The Effect of Forward Gate Bias Stress on the Noise Performance of Mesa Isolated GaN HEMTs

This study investigates degradation of gallium nitride (GaN) high-electron mobility transistor (HEMT) noise performance after both dc and RF stress with forward gate current. The results are used to facilitate optimization of the robustness of GaN low-noise amplifiers (LNAs). It is shown that forward biasing the gate of a GaN HEMT results in permanent degradation of noise performance and gate current leakage, without affecting S-parameters and drain current characteristics. The limit of safe operation of the 2 x 50 mu m devices in this study is found to be between 10 and 20 mW dissipated in the gate diode for both dc and RF stress. We propose that degradation could be caused by excessive leakage through the mesa sidewalls at the edges of each gate finger. Circuit simulations may be used together with device robustness rating to optimize LNAs for maximum input power tolerance. Using a resistance in the gate biasing network of 10 k Omega, it is estimated that an LNA utilizing a 2 x 50 mu m device could withstand input power levels up to 33 dBm without degradation in noise performance.