High Power SiC MESFETs

Abstract

Results of the development of high power, high efficiency silicon carbide RF MESFETs are reported. High power densities of over 3W/mm have been measured for devices with total power output in excess of 20W. The devices have been fabricated using a novel lateral epitaxy technique. The MESFET employs a buried p-type depletion stopper in order to suppress short channel effects and increase the operation voltage. The use of the depletion stopper also allows high RF signal gain, while maintaining high voltage operation capability. High breakdown voltages of over 200 Volts are achieved for single-cell components; however large-area transistors are limited to around 150 Volts. Single-cell components measured on-wafer demonstrate an Ft of 10 GHz and a high unilateral gain. Packaged 6-mm RF transistors have been evaluated using amplifier circuits designed for operation in classes A, AB or C. Operation in class AB demonstrated a saturated power of 20 W and a P1dB of 15W with a linear gain of over 16 dB at Vdd of 60 V for 2.25 GHz operation. Maximum drain efficiency is 56% for class AB operation, 48% at 1 dB compression point and 72% for class C at 2.25 GHz. Preliminary linearity measurements have been performed using a two-tone technique. IM3 values of less than -40 dBc can be achieved even at relatively high power levels.