50 nm In0.8GaP/In0.4AIAs/In0.35GaAs metamorphic HEMTs with ZEP/UV5 bilayer T-gate

By using a novel bilayer resist process, 50 nm In0.8GaP/ ln(0.4)AlAs/In0.35GaAs metamorphic HEMTs on GaAs substrate have been successfully fabficated 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 bilaycr T-gate exhibited excellent characteristics such as a maximum extrinsic transconductance (g(m). max) of 800 mS/mm, an on-state breakdown voltage (BV) of 3V, a current-gain-culoff 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.