Gate assisted turn-off thyristor with cathode shunts and dynamic gate

A 1000V, 200A gate-assisted turn-off thyristor (GATT) is described that was developed for, and is being used in, circuitry for space applications requiring high efficiency and reliability as well as small size and weight. The design features include an interdigitated shunted cathode, a dynamic gate, a means for optimizing the carrier lifetime level, and a bypass diode. The bypass diode is necessary to permit the combination of both dynamic turn-on and gate-assisted turn-off in the same device. Two versions of this diode are described. The device physics of gate-assisted turn-off will be reviewed. Based on this, improvements in the design will be described. It is shown that a prime failure mode can be eliminated and that the gate-assist signal voltage can be substantially decreased by employing a shunted cathode emitter. The test data show excellent turn-on characteristics due to the dynamic gate and the long perimeter of the edge of the main cathode. Turn-off times as short as 3 µsec are obtained. The effect of the gate-assist current on the turn-off time is described. The combination of controlling the carrier lifetime with a precisely controlled and easily variable irradiation dose of high energy electrons with gate assist current provides for simple, precision tailoring of the device characteristics to the intended application.