50nm In0.8GaP/In/ sub 0.4/AlAs/In0.35GaAs metamorphic HEMTs with ZEP=UV5 bilayer T-gate

By using a novel bilayer resist process, 50 nm In_0.8GaP/In_0.4AlAs/In_0.35GaAs metamorphic HEMTs on GaAs substrate have been successfully fabricated with high yield and uniformity. This process has an advantage over the conventional T-gate process. After definition of the bottom layer, the top layer is exposed, which prevents widening of the bottom layer. The devices with a novel bilayer T-gate exhibited excellent characteristics such as a maximum extrinsic transconductance (g_mldrmax) of 800 mS/mm, an on-state breakdown voltage (BV_on) of 3 V, a current-gain-cutoff frequency (f_T) of 254 GHz, and a maximum oscillation frequency (f_max) of 360 GHz in spite of low indium content of 35% in the channel.