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

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 (similar to 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 AIGaN/gallium nitride (GaN) high electron mobility transistor (HEMT) device is used with a channel length of 0.8 mu m and consisting of 2 x 200 mu m(2) 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.