Variation Of Bias Voltage Research Articles

The Tunable Phase Shift of High-Speed PIN Photodetector and Modified Uni-Traveling Carrier Photodetector

We report the phase shift of two types of photodetectors for a variation of bias voltage and optical power. One type is PIN-PD and the other is a modified uni-traveling carrier photodetector (MUTC-PD). In PIN-PD, the phase change shows a photocurrent-dependent variation of about 15 degrees at 3 GHz. It exhibits good stability over a wide bandwidth as the bias voltage changes. By comparison, the phase shift of the MUTC-PD is more sensitive to the bias voltage and the photocurrent. The continuous tunable range of phase shift in MUTC-PD reaches 50 degrees at 10 GHz. It is demonstrated that the adjustable phase shift mainly results from the transit time and the impedance dynamic effects in response to the optical power and bias voltage.

High resolution beam switch antenna based on modified CRLH Butler matrix

AbstractA new beam switch antenna based on a composite right/left‐handed (CRLH) Butler matrix is presented and experimentally validated. The CRLH transmission line (TL) is proposed to increase the number of beams. The proposed CRLH TL has more than 100° phase difference using variable bias voltages. Different combinations of phase shifts are achieved by applying different bias voltages between 0 and 8 V. The CRLH TL is added to the conventional Butler matrix to increase the progressive phase difference between adjacent ports, and consequently, the beam pattern. A 5° beam resolution within a spatial range of 100° is achieved. The measurement results are in good agreement with the simulations.

Piezoelectric properties reflecting nanostructures of tetrathiafulvalene and chloranil complexes using cyclic peptide nanotube scaffolds

AbstractTetrathiafulvalene (TTF) and chloranil were introduced at the side chains of different cyclic tripeptides, which were self‐assembled into peptide nanotubes (PNTs). PNTs were used as scaffolds for alignment of the charge‐transfer complexes between TTF and chloranil, and they were prepared via two methods, one is that mixing a PNT comprising only TTF with a PNT comprising only chloranil (method 1), and the other is that one pot mixing of cyclic tripeptides with TTF and cyclic tripeptides with chloranil to be self‐assembled into PNTs (method 2). These PNTs naturally associated to form PNT bundles. The surface potentials of the PNT bundles became larger for the PNTs carrying charge‐transfer complexes along the PNT (method 2) than those between PNTs (method 1). This bundle of PNT carrying charge‐transfer complexes along the PNT (method 2) showed a hysteresis response in the piezoelectric force curve with varying bias voltages according to piezoelectric force microscope measurements.

Quantification of the Effects of Coating Parameters on the Properties of TiAlZrN Coatings

In this study, TiAlZrN layer was coated on AISI H13 substrate surface with variable substrate bias voltage, Zr target current, and ambient pressure deposition parameters by using closed field unbalanced magnetron sputtering (CFUBMS) technique. The main goal of this paper is to determine the effect percentages of these variable parameters on the properties of TiAlZrN coatings by Analysis of Variance (ANOVA). These coating properties include average grain size, thickness, hardness, adhesion strength and wear resistance. The numerical data obtained as a result of this study will shed light on the select of parameters which have a direct effect on coatings to the researchers who will work on this topic. The parameters used as variables in the deposition process were leveled with Taguchi experimental (33) design method. Average grain size and thickness of coatings were established by SEM images. The average grain sizes of coatings were between 290 and 440 nm and the most effective parameter was substrate bias voltage with 58.4 %. The hardness, adhesion strength and wear properties of the coatings were determined using micro hardness tester, scratch test and ball on disc wear device respectively. The maximum hardness of coatings was 1674 HV, while the wear resistance was increased by 37 times compared to the substrate material. The maximum adhesion strength value of the coatings was reached 56N. The superiority of the effect of substrate bias voltage on the hardness, adhesion strength and wear resistance of the coatings compared to other deposition parameters was again prominent (respectively 86.15%, 53.63% and 70.86%). Also, the hardness and wear resistance properties were found to be directly related to each other. The sample with the highest coating hardness also showed the highest wear resistance performance. In the sample with the lowest hardness, this situation found to be similar.

Ultra-thin GaN nanostructures based self-powered ultraviolet photodetector via non-homogeneous Au-GaN interfaces

We report the fabrication of ultra-thin GaN (0002) nanostructures based self-powered ultraviolet photodetector on Si (111) substrate. Non-homogeneous GaN nano-islands were perceived on Si surface with a thickness of ~30 nm and an average distribution density of 2 × 1010 cm−2. Even at low dimension GaN-nanostructures film, the capability of ultraviolet detection of fabricated photodetector added novelty to this work, where performance parameters such as photosensitivity (~102), detectivity (~109 Jones), responsivity (1.76 mA/W) and noise equivalent power (3.5 × 10−11 WHz−1/2) under self-powered mode were observed. The transient photo-response measurement revealed a rapid rise and decay time constants of ~18 ms and ~27 ms respectively. Under varying optical power (1 mW–13 mW), the GaN photodetector displayed significant enhancement in photocurrent with increasing optical power. The performance of the fabricated detector has been also analysed under varying bias voltage where it revealed significantly enhanced responsivity (23 fold) and detectivity (~1000 fold). Such nanostructured self-powered GaN-based ultraviolet photodetector paves the way towards the fabrication of energy-efficient optoelectronic devices.

Voltage-Controlled Oscillator Design Using MOS Varactor

In this work, voltage-controlled ring oscillator (VCO) by employing the three transistors (3T) XOR gates and NMOS varactor load has been reported. Output load has been varied with the application of reverse body bias voltage of NMOS transistor. VCO circuits with 3 and 5 delay stages have been designed. The output frequency is controlled by coarse and fine tuning techniques. The coarse tuning is provided with the variation in supply voltage (VCT) in the range of 1.8 V to 3.3 V. Further, fine tuning has been obtained with variation in reverse substrate bias voltage of NMOS varactor load from 0 to − 1 V. A three-stage VCO design shows output frequency deviation from 340.136 to 628.930 MHz and power consumption ranges from 0.1658 to 1.1285 mW with coarse tuning technique. Frequency deviation from 340.136 to 333.344 MHz and power consumption deviation from 0.1658 to 0.1648 mW have been obtained with fine tuning in three-stage VCO with fixed VCT of 1.8 V. A five-stage VCO design provides the output frequency from 189.035 to 328.947 MHz with power consumption range varying from 0.1698 mW to 1.1364 mW in coarse tuning mode. Moreover, five-stage VCO with fine tuning shows frequency variations from 328.947 to 326.797 MHz with varied power from 1.1364 to 1.1350 mW having the fixed VCT of 3.3 V. Results have been achieved with SPICE in 0.35-µm CMOS technology. An assessment of proposed VCO with previously reported circuits shows improvements in terms of output frequency range and power consumption.

Effect of bias voltage on the tribological and sealing properties of rubber seals modified by DLC films

Diamond-like carbon (DLC) films were deposited on nitrile butadiene rubber (NBR) by the DC magnetron sputtering under different bias voltages. Raman spectra revealed that the variation of bias voltage could tune the carbon bond structure in DLC films. Both the hardness and Young's modulus increased with the increasing bias voltage. Tribological tests revealed that the DLC-coated NBR prepared at the bias voltage of −200 V exhibited low wear rate due to its high hardness. The sealing property was studied by evaluating the leakage rate of volatile liquid in a simple apparatus. All DLC films resulted in less leakage rate as compared to the raw rubber under large stress. The lowest leakage rate occurred in the DLC-coated NBR prepared with a bias voltage of −200 V, which was associated with the theoretical calculations (Persson's theory). It was attributed to the synergetic effects of the variations of the Young's modulus and root-mean-square (Rms) roughness. The low Young's modulus and Rms, controlled by regulating bias voltage, could enhance actual contact area and reduce the leakage rate.

Fabrication of g-C3N4 Nanomesh-Anchored Amorphous NiCoP2O7: Tuned Cycling Life and the Dynamic Behavior of a Hybrid Capacitor

Developing a novel electrode material with better electrochemical behavior and extended cyclability is a major issue in the field of hybrid capacitors. In this work, we propose a novel strategy for the facile synthesis of nickel–cobalt pyrophosphate nanoparticles anchored on graphitic carbon nitride (NiCoP2O7/g-C3N4) via the simple solvothermal method. Field emission scanning electron microscopy and transmission electron microscopy analysis revealed the uniform anchoring of NiCoP2O7 nanocomposite on g-C3N4 nanosheets. Benefitting from the effect of amorphous nature and a conductive matrix of the NiCoP2O7/g-C3N4 (NP3) composite, the material achieves a specific capacitance of 342 F g–1 at a scan rate of 5 mV s–1. Impressively, the electrode shows long-term cycling stability with 100% capacitance retention over 5000 cycles. Employing activated carbon as an anode and as-prepared NP3 as a cathode, the assembled asymmetric hybrid cell exhibits high-energy density and exceptional cyclability (specific capacitance retention over 10 000 cycles). The outstanding electrochemical and cyclic stability is attributed to the shortest electron-ion pathway with effective interfacial interaction. The low electronic resistance of the NiCoP2O7/g-C3N4 nanocomposite is revealed by varying the bias voltage variation in the electrochemical impedance spectroscopy. Our results promise better utilization of the bimetallic pyrophosphate-anchored g-C3N4 matrix as a potential electrode for high-performance energy storage devices.

InGaAs Diodes for Terahertz Sensing-Effect of Molecular Beam Epitaxy Growth Conditions.

InGaAs-based bow-tie diodes for the terahertz (THz) range are found to be well suited for development of compact THz imaging systems. To further optimize design for sensitive and broadband THz detection, one of the major challenges remains: to understand the noise origin, influence of growth conditions and role of defects for device operation. We present a detailed study of photoreflectance, low-frequency noise characteristics and THz sensitivity of InGaAs bow-tie diodes. The diodes are fabricated from InGaAs wafers grown by molecular beam epitaxy (MBE) on semi-insulating InP substrate under different technological conditions. Photoreflectance spectra indicated the presence of strong built-in electric fields reaching up to 49 kV/cm. It was demonstrated that the spectral density of voltage fluctuations at room temperature was found to be proportional to 1/f, while at lower temperatures, 77–200 K, Lorentzian-type spectra dominate due to random telegraph signals caused by individual capture defects. Furthermore, varying bias voltage, we considered optimal conditions for device room temperature operation in the THz range with respect to signal-to-noise ratio. The THz detectors grown with beam equivalent pressure In/Ga ratio equal to 2.04 exhibit the minimal level of the low-frequency noise, while InGaAs layers grown with beam equivalent pressure In/Ga ratio equal to 2.06 are found to be well suited for fabrication of room temperature bow-tie THz detectors enabling sensitivity of 13 V/W and noise equivalent power (NEP) of 200 pW/√Hz at 0.6 THz due to strong built-in electric field effects.

An Analog CMOS Silicon Photomultiplier Using Perimeter-Gated Single-Photon Avalanche Diodes

Perimeter-gated single-photon avalanche diodes (PGSPADs) have been shown to mitigate premature edge breakdown without unduly increasing the area of the device. PGSPADs are three terminal devices. In this paper, we develop a probability-based SPICE model for the PGSPAD and fully characterize an $18 \times 18$ pixel analog PGSPAD-based CMOS silicon photomultiplier (SiPM). The noise model is derived using theories of carrier thermal generation, carrier diffusion, and inter-band tunneling. Parameters are derived using fabricated PGSPAD devices and model validity is verified with experimental measurements. The designed PGSPAD SiPM is implemented in standard $0.5~\mu \text{m}$ 2-poly, 3-metal CMOS process, and is characterized for dark current, sensitivity, and signal-to-noise ratio (SNR) throughout the visible spectral range for varying bias voltages. Models show that the reduction of dark events in the PGPSAD is primarily caused by a reduction in band-to-band tunneling. Thus, as a function of the applied gate voltage the PGPSAD shows an improvement of SNR over a range of 1 to 1150. The sensitivity of the presented SiPM is $1.06 \times 10^{3}$ A/W/cm2. The designed PGSPAD SiPM shows great promise over standard SiPM for applications, such as neutron detection which requires high sensitivities and high SNRs.

Structural alteration induced by substrate bias voltage variation in diamond-like carbon films fabricated by unbalanced magnetron sputtering

Diamond-like carbon films/coatings (DLC) can be employed in a wide range of applications, but the film quality and performance are strongly dependent on the deposition conditions. In this paper, we attempted to clarify the structural and compositional alterations induced by substrate bias voltage (SBV) variation in DLC films by employing different spectroscopic analyses and to correlate them with the variations of two important film properties, hardness and adhesion energy. A series of DLC films fabricated by unbalanced magnetron sputtering with changing substrate bias voltage were investigated by Raman, FTIR and X-ray photoelectron spectroscopies. The results revealed the presence of sp2 and sp3 carbon chains and rings and various types of hydrocarbon in the tetrahedral amorphous carbon films due to incorporation of hydrogen and oxygen. The reduction in hydrogen content together with a generation of sp2 hydrocarbon rings in response to SBV increase were responsible for increases in Young's modulus and hardness, and, concurrently, for a decrease in film adhesion energy.

Electrochemical characteristics of NixN thin films deposited by DC and HiPIMS reactive magnetron sputtering

This study deals with the DC and HiPIMS reactive magnetron deposition process using a pure nickel target (99.995%) in an Ar-N2 gas mixture with varied nitrogen gas flow and bias voltage (floating or -100 V). The characterization of the NiN films has been carried out by X-ray diffraction (XRD), X-ray photoelectrons spectroscopy (XPS) and Energy dispersive X-ray Spectroscopy (EDXS). XRD measurements have highlighted the deformation of the Ni cubic cell as a function of nitrogen content, and a mixture of nitrided phases (Ni4N, Ni3N and Ni2N) appears for 20% N2 in the discharge. XPS and EDX are well correlated and permit us to determine three zones: metallic between 0 and 20% N2, Ni4N between 20% and 42% N2 and finally Ni3N for N2 above 50%. These three zones are in good agreement with deposition rates and optical emission spectroscopy measurements. Cyclic voltammetry has been performed in a conventional three-electrode cell using neutral, alkaline and acidic aqueous electrolytes. The NixN electrochemical behavior shows a pseudocapacitive charge storage mechanism in LiNO3 and KOH electrolytes using an appropriate voltage window, suitable for supercapacitors, whereas NixN exhibits reversible faradaic redox peaks beyond one potential in KOH, depicting NixN film as a battery-type electrode.

Toward hard yet tough VC coating via modulating compressive stress and nanostructure to enhance its protective performance in seawater

VC nanocomposite coatings with high carbon content were deposited by multi-arc ion plating at varied substrate bias voltages ranging from − 50 to − 250 V. There is a comprehensive study as to coating preparation and corresponding microstructure, phase contents and their relationship with mechanical properties. The results show that carbon bonding is significantly affected by bias voltage. For the coatings deposited at high bias voltage, the appropriate combination of inducing compressive stress and manipulating the nanostructure accounts for the effect of hardening and toughening. The tribological and corrosive responses of nanocomposite VC coatings are implemented in the condition of seawater. The hard yet tough nanocomposite structure makes the coatings have favorable wear resistance. Moreover, the smooth surface and dense structure obtained at high bias voltage jointly improve capacity of anti-corrosion resistance. The results are beneficial to the potential application of VC nanocomposite coating in seawater.

Bias effects on wear and corrosion behavior of amorphous hydrogenated carbon films with zirconia interlayer

This paper describes bias voltage effects during the deposition of amorphous hydrogenated carbon (a-C:H) on an interlayer of zirconia doped with silicon. The a-C:H film was synthesized using a microwave chemical vapor deposition (MPCVD) system. The interlayer was deposited via R.F. sputtering. The a-C:H and the interlayer were deposited on Ti6Al4V titanium alloy, AISI 316 L stainless steel, and silicon wafer. A mixture of methane and hydrogen (CH4 + H2) as a feed gas was needed to grow the a-C:H film. The interlayer was grown using a ZrO2 target stabilized with yttrium (8%) and placed silicon cubes in the greatest erosion zone. The chemical compositions of the a-C:H and the interlayer were determined using energy dispersive X-ray spectroscopy, and the chemical structure was analyzed using Raman spectroscopy on the a-C:H and X-ray diffraction on ZrO2 interlayer. The morphology, surface, and cross section were studied with atomic force microscopy and field emission scanning electron microscopy. The effect of bias voltage variation on the microstructure, mechanical properties, wear, corrosion resistance, and coefficient of friction was studied. The behavior under different normal loads and sliding speeds in the wear test was analyzed. Wear mechanism transitions, wear rate variations, and coefficients were recorded for each bias value applied. The best performance against wear and corrosion was achieved for the film deposited with a bias voltage of −300 V, due the wear rate is reduced as well as the current density compared to lower negative bias voltage values.

Estimation and Analysis of Novel Dynamic Body Biased TSPC Design Technique

This paper targets to present energy efficient high speed true single phase clock dynamic circuit design technique, utilizing a novel body biasing tuner. The threshold voltage is controlled dynamically by dint of a novel body bias tuner so that performance of the circuit is enhanced in terms of power, delay, temperature, voltage, noise and corner variations. Power consumption and delay is computed and analysed for wide range of temperature and 40.78–95.5% saving in power delay product is obtained with the same. Quantification of bias voltage variation effect and process corners to find the effectiveness of the proposed design are examined and it is found to be performing consistently as compared with other techniques. Later on bouncing noise analysis is done for the valuation of noise in the circuit. Comparison of power delay product, transistor count and clock phase is done with several previously reported designs. Comprehensive simulation in cadence using 90 nm technology, shows that the proposed design vanquish conventional and other previously reported dynamic circuit design techniques in all aspect of circuit performance. Further, an arithmetic logic unit for measurement using sensors is implemented as a prolongation of the proposed dynamic circuit design technique.

Electrically and Optically Controlled Wideband Matching of Radio-Absorbing Composites to the Ambient Space

Microwave radio-absorbing metastructures are proposed that possess controlled broadband matching to the ambient space by virtue of an array of varactor-loaded chiral and annular elements in which magnetic resonance are excited. Experimentally in a rectangular waveguide and numerically in free space, it is shown that the tuning of the magnetic resonance frequency leads to a shift in the matching frequency region. The electric control of the magnetic resonance and, accordingly, the matching (25% relative tuning) is achieved by the variation in the reverse bias voltage at the varactor, and the optical control is achieved by directing a red laser pointer to a photodiode connected to the varactor in the photodiode mode.

Tribological studies on self-lubricating (Cr,Al)N+Mo:S coatings at elevated temperature

Due to the high material utilization and the associated resource and energy efficiency, production processes from the field of cold forging of steel are of great importance. At present, environmentally harmful lubricants have to be used to ensure process stability as well as low wear and friction. Due to environmental, economic and legislative aspects, there is an increased research potential to reduce or to completely substitute lubricants. To achieve the goal of lubricant free dry cold forging of steel, physical vapor deposition (PVD) coatings with self-lubricating properties are applied on forming tools. Promising for this application are PVD coatings on the basis of a (Cr,Al)N hard phase with embedded molybdenum and sulfur which simultaneously meet the requirements of high wear resistance and friction reduction. In the presented work, three self-lubricating coatings (Cr,Al)N+Mo:S deposited with varying bias voltage were investigated. The hybrid PVD technology, consisting of direct current and high power pulse magnetron sputtering dcMS/HPPMS, was used for the coating deposition in an industrial coating unit. Two different steels AISI D2 (DIN 1.2379) and AISI M2 (DIN 1.3343) were used as substrate materials. The influences of substrate material and heat treatments at T=250°C were investigated. The samples were analyzed with respect to the universal hardness HU and modulus of indentation EIT using nanoindentation. To determine the interfacial adhesion of the compound coating/substrate, Rockwell indentation and scratch tests were carried out. For the analysis of the tribological behavior, unhardened AISI 5115 (DIN 1.7131) was used as counterpart material. The influence of the elevated temperature on the friction and wear behavior was investigated by Pin-on Disk (PoD) at T=250°C and T=23°C. The wear of the basic bodies as well as the counterparts were analyzed by confocal laserscanning microscopy. The investigations have shown that the high temperature has a significant influence on the friction and wear behavior. The wear rate of the counterparts decreases by up to a factor greater than x=100 compared to the test at T=23°C. Furthermore, the wear rates of the basic body of the uncoated reference specimen increase rapidly at tribological stress at high temperatures. The examined coatings exhibit high wear resistance at elevated temperatures. The contact surface was studied by Raman spectroscopy after the tribological tests. PoD tests have shown, that the applied coatings led to a significantly reduction in friction most likely due to the tribo-chemically induced formation of self-lubricating MoS2 reaction layers.

The correlation between optical and mechanical properties of amorphous diamond-like carbon films prepared by pulsed filtered cathodic vacuum arc deposition

Diamond-like carbon (DLC) films were deposited by pulsed filtered cathodic vacuum arc (FCVA) deposition. The microstructure, mechanical and optical properties of DLC films have been investigated as functions of the variation in the substrate negative direct current bias voltage (Vbias) from 0.0 to 1.5 kV. Raman and X-ray photoelectron spectroscopy results show a correlation between the ID/IG ratio and the microstructure in terms of the sp3/sp2 ratio to Vbias. This fact shows that a significant change in the sp3 content, which is attributed to the transformation from graphite-like to diamond-like, is accompanied by a decreasing ID/IG ratio. The relatively high mass density of the films in the range of 2.51 to 2.79 g/cm3 can be obtained with biasing. The mechanical properties, i.e., the hardness and elastic modulus, were 13–25 and 114–145 GPa, respectively. The improvement of the mechanical properties is due to the formation of the compressive residual stress and the local density depending on Vbias. The relationship between the refractive index and the ID/IG ratio agree well with the microstructure and mechanical properties of DLC films. All of these results indicate a vital role of Vbias in determining the DLC properties.

Electrically tunable robust edge states in graphene-based topological photonic crystal slabs

Topological photonic crystals are optical structures supporting topologically protected unidirectional edge states that exhibit robustness against defects. Here, we propose a graphene-based all-dielectric photonic crystal slab structure that supports two-dimensionally confined topological edge states. These topological edge states can be confined in the out-of-plane direction by two parallel graphene sheets. In the structure, the excitation frequency range of topological edge states can be dynamically and continuously tuned by varying bias voltage across the two parallel graphene sheets. Utilizing this kind of architecture, we construct Z-shaped channels to realize topological edge transmission with diffrerent frequencies. The proposal provides a new degree of freedom to dynamically control topological edge states and potential applications for robust integrated photonic devices and optical communication systems.

Epitaxial growth of GaN nanostructure by PA-MBE for UV detection application

We report the growth of lower aspect ratio, nano-island shaped, lower stress and strain facilitated gallium nitride nanostructures (GaN-NS) on Si (111) substrate via plasma assisted molecular beam epitaxy (PA-MBE) and fabrication of GaN-NS based UV photo-detection device even with NS’s tiny dimensionality. GaN-NS were grown on Si (111) substrate with an inhomogeneous layer of Si3N4 which act as anti-surfactant to Ga atoms and also offer localized compressive strain. The developed strain can be relaxed by the growth of inhomogeneously oriented GaN-NS. The three dimension (3D) growth of GaN-NS in real time was observed by in-situ RHEED technique which displays transformation from streaky to spotty pattern. A micro-Raman technique has been employed to elaborate NS’s crystallinity and lower stress value which is found be in good agreement with related lower strain as evaluated by HR-XRD spectra. A sharp near band edge emission at 363.2 nm is observed by room temperature photoluminescence measurement which signifies the presence of GaN. Metal semiconductor metal Au-GaN-NS/Si(111) device was fabricated to specifically analysed its ability to detect harmful ultraviolet radiations (325 nm) with GaN islands of just 26 nm height and 50 nm width. The performance of the fabricated device was analysed at fixed optical power of 13 mW with varying bias voltages (0.4–3 V).