Utilization of an electron beam resist process to examine the effects of asymmetric gate recess on the device characteristics of AlGaAs/InGaAs PHEMT's

The DC and microwave characteristics of two sets of AlGaAs/InGaAs PHEMT's having a gate length of 0.2 mu m are compared, The first set is composed of devices fabricated using a trilayer electron beam resist process for T-gate recess and metallization, The second set is composed of devices fabricated using a new four-layer electron beam resist process which enables the asymmetric placement of a T-gate in a nide recess trench, Devices fabricated using the four-layer resist process showed improved breakdown voltage, lower gate-drain feedback capacitance, lower output conductance, and higher f(max) with only slight reduction of drain current and transconductance. For example, the off-state drain-source breakdown voltage increased from 5.2 to 12.5 V, and the f(max) increased from 133 to 158 GHz as the drain side cap recess, L-ud, was increased from 0 to 0.55 mu m.