Variation Of Bias Voltage Research Articles

Tailoring of cholesteric plane spacing, dielectric relaxation and optical properties of high temperature chiral nematic phase by UV irradiation

The effect of Ultra Violet (UV) irradiation on the high temperature chiral nematic (N*) mesophase has been investigated. The controlled UV exposure produced bending in rod shape molecules. The bending of molecules affects their long molecular axis; therefore, the relaxation mode associated with the rotation of molecules along the long molecular axis shifts toward the higher frequency. The UV irradiation also increases the cholesteric plane spacing of N*LC molecules. The a.c. conductivity of N*LC has been increased enormously after UV irradiation. The efficiency of opto-dielectric effect has also been evaluated with the variation of bias voltage in the present investigation.

Time-dependent thermoelectric transport for nanoscale thermal machines

We analyze an electronic nanoscale thermal machine driven by time-dependent environment: besides bias and gate voltage variations, we consider also the less prevailing time modulation of the couplings between leads and dot. We provide energy and heat current expressions in such situations, as well as expressions for the power exchanged between the dot+leads system and its outside. Calculations are made in the Keldysh nonequilibrium Green's function framework. We apply these results to design a cyclic refrigerator, circumventing the ambiguity of defining energy flows between subsystems in the case of strong coupling. For fast lead-dot coupling modulation, we observe transient currents which cannot be ascribed to charge tunneling.

Design of a Tunable Low-Frequency and Broadband Radar Absorber Based on Active Frequency Selective Surface

In this letter, we report on the design, fabrication, measurement, and analysis of a tunable low-frequency and broadband radar absorber applied in the frequency range of 1–12 GHz. Numerical simulations indicate that absorbers based on the resistor-loaded frequency selective surface (FSS) can be resistively tuned to give a broadband absorption of exceeding $-\hbox{10 dB}$ between 1 and 12 GHz. Moreover, superior absorbing performance can be achieved by introducing capacitance paralleled with resistance. Measurement results show that the radar absorber, by way of configuration with active FSS (AFSS) controlled by p-i-n diodes, can be tuned to provide a continuously variable reflectivity level of less than $-\hbox{10 dB}$ from 2 to 11.3 GHz with varied bias voltages. Furthermore, experimental results have good agreement with simulations.

Sensitivity Recalibration of MEMS Microphones to Compensate Drift and Environmental Influences

In this paper a new method for sensitivity recalibration of capacitive MEMS microphones is presented. Recalibration can be applied to compensate ageing or environmental influences. Recalibration can be done by measuring the sensitivity for only one bias voltage after a stress test. A microphone with a variable bias voltage can measure its pull-in voltage. Unfortunately, the drift of the pull-in voltage does not correlate with the sensitivity drift. So a true self-calibration without a defined acoustical test signal was impossible.

CMOS oscillator with MOS varactor and body bias tuning

In this paper, designs of voltage controlled oscillator (VCO) using three transistors XNOR gates with variable capacitive load have been presented. Three and five stage VCO circuits have been designed using the concept of reverse body bias and variable NMOS load. The tuning of output frequency has been controlled by coarse and fine tuning methods. Coarse tuning has been achieved with the variation in supply voltage from 1.8 V to 3 V and fine tuning has been obtained with variation in reverse bias voltage of NMOS load from 0 V to −0.8 V. A tuning range of 20% and 19% have been obtained with the proposed three and five stages VCO circuits. Results have been obtained for 0.18 µm CMOS technology. Power consumption and output frequency range of proposed VCO circuits have been compared with earlier reported circuits and proposed circuit's shows improved performance.

Test-beam results of a silicon pixel detector with Time-over-Threshold read-out having ultra-precise time resolution

A time-tagging hybrid silicon pixel detector developed for beam tracking in the NA62 experiment has been tested in a dedicated test-beam at CERN with 10 GeV/c hadrons. Measurements include time resolution, detection efficiency and charge sharing between pixels, as well as effects due to bias voltage variations. A time resolution of less than 150 ps has been measured with a 200 μm thick silicon sensor, using an on-pixel amplifier-discriminator and an end-of-column DLL-based time-to-digital converter.

Comparative Assessment on Ramp and Bias Voltage Variations of Closed Loop Interferometric Fiber Optic Gyroscope

Background/Objectives: The main objective of this paper is to perform a comparative discussion in gyro parameters for three cases: (i) V2π (vary)&Vπ/2 (constant), (ii) Vπ/2 (vary) and V2π (constant) and (iii) both V2π and Vπ/2 are varying simultaneously. Methods/Statistical Analysis: Fibre optic gyroscope has to be operated in closed-loop approach to achieve the inertial-grade-performance. The Closed-Loop Interferometric Fibre Optic Gyroscope (CLIFOG) system depends upon ramp voltage (V2π of IOC) and square-wave biasing signal frequency (f bias ). The digital-phase-ramp-function is used as feedback to system and makes gyro to null condition. The biasing signal voltage (Vπ/2) is 1/4 th of ramp voltage (V2π). If there are any variations in ramp and biasing signal voltages, then it introduces variations in gyro performance. Results: The ramp voltage (V2π) and square wave biasing signal voltage (Vπ/2) is increased from 1% to 10%, decreased to 1% to 10% and performed the various tests for three cases. From results, it was noted that: (i) When V2π is varying and Vπ/2 is kept constant, the scale-factor change is increasing as the error in the signal voltage is also increases. (ii) When V2π is kept constant and Vπ/2 is varying, the change in scale-factor is very minute and maintains the scale-factor linearity. (iii) While varying both V2π and Vπ/2 voltages simultaneously, the device is not responding accordingly as the error is increasing and also scale-factor is out of range subsequently. The effects on the CLIFOG system are described with the derived values in terms of bias and scale-factor. The gyro performance is very sensitive with respect to V2π variations and the percentage error is high in gyro output, but very less effect due to Vπ/2 variations when the ramp voltage (V2π) is constant. Conclusion/Application: The Closed Loop Interferometric Fiber Optic Gyroscope (CLIFOG) system requires a proper resetting of ramp voltage (V2π) in order to avoid the bias and scale factor instabilities.

Investigation of gap-closing interdigitated capacitors for electrostatic vibration energy harvesting

This paper reports on the dynamic characteristics of a MEMS electrostatic harvester employing interdigitated gap-closing topology. Devices are fabricated using SOIMUMPS technology and are characterized with and without biasing voltages for a broad range of excitation accelerations. At low vibration amplitudes the presence of a dc bias causes the resonant frequency peak to shift to lower frequencies with increasing bias. At higher vibration amplitudes the dynamic response of the devices exhibits the behavior of a Duffing oscillator with spring softening due to nonlinear stiffness attributed to the effect of electrostatic forces. Specifically, the devices exhibit sweep direction hysteresis with jump phenomena due to the multivaluedness of the response curve. Amplitude sweeps at constant frequency and varying bias voltage also show jump phenomena, highlighting how slight differences in operating conditions dramatically affect device performance. Spring hardening effects are reported for devices contaminated with dust particles. The paper also discusses SOIMUMPS limitations, the importance of reducing off-axis vibration during testing, characterization methods, and the effect of grounding on parasitic capacitance.

Performance improvement of rectifiers for WPT exploiting thermal energy harvesting

This paper proposes a combined harvesting system to improve the efficiency and flexibility of autonomous wireless network nodes, supplied by means of wireless power transfer technique. In particular, a mixed system for electromagnetic (EM) and thermal energy harvesting (EH), conceived for passive nodes of wireless sensor networks and radio frequency (RF) identification tags, is described. The proposed system aims at increasing the effectiveness and the efficiency of the EH system by integrating an antenna and a rectifier with a thermo-electric generator (TEG) able to perform thermal EH. The energy provided by the thermal harvester is exploited twice: to increase the rectifier efficiency by providing a voltage usable to improve the bias condition of the rectifying diode, and to provide additional dc energy, harvested for free. Ultimately, a great efficiency improvement, especially at low incident RF power, has been observed. The design methodology and the EM performance of a quarter-wavelength patch antenna, integrated with the TEG are resumed. Then, a test campaign to evaluate the thermal EH performance has been carried out. Afterward, a rectifier with variable bias voltage, operating at the same frequency of the antenna, has been opportunely designed to exploit the harvested thermal energy to bias the diode. A measurement campaign has been then carried out to test the efficiency increment obtained and to validate the proposed solution.

A Continuous Viewing Angle Controllable Blue Phase Liquid Crystal Display

In this paper, a blue phase liquid crystal display with fringe-field electrodes in the bottom substrate and a plane common electrode in the top substrate is proposed. For the wide viewing mode, the contrast ratio is above 1000:1 in most all directions; for the narrow viewing angle controllable mode, the high contrast ratio (above 500:1) can be hold in a narrow viewing area. The viewing angle changes continuously and uniformly from very wide viewing angle to narrow viewing angle when the top common electrode applies variable bias voltages. Moreover, the effect of permittivity of the insulation layer which is between the liquid crystal and pixel electrodes is researched, the results show that the insulation layer with high permittivity can obviously reduce the operating voltage.

Physical and chemical characterization of Ag-doped Ti coatings produced by magnetron sputtering of modular targets

Silver-doped Ti films were produced using a single magnetron sputtering source equipped with a titanium target containing implemented silver modules under variation of bias voltage and substrate temperature. The Ti(Ag) films were characterized regarding their morphology, contact angle, phase composition, silver content and distribution as well as the elution of Ag+ ions into cell media.SEM and AFM pictures showed that substrate heating during film deposition supported the formation of even and dense surface layers with small roughness values, an effect that could even be enforced, when a substrate bias voltage was applied instead. The deposition of both Ti and Ag was confirmed by X-ray diffraction. ICP-MS and EDX showed a clear correlation between the applied sputtering parameters and the silver content of the coatings. Surface-sensitive XPS measurements revealed that higher substrate temperatures led to an accumulation of Ag in the near-surface region, while the application of a bias voltage had the opposite effect. Additional elution measurements using ICP-MS showed that the release kinetics depended on the amount of silver located at the film surface and hence could be tailored by variation of the sputter parameters.

Raman Spectroscopy Studies on DLC Films Synthesized by PECVD Method

Diamond like carbon (DLC) is a metastable form of amorphous carbon containing fraction of sp2 and sp3 bonds. Their mechanical properties depend on the sp3 content as well as on the number and size of graphitic nanoclusters. It is noted that properties change significantly depending on the method of preparation of these films. These properties are also altered by the composition of the films. In view of this, the objective of present work was to deposit hydrogenated DLC films on p-type silicon substrate using inductively coupled plasma enhanced chemical vapor deposition (IC-PECVD) technique with varying bias voltage, bias frequency, gas deposition pressure and gas composition ratio. They play important role in film deposition process and are responsible for change in mechanical properties of the film such as hardness and Young's modulus. Raman spectroscopy was used to study the structural arrangement of carbon atoms. Significant change in the mechanical properties of the film was observed which can be attributed to the change in sp3 and sp2 contents in the DLC film. It was observed that the process parameters considerably affect the hardness and Young's modulus of the DLC films. The films of desired mechanical properties can be deposited for various industrial and biomedical applications by maintaining suitable deposition conditions.

Quantum transport characteristics in single and multiple N-channel junctionless nanowire transistors at low temperatures

Single and multiple n-channel junctionless nanowire transistors (JNTs) are fabricated and experimentally investigated at variable temperatures. Clear current oscillations caused by the quantum-confinement effect are observed in the curve of drain current versus gate voltage acquired at low temperatures (10 K–100 K) and variable drain bias voltages (10 mV–90 mV). Transfer characteristics exhibit current oscillation peaks below flat-band voltage (VFB) at temperatures up to 75 K, which is possibly due to Coulomb-blocking from quantum dots, which are randomly formed by ionized dopants in the just opened n-type one-dimensional (1D) channel of silicon nanowires. However, at higher voltages than VFB, regular current steps are observed in single-channel JNTs, which corresponds to the fully populated subbands in the 1D channel. The subband energy spacing extracted from transconductance peaks accords well with theoretical predication. However, in multiple-channel JNT, only tiny oscillation peaks of the drain current are observed due to the combination of the drain current from multiple channels with quantum-confinement effects.

Effects of substrate bias voltage and target sputtering power on the structural and tribological properties of carbon nitride coatings

Effects of substrate bias voltage and target sputtering power on the structural and tribological properties of carbon nitride (CNx) coatings are investigated. CNx coatings are fabricated by a hybrid coating process with the combination of radio frequency plasma enhanced chemical vapor deposition (RF PECVD) and DC magnetron sputtering at various substrate bias voltage and target sputtering power in the order of −400V 200W, −400V 100W, −800V 200W, and −800V 100W. The deposition rate, N/C atomic ratio, and hardness of CNx coatings as well as friction coefficient of CNx coating sliding against AISI 52100 pin in N2 gas stream decrease, while the residual stress of CNx coatings increases with the increase of substrate bias voltage and the decrease of target sputtering power. The highest hardness measured under single stiffness mode of 15.0GPa and lowest residual stress of 3.7GPa of CNx coatings are obtained at −400V 200W, whereas the lowest friction coefficient of 0.12 of CNx coatings is achieved at −800V 100W. Raman and XPS analysis suggest that sp3 carbon bonding decreases and sp2 carbon bonding increases with the variations in substrate bias voltage and target sputtering power. Optical images and Raman characterization of worn surfaces confirm that the friction behavior of CNx coatings is controlled by the directly sliding between CNx coating and steel pin. Therefore, the reduction of friction coefficient is attributed to the decrease of sp3 carbon bonding in the CNx coating. It is concluded that substrate bias voltage and target sputtering power are effective parameters for tailoring the structural and tribological properties of CNx coatings.

Resistance of Outmost Shell- and Embedded-End Contacts of Single- and Multi-Bridged Carbon Nanotubes

Single-bridged (SB) and multi-bridged (MB) carbon nanotubes (CNTs) were laterally grown between two electrodes capped on a thin nickel film, which functioned as catalysts. SB CNTs with outermost shell-end and embedded-end contacts on the electrodes showed varistor- or metal-like current-voltage (IV) characteristics. The devices were measured with fixed-amplitude AC superimposed on varying bias voltages. The MB CNTs contained both meal- and varistor-like CNTs, with the latter dominating the resistance at a higher bias. The results also imply that contact configuration significantly affects electrical interconnection.

Evaluation of bias voltage effect on diamond‐like carbon coating properties deposited on tungsten carbide cobalt

Diamond‐like carbon (DLC) coatings are getting new trends for cutting tool applications. In this research work, the DLC coatings were deposited on 15 × 15 × 5‐mm tungsten carbide cobalt substrates with variation of bias voltage from 0 to 500 V. The DLC films of 400 nm were deposited using filter cathode vacuum arc system, and 100‐nm chromium interlayer was deposited by sputtering. The optimized conditions for plasma pretreatment at different argon flow rates and deposition rates with bias variation were found. The effect of bias voltage on microstructure, tribology, adhesion, and mechanical properties were evaluated. The characterization techniques employed were field emission electron microscopy, Raman spectroscopy, wear test, SEM, scratch test, and nano‐indentation. The effect of substrate pretreatment on film adhesion was also evaluated. It was observed that etching rate increased with the increase in Ar flow rate while DLC deposition and sputtering rates decreased with increase in the bias voltage. The characterization suggests the DLC coatings deposited at 0 V bias as optimum condition because of showing the best results among all other conditions. Copyright © 2014 John Wiley & Sons, Ltd.

Regression Analysis of the Effect of Bias Voltage on Nano‐ and Macrotribological Properties of Diamond‐Like Carbon Films Deposited by a Filtered Cathodic Vacuum Arc Ion‐Plating Method

Diamond‐like carbon (DLC) films are deposited by bend filtered cathodic vacuum arc (FCVA) technique with DC and pulsed bias voltage. The effects of varying bias voltage on nanoindentation and nanowear properties were evaluated by atomic force microscopy. DLC films deposited with DC bias voltage of −50 V exhibited the greatest hardness at approximately 50 GPa, a low modulus of dissipation, low elastic modulus to nanoindentation hardness ratio, and high nanowear resistance. Nanoindentation hardness was positively correlated with the Raman peak ratio Id/Ig, whereas wear depth was negatively correlated with this ratio. These nanotribological properties highly depend on the films’ nanostructures. The tribological properties of the FCVA‐DLC films were also investigated using a ball‐on‐disk test. The average friction coefficient of DLC films deposited with DC bias voltage was lower than that of DLC films deposited with pulse bias voltage. The friction coefficient calculated from the ball‐on‐disk test was correlated with the nanoindentation hardness in dry conditions. However, under boundary lubrication conditions, the friction coefficient and specific wear rate had little correlation with nanoindentation hardness, and wear behavior seemed to be influenced by other factors such as adhesion strength between the film and substrate.

Understanding Scanning Tunneling Microscopy Contrast Mechanisms on Metal Oxides: A Case Study

A comprehensive analysis of contrast formation mechanisms in scanning tunneling microscopy (STM) experiments on a metal oxide surface is presented with the oxygen-induced (2√2×√2)R45° missing row reconstruction of the Cu(100) surface as a model system. Density functional theory and electronic transport calculations were combined to simulate the STM imaging behavior of pure and oxygen-contaminated metal tips with structurally and chemically different apexes while systematically varying bias voltage and tip-sample distance. The resulting multiparameter database of computed images was used to conduct an extensive comparison with experimental data. Excellent agreement was attained for a large number of cases, suggesting that the assumed model tips reproduce most of the commonly encountered contrast-determining effects. Specifically, we find that depending on the bias voltage polarity, copper-terminated tips allow selective imaging of two structurally distinct surface Cu sites, while oxygen-terminated tips show complex contrasts with pronounced asymmetry and tip-sample distance dependence. Considering the structural and chemical stability of the tips reveals that the copper-terminated apexes tend to react with surface oxygen at small tip-sample distances. In contrast, oxygen-terminated tips are considerably more stable, allowing exclusive surface oxygen imaging at small tip-sample distances. Our results provide a conclusive understanding of fundamental STM imaging mechanisms, thereby providing guidelines for experimentalists to achieve chemically selective imaging by properly selecting imaging parameters.

High-performance 320 × 256 long-wavelength infrared photodetector arrays based on CdHgTe layers grown by molecular beam epitaxy

This paper gives the parameters of 320 × 256 element long-wavelength infrared photodetectors fabricated by a new improved technology based on heteroepitaxial mercury-cadmium-tellur structures. In these photodetectors, the variation of the photodiode bias voltage over the area of the array is minimized; inefficient photodiode regions related to both hybridization and spike-shaped growth defects of epitaxial films are eliminated; the current-voltage characteristics of the diodes in the resulting photodetectors are homogeneous and are limited by the diffusion current component up to −400 mV. The dark current is 0.25–0.45 nA, and R 0 A = (0.6–3) · 102 Ω · cm2. The voltage sensitivity, the threshold irradiance, and the average NETD at the maximum sensitivity are 11.8 · 108 V/W, 3.7 · 10−8 W/cm2, and 26.8 mK, respectively. The percentage of defective elements is 1.5%.

Experimental Realization of Tunable Transmission Lines Based on Single-Layer SIWs Loaded by Embedded SRRs

Wave propagation in single layer substrate integrated waveguides (SIWs) loaded by embedded split-ring resonators (ESRRs) is discussed theoretically and experimentally. It is shown that the loaded SIW can support a backward-wave passband below the cutoff frequency (fc) of the host SIW or a stopband will appear above fc if the effective transversal permeability is negative. In addition, varactor-loaded ESSRs (VLESRRs) can show resonance frequency agility through a variable reverse bias voltage applied to the varactors. Next, VLESRRs are loaded in SIWs to realize transmission lines with either tunable passbands (stopbands) below (above) fc of the host SIWs. Both cases are considered in this paper. First, an SIW with fc=7 GHz is loaded by five VLESRRs showing a tunable passband below the cutoff from 1.5 to 4 GHz. Second, an SIW with fc=1.9 GHz and five VLESRRs is discussed where a tunable stopband is achieved above fc from 2 to 4 GHz. In both cases, the reverse-bias voltage applied to the varactors varies from 0 to 20 V. Finally, two fabricated prototypes are provided for each case to validate the analysis. The measured and simulated results are in good agreement.