Enhancement and depletion-mode pHEMT using 6 inch GaAs cost-effective production process

A cost effective enhancement/depletion mode pHEMT MMIC process on 6-inch GaAs wafer is demonstrated by using 0.5μm gate-length optical stepper pHEMT technology. E-mode and D-mode gates are deposited simultaneously in this process simplification. The E-mode pHEMT exhibits a pinch-off voltage of +0.22V (defined at 0.1mA/mm), and a maximum extrinsic transconductance of 400mS/mm at room temperature. The off-state current of E-mode device is typically 0.15μA/mm at V_gs=0V and V_ds=3V. This current is extreme low and is suitable for high density digital circuits with minimized power consumption. On the other hand, a pinch-off voltage of -0.75V and a transconductance of 370mS/mm has been measured for D-mode pHEMT. Due to excellent DC/RF characteristics and good uniformity of E/D pHEMTs from optimized optical gate lithography and front-side process, the D-mode switch and E-mode digital control circuit constitute a monolithic solution to RF control circuits in WLAN and cell phone applications.