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- All Subjects: Electrical Engineering
- Genre: Doctoral Dissertation
Description
In the last few years, significant advances in nanofabrication have allowed tailoring of structures and materials at a molecular level enabling nanofabrication with precise control of dimensions and organization at molecular length scales, a development leading to significant advances in nanoscale systems. Although, the direction of progress seems to follow the path of microelectronics, the fundamental physics in a nanoscale system changes more rapidly compared to microelectronics, as the size scale is decreased. The changes in length, area, and volume ratios due to reduction in size alter the relative influence of various physical effects determining the overall operation of a system in unexpected ways. One such category of nanofluidic structures demonstrating unique ionic and molecular transport characteristics are nanopores. Nanopores derive their unique transport characteristics from the electrostatic interaction of nanopore surface charge with aqueous ionic solutions. In this doctoral research cylindrical nanopores, in single and array configuration, were fabricated in silicon-on-insulator (SOI) using a combination of electron beam lithography (EBL) and reactive ion etching (RIE). The fabrication method presented is compatible with standard semiconductor foundries and allows fabrication of nanopores with desired geometries and precise dimensional control, providing near ideal and isolated physical modeling systems to study ion transport at the nanometer level. Ion transport through nanopores was characterized by measuring ionic conductances of arrays of nanopores of various diameters for a wide range of concentration of aqueous hydrochloric acid (HCl) ionic solutions. Measured ionic conductances demonstrated two distinct regimes based on surface charge interactions at low ionic concentrations and nanopore geometry at high ionic concentrations. Field effect modulation of ion transport through nanopore arrays, in a fashion similar to semiconductor transistors, was also studied. Using ionic conductance measurements, it was shown that the concentration of ions in the nanopore volume was significantly changed when a gate voltage on nanopore arrays was applied, hence controlling their transport. Based on the ion transport results, single nanopores were used to demonstrate their application as nanoscale particle counters by using polystyrene nanobeads, monodispersed in aqueous HCl solutions of different molarities. Effects of field effect modulation on particle transition events were also demonstrated.
ContributorsJoshi, Punarvasu (Author) / Thornton, Trevor J (Thesis advisor) / Goryll, Michael (Thesis advisor) / Spanias, Andreas (Committee member) / Saraniti, Marco (Committee member) / Arizona State University (Publisher)
Created2011
Description
Programmable metallization cell (PMC) technology is based on an electrochemical phenomenon in which a metallic electrodeposit can be grown or dissolved between two electrodes depending on the voltage applied between them. Devices based on this phenomenon exhibit a unique, self-healing property, as a broken metallic structure can be healed by applying an appropriate voltage between the two broken ends. This work explores methods of fabricating interconnects and switches based on PMC technology on flexible substrates. The objective was the evaluation of the feasibility of using this technology in flexible electronics applications in which reliability is a primary concern. The re-healable property of the interconnect is characterized for the silver doped germanium selenide (Ag-Ge-Se) solid electrolyte system. This property was evaluated by measuring the resistances of the healed interconnect structures and comparing these to the resistances of the unbroken structures. The reliability of the interconnects in both unbroken and healed states is studied by investigating the resistances of the structures to DC voltages, AC voltages and different temperatures as a function of time. This work also explores replacing silver with copper for these interconnects to enhance their reliability. A model for PMC-based switches on flexible substrates is proposed and compared to the observed device behavior with the objective of developing a formal design methodology for these devices. The switches were subjected to voltage sweeps and their resistance was investigated as a function of sweep voltage. The resistance of the switches as a function of voltage pulse magnitude when placed in series with a resistance was also investigated. A model was then developed to explain the behavior of these devices. All observations were based on statistical measurements to account for random errors. The results of this work demonstrate that solid electrolyte based interconnects display self-healing capability, which depends on the applied healing voltage and the current limit. However, they fail at lower current densities than metal interconnects due to an ion-drift induced failure mechanism. The results on the PMC based switches demonstrate that a model comprising a Schottky diode in parallel with a variable resistor predicts the behavior of the device.
ContributorsBaliga, Sunil Ravindranath (Author) / Kozicki, Michael N (Thesis advisor) / Schroder, Dieter K. (Committee member) / Chae, Junseok (Committee member) / Alford, Terry L. (Committee member) / Arizona State University (Publisher)
Created2011
Description
Chalcogenide glass (ChG) materials have gained wide attention because of their applications in conductive bridge random access memory (CBRAM), phase change memories (PC-RAM), optical rewritable disks (CD-RW and DVD-RW), microelectromechanical systems (MEMS), microfluidics, and optical communications. One of the significant properties of ChG materials is the change in the resistivity of the material when a metal such as Ag or Cu is added to it by diffusion. This study demonstrates the potential radiation-sensing capabilities of two metal/chalcogenide glass device configurations. Lateral and vertical device configurations sense the radiation-induced migration of Ag+ ions in germanium selenide glasses via changes in electrical resistance between electrodes on the ChG. Before irradiation, these devices exhibit a high-resistance `OFF-state' (in the order of 10E12) but following irradiation, with either 60-Co gamma-rays or UV light, their resistance drops to a low-resistance `ON-state' (around 10E3). Lateral devices have exhibited cyclical recovery with room temperature annealing of the Ag doped ChG, which suggests potential uses in reusable radiation sensor applications. The feasibility of producing inexpensive flexible radiation sensors has been demonstrated by studying the effects of mechanical strain and temperature stress on sensors formed on flexible polymer substrate. The mechanisms of radiation-induced Ag/Ag+ transport and reactions in ChG have been modeled using a finite element device simulator, ATLAS. The essential reactions captured by the simulator are radiation-induced carrier generation, combined with reduction/oxidation for Ag species in the chalcogenide film. Metal-doped ChGs are solid electrolytes that have both ionic and electronic conductivity. The ChG based Programmable Metallization Cell (PMC) is a technology platform that offers electric field dependent resistance switching mechanisms by formation and dissolution of nano sized conductive filaments in a ChG solid electrolyte between oxidizable and inert electrodes. This study identifies silver anode agglomeration in PMC devices following large radiation dose exposure and considers device failure mechanisms via electrical and material characterization. The results demonstrate that by changing device structural parameters, silver agglomeration in PMC devices can be suppressed and reliable resistance switching may be maintained for extremely high doses ranging from 4 Mrad(GeSe) to more than 10 Mrad (ChG).
ContributorsDandamudi, Pradeep (Author) / Kozicki, Michael N (Thesis advisor) / Barnaby, Hugh J (Committee member) / Holbert, Keith E. (Committee member) / Goryll, Michael (Committee member) / Arizona State University (Publisher)
Created2013
Description
As crystalline silicon solar cells continue to get thinner, the recombination of carriers at the surfaces of the cell plays an ever-important role in controlling the cell efficiency. One tool to minimize surface recombination is field effect passivation from the charges present in the thin films applied on the cell surfaces. The focus of this work is to understand the properties of charges present in the SiNx films and then to develop a mechanism to manipulate the polarity of charges to either negative or positive based on the end-application. Specific silicon-nitrogen dangling bonds (·Si-N), known as K center defects, are the primary charge trapping defects present in the SiNx films. A custom built corona charging tool was used to externally inject positive or negative charges in the SiNx film. Detailed Capacitance-Voltage (C-V) measurements taken on corona charged SiNx samples confirmed the presence of a net positive or negative charge density, as high as +/- 8 x 1012 cm-2, present in the SiNx film. High-energy (~ 4.9 eV) UV radiation was used to control and neutralize the charges in the SiNx films. Electron-Spin-Resonance (ESR) technique was used to detect and quantify the density of neutral K0 defects that are paramagnetically active. The density of the neutral K0 defects increased after UV treatment and decreased after high temperature annealing and charging treatments. Etch-back C-V measurements on SiNx films showed that the K centers are spread throughout the bulk of the SiNx film and not just near the SiNx-Si interface. It was also shown that the negative injected charges in the SiNx film were stable and present even after 1 year under indoor room-temperature conditions. Lastly, a stack of SiO2/SiNx dielectric layers applicable to standard commercial solar cells was developed using a low temperature (< 400 °C) PECVD process. Excellent surface passivation on FZ and CZ Si substrates for both n- and p-type samples was achieved by manipulating and controlling the charge in SiNx films.
ContributorsSharma, Vivek (Author) / Bowden, Stuart (Thesis advisor) / Schroder, Dieter (Committee member) / Honsberg, Christiana (Committee member) / Roedel, Ronald (Committee member) / Alford, Terry (Committee member) / Arizona State University (Publisher)
Created2013
Description
The field of flexible displays and electronics gained a big momentum within the recent years due to their ruggedness, thinness, and flexibility as well as low cost large area manufacturability. Amorphous silicon has been the dominant material used in the thin film transistor industry which could only utilize it as N type thin film transistors (TFT). Amorphous silicon is an unstable material for low temperature manufacturing process and having only one kind of transistor means high power consumption for circuit operations. This thesis covers the three major researches done on flexible TFTs and flexible electronic circuits. First the characterization of both amorphous silicon TFTs and newly emerging mixed oxide TFTs were performed and the stability of these two materials is compared. During the research, both TFTs were stress tested under various biasing conditions and the threshold voltage was extracted to observe the shift in the threshold which shows the degradation of the material. Secondly, the design of the first flexible CMOS TFTs and CMOS gates were covered. The circuits were built using both inorganic and organic components (for nMOS and pMOS transistors respectively) and functionality tests were performed on basic gates like inverter, NAND and NOR gates and the working results are documented. Thirdly, a novel large area sensor structure is demonstrated under the Electronic Textile project section. This project is based on the concept that all the flexible electronics are flexible in only one direction and can not be used for conforming irregular shaped objects or create an electronic cloth for various applications like display or sensing. A laser detector sensor array is designed for proof of concept and is laid in strips that can be cut after manufacturing and weaved to each other to create a real flexible electronic textile. The circuit designed uses a unique architecture that pushes the data in a single line and reads the data from the same line and compares the signal to the original state to determine a sensor excitation. This architecture enables 2 dimensional addressing through an external controller while eliminating the need for 2 dimensional active matrix style electrical connections between the fibers.
ContributorsKaftanoglu, Korhan (Author) / Allee, David R. (Thesis advisor) / Kozicki, Michael N (Committee member) / Holbert, Keith E. (Committee member) / Kaminski, Jann P (Committee member) / Arizona State University (Publisher)
Created2012
Description
Programmable Metallization Cell (PMC) is a resistance-switching device based on migration of nanoscale quantities of cations in a solid electrolyte and formation of a conducting electrodeposit by the reductions of these cations. This dissertation presents electrical characterization results on Cu-SiO2 based PMC devices, which due to the na- ture of materials can be easily integrated into the current Complimentary metal oxide semiconductor (CMOS) process line. Device structures representing individual mem- ory cells based on W bottom electrode and n-type Si bottom electrode were fabricated for characterization. For the W bottom electrode based devices, switching was ob- served for voltages in the range of 500mV and current value as low as 100 nA showing the electrochemical nature and low power potential. The ON state showed a direct de- pendence on the programming current, showing the possibility of multi-bit storage in a single cell. Room temperature retention was demonstrated in excess of 105 seconds and endurance to approximately 107 cycles. Switching was observed for microsecond duration 3 V amplitude pulses. Material characterization results from Raman, X-ray diffraction, Rutherford backscattering and Secondary-ion mass spectroscopy analysis shows the influence of processing conditions on the Cu concentration within the film and also the presence of Cu as free atoms. The results seemed to indicate stress-induced void formation in the SiO2 matrix as the driving mechanism for Cu diffusion into the SiO2 film. Cu/SiO2
Si based PMC devices were characterized and were shown to have inherent isolation characteristics, proving the feasibility of such a structure for a passive array. The inherent isolation property simplifies fabrication by avoiding the need for a separate diode element in an array. The isolation characteristics were studied mainly in terms of the leakage current. The nature of the diode interface was further studied by extracting a barrier potential which shows it can be approximated to a Cu-nSi metal semiconductor Schottky diode.
Si based PMC devices were characterized and were shown to have inherent isolation characteristics, proving the feasibility of such a structure for a passive array. The inherent isolation property simplifies fabrication by avoiding the need for a separate diode element in an array. The isolation characteristics were studied mainly in terms of the leakage current. The nature of the diode interface was further studied by extracting a barrier potential which shows it can be approximated to a Cu-nSi metal semiconductor Schottky diode.
ContributorsPuthenthermadam, Sarath (Author) / Kozicki, Michael N (Thesis advisor) / Diaz, Rodolfo (Committee member) / Schroder, Dieter K. (Committee member) / Alford, Terry (Committee member) / Arizona State University (Publisher)
Created2011
Description
Silicon carbide (SiC), long touted as a material that can satisfy the specific property requirements for high temperature and high power applications, was studied quantitatively using various techniques. The electronic band structure of 4H SiC is examined in the first half of this dissertation. A brief introduction to band structure calculations, with particular emphasis on the empirical pseudopotential method, is given as a foundation for the subsequent work. Next, the crystal pseudopotential for 4H SiC is derived in detail, and a novel approach using a genetic algorithm search routine is employed to find the fitting parameters needed to generate the band structure. Using this technique, the band structure is fitted to experimentally measured energy band gaps giving an indirect band gap energy of 3.28 eV, and direct f¡, M, K and L energy transitions of 6.30, 4.42, 7.90 and 6.03 eV, respectively. The generated result is also shown to give effective mass values of mMf¡*=0.66m0, mMK*=0.31m0, mML*=0.34m0, in close agreement with experimental results. The second half of this dissertation discusses computational work in finding the electron Hall mobility and Hall scattering factor for 6H SiC. This disscussion begins with an introductory chapter that gives background on how scattering rates are dervied and the specific expressions for important mechanisms. The next chapter discusses mobility calculations for 6H SiC in particular, beginnning with Rode's method to solve the Boltzmann transport equation. Using this method and the transition rates of the previous chapter, an acoustic deformation potential DA value of 5.5 eV, an inter-valley phonon deformation potential Dif value of 1.25~1011 eV/m and inter-valley phonon energy ℏfÖif of 65 meV that simultaneously fit experimental data on electron Hall mobility and Hall scattering factor was found.
ContributorsNg, Garrick (Author) / Schroder, Dieter K. (Thesis advisor) / Vasileska, Dragica (Committee member) / Skromme, Brian (Committee member) / Alford, Terry (Committee member) / Marinella, Matthew (Committee member) / Arizona State University (Publisher)
Created2010
Description
The goal of this research work is to develop an understanding as well as modelling thermal effects in Si based nano-scale devices using a multiscale simulator tool. This tool has been developed within the research group at Arizona State University led by Professor Dr. Dragica Vasileska. Another research group, headed by Professor Dr. Thornton, also at Arizona State University, provided support with software tools, by not only laying out the physical experimental device, but also provided experimental data to verify the correctness and accuracy of the developed simulation tool. The tool consists of three separate but conjoined modules at different scales of representation. 1) A particle based, ensemble Monte Carlo (MC) simulation tool, which, in the long-time (electronic motion) limit, solves the Boltzmann transport equation (BTE) for electrons, coupled with an iterative solution to a two-dimensional (2D) Poisson’s equation, at the base device level. 2) Another device level thermal modeling tool which solves the energy balance equations accounting for carrier-phonon and phonon-phonon interactions and is integrated with the MC tool. 3) Lastly, a commercial technology computer aided design (TCAD) software, Silvaco is employed to incorporate the results from the above two tools to a circuit level, common-source dual-transistor circuit, where one of the devices acts a heater and the other as a sensor, to study the impacts of thermal heating. The results from this tool are fed back to the previous device level tools to iterate on, until a stable, unified electro-thermal equilibrium/result is obtained. This coupled electro-thermal approach was originally developed for an individual n-channel MOSFET (NMOS) device by Prof. Katerina Raleva and was extended to allow for multiple devices in tandem, thereby providing a platform for better and more accurate modeling of device behavior, analyzing circuit performance, and understanding thermal effects. Simulating this dual device circuit and analyzing the extracted voltage transfer and output characteristics verifies the efficacy of this methodology as the results obtained from this multi-scale, electro-thermal simulator tool, are found to be in good general agreement with the experimental data.
ContributorsQazi, Suleman Sami (Author) / Vasileska, Dragica (Thesis advisor) / Goodnick, Stephen M (Committee member) / Thornton, Trevor J (Committee member) / Ferry, David K (Committee member) / Arizona State University (Publisher)
Created2021
Description
Diamond as a wide-bandgap (WBG) semiconductor material has distinct advantages for power electronics applications over Si and other WBG materials due to its high critical electric field (> 10 MV/cm), high electron and hole mobility (??=4500 cm2/V-s, ??=3800 cm2/V-s), high thermal conductivity (~22 W/cm-K) and large bandgap (5.47 eV). Owing to its remarkable properties, the application space of WBG materials has widened into areas requiring very high current, operating voltage and temperature. Remarkable progress has been made in demonstrating high breakdown voltage (>10 kV), ultra-high current density (> 100 kA/cm2) and ultra-high temperature (~1000oC) diamond devices, giving further evidence of diamond’s huge potential. However, despite the great success, fabricated diamond devices have not yet delivered diamond’s true potential. Some of the main reasons are high dopant activation energies, substantial bulk defect and trap densities, high contact resistance, and high leakage currents. A lack of complete understanding of the diamond specific device physics also impedes the progress in correct design approaches. The main three research focuses of this work are high power, high frequency and high temperature. Through the design, fabrication, testing, analysis and modeling of diamond p-i-n and Schottky diodes a milestone in diamond research is achieved and gain important theoretical understanding. In particular, a record highest current density in diamond diodes of ~116 kA/cm2 is demonstrated, RF characterization of diamond diodes is performed from 0.1 GHz to 25 GHz and diamond diodes are successfully tested in extreme environments of 500oC and ~93 bar of CO2 pressure. Theoretical models are constructed analytically and inii
Silvaco ATLAS including incomplete ionization and hopping mobility to explain space charge limited current phenomenon, effects of traps and Mott-Gurney dominated diode ???. A new interpretation of the Baliga figure of merit for WBG materials is also formulated and a new cubic relationship between ??? and breakdown voltage is established. Through Silvaco ATLAS modeling, predictions on the power limitation of diamond diodes in receiver-protector circuits is made and a range of self-heating effects is established. Poole-Frenkel emission and hopping conduction models are also utilized to analyze high temperature (500oC) leakage behavior of diamond diodes. Finally, diamond JFET simulations are performed and designs are proposed for high temperature – extreme environment applications.
ContributorsSurdi, Harshad (Author) / Goodnick, Stephen M (Thesis advisor) / Nemanich, Robert J (Committee member) / Thornton, Trevor J (Committee member) / Lyons, James R (Committee member) / Arizona State University (Publisher)
Created2022
Description
Wide Bandgap (WBG) semiconductor materials are shaping day-to-day technologyby introducing powerful and more energy responsible devices. These materials have
opened the door for building basic semiconductor devices which are superior in terms of
handling high voltages, high currents, power, and temperature which is not possible using
conventional silicon technology. As the research continues in the field of WBG based
devices, there is a potential chance that the power electronics industry can save billions of
dollars deploying energy-efficient circuits in high power conversion electronics. Diamond,
silicon carbide and gallium nitride are the top three contenders among which diamond can
significantly outmatch others in a variety of properties. However, diamond technology is
still in its early phase of development and there are challenges involved in many aspects of
processing a successful integrated circuit. The work done in this research addresses three
major aspects of problems related to diamond technology. In the first part, the applicability
of compact modeling and Technology Computer-Aided Design (TCAD) modeling
technique for diamond Schottky p-i-n diodes has been demonstrated. The compact model
accurately predicts AC, DC and nonlinear behavior of the diode required for fast circuit
simulation. Secondly, achieving low resistance ohmic contact onto n-type diamond is one
of the major issues that is still an open research problem as it determines the performance
of high-power RF circuits and switching losses in power converters circuits. So, another
portion of this thesis demonstrates the achievement of very low resistance ohmic contact
(~ 10-4 Ω⋅cm2) onto n-type diamond using nano crystalline carbon interface layer. Using
the developed TCAD and compact models for low resistance contacts, circuit level
predictions show improvements in RF performance. Lastly, an initial study of breakdown
characteristics of diamond and cubic boron nitride heterostructure is presented. This study
serves as a first step for making future transistors using diamond and cubic boron nitride –
a very less explored material system in literature yet promising for extreme circuit
applications involving high power and temperature.
ContributorsJHA, VISHAL (Author) / Thornton, Trevor (Thesis advisor) / Goodnick, Stephen (Committee member) / Nemanich, Robert (Committee member) / Alford, Terry (Committee member) / Hoque, Mazhar (Committee member) / Arizona State University (Publisher)
Created2023