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

The DC and microwave characteristics of two sets of AlGaAs/InGaAs PHEMTs having a gate length of 0.2 μm 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_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 μm