AlGaAs/InGaAs PHEMTs with asymmetrically recessed gates achieved through a four layer resist process

The DC and microwave characteristics of two sets of AlGaAs/InGaAs pseudomorphic high electron mobility transistors (PHEMTs) 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 resist process which enables the asymmetric placement of a T-gate in a wide recess trench. Characteristics are compared for devices whose gate length is 0.2 μm and whose extent of cap recess on the drain side of the gate (L_ud) varies from 0 to 0.55 μm. It was found that the devices showed an overall improvement in the characteristics necessary for high power applications as LUd was increased. For example, the off-state drain-source breakdown voltage increased from 5.2 to 12.5 V, the voltage gain increased from 16 to 57, and f_max increased from 133 to 158 GHz as L_ud was increased from 0 to 0.55 μm.