Effect of Gate Insulator Thickness on Characteristics of Normally-off GaN MOSFETs

We have fabricated normally-off two different GaN MOSFETs with Al₂O₃ gate insulator with thickness of 38- and 54-nm and investigated the difference in device performance. From the C-V measurement, relatively higher threshold voltage and smaller threshold voltage shift were observed in the device with 54-nm-thick Al₂O₃ gate insulator compared to those of the device with 38-nm-thick Al₂O₃ gate insulator. Due to the decreased Cox with increased Al₂O₃ thickness, the device with 54-nm-thick Al₂O₃ gate insulator exhibited a little degraded DC performances compared to those of the device with 38-nm-thick Al₂O₃ gate insulator. Also, the device with 54-nm-thick Al₂O₃ exhibited better off-state characteristic with higher breakdown voltage than the device with 38-nm-thick Al₂O₃. However, no significant differences in the gate leakage characteristics were observed with low gate leakage current.