HIGH-TEMPERATURE ELECTRICAL CHARACTERISTICS OF GAAS-MESFETS (25-400-DEGREES-C)

We report on the effects of elevated ambient and substrate temperatures (25-degrees-C up to 400-degrees-C) on the electrical characteristics of integrated GaAs MESFET's in a state-of-the-art commercial technology. The work primarily focuses on the large- and small-signal parameters of the transistors which include threshold-voltage shifts, leakage currents, backgating effects, and variations in small-signal transconductance and output resistance with temperature and frequency. When relevant, we compare our results to silicon MOSFET's. We demonstrate, both analytically and experimentally, the existence of zero-temperature-coefficient ("ZTC") drain currents for enhancement- and for depletion-mode GaAs MESFET's. We present experimental data which show that, while GaAs MESFET's generally display degradation mechanisms similar to those of silicon MOSFET's with increasing temperature, they incur several additional effects, prominent among which are a) increasing gate leakage currents, b) Schottky-barrier height lowering, c) decreasing large- and small-signal (gate) input resistances, d) decreasing sensitivity to sidegating and backgating up to 200-degrees-C approximately, and e) increasing small-signal drain resistance.