DC and RF characteristics of AlGaN/GaN HFET using RuO₂-based gate for high power and high temperature application

Al_0.25Ga_0.75N/GaN HFETs grown on a sapphire substrate were fabricated using an RuO₂ based Schottky contact. The Schottky contact characteristics for various gate metals, such as RuO₂/Au, Pt/Au, Ni/Au, and Ni/Pt/Au, were compared, and showed that the RuO₂/Au metal scheme was superior to the others. RuO₂-gated AlGaN/GaN HFETs with a 220 Å and 270 Å-thick Al_0.25Ga_0.75N layer exhibited a maximum drain current of 689 and 808 mA/mm at V_GS = +1 V, respectively. An HFET with a 220 Å-thick Al_0.25Ga_0.75N layer exhibited a current gain cut-off frequency of 27 GHz and maximum oscillation frequency of 46 GHz for a gate length of 0.8 μm. The RF output power density for the device was 1.12 W/mm at 1.8 GHz.