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
${R}_{\text {L}}$
in a small-signal model (SSM) and show that the channel resistance has a strong bias dependence. It has been observed that
${R}_{\text {L}}$
dominates above the threshold voltage (
$> {V}_{\text {TH}}$
) and insignificant near to the threshold voltage (
$\sim {V}_{\text {TH}}$
). Moreover, we show that the channel resistance (
${R}_{\text {L}}$
) yields a significant change in drain-to-source resistance (
${R}_{\text {ds}}$
) and capacitance (
${C}_{\text {ds}}$
) of 23% and 30%, respectively. It has also been observed that to match the measured intrinsic Y-parameter,
${R}_{\text {L}}$
is important. An AlGaN/gallium nitride (GaN) high electron mobility transistor (HEMT) device is used with a channel length of
$0.8~\mu \text{m}$
and consisting of 2
$\times 200\,\,\mu \text{m}^{{2}}$
gate width for the analysis. The effect of
${R}_{\text {L}}$
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.