Reliable 4H-SiC MOSFET with High Threshold Voltage by Al2O3-Inserted Gate Insulator

Abstract

We investigated the effect of an Al2O3 insertion layer in the gate insulator to make Vth higher and to improve the transconductance Gm in a SiC-MOSFET. Insertion of the Al2O3 layer successfully enlarged Vth by about 4 V. The Vth difference sub-threshold Id-Vg characteristics measured by sweeping the gate voltage bi-directionally indicates that insertion of the Al2O3 layer decreased the number of traps of electrons in the gate insulator. Due to this decrease, device reliability in long-term operation was improveed by smaller Vth shift in PBTI. It was also found that the insertion of the Al2O3 layer improved Gm by two times. Using this gate insulator, we succeeded in fabricating 600 V 20 A-class vertical SiC DMOSFETs with a high Vth (>5 V) and low Ron of 3 mΩcm2.