Orders Of Resistance Change Research Articles

Chalcogenide Phase-Change Material Germanium Telluride for Radio-Frequency Applications: An overview

Chalcogenide phase-change materials (PCMs) have been widely used in optical storage media and nonvolatile memory devices applications. Over the past several years, there has been interest in exploiting PCM technology, especially germanium telluride (GeTe) and its alloys, for radio-frequency (RF) applications. The principle of operation of PCM-based RF devices is based on the ability of the material to transform from a high-resistivity (amorphous phase) to low-resistivity state (crystalline phase) and vice versa, with the application of a short, thermal pulse. Actuation pulses are applied to microheaters embedded with the PCM junction to switch between the two states. The PCM switch can exhibit more than five orders of resistance change between the two states. PCM-based RF switches are expected to bridge the gap between semiconductor switches and microelectromechanical systems (MEMS) switches as they combine the low insertion loss performance of MEMS technology and the small size and reliability performance of semiconductor technology. In addition to miniaturization, GeTe-based switches offer unique latching functionality and ease of monolithic integration with other RF circuits. This article presents an overview of PCM technology and its applications to RF circuits. A brief history of the technology is presented first, followed by a discussion of the basic characteristics of PCMs. The steps of a fabrication process of PCM RF devices are illustrated. A description of RF-PCM switch is presented in detail along with a comparison between RF performance of PCM switches and other existing commercial switches. As examples of application of the PCM technology to other RF circuits, the article concludes by presenting a crossbar switch matrix, phase shifter, and variable attenuator, realized using the PCM technology.

Fabrication of smooth thin film of vanadium oxides ($$\hbox {VO}_x$$) using pulsed laser deposition

We report the synthesis of vanadium oxide thin films by the pulsed laser deposition under different parameter conditions on $$\hbox {Si/SiO}_2$$ substrates using $$\hbox {V}_2\hbox {O}_5$$ target. The objective of the present work was to achieve smooth $$\hbox {VO}_2$$ thin film in a single step. Synergistic effect of the deposition parameters on the phase of vanadium oxides is studied by a series of experiments designed using Taguchi analysis. Conditions for depositing different oxides of vanadium like $$\hbox {VO}_2$$, $$\hbox {V}_2\hbox {O}_3$$, $$\hbox {V}_3\hbox {O}_5$$ and a new phase, $$\hbox {V}_7\hbox {O}_{16}$$ was established. The range of parameters varied were: gas pressure: $$10^{-3}$$–5 $$\times$$ $$10^{-2}$$ mbar; temperature: 500–700 $$^\circ$$C; target-substrate distance: 30–40 mm and laser energy: 100–200 mJ. $$\hbox {VO}_2$$ film with surface roughness of 3.68 nm having a semiconductor-to-metal transition (SMT) at 72 $$^\circ$$C with 2–3 orders of resistance change was achieved. Taguchi model was statistically analyzed to determine the suitable condition as well as effect of deposition parameters to obtain phase pure $$\hbox {VO}_2$$ thin film. The optimum condition for deposition was found to be: gas pressure: 5 $$\times$$ $$10^{-2}$$ mbar; temperature: 600 $$^\circ$$C; distance: 35 mm, and laser energy: 200 mJ after analyzing using Taguchi model.

Characterization, Optimization, and Fabrication of Phase Change Material Germanium Telluride Based Miniaturized DC–67 GHz RF Switches

This paper presents the characterization, optimization, and fabrication of phase change material (PCM) germanium telluride (GeTe) based RF switches investigating the materials’ aspect and design parameters of the switches and their impact on the RF performance. Surface properties of GeTe thin films are investigated through atomic force microscopy (AFM), scanning electron microscopy (SEM), and cross-wafer resistance mapping measurements. Optimized GeTe thin films exhibit over five orders of resistance change. Various GeTe switch design constraints are studied via cross sectioning of the fabricated device using a focused ion beam (FIB)-SEM. Current-carrying capacity and resistance of microheaters are extracted using electrical characterization. The RF performance of the PCM switches is optimized using diverse design parameters and characterization of PCM thin films. A six-layer microfabrication process is presented for monolithically integrating RF circuits with PCM switches. Methods to reduce parasitic elements in PCM switches are discussed. The RF performance of the optimized PCM based switch is simulated and measured demonstrating better than 0.4 dB of insertion loss and a return loss better than 20 dB from dc to 67 GHz.

Evaluation of characteristics in VOx microbolometer fabricated by MOD on Si3N4/SiO2 membrane

AbstractVOx thin films were fabricated on Si3N4/SiO2/Si substrates by firing precursor films, which were fabricated by metal‐organic decomposition (MOD), with a reduced pressure. Resistance‐temperature (R‐T) characteristics of the films indicating the phase transition from metal to insulator with about 4 orders of resistance change specified with VO2 (M) were obtained. Furthermore, the films fabricated with a firing temperature of 580‐600°C had temperature coefficient of resistance (TCR) of −2.8 to −2.9 %/K at room temperature. After fabricating VOx microbolometers with 40 × 10 μm2 using the films on Si3N4/SiO2/Si substrates, Si with a thickness of about 340 μm was etched using Deep‐RIE and XeF2 vapor etching from the backside of the substrate. Then, the VOx microbolometer was completed on Si3N4/SiO2 membrane. The VOx microbolometer on Si3N4/SiO2 membrane had a high DC sensitivity of 2310 W−1, which was about 15 times higher than that of the microbolometer on the Si3N4/SiO2/Si substrate.

Ultrahigh Sensitive and Flexible Magnetoelectronics with Magnetic Nanocomposites: Toward an Additional Perception of Artificial Intelligence.

In recent years, flexible magnetoelectronics has attracted a great attention for its intriguing functionalities and potential applications, such as healthcare, memory, soft robots, navigation, and touchless human-machine interaction systems. Here, we provide the first attempt to demonstrate a new type of magneto-piezoresistance device, which possesses an ultrahigh sensitivity with several orders of resistance change under an external magnetic field (100 mT). In our device, Fe-Ni alloy powders are embedded in the silver nanowire-coated micropyramid polydimethylsiloxane films. Our devices can not only serve as an on/off switch but also act as a sensor that can detect different magnetic fields because of its ultrahigh sensitivity, which is very useful for the application in analog signal communication. Moreover, our devices contain several key features, including large-area and easy fabrication processes, fast response time, low working voltage, low power consumption, excellent flexibility, and admirable compatibility onto a freeform surface, which are the critical criteria for the future development of touchless human-machine interaction systems. On the basis of all of these unique characteristics, we have demonstrated a nontouch piano keyboard, instantaneous magnetic field visualization, and autonomous power system, making our new devices be integrable with magnetic field and enable to be implementedinto our daily life applications with unfamiliar human senses. Our approach therefore paves a useful route for the development of wearable electronics and intelligent systems.

Junction size dependence of ferroelectric properties in e-beam patterned BaTiO3 ferroelectric tunnel junctions

We investigate the switching characteristics in BaTiO3-based ferroelectric tunnel junctions patterned in a capacitive geometry with circular Ru top electrode with diameters ranging from ∼430 to 2300 nm. Two different patterning schemes, viz., lift-off and ion-milling, have been employed to examine the variations in the ferroelectric polarization, switching, and tunnel electro-resistance resulting from differences in the pattering processes. The values of polarization switching field are measured and compared for junctions of different diameter in the samples fabricated using both patterning schemes. We do not find any specific dependence of polarization switching bias on the size of junctions in both sample stacks. The junctions in the ion-milled sample show up to three orders of resistance change by polarization switching and the polarization retention is found to improve with increasing junction diameter. However, similar switching is absent in the lift-off sample, highlighting the effect of patterning scheme on the polarization retention.

Terahertz transmission characteristics across the phase transition in VO2 films deposited on Si, sapphire, and SiO2 substrates

Vanadium dioxide (VO2) films were deposited on high-purity Si, sapphire, and SiO2 substrates by an organic sol-gel method. The effect of the substrate on the structure, morphology, and phase transition properties of the VO2 films was demonstrated. We proposed that the film-substrate interaction induced the differences in the fraction of the +4 valence state vanadium oxide phase, surface morphology, and grain size for the VO2 films. The VO2 film on the Si substrate exhibited a switching property of about 2 orders of change in electrical resistivity. By contrast, the VO2 films on the sapphire and SiO2 substrates exhibited a switching property of about 3 orders of change in resistivity. The THz transmission across the phase transition in the VO2 films was quite different in the transmission modulation ratio, the width, and the slope of the hysteresis loop. In particular, the VO2 films on the sapphire and SiO2 substrates have the same reduction in THz transmission by about 46% comparing with about 35% in the VO2 film on the Si substrate. Furthermore, the VO2 film on the SiO2 substrate exhibits the widest hysteresis loop with the steepest slope.

LPG Gas-Sensing System With $\hbox{SnO}_{2}$ Thin-Film Transducer and 0.7-$\mu\hbox{m}$ CMOS Signal Conditioning ASIC

The design and implementation of a complete gas sensor system for liquified petroleum gas (LPG) gas sensing are presented. The system consists of a SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> transducer, a lowcost heater, an application specific integrated circuit (ASIC) with front-end interface circuitry, and a microcontroller interface for data logging. The ASIC includes a relaxation-oscillator-based heater driver circuit that is capable of controlling the sensor operating temperature from 100degC to 425degC. The sensor readout circuit in the ASIC, which is based on the resistance to time conversion technique, has been designed to measure the gas sensor response over three orders of resistance change during its interaction with gases.

Advantages of inductively coupled plasma-assisted sputtering for preparation of stoichiometric VO 2 films with metal–insulator transition

Inductively coupled plasma (ICP)-assisted sputtering with an internal coil enabled deposition of stoichiometric crystalline vanadium dioxide (VO 2) films on a sapphire (Al 2O 3) (001) substrate under widely various deposition conditions. The films showed a metal–insulator (M–I) transition around temperatures of 68 °C with several orders of change in resistivity. Particularly, low-temperature (250 °C) growth of VO 2 film with two orders transition decade was achieved in ICP-assisted sputtering, in contrast with conventional sputtering, which required 400 °C for VO 2 growth. Rutherford back scattering (RBS) measurements revealed that the VO 2 film prepared by ICP-assisted sputtering was exactly stoichiometric, containing no impurity atoms from the inserted coil material. The ICP-assisted sputtering was examined in comparison to conventional sputtering in view of plasma characteristics.

Electric Field Induced Metal-Insulator Transition of Vanadium Dioxide Films on Sapphire Substrate Prepared by Inductively Coupled Plasma-Assisted Sputtering

Single phase monoclinic vanadium dioxide (VO2) films were successfully grown on sapphire (001) substrate by means of an inductively coupled plasma (ICP)-assisted sputtering with an internal coil. In x-ray diffraction patterns, we observed reflections originating from monoclinic VO2 with a main peak at 2θ = 39.77° corresponding to VO2 (020) for films on sapphire (001) substrates. The VO2 films exhibited metal-insulater transition (MIT) at temperatures around 65°C with three orders of change in resistivity. A simple device of VO2 film on sapphire (001) substrate having aluminum electrodes as ohmic contacts with gap separation of 1.0 mm showed current jump at an applied voltage of 48 V. The current jumped from 7 mA to 200 mA which was a limited value of voltage source.

Growth of VO 2 films with metal-insulator transition on silicon substrates in inductively coupled plasma-assisted sputtering

Single-phase monoclinic vanadium dioxide (VO 2) films were grown on a Si(100) substrate using inductively coupled plasma (ICP)-assisted sputtering with an internal coil. The VO 2 film exhibited metal-insulator (M-I) transition at around 65 °C with three orders of change in resistivity, with a minimum hysteresis width of 2.2 °C. X-ray diffraction showed structural phase transition (SPT) from monoclinic to tetragonal rutile VO 2. For conventional reactive magnetron sputtering, vanadium oxides with excess oxygen (V 2O 5 and V 3O 7) could not be eliminated from stoichiometric VO 2. Single-phase monoclinic VO 2 growths that are densely filled with smaller crystal grains are important for achieving M-I transition with abrupt resistivity change.

Modeling of Piezoresistively-Controlled Electromechanical Smart Material

A finite element model of a proposed smart material was developed. This is an initial investigation into using a piezoresistive sensor in conjunction with a multilayer ceramic actuator and a resistor network as the control circuit. A device model, incorporating piezoresistive composites (with orders of magnitude change in resistivity) and piezoelectric actuators has also been constructed. The model accounts for all relevant material properties and configurations. The software also provides a method of optimizing geometry to obtain desired response. At present the 2-D case predicts a material package with a controllable compliance. This can be extended to a 3-D case consistent with available components.

Resistivity Mapping of Sandstone Stratigraphic Traps: ABSTRACT

Many Cretaceous stratigraphic oil accumulations of Wyoming may be mapped with log resistivity, because the clay-rich edges of sandstone bodies have lower resistivity and the clay poor centers of the sandstones have higher resistivity. Although many factors affect log resistivity, variation of the clay content of a sandstone body causes several orders of magnitude change in resistivity in and around a given stratigraphic trap. Resistivity maps generally agree with SP isopach maps, but tend to show the location of the most porous and permeable clay-poor sandstones, rather than the total sand thickness. Resistivity maps are also useful when no SP is evident outside the developed sand body or when clay fill makes SP unreliable. Although the presence of carbonate cement, coals, and lignites, etc., complicate interpretation of resistivity maps in some formations, the tool is usually effective in simple clay-quartz formations. The tool is particularly useful during development drilling of a stratigraphic trap. The use of resistivity mapping is illustrated with a number of Muddy and Dakota stratigraphic oil fields in the Powder River basin of Wyoming at Hilight, Recluse, South Glenrock, Gas Draw, and Coyote Creek. End_of_Article - Last_Page 956------------