NiOx gate oxide for enhanced thermal stability of threshold voltage in GaN MIS-HEMTs up to 400 °C

This study demonstrates the high-temperature operation of AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) based on nickel oxide (NiOx) as an intermediate gate oxide, achieving stable performance up to 400 °C. Compared to the control sample with only an SiNx gate dielectric, the proposed device exhibited significant improvements: (1) enhanced thermally induced VTH stability, (2) a flat transconductance (gm) curve indicating improved linearity, and (3) lower and stable drain-to-source saturation voltage (VDS,sat). Notably, the ΔVTH shift for D-mode MIS-HEMT with NiOx was effectively reduced to ∼+0.4 V, compared to ∼−1.4 V in the control sample, over a temperature range from 25 to 400 °C. This improvement is attributed to hole carrier generation in the NiOx layer, which increases the depletion region and stabilizes the stored charge underneath the gate at high temperatures. This work demonstrates that the NiOx gate oxide layer significantly enhances VTH stability and linearity in GaN MIS-HEMT, ensuring reliable and stable device operation at high temperatures.