Browsing by Author "Michael Escuti, Committee Member"

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3D Integral Invariant Signatures And Their Application on Face Recognition
(2007-09-17) Feng, Shuo; Hamid Krim, Committee Chair; Irina Kogan, Committee Member; Michael Escuti, Committee Member; Griff Bilbro, Committee Member
Curves are important features in computer vision and pattern recognition, and their classification under a variety of transformations, such as Euclidean, affine or projective, poses a great challenge. Invariant features of these curves turn out to be crucial to simplifying any classification procedure. This, as a result, has recently led to a renewed research interest in transformation invariants. In this thesis, new explicit formulae for integral invariants for curves in 3D with respect to the special and the full affine groups are presented.The development of the 3D integral invariant are based on an inductive approach in terms of Euclidean invariants. For the first time, a clear geometric interpretation of both 2D and 3D integral invariants is presented. Since integration attenuates the effects of noise, integral invariants have advantages in computer vision applications. We use integral invariants to construct global and local signatures that characterize curves up to the special affine transformations, subsequently extended to the full affine group. Global Signatures are independent of parameterization, and Local Signatures are independent of both parameterizationa and initial point selection. We analyze the robustness of these invariants in their application to the problem of classification of noisy spatial curves extracted as characteristics from a 3D object. Our investigation of 2D and 3D integral invariants and signatures, originally motivated by Biometrics applications, are successfully implemented and applied to face recognition to eliminate the effects of pose and facial expression. A high recognition performance rate of 95% is achieved in the test with a large face data set.
Applications of Redox Active Molecules in Solid State Electronics Devices and Organic Photovoltaic Cells
(2009-12-08) Chen, Zhong; Veena Misra, Committee Chair; Carl Osburn, Committee Member; Michael Escuti, Committee Member; Orlin Velev, Committee Member
Redox active molecules have been studied for several years due to their interesting charge storage properties for future application in molecular memory devices with multi-bit low-voltage operation and ultimate scalability. Hybrid Si-Molecular devices with liquid electrolyte as gate contact have been demonstrated for future DRAM and FLASH memories. The focus of this dissertation work has been on developing the completely solid state hybrid Si-Molecular devices embedded with redox active molecules to facilitate ease of integration. In addition, redox active molecules have also been explored in potential application in organic photovoltaic cells. This work exploits the charge storage properties of redox molecules in solid state devices and the absorption profile of the redox polymers. The charge transfer and charge screening process in conventional electrochemical cell with liquid electrolyte has been characterized using cyclic voltammetry measurements. The role of the liquid electrolyte and the electrical double layer in electrochemical cell for the redox process has been discussed. The solid state approach to hybrid Si-Molecular devices has been proposed. The solid state dielectric layer has been considered to replace electrical double layer. The requirements of dielectric layer and deposition methods in solid state molecular memory device are investigated for preservation and characterization of the redox molecules. AlN, Al2O3 and HfO2 are deposited and examined on top of redox active polymers or redox monolayer in metal-insulator-molecules-silicon (MIMS) or metal-insulator-molecules-metal (MIMM) capacitors. The CyV measurements indicate that the redox properties are preserved after dielectric layer deposition on molecules. The leakage of MIMM capacitors has been greatly improved after the optimization on HfO2 atomic layer deposition conditions and the W/WN gate stack. The low leakage current of MIMM structure provide a reliable test platform for redox molecules as well as the other molecule with more functionalities. The redox process in the ionic cell has been modeled with equivalent circuits. The capacitance at different frequencies for EMS capacitors is simulated to study the electrical properties of the solid state molecular device. The frequency dispersion of capacitance measurements for MIMM capacitance has been explored for understanding the redox charging or trapping in the molecular layer. Si nano-membranes are fabricated as an alternative contact to molecules. Solid state molecular transistors are demonstrated for the possible application in FLASH memory. Redox polymers are investigated for the application in renewable energy area. The organic nanoparticles-polymer solar cell has been compared with conventional bulk Si solar cell. The integration of redox polymers helps to improve the absorption profile of active layer in organic solar cells. Organic solar cells with P3HT and PCBM are fabricated and characterized for the future incorporation of redox molecules. In summary, this work provides the fundamental insights and realistic approaches for the applications of redox active molecules with unique charge storage properties into solid state electronic devices and organic photovoltaic cells, which may enable the solutions for the low cost multi-bit low-voltage scalable molecular memories as well as the high efficiency organic solar cell embedded with redox molecules.
Electron and Ion-beam Characterization of Nitride Semiconductor Devices.
(2006-12-06) Parish, Chad Michael; Phillip Russell, Committee Chair; Dieter Griffis, Committee Member; Gerd Duscher, Committee Member; Michael Escuti, Committee Member
Gallium nitride (GaN) and its alloys are used to manufacture green-to-ultraviolet range light emitting diodes (LEDs) for the solid-state lighting industry. However, heteroepitaxial growth on substrates such as 6H-SiC or -Al2O3 results in LEDs with large densities of crystal defects; the optical and electronic properties of these defects, and their influences on LED device performance, are not yet well understood. Controlling and optimizing processing in modern optoelectronic materials, such as GaN, requires a high-resolution characterization technique to probe the localized bandstructure of the materials and their defects in order to relate properties to processing. The beam-injection modes of scanning electron microscopy (SEM) fulfill this need. When an SEM is used to examine a semiconductor, the electron beam injects electron-hole pairs (EHPs) into the semiconductor's band structure. Cathodoluminescence (CL) and electron-beam-induced current (EBIC) are SEM techniques that take advantage of this localized beam-injection of EHPs, and are used to directly probe the optoelectronic behavior of semiconductor materials, devices, and defects. This work examines the optoelectronic properties of defects in GaN-based LED devices. First, computer modeling of the polarization fields in quantum wells was performed, and quantitative predictions of cathodoluminescence peak shifts during electron injection, under varying conditions of electrical bias, were made. Experimental conditions and mathematical treatments for accurate EBIC quantification of the minority carrier diffusion length in GaN light-emitting diodes (LEDs) were developed and refined, as were combined CL and EBIC techniques for the study defect populations in GaN LEDs. Additionally, the effects of focused-ion-beam milling as a cross-sectional sample preparation technique for GaN were studied by CL and EBIC. Limitations and possible extensions to these techniques are also be discussed. By using SEM-EBIC/CL to pinpoint defects in LED devices, site-specific FIB microsampling has been used to prepare samples of defected areas for transmission electron microscopy (TEM). Analyses of these samples have shown how the identity of crystal defects within the devices directly relates to the optoelectronic behavior observed in EBIC and CL.
Low Resistivity Contact Methodologies for Silicon, Silicon Germanium and Silicon Carbon Source/Drain Junctions of Nanoscale CMOS Integrated Circuits.
(2009-12-03) Alptekin, Emre; Mehmet C. Ozturk, Committee Chair; Thomas P. Pearl, Committee Member; Michael Escuti, Committee Member; Veena Misra, Committee Member
State-of-the-art p-channel metal oxide semiconductor field effect transistors (MOSFETs) employ Si(1-x)Ge(x) source/drain junctions to induce uniaxial compressive strain in the channel region in order to achieve hole mobility enhancement. It is also know that the elec- tron mobility can be enhanced if the MOSFET channel is under uniaxial tension, which can be realized by replacing Si(1-x)Ge(x) with Si(1-y)C(y) epitaxial layers in recessed source/drain regions of n-channel MOSFETs. This dissertation focuses on epitaxy of Si(1-y)C(y) layers and low resistivity contacts on Si, Si(1-x)Ge(x), and Si(1-y)C(y) alloys. While these contacts are of particular importance for future MOSFETs, other devices based on these semiconductors can also benefit from the results presented in this dissertation. The experimental work on Si(1-y)C(y) epitaxiy focused on understanding the impact of various process parameters on carbon incorporation, substitutionality, growth rate, phosphorus incorporation and activation in order to achieve low resistivity Si(1-y)C(y) films with high substitutional carbon levels. It was shown, for the first time, that phosphorus lev- els above 1.3x10^(21) cm^(-3) can be achieved with 1.2% fully substitutional carbon in epitaxial layers. Specific contact resistivity (C) on strained Si(1-x)Ge(x) layers was evaluated using the existent results from the band structure calculations. Previous work on this topic mainly focused on barrier height and the doping density at the interface. In this work, the impact of the tunneling effective mass on specific contact resistivity was calculated for the first time for strained Si(1-x)Ge(x) alloys. It was shown that due to the exponential dependence of contact resistivity on this parameter tunneling effective mass may have a strong impact on contact resistivity. This is especially important for strained alloys in which the tunneling effective mass is dependent on the strain. The contact resistivity was found to decrease with Ge concentration due to the smaller tunneling effective mass in strained Si(1-x)Ge(x). These calculations can also be extended to Si(1-y)C(y) junctions when better models for the Si(1-y)C(y) band structure are available. Two different metallization schemes have been considered. In the first approach, two band edge silicides are used to achieve low-resistivity contacts on complimentary MOSFETs. For this purpose, experiments on band edge silicides including PtSiGe, NiSiC and ErSiC were conducted. The impact of Ge and C on silicide formation and the barrier height at the interface was investigated. Barrier height values around 0.3 eV were achieved with PtSiGe and ErSiC contacts formed on p-Si(1-x)Ge(x)and n-Si(1-y)C(y), respectively. Due to the exponential dependence of contact resistivity on barrier height, this barrier height is low enough to yield contact resistivity figures below 10^(-8) Ohm-cm^(2) even with modest doping levels. On the other hand, smaller barrier height values will be needed for Schottky barrier MOSFETs. It is more desirable to use a single metal contact metal on both p- and n-channel MOSFETs, which requires tuning of the barrier height. Impurity implantation was considered as a means to achieve barrier height tuning. Extremely small barrier height values below 0.1 eV were obtained by sulfur segregation for the silicides of Pt, Ni and NiPt on n-type Si and Si(1-y)C(y). Indium segregation was used for the first time to lower the hole barrier height to obtain barrier height values below 0.2 eV on p-Si. The results provide several approaches that can be used to form low resistivity contacts. We believe that the knowledge gained from this work is expected to have a significant impact on choosing the most effective and economical approach to form low-resistivity contacts in CMOS manufacturing.