Ir/Al multilayer Gates for High Temperature Operated AlGaN/GaN HEMTs

The fabrication and characterization of the sequentially evaporated Ir/Al multilayer gates of AlGaN/GaN circular high electron mobility transistors formed by high temperature oxidation is reported. Annealing at temperature of 800 °C, for 60 s in O2 ambient makes possible to form a sharp gate interface with a high Schottky barrier height at RT (φb = 1.2 eV). It is also shown that high temperature oxidation can be an effective approach in reducing of both the gate and drain leakage currents of high electron mobility transistors (more than six orders). A comprehensive microstructural, electrical, and electro‐thermal characterization of the Ir/Al gates is carried out to study the thermal stability of the gate interface and high temperature performance of the devices. Stable operation of the devices with multilayer Ir/Al gates in the temperature range up to 500 °C is demonstrated. Here, it is proposed that the thermal stability of the interface is controlled by the formed aluminum oxide interfacial layer. Finally, perfectly clear pinch‐off characteristics and thermally induced threshold voltage (Vth) instability as low as −0.58 mV °C−1 are achieved. In this paper, AlGaN/GaN circular high electron mobility transistors (C‐HEMTs) capable to operate at elevated temperatures are presented. To withstand high temperature operation, a new design concept of the Schottky gate electrode is introduced. It consists of Ir/Al multilayers formed by high temperature oxidation (annealing in O2 at T = 800 oC for 60 s). It provides (a) high thermally stable Schottky barrier height, (b) low leakage currents, and (c) gate to be free of Au.