Current Tailing Research Articles

Investigation of trapping/de-trapping dynamics of surface states in AlGaN/GaN high-electron mobility transistors based on dual-gate structures

The mechanism of current collapse in AlGaN/GaN high-electron-mobility transistors (HEMTs) passivated with low-pressure chemical vapor deposited (LPCVD)-SiNx layers, is revealed by a double-sweep current-voltage measurement of a dual-gate HEMT structure. It provides an in-situ observation of the trapping/de-trapping process of surface states in HEMTs under high-voltage switching stress, by examining the gate-to-gate surface-hopping leakage IS along with several critical features, such as sweeping-rate and voltage-dependent onset voltage, turn-on slope, onset voltage hysteresis, and current tailing, etc. It is also verified that the plasma-enhanced atomic layer deposited (PEALD) 3-nm -SiNx interfacial layer inserted between the LPCVD-SiNx passivation and the AlGaN barrier, is beneficial for suppressing the surface-trap-induced current collapse in AlGaN/GaN HEMTs.

High efficiency single‐pulse controlled switched reluctance motor drive based on novel multilevel converter

Due to the high back electromotive force and short commutation time at high speed, the phase current of switched reluctance motor (SRM) is difficult to reach a large value, which limits the output performance of the motor in high-speed operation. This paper proposes a novel multilevel converter (MLC) with fast excitation and fast demagnetisation capability, which allows each phase to control independently even in overlapping conduction operation and is suitable for SRM with any number of phases. The excitation current in the rising inductance region is increased by high-voltage fast excitation, thus increasing the phase current level of the motor at high speed; the current tailing in the falling inductance region is suppressed by high-voltage fast demagnetisation, thereby reducing the generation of negative torque. Based on the novel MLC, a maximum torque per ampere (MTPA) control strategy is designed, and closed-loop control of the boost capacitor voltage is developed. By optimising control, the output torque and efficiency of switched reluctance motor drive (SRD) are greatly improved, and the constant power operation range is extended. Simulation study and experimental results verify the effectiveness of the proposed scheme.

A critical review on environmental implications, recycling strategies, and ecological remediation for mine tailings.

Mine tailings, generated from the extraction, processing, and utilization of mineral resources, have resulted in serious acid mine drainage (AMD) pollution. Recently, scholars are paying more attention to two alternative strategies for resource recovery and ecological reclamation of mine tailings that help to improve the current tailing management, and meanwhile reducethe negative environmental outcomes. This review suggests that the principles of geochemical evolution may provide new perspective for the future in-depth studies regarding the pollution control and risk management. Recent advances in three recycling approaches of tailing resources, termed metal recovery, agricultural fertilizer, and building materials, are further described. These recycling strategies are significantly conducive to decrease the mine tailing stocks for problematic disposal. In this regard, the future recycling approaches should be industrially applicable and technically feasible to achieve the sustainable mining operation. Finally, the current state of tailing phytoremediation technologies is also discussed, while identification and selection of the ideal plants, which is perceived to be the excellent candidates of tailing reclamation, should be the focus of future studies. Based on the findings and perspectives of this review, the present study can act as an important reference for the academic participants involved in this promising field.

A Method for Suppressing Electrical Stimulation Artifacts from Electromyography.

When surface electromyography (EMG) signal is used in a real-time functional electrical stimulation (FES) system for feedback control, the artifact from electrical stimulation is a key challenge for EMG signal processing. To address this challenge, this study proposes a novel method to suppress stimulation artifacts in the EMG-driven closed-loop FES system. The proposed method is inspired by an experimental study that compares artifacts generated by electrical stimulations with different current intensities. It is found that (1) spikes of stimulation artifacts are susceptible to the current intensity and (2) tailing components are similar under different current intensities. Based on these observations, the proposed method combines the blanking and template subtracting strategies for suppressing stimulation artifact. The length of blanking window for suppressing the stimulation spike is adaptively determined by a spike detection algorithm and the first-order derivative analysis of signal. An autoregressive model is used to estimate the tailing part of stimulation artifact, which is an adaptive template for subtracting the artifact. The proposed method is evaluated on both semi-synthetic and experimental datasets. Verified on the semi-synthetic dataset, the proposed method achieves better performance than the classic blanking method. Validated on the experimental dataset, the proposed method substantially decreases the power of stimulation artifact in the EMG. These results indicate that the proposed method can effectively suppress the stimulation artifact while retains the useful EMG signal for an EMG-driven FES system.

Analysis of Strategy for Achieving Zero-Current Switching in Full-Bridge Converters

Conventional zero-voltage and zero-current-switching (ZVZCS) full-bridge converters are widely used because they can realize zero-voltage switching (ZVS) for the leading leg and zero-current switching (ZCS) for the lagging leg. However, the large turn-off loss of the leading leg is still unacceptable in high-voltage high-power applications where insulated-gate bipolar transistors (IGBTs) with current tailing are employed. Hence, it is preferable to achieve ZCS for all IGBTs of full-bridge converters. This paper analyzes the ZCS conditions for pulsewidth modulated (PWM) full-bridge converters and proposes a general strategy for achieving ZCS for main switches, including the control strategy and design method of the topology. Based on this theory, a novel ZCS PWM full-bridge converter with simple auxiliary circuit is derived and tested. It can achieve ZCS not only for the main switches of full-bridge converter, but for the auxiliary switch as well, and obtain high efficiency. The operation principle of the proposed ZCS PWM full-bridge converter and the design procedure are presented. The experimental results of a 600 V/2.5 kW prototype are also included to verify the theoretical analysis.

Development of highly reliable static random access memory for 40-nm embedded split gate-MONOS flash memory

High quality static random access memory (SRAM) for 40-nm embedded MONOS flash memory with split gate (SG-MONOS) was developed. Marginal failure, which results in threshold voltage/drain current tailing and outliers of SRAM transistors, occurs when using a conventional SRAM structure. These phenomena can be explained by not only gate depletion but also partial depletion and percolation path formation in the MOS channel. A stacked poly-Si gate structure can suppress these phenomena and achieve high quality SRAM without any defects in the 6σ level and with high affinity to the 40-nm SG-MONOS process was developed.

Soft switching active snubbers for DC/DC converters

A soft-switching active snubber is proposed to reduce the turn-off losses of the insulated gate bipolar transistor (IGBT) in a buck power converter. The soft-switching snubber provides zero-voltage switching for the IGBT, thereby reducing its high turn-off losses due to the current tailing. The proposed snubber uses an auxiliary switch to discharge the snubber capacitor. This auxiliary switch also operates at zero-voltage and zero-current switching. The size of the auxiliary switch compared to the main switch makes this snubber a good alternative to the conventional snubber or even to passive low-loss snubbers. The use of the soft-switching active snubber permits the IGBT to operate at high frequencies with an improved RBSOA. In the experimental results reported for a 1 kW, 40 kHz prototype, combined switching/snubbing losses are reduced by 36% through the use of the active snubber compared to a conventional RCD snubber. The use of an active snubber allows recovery of part of the energy stored in the snubber capacitor during turn-off. The generic snubber cell for the buck power converter is generalized to support the common nonisolated DC/DC power converters (buck, boost, buck-boost, Cuk, sepic, zeta) as well as isolated DC/DC power converters (forward, flyback, Cuk, and sepic).

A soft switching active snubber optimized for IGBT's in single switch unity power factor three-phase diode rectifiers

This paper describes a soft switching active snubber for an IGBT operating in a single switch unity power factor three-phase diode rectifier. The soft switching snubber circuit provides zero-voltage turn-off for the main switch. The high turn-off losses of the IGBT due to current tailing are reduced by zero-voltage switching. This allows the circuit to be operated at very high switching frequencies with regulated DC output voltage, high quality input current and unity input power factor. Simulation and experimental results are included.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Application of insulated gate bipolar transistor to zero-current switching converters

The problems associated with insulated-gate bipolar transistor (IGBT) devices in PWM converters, such as turn-off current tailing and turn-off latching, are largely avoided in zero-current switching resonant converters. Phenomena induced by dv/dt, such as the power losses and latching, are identified as the predominant problems in using IGBT devices for very-high-frequency resonant operations. The discussion and the verification of the results presented are focused on buck-type converters in the zero-current switching family. >

An optimized and reliable LDD structure for 1-µm NMOSFET based on substrate current analysis

Optimization of the n-region concentration for n-channel MOSFET's with a lightly doped drain (LDD) structure was investigated, based on an analysis of the substrate current characteristics. When a substrate current tailing is observed, which is peculiar to the LDDFET with a low-concentration n-region, a gate current is not observed, which suggests strong resistance against hot-carrier injection. This was confirmed by a bias stress test. The optimized surface concentration for the n-region ranges from 1 × 1018cm-3to 2.5 × 1018cm-3under negligible V TH shift and less than 25-percent driving capability degradation, compared to values for a conventional MOSFET.

An Optimized and Reliable LDD Structure for 1-/spl mu/m NMOSFET Based on Substrate Current Analysis

Optimization of the n/sup -/ region concentration for n-channel MOSFET's with a lightly doped drain (LDD) structure was investigated, based on an analysis of the substrate current characteristics. When a substrate current tailing is observed, which is peculiar to the LDDFET with a low-concentration n-region, a gate current is not observed, which suggests strong resistance against hot-carrier injection. This was confirmed by a bias stress test. The optimized surface concentration for the n/sup -/ region ranges from 1 x 10/sup18/ cm/sup -3/ to 2.5 X 10/sup 18/ cm/sup -3/ under negligible V/sub TH/ shift and less than 25-percent driving capability degradation, compared to values for a conventional MOSFET.