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

The DC and microwave characteristics of two sets of AlGaAs/InGaAs PHEMTs having a gate length of 0.2 /spl 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 wide 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/sub 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/sub max/, increased from 133 to 158 GHz as the drain side cap recess, L/sub ud/, was increased from 0 to 0.55 /spl mu/m.