High performance of 0.15μm quasi enhancement-mode (E-mode) In0.4GaAs/In0.4AlAs metamorphic HEMTs on GaAs substrate using new triple-gate technology

In this paper, a novel gate technology with triple shaped gate structure has been proposed and developed in order to minimize unwanted gate fringing capacitance. Because high gate stem height was difficult to fabricate by means of conventional direct electron beam (e-beam) lithography method, additional PMGI sacrificial layer was utilized in this new scheme. Increasing gate stem height as an amount of PMGI resist thickness and forming T-shaped gate structure on top of the PMGI layer, triple shaped gate structure could be finally obtained. Applying the developed technology to the fabrication of 0.15μm In_0.4GaAs/In_0.4AlAs metamorphic HEMTs (M-HEMTs), excellent device cutoff frequency (f_T) performance of 164 GHz even with 0.15μm technology has been shown owing to the remarkable reduction of gate fringing capacitance. In addition, the usage of 40% indium content in barrier layer gave rise to the improvements in Schottky gate characteristics such as gate turn-on voltage (V_on) of +1.03 V and reverse breakdown voltage (BV_GD) of -7.8 V, which has important meanings in enhancement-mode operation devices.