Demonstration of Bilayer Gate Insulator for Improved Reliability in GaN-on-Si Vertical Transistors

We demonstrate that the use of a bilayer gate oxide (2.5 nm Al
2
O
3
+ 35 nm SiO
2
) can substantially improve the reliability of GaN-on-Si vertical MOSFETs, with respect to a conventional uni-layer (35 nm Al
2
O
3
) insulator. Specifically, we show that, compared to the uni-layer insulator, devices with bilayer dielectric have (i) two-orders of magnitude lower gate leakage, (ii) 11 V higher average breakdown voltage, (iii) a steeper Weibull distribution, and 10-year lifetime at 17.8 V (same lifetime is obtained at 3.4 V with uni-layer insulator). Extended reliability testing is carried out to investigate the degradation process; evidence for hot-spot generation is obtained by electroluminescence microscopy. With regard to dc performance, the bilayer insulator ensures comparable drain current for the same bias point.