DC Conditions Research Articles

Novel Trench Inner-Spacer Scheme to Eliminate Parasitic Bottom Transistors in Silicon Nanosheet FETs

A novel and feasible trench inner-spacer (TIS) scheme to eliminate undesired parasitic bottom transistors (trpbt) in gate-all-around (GAA) nanosheet (NS) field-effect transistors (FETs) is proposed based on fully calibrated Technology Computer-Aided Design (TCAD) simulation. Highly doped punch-through stopper (PTS) layers are generally used to suppress trpbt. Unfortunately, trpbt is still a fatal failure factor in electrical performance degradation when the source/drain (S/D) recess is overetched. Moreover, the proposed TIS scheme prevents the diffusion of S/D dopants toward the PTS region beneath the bottom gate, thereby inhibiting the formation of trpbt. Furthermore, the TIS-NSFETs exhibit excellent immunity to overetched S/D recess depth variations. Additionally, the thermal characteristics of the TIS scheme are compared to that of the bottom oxide (BOX) scheme forming dielectrics beneath the S/D epitaxies, one of the methods used to suppress trpbt. Lattice temperature caused by self-heating and thermal resistance in the TIS-NSFETs are much lower than that in the BOX-NSFETs for both n/p-type devices. The thermal advantage of TIS-NSFETs compared to BOX-NSFETs is confirmed in both DC and AC conditions, similar to an actual operating environment. Therefore, the proposed TIS scheme is highly recommended to eliminate the undesired trpbt without critical DC/AC degradation and to resolve poor heat dissipation problems in the BOX scheme simultaneously.

Effect of Y2O3 on the Electrical Contact Behavior of Al2O3-Cu/MoTa Composites

With the massive penetration of electronics into human life, higher demands are placed on electrical contacts. Among them, the lifetime of electrical contacts and safety are the most concerning. In this research, Al2O3-Cu/25Mo5Ta and 0.5Y2O3/Al2O3-Cu/25Mo5Ta composites were prepared by using ball milling and powder metallurgy methods. The two composites were subjected to 10,000 contact opening and closing electrical contact experiments and the arc duration and arc energy were analyzed. The results show that the addition of Y2O3 has a slight effect on the mechanical properties of the Al2O3-Cu/25Mo5Ta composites but has a significant effect on the electrical contact performance. Y2O3 can reduce the mass loss of the electrical contacts during the electrical contact process, which prolongs their service life. The addition of Y2O3 decreased the average arc duration and arc energy of the electrical contact material by 21.53% and 18.02%, respectively, under the experimental conditions of DC 30 V, 10 A. TEM results showed that nanoscale YTaO4 with excellent thermal stability was generated during the sintering process, which has a positive effect on the electrical contact performance of the composites.

Response of one-dimensional ionised layer to oscillatory electric fields

To provide fundamental insights into the response of laminar flames to alternating current (AC) electric fields, a simplified one-dimensional model using an ionised layer model is formulated with the conservation equations for the ion species with ionisation, recombination, and transport due to molecular diffusion and electric mobility. A parametric study is conducted to investigate the response of the ion layer at different voltages and oscillation frequencies, and the results are examined mainly in terms of the net current–voltage (I–V) characteristics. As the oscillation frequency is increased, a nonmonotonic response in the I–V curve is seen such that the current may exceed the saturation condition corresponding to the steady DC condition. In general the current reaches a peak as the unsteady time scale becomes comparable to the ion transport time scale, which is dictated by the mobility, and eventually becomes attenuated at higher frequencies to behave like a low-pass filter. The extent of the peak current rise and the cut-off frequency are found to depend on the characteristic time scales of the ion chemistry and mobility-induced transport. The simplified model serves as a framework to characterise the behaviour of complex flames in terms of the dominant ionisation and transport processes. The current overshoot behaviour may also imply that the overall effect of the electric field may be further magnified under the AC conditions, motivating further studies of multi-dimensional flames for the ionic wind effects.

The use of AE technique for identifying ductility degradation against cryogenic on flexural performance of UHPC at various temperature conditions

This paper reports the flexural performance of ultra-high performance concrete (UHPC) exposure to six temperature conditions, including ambient temperature (A), after exposure to 200 °C (EA), in-situ −170 °C (DC), in-situ −170 °C after exposure to 200 °C (IDC), after exposure to −170 °C (AC), after exposure to 200 °C and −170 °C (AEC). The cracking characteristics of UHPC under the coupling effect of cryogenic and external load is identified with acoustic emission (AE) technology. The results show that DC condition is the most efficient in enhancing flexural strength and toughness due to frozen water and improved bond strength. A nonlinear relationship between first-peak deflection and first-peak flexural strength is observed because of the changed flexural modulus at different temperature conditions. The increasing shear cracks in linear-elastic stage is attributed to the fracture process of frozen water, which can account for the significant increase of first-peak strength at DC and IDC conditions. Cryogenic-induced ductility degradation is observed in the flexural behaviour of UHPCs at DC and IDC conditions, which is attributed to higher energy release rate. Furthermore, pre-exposure to 200 °C reduced the positive influence of cryogenic temperature on flexural performance and the negative effect of cryogenic temperature on ductility because of the initiated cracks around steel fibers.

Deep UV AlGaN LED reliability for long duration space missions

Space-based gravitational wave detection will be carried out by the laser interferometer space antenna (LISA), a joint European Space Agency and NASA collaboration. The configuration of this antenna will include three identical spacecraft in a triangular formation separated by 2.5×106km, flying in a drag-free formation around free-falling test masses. Charging of the test masses by cosmic ray fluxes and solar energetic particles must be compensated by photons that contain more energy than the effective work function of gold (4.3±0.4eV). The UV photons will be provided by AlGaN light emitting diodes, which must operate reliably for the duration of the mission. We have tested a large number (96 for dc and pulsed testing, more than 200 for all tests) of UV LEDs over a period of up to 600 days to characterize their performance over a wide range of operating conditions, assessing the lifetime performance under dc (1–80mA drive current) and pulsed conditions (500–100 000 pulses per second) and temperatures ranging from 20 to 80°C. Degradation of UV light output is faster at elevated temperatures and dc conditions. Preselection of LEDs based on initial spectral ratio of peak-to-midgap emission and ideality factor provides a positive correlation with subsequent reliability. The UV LEDs used for LISA will need to support 2 years of cruise and commissioning plus a 4-year baseline science mission.

Space Charge Characteristics of Natural Ester Oil-Impregnated Paper With Different Moisture Contents

Mineral oil is the most common dielectric liquid for high-voltage direct current (HVDC) converter transformers. However, natural ester oil receives much attention as an alternative dielectric liquid due to its environmental friendliness and low fire risk. Moisture is one of the most dangerous substances, which accelerates the degradation of oil-paper insulation systems. Thus, this article investigates the impact of moisture on space charge characteristics of the natural ester oil-impregnated paper by comparing it with the mineral oil-impregnated paper. Space charge accumulation is a typical phenomenon under dc conditions, and its presence can lead to electric field distortion and accelerate insulation aging. The space charge profiles in oil-impregnated papers with different moisture contents are obtained by the pulsed electroacoustic (PEA) method. It has been found that the hydrophilic characteristic of natural ester oil leads to a slow process of forming heterocharges in the natural ester oil-impregnated paper. On the other hand, the hydrophobic characteristic of mineral oil results in faster heterocharge formation in the mineral oil-impregnated paper.

Effects of duty cycle on properties of Ni–P–Al2O3 nanocomposite deposited layer prepared by pulse-assisted jet electrochemical deposition

In order to improve the surface quality of the nanocomposite deposited layer, the pulse technology was introduced to the jet electrochemical deposition process, and the Ni–P–Al2O3 nanocomposite deposited layer was successfully prepared. By changing the pulse duty cycle to prepare the composite deposited layer and comparing it with the Ni–P–Al2O3 composite deposited layer prepared under the DC condition and the Ni–P deposition layer prepared under the condition of better pulse duty cycle, the influence of pulse duty cycle on its related performance is explored. In this study, SEM, metallurgical microscope, XRD and EDS were used to analyze the surface morphology, section morphology, phase and composition of Ni–P–Al2O3 deposited layers under different experimental conditions. The hardness and elastic-plastic mechanical properties of the nanocomposite deposited layer were evaluated by hardness tester and nanoindentation tester, and the corrosion resistance of the deposited layer was evaluated by electrochemical workstation. The results showed that the Al content in the deposition layer first increases and then decreases with the increase of the pulse duty cycle, and reaches the highest level of 1.77 wt% when the pulse duty cycle is 60%. The surfaces of the deposited layers prepared under this condition were uniformly dense with better corrosion resistance and the highest hardness value reached was 817.4 HV. At the same time, the elastic recovery ratio he/hmax reached the maximum with a value of 0.36, and the resistance to deformation reached the best.

Prevalence of dental caries in the permanent dentition amongst 12-year-olds in Africa: a systematic review and meta-analysis

BackgroundDental caries (DC) is highly prevalent condition affecting mostly young children. There has been no systematic review done on the prevalence of DC amongst 12-year -olds in Africa. Although some African countries have reported a decrease in DC prevalence, others have shown an increase and it is essential to measure current trends in order to identify strategies and programmes that could assist in reducing DC in Africa. The aim of this systematic review was to determine the prevalence of DC (condition) amongst the permanent dentition of 12-year-old children (population) in Africa (context).MethodsA systematic review and meta-analysis was performed. Peer reviewed cross-sectional articles from January 2000 until December 2021 was searched and this included the following databases: Pubmed (Medline); SCOPUS; CINAHL (via EBSCOhost); Academic Search Complete (via EBSCOhost); Dentistry and Oral Sciences Sources (via EBSCOhost); and Science Direct. The search was last updated on the 10th January 2022. Joanna Briggs Institute critical appraisal tools were used to assess risk of bias. Prevalence figures were stratified by Urban/Rural status, country and time using a random-effects model. All studies performed on children 12-year-olds on the African continent were included. The prevalence of DC and the DMFT scores were the primary and secondary outcome measures, respectively. Only articles consisting of 12-year-old children who reside in Africa were included in this study. The systematic review was registered with Prospero CRD42021293666.Results18,080 participants were included in this review. A total of thirty studies were included in the review. The pooled effect size of dental caries severity was 1.09 (CI 0.91–1.27) and the overall prevalence was 36% (CI 29.4–41.7%). Eritrea (78%) had the highest prevalence of DC while Zambia had the lowest (11%); Eritrea also had the highest DMFT score (2.5) with Sudan having the lowest score (0.49). Urban cities had the highest DMFT score (1.32, CI 0.97–1.68), compared to rural cities (1.13, CI 0.86–1.4) and there was an increasing trend in DC prevalence over time from 28% (CI 23–34%) in 2000 to 2005 to 57% (CI 43–72%) in studies conducted after 2015. The risk of bias was very low where majority of the studies scored more than 50% in the JBI critical appraisal tool.ConclusionsThere was a wide discrepancy in the DC prevalence and scores across the different countries, settings (rural versus urban) and there was an increase in the prevalence over time. This review was self-funded.

Improved CPS-PWM Approach for Over-Modulation Operations of Hybrid Modular Multilevel Converter

The over-modulation capability of the hybrid modular multilevel converter (MMC), mixed by half-bridge and full-bridge submodules (SMs), has acquired widespread attention recently, which can significantly increase the design freedom of the hybrid MMC. When the hybrid MMC is applied in the medium-voltage occasions, an improved carrier phase shift pulsewidth modulation (CPS-PWM) approach is put forward in this article for its over-modulation operation under the nominal and variable dc conditions. It is featured with high flexibility, adjustability, and simple implementation. A new standard voltage is introduced to normalize the modulation wave, by which there is always a sufficient margin between the peaks of the normalized modulation wave and carrier waves under any modulation indexes. Also, it can perform well when the nominal dc voltage of the hybrid MMC is not the integer multiple of SM voltage. Moreover, the carrier wave arrangements are decoupled with the number of SMs, dc voltage, and ac voltage, so the variable dc operation of the hybrid MMC can be achieved without rearranging the carrier waves. Finally, the simulations and experiments are carried out to confirm the effectiveness of the proposed CPS-PWM approach for over-modulation operations under the steady-state and variable dc conditions.

PV용 Interleaved Converter의 MPPT 및 전류 평형을 위한 DSP 기반의 제어기 설계 및 HILS 검증

This paper proposes a digital controller designed for maximum power point tracking control and phase current balancing control for PV system. A variable-step incremental conductance method is applied for maximum power point tracking. For phase current balance of the interleaved boost converter, an average current balance control method that reduces the control instability due to phase difference of the phase currents and A/D conversion is proposed. The ADC frequency is set to 2 times the switching frequency and 10 times the MPPT frequency. The designed controller is implemented in the TMS320F28335 DSP, and through PLECS simulation, the superiority of the proposed controller compared to the open loop and the proposed average current balance control method compared to the general control method are verified. Finally, the performance of the proposed controller under dc and sine wave insolation conditions is verified through HIL-Simulation.

Online correction method of IGBT lifetime evaluation based on bonding wire failure monitoring

Insulated gate bipolar transistor (IGBT) modules are widely used as power switching devices. In actual working conditions, the failure of bonding wires is one of the most important failure modes. At present, the influence of bonding wire failure is not considered in the reliability evaluation of the device, resulting in a large error in the life prediction result. Therefore, this paper proposes a life evaluation method for IGBT modules that takes into account the failure of the bonding wire. The transient thermal impedance of 1200 V/50 A IGBT module under the failure conditions of different numbers of bonding wires is calculated by constructing a finite element simulation model of device electro-thermal coupling. Both simulation and experimental results show that with the increase of the number of bonding wire failures, the transient thermal impedance curve of the device rises and the steady-state thermal impedance increases. The Foster thermal network models of the devices are updated, and the number of power cycles of the device with bonding wire failure under DC and sinusoidal pulse width modulation (SPWM) conditions is calculated. When the number of bonding wire failures and fatigue accumulation have a linear relationship, the life will be reduced by 48.29% compared to the healthy state.

Improving the stability of the coating properties for group plasma electrolytic oxidation

The features of forming coatings on the aluminum alloy with plasma electrolytic oxidation (PEO) method at parallel treatment of workpieces are considered. The nature of surface microdischarges leads to uneven distribution of electrical current through individual workpieces being parallel treated in a group and, as a consequence, a significant dispersion of such coatings characteristics as thickness, through porosity, dielectric strength under AC and DC conditions and microhardness. Wherein, the stability of coatings characteristics increases with PEO treatment duration. The algorithms for automatic correction of the PEO mode which significantly increase the stability of protective coatings characteristics has been developed.

Characterization and Analysis of Hot Carrier Degradation Under DC and Large-Signal RF Stress in a PDSOI Floating-Body NFET-Based Power Amplifier Cell Under WiFi Operating Conditions

This paper presents an extensive experimental analysis of hot carrier degradation (HCD) due to DC and large-signal RF stress on a power amplifier (PA) cell in the sub-7GHz frequency band. The reported PA cell is fabricated in a 45-nm RFSOI technology and consists of a single n-channel floating body partially depleted SOI FET. The impact of HCD on the class, conduction angle ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta $ </tex-math></inline-formula> ), and performance of the PA cell is analyzed under DC and large-signal RF stress conditions. Generation of defects and their types, i.e., whether oxide or interface traps, are understood using a combination of RF and DC stress conditions. Our detailed analysis distinguishes HCD mechanisms dominated by oxide and interface traps by studying time slope exponents, changes in the subthreshold swing, threshold voltage, and peak transconductance. The impact of RF stress on the PA cell lifetime is also extracted using a semiempirical model.

An investigation on the performance of gold layer based cyanide-free HAuCl4 electroplating process under different power conditions

Gold electroplating experiment was carried out by cyanide-free chloroauric acid-based (HAuCl4-based) electroplating process in this paper. Smooth, uniform and golden thick gold layers can all be obtained after 6 h under DC, UD and PR condition. With the changing of power, the macroscopic characteristics and structure of gold layers change obviously. Sample has the best luster under PR condition. SEM images show that microstructure of gold layers vary at different power condition. AFM images show that gold layer under PR condition has the lowest surface roughness. After polishing, samples obtained under DC and UD condition have different densities of pores, while the pores are almost invisible under PR condition. XRD tests show under DC power supply, sample has no obvious orientation. The texture coefficient of (220) crystal plane of gold plating under UD condition can reach to 62.5%, and that of (200) crystal plane under PR condition can reach up to 98.9%. Texture of each sample calculated by XRD data can be verified by EBSD. Gold layer under PR condition has the highest hardness, which can reach up to 98.05 × 10−2 GPa. Gold layer under PR condition possess a number of advantages over the other powers. For pure hard gold, HAuCl4-based baths is a suitable alternative to cyanide-based baths.

Comparison of junction temperature variations of IGBT modules under DC and PWM power cycling test conditions

Comparison of junction temperature variations of IGBT modules under DC and PWM power cycling test conditions

Partial discharge characteristics of free moving metal particles in gas insulated systems under DC and AC voltages

AbstractFree conductive particles in a gas‐insulated metal‐enclosed system produce partial discharges during movement, resulting in insulator flashover and insulation failures. This study focuses on the partial discharge property of free conductive particles under DC and AC voltages. The relationship between the micro‐discharge property and the intrinsic properties of the particles was obtained based on experimental tests. The results show that under DC conditions, the local discharge property varies linearly with particle size and density. The discharge probability of particles in SF6 is significantly reduced compared with that in air, while the discharge magnitude rapidly increases if the lift voltage exceeds a certain value. Under AC conditions, the partial discharge generated by the particle becomes less random, and the amplitude and phase angle of the discharge are not significantly related. As the size of the electrode decreases, the partial discharge current generated by the particles on the surface of the electrode with an uneven electric field increases significantly. This research provides a basis for the optimization of withstand voltage test method and its applications.

Design of microwave β-(Al x Ga x )2O3/Ga2O3 lateral Schottky barrier diodes

High power microwave Schottky barrier diodes (SBDs) are required to develop detectors and mixers in advance the millimeter-wave (mm-wave) wireless technologies such as fifth generation long-term evolution. To achieve high efficiency and sensitivity in SBDs, materials/structures with high mobility and low series resistance are needed. In this regard, we have proposed the two dimensional electron gas of β-(Al x Ga)2O3/Ga2O3 heterostructure channel lateral SBDs (LSBDs) for the first time. To design high performance LSBDs, detailed physical models of both β-(Al x Ga)2O3 and Ga2O3 were studied and characterized with experimental results. These physical models were used to perform realistic numerical simulations of DC, small signal and large signal conditions. It was observed that the structural and compositional aspects of heterostructure are largely influencing the small signal sensitivity and cut-off frequencies. Also the large signal analysis reveals that the LSBD can operate in linear detection of microwave signals, up to 38 dBm. By scaling down the device to a sub-micron channel length, a cut-off frequency of 1.5 THz was achieved in the proposed LSBD. Comparison with state-of-the-art SBDs, the observations from DC, small signal and large signal analysis recommend the proposed β-(Al x Ga)2O3/Ga2O3 LSBDs for high power and mm-wave/sub-THz detector/mixer application.

A Robust Testing Method for DC and AC Capacitors With Minimum Required Power Supply

This letter proposes a testing method to emulate realistic stress conditions of dc and ac capacitors, with minimum required power supply and robust operation at the presence of capacitor degradation. It is especially suitable for parameter characterization and accelerated degradation testing of high-voltage and high-ripple current power electronic capacitors. The circuit architecture of the proposed testing method and the constraints of the testing samples under given designs are discussed. Proof-of-concept experiments on both dc and ac capacitors verify the feasibility.

Investigation into Layer Number Effect on Breakdown Strength of Multi-Layer Polymer Films.

The layer number effect on electric breakdown strength (EBD) of multi-layer polymer films is investigated using 10-μm polypropylene (PP) films under a dc condition. The layer number, n, of the films during the test is as large as 120. It is observed that the relation between EBD and n conforms to a minus power law, i.e., EBD(n) = E1′n−a, where the power exponent, a, is 0.27, E1′ is a constant. By reviewing the experimental data in references, it is found that the power law holds true for different types of polymers in different test conditions, but the value of a varies from 0.072 to 0.5. The variation of a is explained in perspective of the discontinuous structures within films and those between films. A small value of a means a good purity level of the film, which is due to the decrease of the size of the inter-layer defects. A large value of a means a poor purity level of the films, which is due to the increase of the amount of intra-layer defects. Both factors influence the value of a, leading to the variation of a.

Evidences of accumulation points: Effect of high voltage DC conditioning on concave electrodes insulated by large vacuum gaps

Counterintuitive experimental evidences have been observed during High Voltage Direct Current (HVDC) tests of two concave, axial-symmetric, electrodes insulated by large vacuum gaps of 3 and 7 cm with voltages from 150 to 370 kVdc. The dissipation of microdischarge power during the conditioning procedure occurs mostly on the anodic side in a region close to the axis of the system where the electric field is at a minimum, far from the positions where the breakdowns have been observed. The analyses of the phenomena are carried out by comparing the temporal evolution of voltages, currents, pressure, measurements of x-ray energy spectra, and images from infrared and visible light cameras. Numerical simulations, based on ray-tracing algorithm, correctly identify the positions where the power dissipation of microdischarges occurs. A mutual exchange of charged particles in the electrostatic field between electrodes seems a reasonable physical mechanism to interpret the observations. These findings suggest a new perspective to review the current literature and interpret new results considering geometric details which were so far omitted: the areas with the most intense electric field, typically located on the surfaces of the electrodes under test, are not necessarily the sole surfaces involved in the HVDC conditioning in high vacuum.