2- to 20-GHz Switch Using III-Nitride Capacitively Coupled Contact Varactors

We report on the low-loss microwave switch monolithic microwave integrated circuit (MMIC) built using voltage-controlled capacitors formed by the two Schottky contacts deposited over an AlGaN/GaN heterostructure. A symmetrical structure of the varactor allows for either positive or negative control voltage. A small electrode and a spacing size of 2 μm ensure low on-impedance. The fabricated series-shunt switch MMIC shows 0.8-dB insertion loss and 28-dB isolation at 18 GHz and the maximum linear power of 34 dBm at 10 GHz and 38 dBm at 18 GHz (extrapolated from 2- to 10-GHz data). The device does not require contact alignment or annealing; it is robust, simple to fabricate, and well suited for MMICs.