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Full-Text Articles in Engineering

Influence Of Materials And Design Parameters On Zinc Oxide Surface Acoustic Devices, Samuel B. Dewhitt Jun 2022

Influence Of Materials And Design Parameters On Zinc Oxide Surface Acoustic Devices, Samuel B. Dewhitt

Theses and Dissertations

This thesis presents research into Zinc Oxide (ZnO) based resonators to include Width Extensional Mode (WEM), Length Extensional Mode (LEM), and Surface Acoustic Wave (SAW) devices. The design and operation of ZnO based SAW devices are investigated further to characterize design parameters and operating modes. Their design, fabrication, and results are discussed in detail. SAW device testing in conjunction with X-Ray Diffractometry (XRD) and Atomic Force Microscopy (AFM) are utilized to characterize ZnO and its deposition parameters on a variety of different substrates and interlayers, with different deposition temperatures and annealing parameters. These substrates include silicon, silicon oxide-on-silicon, and sapphire …


Characterization Of Reactive Ion Etch Chemistries Using Direct Write Lithography, Dylan T. Martin-Abood Mar 2020

Characterization Of Reactive Ion Etch Chemistries Using Direct Write Lithography, Dylan T. Martin-Abood

Theses and Dissertations

The DoD requires a variety of COTS and number of custom microelectronics to provide important functionality to critical military systems. Photolithography and DRIE are two techniques commonly used in the development of deep anisotropic features for the fabrication and modification of microelectronics and MEMS. However, standard photolithography techniques are ineffective for unique substrate geometries and DRIE processes require a chemical passivation step only applicable to Si substrates. This work confirmed the capability of RIE using DWL to perform deep, highly selective, anisotropic etching on elevated, non-circular substrates.


Improvements To Micro-Contact Performance And Reliability, Tod V. Laurvick Dec 2016

Improvements To Micro-Contact Performance And Reliability, Tod V. Laurvick

Theses and Dissertations

Microelectromechanical Systems (MEMS) based devices, and specifically microswitches, continue to offer many advantages over competing technologies. To realize the benefits of micro-switches, improvements must be made to address performance and reliability shortfalls which have long been an issue with this application. To improve the performance of these devices, the micro-contacts used in this technology must be understood to allow for design improvements, and offer a means for testing to validate this technology and determine when such improvements are ready for operational environments. To build devices which are more robust and capable of continued operation after billions of cycles requires that …


Characterization For The Development Of The Hybrid Multi-Junction Silicon Germanium Solar Cell, Jimmy J. Lohrman Mar 2016

Characterization For The Development Of The Hybrid Multi-Junction Silicon Germanium Solar Cell, Jimmy J. Lohrman

Theses and Dissertations

Based on the previous development of the hybrid multi-junction silicon (HMJ-Si) solar cell, this work characterized the preceding design for the development of the hybrid multi-junction silicon germanium (HMJ-SiGe) solar cell. Seven focus areas were investigated: diffraction pattern generation, photon propagation, silicon diffusion processing, ohmic contacts, the distributed Bragg reflector (DBR), the Fresnel zone plate (FZP), and the germanium/germanium telluride (Ge/GeTe) pn-junction Diffraction patterns were theoretically examined, and contact grating design characterization for reflectance and transmittance properties was modeled using rigorous coupled wave analysis. An improved silicon diffusion process follower was developed, and theoretical study and experimental assessment were accomplished …


Optically Stimulated Luminescence From Ag-Doped Lithium Tetraborate (Li2b4o7), Ember S. Maniego Mar 2016

Optically Stimulated Luminescence From Ag-Doped Lithium Tetraborate (Li2b4o7), Ember S. Maniego

Theses and Dissertations

Silver-doped lithium tetraborate (Li2B4O7) crystals emit optically stimulated luminescence (OSL) in response to stimulating light around 400 nm. Photoluminescence, optical absorption, and electron paramagnetic resonance (EPR) were used to identify the defects in the crystal that cause this OSL. Lithium tetraborate crystals have Ag+ ions at Li+ sites and at interstitial sites. Upon ionization at room temperature via x rays, electron-hole pairs are generated. The electrons are trapped at Ag+ occupying interstitial sites, while the holes are trapped at Ag+ at lithium sites. The trapped electron centers become Ag0 …


Neutron Radiation Effects On Ge And Gesn Semiconductors, Christopher T. O'Daniel Mar 2016

Neutron Radiation Effects On Ge And Gesn Semiconductors, Christopher T. O'Daniel

Theses and Dissertations

Two different semiconductor materials received neutron radiation for assessment of radiation damage. The two materials are undoped bulk Ge and epitaxial Ge0.991Sn0.009, which is doped heavily with phosphorous. At room temperature, the Ge sample has direct and indirect bandgaps at 0.78 eV and 0.66 eV, respectively. The Ge0.991Sn0.009 sample has direct and indirect bandgaps at 0.72 eV and 0.63 eV, respectively. Two samples of each material were exposed to research reactor neutrons, delivering a 1 MeV equivalent neutron fluence of 2.52 × 1015 n/cm2. In order to assess the radiation …


Subtractive Plasma-Assisted-Etch Process For Developing High Performance Nanocrystalline Zinc-Oxide Thin-Film-Transistors, Thomas M. Donigan Mar 2015

Subtractive Plasma-Assisted-Etch Process For Developing High Performance Nanocrystalline Zinc-Oxide Thin-Film-Transistors, Thomas M. Donigan

Theses and Dissertations

Thin-Film-Transistors (TFTs) employing undoped zinc-oxide (ZnO) thin-films are currently being investigated by the Air Force for microwave switching applications. Since the on-resistance (R(on)) of the device scales with channel length (LC), ZnO TFT optimization should be focused on reducing LC, therefore minimizing the associated insertion losses. In this research, deep sub-micron scaling of ZnO TFTs was undertaken using a subtractive reactive-ion-etch (RIE) process. Under optimum processing conditions, ZnO TFTs with LC as small as 155 nm were successfully demonstrated. The active ZnO channels of the TFTs were patterned by selective SF6-RIE of a tungsten ohmic film through electron-beam defined openings …


Contact Resistance Evolution And Degradation Of Highly Cycled Micro-Contacts, Christopher L. Stilson Mar 2014

Contact Resistance Evolution And Degradation Of Highly Cycled Micro-Contacts, Christopher L. Stilson

Theses and Dissertations

Reliable microelectromechanical systems (MEMS) switches are critical for developing high performance radio frequency circuits like phase shifters. Engineers have attempted to improve reliability and lifecycle performance using novel contact metals, unique mechanical designs and packaging. Various test fixtures including: MEMS devices, atomic force microscopes (AFM) and nanoindentors have been used to collect resistance and contact force data. AFM and nanoindentor test fixtures allow direct contact force measurements but are severely limited by low resonance sensors, and therefore low data collection rates. This thesis reports the contact resistance evolution results and fabrication of thin film micro-contacts dynamically tested up to 3kHz. …


Novel Test Fixture For Characterizing Microcontacts: Performance And Reliability, Benjamin F. Toler Mar 2013

Novel Test Fixture For Characterizing Microcontacts: Performance And Reliability, Benjamin F. Toler

Theses and Dissertations

Engineers have attempted to improve reliability and lifecycle performance using novel micro-contact metals, unique mechanical designs and packaging. Contact resistance can evolve over the lifetime of the micro-switch by increasing until failure. This work shows the fabrication of micro-contact support structures and test fixture which allow for micro-contact testing, with an emphasis on the fixture's design to allow the determination and analysis of the appropriate failure mode. The other effort of this investigation is the development of a micro-contact test fixture which can measure contact force and resistance directly and perform initial micro-contact characterization, and two forms of lifecycle testing …


Optical Metamaterial Design, Fabrication And Test, Jack P. Lombardi Mar 2011

Optical Metamaterial Design, Fabrication And Test, Jack P. Lombardi

Theses and Dissertations

Metamaterials, materials that make use of naturally occurring materials and designed structures to create materials with special properties not found in nature, are a fascinating new area of research, combining the fields of physics, microfabrication, and material science. This work will focus on the development of metamaterials operating in the visible and infrared which will be constructed and tested for basic optical properties. Possible applications for these materials will not be investigated. The this work will go into the fabrication and test of layered metal-dielectric structures, called layered metamaterials, as these structures hold potential for applications in advanced optical systems. …


Electromagnetic Modeling And Measurement Of Adaptive Metamaterial Structural Elements, Matthew E. Jussaume Mar 2011

Electromagnetic Modeling And Measurement Of Adaptive Metamaterial Structural Elements, Matthew E. Jussaume

Theses and Dissertations

This document addresses two major obstacles facing metamaterial development: uncertainty in the characterization of electromagnetic field behavior in metamaterial structures and the relatively small operational bandwidth of metamaterial structures. To address the first obstacle, a method of prediction aided measurement is developed and exploited to examine the field interactions within metamaterial devices. The fusion of simulation and measurement techniques enhances the understanding of the physical interactions of fields in the presence of metamaterials. To address the second obstacle, this document characterizes the effectiveness of an adaptive metamaterial design that incorporates a microelectromechanical systems (MEMS) variable capacitor. Applying voltages to the …


High Power Microwave (Hpm) And Ionizing Radiation Effects On Cmos Devices, Nicholas A. Estep Mar 2010

High Power Microwave (Hpm) And Ionizing Radiation Effects On Cmos Devices, Nicholas A. Estep

Theses and Dissertations

Integrated circuits (ICs) are inherently complicated and made worse by increasing transistor quantity and density. This trend potentially enhances concomitant effects of high energy radiation and local or impressed electromagnetic interference (EMI). The reduced margin for signal error may counter any gain in radiation hardness from smaller device dimensions. Isolated EMI and ionizing radiation studies on circuits have been conducted extensively over the past 30 years. However, little focus has been placed on the combined effects. To investigate the effect of combined EMI and ionizing radiation, two complementary metal oxide semiconductor (CMOS) inverter technologies (CD4069 and SN74AUC1G04) were analyzed for …


Development And Demonstration Of A Field-Deployable Fast Chromotomographic Imager, Daniel C. O'Dell Mar 2010

Development And Demonstration Of A Field-Deployable Fast Chromotomographic Imager, Daniel C. O'Dell

Theses and Dissertations

A field deployable hyperspectral imager utilizing chromotomography (CT), with a direct vision prism (DVP) as the dispersive element, has been constructed at AFIT. This research is focused on the development and demonstration of the CT imager. An overview of hyperspectral imaging, chromotomography, a synopsis of reconstruction algorithms, and other CT instruments are given. The importance of component alignment, instrument calibration, and exact prism angular position data are discussed. A simplistic \shift and add" reconstruction algorithm was utilized for this research. Although limited in its ability to reconstruct a spatially and spectrally diverse scene, the algorithm was adequate for the testing …


Micro-Scale Flapping Wings For The Advancement Of Flying Mems, Nicholas R. Coleman Mar 2009

Micro-Scale Flapping Wings For The Advancement Of Flying Mems, Nicholas R. Coleman

Theses and Dissertations

This research effort presents conceptual micro scale air vehicles whose total dimensions are less than one millimeter. The initial effort was to advance the understanding of micro aerial vehicles at sub-millimeter dimensions by fabricating and testing micro scale flapping wings. Fabrication was accomplished using a surface micromachining process called PolyMUMPs™. Both rigid mechanical structures and biomimetic devices were designed and fabricated as part of this effort. The rigid mechanical structures focused on out of plane deflections with solid connections and assembling a multiple hinge wing structure through the aid of residual stress. These devices were actuated by double hot arm …


A Mems Multi-Cantilever Variable Capacitor On Metamaterial, Luke A. Rederus Feb 2009

A Mems Multi-Cantilever Variable Capacitor On Metamaterial, Luke A. Rederus

Theses and Dissertations

Negative refractive index materials are an example of metamaterials that are becoming increasingly popular. Research into these metamaterials could possibly be the first steps toward bending electromagnetic radiation (i.e., microwaves, light, etc.) around an object or person. Split ring resonators (SRR) are classified as metamaterials that create an artificial magnetic response from materials with no inherent magnetic properties. Once fabricated, an SRR has a specific resonant frequency due to its permanent geometry. This research introduces a new concept of using a variable capacitive micro- electro-mechanical system (MEMS) device located at the gap of an SRR to mechanically alter the capacitance …


Sensitivity Analysis Of Algan/Gan Hemts To Process Variation, Adam J. Liddle Mar 2008

Sensitivity Analysis Of Algan/Gan Hemts To Process Variation, Adam J. Liddle

Theses and Dissertations

A sensitivity analysis of AlGaN/GaN HEMT performance on material and process variations was performed. Aluminum mole fraction, barrier thickness, and gate length were varied ± 5% over nominal values to determine how sensitive simulated device performance was to changes in these 3 parameters. Simulated data was generated with the Synopsys TCAD software suite using a physics-based HEMT model. To validate model performance, simulated data was correlated with experimental data, which consisted of wafer epilayer characterization data as well as DC and small-signal RF device performance data from 1-26 GHz. Trends were observed in the experimental data due to variations in …


Piezo-Electrochemical Transducer Effect (Pect) Intercalated Graphite Micro-Electromechanical Actuators, Glen A. Kading Nov 2007

Piezo-Electrochemical Transducer Effect (Pect) Intercalated Graphite Micro-Electromechanical Actuators, Glen A. Kading

Theses and Dissertations

The purpose of this research is to investigate the Piezo-Electrochemical Transducer (PECT) effect in intercalated graphite as a possible mechanism of actuation for micro-electromechanical systems (MEMS). This dissertation presents the results of research into the PECT effect in H2SO4-intercalated graphitized carbon fibers, including both electrical and mechanical characteristics of this effect. PECT fibers achieve up to 1.7% strain at 1.4 V of applied potential. In contrast, the piezoelectric material polyvinylidene difluoride (PVDF) generates only 0.01% strain and polysilicon thermal expansion between 0.02 and 0.06% strain depending on the thermal conductivity of the particular polysilicon that the actuators are fabricated in. …


Hybrid Micro-Electro-Mechanical Tunable Filter, Edward M. Ochoa Sep 2007

Hybrid Micro-Electro-Mechanical Tunable Filter, Edward M. Ochoa

Theses and Dissertations

While advantages such as good thermal stability and processing-chemical compatibilities exist for common monolithic-integrated micro-electro-mechanically tunable filters (MEM-TF) and MEM-tunable vertical cavity surface emitting lasers (MT-VCSEL), they often require full processing to determine device characteristics. Alternatively, the MEM actuators and the optical parts may be fabricated separately, then subsequently bonded. This "hybrid approach" potentially increases design flexibility. Since hybrid techniques allow integration of heterogeneous material systems, "best of breed" compound optoelectronic devices may be customized to enable materials groups to be optimized for tasks they are best suited. Thus, as a first step toward a hybrid (AlxGa1- …


Investigation Of Gate Current In Neutron Irradiated AlXGa1-XN/Gan Heterogeneous Field Effect Transistors Using Voltage And Temperature Dependence, Thomas E. Gray Mar 2007

Investigation Of Gate Current In Neutron Irradiated AlXGa1-XN/Gan Heterogeneous Field Effect Transistors Using Voltage And Temperature Dependence, Thomas E. Gray

Theses and Dissertations

The gate current of Al27Ga73N/GaN heterogeneous field effect transistors (HFETs) is investigated using current-voltage (IV) and current-temperature (IT) measurement demonstrating that trap assisted tunneling (TAT) is the primary current mechanism. A thermionic trap assisted tunneling (TTT) model is used with variables of Schottky barrier height, trap energy, donor density and trap density. This results in a sigma of 1.38x10-8 A for IT data measured between 85K and 290K and for IV data measured between 0.0 V and -4.0 V. High energy (>0.5 MeV) neutron irradiation confirms an increase of gate current with fluence. An …


Air Gap Error Compensation For Coaxial Transmission Line Method Of Electromagnetic Material Characterization, Ronald G. Fehlen Mar 2006

Air Gap Error Compensation For Coaxial Transmission Line Method Of Electromagnetic Material Characterization, Ronald G. Fehlen

Theses and Dissertations

This research analyzes material characterization measurements from 50 Mhz to 3.05 GHz where an axially symmetric air gap exists between the sample material and the inner or outer conductor. Higher order fields are excited by the air gap and are accounted for through modal analysis methods. A root search minimizes the difference between the calculated scattering parameters from the modal method and the experimentally measured scattering parameters. The root is the permittivity and permeability of the material. This method is tested with a non-magnetic material and a heavily loaded magnetic material. An error analysis based on dimension measurement uncertainty is …


Computational Modeling Of The Dielectric Barrier Discharge (Dbd) Device For Aeronautical Applications, Christopher S. Charles Mar 2006

Computational Modeling Of The Dielectric Barrier Discharge (Dbd) Device For Aeronautical Applications, Christopher S. Charles

Theses and Dissertations

Dielectric Barrier Discharge (DBD) type devices, when used as plasma actuators, have shown significant promise for use in many aeronautical applications. Experimentally, DBD actuator devices have been shown to induce motion in initially still air, and to cause re-attachment of air flow over a wing surface at a high angle of attack. This thesis explores the numerical simulation of the DBD device in both a lD and 2D environment. Using well established fluid equation techniques, along with the appropriate approximations for the regime under which these devices will be operating, computational results for various conditions and geometries are explored. In …


High-Temperature Ferromagnetism In Transition Metal Implanted Wide-Bandgap Semiconductors, Jeremy A. Raley Jun 2005

High-Temperature Ferromagnetism In Transition Metal Implanted Wide-Bandgap Semiconductors, Jeremy A. Raley

Theses and Dissertations

Material with both semiconductor and magnetic properties, which is commonly called a dilute magnetic semiconductor (DMS), will prove most useful in the fabrication of spintronic devices. In order to produce a DMS at above room temperature, transition metals (TMs) were implanted into host semiconductors of p-GaN, Al0.35Ga0.65N, or ZnO. Magnetic hysteresis measurements using a superconducting quantum interference device (SQUID) magnetometer show that some of the material combinations clearly exhibit ferromagnetism above room temperature. The most promising materials for creating spintronic devices using ion implantation are p-GaN:Mn, Al0.35Ga0.65N:Cr, and Fe-implanted ZnO nanotips on …


Using Multiple Mems Imus To Form A Distributed Inertial Measurement Unit, Ryan D. Hanson Mar 2005

Using Multiple Mems Imus To Form A Distributed Inertial Measurement Unit, Ryan D. Hanson

Theses and Dissertations

MEMS IMUs are readily available in quantity and have extraordinary advantages over conventional IMUs in size, weight, cost, and power consumption. However, the poor performance of MEMS IMUs limits their use in more demanding military applications. It is desired to use multiple distributed MEMS IMUs to simulate the performance of a single, more costly IMU, using the theory behind Gyro-Free IMUs. A Gyro-Free IMU (GF-IMU) uses a configuration of accelerometers only to measure the three accelerations and three angular rotations of a rigid body in 3-D space. Theoretically, almost any configuration of six distributed accelerometers yields sufficient measurements to solve …


Deviation Of Time-Resolved Luminescence Dynamics In Mwir Semiconductor Materials From Carrier Recombination Theory Predictions, Peter M. Johnson Mar 2004

Deviation Of Time-Resolved Luminescence Dynamics In Mwir Semiconductor Materials From Carrier Recombination Theory Predictions, Peter M. Johnson

Theses and Dissertations

Time resolved luminescence spectroscopy was used to characterize luminescence decay curves for a bulk InAs sample and an InAsSb type-I quantum-well sample over the first 3ns following excitation. The luminescence decay curves were then converted to carrier densities and used to find recombination coefficients that provided the least-squared-error solution of the rate equation describing carrier recombination. Recombination coefficients describing Shockley Read-Hall (ASRH) radiative (Brad) and Auger (CAug) recombination were determined at two different temperatures and four excitation powers, then analyzed for consistency and physical significance. For all of the resulting least …


Quantum Mechanical Calculations Of Monoxides Of Silicon Carbide Molecules, John W. Roberts Jr. Mar 2003

Quantum Mechanical Calculations Of Monoxides Of Silicon Carbide Molecules, John W. Roberts Jr.

Theses and Dissertations

Modern semiconductor devices are principally made using the element silicon. In recent years, silicon carbide (SiC), with its wide band-gap, high thermal conductivity, and radiation resistance, has shown prospects as a semiconductor material for use in high temperature and radiation environments such as jet engines and satellites. A limiting factor in the performance of many SiC semiconductor components is the presence of lattice defects formed at oxide dielectric junctions during processing. Recent theoretical work has used small quantum mechanical systems embedded in larger molecular mechanics structures to attempt to better understand SiC surfaces and bulk materials and their oxidation. This …


Stress Analysis Of Silicon Carbide Microeletromechanical Systems Using Raman Spectroscopy, Stanley J. Ness Mar 2003

Stress Analysis Of Silicon Carbide Microeletromechanical Systems Using Raman Spectroscopy, Stanley J. Ness

Theses and Dissertations

During the fabrication of Micro-Electro-Mechanical Systems (MEMS), residual stress is often induced in the thin films that are deposited to create these systems. These stresses can cause the device to fail due to buckling, curling, or fracture. Government and industry are looking for ways to characterize the stress during the deposition of thin films in order to reduce or eliminate device failure. Micro-Raman spectroscopy has been successfully used to analyze poly-silicon MEMS devices made with the Multi-User MEMS Process (MUMPS trade name). Micro-Raman spectroscopy was selected because it is nondestructive, fast and has the potential for in situ stress monitoring. …


Total Dose Effects Of Ionizing And Non-Ionizing Radiation On Piezoresistive Pressure Transducer Chips, Samuel J. Willmon Mar 2003

Total Dose Effects Of Ionizing And Non-Ionizing Radiation On Piezoresistive Pressure Transducer Chips, Samuel J. Willmon

Theses and Dissertations

The effects of ionizing and non ionizing radiation on the resistivity of silicon based, piezoresistive bulk micro-machined chips from pressure transducers were examined. Standard current-voltage (I-V) measurements were taken in-situ and post-irradiation during isothermal annealing at room temperature. One group of chips was irradiated to a maximum total gamma dose of lMrad(Si) in the 11,000 Ci (60) Co gamma cell at Ohio State University. The second group of chips was irradiated at the Ohio State University Research Reactor facility to a maximum total neutron dose of 4 Mrad(Si) using beam port Hi. The resistivity was shown to decrease during gamma …


Fabrication Techniques For Iii-V Micro-Opto-Electro-Mechanical Systems, Jeremy A. Raley Mar 2002

Fabrication Techniques For Iii-V Micro-Opto-Electro-Mechanical Systems, Jeremy A. Raley

Theses and Dissertations

This thesis studies selective etching techniques for the development of AlxGa1-xAs micro-opto-electro-mechanical systems (MOEMS). New MEMS technology based on materials such as AlxGa1-xAs enables the development of micro-systems with embedded active micro-optical devices. Tunable micro-lasers and optical switching based on MOEMS technology will improve future wavelength division multiplexing (WDM) systems. WDM vastly increases the speed of military communications and sensor data processing. From my designs, structures are prepared by molecular beam epitaxy. I design a mask set for studies of crystal plane selectivity. I perform a series of experiments on the selective …


Design And Fabrication Of Micro-Electro-Mechanical Structures For Tunable Micro-Optical Devices, Michael C. Harvey Mar 2002

Design And Fabrication Of Micro-Electro-Mechanical Structures For Tunable Micro-Optical Devices, Michael C. Harvey

Theses and Dissertations

Tunable micro-optical devices are expected to be vital for future military optical communication systems. In this research I seek to optimize the design of a microelectromechanical (MEM) structure integrated with a III-V semiconductor micro-optical device. The resonant frequency of an integrated optical device, consisting of a Fabry-Perot etalon or vertical cavity surface emitting laser (VCSEL), may be tuned by applying an actuation voltage to the MEM Flexure, thereby altering the device's optical cavity length. From my analysis I demonstrate tunable devices compatible with conventional silicon 5V integrated circuit technology. My design for a Fabry-Perot etalon has a theoretical tuning range …


Investigation Of Ge2Te2Sb5 Chalcogenide Thin Film For Use As An Analog Memory, Travis F. Blake Mar 2000

Investigation Of Ge2Te2Sb5 Chalcogenide Thin Film For Use As An Analog Memory, Travis F. Blake

Theses and Dissertations

This work investigates the feasibility of using Ge2Te2Sb5 chalcogenide films for analog memory. Thick film chalcogenide memory devices provided by Ovonyx, Inc. are characterized to determine how well the devices meet the repeatability, stability and predictability criteria needed to accurately store analog data values. Chalcogenide memory devices take advantage of the phase-shifting nature of chalcogenide materials to store the analog data as a resistance level. An automated test system was developed to characterize the material and the prototype devices with the goal to determine the 1) non-destructive readability of the device at different resistance values; …