Browsing by Subject "Electrodes"
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Item A.C. impedance studies of electrode surfaces and electrode reactions(Texas Tech University, 1989-05) Young, Joe PingNot availableItem Compact gate capacitance and gate current modeling of ultra-thin (EOT ~ 1 nm and below) SiO₂ and high-k gate dielectrics(2006) Li, Fei, 1972-; Register, Leonard F.; Banerjee, SanjayThe Metal-Oxide-Silicon (MOS) gate dielectrics have to be scaled down to about 1 nm to 0.5 nm equivalent oxide thicknesses (EOTs) to maintain the projected gate control over the silicon channel for ultra-large-scale-integrated (ULSI) circuits in the next generation. Various high-dielectric-constant (high-κ) materials and metal gate electrodes are being studied heavily as the replacements for conventional SiO2 dielectrics and polysilicon gate electrode to overcome the increasingly deleterious gate leakage current and polysilicon related problems (polydepletion effects, B penetration, etc.) in conventional MOS devices. Furthermore, quantum mechanical (QM) effects and FermiDirac statistics in both the Si substrate (subband formation, wave function penetration effects, etc.) and gate dielectrics (direct and Fowler-Nordheim (F-N) tunneling effects) have to be fully understood and simulated to interpret the measured gate capacitance (CgVg) and gate current (Ig-Vg) behavior precisely. Although such behavior can be somewhat addressed in numerical studies of gate stacks, the increasing physical complexity of the problem has made it difficult to create compact models applicable to and below ~ 1 nm EOTs. And while such numerical Cg-Vg and Ig-Vg simulators can provide a physically accurate and comprehensive understanding of these effects, efficient analytic Cg-Vg and Ig-Vg models with similar accuracy are required for practical every-day device and ULSI circuit simulations. In this work, a computationally efficient and accurate physicallybased integrated gate capacitance and gate current model of MOS devices with advanced ultra-thin EOT oxides (down to ~0.5 nm) is introduced for current and future integrated circuit technology nodes. With the aid of self-consistent numerical Schrödinger-Poisson calculations, the QM effects have been reconsidered in this model. The 2/3 power law for the lowest quantized energy level versus field relations (E1 ∝ Fox 2/3), often used in compact models, was refined to 0.61 for electrons and 0.64 for holes, respectively, in the substrate in the regimes of moderate to strong inversion and accumulation to address primarily barrier penetration more accurately. The filling of excited states consistent with Fermi-Dirac statistics has been addressed. Within the same framework for surface potential and available carriers for tunneling, a modified version of the conventional Wentzel-Kramers-Brillouin (WKB) approximation allows for the effects of the abrupt material interfaces and non-parabolicities in complex bandstructures of the individual dielectrics on the tunneling current (both direct and F-N). The model was implemented and tested by comparisons to both numerical calculations down to 0.5 nm, and to experimental data from n-MOS or p-MOS metal-gate devices with SiO2, Si3N4 and high- κ (e.g., HfO2) gate dielectrics on (100) Si with EOTs down to ~1 nm. The compact model has also been adapted to address interface states, and poly-depletion and polyaccumulation effects on gate capacitance. A nonlinear least-square fitting program is demonstrated for fast and automatic gate characterization and parameter extraction for the 45-nm CMOS technology node and beyond.Item The development and application of glucose electrodes based on "wired" glucose oxidase(2001-12) Chen, Ting; Heller, AdamThe sensitivity of rapidly responding “wired” glucose sensing microelectrodes with a tailored outer membrane was examined in vivo. It is shown that these microsensors maintained in vivo sensitivities similar to those in buffer before the implantation and after the explantation when implanted intravenously or intraperitoneally for several hours in the rat. Maintenance of the sensitivity in vivo provides the basis for pre-calibrating the microsensors in vitro, lifting the requirement of in vivo calibration. The in vitro calibration results can be used by the patients as a reference in judging the reliability of sensor readings. The causes of much more rapid decaying current in the “wired” glucose oxidase-based microelectrodes in serum compared to their sensitivity in buffer were studied. Urate and transition metal ions were identified as two main causes for the loss in current. Urate is electrooxidized to dimeric or trimeric products, which precipitate in the electrocatalytic film, reducing the mobility of the redox sites of the polymer. Transition metal ions coordinatively crosslink pyridine or imidazole functions of the redox polymers and also inhibit glucose oxidase. Implantable “wired” glucose microsensors with novel polyionic membrane for mass transport-controlling were developed and tested in the jugular veins and in the intrascapular subcutaneous region of non-diabetic SpragueDawley rats. The micromembranes were assembled by sequentially chemisorbing polyanions and polycations on miniature enzyme electrodes. The sequential chemisorption process allowed the simultaneous tailoring of their sensitivity, dynamic range, drift and selectivity. The membranes also retained transition metal ions that bound to and damaged the redox polymer “wiring” the enzyme. All of the in vivo data points measured by the microsensors were clinically accurate after correcting the lag time of the glycemia in the subcutaneous fluid behind that of blood withdrawn from the vein. The “wired” glucose enzyme microelectrode was also used as the microanode in developing a compartmentless miniature biofuel cell intended to be an implanted mini power source for medical microdevice. The glucose-oxidizing anode was combined with a high current output “wired” laccase microcathode, which catalyzes the electro-reduction of O2 to water. The areas of the anode and the cathode of the cell are much smaller than any previously reported fuel cell. The power density of the cell exceeds by a factor of five that of the highest power density of earlier reported glucose-air biofuel cells. The effects of different buffers, oxygen concentration, pH and chloride on cell current were investigated.Item Electrode erosion from high current, high energy moving arcs(Texas Tech University, 1988-08) Lehr, F. MarkNot availableItem Electrode erosion measurements in a high energy spark gap(Texas Tech University, 1982-08) Donaldson, Anthony LyleNot availableItem Electron transport in nanoparticle single-electron transistors(2007-12) Luo, Kang, 1976-; Yao, Zhen, Ph. D.Electron transport in nanoparticle single-electron transistors (SETs) is a fruitful method to explore a wide range of physical phenomena at the nanometer scale. In this thesis, we investigate electron transport in SETs incorporating various nanoparticles, including gold nanoparticles in both classical and quantum regimes and Pb nanoparticle in both superconducting and normal states. SETs have been successfully fabricated by incorporating individual gold nanoparticles into the gaps between two electrodes. Although single-electron tunneling behavior is prominent, quantized energy levels cannot be resolved in these SETs due to their relatively large particle sizes. A novel method has been developed to achieve SETs incorporating gold nanoparticles whose sizes are small enough to resolve discrete quantum energy levels. The devices consist of spontaneously-formed ultrasmall gold nanoparticles linked by alkanedithiols to gold electrodes. The devices reproducibly exhibit addition energies of a few hundred meV, which enables the observation of single electron tunneling at room temperature. At low temperatures, resonant tunneling through discrete energy levels in the Au nanoparticles is observed, which is accompanied by the excitations of molecular vibrations at large bias voltage. Having explored the SETs in normal state, we have extended the experiments to superconducting single-electron transistors (SSETs). We first fabricated and characterized Pb superconducting electrodes with nanometer-sized separation. Our observation clearly shows that conventional Barden-Cooper-Schrieffer theory remains valid to interpret the tunneling behavior between two nanometer-spaced Pb electrodes. Furthermore, by incorporating Pb nanoparticles between the two Pb electrodes, we have fabricated SSETs and investigated the transport properties of these devices. In the superconducting state, the conductance is suppressed by a combination of the single electron tunneling effect and the absence of density of states within the superconducting gap. In the suppression regime, the tunneling spectroscopy shows current features that arise from quasiparticle tunneling caused by singularity matching. At low temperature, the features can only be observed for odd charge states in SSETs. At high temperature, the odd-even parity effect is smeared out. Upon application of a magnetic field, the superconducting state is suppressed and single-electron tunneling behavior for normal metallic nanoparticles is recovered.Item Erosion phenomena of arcing electrodes(Texas Tech University, 1980-05) Petr, Rodney AlanNot availableItem Functionalized crown ethers as ionophores in ion selective electrodes(Texas Tech University, 1986-12) Cason, Charles VictorNot availableItem Hafnium dioxide gate dielectrics, metal gate electrodes, and phenomena occurring at their interfaces(2004) Schaeffer, James Kenyon; Ekerdt, John G.As metal-oxide-semiconductor field-effect transistor (MOSFET) gate lengths scale down below 45 nm, the gate oxide thickness approaches 1 nm equivalent oxide thickness. At this thickness, conventional silicon dioxide (SiO2) gate dielectrics suffer from excessive gate leakage. Higher permittivity dielectrics are required to counter the increase in gate leakage. Hafnium dioxide (HfO2) has emerged as a promising dielectric candidate. HfO2 films deposited using metal organic chemical vapor deposition are being studied to determine the impact of process and annealing conditions on the physical and electrical properties of the gate dielectric. This study indicates that deposition and annealing temperatures influence the microstructure, density, impurity concentration, chemical environment of the impurities, and band-gap of the HfO2 dielectric. Correlations of the electrical and physical properties of the films indicate that impurities in the form of segregated carbon clusters, and low HfO2 density are detrimental to the leakage properties of the gate dielectric. Additionally, as the HfO2 thickness scales, the additional series capacitance due to poly-silicon depletion plays a larger roll in reducing the total gate capacitance. To solve this problem, high performance bulk MOSFETs will require dual metal gate electrodes possessing work functions near the silicon band edges for optimized drive current. This investigation evaluates TiN, Ta-Si-N, Ti-Al-N, WN, TaN, TaSi, Ir and IrO2 electrodes as candidate electrodes on HfO2 dielectrics. The metal-dielectric compatibility was studied by annealing the gate stacks at different temperatures. The physical stability and effective work functions of metal electrodes on HfO2 are discussed. Finally, Fermi level pinning of the metal is a barrier to identifying materials with appropriate threshold voltages. The contributions to the Fermi level pinning of platinum electrodes on HfO2 gate dielectrics are investigated by examining the impact of oxygen and forming gas anneals on the effective work function of platinum-HfO2-silicon capacitors. Oxygen anneals result in higher effective work functions for platinum on HfO2 than forming gas anneals. The presence of interfacial oxygen vacancies or Pt-Hf bonds is believed to be responsible for a degree of pinning that is stronger than predicted from the metal induced gap states model alone.Item Hybrid integrated electrocardiogram electrodes(Texas Tech University, 1978-05) Griffith, Michael ENot availableItem Impact of surface conditioning of large area electrodes on the dielectric strength of water(Texas Tech University, 2004-08) Wetz, David A.Due to water's high dielectric constant, 6r = 81, there is considerable interest in breakdown phenomena in water, particularly as an insulator and/or switching media in pulsed power systems. In numerous research efforts conducted over the last several decades, it has been documented that electrical breakdown in water is initiated from localized field enhancements on the electrode surface caused from asperities or microprotrusions on the electiode surface. The research conducted here attempts to determine the impact of electiode surface conditions on the holdoff voltage of a water gap. In this document, experimental results are presented on the impact electrode material and surface treatment has on the dielectric strength of water. A 4mm water gap was tested under pulsed conditions with pulse widths greater than 1 /is, peak electric fields over 1 MV/cm and peak currents over 20 kA. Stainless steel electrodes machined with a Bruce profile and an effective area of 5cm^ were tested with surface roughnesses ranging from .34 /.im to 1.41 /xm. Results comparing electiodes that have additionally been electropohshed are compared to those without an additional tieatinent. These various surface tieatments remove microprotrusions from the electiode surface and reduce localized field enhancements. It is believed that this technique will minimize the number of breakdown initiation points, thereby, increasing tiie dielectiic stiength. Results are given on the degree to which each finish improves the dielectiic stiength of water.Item Insulated Electrocardiogram Electrodes(Texas Tech University, 1972-05) David, Robert MyersNot Available.Item Interface engineering and reliability characteristics of HfO₂ with poly Si gate and dual metal (Ru-Ta alloy, Ru) gate electrode for beyond 65nm technology(2004) Kim, Young-Hee; Lee, Jack Chung-YeungItem Investigation of shock pressures in high current spark gap electrodes(Texas Tech University, 1995-08) Wofford, MicheleGenerally, the limiting component in a pulsed power system is the switch This is due to the fact at some point, the switch transfers all of the energy in the system High voltage and current create a rough environment for switch electrodes and insulators. In previous studies of switch reliability and lifetime, electrode erosion has received much attention. This investigation deals with the mechanisms behind electrode fracture, which presents an immediate problem, rather than erosion, which has long-term effects on switch performance. The switches under study are spark gaps with graphite electrodes. The spark gap closes when an electric arc forms between the electrodes, and current conduction begins Strong mechanical forces are generated as the arc forms and impact the electrodes. The purpose of this research is to determine the dominant pressure mechanism of electrode fracture, and the propagation of the pressure wavefront through the electrode. Energy is stored in a 5 kJ, 60 kV capacitor, and shorted through the spark gap. This is done to duplicate prior experimental work at Physics International Company. Operating parameters, such as gap spacing, air pressure, charging voltage, inductance, and magnetic pulse shaping, are varied, and mechanical pressure is measured using a strain gage mounted on a ceramic bar. Experimental data from the strain gage is compared to theoretical modeling done in Mathcad and PSPICE.Item Mass transfer in the cone and plate system and its applications(Texas Tech University, 1980-05) Lo, Jen-tsenMass transfer and electrode reaction for an electrochemical process in the cone and plate geometry was studied. Analytical expressions for the concentration profiles and current distribution were obtained for the following four cases: (i) unsteady state electrolysîs below limiting current conditions; (ii) unsteady state electrolysis at limiting current conditions; (iii) steady state electrolysis below the limiting current conditions; (iv) steady state electrolysis at limiting current conditions. The reaction order, the reaction rate constant, the electrode reaction transfer coefficient, the number of electrons involved, and the diffusion coefficient can be determined by solving for the current necessary to maintain a constant potential difference across the electrodes (potentiostatic method).Item Metal cation complexation and separation with macrocyclic polyether ligands(Texas Tech University, 2004-12) Vogel, Howard FAt Hanford, Washington, the Department of Energy maintains a site that contains approximately 6x10^7 gallons (2 x l0^8 liters) of waste left over from the development of nuclear weapons after WWII. This volume of material is too great to be stored in Yucca Mountain. Separation of the high-level radionuclides from the bulk of the material will allow the remainder to be treated and disposed of as low-level waste. Once separated, the high-level nuclides are then available for use in commercial applications, such as medical imaging and remote power plants. This study explores the use of crown and lariat ethers for the separation of metal ions. A large number of compounds varying in specific structural aspects are studied using isothermal titration calorimetry (ITC), which directly determines the association constant, stoichiometry, and enthalpy of each metal-ligand system. Augmenting the ITC study is the intense study of a small selection of compounds. These compounds are studied under various conditions using a variety of techniques, such as ion-selective electrodes (ISE) and solvent extraction (SE), allowing for a fuller understanding of their association behavior. The presence of metal ion is our world is ubiquitous. Some of these metals are benign, or even necessary for life. Others are harmful in minute quantities. The ability to selectively remove specific metal ions from waste streams, the environment, and our bodies will be an important process in years to come.Item New crown ether compounds and their alkali metal ion complexation(Texas Tech University, 1994-05) Torun, LokmanNOT AVAILABLEItem Simulation and analysis of the role of the electrodes in power degradation of alkali metal thermal to electric converter(Texas Tech University, 2000-08) Chowdhury, Sirajus SalekinRecently, much work has been done on the design of the Alkali Metal Thermalto-Electric Converter (AMTEC). One of the major problems yet to solve in AMTEC is its power degradation with time. During the extended testing of the AMTEC, maximum power output of the AMTEC was found to be decreasing from 2.45 W to 1.27 W after 18,000 hours of operation. Therefore, it is important to investigate and minimize the power degradation of AMTEC as much possible. AMTEC uses TiN electrodes which degrade with time due to the grain growth and surface self-diffusion. In this project, the role of the electrode on the overall power degradation was investigated and reasons of the degradation were established qualitatively and quantitatively. The electrode was found 17% on average responsible for the overall degradation of power output. This work was also extended in finding possible remedies and modifications in the electrode material. Finally, RhW, and RhiW electrodes were found to be the better electrodes considering their improved grain growth and surface self-diffusion behavior.Item Simulation of Planar-Disk and Tubular Electrodes(Texas Tech University, 1973-08) Flanagan, James BrianNot Available.Item A study into the non-invasive manipulation of skin blood flow utilizing electrotherapy techniques integrating Eastern and Western research to create an engaging, open-ended classroom experiences.(2013-08) Casselman, James Edwin; Diller, K. R. (Kenneth R.)The research to date, of transcutaneous electric nerve stimulation on cutaneous blood flow, is equivocal. The purpose of this report is to review the TENS body of knowledge, in particular synthesizing the literature on acupuncture stimulation of cutaneous blood flow with the two fold goal of creating a protocol to increase skin blood flow through the exogenous application of electrical stimulation, as well as creating an engaging engineering challenge for high school anatomy and physiology students. The hypothesis developed was TENS stimulation with electrode placement on specific acupuncture points would influence cutaneous blood flow as measured using laser Doppler flowmetry. The findings of this project did not support the hypothesis of TENS or Interferential electrical stimulation, in combination with acupuncture points or not, influencing skin blood flow. Perhaps this is due to the physiological differences between glabrous and non-glabrous skin and the different electrical resistances of each dermal layer, nerve stimulation, age and gender of subject or some combination thereof. These equivocal findings may also be the result of inconsistencies in testing protocols, such as subject preconditioning or not, subject’s position during administration of stimulation, electrode size and placement to name a few. Ultimately, this report provides a summary of the research to date, as well as outlining how this research could be adapted to supply engaging bio engineering challenges in the classroom including challenges to develop a model for delivering current to muscle; develop a model for skin blood flow management to name a few.