GaN Ring Oscillators Operational at 500 °C Based on a GaN-on-Si Platform

A study of GaN for high temperature (HT, up to 500 °C) digital circuits was conducted. A HT-robust GaN-on-Si technology based on enhancement-mode p-GaN-gate AlGaN/GaN high electron mobility transistors (HEMTs) and depletion-mode AlGaN/GaN HEMTs was proposed and used to implement different digital circuit configurations, namely E/D-mode and E/E-mode (E: enhancement, D: depletion). The E/D-mode inverter was found to offer significantly better performance in terms of voltage swing, noise margin, and gain, across temperature and V DD scaling. As calculated from E/D-mode ring oscillators (ROs) with L G = 2 μm, a RO exhibited a propagation delay (t p ) of < 1.48 ns/stage at 500 °C. The best RO achieved t p < 0.18 ns/stage at 25 °C. To the best of the authors' knowledge, the proposed technology sets a new boundary of t p vs. L G in wide band gap digital logic, and is operational at the highest reported temperature (500 °C) of a GaN digital circuit. The results reflect the promising potential of the proposed technology for emerging HT applications at 500 °C and beyond.