Electrothermal Access Resistance Model for GaN-Based HEMTs

The high-power density in GaN-based high-electron-mobility transistors (HEMTs) increases demands on the accurate extraction and modeling of electrothermal effects such as self-heating. This paper presents a new electrothermal model of the access resistances in GaN HEMTs, taking into account both self heating and bias dependence. A coplanar ungated transfer length method (TLM) structure has been used to extract the resistance versus temperature, bias, and RF power. The temperature dependence is extracted from dc measurements at ambient temperatures between 293 and 443 K. Small-signal measurements are used to extract the time constants in the thermal impedance. The bias dependence of the current is characterized by isothermal large-signal RF measurements between 1 and 6 GHz. A new method for extracting the thermal resistance from the large-signal measurements together with temperature-dependent dc measurements is also presented.