Temperature-Dependent Access Resistances in Large-Signal Modeling of Millimeter-Wave AlGaN/GaN HEMTs
In this paper, a new method for the separate extraction of the temperature-dependent source (<inline-formula> <tex-math notation="LaTeX">$R_{s}$ </tex-math></inline-formula>) and drain (<inline-formula> <tex-math notation="LaTeX">$R_{d}$ </tex-math></inline-formula>) access resistances in gallium nitride (GaN) high electron-mobility transistors (HEMTs) by using the definition of access resistances is reported. Based on this method, the temperature-dependent access resistances (TDARs) of a <inline-formula> <tex-math notation="LaTeX">$0.15~\mu \text{m}$ </tex-math></inline-formula> gate-length GaN HEMT with unequal gate-source and gate-drain distance are extracted. By integrating the extracted access resistances into a modified Angelov model, the effects of TDARs on millimeter-wave (mmW) large-signal performance of the <inline-formula> <tex-math notation="LaTeX">$0.15~\mu \text{m}$ </tex-math></inline-formula> GaN HEMT at different ambient temperatures (i.e., −55 °C, 25 °C, and 85 °C) are investigated. Moreover, the influence of temperature coefficient difference between <inline-formula> <tex-math notation="LaTeX">$R_{s}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$R_{d}$ </tex-math></inline-formula> due to the asymmetry of the device has been also revealed. The results show that the TDARs have large impact on the large-signal modeling of mmW GaN HEMTs, and the temperature coefficients of <inline-formula> <tex-math notation="LaTeX">$R_{s}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$R_{d}$ </tex-math></inline-formula> need to be considered separately in the modeling of asymmetric GaN HEMTs. The proposed TDARs extraction method would be useful for accurate modeling of GaN HEMTs at mmW frequencies.