Turn-on Transition Research Articles

Avoiding Si MOSFET Avalanche and Achieving Zero-Voltage Switching for Cascode GaN Devices

The cascode structure is widely used for high-voltage normally-on wide-bandgap devices. However, the interaction between the high-voltage normally-on device and the low-voltage normally-off Si MOSFET may induce undesired features. This paper analyzes the voltage distribution principle during the turn-off transition as well as the zero-voltage-switching (ZVS) principle during the turn-on transition for cascode GaN devices. The capacitance mismatch between high-voltage normally-on GaN switch and the low-voltage Si MOSFET causes the Si MOSFET to avalanche, and internal high-voltage GaN switch lose the ZVS condition. This issue must be solved in consideration of both power loss and reliability. A simple and effective solution is proposed by adding an extra capacitor to compensate the capacitance mismatch, thereby avoiding Si MOSFET avalanche and achieving true ZVS for cascode GaN devices. The benefits and small penalty of this solution are analyzed in detail. The theoretical analysis is validated by experiments, which are implemented based on a 600-V cascode GaN device. The experiment shows that the proposed method improves the 600-V cascode GaN devices performance significantly in high-frequency applications. The analysis and proposed solution are also applicable to other cascode devices.

Turn-on of High-Voltage SiC Thyristors for Fast-Switching Applications

This paper is focused on the characterization of the turn-ON transition of high-voltage SiC thyristors of different epi-layer thicknesses and active-area sizes to determine their suitability and limitations in high- $dI/dt$ , fast-switching applications. The unique aspects of this paper include the very high current density being switched through the thyristors over a short period of time at initial turn-ON, resulting in very high instantaneous dissipated power over the small device volume. The devices that were characterized were 6-kV, 0.5-cm2 thyristors; 10-kV, 1.05-cm2 thyristors; and 15-kV, 1.05-cm2 thyristors, all fabricated by Cree, Inc. (now Wolfspeed) for the U.S. Army Research Laboratory. The highest dI/dt and the current density were 13 kA/ms and 3.2 kA/cm2 for a parallel pair of 0.5-cm2 thyristors, with pulsed current peaking 250 ns from initial gate trigger. All devices evaluated were capable of switching a current pulse >2 kA/cm2 within a period of less than $2~\mu \text{s}$ . These evaluations have broad application in helping to inform SiC device design tradeoffs for increasing epi thickness, increasing device area, and the effects of lifetime enhancement processes. Results are also presented for initial exploration of fast-switching applications for these devices.

Characterization and Physical Modeling of Turn-On Voltage, Saturation Voltage and Transition Slope in Graphene Barristors

In this paper, we present theoretical definitions and physical backgrounds of turn-on voltage, saturation voltage and transition slope in graphene-based variable-barrier transistors (barristors). We show that they are three main characteristics parameters of the device and are of the key factors in determining whether barristor is applicable for the future nanoelectronics. Furthermore, because of the importance of physical modeling of semiconductor devices, we address this issue and develop physical expressions, in closed form, for these characteristics. We also investigate the conformity of the functional dependence of our models and their results variations regarding to the device parameters with the reports of the previous works. Finally, we physically discuss how the variation of the device parameters, such as bias condition and doping density, can influence the aforesaid main characteristics of barristor.

A High-Voltage Class-D Power Amplifier With Switching Frequency Regulation for Improved High-Efficiency Output Power Range

This paper describes the power dissipation analysis and the design of an efficiency-improved high-voltage class-D power amplifier. The amplifier adaptively regulates its switching frequency for optimal power efficiency across the full output power range. This is based on detecting the switching output node voltage level at the turn-on transition of the power switches. Implemented in a 0.14 $\mu$ m SOI BCD process, the amplifier achieves 93% efficiency at 45 W output power, ${>}80\hbox{\%}$ power efficiency down to 4.5 W output power and ${>}49\hbox{\%}$ efficiency down to 0.45 W output power.

A ZCS buck excitation converter for electric vehicle with wound rotor synchronous motors

In this paper, a high power density zero-current switching (ZCS) Buck excitation converter for electric vehicle (EV) with wound rotor synchronous motors is proposed. To eliminate the pulse noises in excitation current when considering the parasitic parameters for the rotor coil, a small coupled inductor and a small resonant capacitor are combined with basic Buck circuit. Owing to the existence of resonance, zero-current soft-switching for both turn-on and turn-off transitions is achieved, and more importantly, a constant output current without any spikes is guaranteed, which contributes to efficiency promotion and electromagnetic interference (EMI) reduction. Since no large-sized output filters or resonant components are adopted, the volume of the converter is minimised. In the end, PSIM simulation results are presented to verify the feasibility of theoretical analysis.

A Novel Soft Switched Cycloinverter

A novel soft switched insulated-gate bipolar transistor (IGBT)-based cycloinverter, which is capable of converting voltage at the main frequency to voltage at high frequency, is proposed to improve the previously proposed pulse width modulation cycloinverter. An auxiliary switch, along with an inductor, is used to have simultaneous zero-current switching and zero-voltage switching for turn-on transitions of the IGBT in order to mitigate the internal losses and total harmonic distortion factor in the inverter. The principle of operation and design consideration are presented. The proposed cycloinverter is compared with a conventional hard switched cycloinverter, and it has been demonstrated that the losses have been reduced approximately 50% by this new switching technique and the efficiency of the inverter is increased significantly. A prototype of the cycloinverter is developed in the laboratory for verification of the simulation results. Experimental results are found in good agreement to the simulated results.

Effects of Gate Field Plates on the Surface State Related Current Collapse in AlGaN/GaN HEMTs

During off-state, the influence of surface-trapped electron charges induced by high-field stress near the gate electrode of AlGaN/GaN power high-electron mobility transistor devices causes a reduction in two-dimensional electron gas (2DEG) carrier density at the heterointerface. In a pulse turn-on operation, the weakened 2DEG channel results in a higher on-state conduction resistance during the transient, known as the current collapse phenomenon. The phenomenon increases the switching loss by a higher on-state resistance and prolonged turn-on transition time, thus limits the device operating frequency range. In this paper, such a phenomenon is modeled, analyzed by Sentaurus TCAD simulation, and verified by the laboratory measurement data, with the emphasis on the influence of field plates toward the current collapse. The spatial distributions of trapped electrons and excess free electrons along the AlGaN surface are modeled and analyzed to arrive at the quantitative relationships among the trapped electron density, on-resistance increase, and the electric field distribution which provide a reliable criterion for current collapse reduction. It was found that, with a proper field plate design, it is possible to achieve an improvement on transient on-state resistance and the current recovery time.

Resistance Switching Characteristics in Zirconium Oxide

The resistance switching behavior in sputtered Ti/ZrO2/Pt sandwiched structure was investigated for nonvolatile memory application. Multiple current-voltage measurements reveal highly uniform distribution of the conduction current and switching voltage. This bipolar resistive switching driven by bias of proper magnitude and polarity is interpreted by filament model. The reset threshold increases with the compliance setting imposed on the turn-on transition, while the switching currents in high and low resistance states are not varied for different top-electrode areas. Both characteristics are ascribed to the electro-chemical reactions of field-induced reduction-oxidation processes.

Energy Storage System with Voltage Equalization Strategy for Wind Energy Conversion

In this paper, an energy storage system with voltage equalization strategy for wind energy conversion is presented. The proposed energy storage system provides a voltage equalization strategy for series-connected lead-acid batteries to increase their total storage capacity and lifecycle. In order to draw the maximum power from the wind energy, a perturbation-and-observation method and digital signal processor (DSP) are incorporated to implement maximum power point tracking (MPPT) algorithm and power regulating scheme. In the proposed energy storage system, all power switches have zero-voltage-switching (ZVS) feature at turn-on transition. Therefore, the conversion efficiency can be increased. Finally, a prototype energy storage system for wind energy conversion is built and implemented. Experimental results have verified the performance and feasibility of the proposed energy storage system for wind energy conversion.

PV Power-Generation System with a Phase-Shift PWM Technique for High Step-Up Voltage Applications

A PV power-generation system with a phase-shift pulse-width modulation (PWM) technique for high step-up voltage applications is proposed. The proposed power-generation system consists of two stages. In the input stage, all power switches of the full-bridge converter with phase-shift technique can be operated with zero-current switching (ZCS) at turn-on or turn-off transition. Hence, the switching losses of the power switches can be reduced. Then, in the DC output stage, a voltage-doubler circuit is used to boost a high dc-link bus voltage. To supply a utility power, a dc/ac inverter is connected to induce a sinusoidal source. In order to draw a maximum power from PV arrays source, a microcontroller is incorporated with the perturbation and observation method to implement maximum power point tracking (MPPT) algorithm and power regulating scheme. In this study, a full load power of 300 W prototype has been built. Experimental results are presented to verify the performance and feasibility of the proposed PV power-generation system.

A New Single-Phase Soft-Switching Power Factor Correction Converter

In this paper, single-phase soft-switching power factor correction (PFC) circuit is developed with a new active snubber cell. This active snubber cell provides zero-voltage transition turn ON and zero-current transition turn OFF for the main switch without any extra current or voltage stresses. Auxiliary switch is turned ON and OFF with zero-current switching (ZCS) without additional voltage stress. Although, there is a current stress on the auxiliary switch, it is decreased by diverting a part of the current to the output side with coupling inductance. The output current and voltage are controlled by the proposed PFC converter in very wide line and load range. This PFC converter has simple structure, low cost, and ease of control as well. In this study, a detailed steady-state analysis of the new converter is presented, and this theoretical analysis is verified exactly by 100 kHz and 300 W prototypes. This prototype has 98% total efficiency and 0.99 power factor with sinusoidal current shape.

Electrostatic Switching in Vertically Oriented Nanotubes for Nonvolatile Memory Applications

AbstractWe have demonstrated electrostatic switching in vertically oriented nanotubes or nanofibers, where a nanoprobe was used as the actuating electrode inside an SEM. When the nanoprobe was manipulated to be in close proximity to a single tube, switching voltages between 10 V – 40 V were observed, depending on the geometrical parameters. The turn-on transitions appeared to be much sharper than the turn-off transitions which were limited by the tube-to-probe contact resistances. In many cases, stiction forces at these dimensions were dominant, since the tube appeared stuck to the probe even after the voltage returned to 0 V, suggesting that such structures are promising for nonvolatile memory applications. The stiction effects, to some extent, can be adjusted by engineering the switch geometry appropriately. Nanoscale mechanical measurements were also conducted on the tubes using a custom-built nanoindentor inside an SEM, from which preliminary material parameters, such as the elastic modulus, were extracted. The mechanical measurements also revealed that the tubes appear to be well adhered to the substrate. The material parameters gathered from the mechanical measurements were then used in developing an electrostatic model of the switch using a commercially available finite-element simulator. The calculated pull-in voltages appeared to be in agreement to the experimentally obtained switching voltages to first order.

Resonant Dynamics of Nonlinear Optical Microdisks

An investigation into the relationship between two-photon-induced carrier dynamics and nonlinear optical resonance is carried out for an InP microdisk. A phenomenological model is developed and algebraic solutions are presented for the resulting bistability turn-on and turn-off transition points. It is shown that the offset between the operating wavelength and the un-illuminated resonance wavelength plays a critical role in defining the optical bus line intensity requirements at the input and the intensity contrast ratio at the output.

Interleaved Zero-Current-Transition Buck Converter

This paper introduces interleaved zero-current-transition (ZCT) converters where two sets of switches are operating out-of-phase and share the load power equally. Turn-on transitions at zero current and a significant reduction of the losses associated with diode reverse recovery are accomplished through addition of two small inductors. This paper describes a 30-kW (300 V/100 A) interleaved ZCT buck converter operating at 32-kHz effective switching frequency. Losses and efficiency of the experimental prototype compare favorably against the standard and interleaved hard-switched buck converters. Constant frequency operation with low switching losses and low output current ripple is very well suited for the realization of dc power supplies in plasma processes.

Use of a SLALOM as an optical frequency multiplier and pulse compressor

A SLALOM (semiconductor laser amplifier in the loop mirror) for optical frequency multiplication and pulse compression is presented theoretically. The influence of the relatively slow turn-on transition of the SLA and the window size to the switching window is discussed, and is neglected, instead of the sudden step for the transition in the short control pulse case in a previous paper 1. We make use of the two windows, which are created by the appropriate parameters of the proposed configuration, to multiply the optical pulse rate in the relatively long control pulse case. When the second window disappears in the short control pulse case, the device can be used as a pulse compressor. Analysis demonstrates that the 10 Gbit/s optical clock signal can be doubled to 20 Gbits/s, and a 100 ps pulse can be compressed to 34 ps at a rate of 2.5 Gbits/s with this device. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 187–191, 2000.

Use of a SLALOM as an optical frequency multiplier and pulse compressor

A SLALOM (semiconductor laser amplifier in the loop mirror) for optical frequency multiplication and pulse compression is presented theoretically. The influence of the relatively slow turn-on transition of the SLA and the window size to the switching window is discussed, and is neglected, instead of the sudden step for the transition in the short control pulse case in a previous paper 1. We make use of the two windows, which are created by the appropriate parameters of the proposed configuration, to multiply the optical pulse rate in the relatively long control pulse case. When the second window disappears in the short control pulse case, the device can be used as a pulse compressor. Analysis demonstrates that the 10 Gbit/s optical clock signal can be doubled to 20 Gbits/s, and a 100 ps pulse can be compressed to 34 ps at a rate of 2.5 Gbits/s with this device. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 187–191, 2000.

Modeling the positive-feedback regenerative process of CMOS latchup by a positive transient pole method. I. theoretical derivation

A novel method to characterize the mechanism of positive-feedback regeneration in a p-n-p-n structure during CMOS latchup transition is developed. It is based on the derived time-varying transient poles in large-signal base-emitter voltages of the lumped equivalent circuit of a p-n-p-n structure. Through calculating the time-varying transient poles during CMOS latchup transition, if is found that there exists a transient pole to change from negative to positive and then this pole changes to negative again. A p-n-p-n structure, which has a stronger positive-feedback regeneration during turn-on transition, will lead to a larger positive transient pole. The time when the positive transient pole occurs during CMOS latchup transition is the time when the positive-feedback regeneration starts. By this positive transient pole, the positive-feedback regenerative process of CMOS latchup can be quantitatively characterized.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

DYNAMIC PERFORMANCE OF MCTs UNDER INDUCTIVE LOAD CONDITIONS

PMOS-controlled thyristors (PMCTs) were tested in a single-switch configuration under inductive-load hard-switching conditions. The transient current and voltage waveforms during the turn-on and turn-off transitions were observed for 50 A/1000 V devices. The experimental waveforms are given for the anode current, the inductor current, the anode-to-cathode voltage, and the gate-to-anode drive voltage. These waveforms were obtained for periodic gate drive voltage at 6.5 kHz. The test circuit was operated at power levels of up to 370 W. The measured turn-on time was 0.255 μs at an anode-to-cathode voltage of 270 V and the measured turn-off time was 1.6 μs at an anode current of 16 A. The measured storage time was 1 μs. The measured input capacitance of the MCT was 13.5 nF and the output capacitance was 66.7 nF. It was found that the input and output capacitances of PMCTs are approximately linear.

Nonquasi-static effects in saturated bipolar circuits

A nonquasi-static (NQS) model accounting for intrinsic carrier propagation delays in both B/E and B/C junctions is implemented in the ASTAP circuit simulator to evaluate the impact of non-quasi-static effects in saturated bipolar circuits. It is shown that while the extra delay introduced by the NQS effects during the turn-on transition is primarily due to the normal mode B/E NQS delay time, the more severe NQS delay in the turnoff transition is caused mainly by the removal of the saturation overdrive charges and the longer inverse mode B/C NQS delay time.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>