P plus Base Doping Optimization of 6-in Gate Commutated Thyristors for Hybrid DC Circuit Breaker Application

The 6-in gate commutated thyristor (GCT) is suitable for hybrid dc circuit breaker (HDCB) application with its large chip area and high maximum controllable current (MCC), compared with traditional 4-in GCTs. P+ base doping dispersion control is of vital importance in the 6-in GCT chip. Based on the strong correlation between P+ base doping and the gate-cathode breakdown voltage ( $V_{gbr}$ ), P+ base doping dispersion is characterized through $V_{gbr}$ . Test results show that $V_{gbr}$ dispersion in the 6-in GCT sample with etched depth of around 10 mu m is about 2 V with the average $V_{gbr}$ of around 22 V. While $V_{gbr}$ dispersion in the sample with etched depth of above 20 mu m is above 6 V with the average $V_{gbr}$ of around 27 V. These are consistent with the 2-D simulation results. Then, P+ base doping parameter design is optimized through experiment. Both turn-on and turn-off characteristics of 6-in GCT samples with different P+ base doping parameter designs are compared with HDCB application. The final optimized 6-in GCT chip has no difficulty in turning on under a low dc-link voltage below 100 V and it can turn off 13 kA with the overvoltage of about 4.5 kV successfully, which shows potential in HDCB application.