Small-Signal Analysis of Channel Resistance R L at Low Gate Bias Voltages in AlGaN/GaN HEMTs

Abstract

In this article, we present the effect of low gate bias on $R_{L}$ in a small-signal model (SSM) and show that the channel resistance has a strong bias dependence. It has been observed that $R_{L}$ dominates above the threshold voltage (> $V_{TH}$ ) and insignificant near to the threshold voltage (~ $V_{TH}$ ). Moreover, we show that the channel resistance ( $R_{L}$ ) yields a significant change in drain-to-source resistance ( $R_{ds}$ ) and capacitance ( $C_{ds}$ ) of 23% and 30%, respectively. It has also been observed that to match the measured intrinsic Y-parameter, $R_{L}$ is important. An AlGaN/gallium nitride (GaN) high electron mobility transistor (HEMT) device is used with a channel length of 0.8 μm and consisting of 2 x 200 μm² gate width for the analysis. The effect of $R_{L}$ in the intrinsic part of the SSM has been verified and the results show good agreement between simulated and measured S-parameters data up to 40 GHz.