that using extremely powerful pulsed lasers one can field emit electrons from a metallic surface, the combination of plasmonics into a field emitting device has the potential to dramatically lower the incident optical power needed to produce field emission. This could enable extremely fast opto-electronic devices. This thesis presents work in progress to realize a plasmonically enhanced field emission opto-electronic modulator that is designed to operate at 1550 nm and is integratable with existing silicon photonics platforms.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/Z9RJ4GG4, author = {Sadek, Akram Sarwat}, title = {Wireless Nano and Molecular Scale Neural Interfacing}, school = {California Institute of Technology}, year = {2017}, doi = {10.7907/Z9RJ4GG4}, url = {https://resolver.caltech.edu/CaltechTHESIS:12162016-094948729}, abstract = {Nanoscale circuits and sensors built from silicon nanowires, carbon nanotubes and other devices will require methods for unobtrusive interconnection with the macroscopic world to fully realise their potential; the size of conventional wires precludes their integration into dense, miniature systems. The same wiring problem presents an obstacle in our attempts to understand the brain by means of massively deployed nanodevices, for multiplexed recording and stimulation in vivo. We report on a nanoelectromechanical system that ameliorates wiring constraints, enabling highly integrated sensors to be read in parallel through a single output. Its basis is an effect in piezoelectric nanomechanical resonators that allows sensitive, linear and real-time transduction of electrical potentials. We interface multiple signals through a mechanical Fourier transform using tuneable resonators of different frequency and extract the signals from the system optically. With this method we demonstrate the direct transduction of neuronal action potentials from an extracellular microelectrode. We further extend this approach to incorporate nanophotonics for an all-optical system, coupled via a single optical fibre. Here, the mechanical resonators are both driven and probed optically, but modulated locally by the voltage sensors via the piezoelectric effect. Such piezophotonic nanoelectromechanical systems may be integrated with nanophotonic resonators, allowing concordant multiplexing in both the radiofrequency and optical bandwidths. In principle, this would allow billions of sensor channels to be multiplexed on an optical fibre. With view to eventually integrating such technology into a neural probe, we develop fabrication methods for crafting wired silicon neural probes via photolithography and electron beam lithography. Finally, to complement recording, we propose novel ideas for wireless, multiplexed neural stimulation through the use of radiofrequency-sensitive molecular scale resonators.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/Z9P848V6, author = {Goldberg, Mark David}, title = {Development of Microfluidic Devices with the Use of Nanotechnology to Aid in the Analysis of Biological Systems Including Membrane Protein Separation, Single Cell Analysis, and Genetic Markers}, school = {California Institute of Technology}, year = {2015}, doi = {10.7907/Z9P848V6}, url = {https://resolver.caltech.edu/CaltechTHESIS:06022015-150554177}, abstract = {Computation technology has dramatically changed the world around us; you can hardly find an area where cell phones have not saturated the market, yet there is a significant lack of breakthroughs in the development to integrate the computer with biological environments. This is largely the result of the incompatibility of the materials used in both environments; biological environments and experiments tend to need aqueous environments. To help aid in these development chemists, engineers, physicists and biologists have begun to develop microfluidics to help bridge this divide. Unfortunately, the microfluidic devices required large external support equipment to run the device. This thesis presents a series of several microfluidic methods that can help integrate engineering and biology by exploiting nanotechnology to help push the field of microfluidics back to its intended purpose, small integrated biological and electrical devices. I demonstrate this goal by developing different methods and devices to (1) separate membrane bound proteins with the use of microfluidics, (2) use optical technology to make fiber optic cables into protein sensors, (3) generate new fluidic devices using semiconductor material to manipulate single cells, and (4) develop a new genetic microfluidic based diagnostic assay that works with current PCR methodology to provide faster and cheaper results. All of these methods and systems can be used as components to build a self-contained biomedical device.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/Z9D50JXC, author = {Homyk, Andrew P.}, title = {Scalable Methods for Deterministic Integration of Quantum Emitters in Photonic Crystal Cavities}, school = {California Institute of Technology}, year = {2015}, doi = {10.7907/Z9D50JXC}, url = {https://resolver.caltech.edu/CaltechTHESIS:06022015-141742970}, abstract = {We investigated four unique methods for achieving scalable, deterministic integration of quantum emitters into ultra-high Q{V photonic crystal cavities, including selective area heteroepitaxy, engineered photoemission from silicon nanostructures, wafer bonding and dimensional reduction of III-V quantum wells, and cavity-enhanced optical trapping. In these areas, we were able to demonstrate site-selective heteroepitaxy, size-tunable photoluminescence from silicon nanostructures, Purcell modification of QW emission spectra, and limits of cavity-enhanced optical trapping designs which exceed any reports in the literature and suggest the feasibility of capturing- and detecting nanostructures with dimensions below 10 nm. In addition to process scalability and the requirement for achieving accurate spectral- and spatial overlap between the emitter and cavity, these techniques paid specific attention to the ability to separate the cavity and emitter material systems in order to allow optimal selection of these independently, and eventually enable monolithic integration with other photonic and electronic circuitry.
We also developed an analytic photonic crystal design process yielding optimized cavity tapers with minimal computational effort, and reported on a general cavity modification which exhibits improved fabrication tolerance by relying exclusively on positional- rather than dimensional tapering. We compared several experimental coupling techniques for device characterization. Significant efforts were devoted to optimizing cavity fabrication, including the use of atomic layer deposition to improve surface quality, exploration into factors affecting the design fracturing, and automated analysis of SEM images. Using optimized fabrication procedures, we experimentally demonstrated 1D photonic crystal nanobeam cavities exhibiting the highest Q/V reported on substrate. Finally, we analyzed the bistable behavior of the devices to quantify the nonlinear optical response of our cavities.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/Z9K935FM, author = {Chang, Chieh-Feng}, title = {Wafer-Scalable Fabrication of Metal Nanostructures for Plasmonics-Assisted Biomedical Sensing Applications}, school = {California Institute of Technology}, year = {2015}, doi = {10.7907/Z9K935FM}, url = {https://resolver.caltech.edu/CaltechTHESIS:06022015-015750109}, abstract = {Plasmonics provides many opportunities of sensing and detection since it combines the nanoscale spatial confinement and the optical temporal resolution. The wireless nature of photonic investigation, moreover, is very desirable for biomedical applications. Plasmonic metals, however, are difficult to pattern with great nanoscopic precision, and traditional approaches were time-consuming, non-scalable, stochastically-manufactured, or highly-limiting in the pattern designs. In this work, wafer-scalable nanofabrication methods are presented for various plasmonic structures for biomedical sensing applications. The fabrication steps have ready counterparts in commercial semiconductor foundries and therefore can be directly applied for mass production.
The fabrication and measurement of extraordinary transmission (EOT) are discussed in Chapter 2. Fabrication options are available for substrates like silicon-on-sapphire and silicon-on-glass, so that the devices can be mechanically robust for user-friendliness. The metal layer can also be varied for EOT applications in different ranges of wavelengths. The EOT nanostructures can be fabricated to be polarization-sensitive, and the concept of fluorescence-based EOT assays is demonstrated.
The fabrication and applications of surface-enhanced Raman spectroscopy (SERS) are then discussed. With a hybrid approach, the top-down designing defines uniform SERS nanostructures on a chip, while the bottom-up process of thermal reflow increases the fabrication precision beyond the lithography resolution limit. Based on the thiophenol study, an enhancement factor greater than 1010 can be achieved. The first Raman spectrum of tracheal cytotoxin is demonstrated without any special sample preparation, and thrombin binding could be easily resolved through chip functionalization. The binding dynamics of ethyl mercaptan, which is similar to the highly toxic gas of hydrogen sulfide, can be detected with a good resolution in time at a low concentration.
With a few more steps of fabrication, the plasmonic structures can be integrated into systems that do not call for laboratory infrastructures. A built-in micro-channel on a chip can make the device useful without dedicated support of a microscope or additional microfluidic structures. The nanostructures can also be transferred onto flexible substrates for better conformity onto various surfaces. Finally, the SERS structures can be transferred onto a fiber tip for in-field or through-the-needle applications, especially when combined with a portable Raman-scope.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/Z98050MN, author = {Mujeeb-U-Rahman, Muhammad}, title = {Integrated Microsystems for Wireless Sensing Applications}, school = {California Institute of Technology}, year = {2014}, doi = {10.7907/Z98050MN}, url = {https://resolver.caltech.edu/CaltechTHESIS:06062014-160929992}, abstract = {Personal health monitoring is being considered the future of a sustainable health care system. Biosensing platforms are a very important component of this system. Real-time and accurate sensing is essential for the success of personal health care model. Currently, there are many efforts going on to make these sensors practical and more useful for such measurements. Implantable sensors are considered the most widely applicable and most reliable sensors for such accurate health monitoring applications. However, macroscopic (cm scale) size has proved to be a limiting factor for successful use of these systems for long time and in large numbers. This work is focused to resolve the issues related with miniaturizing these devices to a microscopic (mm scale) size scale which can minimize many practical difficulties associated with their larger counterparts currently.
To accomplish this goal of miniaturization while retaining or even improving on the necessary capabilities for such sensing platforms, an integrated approach is presented which focuses on system-level miniaturization using standard fabrication procedures. First, it is shown that a completely integrated and wireless system is the best solution to achieve desired miniaturization without sacrificing the functionality of the system. Hence, design and implementation of the different components comprising the complete system needs to be done according to the requirements of the overall integrated system. This leads to the need of on-chip functional sensors, integrated wireless power supply, integrated wireless communication and integrated control system for realization of such system. In this work, different options for implementation of each of these subsystems are compared and an optimal solution is presented for each subsystem. For such complex systems, it is imperative to use a standard fabrication process which can provide the required functionality for all subsystems at smallest possible size scale. Complementary Metal Oxide Semiconductor (CMOS) process is the most appropriate of the technologies in this regard and has enabled incredible miniaturization of the computing industry. It also provides options for designing different subsystems on the same platform in a monolithic process with very high yield. This choice then leads to actual designs of subsystems in the CMOS technology using different possible methods. Careful comparison of these subsystems provides insights into different design adjustments that are made until the desired functions are achieved at the desired size scale. Integration of all these compatible subsystems in the same platform is shown to provide the smallest possible sensing platform to date.
The completely wireless system can measure a host of different important analyte and can transmit the data to an external device which can use it for appropriate purpose. Results on measurements in phosphate buffer solution, blood serum and whole blood along with wireless communication in real biological tissues are provided. Specific examples of glucose and DNA sensors are presented and the use for many other relevant applications is also proposed. Finally, insights into animal model studies and future directions of the research are discussed.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/Z9W9575D, author = {Rajagopal, Aditya}, title = {Microfabricated Tools and Engineering Methods for Sensing Bioanalytes}, school = {California Institute of Technology}, year = {2014}, doi = {10.7907/Z9W9575D}, url = {https://resolver.caltech.edu/CaltechTHESIS:06052014-214022941}, abstract = {There is a convergence between the needs of the medical community and the capabilities of the engineering community. For example, the scale of biomedical devices and sensors allow for finer, more cost-effective quantification of biological and chemical targets. By using micro-fabrication techniques, we design and demonstrate a variety of microfluidic sensors and actuators that allow us to interact with a biochemical environment. We demonstrate the performance of microfluidic blood-filtrations chips, immune-diagnostic assays, and evaporative coolers. Furthermore, we show how micro-fabricated platinum filaments can be used for highly localized heating and temperature measurement. We demonstrate that these filaments can be used as miniature IR spectroscopic sources. Finally, we describe and demonstrate novel combinatorial coding methods for increasing the information extracted from biochemical reactions. We show proof-principle of these techniques in the context of Taqman PCR as well as persistence length PCR.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/Z9HH6H2D, author = {Malik, Imran Raouf}, title = {Point of Care Molecular Diagnostics for Humanity}, school = {California Institute of Technology}, year = {2014}, doi = {10.7907/Z9HH6H2D}, url = {https://resolver.caltech.edu/CaltechTHESIS:06062014-102704108}, abstract = {
Diagnostics of disease at POC (point of care) has been declared one of the Grand Challenge by the Bill and Melina Gates Foundation (BMGF). Infectious diseases constitute a major cause of disease burden and cause more than half a billion Disability-Adjusted Life Years (DALYs) and millions of deaths each year. They have an especially large effect on children under 5 years of age. We have analyzed data from the GBD 2010 (Global Burden of Disease) project to emphasize the damage caused by infectious diseases, and highlight the opportunity of using diagnostic tools to rapidly identify and treat diseases. To motivate the work of this thesis, we quantify the expected impact of appropriate diagnostic technologies.
We have also analyzed the requirements that a diagnostic tool should meet to generate the maximal global impact. We present various existing TPPs (Target Product Profiles) from different organizations and suggest some additions to these existing TPPs. We explain the particular molecular pathology technologies which have the potential to allow deployment of functional products in the developing world for point-of-care pathogen detection, especially in low-resource settings.
We perform a detailed analysis on existing polymerase chain reaction (PCR) systems and describe the problems caused with thermal performance and optical interrogation. We list the requirements that disposable cartridges for such instruments should meet and suggest a metal base design with polymer top. After detailed FEA simulations, we demonstrate that the thermal response can be modeled using a one-dimensional (1D) lumped element system. We show improvements in thermal response due to using a metal base and the effect of fluid height. We also performed thermal-structural simulations to quantify the stresses on the adhesive bonds of metal/polymer cartridges. Next, we explain fabrication of these cartridges. We show methods to dispense adhesive using a robot and a custom made jig to spread the adhesive during curing. The cartridge was tested with different PCR reagents and we obtained reaction efficiencies approaching those of the commercial real time PCR machines. Our fabrication technique is useful to join dissimilar materials and is production friendly. By developing custom software, we observed the cartridge performance in a continuous manner. We could see the thermal response of cartridges by continuous fluorescence monitoring, and used reflective aluminum which increase light collection efficiency.
We then present a simple and robust new way for thermal cycling. Robust thermal cycling has been a major challenge conducting PCR, especially in point of care situations. Here, we suggest a contact cooling approach, in which the cartridge rests on a thin metal plate with an integrated thin heater constructed from flexible printed circuit board (PCB) material. We use a solenoid to move a metal plate to cool down the sample cartridge during cycling. The metal plate then rests on a larger heat sink to disperse the shuttled heat. Our design is dust and water proof and was verified on a bench-top prototype.
A novel optical design for fluorescence detection during qPCR is also described. We suggest a lateral illumination waveguide geometry with prism coupling that eliminates lenses and is integrated into an injection molded cartridge. The light is homogenized using a light guide, and we quantify the sources of scattered stray light from the chamber edge by performing ray tracing simulations to optimize the precise geometry. The design is tolerant to misalignments and enables easy coupling of LED light into the chamber. As the light collection efficiency is high, the size of the chamber can be very small. We tested real PCR reactions using this concept and observed a rapid integration time, enabling very fast reading.
Sample preparation has been another challenge for all point-of-care (POC) lab-on-chip devices for many years. Here, we propose a new design which is robust, fast, flexible and simple, and uses a sliding seal to move the collected sample between various reservoir chambers. The sample moves on a slider sandwiched between seals that shuttles a DNA binding membrane between different reactions. Thus, size and volumes of reagents can be increased without increasing dead volumes. This design is easily automated, and positive displacement of fluids can work with many reagents without worrying about their characteristics such as foaming. The speed of the sample preparation protocols is high and complex protocols can be ported on this design concept, which we tested on real clinical samples and obtained impressive results. We designed and injection molded devices to test and verify this concept.
Finally, we focus on instrumentation and software required to allow our technology to be used at the POC. We describe our embedded electronics and describe the powerful micro-controller and various high performance ICs that are used to construct a fully functional for sample to answer instrument. We developed various versions of software. The developer software allows us to control our system and bench top setup. Our end user product includes a tablet and cell phone software interface. Software was developed for a windows 8 tablet, windows 8 phone and an Android based devices.
To conclude, we very briefly describe the POC systems that are under development: A portable qPCR system with a separate cartridge design, and a universal sample to answer system that performs qPCR, sample preparation and sample to answer protocols in one box depending on the cartridge.
As per best of our knowledge the cost of this technology is much lower than any other option in its class. The sample to answer instrument is expected to cost less than $500. The test cost is expected to be less than $5. The performance is not compromised. We hope that this work can help bring a transformative change in the practice of pathology especially in the developing world.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/6F0A-TD74, author = {Huang, Jingqing}, title = {Wavelength-scale Confinement of Light and Its Applications in On-Chip Photonic Devices}, school = {California Institute of Technology}, year = {2012}, doi = {10.7907/6F0A-TD74}, url = {https://resolver.caltech.edu/CaltechTHESIS:05062012-225422868}, abstract = {
We present design and experimental work toward building room temperature, continuous-wave (CW) lasers with a cavity that confines light to a volume of ≤ (λ/n)3. We begin with the mechanisms of strong optical confinement using dispersive metals and photonic crystals. Finite-difference time-domain methods (FDTD) are used to simulate the behavior of electromagnetic fields in the cavity; fast Fourier transform from FDTD-generated near-field data calculates the far-field radiation pattern from the microcavity laser.
We then present our investigations into designs where metals are incorporated into microdisk and photonic crystal optical cavities to curb or redirect radiation loss. The significant effects of boundary conditions and substrate feedback on far-field radiation directionality are studied. We evaluate the threshold gain required to achieve room temperature lasing in these metallo-dielectric cavities.
While studying the confinement mechanism of photonic crystals on metal substrate, it became clear that room temperature lasing can be achieved in optically-thick photonic crystal cavities, where the thicker semiconductor layer would give us more freedom in designing the vertical p-i-n doping profile within, for a less resistive and leaky electrical path for current injection operation. We fabricate and demonstrate single-mode room temperature lasing by optical pumping in an optically- thick single-defect cavity.
We move on to present our design and characterization of coupled-cavity photonic crystal lasers operating with CW, high output power, and directional emission. Single-mode stable emission with output power on the order of 10 μW and linear polarization was achieved. Moreover, we switched from the commonly used InGaAsP quantum well material to the lesser-known InAsP quantum wells in InP cladding, and found that the large band-edge offset between InAsP and InP made a world of difference in achieving high power operation despite the large thermal resistance in the device.
For a microcavity laser with directional radiation, Purcell-enhanced spontaneous emission, and diminished effects due to feedback from surrounding structures such as the substrate, nanobeam photonic crystal lasers are analyzed, fabricated, and characterized. Despite thermal resistance an order of magnitude higher than their 2D counterparts, quasi-CW operation with a soft threshold turn-on was achieved.
Much work was done to optimize fabrication techniques in order to realize the optical cavity designs with little fabrication error. We detail the high-contrast hydrogen silsesquioxane (HSQ) electron-beam lithography and deep vertical dry etch procedures especially developed for this work.
Lastly, related projects on nonlinear silicon photonic devices are presented. Synthetic nonlinear polymer is integrated on to the silicon photonic platform to achieve low half-wave voltage electro-optic modulation. Causes and magnitude of the nonlinear loss particular to silicon waveguides with sub-μm2 cross-section are evaluated.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/QCW6-0C39, author = {Walavalkar, Sameer Sudhir}, title = {Optical, Mechanical, and Electronic Properties of Etched Silicon Nanopillars}, school = {California Institute of Technology}, year = {2011}, doi = {10.7907/QCW6-0C39}, url = {https://resolver.caltech.edu/CaltechTHESIS:05162011-142708481}, abstract = {This work focuses on the fabrication, characterization and applications of silicon nanopillars. We explain the techniques involved in creating sub 50 nm diameter pillars with aspect ratios of 60:1. Original work encompassed the use of a novel etch mask made of reactive ion sputtered aluminum oxide, ‘pseudo-Bosch’ inductively coupled reactive ion etching (ICP-RIE) to etch structures on the nanoscale. These methods demonstrate a unique approach to the largely ‘bottom-up’ technology used in nanowire fabrication.
We also explored the self-terminating oxidation behavior of convex, two-dimension silicon structures. It was found that during the oxidation process, strain built up at the moving Si-SiO2 interface eventually led to a cessation of oxidation. This was used to predictably reduce the diameter of these pillars to 2 nm, making ‘nanowhiskers.’ We were able to characterize the results of this oxidation non-destructively by utilizing reflection mode transmission electron microscopy (R-TEM).
Using spun-on PMMA and an electron beam to constrict it and bend the pillars, we were able to incorporate as much as 25% strain. More interestingly this deformation appeared to be elastic, as the pillars, once freed from the polymer, would snap back to their upright position.
A consequence of the creation of silicon nanowhiskers was that silicon, a normally poor light emitter due to its indirect bandgap, became photoluminescent. As we reduced the diameter we noticed that the bandgap became direct and the emission peak was blue-shifted. We were able to utilize a tight-binding model (TBM) that was modified by the oxidation induced strain. This modified model predicted the blue-shift in peak emission wavelength with decreasing pillar diameter. The strain induced in the pillar during the oxidation played a significant role in the peak emission wavelength and shape of the bandstructure. By corrugating the pillars with an oscillating etch technique we were able to turn our nanopillars into quantum dots which also proved to photoluminesce.
Finally we look at the possibilities of creating a silicon light emitting diode. By creating a double-gated structure it is possible to overcome the difficulties encountered with sub 5 nm diameter pillars. A possible fabrication process, and the current work done to implement it, is presented as well as a simulation explaining the behavior of this device in the future.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/PEET-AM61, author = {Walker, Christopher}, title = {Fabrication of Microfluidic Structures by Automated Laser Ablation and Automation of Optical Testing}, school = {California Institute of Technology}, year = {2010}, doi = {10.7907/PEET-AM61}, url = {https://resolver.caltech.edu/CaltechTHESIS:06072010-060526366}, abstract = {A versatile, semi-automated instrument to fabricate embedded devices by laser ablation was designed, built, and tested. The expertise required for this came partially from the development of an optical testing system. This system and its utility in testing silicon on oxide waveguide structures are briefly explored. Processes for reproducibly fabricating microfluidic channels and vias were developed. Using one of these processes, design rules for more complex features were developed, and fully three dimensional structures realized. The phenomenon of nonlinear fluidic resistance in deformable channels was explored; a simple analytical model was designed, and compared favorably to measured data. Finally, using this effect, fully embedded valves were developed. With the combination of large scale accurate feature placement, a developed process for three dimensional features, and the development of valves, this instrument is capable of fabricating complex systems of devices, and should prove a useful tool in the future.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/Z9MW2FBC, author = {Henry, Michael David}, title = {ICP Etching of Silicon for Micro and Nanoscale Devices}, school = {California Institute of Technology}, year = {2010}, doi = {10.7907/Z9MW2FBC}, url = {https://resolver.caltech.edu/CaltechTHESIS:05262010-152815609}, abstract = {The physical structuring of silicon is one of the cornerstones of modern microelectronics and integrated circuits. Typical structuring of silicon requires generating a plasma to chemically or physically etch silicon. Although many tools have been created to do this, the most finely honed tool is the Inductively Couple Plasma Reactive Ion Etcher. This tool has the ability to finesse structures from silicon unachievable on other machines. Extracting structures such as high aspect ratio silicon nanowires requires more than just this tool, however. It requires etch masks which can adequately protect the silicon without interacting with the etching plasma and highly tuned etch chemistry able to protect the silicon structures during the etching process.
In the work presented here, three highly tuned etches for silicon, and its oxide, will be described in detail. The etches presented utilize a type of etch chemistry which provides passivation while simultaneously etching, thus permitting silicon structures previously unattainable. To cover the range of applications, one etch is tuned for deep reactive ion etching of high aspect ratio micro-structures in silicon, while another is tuned for high aspect ratio nanoscale structures. The third etch described is tuned for creating structures in silicon dioxide. Following the description of these etches, two etch masks for silicon will be described. The first mask will detail a highly selective etch mask uniquely capable of protecting silicon for both etches described while being compatible with mainstream semiconductor fabrication facilities. This mask is aluminum oxide. The second mask detailed permits for a completely dry lithography on the micro and nanoscale, FIB implanted Ga etch masks. The third chapter will describe the fabrication and in situ electrical testing of silicon nanowires and nanopillars created using the methods previously described. A unique method for contacting these nanowires is also described which has enabled investigation into the world of nanoelectronics. The fourth and final chapter will detail the design and construction of high magnetic fields and integrated planar microcoils, work which was enabled by the etching detailed here. This research was directed towards creation of a portable NMR machine.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/CZBG-5917, author = {Khankhoje, Uday Kiran}, title = {Photon Confinement in Photonic Crystal Cavities}, school = {California Institute of Technology}, year = {2010}, doi = {10.7907/CZBG-5917}, url = {https://resolver.caltech.edu/CaltechTHESIS:05272010-215001543}, abstract = {
In this thesis, the use of photonic crystal cavities for experiments in cavity quantum-electrodynamics is described. To this end, the propagation of light in photonic crystals, and the creation of cavities by making defects in the photonic crystal lattice, is discussed. By drawing an analogy with Fabry-Perot etalons, the mechanism of light confinement in these cavities is explained. It is shown that by engineering the immediate cavity neighborhood, the mirror reflectivities can be increased, resulting in a very high quality factor (Q) and low mode volume. Photonic crystal cavity designs used in this thesis are introduced, along with numerically computed data of their performance.
Device fabrication in gallium arsenide wafers is described in detail, with special attention to address factors that lead to a lack of reproducibility. Over the course of this thesis effort, several thousand cavities were fabricated, and a wide range of Qs were recorded. Careful experiments were performed to determine the causes of low Qs, both at the wafer growth level, and at the fabrication level. Technological improvements in wafer growth are reported, as well as fabrication techniques to improve cavity Q.
These cavities contain indium arsenide quantum dots (QDs) as internal light sources. Cavity-induced enhancement of QD light emission is discussed, along with interferometric measurements of photon correlations. It is found that light emission from coupled QD-cavity systems is highly non-classical, and this quantum nature is characterized by means of a second order correlation function.
To conclude, a novel application of high-Q cavities is discussed, that of an electrically-pumped laser fabricated in a 1D nanobeam cavity. The salient feature of such a geometry is that a high Q is retained even with the introduction of gold in the cavity vicinity. Finally, approaches to improve cavity Q by material system optimizations are explored. In the first approach, QD growth in III-V material systems with light emission wavelengths in the telecommunications wavelength range (λ ≈ 1.55 μm) is discussed, and in the second, the growth of III-V-based active media in silicon structures is considered.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/VKA1-B695, author = {Shearn, Michael Joseph, II}, title = {Silicon Integrated Optics: Fabrication and Characterization}, school = {California Institute of Technology}, year = {2010}, doi = {10.7907/VKA1-B695}, url = {https://resolver.caltech.edu/CaltechTHESIS:05232010-110330796}, abstract = {For decades, the microelectronics industry has sought integration and miniaturization as canonized in Moore’s Law, and has continued doubling transistor density about every two years. However, further miniaturization of circuit elements is creating a bandwidth problem as chip interconnect wires shrink as well. A potential solution is the creation of an on-chip optical network with low delays that would be impossible to achieve using metal buses. However, this technology requires integrating optics with silicon microelectronics. The lack of efficient silicon optical sources has stymied efforts of an all-Si optical platform. Instead, the integration of efficient emitter materials, such as III-V semiconductors, with Si photonic structures is a low-cost, CMOS-compatible alternative platform.
This thesis focuses on making and measuring on-chip photonic structures suitable for on-chip optical networking. The first part of the thesis assesses processing techniques of silicon and other semiconductor materials. Plasmas for etching and surface modification are described and used to make bonded, hybrid Si/III-V structures. Additionally, a novel masking method using gallium implantation into silicon for pattern definition is characterized. The second part of the thesis focuses on demonstrations of fabricated optical structures. A dense array of silicon devices is measured, consisting of fully-etched grating couplers, low-loss waveguides and ring resonators. Finally, recent progress in the Si/III-V hybrid system is discussed. Supermode control of devices is described, which uses changing Si waveguide width to control modal overlap with the gain material. Hybrid Si/III-V, Fabry-Perot evanescent lasers are demonstrated, utilizing a CMOS-compatible process suitable for integration on in electronics platforms. Future prospects and ultimate limits of Si devices and the hybrid Si/III-V system are also considered.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/VJX4-5T05, author = {Wang, Guangxi}, title = {Compact Nonlinear Optical Devices in Silicon-Polymer Hybrid Material System}, school = {California Institute of Technology}, year = {2009}, doi = {10.7907/VJX4-5T05}, url = {https://resolver.caltech.edu/CaltechETD:etd-03232009-014403}, abstract = {Recently, integrated silicon photonics has become a topic of rising interests, due to its great potential to induce significant improvements in modern communication and computation systems. While optics is often viewed as a favorable solution to many issues faced by the rapidly evolving microelectronic technology, the high cost, large physical size, and discrete configuration of conventional optics have largely restricted its applications. The introduction of silicon nanophotonics permits a new look at the idea of incorporating optics with traditional electronic integrated circuits in a sensible and feasible fashion.
In this dissertation, emphasis is placed on investigating nonlinear devices built in silicon but complemented by nonlinear polymer materials. Basic optical guiding and coupling components for silicon on insulator platform are first discussed, followed by a detailed description of the design, fabrication, and testing procedures of a Pockels effect electro-optic modulator based on nonlinear polymer-coated silicon nanostructures. Discussion is further expanded on other related devices that also make use of the second-order nonlinear effect, and designs to improve the speed and efficiency of existing devices are also elaborated. Finally, a third-order nonlinear all-optical modulation device is presented with a series of carefully designed experiments to verify its ultrafast operation.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/2E06-0W63, author = {Chen, Yan}, title = {Integration of Dye Lasers and Microfluidics for Biochemical Analysis}, school = {California Institute of Technology}, year = {2009}, doi = {10.7907/2E06-0W63}, url = {https://resolver.caltech.edu/CaltechETD:etd-07202008-164745}, abstract = {This dissertation describes the study of two important aspects of integration in microfluidics: optics and biochemistry. In optics integration, two types of miniaturized dye lasers, namely the solid-state polymer dye lasers and optofluidic dye lasers were demonstrated. Both of the dye lasers possess a resonant cavity with circular grating geometry, and they are suitable to serve as low-threshold, surface-emitting coherent light source in microfluidic networks. The mass production and large scale fabrication of such low-cost dye laser arrays can be realized by the well developed nanoimprint and soft lithography, making this technology attractive for various biochemical applications. In biochemistry integration, a microfluidic system was developed to fully utilize the complexity of microfluidic circuits to process single cells and extract gene expression information in a parallel manner. The work presented here explored both the optics and biochemistry integration in microfluidics, which are the key issues for further development of complete “lab-on-a-chip” systems.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/3XYZ-BW96, author = {Emery, Teresa Holly}, title = {Fabrication of Nanowire-based Magnetic Structures for Magnetic Resonance Applications}, school = {California Institute of Technology}, year = {2008}, doi = {10.7907/3XYZ-BW96}, url = {https://resolver.caltech.edu/CaltechETD:etd-06062008-115513}, abstract = {
The development and fabrication of novel magnetic nanowire devices is presented. These devices are used both to explore the fundamental physics of single domain particles, and to provide signal amplification and increased resolution in magnetic resonance imaging. Fabrication protocols for the creation of nickel nanowires were developed using both electron beam lithography and electroplating into nanoporous templates. The templates for electroplating were created by anodizing aluminum in either oxalic or sulfuric acids. The templates are 15 to 25 mum thick and composed of highly ordered pores of 40 nm and 20 nm in diameter respectively. Nanowire samples formed by each protocol are characterized using an alternating gradient magnetometer to measure magnetic hysteresis loops. The magnets formed by electroplating were found to be much closer to ideal single domain magnets than those written via electron beam. Coercivities over to 1000 Oe were observed.
Individual cylindrical nanowires of 70 nm diameter were contacted using focused ion beam assisted platinum deposition. A contacted nanowire was tested in a cryostat to determine the temperature dependence of the magneto-resistive properties of the wire. Sections of plated nanowires still in the anodized aluminum template were examined for their reversible transverse susceptibility for applications in signal amplification in magnetic resonance imaging systems. A process of selectively plating into the aluminum templates to create shape magnets with interesting magnetic fields was developed for creating magnetic "lenses’ with focal points above the plane of the substrate. Finally, an inductive stripe loop array was fabricated for use in stripe sensor tomography. These developments will enable future work on magnetic resonance imaging using a background of patterned templates for amplification.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/BWQC-RE07, author = {Maltezos, George Manuel}, title = {Microfluidic Devices for Accessible Medical Diagnostics}, school = {California Institute of Technology}, year = {2007}, doi = {10.7907/BWQC-RE07}, url = {https://resolver.caltech.edu/CaltechETD:etd-05282007-161248}, abstract = {This thesis covers devices exploring basic areas of physical and biological research including: surface plasmon enhanced InGaN light-emitting diode, analysis of using AlGaN emitters coupled with thin film heaters to cure onychomycosis infections, tunable organic transistors that use microfluidic source and drain electrodes, as well as an electrical microfluidic pressure gauge for PDMS MEMS. Also analyzed are devices created through the use of novel three-dimensional rapid prototyping techniques, such as: the replication of three-dimensional valves from printed wax molds, chemically robust three-dimensional monolithic SIFEL fluoropolymer microfluidics, microfluidic valves for customized radioactive positron emission dyes, reduction of microfluidic control inputs through the use of pressure multiplexing, bicuspid-inspired microfluidic check valves and microfluidic three-dimensional separation column. Devices created to analyze blood are also treated including: a microfluidic device to extract blood plasma from a fingerstick; inexpensive, portable immunoassay devices and their use in in small cell lung carcinoma and multiple sclerosis; as well as a device to screen metastasizing cancer cells. Devices created to perform polymerase chain reactions are also studied, including: an evaporative cooler for microfluidic channels, thermal management in microfluidics using micro-Peltier junctions in a microfluidic polymerase chain reaction system, and an accessible polymerase chain reaction system.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/C2WY-TG62, author = {Zhang, Zhaoyu}, title = {Towards Functional Miniaturized Lasers}, school = {California Institute of Technology}, year = {2007}, doi = {10.7907/C2WY-TG62}, url = {https://resolver.caltech.edu/CaltechETD:etd-05162007-123028}, abstract = {In this thesis, nanometer scale semiconductor lasers and micrometer scale polymer based dye lasers are our focus in bringing the miniaturized lasers to applications in data transmission; ultra-small chemical / biological sensors; and ultra-compact spectroscopic sources. Combining the advantage of electrically driven semiconductor lasers and the advantage of a broad emission spectrum of dye molecules would utilize the highly dense multi-functional lab-on-a-chip by integrating microfluidic PCR, microfluidic fluorescent detection system, and compact visible and NIR detectors which are commercially available. On the other hand, in the meantime of pushing the size limit of the laser cavities, new phenomena with the nanoscale lasers enable further exploration and understanding in fundamental physics. In the first part of this thesis, two sub-micron scale semiconductor lasers are presented. The smallest lasers utilizing the disk structures—with diameters of approximately 600 nm—were realized in the InGaP/InGaAlP quantum well material system at room temperature, featuring ultra-small mode volumes of approximately 0.03 cubic?microns, and exhibiting single-mode operation at low threshold powers. And the first visible photonic crystal ultra-small mode volume lasers, with cavity volumes of approximately 0.01 cubic?microns, are realized in the same material system. They are ideally suited for use as spectroscopic sources and both of them can be lithographically tuned from 650 – 690 nm. In the second part of this thesis, two sub-millimeter-scale polymer-based dye lasers—a poly(dimethylsiloxane) (PDMS)-based mechanically tunable DFB dye laser and a poly(methylmethacrylate) (PMMA)-based second-order circular grating distributed feedback dye laser—are presented. Both of them are compatible with microfluidic technology, which gives freedom in integrating the lasers with the microfluidic chips. Compared to the soft lithography used in the PDMS-based dye laser, the nanoimprint lithography used in the PMMA-based dye laser would be more useful for fabricating ultra-small dye lasers and enabling mass production in the near future. At the end of the thesis, a nano-linewidth metal grating mask pattern transferred transient grating (MPT-TG) technique is described as a potential technique using the ultra-small lasers for molecular-dynamics study in solutions.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/2746-3104, author = {Maune, Brett Michael}, title = {Fluidic and Polymeric Integration and Functionalization of Optical Microresonators}, school = {California Institute of Technology}, year = {2006}, doi = {10.7907/2746-3104}, url = {https://resolver.caltech.edu/CaltechETD:etd-11222005-163249}, abstract = {Optical resonators are structures that spatially confine and temporally store light. The use of such resonators continues to permeate throughout society as improvements in their design and fabrication qualify them to fulfill an ever-increasing array of technological and scientific applications. Traditionally, resonators have primarily been used in lasers and as filters, and more recently have been utilized in other areas including chemical sensing, spontaneous emission modulation, and quantum electrodynamics experiments. In many of these applications, the functionalities of the resonators are solely derived from the geometry and material composition of the resonators themselves. The central theme of this thesis is the investigation of further increasing a resonator’s functionality through its integration with fluidic and polymeric materials.
The thesis begins with an investigation of integrating silicon ring resonators with electro-optic polymer and liquid crystal in an effort to tune the resonators’ resonant wavelengths. Although the electro-optic polymer efforts are a failure, we are able to electrically tune the rings’ resonances using electrodes and the reorientation of liquid crystal surrounding the resonators. We then take the knowledge and experience acquired from these experiments and pursue the functionalization of photonic crystal laser resonators, a relatively new class of microresonators constructed from a thin slab of InGaAsP quantum well material with a periodic array of holes etched through the slab. To this end, we first infiltrate the porous resonators with liquid crystal and construct liquid crystal cells around the devices. We are then able to tune the lasing wavelengths by reorienting the liquid crystal with a voltage applied across the cell. Next, we devise a new photonic crystal cavity designed to optimally interact with infiltrated birefringent materials, by supporting two orthogonally polarized high-Q modes. Again, we infiltrate the cavity with liquid crystal, but this time optically control the liquid crystal orientation with a photoaddressable polymer film. By doing so we are able to realize a fundamentally new laser tuning method by reversibly Q-switching a resonator’s lasing mode between the two cavity modes and thereby control the laser’s emission wavelength and polarization. The successful fluidic and polymeric integration with optical resonators presented in this thesis demonstrates some of the possible synergies that can be obtained with such integration and suggests that further enhancements in resonator functionality is possible.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/8124-DA56, author = {Hochberg, Michael}, title = {Integrated Ultrafast Nonlinear Optical Devices in Silicon}, school = {California Institute of Technology}, year = {2006}, doi = {10.7907/8124-DA56}, url = {https://resolver.caltech.edu/CaltechETD:etd-05252006-160420}, abstract = {Silicon-on-insulator (SOI) provides an intriguing system for developing massively integrated optics. By leveraging the processes and systems developed for electronics fabrication, it is possible to make highly repeatable devices where complexity can be scaled up through the use of wafer-scale batch fabrication. Because the mode concentration in silicon waveguides is two orders of magnitude higher than in fibers, it is possible to construct very compact nonlinear optical devices within this system, enabling the miniaturization and integration of ultrafast nonlinear devices. We have developed a library of devices, including both dielectric and plasmonic waveguides, as well as resonators, splitters, and a variety of other basic optical components.
Using these components to construct integrated devices of moderate complexity, we have demonstrated Pockels’ Effect-based ring modulators, optical rectification-based detectors, four-wave mixing devices, and ultrafast intensity modulators, which operate at speeds in excess of 2 Terahertz. By integrating optical polymers through evanescent coupling to high-mode-confinement silicon waveguides, the effective nonlinearity of the waveguides can be greatly increased. The combination of high mode confinement, multiple integrated optical components, and high nonlinearity produces all-optical ultrafast devices operating at power levels compatible with modern continuous-wave telecommunication systems. Although far from commercial modulator standards in terms of extinction, these modulator devices are a first step toward large scale integrated ultrafast optical logic in silicon, and are two orders of magnitude faster than existing free-carrier-based silicon devices.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/04XY-C430, author = {Vyawahare, Saurabh}, title = {Manipulating Fluids: Advances in Micro-Fluidics, Opto-Fluidics and Fluidic Self-Assembly}, school = {California Institute of Technology}, year = {2006}, doi = {10.7907/04XY-C430}, url = {https://resolver.caltech.edu/CaltechETD:etd-05252006-223101}, abstract = {
This dissertation describes work in three inter-related areas – micro-fluidics, opto-fluidics and fluidic self-assembly. Micro-fluidics has gotten a boost in recent years with the development of multilayered elastomeric devices made of poly (dimethylsiloxane) (PDMS), allowing active elements like valves and pumps. However, while PDMS has many advantages, it is not resistant to organic solvents. New materials and/or new designs are needed for solvent resistance. I describe how novel fluorinated elastomers can replace PDMS when combined with three dimensional (3-D) solid printing. I also show how another 3-D fabrication method, multilayer photo-lithography, allows for fabrication of devices integrating filters. In general, 3-D fabrications allow new kinds of micro-fluidic devices to be made that would be impossible to emulate with two dimensional chips.
In opto-fluidics, I describe a number of experiments with quantum dots both inside and outside chips. Inside chips, I manipulate quantum dots using hydrodynamic focusing to pattern fine lines, like a barcode. Outside chips, I describe our attempts to create quantum dot composites with micro-spheres. I also show how evaporated gold films and chemical passivation can then be used to enhance the emission of quantum dots.
Finally, within fluids, self-assembly is an attractive way to manipulate materials, and I provide two examples: first, a DNA-based energy transfer molecule that relies on quantum mechanics and self-assembles inside fluids. This kind of molecular photonics mimics parts of the photosynthetic apparatus of plants and bacteria. The second example of self-assembly in fluids describes a new phenomena - the surface tension mediated self assembly of particles like quantum dots and micro-spheres into fine lines. This self assembly by capillary flows can be combined with photo-lithography, and is expected to find use in future nano- and micro-fabrication schemes.
In conclusion, advances in fluidics, integrating materials like quantum dots and solvent resistant elastomers along with 3-D fabrication and methods of self assembly, provide a new set of tools that significantly expand our control over fluids.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/SRA3-F079, author = {Baehr-Jones, Tom Wetteland}, title = {Novel Modulation and Detection Mechanisms in Silicon Nanophotonics}, school = {California Institute of Technology}, year = {2006}, doi = {10.7907/SRA3-F079}, url = {https://resolver.caltech.edu/CaltechETD:etd-05052006-225043}, abstract = {A number of nanophotonic integrated circuits are presented, which take advantage of the unique properties that light has when guided in very small waveguides to achieve novel functionality. The devices studied are designed to operate with light in the 1400-1600 nm range.
Nanophotonic integrated circuits are tiny waveguides and other optical devices that are fabricated on the nanometer (10-9 meter) scale. These waveguides are often two orders of magnitude smaller than more conventional optical waveguides, such as a fiber optical cable. This reduction in size is interesting because it opens the possibility that expensive optical components might be integrated in very small areas on a chip, and also because the concentrated fields that result from this compression can be used to produce new optical functionality.
First, the techniques used to design passive optical structures, and the methods used to test them, are discussed. Most of the waveguides studied are fabricated from 110 nm thick layers of silicon from silicon-on-insulator wafers. The best waveguide loss achieved was -2.8 dB/cm. Also described are waveguides based on utilizing surface plasmon waves to guide light.
The use of second order nonlinear optical polymers for modulation is also discussed. These polymers are integrated into Silicon slot waveguides, where the Silicon itself serves as the electrode. Modulation is achieved via the Pockels effect. The modulation figure of merit obtained for the device is superior to the contemporary state of the art, an improvement due to the nanoscale nature of the waveguide. Additionally, detectors based on these same polymers and waveguide geometry are presented. Though the detection efficiency is not very high, the detectors are interesting because they do not require any external power supply, and because they have virtually no speed ceiling.
Finally, the use of third order nonlinear optical polymers for all-optical modulation is discussed. When integrated with ridge waveguides, such polymers enable all-optical modulation. Several experiments are described that demonstrate that all-optical modulation has been achieved.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/DH6C-2C59, author = {Neal, Terrell Demetris}, title = {Surface Plasmon Enhanced Light Emission from Organic Light Emitters}, school = {California Institute of Technology}, year = {2006}, doi = {10.7907/DH6C-2C59}, url = {https://resolver.caltech.edu/CaltechETD:etd-09222006-151349}, abstract = {We have experimentally verified that visible light emission for various organic light emitters can be enhanced through the use of surface plasmon coupling layers. By matching the plasmon frequency of a thin unpatterned silver film to the emission of a dye-doped polymer deposited onto this metal surface, we have observed an 11-fold enhancement of light emission. By patterning the silver layer, we estimate that the plasmon frequency can be tuned to match dye-doped polymer emission frequencies, and even larger emission enhancements as well as extraction efficiencies are expected. Carrier dynamics of such plasmon-enhanced organic light emitters were studied and a recombination rate increase due to surface plasmon polaritons was experimentally observed. Internal quantum efficiency data from the polyfluorenes studied follow the trend supported by the time-resolved photoluminescence measurements. Also, we have presented a way to extend the lifetime of organic light emitters by reducing the photodegredation effects from photo-oxidation using surface plasmon coupling.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/NV9T-SC75, author = {Witzens, Jeremy}, title = {Dispersion in Photonic Crystals}, school = {California Institute of Technology}, year = {2005}, doi = {10.7907/NV9T-SC75}, url = {https://resolver.caltech.edu/CaltechETD:etd-05242005-094353}, abstract = {Investigations on the dispersive properties of photonic crystals, modified scattering in ring-resonators, monolithic integration of vertical-cavity surface-emitting lasers and advanced data processing techniques for the finite-difference time-domain method are presented.
Photonic crystals are periodic mesoscopic arrays of scatterers that modify the propagation properties of electromagnetic waves in a similar way as “natural” crystals modify the properties of electrons in solid-state physics. In this thesis photonic crystals are implemented as planar photonic crystals, i.e., optically thin semiconductor films with periodic arrays of holes etched into them, with a hole-to-hole spacing of the order of the wavelength of light in the dielectric media. Photonic crystals can feature forbidden frequency ranges (the band-gaps) in which light cannot propagate. Even though most work on photonic crystals has focused on these band-gaps for application such as confinement and guiding of light, this thesis focuses on the allowed frequency regions (the photonic bands) and investigates how the propagation of light is modified by the crystal lattice. In particular the guiding of light in bulk photonic crystals in the absence of lattice defects (the self-collimation effect) and the angular steering of light in photonic crystals (the superprism effect) are investigated. The latter is used to design a planar lightwave circuit for frequency domain demultiplexion. Difficulties such as efficient insertion of light into the crystal are resolved and previously predicted limitations on the resolution are circumvented. The demultiplexer is also fabricated and characterized.
Monolithic integration of vertical-cavity surface-emitting lasers by means of resonantly enhanced grating couplers is investigated. The grating coupler is designed to bend light through a ninety-degree angle and is characterized with the finite-difference time-domain method. The vertical-cavity surface-emitting lasers are fabricated and characterized.
A purely theoretical section of the thesis investigates advanced data processing techniques for the finite-difference time-domain method. In particular it is shown that an inner product can be used to filter out specific photonic crystal modes or photonic crystal waveguide modes (Bloch-modes). However it is also shown that the numerical accuracy of this inner product severely worsens for Bloch modes with very low group velocities.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/HKW9-4K53, author = {Gunn, Lawrence Cary, III}, title = {Integration of Complex Optical Functionality in a Production CMOS Process}, school = {California Institute of Technology}, year = {2005}, doi = {10.7907/HKW9-4K53}, url = {https://resolver.caltech.edu/CaltechETD:etd-06012005-091623}, abstract = {Optical functionality has been developed within the confines of an existing CMOS process. As of this writing, 10Gigabit modulators, electrically tunable optical filters, waveguides, and grating coupler technology have been successfully implemented alongside the existing transistors in the Freescale Hip7SOI process. This technology will be used to manufacture high bandwidth optical interconnections directly on silicon chips, allowing a new type of network and computing infrastructure to be developed.
This work is covered in two distinct phases. First, the exploratory work done to gain experience with high index contrast silicon waveguides primarily served to uncover challenges related with simulation of these devices, and with the practical limitations of efficiently coupling the resulting waveguide devices with the outside world.
The second phase began as the grating coupler emerged to address the coupling challenge. It became feasible to conceive of a commercially viable technology based on silicon photonics. The coupler has been evolved to a high level, currently achieving coupling loss of less than 1dB. Once the light is on chip, filtering and modulation technology are implemented. The reverse-biased plasma dispersion modulator has a 3dB roll-off of 10GHz, and an insertion loss less than 5dB. Optical filters based on ring resonators, arrayed waveguide gratings, and interleavers have all been implemented, often with world record performance, and many of the devices have been made electronically tunable to compensate for manufacturing variations and environmental excursions.
Finally, circuitry has been designed and constructed on the same die with the optical functionality, fully demonstrating the ability to achieve monolithic integration of these devices.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/JVSC-D109, author = {Adams, Mark Lee}, title = {Integration of Optoelectronics and Microfluidics for Biological and Chemical Sensing}, school = {California Institute of Technology}, year = {2004}, doi = {10.7907/JVSC-D109}, url = {https://resolver.caltech.edu/CaltechETD:etd-12162003-151751}, abstract = {Over the past decade, rapid advances in microfluidics have led to the creation of valves, pumps, mixers, multiplexers, along with a large variety of other devices. This technology has allowed for many fluidics applications to be performed on a chip that is approximately an inch square in area. Such applications include cell sorting, PCR on chip, crystal growth, combinatorial mixing and many others. Although the complexity of these devices may seem overwhelming, they are based on simple process called multilayer soft lithography, which uses a silicone-based elastomer to create these amazing devices. However, with the current state of technology, the applications are somewhat limited. New devices need to be created to further such fields as fluidic logic and biomimetics.
Another major issue that challenges true acceptance of microfluidics is the need for a typically large interrogation setup to determine what is actually happening in the flow cell. In general, a microfluidic chip is placed under a bench top optical microscope in order to perform either colorimetric, absorption, or luminescence spectroscopy. Through these methods everything from cells to chemicals can be identified; however, a true lab-on-a-chip must not rely on something as cumbersome as a microscope. Integrated sensors must be developed to truly make lab-on-a-chip reasonable.
Through this thesis, several approaches for realization of integrated optoelectronic microfluidic systems are presented. The systems are capable of performing optical interrogation of analyte, from both outside of the flow cell as well as directly inside a flow channel. Also, some novel microfluidic devices which should pave the way for greater advancement in the field of microfluidics are discussed. Through the technologies presented, true lab-on-a-chip systems should be even closer to realization.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/1MNR-PW32, author = {Husain, Ali}, title = {Nanotube and Nanowire Devices}, school = {California Institute of Technology}, year = {2004}, doi = {10.7907/1MNR-PW32}, url = {https://resolver.caltech.edu/CaltechETD:etd-05252004-113507}, abstract = {The microelectronic revolution has spawned many fields that take advantage of the incredibly small size devices that can be made. However, the limits of photolithography and even electron beam lithography are fast approaching. Future progress in miniaturization of electronics, mechanical devices and optical structures will require new processes and materials.
The work presented in this thesis is an investigation into the possibilities of using new nanomaterials to fabricate simple devices. It is a challenge to integrate these materials with traditional microfabrication techniques. The processes commonly used to make electronics can damage or destroy some nanomaterials. Also, it is difficult to place and orient these novel substances. Finally, at the nanometer scale, different physical properties emerge due to confinement effects and the large surface-area-to-volume ratio.
We have fabricated devices out of carbon nanotubes and electrodeposited nanowires. The nanowires have been fabricated in gold, platinum, silver and nickel. For all the nanowires except silver we have measured the temperature dependence of the resistance and found that it is consistent with bulk metals. We have created and tested crossed nickel nanowires for magnetoresistive effects and found none.
From the platinum wires we have fabricated and tested the first doubly clamped resonator fabricated out of “bottom-up” materials. This resonator has much lower Q than comparable devices made by traditional techniques. The resonator also exhibits non-linear behavior well described by the Duffing oscillator.
From carbon nanotubes we have created a doubly-clamped beam. In addition, we have created a novel carbon nanotube field emission device with integrated grid. Work is ongoing to achieve experimental results from these devices.
The appendix describes photonic crystal defect cavity lasers, which offers interesting potential for integration with nanotubes and nanowires.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/WD4W-XQ37, author = {Yoshie, Tomoyuki}, title = {Planar Photonic Crystal Nanocavities with Active Quantum Nanostructures}, school = {California Institute of Technology}, year = {2004}, doi = {10.7907/WD4W-XQ37}, url = {https://resolver.caltech.edu/CaltechETD:etd-05272004-095431}, abstract = {Extreme photon localization is applicable to constructing building blocks in photonic systems and quantum information systems. A finding fact that photon localization in small space modifies the radiation process was reported in 1944 by Purcell, and advances in fabrication technology enable such structures to be constructed at optical frequencies. Many demands of building compact photonic systems and quantum information systems have enhanced activities in this field. The photonic crystal cavity has potential in providing a cavity that supports only the fundamental mode of (lambda/2n)^3 together with good confinement of light within a resonator. This thesis addresses experimental and theoretical aspects of building such photon localization blocks embedding active quantum nanostructures in a planar photonic crystal platform. Examples given in this thesis are (1) quantum dot photonic crystal nanolasers, (2) high-speed photonic crystal nanolasers, and (3) light-matter coupling in a single quantum dot photonic crystal cavity system.
(3) Onset of intermediate light-matter coupling was demonstrated in a single quantum dot photonic crystal cavity system. A tripling in Q/V (quality factor divided by mode volume) is found to enable photons to start a strong interaction with a single quantum dot.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/BWJB-7K61, author = {Barsic, David Nicholas}, title = {Small-Scale Liquid-State Dynamics in Nanometer Size Devices}, school = {California Institute of Technology}, year = {2004}, doi = {10.7907/BWJB-7K61}, url = {https://resolver.caltech.edu/CaltechETD:etd-12122003-110405}, abstract = {This dissertation will present research on state-of-the-art micrometer- and nanometer-scale machining techniques to fabricate fluid channels with integral sensing electrodes. The motivation for this project is to create new instruments for investigating the behavior and properties of particles or molecules in solution and confined in a fluid channel with cross-sectional dimensions ranging from less than 50 nanometers to one micron.
The objective of this research is to develop techniques for building fluid analysis systems which combine fluid channels with sensing electrodes. Design of physical devices and the measurement circuit are both important steps in accomplishing this task. The design issues necessary for optimizing these aspects are investigated in detail. The size scale of these systems is at the lower limit achievable with current technology. Such devices require critical dimensions of less than 100 nanometers in order to perform measurements on small-scale fluid systems. Applications of this type of system include detection of both the presence and the motion of particles and molecules suspended in the small volume of fluid confined within the fluid channel. The motion of particles in the fluid channel is detected by measuring the change in electrode capacitance as particles move past the electrodes. Typical fluid volumes used in this type of system range from 50 femtoliters to less than one femtoliter.
Accomplishing this task required a careful look at the machining techniques for making microscopic devices. The approach is to use lithographic and circuit manufacturing techniques to make small fluid channels on either side of which are sets of electrodes. Existing techniques for making small-scale devices were modified to provide the required performance. In some cases the development of entirely new techniques was necessary.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/SB3Y-8Z20, author = {Lončar, Marko}, title = {Nanophotonic Devices Based on Planar Photonic Crystals}, school = {California Institute of Technology}, year = {2003}, doi = {10.7907/SB3Y-8Z20}, url = {https://resolver.caltech.edu/CaltechETD:etd-06022003-042444}, abstract = {Photonic Crystals, man-made periodic structures with a high refractive index contrast modulation, have recently become very interesting platform for the manipulation of light. The existence of a photonic bandgap, a frequency range in which propagation of light is prevented in all directions, makes photonic crystals very useful in applications where spatial localization of light is required. Ideally, by making a three-dimensional photonic crystal, propagation of light in all three dimensions can be controlled. Since fabrication of 3-D structures is still a difficult process, a more appealing approach is based on the use of lower dimensional photonic crystals. A concept that has recently attracted a lot of attention is a planar photonic crystal based on a dielectric membrane, suspended in the air, and perforated with a two-dimensional lattice of holes.
In this thesis theoretical and experimental study of planar photonic crystal nanolasers, waveguides and super-dispersive elements is presented. Room temperature operation of low-threshold nanolaser is demonstrated, both in air and in different chemical solutions. For the first time, we have demonstrated that photonic crystal nanocavity lasers can be used to perform spectroscopic tests on ultra-small volumes of analyte. Our porous cavity design permits the introduction of analyte directly into the high optical field of the laser cavity, and therefore it is ideally suited for the investigation of interaction between light and matter on a nanoscale level. We showed that small changes in refractive index of the ambient surrounding the laser can be detected by observing the shifts in emission wavelengths of the laser. Our lasers can be integrated into large arrays to permit the analysis of many reagents at the same time. The nanolasers can also be integrated with photonic crystal waveguides to form the integrated systems of higher complexities. Theoretical and experimental investigation of various photonic crystal waveguide designs is discussed. Details of the fabrication procedure used to realize nanophotonic devices in silicon on insulator as well as InGaAsP materials are presented.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/VDXC-S449, author = {Vučković, Jelena}, title = {Photonic Crystal Structures for Efficient Localization or Extraction of Light}, school = {California Institute of Technology}, year = {2002}, doi = {10.7907/VDXC-S449}, url = {https://resolver.caltech.edu/CaltechETD:etd-08252004-130544}, abstract = {Three-dimensional (3D) photonic crystals offer the opportunity of light manipulation in all directions in space, but they are very difficult to fabricate. On the other hand, planar photonic crystals are much simpler to make, but they exhibit only a “quasi-3D” confinement, resulting from the combined action of 2D photonic crystal and internal reflection. The imperfect confinement in the third dimension produces some unwanted out-of-plane loss, which is usually a limiting factor in performance of these structures. This thesis proposes how to fully take advantage of the relatively simple fabrication of planar photonic crystals, by addressing a problem of loss-reduction.
One of the greatest challenges in photonics is a construction of optical microcavities with small mode volumes and large quality factors, for efficient localization of light. Beside standard applications of these structures (such as lasers or filters), they can potentially be used for cavity QED experiments, or as building blocks for quantum networks. This work also presents the design and fabrication of optical microcavities based on planar photonic crystals, with mode volumes of the order of one half of cubic wavelength of light (measured in material) and with Q factors predicted to be even larger than 10000.
In addition to photonic crystals fabricated in semiconductors, we also address interesting properties of metallic photonic crystals and present our theoretical and experimental work on using them to improve the output of light emissive devices.
Feature sizes of structures presented here are below those achievable by photolithography. Therefore, a high resolution lithography is necessary for their fabrication. The presently used e-beam writing techniques suffer from limitations in speed and wafer throughput, and they represent a huge obstacle to commercialization of photonic crystals. Our preliminary work on electron beam projection lithography, the technique that could provide us with the speed of photolithography and the resolution of e-beam writing, is also discussed in this thesis.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/y7hm-zq23, author = {Painter, Oskar Jon}, title = {Optical Nanocavities in Two-Dimensional Photonic Crystal Planar Waveguides}, school = {California Institute of Technology}, year = {2001}, doi = {10.7907/y7hm-zq23}, url = {https://resolver.caltech.edu/CaltechETD:etd-12282005-111605}, abstract = {One of the most fundamental properties of a physical system is its energy-momentum dispersion. The electronic dispersion present in semiconductor crystals results in energy gaps which play an extremely important role in the physics of many of the electronic and optical devices we use today. A similar dispersion for electromagnetic waves can be found in periodic dielectric structures. Owing to their strong dispersion, these “photonic crystals” can be used to manipulate light at sub-wavelength scales. The majority of this thesis is concerned with the design and implementation of optical resonant cavities formed by introducing small local imperfections into a periodically perforated slab waveguide. Light becomes localized to these “defect” regions, forming optical cavities with modal volumes approaching the theoretical limit of a cubic half-wavelength.
The resonant cavities studied in this thesis are fabricated using electron-beam lithography, anisotropic dry etching, and selective wet etching. These methods are used to create a two-dimensional array of cylindrical air holes in a free-standing waveguide structure. A multi-quantum-well Indium Gallium Arsenide Phosphide (InGaAsP) active region is epitaxially grown within the waveguide in order to provide light emission in the 1.5 µm band. Optical pumping of the active region is then used to probe the resonant structure of the photonic crystal cavities.
Numerical finite-difference time-domain simulations and qualitative predictions based on symmetry arguments are used to label the different resonant modes present in the cavity photoluminescence spectra. It is found that both donor and acceptor type modes are localized within the defect cavities. Pulsed lasing action is observed in cavity modes with modal volumes as small as 2(λ/2n)³. Lithographic adjustments in the scale and symmetry of the cavity geometry are also used to tune the resonant mode wavelength, split mode degeneracies, and adjust the emission pattern and polarization of the defect modes.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/kvvd-em02, author = {Lee, Reginald K.}, title = {Lasing and modified spontaneous emission in photonic crystal structures and microcavities}, school = {California Institute of Technology}, year = {2000}, doi = {10.7907/kvvd-em02}, url = {https://resolver.caltech.edu/CaltechETD:etd-06102005-082207}, abstract = {NOTE: Text or symbols not renderable in plain ASCII are indicated by […]. Abstract is included in .pdf document.
Semiconductor light-emitting devices in the near-infrared (1.55 µm) based on microfabricated photonic crystal structures are demonstrated. The photonic structures consist of two-dimensional arrays of air holes patterned into an optically thin, airsuspended InGaAsP slab by high-resolution electron beam lithography and various dry etching techniques.
Two types of microcavities are examined. The first are larger hexagonally shaped cavities in the range of 10 to 20 µm in size and bounded by the photonic crystal structure. Cavity mode spontaneous emission at room temperature under optical pumping is used to demonstrate mode confinement due to the in-plane bandgap. No cavity mode peaks in the emission spectrum are seen if the in-plane bandgap is not spectrally aligned with the material emission. Pulsed lasing is also demonstrated with the lasing threshold at 66 mW peak incident optical pump power at a duty cycle of less than 1% in order to minimize membrane heating. Changes in the pump geometry is shown to result in controllable lasing mode switching. This behaviour is explained in terms of mode Q, lasing threshold and enhanced spontaneous emission into the mode.
The second type of microcavity consists of a single point defect into photonic lattice with a modal volume of […]. Cavity quality factors up to 250 are demonstrated and suppressed spontaneous emission due to the bandgap except at the mode frequency is shown. Pulsed lasing at 143 K under optical pumping is demonstrated.
The fundamental modification of the spontaneous emission rate due to the in-plane bandgap in a photonic crystal slab structure with no microcavity is experimentally and numerically examined. Incomplete bandgaps are theoretically shown to be able to strongly inhibit spontaneous emission. High density of states points in the band-structure are seen to greatly enhance the spontaneous emission rate. Measurements using phase sensitive spectroscopy of the spontaneous emission rate from quantum wells in the photonic crystal slab show a greater than 10 times inhibition of the emission rate in the in-plane bandgap. Experimental evidence for saturation of the surface recombination at relatively low pumping levels is found.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Yariv, Amnon}, } @phdthesis{10.7907/0D20-Y875, author = {Chou, Hou-Pu}, title = {Microfabricated devices for rapid DNA diagnostics}, school = {California Institute of Technology}, year = {2000}, doi = {10.7907/0D20-Y875}, url = {https://resolver.caltech.edu/CaltechTHESIS:10012010-091302341}, abstract = {Science makes new technology and technology pushes science forward. For biological studies and hospital diagnoses, knowledge and techniques accumulated from other fields, such as semiconductors, optics, electronics, and chemistry, are generating huge impacts in almost every aspect and for almost everyone involved. Among these, tools for DNA diagnostics play a very important role. They are also essential to many genetic studies, drug discovery, and even forensic identifications.
Working with Professor Stephen Quake, Professor Axel Scherer, and my colleagues in Caltech, I have developed several building blocks for rapid DNA sizing, cell sorting, molecular fingerprinting, and hybridization assays, based on those newly available technologies. First, a microfabricated flow-cell device was developed using ‘soft lithography’. It offers a small, cheap, robust, and contamination-free alternative to the complicated glass-capillary structure used in a conventional flow cytometer. Based on this device, a highly sensitive single-molecule DNA sizing system was demonstrated. It is 100 times faster and requires a million times less sample than pulsed-field gel electrophoresis. For DNA molecules of 1-200 kbp, it has comparable resolution, which improves with increasing DNA length. To serve as a real substitute for a conventional flow cytometry, DNA and cell sorting has also been demonstrated under this system. Simple enclosed actuation schemes are implemented and system downtime due to capillary cleaning is totally eliminated because the device costs only pennies to make and thus becomes disposable. Therefore, there is no cross-contamination issue for both DNA sizing and cell sorting applications. Using this system, prototype work for rapid DNA molecular fingerprinting was devised as an alternative to the widely used Southern blot fingerprinting protocol. Molecular evolution, VNTR fingerprinting of human forensic samples, disease diagnosis based on restriction fragment length polymorphism (RFLP), and simple DNA genomic mapping can all be accomplished with this system. Because of the great flexibility of microfabrication, more complicated functions can also be designed and incorporated into these flow-cell devices. Therefore, this single-molecule sizing system can become a key component in the family of lab-on-a-chip devices.
In addition, a multilayer soft lithography technique was invented, allowing monolithic microvalves and micropumps to be built into these flow-channel devices. Active microfluidic systems containing on-off valves, switching valves and pumps were made, entirely out of elastomer. The softness of these materials allows the device area to be reduced by more than two orders of magnitude compared with silicon-based devices. An actuation volume as small as about one picoliter is demonstrated. The other advantages of soft lithography, such as rapid prototyping, ease of fabrication, and biocompatibility, are retained. Based on these active components, an integrated diagnostic chip was built. More than two orders of magnitude improvement in terms of binding speed and efficiency over passive devices was shown. Selective surface patterning of DNA molecules, biotin, and avidin within the chips by elastomeric flow channels was also shown. With active pumping, we are able to make a rotary motion in these microfluidic devices and show fast inline mixing which overcomes the limitation of laminar flow in this low-Reynolds number regime. Moreover, the problem of buffer depletion due to electrolysis in electroosmotic or electrophoretic flow control does not exist in these devices.
All of these serve as fast, cheap, and robust alternatives to many conventional techniques used widely in biological studies and hospital pathogenic diagnosis. They are all very simple to fabricate and easy to use. If desired, more complicated flow patterns and functions can also be incorporated with much less effort than their silicon counterparts. We anticipate that more applications and devices based on these systems and techniques will be developed rapidly in the near future.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel and Quake, Stephen R.}, } @phdthesis{10.7907/WEP6-MN90, author = {Wong, Joyce Y.}, title = {Perpendicular patterned media for high density magnetic storage}, school = {California Institute of Technology}, year = {2000}, doi = {10.7907/WEP6-MN90}, url = {https://resolver.caltech.edu/CaltechETD:etd-05032007-080831}, abstract = {Current longitudinal thin-film media in magnetic hard-disk drives are facing an oncoming limit caused by the superparamagnetic effect, in which the individual grains in the medium become so small that they are no longer stable against thermal fluctuation. This situation is undesirable as the stored information may be lost within an unexpectedly short time frame. There have been several proposed solutions in addressing the superparamagnetic limit, and one of them is perpendicular patterned media. In this approach, a periodic array of magnetic pillars is defined lithographically on a non-magnetic substrate. Binary data of “1” or “0” can be stored in each of these elements, which have two possible magnetization directions perpendicular to the plane of the medium.
In our perpendicular patterned media design, Ni columns of 150-230nm diameter with a 6:1 aspect ratio are embedded in an (AlGa)2O3/GaAs substrate. The fabrication procedure uses a combination of high resolution electron beam lithography, dry etching, and electroplating. The high aspect ratio in the column is achieved by taking advantage of the high etching rate and selectivity of AlGaAs/GaAs over (AlGa)203 in the Cl2 chemically assisted ion beam etching process. In addition to being a robust etching mask, the (AlGa)2O3 layer also plays an important role in the chemical mechanical polishing procedure to remove the overplated Ni mushrooms.
Once the Ni columns are fabricated, magnetic characterization is performed using magnetic force microscopy and scanning magnetoresistance microscopy. The former measurement confirms that the electroplated Ni columns are magnetic while the latter determines whether the individual columns are stable enough to retain the recorded information. We have successfully demonstrated recording in our 170nm diameter Ni column array arranged in a square format using a commercial read/write head. This is the first demonstration of single magnetic column per bit data storage in a prototype perpendicular patterned medium. Furthermore, we have recorded in higher density Ni column arrays in the form of tracks, corresponding to 1.3 and 2.6Gbits/in.2. Even though we are limited by the spatial resolution of the magnetoresistive read sensor, we have continued to pursue higher density structures up to an areal density of 350Gbits/in.2. Consideration of the issues in high resolution patterning and the magnetic stability of the individual columns have prompted researchers in the magnetic recording industry to anticipate the ultimate storage limit of perpendicular patterned media to be around 1Tbits/in.2}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/sjy2-r565, author = {Cheng, Chuan-cheng}, title = {Nanofabrication and Characterization of Photonic Crystals}, school = {California Institute of Technology}, year = {1998}, doi = {10.7907/sjy2-r565}, url = {https://resolver.caltech.edu/CaltechETD:etd-01182008-132046}, abstract = {Both techniques and applications of nanofabrication have been explored in the field of periodic dielectric nanostructures. These periodic dielectric structures are expected to exhibit interesting properties in both fields of physics and engineering. These artificial nanostructures are named “photonic crystals” because photons demonstrate similar behavior in these structures as electrons in natural semiconductor crystals. In order to construct these crystals in the optical regime, suitable nanofabrication techniques have to be developed and demonstrated, including high resolution electron beam lithography and anisotropic chemically assisted ion beam etching. In this work, both 2D and 3D photonic crystals are fabricated and characterized in the near-infrared range.
In the first part of this thesis, exploration of resolution limit of nanofabrication will be demonstrated and discussed. 15nm structures with 30nm period dot arrays and 20nm line width with 40mn period gratings are presented. Along with high resolution lithography, anisotropic pattern transfer is also developed. These powerful fabrication techniques enable us to miniaturize the dimension of both electronic and optical devices into the nanometer regime.
In the second and third part of this thesis, detailed experiments and characterization of 2D and 3D photonic crystals are discussed. A brief introduction and a theoretical simulation are also presented. In the second part, computer generated form-birefringent nanostructures are first discussed and their performance demonstrated to agree well with design using rigorous coupled wave analysis (RCWA). In-plane 2D photonic crystals used as beam splitting micropolarizers are introduced and fabricated. High extinction ratios (>820:1) between transmitted TE and TM modes are measured. These in-plane photonic crystals are the first working devices using the idea of 2D photonic crystals. Three-dimensional artificial photonic crystals with a complete 3D bandgap represent a more attractive idea.
In the third part of this thesis, we challenge the nanofabrication limits encountered when fabricating a 3D photonic crystal. The first three-dimensional photonic crystals with a forbidden photonic bandgap lying in the near infrared region of the electromagnetic spectrum, 1.1 μm < λ < 1.5 μ, just beyond the electronic band-edge of Gallium Arsenide (GaAs) are demonstrated in the world. These 3D photonic crystals were originally proposed by E. Yablonovitch and can now be fabricated using anisotropic angle etching at three directions through a hexagonal hole array mask. The field distribution using filtered finite-difference time-domain (FFDTD) calculation is briefly discussed. Development of the fabrication techniques and the optical transmission characterization are shown. Photonic crystals with up to six repeating layers are obtained and presented 90% attenuation of transmission measurement in the bandgap region. We also show the spectral shift in the transmission measurement corresponding with 2D lithographic control of microfabrication. Those artificial photonic crystals are expected to be useful in the study of inhibition of spontaneous emission and single-mode light-emitting diodes.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Scherer, Axel}, } @phdthesis{10.7907/80x4-rf73, author = {Drolet, Jean-Jacques P.}, title = {Optoelectronic devices for information storage and processing}, school = {California Institute of Technology}, year = {1997}, doi = {10.7907/80x4-rf73}, url = {https://resolver.caltech.edu/CaltechETD:etd-01102008-090916}, abstract = {
Optoelectronic information storage and processing systems offer many important advantages compared to their electronic and magnetic counterparts: speed, massive parallelism and insensitivity to interference. Optoelectronic devices are a pivotal technology in the implementation of such systems. Devices consisting of optical inputs and outputs and information processing circuits are needed to interface optoelectronic components and modules to electronic systems, and to perform operations that are more difficult to reliably implement using optics alone. The main thrust of our research is to develop and evaluate optoelectronic technologies conducive to highly integrated optoelectronic components and systems for cost-effective information storage and processing.
At the device level, we describe a simple and inexpensive method for fabricating liquid crystal modulators on silicon integrated circuits. The modulators provide analog amplitude or phase modulation at low voltages. They are compatible with mainstream very-large-scale-integration processes and require only a minimal amount of post-processing performed on conventionally fabricated die. Experimental data are presented and compared to theoretical predictions.
At the chip level, we present an innovative optoelectronic integrated circuit functioning as an optically or electrically addressed spatial light modulator. The device merges the functions of a spatial light modulator and a detector array in a holographic memory system. Moreover, it helps refresh dynamic holograms which slowly decay in a read/write photorefractive memory as a result of their exposure to the reference beam. When combined with the technique of conjugate readout, this device allows a lens-less data path and a very compact, self-aligning integration of the memory module. We also describe two neural arrays, using self-electro-optic-effect devices bonded to a silicon integrated circuit, and light-emitting diodes grown on a commercially processed gallium arsenide integrated circuit.
Finally, at the system level, we describe several integrated system architectures for holographic information storage and processing based on conjugate readout and the aforementioned device. We formulate storage density and cost projections. We report on laboratory prototypes of integrated modular holographic memory. Dynamic holograms were sustained over 50 refresh/decay cycles. Experimental data is presented.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Psaltis, Demetri}, } @phdthesis{10.7907/79nd-7w93, author = {O’Brien, John David}, title = {Design, growth, and characterization of vertical cavity surface emitting lasers}, school = {California Institute of Technology}, year = {1996}, doi = {10.7907/79nd-7w93}, url = {https://resolver.caltech.edu/CaltechETD:etd-05252005-084438}, abstract = {Vertical cavity surface emitting laser design, growth, and characterization is discussed. Theoretical models for gain in semiconductors as well as for the threshold gain in vertical cavity lasers is presented. The distributed Bragg mirrors used in these lasers are treated theoretically using the coupled-mode approach and with a matrix method that is generalized to include gain and loss. The growth by molecular beam epitaxy of these structures is also discussed including steps taken to obtain precise, reproducible growth rates. Specific problems and tradeoffs encountered in the growth include greater oxygen incorporation at the lower substrate temperatures needed to ensure precise thickness control. Beryllium diffusion is also discussed and SIMS measurements are presented. Two types of vertical cavity lasers are demonstrated. The first is a hybrid semiconductor/dielectric structure. In this design, the n-doped mirror and the optical cavity are epitaxially grown semiconductors and the top mirror is a SiO2/Si3/N4 distributed Bragg reflector added to the structure by reactive sputter deposition. These lasers have InGaAs quantum wells and are top-emitting near 980 nm. This design has the advantage of removing the top mirrors from the current path which reduces the series resistance. Threshold voltages of 1.8-1.9 V were obtained from 18 µm diameter lasers. In addition, the hybrid structure allows characterization before the deposition of the top mirror. Measurements of the carrier distribution and the temperature of the devices operating without the top mirrors are presented. A minimum lasers threshold current of 2.5 mA was obtained from a 6 µm diameter laser, and a maximum peak power of 1.67 mW was obtained from a 12 µm diameter laser. The lasers exhibit strongly index-guided transverse modes and are multi-moded above threshold.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Yariv, Amnon}, } @phdthesis{10.7907/vrda-c377, author = {Tsai, Charles Su-Chang}, title = {Optoelectronic structure fabrication by organometallic vapor-phase epitaxy and selective epitaxy}, school = {California Institute of Technology}, year = {1996}, doi = {10.7907/vrda-c377}, url = {https://resolver.caltech.edu/CaltechETD:etd-12222007-114128}, abstract = {NOTE: Text or symbols not renderable in plain ASCII are indicated by […]. Abstract is included in .pdf document.
The internal configuration and external supports of OMVPE reactors are examined. The quality of epitaxial layers deposited by an OMVPE reactor is strongly influenced by its internal configuration. The quality of the external supports determines the safety, the environmental impact, and the operating efficiency of the OMVPE reactor.
Optoelectronic structures are fabricated by selective epitaxy. The morphology and growth behavior of GaAs, AlGaAs, and InGaAs using selective epitaxy are presented. Highly selective growth can be achieved through the use of organometallic compounds which contain halogens. The selective growth of nanometer-scale GaAs wire and dot structures is demonstrated. Spectrally-resolved cathodoluminescence images as well as pectra from single dots and wires, passivated by an additional AIGaAs layer, are presented. A blue shifting of the GaAs luminescence peak is observed as the size scale of the wires and dots decreases. Formation of highly-uniform and densely-packed arrays of GaAs dots by selective epitaxy is described. The smallest GaAs dots formed are 15-20 nm in base diameter and 8-10 nm in height with slow-growth crystallographic planes limiting growths of individual dots. Completely selective GaAs growth within dielectric-mask openings at these small size-scales is also demonstrated. The technique of facet-modulation selective epitaxy and its application to quantum-well wire doublet fabrication are described. The smallest wire fabricated has a crescent cross-section less than 140 […] thick and less than 1400 […] wide.
The development of OMVPE epitaxial layers for a visible-wavelength vertical-cavity surface-emitting laser (VCSEL) is presented. The defect density of the mirror layers was reduced to a negligible level by optimizing gas switching. Electroluminescence spectrum of an InGaP heterostructure p-n diode is presented. The defect density of the active region was also reduced to a negligible level by optimizing the gas-switching sequences.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Vahala, Kerry J.}, } @phdthesis{10.7907/1f05-ek48, author = {Salvatore, Randal A.}, title = {Ultrashort and ultrahigh-repetition-rate pulses from passively mode-locked semiconductor lasers}, school = {California Institute of Technology}, year = {1996}, doi = {10.7907/1f05-ek48}, url = {https://resolver.caltech.edu/CaltechETD:etd-01072008-092000}, abstract = {This thesis is an investigation into both the fundamental and experimental aspects of using semiconductor lasers to generate extremely short (100’s of fs) and very high repetition frequency (> 50 GHz) optical pulses. The pulses are produced through modelocking, a technique of forcing a laser to operate in a number of optical modes simultaneously and to hold a constant phase relationship between these modes. Both the shortest and highest repetition rate pulses have been obtained from passive modelocking. An inherently nonlinear technique which does not use any active external timing source. Two structures, ridge-waveguide stripe lasers and liquid phase epitaxy (LPE) regrown lasers, were used to directly generate picosecond width pulses. Using cross-correlation techniques, pulse shape and phase measurements are made. Linear dispersion compensation is shown to achieve nearly a factor of 20 in pulse compression. Stable pulses down to 260 fs are generated.
Showing that exitonic effects are not essential in these devices, wavelength tunability was combined with dispersion compensation to create the first broadly tunable subpicosecond semiconductor source. The device is found to give tunability ranges and mode-locked spectral widths that are comparable to the best results achieved in dye lasers in terms of fractions of the operating gain spectral width. Results for different regimes in the tuning range are examined, and pulses directly from the laser are found to have about a 2 to 1 fall-time to rise-time ratio. A significant nonlinear chirp is found only when the laser is tuned to the short wavelength side of its tuning range and was determined to cause long tails in the autocorrelations of compressed pulses. Additionally, spread-resistant pulses are described and experimentally analyzed.
The case of high-repetition-rate modelocking, which more likely involves about 5 modes instead of 5000 modes, is examined. Approximations in the leading theory of passive modelocking are shown to be inadequate in this case. A steady-state model for high-repetition-rate modelocking is developed including phase effects and is tailored to parameters of semiconductor lasers. Self-consistent solutions show that a lower threshold gain can exist for a supermode than for single mode operation. Predictions of the laser’s behavior upon modifying key material, geometric, and bias parameters are made. Experimental results show that through adjustment of the gain current, “chirp-controlled” modelocking is obtained with operation in any of the three chirp regimes (up-chirped, chirp-free, or down-chirped). This pulse chirp and resulting broadening are due to the algebraic addition of opposite-signed chirps from saturation of the absorber and gain sections. Theoretical modelling from the supermode analysis also traverses the same chirp regimes when the photon intensity is increased.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Yariv, Amnon}, }