Thermal considerations in high average power microwave pin diode switches

The temperature sensitivity of p-i-n diode chip parameters responsible for the absorption and removal of heat in high-average-power switches is discussed. The absorption of heat is controlled by the temperature-sensitive forward and reverse bias resistances. The removal of heat is dominated by the variation in thermal impedance as a function of temperature. These variables combine in high-power p-i-n diode switches to produce a phenomenon commonly called thermal runaway. An empirical relationship derived from the data presented is used to generate a nonlinear model for temperature rise as a function of input power. Reasonable correspondence between the empirical model and measured junction temperature was observed using a 1-kW continuous wave (CW) single-pole, double-throw (SPDT) waveguide switch.<>