High-Temperature Microwave Performance of Submicron AlGaN/GaN HEMTs on SiC

The effect of temperature on the small-signal radio-frequency (RF) performance of submicron AlGaN/GaN high-electron-mobility transistors on SiC has been studied from room temperature (RT) up to 600 K. A relation between ambient and channel temperatures has been established by means of finite-element simulations. The thermal behavior of the intrinsic parameters $C_{\rm gs}$, $C_{\rm gd}$, $g_{m, {\rm int}}$, and $g_{\rm ds}$ has been extracted accurately from RF measurements by means of the small-signal equivalent circuit. Main dc parameters $(I_{D}, g_{m, {\rm ext}})$ show reductions close to 50% between RT and 600 K, mainly due to the decrease in the electron mobility and drift velocity. In the same range, $f_{T}$ and $f_{\max}$ suffer a 60% decrease due to the reduction in $g_{m, {\rm ext}}$ and a slight increase of $C_{\rm gs}$ and $C_{\rm gd}$. An anomalous thermal evolution of $C_{\rm gd}$ at low $I_{D}$ has been identified, which is indicative of the presence of traps.