Browsing by Subject "Nanoelectronics"
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Item Epioptics of stepped silicon surfaces(2011-05) Ehlert, Robert; Downer, Michael Coffin; Demkov, Alexander A.; Ekerdt, John G.; Fink, Manfred; Li, XiaoqinSpectroscopic second-harmonic generation (SHG) and reflectance-anisotropy spectroscopy (RAS) are used to probe molecular adsorption on clean reconstructed single-domain stepped Si(001) in ultra-high vacuum (UHV). We implement a simplified bond hyperpolarizability model (SBHM) as a common microscopic analysis for SHG and RAS. Three different scenarios are studied: (i) The dissociative adsorption of molecular hydrogen on dangling bonds of D[subscript B] step-edges. (ii) Structural changes to rebonded r-D[subscript B] steps induced by exposure to atomic hydrogen. (iii) The adsorption of cyclopentene on Si(001)(2x1) terrace dimers in a [2+2] cycloaddition pathway. Using the SBHM we develop a new optical fingerprinting method to isolate, identify and monitor individual types of bonds (e.g. dimers, rebonds, dangling bonds, backbonds) and their chemical activity on a single-domain stepped Si(001) surface using nonresonant, but rotationally-anisotropic, second-harmonic generation (RA-SHG). The methods presented here will be applicable to many material systems and allow to track, in-situ and in real-time, the chemical action of adsorbates on surfaces.Item Graphene and III-V channel metal-oxide-semiconductor field-effect devices for post-Si CMOS applications(2013-12) Ramón, Michael Edward; Banerjee, Sanjay; Akinwande, Deji; Tutuc, Emanuel; Lee, Jack C; Sreenivasan, S. V.To meet the demands for continuous transistor scaling and performance improvements required by the ITRS, there has been a tremendous amount of effort related to alternative high mobility channel materials as potential Si replacements for MOSFET fabrication. Two particularly attractive material systems include III-V substrates and graphene. Thus far, the high trap density which characterizes high-κ dielectrics and the III-V/high-κ dielectric interface remains an obstacle to III-V substrate integration. In a first aspect of this work, charge traps within the gate stack of III-V MOSFETs, as well as at the III-V/dielectric interface, were examined to better understand their impact on III-V device performance. In particular, a pulsed I-V measurement technique was used to assess the impact of fast and slow transient charging effects on various III-V transistors with ALD-deposited Al2O3 gate dielectric. The charge pumping technique was also utilized to determine the density of interface traps, including their energy distribution and position profile, providing further understanding into the nature of traps in the III-V/high-κ system. Graphene has also attracted considerable interest owing to its high intrinsic mobility, large current densities, thermodynamic and mechanical stability. Yet, a primary challenge to the integration of graphene substrates is the lack of high quality, large-area graphene. Thus, in another aspect of this work, large-area graphene was synthesized by CVD of acetylene on Co thin films, and the influence of Co film thickness on graphene synthesis was studied. Resulting graphene films were characterized using Raman spectroscopy and back-gated GFETs were fabricated. Taking advantage of graphene’s intrinsic ambipolar electron-hole symmetry, GFET frequency doublers were fabricated on low-capacitance, single-crystal quartz substrates. GFETs frequency doublers were found to operate beyond their transit frequency (fT), and in the limit of vanishing device non-idealities, their maximum conversion gain was determined to approach a near lossless value. To further understand and improve GFET RF performance, the impact of parasitic resistances was experimentally examined. RF measurements as a function of temperature and modulated access resistance highlight the strong influence of RC on scaled devices, while the impact of RA becomes more evident for devices with large access regions.Item Nanoelectronics based on epitaxial oxides(2015-08) Hu, Ph. D., Chengqing; Yu, Edward T.; Lee, Jack C; Register, Leonard F; Ekerdt, John G; Sun, NanCrystalline oxide materials and heterostructures have been under extensive investigation owing to the richness of the physical, chemical, and electrical properties they exhibit, including ferromagnetism, ferroelectricity, ferrotoroidicity, superconductivity, metal-insulator transition, multiferroics, and 2-dimensional electron liquids. In recent years, the advancement of thin film growth techniques such as molecular beam epitaxy and atomic layer deposition has made possible monolithic integration of these crystalline oxide materials with mainstream semiconductor substrate materials such as Si and Ge, which opens new avenues for improving existing device performance and provides many opportunities for adding various solid-state device functionalities to electronic devices that are unachievable with conventional semiconductor materials. Epitaxial oxide heterostructures with a perovskite crystal structure are emerging as outstanding candidates for realization of devices in which diverse material properties - ferromagnetism, piezoelectricity, ferroelectricity, and others - are flexibly coupled to achieve new functionality. In the first part of this dissertation, the strain-dependent ferromagnetism in LaCoO3, piezoelectric response in SrTiO3, and their strain coupling in a single-crystal oxide heterostructure grown on Si (001) are employed to enable a novel approach to modulating ferromagnetism and magnetoresistance by application of a gate voltage in a suitably fabricated device. The second part of the dissertation addresses the resistive switching behavior and physics of epitaxial single-crystal anatase TiO2 on silicon and demonstrates several unique advantages of using single-crystal metal oxide films as an active switching layer, including a high ON/OFF ratio, a great potential for device scaling, highly linear current-voltage characteristics, and room-temperature, reproducible quantization of conductance, etc. Finally, epitaxial SrHfO3-based gate stacks for Ge metal-oxide-semiconductor devices are investigated as an approach to alleviate the gate dielectric interface quality problem that has tremendously hampered the adoption of next-generation Ge-based transistors. Different methods are shown to effectively decrease the interface trap density, and the gate stacks developed in this dissertation represent the state of the art in terms of the combination of equivalent oxide thickness and gate leakage. In summary, this dissertation presents several results in the design and modeling, process integration, characterization, and analysis of device prototypes for functional and nano- electronics applications using epitaxial oxide films. These results provide a foundation for further exploration of solid-state device applications using epitaxial crystalline oxide materials.Item Nanoscale graphene for RF circuits and systems(2013-08) Parrish, Kristen Nguyen; Akinwande, DejiIncreased challenges in CMOS scaling have motivated the development of alternatives to silicon circuit technologies, including graphene transistor development. In this work, we present a circuit simulator model for graphene FETs, developed to both fit measured data and predict new behaviors, motivating future research. The model is implemented in Agilent ADS, a circuit level simulator that is commonly used for non-standard transistor technologies, for use with parameter variation analyses, as well as easy integration with CMOS design kits. We present conclusions drawn from the model, including analyses on the effects of contact resistance and oxide scaling. We have also derived a quantum-capacitance limited model, used to intuit intrinsic behaviors of graphene transistors, as well as outline upper bounds on performance. Additionally, the ideal frequency doubler has been examined and compared with graphene, and performance limits for graphene frequency multipliers are elucidated. Performance as a demodulator is also discussed. We leverage this advancement in modeling research to advance circuit- and system-level research using graphene transistor technology. We first explore the development of a GHz planar carbon antenna for use on an RF frontend. This research is further developed in work towards the first standalone carbon radio on flexible plastics. A front end receiver, comprised of an integrated carbon antenna, transmission lines, and a graphene transistor for demodulation, are all fabricated onto one plastic substrate, to be interfaced with speakers for a full radio demo. This complete system will motivate further research on graphene-on-plastic systems.Item Test and characterization of engineering nanocoatings for mems and nanoenergetic materials(2012-05) Vijayasai, Ashwin; Dallas, Timothy E. J.; Gale, Richard O.; Pantoya, Michelle; Weeks, Brandon L.; Hase, William L.; Yeo, ChangdongThis dissertation presents the development, test and characterization of engineered nanocoatings for MEMS and nano-energetic reactive materials. Surface modification on MEMS and nano-energetic reactive materials are developed using a commercially available nanocoating tool. Surface modifications include Chemical Vapor Deposition of Fluorocarbon SAM and nanoparticles and Atomic Layer Deposition of thin oxides. Detailed descriptions of the nanocoating process and their chemical reactions are explained. An F-SAM coated MEMS tribogauge is characterized to estimate the adhesive and frictional forces. In-situ frictional measurements were made. Increasing adhesion force was observed for increasing number of load cycles. The tribogauge is later used as an ex-situ characterization tool to observe the performance of various nanocoating recipes for F-SAM coating. Characterization of the tribogauge is performed using an electronic sense tool. Contact angle goniometer was used to characterize the performance of various recipes. Various types of nanocoatings were deposited on witness samples and nano-energetic materials. A comparison study of underwater combustion tests were made on these thermite pellets. An aging study was performed on both nanocoated witness samples and pellets. The aging experiment is performed by submerging them in de-ionized water for 10 days. Contact angle goniometer and few optical microscopes were used to characterize the performance of various recipes. Apart from the nanocoating based projects, this dissertation briefly explains other projects that were part of the graduate program. A brief description and initial results of a few MEMS device designs are explained in this dissertation. As part of future work new MEMS devices were designed that will allow follow-up nanocoatings projects.