GaN-Based High Temperature and Radiation-Hard Electronics for Harsh Environments

We develop novel GaN-based high temperature and radiation-hard electronics to realize data acquisition electronics and transmitters suitable for operations in harsh planetary environments. In this paper, we discuss our research on AlGaN/GaN metal-oxide-semiconductor (MOS) transistors that are targeted for 500 °C operation and >2 Mrad radiation hardness. For the target device performance, we develop Schottky-free AlGaN/GaN MOS transistors, where a gate electrode is processed in a MOS layout using an Al₂O₃ gate dielectric layer. The AlGaN/GaN MOS transistors fabricated with the wide-bandgap gate oxide layer enable Schottky-free gate electrodes, resulting in a much reduced gate leakage current and an improved sub-threshold current than the current AlGaN/GaN field effect transistors. In this study, characterization of our AlGaN/GaN MOS transistors is carried out over the temperature range of 25 °C to 500 °C. The I _ds–V _gs and I _ds–V _ds curves measured as a function of temperature show an excellent pinch-off behavior up to 450 °C. Off-state degradation is not observed up to 400 °C, but it becomes measurable at 450 °C. The off-state current is increased at 500 °C due to the gate leakage current, and the AlGaN/GaN MOS HEMT does not get pinched-off completely. Radiation hardness testing of the AlGaN/GaN MOS transistors is performed using a 50 MeV ⁶⁰Co gamma source to explore effects of TID (total ion dose). Excellent I _ds–V _gs and I _ds–V _ds characteristics are measured even after exposures to a TID of 2 Mrad. A slight decrease of saturation current (ΔI _dss ∼3 mA/mm) is observed due to the 2 Mrad irradiation.