AC Characteristics Research Articles

DC and RF Performance Optimization of Source Pocket Designed Hybrid-Dielectric Vertical Nanowire Tunnel-FET: Low Power Perspective

This article addresses a new source pocket designed hybrid-dielectric vertical nanowire tunnel-FET (SP-HD-VNW-TFET). The existence of a source pocket at the source and channel boundary is shown such that the potential barrier at the tunnel-junction is minimized which causes ON current to rise. This article studied a comparison between a SP-HD-VNW-TFET device and source pocket vertical nanowire tunnel field effect transistor (SP-VNW_TFET). Using a hetero/hybrid-dielectric material boosts the electric field, resulting in higher tunneling current (1.72 × 10−6 A μm−1). The device has undergone detailed investigation of both DC and AC characteristics like On-current, Off-current, ION/IOFF, Subthreshold-swing, VT, gm, fT, GWB, and TFP. Source Pocket engineering and Hybrid dielectric inclusion increase device properties, including on-current and subthreshold swing (SS). The device’s electrical properties have been evaluated and compared using the Sentaurus TCAD Tool.

Hall effect thruster impedance characterization in ground-based vacuum test facilities

Hall effect thrusters (HETs) are typically regarded as DC electric propulsion devices as they are operated with isolated DC power supplies. However, it is well known that the HET’s discharge current possesses oscillations of varying magnitudes and frequencies and is thus a function of time with AC characteristics. The observed oscillations are caused by plasma processes associated with ion, electron, and neutral particle dynamics that occur inside the HET’s discharge channel and in the plume as the HET electrically interacts with its local operating environment. The extent to which plasma oscillations impact HET discharge dynamics is difficult to quantify due to the complexity of analyzing AC signals, given that the HET is a nonlinear, time-variant electrical load. In this work, we overcome the challenge of nonlinearity and time-variance of HETs by conducting a small-signal impedance analysis to characterize the effective resistance and reactance of the HET discharge with a novel and versatile impedance measurement diagnostic. The impedance magnitude and phase of a 7-kW class HET were measured from 100 Hz to 300 kHz with an excitation signal of ± 2 Vpk for two discharge operating conditions on krypton: 4.5 kW, 15 A and 6 kW, 20 A. The results were used to quantify resistive, capacitive, and inducive characteristics present within the HET discharge signature. For the 4.5 kW, 15 A thruster operating condition, the breathing mode capacitance was estimated to be 12.6 µF with an inductance of 15.3 µH. Furthermore, the impedance characteristics of the breathing mode are within ± 2.4 kHz of the power spectral density plots independently generated by time-resolved oscilloscope traces indicating good agreement in the frequency domain. Thus, the impedance measurement tool is a new diagnostic for characterizing the impedance and associated AC characteristics of HETs.

Modulation Strategy with Minimum Switching Losses for Three-Phase Non-Isolated AC–DC Matrix Converters

This paper presents an analysis of the operational characteristics of three-phase AC–DC matrix converters, which operate as rectifiers but possess a range of additional capabilities. These include the ability to reverse the power flow, control the input power factor, and generate a multilevel output voltage. The analysis yields a modulation strategy that minimizes switching losses. The proposed modulation strategy is compared with seven well-known space vector modulation strategies in terms of efficiency and distortion of input and output current. The performance is experimentally validated.

Investigation of the Electrical Characteristics of AlGaN/AlN/GaN Heterostructure MOS-HEMTs with TiO2 High-k Gate Insulator

This paper investigates the impact of TiO2 high-k gate insulator on the electrical characteristics of AlGaN/AlN/GaN MOS-HEMT transistors using MATLAB and Atlas-TCAD simulation software. The physical analytical model of the MOS-HEMTs is used for simulation from Al2O3, HfO2, and TiO2 as the gate dielectric materials, which provide higher performance and reliability of the MOS-HEMT devices. The device shows a good improvement in its result of the DC and AC characteristics with different permittivity of insulator materials. Thus, the DC and AC performance of GaN MOS-HEMTs is higher than with other insulators, such as Al2O3 and HfO2 by using TiO2 as the gate dielectric. Moreover, the simulation results proved that TiO2 is the better gate dielectric material to enhance the electrical reliability of the power switching devices for high-temperature applications such as electric automobiles.

Simulation study on temperature characteristics of AlN/ β-Ga2O3 HEMT

This paper reports a comprehensive analysis of temperature on DC and AC characteristics of AlN/β-Ga2O3 HEMT. As the temperature increases from 300 °C to 500 °C, the drain current (IDS) decreases by 50 %, leading to a 50 % decrease in transconductance (gm) without self heating effect. This decrease in maximum gm further resulted in a significant reduction of 49 % in the cut-off frequency (fT). Incorporating the self-heating effect, while the threshold voltage (Vth) remains unaffected, the maximum gm experiences a marked decrease. At 300 °C, the decrease reaches 58 %, while at 500 °C, the decrease is 36 %. Additionally, the saturation IDS shows a negative differential resistance phenomenon. Furthermore, the decrease at 300°Cin fT reaches 45 %, while at 500 °C, the decrease is 30 %. The main reason for the performance degradation caused by self heating effect at low temperatures is that the peak temperature at the channel of the device increases more significantly at low temperatures, resulting in a more significant decrease in mobility.

Design Analysis of 4H-SiC MOSFET for High Power Application

Abstract Silicon Carbide has emerged as a promising candidate due to its superior material properties such as high breakdown voltage, wide bandgap, and high thermal conductivity. A new vertical trench-based high power MOSFET (VTMOS) on 4H-SiC is presented. The VTMOS device features two trenches, each containing a poly-Si gate positioned on opposite sides of the P-base region. This configuration results in two parallel channels within the device. The unique design of the VTMOS leverages the RESURF effect and parallel conduction of the drive current, leading to notable performance improvements. The AC and DC characteristics of the VTMOS are analyzed and compared with PRMOS using 2-D simulations. The results demonstrate the superior performance of the VTMOS compared to the PRMOS. Specifically, the VTMOS exhibits 2.35 times higher drive current, an 88% enhancement in gain, 52% higher breakdown voltage, an 11% reduction in threshold potential, a 43% decrease in on-resistance, and 5.55 times higher FOM compared to the PRMOS.

Conversion of municipal garden waste to activated carbon: Laboratory production and characterization comparing production parameters

This research aims to investigate the potential of the municipal garden waste as a new precursor to generate activated carbon by CO2 activation. TGA analysis shows the distinctive thermal degradation nature of garden waste. The activation of the garden waste enhanced its surface area where well-developed internal micro-mesoporous structure is also noticed. The results suggest that most of the volatiles decomposed at temperatures beyond 450 °C. A decrease in char yield, increase in surface area and pore volume and weakening of oxygen and hydrogen-containing groups were observed at higher pyrolysis temperatures. Raman and XRD support the amorphous and porous graphitic structure of carbon. Carbonization temperature of 500 °C and activation temperature of 800 °C were shown to produce the better-quality AC where highest surface area of 363.32 m2/g and highest pore volume of 0.095 cm3/g was achieved. Compared to the pyrolysis temperature, pyrolysis steps did not have notable contribution to the AC characteristics.

Research on improving the efficiency of electricity transmission

A study of ways to modernize the current-carrying part of overhead lines to improve the efficiency of electricity transmission through the use of innovative types of wires was conducted. The technical and economic characteristics of AC, ACCR, and AERO-Z wires were analyzed. The results of the analysis revealed that further improvement of the design of AC wires should be based on new progressive developments that would meet such technical requirements as reliability, survivability and durability; corrosion resistance; high adhesion ability; resistance to vibration during operation under the influence of adverse climatic factors; resistance to environmental temperature effects. As an innovative solution to this issue, high-temperature (ACCR) and specially designed (AERO-Z) wires have been developed in foreign countries. A comparative analysis of the types of wires used in Ukrainian power grids with innovative types of wires used in power grids of foreign countries was performed. The results of the comparison of AC, ACCR, and AERO-Z wires show that the factor that limits the scope of application of ACCR wire, even for spans with extremely high requirements for power transmission characteristics, is its extremely high cost. This is because the technical characteristics of this wire are better than those of AC wire and it has a relatively low cost compared to ACCR wire, and its special design is adapted to adverse climatic conditions that affect the characteristics of electricity transmission.

Noise behavior in GaAs0.2Sb0.8/GaSb heterojunction Source-All-Around vertical Tunnel FET: A comprehensive study

This article offers a comprehensive noise analysis of a GaAs0.2Sb0.8/GaSb heterojunction Source-All-Around Vertical Tunnel FET (SAA-VTFET), examining generation-recombination (GRN), flicker (FN), and diffusion (DN) noise. It pioneers an investigation into noise behavior under the influence of interface traps, temperature variations, and frequencies. Analysis includes both output current noise power spectral density (Sid) and input voltage noise power spectral density (Svg). Furthermore, the sensitivity of noise PSD is noted to be maximum at lower Vgs (gate bias voltage), suggesting that trap-assisted tunneling (TAT) and Shockley-Read-Hall (SRH) recombination dominate over band-to-band tunneling in this region. For enhanced clarity, this study also includes an analysis of the impact of traps and temperature on both AC and DC characteristics.

Investigating the Impact of Hardness on Dielectric Breakdown Characteristics of Polyurethane.

Polymeric materials play a vital role in high-voltage insulation, but their insulating properties can deteriorate over time, leading to insulation failures. The presence of voids resulting from manufacturing defects or external stresses can create a highly divergent field, further contributing to this issue. However, certain polymers, such as polyurethane (PU), possess self-healing properties that enable them to repair these voids and restore a uniform electric field distribution, thereby ensuring the reliability of the insulation. Surprisingly, the potential of PU as an insulating material in high-voltage applications remains unexplored. However, the self-healing capability of PU decreases with an increase in the hardness of the material. Therefore, in this study, the dielectric breakdown properties of PU with different levels of hardness, rated on the Shore scale as 40° (soft), 70° (medium), and 90° (hard), were investigated. The AC and DC dielectric breakdown characteristics of these PU variants and dielectric spectra were examined. Additionally, the study explores the relationship between the dielectric properties and the hardness of the material. Our findings revealed that the dielectric breakdown strength of PU increases as the material's hardness is increased under both AC and DC electric stress. However, this may come at the cost of reduced self-healing capabilities of PU. Therefore, there is a need to balance the hardness of the material with its ability to recover from breakdown events. The findings from this study can be useful for researchers and engineers, as they offer valuable insights into the dielectric properties of PU at various hardness levels.

A novel double-gate trench SOI LDMOS with double-dielectric material by TCAD simulation study

In this paper, a novel double-gate trench silicon-on-insulator lateral double-diffused metal oxide semiconductor field-effect transistor (LDMOS) with double-dielectric material (DGDK-LDMOS) is proposed. DGDK-LDMOS has two dielectric materials: a reverse-L-shaped high-k (HK) thin film and an low-k (LK) buried oxide layer. The HK thin film optimizes the electric field distribution on the drift region surface, attracting electric flux, and the excellent withstand voltage of the LK buried oxide layer can significantly improve the breakdown voltage (BV) and reduce specific on-resistance (R on,sp) of the device. The modulation mechanism of LDMOS by HK thin film and LK buried oxide layer is analyzed. The results show that compared with conventional LDMOS, when the permittivity of HK thin film is 25 and the permittivity of LK buried oxide is 3, the BV of DGDK-LDMOS is increased by 89.6%, the R on,sp is decreased by 26.4%, and the figure of merit (FOM, FOM = BV2/R on,sp) is increased by 397.2% from 3.6 MW cm−2 to 17.9 MW cm−2. Meanwhile, the output characteristics, transfer characteristics, lattice temperature, AC characteristics and switching characteristics of DGDK-LDMOS are also discussed and compared.

AC Characteristics of van der Waals Bipolar Junction Transistors Using an MoS2/WSe2/MoS2 Heterostructure.

Two-dimensional layered materials, characterized by their atomically thin thicknesses and surfaces that are free of dangling bonds, hold great promise for fabricating ultrathin, lightweight, and flexible bipolar junction transistors (BJTs). In this paper, a van der Waals (vdW) BJT was fabricated by vertically stacking MoS2, WSe2, and MoS2 flakes in sequence. The AC characteristics of the vdW BJT were studied for the first time, in which a maximum common emitter voltage gain of around 3.5 was observed. By investigating the time domain characteristics of the device under various operating frequencies, the frequency response of the device was summarized, which experimentally proved that the MoS2/WSe2/MoS2 BJT has voltage amplification capability in the 0-200 Hz region. In addition, the phase response of the device was also investigated. A phase inversion was observed in the low-frequency range. As the operating frequency increases, the relative phase between the input and output signals gradually shifts until it is in phase at frequencies exceeding 2.3 kHz. This work demonstrates the signal amplification applications of the vdW BJTs for neuromorphic computing and wearable healthcare devices.

A robust unified data-driven protection scheme for hybrid AC/DC transmission lines

To meet rising energy demands, reduce carbon emissions, and address climate change, the importance of hybrid AC/DC transmission has increased. The effective utilization of high-voltage DC in existing AC transmission lines will reduce costs and losses and increase the existing transmission capacity. Therefore, the protection schemes of fault detection, location, and classification are complicated because of the different characteristics of AC and DC in the same transmission network. The existing protection schemes mostly utilize threshold-based criteria and cannot ensure hybrid network protection. To overcome these challenges, a unified data-driven protection scheme (UDDPS) using distinctive features is proposed to detect and identify (either AC or DC) and classify both AC/DC faults of hybrid transmission lines (HTLs). The UDDPS has ensured the protection of AC/DC lines by timely intervening faults and effectively isolating the respective relays of the faulty lines. The fault current data are retrieved during a fault abnormality using distinctive retrieved features from the single end of the HTL. The proposed scheme applies to multi-transmission networks and is independent of the communication channels. Extensive simulation scenarios, such as fault/no-fault, varying fault locations, and near and far locations with low/high impedances, were examined in MATLAB/Simulink to train the UDDPS. The UDDPS successfully detected and identified hybrid AC/DC line faults with 100% accuracy and further classified the AC and DC faults with 97.61 % and 99.20 % accuracy. The efficacy and robustness of the proposed technique were confirmed by comparison with the existing schemes of support vector machine, decision tree, and LSTM. The UDDPS surpassed in terms of the overall model under a normal and noisy environment.

Analysis and optimization of lead-free perovskite solar cells: investigating performance and electrical characteristics

Several studies on solar cells using SCAPS-1D were conducted to investigate their performance, which are typically limited to I–V analysis for DC characterization. Therefore, in the present study, a very wide frequency range from 10–2 Hz to 1012 Hz was employed to explore diffusion processes and investigate the performance of lead-free Perovskite Solar Cells (PSCs) featuring as a novel heterostructure. These investigations concern the optimization of MASnI3 thickness as an absorber. Additionally, the impact of series (Rs) and shunt (Rsh) resistances is also examined. From the I–V analysis, it was determined that the power efficiency (PCE) could be achieved at a thickness of 0.6 µm. Increasing the series resistance (Rs) led to a significant decrease in the fill factor (FF) and (PCE), whereas the shunt resistance (Rsh) demonstrated a notable improvement in both (FF) and (PCE). Analysis of AC characteristics revealed complex impedance (Z*) and modulus (M*) indicative of main ionic transport, recombination, and diffusion processes crucial for optimization. An appropriate equivalent circuit model was developed and validated through deconvolution and theoretical considerations, yielding parameters such as the time constant for each process. It was observed that ionic conductivity and electronic diffusion play key roles in balancing charge collection and recombination losses. The critical influence of series and shunt resistance on low and high-frequency processes was emphasized, underscoring their significance in solar cell efficiency. A strong correlation was established between the evolution of time constants for each process and power conversion efficiency (PCE).

Dynamic stabilisation of magnetic fields measured inside a magnetically shielded room using an external coil system *

Magnetoencephalography (MEG) system based on optically pumped magnetometers (OPMs) requires a magnetically shielded room (MSR) to establish a stable near-zero field environment. Affected by external environmental electromagnetic interference, the magnetic noise in the MSR will become very severe. In order to overcome this problem, this paper proposes a method for dynamic stabilisation of magnetic fields measured inside a MSR using an external coil system. Firstly, the field form of the external compensation coil was analysed by taking the AC characteristics of the material into consideration. Then, the linear characteristic of the control system is studied and a high performance magnetic noise suppression controller is designed based on the environment noise characteristics. Finally, simulation and experimental are carried out through a self-developed 1250 mm × 1250 mm × 2100 mm MSR, which indicates that the proposed method can effectively suppress dynamic magnetic fluctuation and noise.

Design and characterization of cell topology effect on SiC VDMOSFETs for high power and frequency applications

In this paper, we present a comprehensive investigation of the impact of cell topology and pitch reduction on the DC and AC characteristics of 1200V-rated 4H-SiC planar VDMOSFETs. We have designed and fabricated four different cell topologies, namely linear, square, hexagonal, and staggered cell, in order to characterize their performance. Among the various cell types, the hexagonal cell exhibits the most favorable specific on-state resistance (Ron,sp) value. However, it is worth noting that the breakdown values of both the hexagonal and staggered square cells fall significantly below the simulated values. This is attributed to the interaction between the irregular cell boundaries and the edge cell termination region. Furthermore, we observed that the linear cell has the highest gate resistance compared to the other cell types. Additionally, the linear cell also demonstrates a lower input capacitance than the other cells. This can be attributed to its longer gate trasmission line and smaller area. Lastly, we performed dynamic double pulse tests on the fabricated VDMOSFETs to compare their switching characteristics. It was concluded that linear cell VDMOS is suitable for high switching applications, while square, hexagonal and S.S cell VDMOS are better suited for lower switching applications that require a high output current.

High‐Frequency fT and fmax in Organic Transistors: Performance and Perspective

AbstractIn state‐of‐the‐art organic transistors, the transit frequency fT is reported to be fT = 40 MHz for vertical organic transistors, where a voltage‐normalized fT corresponds to 0.36 MHz V−2. The reported highest fT for conventional organic transistors is fT = 160 MHz, where the voltage‐normalized fT is 0.1 MHz V−2. While the reported transit frequency fT of n‐MOSFETs for silicon technology when normalized by the applied biases exceeds 300 GHz V−2. The reported carrier mobility of organic semiconductors is over 100 cm2 V−1 s−1, which is almost an order of magnitude lower than that of silicon. However, the transit frequency fT of organic transistors lags far behind silicon technology by about six orders of magnitude at a comparable device length below 300 nm. In this work, a technology computer‐aided design (TCAD) simulator is adjusted to the experimental DC and AC characteristics of the 200 nm device length vertical organic permeable‐base transistors (OPBTs) based on C60 as semiconductor. The AC performance of the devices is investigated and quantitatively analyzed the influence and contribution of key design, structure and material parameters that determine fT and fmax. The feasible ways to enhance and optimize the highest achievable fT and fmax are identified to reach the and overcome the limitations to high‐frequency operation in organic transistors.

Compact Modeling of Advanced Gate-All-Around Nanosheet FETs Using Artificial Neural Network.

As the architecture of logic devices is evolving towards gate-all-around (GAA) structure, research efforts on advanced transistors are increasingly desired. In order to rapidly perform accurate compact modeling for these ultra-scaled transistors with the capability to cover dimensional variations, neural networks are considered. In this paper, a compact model generation methodology based on artificial neural network (ANN) is developed for GAA nanosheet FETs (NSFETs) at advanced technology nodes. The DC and AC characteristics of GAA NSFETs with various physical gate lengths (Lg), nanosheet widths (Wsh) and thicknesses (Tsh), as well as different gate voltages (Vgs) and drain voltages (Vds) are obtained through TCAD simulations. Subsequently, a high-precision ANN model architecture is evaluated. A systematical study on the impacts of ANN size, activation function, learning rate, and epoch (the times of complete pass through the entire training dataset) on the accuracy of ANN models is conducted, and a shallow neural network configuration for generating optimal ANN models is proposed. The results clearly show that the optimized ANN model can reproduce the DC and AC characteristics of NSFETs very accurately with a fitting error (MSE) of 0.01.

Analysis of harmonic characteristics of UHV AC / DC power network considering the influence of geomagnetic storm

The resultant harmonic effect of geomagnetically induced current (GIC) caused by geomagnetic storm has an impact on the safe and reliable operation of ultra-high voltage (UHV) AC / DC power grid in China, which in severe cases may lead to power grid breakdown or even large-scale blackout. Firstly, the harmonic effect model of converter transformer under the action of GIC is established based on the GIC calculation results of China's UHV power grid during the super-geomagnetic storm in November 2004. The harmonic voltage of transformer equivalent model port is described in phasor form. Secondly, the characteristic harmonic model of the converter is established based on the switching function modulation theory. By analyzing the working principle of the equivalent circuit of 12-pulse rectifier, the harmonic coupling model between DC magnetic bias harmonic voltage of transformer and converter is established, and the harmonic coupling characteristics of AC / DC power network under the action of GIC are analyzed. Lastly, the simulation model of ±800 kV UHV AC / DC transmission system in China is built by using PSCAD/EMTDC software as the simulation platform. The non-characteristic harmonic current and voltage on the AC side and DC side of the AC / DC power grid are calculated. The results show that the harm caused by GIC invading converter transformer is more serious than that caused by GIC invading UHV transformer. When both of them are invaded by GIC, the non-characteristic harmonics generated by mutual superposition and coupling have a greater impact on the power grid. The research results of this paper can provide a theoretical basis for space disaster prevention of UHV AC / DC power grid in China.

Production and evaluation of activated carbon from Saudi Arabian Acacia Tortilis tree bark by microwave and low temperature activation process

In the present work, activated carbon was prepared from Acacia Tortilis tree bark, utilizing phosphoric acid chemical activation, and microwave irradiation (AC-MWI). Activated carbon was also prepared by conventional phosphoric acid chemical activation and low temperature carbonization (AC-CA). Characterization of the activated carbons were performed by proximate analysis adopting ASTM standard procedures. BET-specific surface area, total ash content, bulk density, moisture content, pH, pore volume and iodine number were determined. Comparison of characteristics for both carbons, with the characteristics of AC available in the literature and commercially available in the market was performed. Comparison showed that activated carbon produced from Acacia Tortilis tree bark is well comparable with the reported characteristics of AC in literature and commercially available in market. It was found that AC-MWI has higher BET-specific surface area than AC-CA (836 m2/g and 687 m2/g respectively). Results depict that there is an increase of 22.3% in microspores component and 21.7% BET- specific surface area obtained in AC-MWI as compared to AC-CA. Similarly, the corresponding pore volume obtained (4.97 cm3/g and 4.07 cm3/g respectively) demonstrating better values as compared to the commercial ACs (<1 cm3/g). Additionally, it was found that AC can be produced by microwave irradiation in about 48.5% less time when compared to conventional low temperature heating. The adsorption study of produced ACs was performed using methylene blue as a contaminant. Study showed that MB removal rate initially increased with increase in contact time, which decreased with time until steady state was reached. Adsorption data of MB was fitted to Freundlich, Langmuir and Temkin adsorption isotherm models. All models show reasonable correlation, however, Freundlich isotherm is best to describe the MB adsorption on AC-MWI based on correlation coefficient R2 value (0.9985). The results revealed the feasibility of microwave heating for preparation of high surface area activated carbons from Acacia Tortilis tree bark.