Matching Items (261)
Description
The main objective of this project was to create a framework for holistic ideation and research about the technical issues involved in creating a holistic approach. Towards that goal, we explored different components of ideation (both logical and intuitive), characterized ideation states, and found new ideation blocks with strategies used to overcome them. One of the major contributions of this research is the method by which easy traversal between different ideation methods with different components were facilitated, to support both creativity and functional quality. Another important part of the framework is the sensing of ideation states (blocks/ unfettered ideation) and investigation of matching ideation strategies most likely to facilitate progress. Some of the ideation methods embedded in the initial holistic test bed are Physical effects catalog, working principles catalog, TRIZ, Bio-TRIZ and Artifacts catalog. Repositories were created for each of those. This framework will also be used as a research tool to collect large amount of data from designers about their choice of ideation strategies used, and their effectiveness. Effective documentation of design ideation paths is also facilitated using this holistic approach. A computer tool facilitating holistic ideation was developed. Case studies were run on different designers to document their ideation states and their choice of ideation strategies to come up with a good solution to solve the same design problem.
ContributorsMohan, Manikandan (Author) / Shah, Jami J. (Thesis advisor) / Huebner, Kenneth (Committee member) / Burleson, Winslow (Committee member) / Arizona State University (Publisher)
Created2011
Description
There will always be a need for high current/voltage transistors. A transistor that has the ability to be both or either of these things is the silicon metal-silicon field effect transistor (MESFET). An additional perk that silicon MESFET transistors have is the ability to be integrated into the standard silicon on insulator (SOI) complementary metal oxide semiconductor (CMOS) process flow. This makes a silicon MESFET transistor a very valuable device for use in any standard CMOS circuit that may usually need a separate integrated circuit (IC) in order to switch power on or from a high current/voltage because it allows this function to be performed with a single chip thereby cutting costs. The ability for the MESFET to cost effectively satisfy the needs of this any many other high current/voltage device application markets is what drives the study of MESFET optimization. Silicon MESFETs that are integrated into standard SOI CMOS processes often receive dopings during fabrication that would not ideally be there in a process made exclusively for MESFETs. Since these remnants of SOI CMOS processing effect the operation of a MESFET device, their effect can be seen in the current-voltage characteristics of a measured MESFET device. Device simulations are done and compared to measured silicon MESFET data in order to deduce the cause and effect of many of these SOI CMOS remnants. MESFET devices can be made in both fully depleted (FD) and partially depleted (PD) SOI CMOS technologies. Device simulations are used to do a comparison of FD and PD MESFETs in order to show the advantages and disadvantages of MESFETs fabricated in different technologies. It is shown that PD MESFET have the highest current per area capability. Since the PD MESFET is shown to have the highest current capability, a layout optimization method to further increase the current per area capability of the PD silicon MESFET is presented, derived, and proven to a first order.
ContributorsSochacki, John (Author) / Thornton, Trevor J (Thesis advisor) / Schroder, Dieter (Committee member) / Vasileska, Dragica (Committee member) / Goryll, Michael (Committee member) / Arizona State University (Publisher)
Created2011
Description
ABSTRACT The purpose of this study is to demonstrate that stable lipid bilayers can be set up on an array of silicon micropores and can be used as sites for self-inserting ion-channel proteins which can be studied independently of each other. In course of this study an acrylic based holder was designed and machined to ensure leak-free fluidic access to the silicon micropores and physical isolation of the individual array channels. To measure the ion-channel currents, we simulated, designed and manufactured low-noise transimpedance amplifiers and support circuits based on published patch clamp amplifier designs, using currently available surface-mount components. This was done in order to achieve a reduction in size and costs as well as isolation of individual channels without the need for multiplexing of the input. During the experiments performed, stable bilayers were formed across an array of four vertically mounted 30 µm silicon micropores and OmpF porins were added for self insertion in each of the bilayers. To further demonstrate the independence of these bilayer recording sites, the antibiotic Ampicillin (2.5 mM) was added to one of the fluidic wells. The ionic current in each of the wells was recorded simultaneously. Sub-conductance states of Ompf porin were observed in two of the measurement sites. In addition, the conductance steps in the site containing the antibiotic could be clearly seen to be larger compared to those of the unmodified site. This is due to the transient blocking of ion flow through the porin due to translocation of the antibiotic. Based on this demonstration, ion-channel array reconstitution is a potential method for efficient electrophysiological characterization of different types of ion-channels simultaneously as well as for studying membrane permeation processes.
ContributorsRamakrishnan, Shankar (Author) / Goryll, Michael (Thesis advisor) / Thornton, Trevor J (Committee member) / Blain Christen, Jennifer M (Committee member) / Arizona State University (Publisher)
Created2011
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
The theme for this work is the development of fast numerical algorithms for sparse optimization as well as their applications in medical imaging and source localization using sensor array processing. Due to the recently proposed theory of Compressive Sensing (CS), the $\ell_1$ minimization problem attracts more attention for its ability to exploit sparsity. Traditional interior point methods encounter difficulties in computation for solving the CS applications. In the first part of this work, a fast algorithm based on the augmented Lagrangian method for solving the large-scale TV-$\ell_1$ regularized inverse problem is proposed. Specifically, by taking advantage of the separable structure, the original problem can be approximated via the sum of a series of simple functions with closed form solutions. A preconditioner for solving the block Toeplitz with Toeplitz block (BTTB) linear system is proposed to accelerate the computation. An in-depth discussion on the rate of convergence and the optimal parameter selection criteria is given. Numerical experiments are used to test the performance and the robustness of the proposed algorithm to a wide range of parameter values. Applications of the algorithm in magnetic resonance (MR) imaging and a comparison with other existing methods are included. The second part of this work is the application of the TV-$\ell_1$ model in source localization using sensor arrays. The array output is reformulated into a sparse waveform via an over-complete basis and study the $\ell_p$-norm properties in detecting the sparsity. An algorithm is proposed for minimizing a non-convex problem. According to the results of numerical experiments, the proposed algorithm with the aid of the $\ell_p$-norm can resolve closely distributed sources with higher accuracy than other existing methods.
ContributorsShen, Wei (Author) / Mittlemann, Hans D (Thesis advisor) / Renaut, Rosemary A. (Committee member) / Jackiewicz, Zdzislaw (Committee member) / Gelb, Anne (Committee member) / Ringhofer, Christian (Committee member) / Arizona State University (Publisher)
Created2011
Description
In very small electronic devices the alternate capture and emission of carriers at an individual defect site located at the interface of Si:SiO2 of a MOSFET generates discrete switching in the device conductance referred to as a random telegraph signal (RTS) or random telegraph noise (RTN). In this research work, the integration of random defects positioned across the channel at the Si:SiO2 interface from source end to the drain end in the presence of different random dopant distributions are used to conduct Ensemble Monte-Carlo ( EMC ) based numerical simulation of key device performance metrics for 45 nm gate length MOSFET device. The two main performance parameters that affect RTS based reliability measurements are percentage change in threshold voltage and percentage change in drain current fluctuation in the saturation region. It has been observed as a result of the simulation that changes in both and values moderately decrease as the defect position is gradually moved from source end to the drain end of the channel. Precise analytical device physics based model needs to be developed to explain and assess the EMC simulation based higher VT fluctuations as experienced for trap positions at the source side. A new analytical model has been developed that simultaneously takes account of dopant number variations in the channel and depletion region underneath and carrier mobility fluctuations resulting from fluctuations in surface potential barriers. Comparisons of this new analytical model along with existing analytical models are shown to correlate with 3D EMC simulation based model for assessment of VT fluctuations percentage induced by a single interface trap. With scaling of devices beyond 32 nm node, halo doping at the source and drain are routinely incorporated to combat the threshold voltage roll-off that takes place with effective channel length reduction. As a final study on this regard, 3D EMC simulation method based computations of threshold voltage fluctuations have been performed for varying source and drain halo pocket length to illustrate the threshold voltage fluctuations related reliability problems that have been aggravated by trap positions near the source at the interface compared to conventional 45 nm MOSFET.
ContributorsAshraf, Nabil Shovon (Author) / Vasileska, Dragica (Thesis advisor) / Schroder, Dieter (Committee member) / Goodnick, Stephen (Committee member) / Goryll, Michael (Committee member) / Arizona State University (Publisher)
Created2011
Description
The past two decades have been monumental in the advancement of microchips designed for a diverse range of medical applications and bio-analysis. Owing to the remarkable progress in micro-fabrication technology, complex chemical and electro-mechanical features can now be integrated into chip-scale devices for use in biosensing and physiological measurements. Some of these devices have made enormous contributions in the study of complex biochemical processes occurring at the molecular and cellular levels while others overcame the challenges of replicating various functions of human organs as implant systems. This thesis presents test data and analysis of two such systems. First, an ISFET based pH sensor is characterized for its performance in a continuous pH monitoring application. Many of the basic properties of ISFETs including I-V characteristics, pH sensitivity and more importantly, its long term drift behavior have been investigated. A new theory based on frequent switching of electric field across the gate oxide to decrease the rate of current drift has been successfully implemented with the help of an automated data acquisition and switching system. The system was further tested for a range of duty cycles in order to accurately determine the minimum length of time required to fully reset the drift. Second, a microfluidic based vestibular implant system was tested for its underlying characteristics as a light sensor. A computer controlled tilt platform was then implemented to further test its sensitivity to inclinations and thus it‟s more important role as a tilt sensor. The sensor operates through means of optoelectronics and relies on the signals generated from photodiode arrays as a result of light being incident on them. ISFET results show a significant drop in the overall drift and good linear characteristics. The drift was seen to reset at less than an hour. The photodiodes show ideal I-V comparison between photoconductive and photovoltaic modes of operation with maximum responsivity at 400nm and a shunt resistance of 394 MΩ. Additionally, post-processing of the tilt sensor to incorporate the sensing fluids is outlined. Based on several test and fabrication results, a possible method of sealing the open cavity of the chip using a UV curable epoxy has been discussed.
ContributorsMamun, Samiha (Author) / Christen, Jennifer Blain (Thesis advisor) / Goryll, Michael (Committee member) / Yu, Hongyu (Committee member) / Arizona State University (Publisher)
Created2011
Description
Overcrowding of Emergency Departments (EDs) put the safety of patients at risk. Decision makers implement Ambulance Diversion (AD) as a way to relieve congestion and ensure timely treatment delivery. However, ineffective design of AD policies reduces the accessibility to emergency care and adverse events may arise. The objective of this dissertation is to propose methods to design and analyze effective AD policies that consider performance measures that are related to patient safety. First, a simulation-based methodology is proposed to evaluate the mean performance and variability of single-factor AD policies in a single hospital environment considering the trade-off between average waiting time and percentage of time spent on diversion. Regression equations are proposed to obtain parameters of AD policies that yield desired performance level. The results suggest that policies based on the total number of patients waiting are more consistent and provide a high precision in predicting policy performance. Then, a Markov Decision Process model is proposed to obtain the optimal AD policy assuming that information to start treatment in a neighboring hospital is available. The model is designed to minimize the average tardiness per patient in the long run. Tardiness is defined as the time that patients have to wait beyond a safety time threshold to start receiving treatment. Theoretical and computational analyses show that there exists an optimal policy that is of threshold type, and diversion can be a good alternative to decrease tardiness when ambulance patients cause excessive congestion in the ED. Furthermore, implementation of AD policies in a simulation model that accounts for several relaxations of the assumptions suggests that the model provides consistent policies under multiple scenarios. Finally, a genetic algorithm is combined with simulation to design effective policies for multiple hospitals simultaneously. The model has the objective of minimizing the time that patients spend in non-value added activities, including transportation, waiting and boarding in the ED. Moreover, the AD policies are combined with simple ambulance destination policies to create ambulance flow control mechanisms. Results show that effective ambulance management can significantly reduce the time that patients have to wait to receive appropriate level of care.
ContributorsRamirez Nafarrate, Adrian (Author) / Fowler, John W. (Thesis advisor) / Wu, Teresa (Thesis advisor) / Gel, Esma S. (Committee member) / Limon, Jorge (Committee member) / Arizona State University (Publisher)
Created2011
Description
Zinc oxide (ZnO), a naturally n-type semiconductor has been identified as a promising candidate to replace indium tin oxide (ITO) as the transparent electrode in solar cells, because of its wide bandgap (3.37 eV), abundant source materials and suitable refractive index (2.0 at 600 nm). Spray deposition is a convenient and low cost technique for large area and uniform deposition of semiconductor thin films. In particular, it provides an easier way to dope the film by simply adding the dopant precursor into the starting solution. In order to reduce the resistivity of undoped ZnO, many works have been done by doping in the ZnO with either group IIIA elements or VIIA elements using spray pyrolysis. However, the resistivity is still too high to meet TCO's resistivity requirement. In the present work, a novel co-spray deposition technique is developed to bypass a fundamental limitation in the conventional spray deposition technique, i.e. the deposition of metal oxides from incompatible precursors in the starting solution. With this technique, ZnO films codoped with one cationic dopant, Al, Cr, or Fe, and an anionic dopant, F, have been successfully synthesized, in which F is incompatible with all these three cationic dopants. Two starting solutions were prepared and co-sprayed through two separate spray heads. One solution contained only the F precursor, NH 4F. The second solution contained the Zn and one cationic dopant precursors, Zn(O 2CCH 3) 2 and AlCl 3, CrCl 3, or FeCl 3. The deposition was carried out at 500 °C; on soda-lime glass in air. Compared to singly-doped ZnO thin films, codoped ZnO samples showed better electrical properties. Besides, a minimum sheet resistance, 55.4 Ω/sq, was obtained for Al and F codoped ZnO films after vacuum annealing at 400 °C;, which was lower than singly-doped ZnO with either Al or F. The transmittance for the Al and F codoped ZnO samples was above 90% in the visible range. This co-spray deposition technique provides a simple and cost-effective way to synthesize metal oxides from incompatible precursors with improved properties.
ContributorsZhou, Bin (Author) / Tao, Meng (Thesis advisor) / Goryll, Michael (Committee member) / Vasileska, Dragica (Committee member) / Yu, Hongbin (Committee member) / Arizona State University (Publisher)
Created2013
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