Current Crowding in High Performance Low-Loss HFET RF Switches

We report on an integrated low-loss, high-isolation RF switch using large periphery AlGaN/GaN heterostructure field-effect transistors (HFETs) connected in a Gamma-cell configuration. The insertion loss was below 0.27 dB and isolation exceeded 28 dB in the frequency range from direct current to 2 GHz. The unit-width ON resistance of large periphery HFETs was slightly higher than that of narrower devices due to current crowding in the metal electrodes. Modeling of the observed current crowding effect predicts that an optimized design will yield less than a 0.1 dB insertion loss, which is comparable to the best RF MEMS.