Design and fabrication of Emitter Controlled Thyristor

The Emitter Controlled Thyristor (ECT) is a new MOS-Gated Thyristor (MGT) that combines the ease of a MOS gate control with the superior current carrying capability of a thyristor structure for high-power applications. An ECT is composed of an emitter switch in series with the thyristor, an emitter-short switch in parallel with the emitter junction of the thyristor, a turn-on FET and the main thyristor structure. Numerical analysis shows that the ECT also offers superior high voltage current saturation capability even for high breakdown voltage ratings. Two different ECT structures are investigated in this research from numerical simulations to experimental fabrications.

A novel ECT structure that utilizes IGBT compatible fabrication process was proposed. The emitter short FET, emitter switch FET and turn-on FET are all integrated with a high voltage thyristor. Numerical simulation results show that the ECT has a better conductivity modulation than that of the IGBT and at the same time exhibits superior high voltage current saturation capability, superior FBSOA and RBSOA. The technology trade-off between turn-off energy loss and forward voltage drop of the ECT is also better than that of the IGBT because of the stronger conductivity modulation. A novel self-aligned process is developed to fabricate the device. Experimental characteristics of the fabricated ECT devices show that the ECT achieves lower forward voltage drop and superior high voltage current saturation capability.

A Hybrid ECT (HECT) structure was also developed in this research work. The HECT uses an external FET to realize the emitter switching function, hence a complicated fabrication issue was separated into two simple one. The cost of the fabrication decreases and the yield increases due to the hybrid integration. Numerical simulations demonstrate the superior on-state voltage drop and high voltage current saturation capability. A novel seven-mask process was developed to fabricate the HECT. Experimental results show that the HECT could achieve the lower forward voltage drop and superior current saturation capability. The resistive switching test was carried out to demonstrate the switching characteristics of the HECT.