The switching behavior of semiconductor devices responds to charge/discharge phenomenon of terminal capacitance in the device. The differential capacitance in a semiconductor device varies with the applied voltage in accordance with the depleted region thickness. This study develops a C - V characterization system for high-voltage power transistors (e.g., MOSFET, insulated gate bipolar transistor, and JFET), which realizes the selective measurement of a specified capacitance from among several capacitances integrated in one device. Three capacitances between terminals are evaluated to specify device characteristics-the capacitance for gate-source, gate-drain, and drain-source. The input, output, and reverse transfer capacitance are also evaluated to assess the switching behavior of the power transistor in the circuit. Thus, this paper discusses the five specifications of a C -V characterization system and its measurement results. Moreover, the developed C -V characterization system enables measurement of the transistor capacitances from its blocking condition to the conducting condition with a varying gate bias voltage. The measured C -V characteristics show intricate changes in the low-bias-voltage region, which reflect the device structure. The monotonic capacitance change in the high-voltage region is attributable to the expansion of the depletion region in the drift region. These results help to understand the dynamic behavior of high-power devices during switching operation.

/pdf/measuring-terminal-capacitance-and-its-voltage-dependency-4o5a3iy85v.pdf

Measuring Terminal Capacitance and Its Voltage Dependency for High-Voltage Power Devices

There has been a rapid improvement in SiC materials and power devices during the last few years. SiC unipolar devices such as Schottky diodes, JFETs and MOSFETs have been developed extensively and advantages of insertion of such devices in power electronic systems have been demonstrated [1, 2]. However, unipolar devices for high voltage systems suffer from high drift layer resistance that gives rise to high power dissipation in the on-state. For such applications, bipolar devices are preferred due to their low on-resistance. In this article, the physics and technology of SiC bipolar devices, namely Bipolar Junction Transistors (BJTs), Insulated Gate Bipolar Transistors (IGBTs), and Gate Turn Off Thyristors (GTOs), are discussed. A detailed review of the current status and future trends in these devices is given with an emphasis on the device design and characterization. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Design and technology considerations for SiC bipolar devices: BJTs, IGBTs, and GTOs

A compact and accurate analytical charge control model for finding gate capacitance of Al m Ga 1− m N/GaN MODFET is presented. This temperature dependent model incorporates the effect of strain relaxation, donor neutralization and free carrier generation in the Al m Ga 1− m N layer. Non-linear Fermi potential ( E F )-variation with the sheet carrier concentration ( n s ), and the charge induced in the two-dimensional electron gas (2-DEG) due to highly dominant effects of spontaneous and piezoelectric polarization at the heterojunction of MODFET are also considered. The model is based on closed form expression and does not involve any fitting parameter or elaborate computation. Agreement of calculated data with published simulated/experimental data proves the validity and applicability of the model.

Temperature and polarization dependent polynomial based non-linear analytical model for gate capacitance of AlmGa1−mN/GaN MODFET

We fabricated a multi-mesa-channel (MMC) structure by forming a periodic trench just under a gate electrode to improve the uniformity of effective electric field in the channel in an AlGaN/GaN high electron mobility transistor (HEMT). A unique performance, i.e., a nearly temperature-independent saturation drain current, was observed in the MMC device in a wide temperature range. A two-dimensional (2D) potential calculation indicates that the mesa-side gate effectively modulates the potential, resulting in a field surrounding 2D electron gas. Such a surrounding-field effect and a relatively lower source access resistance may be related to a unique current behavior in the MMC HEMT.

/pdf/nearly-temperature-independent-saturation-drain-current-in-a-2z8t5xp9kj.pdf

Nearly Temperature-Independent Saturation Drain Current in a Multi-Mesa-Channel AlGaN/GaN High Electron Mobility Transistor

This paper presents a novel system configuration for voltage source converter (VSC)-based high-voltage direct current (HVDC) transmission connected to a large-scale offshore wind power plant (WPP). The proposed scheme is reconfigured at the onshore end to achieve shunt and series compensation, which is named as `Unified-VSC-HVDC' (U-VSC-HVDC). A mathematical model of the proposed configuration is derived to determine the rating of the employed series and shunt converters. To achieve a flexible control strategy for balanced and unbalanced fault conditions, the proposed transient management scheme employs positive and negative sequence controllers for the series compensation. The negative sequence voltage components are determined in such a way as to minimize power oscillations caused by asymmetrical faults, and hence to reduce DC link voltage overshoots. A test system comprised of a detailed representation of the proposed configuration is simulated and evaluated using PSCAD/EMTDC. A comprehensive study validates the capability of the proposed configuration and transient management scheme for achieving smooth power transfer and superior transient performance of the electrical grid. Also, it minimizes the possibilities of electrical network propagations in response to symmetrical and asymmetrical grid faults.

Novel Configuration and Transient Management Control Strategy for VSC-HVDC

Shubnikov-de Haas (SdH) oscillation and Hall measurement results were compared with HEMT DC and RF characteristics for two different MOCVD grown AlGaN-GaN HEMT structures on semiinsulating 4H-SiC substrates. A HEMT with a 40-nm, highly doped AlGaN cap layer exhibited an electron mobility of 1500 cm/sup 2//V/s and a sheet concentration of 9/spl times/10/sup 12/ cm at 300 K (7900 cm/sup 2//V/s and 8/spl times/10/sup 12/ cm/sup -2/ at 80 K), but showed a high threshold voltage and high DC output conductance. A 27-nm AlGaN cap with a thinner, lightly doped donor layer yielded similar Hall values, but lower threshold voltage and output conductance and demonstrated a high CW power density of 6.9 W/mm at 10 GHz. The 2DEG of this improved structure had a sheet concentration of n/sub SdH/=7.8/spl times/10/sup 12/ cm/sup -2/ and a high quantum scattering lifetime of /spl tau//sub q/=1.5/spl times/10/sup -13/ s at 4.2 K compared to n/sub SdH/=8.24/spl times/10/sup 12/ cm/sup -2/ and /spl tau//sub q/=1.72/spl times/10/sup -13/ s for the thick AlGaN cap layer structure, Despite the excellent characteristics of the films, the SdH oscillations still indicate a slight parallel conduction and a weak localization of electrons. These results indicate that good channel quality and high sheet carrier density are not the only HEMT attributes required for good transistor performance.

Carrier transport related analysis of high-power AlGaN/GaN HEMT structures

SiC GTO thyristors may soon be the best available choice for very high-power switching. At this time, the authors have developed new operational techniques, growth requirements and pn-pn-pn type structures to address the issues of high on-state voltage, poor turn-off gain, and inability to reach predicted breakover voltages. They present these findings using experimental measurements and numerical simulations.

Advanced operational techniques and pn-pn-pn structures for high-power silicon carbide gate turn-off thyristors

This paper reports on the first demonstration of a half-bridge power inverter constructed from silicon carbide gate turn-off thyristors (GTOs) operated in the conventional GTO mode. This circuit was characterized with input bus voltages of up to 600 VDC and 2 A (peak current density of 540 A/cm/sup 2/) with resistive loads using a pulse-width modulated switching frequency of 2 kHz. We discuss the implications of the thyristor's electrical characteristics and the circuit topology on the overall operation of the half-bridge circuit. This work has determined the conservative critical rate of rise value of the off-state voltage to be 200 V//spl mu/s in these devices.

Half-bridge inverter using 4H-SiC gate turn-off thyristors

Future US Army motor control applications will require power devices to operate for thousands of hours at case temperatures of 150/spl deg/C and higher. For reliable operation of silicon (Si)-base power electronic, the operational case temperature must be below 120/spl deg/C. Because of this temperature limitation of Si, new wide bandgap materials such as silicon carbide (SiC) are being investigated. The wide bandgap material allows SiC devices to operate at temperatures significantly greater than 150/spl deg/C. For high power and high voltage applications the gate turn-off thyristor (GTO) is the switch of choice. This paper presents the results of a SiC GTO and a SiC p-i-n diode both operating at case temperatures up to 150/spl deg/C. The GTO switches into an inductive load with currents up to 5 Amps, baseplate temperature up to 150/spl deg/C and switching frequency up to 10 kHz.

High temperature inductive switching of SiC GTO and diode

A silicon carbide power module has been developed to demonstrate a high-temperature, 10 kW AC drive application. Several goals for this development include temperature dependent parameter evaluation of parallel-connected transistors and junction barrier Schottky diodes at 150 /spl deg/C operating temperature. Next, design of a high-thermal conductivity substrate to cool the modules based on predicted losses. Finally the integration into a variable speed AC drive using a DSP-based V/F motor controller. Test results for the 10 kW AC drive are provided to demonstrate power module performance up to 180 /spl deg/C.

/pdf/silicon-carbide-power-semiconductor-module-development-for-a-59ggizqhdq.pdf

Silicon carbide power semiconductor module development for a high temperature 10 kW AC drive

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