High-efficiency 35-GHz GaAs MESFET's

Ka-band GaAs FET's with power output in excess of 200 mW and with efficiencies of more than 20 percent are described. Both ion-implanted and VPE-grown wafers were used. Deep UV (300-nm) lithography and chemical etching was employed to obtain a final gate length of 0.5 µm. These FET chips were flip-chip mounted and had a very low thermal resistance of 50°C/W for a total source periphery of 0.6 mm. At 35 GHz an output power of 220 mW with 21-percent efficiency at 3-dB gain was obtained from a 0.6-mm cell.