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.

I. Introduction

Solid state RF switches are important components of Radar T/R modules, satellite communication systems and Joint Tactical Radio Systems (JTRS). Recently, high power switches made of AlGaN/GaN heterostructure field-effect transistors (HFETs) demonstrated superior performance over other RF switching devices in terms of maximum power density, bandwidth, operating temperature and breakdown voltage. Many applications including JTRS and low-noise receivers require RF switches with a very low insertion loss, typically below 0.3 dB. Exceptionally high 2-D electron gas densities at the AlGaN/GaN interface make III-Nitride HFET-based RF switches ideal candidates for such applications. Since low-loss switches dissipate little RF power, they can be fabricated over low-cost sapphire substrates. The feasibility of high-power broadband monolithically integrated III-Nitride HFET RF switches has been demonstrated in [1]. Large-signal analysis and experimental data show that switching powers exceeding can be achieved using this device [2].