Silicon Carbide Gate Turn-off Thyristor Research Articles

Modeling and Analysis of SiC GTO Thyristor’s Dynamic Turn-On Transient

The fast turn-on speed of silicon carbide (SiC) gate-turn-off (GTO) thyristor is preferred for pulse power applications. However, the turn-on delay phenomenon hinders its improvement. In this article, the dynamic turn-on transient process of SiC GTO thyristor is investigated and analyzed extensively by means of both numerical simulation and physical modeling. The physical mechanism behind its turn-on transient process is discussed in detail. A physical model based on the charge-control theory is proposed to identify the dominant factors influencing the dynamic turn-on transient. Then the theoretical analysis is quantitatively made on the parameter design of GTO’s unit cell, and methods to increase the turn-on switch speed are extensively discussed. This study provides not only in-depth physical insights into the device’s turn-on characteristics, but also designs guidelines for the advancement of SiC GTO thyristor.

Effects of Neutron Irradiation on the Static and Switching Characteristics of High-Voltage 4H-SiC p-type Gate Turn-off Thyristors

Silicon carbide (SiC) has shown substantial promise in the fabrication of high-power devices, and SiC Schottky diodes and field-effect transistors (FETs) have been considered as potential candidates for outerspace and sensors applications. Due to the multipolar structure, SiC gate turn-off thyristor (GTO) device is relatively sensitive to the irradiation-induced point defects. However, how SiC GTO devices perform under neutron irradiation still needs to be clarified. In this paper, the effects of neutron irradiation on the static and dynamic switch characteristics of high-voltage 4H-SiC GTOs are investigated for the first time. For the static electrical properties, it is found that the forward current significantly decreases with the increasing neutron irradiation fluence. While the cathode leakage current in the blocking characteristics shows an insignificant change up to a neutron fluence of ${1.0} \times {10}^{{13}}$ n/cm2. For the switching characteristics, both the pulse peak current and di/dt show substantial reduction as the neutron fluence increases while the delay time increases after irradiation. The degraded performance of the static and dynamic characteristics of SiC GTO devices was then analyzed and attributed to the weakened conductivity modulation and reduced carrier injection efficiency into the drift layer. These two aspects originate from the significantly reduced carrier lifetime and deteriorated forward characteristics of anode-gate diodes, respectively.

Thermal and electrical evaluation of SiC GTOs for pulsed power applications

For applications which require high peak current and fast rise time, silicon carbide (SiC) material is ideal because of its ability to tolerate high localized temperatures generated during switching. This research was performed to investigate SiC devices for pulse power applications and to analyze the failure of the devices. Seven 2 mm/spl times/2 mm SiC gate turn-off thyristors (GTOs) manufactured by Cree, Inc., Durham, NC, were evaluated. The devices were tested at single shot and under repetitive stress using a ring-down capacitor discharge circuit. The current pulsewidth was 2 /spl mu/s with a peak current of 1.4 kA (current density of 94.6 kA/cm/sup 2/) and a maximum di/dt of 2.36 kA//spl mu/s. The maximum power dissipated within the devices was 240 kW. Thermal modeling of these devices was done using ANSYS to analyze the heating and cooling. A two-dimensional model was used that included the device package and bonding materials. The maximum amount of power dissipated was calculated from the 1000-A, 2-/spl mu/s pulse. No further power input was added to the model and the heat transfer was plotted on an exponential scale. It was found that heat applied to a 2-/spl mu/m-thick region of the fingers yielded a temperature greater than 800/spl deg/C in the device. It took 1.0E/sup -02/ s for this heat to dissipate and for the device to return to 23/spl deg/C. The minimum and maximum stresses were found to be -2.83E/sup +09/ Pa and 4.06E/sup +08/ Pa, respectively.

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

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.

Inductive switching of 4H-SiC gate turn-off thyristors

The high-temperature operation of a silicon carbide gate turn-off thyristor is evaluated for use in inductively loaded switching circuits. Compared to purely resistive load elements, inductive loads subject the switching device to higher internal power dissipation. The ability of silicon carbide components to operate at elevated temperatures and high power dissipations are important factors for their use in future power conversion/control systems. In this work, a maximum current density of 540 A/cm/sup 2/ at 600 V was switched at a frequency of 2 kHz and at several case temperatures up to 150/spl deg/C. The turn-off and turn-on characteristics of the thyristor are discussed.

Half-bridge inverter using 4H-SiC 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.

Silicon carbide distributed buffer gate turn-offthyristorstructure for blocking high voltages

Silicon carbide gate turn-off thyristor simulations indicate that including within the drift region an n-type layer, doped 5 × 1016 cm-3 and located 3 µm below the top of the drift region, improves the forward blocking state electrostatic field profile. This structure, with a 15 µm total drift region thickness and no other field termination, blocks 2211 V, against 757 V if the n-type buffer layer is left out.

4H-SiC power devices for use in power electronic motor control

Silicon carbide (SiC) is an emerging semiconductor material which has been widely predicted to be superior to both Si and GaAs in the area of power electronic switching devices. This paper presents an overview of SiC power devices and concludes that the MOS turn-off thyristor (MTO™), comprising of a hybrid connection of SiC gate turn-off thyristor (GTO) and MOSFET, is one of the most promising near term SiC switching device given its high power potential, ease of turn-off, 500°C operation and resulting reduction in cooling requirements. The use of a SiC and an anti-parallel diode are primary active components which can then be used to construct an inverter module for high-temperature, high-power direct current (d.c.) motor control.