A packaged 20-GHz 1-W GaAs MESFET with a novel via-hole plated heat sink structure

A novel via-hole plated-heat-sink (PHS) structure with an improved gate-packing density is developed for K-band GaAs power FETs. The gate-packing density is increased to four times greater than that in the conventional direct via-hole structure, by making via holes under the source-grounding pads fabricated outside the FET active area. The increase in the gate-packing density allows the design of a high-power, high-frequency FET with a larger gate periphery. The resultant 2.4-mm-gate-periphery device with 700-nm gate length delivered 1.1 W (30.4 dBm) of output power with 5.0-dB gain and 19.2-percent power-added efficiency at 20 GHz and 0.74 W (28.7 dBm) at 30 GHz. The same type of device assembled in the hermetically sealed package delivered 1.0 W (30 dBm) of output power with 4.8-dB gain and 13-percent power-added efficiency at 20 GHz. Thermal and mechanical tests demonstrated the reliability of the FET.