The gate-length dependent performance of AlGaN/GaN HFETs with silicon nitride passivation

A comparison has been made of the performance of AlGaN/GaN HFETs, with gate-lengths in the range 0.2 to 2.0 /spl mu/m, both with and without silicon nitride passivation. Values of I/sub DSS/ up to 750 mAmm/sup -1/ were seen with pulsed measurements, which eliminate self-heating. For a gate-length of 0.2 /spl mu/m, a f/sub t/ value of 32 GHz and f/sub max/ of 72 GHz were seen, increasing to 37 GHz and 79 GHz respectively, after passivation. Passivation also caused an increase in V/sub p/, particularly at short gate-lengths. An explanation, based on the contribution of stress in the passivation layer, is proposed. It gives qualitative agreement with measurements.