Research of electromagnetic-thermal coupling mechanism based on a physical model of AlGaN/GaN HEMTs

A single-finger physical model of 180 nm gate-length and 75 μm gate-width AlGaN/GaN HEMTs is described including lateral structure and vertical material parameters. The Farahmand Modified Caughey Thomas fitting function and the Monte Carlo model are used to express the 2DEG mobility in low and high field respectively. Then DC characteristics is simulated and the initial condition generated by self-heating effect is determined under DC bias. Electromagnetic-thermal (EM-T) coupling mechanism during the whole process is analyzed and the AlGaN/GaN HEMT structure is calculated combining with equations in electromagnetic field, microelectronics and thermal field under different RF input signals. Finally, high frequency characteristics of the device is obtained. The result shows that the highest junction temperature is 126 under -2 V gate voltage, 25 V drain voltage and 16 dBm CW RF input signal. The current gain cutoff frequency (fT), the maximum frequency of oscillation (fmax) and the maximum available power gain (MAG) at 40 GHz decrease 13%, 17% and 18%, respectively, at 16 dBm by contrasting to 8dBm.