Nanofabrication of 80 nm asymmetric T shape gates for GaN HEMTs

This paper tackles the issue of current collapse frequently seen in AlGaN/GaN based high electron mobility transistors, caused by peak electric field on the device surface around the gate edges, which are worsened when shrinking the gate length down to sub-100 nm for high frequency operation. To improve the device performance, a new configuration of T shape gates with asymmetric arms is proposed, based on our device simulation results. 3D grayscale electron beam lithography was developed to fabricate various shapes of the asymmetric T shape gates, indicating that such kind of gate configuration is technically feasible. The asymmetric T shape gates developed in this work to some extent can suppress the electric field on the gate edge efficiently as well as reduce the parasitic capacitance between the gate and the drain, leading to higher operation frequency. Applications of such a gate onto the GaN based HEMTs are hopefully to achieve high breakdown voltage for high frequency operation.