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- Genre: Masters Thesis
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Description
The dissolution of metal layers such as silver into chalcogenide glass layers such as germanium selenide changes the resistivity of the metal and chalcogenide films by a great extent. It is known that the incorporation of the metal can be achieved by ultra violet light exposure or thermal processes. In this work, the use of metal dissolution by exposure to gamma radiation has been explored for radiation sensor applications. Test structures were designed and a process flow was developed for prototype sensor fabrication. The test structures were designed such that sensitivity to radiation could be studied. The focus is on the effect of gamma rays as well as ultra violet light on silver dissolution in germanium selenide (Ge30Se70) chalcogenide glass. Ultra violet radiation testing was used prior to gamma exposure to assess the basic mechanism. The test structures were electrically characterized prior to and post irradiation to assess resistance change due to metal dissolution. A change in resistance was observed post irradiation and was found to be dependent on the radiation dose. The structures were also characterized using atomic force microscopy and roughness measurements were made prior to and post irradiation. A change in roughness of the silver films on Ge30Se70 was observed following exposure. This indicated the loss of continuity of the film which causes the increase in silver film resistance following irradiation. Recovery of initial resistance in the structures was also observed after the radiation stress was removed. This recovery was explained with photo-stimulated deposition of silver from the chalcogenide at room temperature confirmed with the re-appearance of silver dendrites on the chalcogenide surface. The results demonstrate that it is possible to use the metal dissolution effect in radiation sensing applications.
ContributorsChandran, Ankitha (Author) / Kozicki, Michael N (Thesis advisor) / Holbert, Keith E. (Committee member) / Barnaby, Hugh (Committee member) / Arizona State University (Publisher)
Created2012
Description
Scaling of the classical planar MOSFET below 20 nm gate length is facing not only technological difficulties but also limitations imposed by short channel effects, gate and junction leakage current due to quantum tunneling, high body doping induced threshold voltage variation, and carrier mobility degradation. Non-classical multiple-gate structures such as double-gate (DG) FinFETs and surrounding gate field-effect-transistors (SGFETs) have good electrostatic integrity and are an alternative to planar MOSFETs for below 20 nm technology nodes. Circuit design with these devices need compact models for SPICE simulation. In this work physics based compact models for the common-gate symmetric DG-FinFET, independent-gate asymmetric DG-FinFET, and SGFET are developed. Despite the complex device structure and boundary conditions for the Poisson-Boltzmann equation, the core structure of the DG-FinFET and SGFET models, are maintained similar to the surface potential based compact models for planar MOSFETs such as SP and PSP. TCAD simulations show differences between the transient behavior and the capacitance-voltage characteristics of bulk and SOI FinFETs if the gate-voltage swing includes the accumulation region. This effect can be captured by a compact model of FinFETs only if it includes the contribution of both types of carriers in the Poisson-Boltzmann equation. An accurate implicit input voltage equation valid in all regions of operation is proposed for common-gate symmetric DG-FinFETs with intrinsic or lightly doped bodies. A closed-form algorithm is developed for solving the new input voltage equation including ambipolar effects. The algorithm is verified for both the surface potential and its derivatives and includes a previously published analytical approximation for surface potential as a special case when ambipolar effects can be neglected. The symmetric linearization method for common-gate symmetric DG-FinFETs is developed in a form free of the charge-sheet approximation present in its original formulation for bulk MOSFETs. The accuracy of the proposed technique is verified by comparison with exact results. An alternative and computationally efficient description of the boundary between the trigonometric and hyperbolic solutions of the Poisson-Boltzmann equation for the independent-gate asymmetric DG-FinFET is developed in terms of the Lambert W function. Efficient numerical algorithm is proposed for solving the input voltage equation. Analytical expressions for terminal charges of an independent-gate asymmetric DG-FinFET are derived. The new charge model is C-infinity continuous, valid for weak as well as for strong inversion condition of both the channels and does not involve the charge-sheet approximation. This is accomplished by developing the symmetric linearization method in a form that does not require identical boundary conditions at the two Si-SiO2 interfaces and allows for volume inversion in the DG-FinFET. Verification of the model is performed with both numerical computations and 2D TCAD simulations under a wide range of biasing conditions. The model is implemented in a standard circuit simulator through Verilog-A code. Simulation examples for both digital and analog circuits verify good model convergence and demonstrate the capabilities of new circuit topologies that can be implemented using independent-gate asymmetric DG-FinFETs.
ContributorsDessai, Gajanan (Author) / Gildenblat, Gennady (Committee member) / McAndrew, Colin (Committee member) / Cao, Yu (Committee member) / Barnaby, Hugh (Committee member) / Arizona State University (Publisher)
Created2012
Description
Efficiency of components is an ever increasing area of importance to portable applications, where a finite battery means finite operating time. Higher efficiency devices need to be designed that don't compromise on the performance that the consumer has come to expect. Class D amplifiers deliver on the goal of increased efficiency, but at the cost of distortion. Class AB amplifiers have low efficiency, but high linearity. By modulating the supply voltage of a Class AB amplifier to make a Class H amplifier, the efficiency can increase while still maintaining the Class AB level of linearity. A 92dB Power Supply Rejection Ratio (PSRR) Class AB amplifier and a Class H amplifier were designed in a 0.24um process for portable audio applications. Using a multiphase buck converter increased the efficiency of the Class H amplifier while still maintaining a fast response time to respond to audio frequencies. The Class H amplifier had an efficiency above the Class AB amplifier by 5-7% from 5-30mW of output power without affecting the total harmonic distortion (THD) at the design specifications. The Class H amplifier design met all design specifications and showed performance comparable to the designed Class AB amplifier across 1kHz-20kHz and 0.01mW-30mW. The Class H design was able to output 30mW into 16Ohms without any increase in THD. This design shows that Class H amplifiers merit more research into their potential for increasing efficiency of audio amplifiers and that even simple designs can give significant increases in efficiency without compromising linearity.
ContributorsPeterson, Cory (Author) / Bakkaloglu, Bertan (Thesis advisor) / Barnaby, Hugh (Committee member) / Kiaei, Sayfe (Committee member) / Arizona State University (Publisher)
Created2013
Description
Over decades, scientists have been scaling devices to increasingly smaller feature sizes for ever better performance of complementary metal-oxide semiconductor (CMOS) technology to meet requirements on speed, complexity, circuit density, power consumption and ultimately cost required by many advanced applications. However, going to these ultra-scaled CMOS devices also brings some drawbacks. Aging due to bias-temperature-instability (BTI) and Hot carrier injection (HCI) is the dominant cause of functional failure in large scale logic circuits. The aging phenomena, on top of process variations, translate into complexity and reduced design margin for circuits. Such issues call for “Design for Reliability”. In order to increase the overall design efficiency, it is important to (i) study the impact of aging on circuit level along with the transistor level understanding (ii) calibrate the theoretical findings with measurement data (iii) implementing tools that analyze the impact of BTI and HCI reliability on circuit timing into VLSI design process at each stage. In this work, post silicon measurements of a 28nm HK-MG technology are done to study the effect of aging on Frequency Degradation of digital circuits. A novel voltage controlled ring oscillator (VCO) structure, developed by NIMO research group is used to determine the effect of aging mechanisms like NBTI, PBTI and SILC on circuit parameters. Accelerated aging mechanism is proposed to avoid the time consuming measurement process and extrapolation of data to the end of life thus instead of predicting the circuit behavior, one can measure it, within a short period of time. Finally, to bridge the gap between device level models and circuit level aging analysis, a System Level Reliability Analysis Flow (SyRA) developed by NIMO group, is implemented for a TSMC 65nm industrial level design to achieve one-step reliability prediction for digital design.
ContributorsBansal, Ankita (Author) / Cao, Yu (Thesis advisor) / Seo, Jae sun (Committee member) / Barnaby, Hugh (Committee member) / Arizona State University (Publisher)
Created2016
Description
This thesis describes the design of a Single Event Transient (SET) duration measurement test-structure on the Global Foundries (previously IBM) 32-nm silicon-on insulator (SOI) process. The test structure is designed for portability and allows quick design and implementation on a new process node. Such a test structure is critical in analyzing the effects of radiation on complementary metal oxide semi-conductor (CMOS) circuits. The focus of this thesis is the change in pulse width during propagation of SET pulse and build a test structure to measure the duration of a SET pulse generated in real time. This test structure can estimate the SET pulse duration with 10ps resolution. It receives the input SET propagated through a SET capture structure made using a chain of combinational gates. The impact of propagation of the SET in a >200 deep collection structure is studied. A novel methodology of deploying Thick Gate TID structure is proposed and analyzed to build multi-stage chain of combinational gates. Upon using long chain of combinational gates, the most critical issue of pulse width broadening and shortening is analyzed across critical process corners. The impact of using regular standard cells on pulse width modification is compared with NMOS and/or PMOS skewed gates for the chain of combinational gates. A possible resolution to pulse width change is demonstrated using circuit and layout design of chain of inverters, two and three inputs NOR gates. The SET capture circuit is also tested in simulation by introducing a glitch signal that mimics an individual ion strike that could lead to perturbation in SET propagation. Design techniques and skewed gates are deployed to dampen the glitch that occurs under the effect of radiation. Simulation results, layout structures of SET capture circuit and chain of combinational gates are presented.
ContributorsMasand, Lovish (Author) / Clark, Lawrence (Thesis advisor) / Holbert, Keith E. (Committee member) / Barnaby, Hugh (Committee member) / Arizona State University (Publisher)
Created2017
Description
The RADiation sensitive Field Effect Transistor (RADFET) has been conventionally used to measure radiation dose levels. These dose sensors are calibrated in such a way that a shift in threshold voltage, due to a build-up of oxide-trapped charge, can be used to estimate the radiation dose. In order to estimate the radiation dose level using RADFET, a wired readout circuit is necessary. Using the same principle of oxide-trapped charge build-up, but by monitoring the change in capacitance instead of threshold voltage, a wireless dose sensor can be developed. This RADiation sensitive CAPacitor (RADCAP) mounted on a resonant patch antenna can then become a wireless dose sensor. From the resonant frequency, the capacitance can be extracted which can be mapped back to estimate the radiation dose level. The capacitor acts as both radiation dose sensor and resonator element in the passive antenna loop. Since the MOS capacitor is used in passive state, characterizing various parameters that affect the radiation sensitivity is essential. Oxide processing technique, choice of insulator material, and thickness of the insulator, critically affect the dose response of the sensor. A thicker oxide improves the radiation sensitivity but reduces the dynamic range of dose levels for which the sensor can be used. The oxide processing scheme primarily determines the interface trap charge and oxide-trapped charge development; controlling this parameter is critical to building a better dose sensor.
ContributorsSrinivasan Gopalan, Madusudanan (Author) / Barnaby, Hugh (Thesis advisor) / Holbert, Keith E. (Committee member) / Yu, Hongyu (Committee member) / Arizona State University (Publisher)
Created2010
Description
Proton beam therapy has been proven to be effective for cancer treatment. Protons allow for complete energy deposition to occur inside patients, rendering this a superior treatment compared to other types of radiotherapy based on photons or electrons. This same characteristic makes quality assurance critical driving the need for detectors capable of direct beam positioning and fluence measurement. This work showcases a flexible and scalable data acquisition system for a multi-channel and segmented readout parallel plate ionization chamber instrument for proton beam fluence and positioning detection. Utilizing readily available, modern, off-the-shelf hardware components, including an FPGA with an embedded CPU in the same package, a data acquisition system for the detector was designed. The undemanding detector signal bandwidth allows the absence of ASICs and their associated costs and lead times in the system. The data acquisition system is showcased experimentally for a 96-readout channel detector demonstrating sub millisecond beam characteristics and beam reconstruction. The system demonstrated scalability up to 1064-readout channels, the limiting factor being FPGA I/O availability as well as amplification and sampling power consumption.
ContributorsAcuna Briceno, Rafael Andres (Author) / Barnaby, Hugh (Thesis advisor) / Brunhaver, John (Committee member) / Blyth, David (Committee member) / Arizona State University (Publisher)
Created2021