RF power limiter using capacitively-coupled contacts III-nitride varactor

Reported is a low-loss RF power limiter built using a voltage-controlled capacitor formed by two planar Schottky contacts deposited over an AlGaN/GaN heterostructure. The symmetrical structure of the varactor enables dual-polarity voltage clamping. Small electrode size and electrode spacing of 2 µm ensures a low impedance and low loss. Varying the varactor width in the range 0.25 – 1 mm allows tuning of the limiting powers in the range 17 – 40 dBm, also dependent on the operating frequency. The small-signal loss at 10 GHz is 0.2 – 0.67 dB. The varactor structure fabrication does not require gate alignment or annealing; the device is robust and fully compatible with MMICs; it also provides the DC block with around 95 V breakdown. The PL operation in the temperature range 25 – 200oC without significant parameter degradation was demonstrated. Power limiter CW stress during 100 h at 24 dBm revealed no performance degradation.