Degradation and breakdown in thin oxide layers: mechanisms, models and reliability prediction

In this article, the gate-first technology was developed in GaN-based HEMTs on silicon with low-temperature (LT) Ta/Al/CuW ohmic contacts. Benefiting from the 20 nm high-quality in-situ SiNx layer, the gate-first device with LT Ta/Al/ CuW ohmic contacts shows a maximum dielectric electric field strength of 13.5 MV/cm and a high Baliga' Figure of Merit (BFOM) of 424 MW/cm2, which is 20.5% and 61.8% higher than that of the gate-first device with high-temperature (HT) Ti/Al/Ni/Au ohmic contacts, respectively. Moreover, the proposed device also demonstrates a negligible threshold voltage shift based on different gate stress bias and stress time measurements. By fitting the data with a power law, the lifetime was extrapolated to 63.2% of failures at 25 °C after 20 years, resulting in operating gate voltages of 9.2 V and 11.1 V (about 4.6 MV/cm and 5.6 MV/cm) for the gate-first devices with HT Ti/Al/Ni/Au and LT Ta/Al/CuW ohmic contacts, respectively. These results illustrate that the gate-first device with LT Au-free ohmic contacts has great potential in high-voltage applications.