Thermal 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 due to 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 times 2 mm SiC gate turn-off thyristors (GTOs) manufactured by Cree were evaluated. The devices were tested at single shot and under repetitive stress using a ring-down capacitor discharge circuit. The current pulse width was 2 mus with a peak current of 1.4 kA (current density of 94.6 kA/cm2) and a maximum di/dt of 2.36 kA/mus. 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. The model used was a 2-D model that included the device package, and bonding materials. The maximum amount of power dissipated was calculated from the 1000 A, 2 mus 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 mum thick region of the fingers yielded a maximum temperature of 2,500 degC in the device. It took 1.0E^-02 seconds for this heat to dissipate and for the device to return to 23C. The minimum and maximum stresses were found to be -2.83E⁺⁰⁹ Pa and 4.06E⁺⁰⁸ Pa, respectively. It was also found that the thickness of the heat generation region did not affect the final time to cool, but did affect the maximum temperature reached