Study of Gate Junction Temperature in GaAs pHEMTs Using Gate Metal Resistance Thermometry

Gate junction temperature is presented as the crucial parameter for modeling thermal degradation in GaAs device reliability studies, and sufficient for modeling the impact of temperature on device terminal characteristics. Gate metal resistance thermometry (GMRT) is applied to a GaAs pseudomorphic high-electron mobility transistor to measure its gate junction temperature. It is found that gate leakage current due to impact ionization can interfere with dc GMRT measurements. To the best of our knowledge, for the first time it is demonstrated that this can be largely avoided by instead applying an ac version of GMRT. However, the dynamic resistance of the gate leakage current path can interfere with ac GMRT. Measurements and thermal finite element method simulations of devices at constant power dissipation conclude that the bias dependence of the channel heat source profile affects the gate junction temperature. A parameter extraction technique is presented and used in device lifetime calculations to demonstrate MTTF variations of more than an order of magnitude (despite fixed power) due to bias-dependent self-heating.