Channel Thickness Impact on the Small- and Large-Signal RF Performance of GaN HEMTs on Si with a cGaN Back-Barrier

We examine the influence of scaling the GaN channel thickness from 100nm to 35nm on the RF performance for GaN HEMTs on Si with a cGaN back-barrier with gate lengths ranging from 70nm to 190nm. Thinner GaN channels notably improve the short channel effects. However, there is a degradation in the on-state performance associated with an increase in dispersion. These trade-offs translate to a ~33%, ~20% decline in
$f_{\mathrm{T}}, f_{\text{MAX}}$
respectively, for 70nm devices. While the large-signal metrics, PSAT and PAE, at 6GHz drop by ~46% and ~18%, respectively. We also consider the lateral downscaling of the gate-to-drain and gate-to-source spacings, which proves beneficial in boosting PSAT, up to 3.4W/mm, by increasing the extrinsic transconductance by ~20%.