Browsing by Author "Frensley, William R."
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Item Circuit Level Modeling of Spintronic Devices(2017-12) Sharma, Nishtha; 0000-0001-7404-8806 (Sharma, N); Marshall, Andrew; Frensley, William R.It is an exciting time for circuit designers working on beyond-CMOS logic and memory design. Many alternative technologies to conventional Complementary Metal Oxide Semiconductor (CMOS) technology have been proposed in recent years and there is an ongoing effort by many state of the art research institutes around the world to fabricate these devices. The magneto-electric (ME) devices are just one class of beyond-CMOS device, but they offer some advantages which make them a very promising group of devices, including non-volatility, voltage control, together with low power operation. These devices are extremely compact compared to the CMOS equivalents. Many of the advantages of the ME devices are known although there have been no quantitative studies for the calculation of the energy requirements of voltage control of magnetism, thus it is important to understand the trade-offs of the components. Perceiving a need for a modeling platform for simulating the possible logic circuits that can be derived from the ME devices and also perform an energy-delay evaluation of these devices, we developed Verilog-A models. These are used as a modeling platform for simulating ME devices in Spectre to evaluating their performance compared to conventional CMOS at the circuit level.Item Development of a Long-Wave Infrared Band-Edge Thermometry Instrument(2018-12) Marquis, Jeremy Michael; 0000-0002-4381-5782 (Marquis, JM); Frensley, William R.Accurate measurement of substrate temperature is one of the most critical process control parameters for molecular beam epitaxy (MBE) growth. Band-edge thermometry instruments have proven to be a valuable tool for process control during MBE growth of semiconductor films, providing as high as ±1 °C temperature resolution. The increasing use of InAs, GaSb, and AlSb III-V materials necessitates a method for accurately measuring the temperature of their lattice-matched GaSb substrates. Current-technology instruments typically rely on InGaAs detector materials which have a maximum wavelength λ detection of ~1.7 µm, but GaSb substrates have a band gap corresponding to > 2 µm wavelength. MBE growth needs a band-edge thermometry instrument capable of λ > 2 µm for process control. Such an instrument has been developed using an InAs/InGaSb strained-layer superlattice detector sensitive sensitive to 2-9.5 µm long-wave IR wavelengths.Item Development of Softening Polymer-based Spinal Cord Stimulation Leads for Chronic Applications(2021-12-01T06:00:00.000Z) Garcia Sandoval, Aldo; Voit, Walter E.; Pancrazio, Joseph; Frensley, William R.; Cogan, Stuart; Ware, TaylorSpinal cord stimulation (SCS) leads are a type of neural interface that can be implanted in the epidural space and deliver electrical pulses to change or block signals traveling to the brain. SCS leads are commonly used to alleviate chronic back pain resulting from failed back surgery syndrome and other injury and disease-related conditions. Recently, researchers have tried to develop treatments to restore movement in patients with a spinal cord injury. However, clinical cervical SCS has been limited by the size of the SCS leads, the small epidural space around the cervical spinal cord, and the large degree of movement of the neck. Furthermore, commercially available SCS leads are not compatible for their use in small animal models where most of the preclinical research is done. Therefore, in this dissertation work, we (1) have developed a thinfilm softening SCS lead that can be implanted in the cervical spinal cord of a rat model and evoke muscle responses after SCS. (2) We have also developed ester-free nondegradable softening polymer-based SCS leads, and (3) have shown their in vitro long-term electrochemical stability to assess their potential use in chronic studies.Item Electrical Design of InAs-Sb/GaSb Superlattices for Optical Detectors using Full Bandstructure Sp³s* Tight-Binding Method and Bloch Boundary ConditionsMir, Raja N.; Frensley, William R.; 0000 0000 3595 8922 (Frensley, WR); 93078927 (Frensley)InAs-Sb/GaSb type-II strain compensated superlattices (SLS) are currently being used in mid-wave and long-wave infrared photodetectors. The electronic bandstructure of InSb and GaSb shows very strong anisotropy and non-parabolicity close to the Γ-point for the conduction band (CB) minimum and the valence band (VB) maximum. Particularly around the energy range of 45-80 meV from band-edge we observe strong non-parabolicity in the CB and light hole VB. The band-edge dispersion determines the electrical properties of a material. When the bulk materials are combined to form a superlattice we need a model of bandstructure which takes into account the full bandstructure details of the constituents and also the strong interaction between the conduction band of InAs and valence bands of GaSb. There can also be contact potentials near the interface between two dissimilar superlattices which will not be captured unless a full bandstructure calculation is done. In this study, we have done a calculation using second nearest neighbor tight binding model in order to accurately reproduce the effective masses. The calculation of mini-band structure is done by finding the wavefunctions within one SL period subject to Bloch boundary conditions ψ(L) = ψ(0) e(ikL). We demonstrate in this paper how a calculation of carrier concentration as a function of the position of the Fermi level (EF) within bandgap(Eg) should be done in order to take into account the full bandstructure of broken-bandgap material systems. This calculation is key for determining electron transport particularly when we have an interface between two dissimilar superlattices.Item Extended-gate MOSFET for High Sensitivity Photodetectors and pH Sensors(2021-12-01T06:00:00.000Z) Liu, Jinbo; Young, Chadwin D.; Hu, Walter; Anderson, William; Frensley, William R.; Zakhidov, Anvar A.; Gu, QingOver the past years, semiconductors have been greatly used in sensors. With the development semiconductor technology, the semiconductor sensors showed high sensitivity, large integration and reliable stability. Ion-Sensitive Field Effect Transistor (ISFET) changed the gate electrode of Metal-oxide-semiconductor Field Effect Transistor (MOSFET) from metals to electrolyte. In this dissertation, the perovskite, which is a kind of material with large light absorption coefficient, is used to replace the electrolyte in ISFET based on the structure of ISFET to create high sensitivity photodetector. The perovskite is deposited on a silicon wafer and physically separated with MOSFET. Besides taking both advantages of perovskite with excellent optoelectrical property and silicon as a single crystal with good electrical property to get high responsivity, this extended-gate structure provides convenience for changing the capacitance of perovskite and removing the influence of light on MOSFET. The frequency of electrical signal on perovskite can modulate the capacitance of perovskite, which can be used when the capacitance of perovskite is too high compared with MOSFET. The ionic movement influence, which degrees the performance of this photodetector, can be reduced by adding another MOSFET served as current source at the gate of original MOSFET. Inspired by the ionic movement of perovskite, this dissertation also proves ionic movement in pH electrolyte deteriorates the sensitivity of ISFET by electrical measurement. The extended gate structure is utilized to separate the MOSFET and pH capacitance so the MOSFET is free from changing of temperature. Low temperature can decrease the mobility of ions in pH electrolyte especially after the phase change from liquid to solid. The ions in electrolyte can’t follow the high frequency bias voltage so the ionic movement is less at high frequency. Our results show that the ISFETs have larger sensitivity in low temperature and high frequency since the ionic movement can be suppressed by low temperature and high frequency.Item Processing and Characterization of CeRAM: a Non-volatile Non-filamentary Resistive Memory(May 2023) Prasad, Rohan 1999-; Young, Chadwin D.; Frensley, William R.; Lee, Jeong-BongMemory technologies have been evolving for a long time to provide durable and fast operation while not being very expensive. SRAM, DRAM, and Flash are traditional memories with advantages over each other in terms of speed, cost, reliability, and non-volatility. In addition, several emerging memory technologies are coming forward to solve one or more problems associated with existing memory technologies. CeRAM is one such memory technology projected to have several benefits over existing memory technologies. CeRAM, where ‘Ce’ stands for ‘Correlated Electrons’, is a resistive memory that undergoes switching through orbital interaction of atoms and bandgap variation in the material. In addition to being non-volatile, CeRAM is seen to have fast switching, and due to a rather simple fabrication process, CeRAM is relatively less expensive, as well. This gives CeRAM a potential edge over the existing memory technologies in terms of speed, cost, and memory retention. This project explores the operation of CeRAM memory devices and how durable and reliable they can be. The thesis indulges in the fabrication methodology of the device and investigates the performance through different tests. Stable two-state operation is demonstrated in these memory devices in terms of setting and resetting. Moreover, these devices offer promising endurance from room temperature to high-temperature environments (i.e., up to 200C), thereby expanding the scope of application of these memory devices. This project attempts to establish a functioning memory device that can work well in terms of writing or programming the memory, reading the distinctive memory states, competent endurance, and high-temperature operation. The results are promising, and more work can enhance the performance of these devices. It can potentially lead to reliable non-volatile memory technology that does not compromise speed and cost-effectiveness.