Reduced intermodulation distortion of AlGaAs/InGaAs doped-channel FETs by air-bridge gate process

Conventional mesa isolation process in AlGaAs/InGaAs doped-channel FETs results in the gate contacting the exposed highly n-type doped channel at the mesa sidewall, forming a parasitic gate leakage path. In this report, we suppress the gate leakage from the mesa-sidewall to increase the gate-to-drain breakdown voltage (BV_gd) and the microwave power performance by using the air-bridge gate structure. The device gate leakage characteristics under high input power swing are particularly investigated in terms of the 3rd-intermodulation distortion, which are sensitive to the sidewall gate leakage. The air-bridge gate DCFETs provide not only a lower power gain at higher input powers but also a lower IM3 power than those characteristics in conventional DCFETs.