High-$f_{{\rm MAX}}$ High Johnson's Figure-of-Merit 0.2- $\mu{\rm m}$ Gate AlGaN/GaN HEMTs on Silicon Substrate With ${\rm AlN}/{\rm SiN}_{{\rm x}}$ Passivation

This letter reports a 0.2-
$\mu{\rm m}$
gate AlGaN/GaN high-electron-mobility transistors (HEMTs) on an Si substrate passivated with an
${\rm AlN}/{\rm SiN}_{{\rm x}}$
(4/20 nm) stack layer. The 4-nm-thick AlN was grown by plasma-enhanced atomic-layer-deposition. The
${\rm AlN}/{\rm SiN}_{{\rm x}}$
-passivated HEMTs exhibit a high maximum drain current of 930 mA/mm, an three-terminal OFF-state breakdown voltage
$({BV}_{{\rm DS}})$
of 119 V, and a small threshold voltage shift of 130 mV in a wide drain bias range
$(V_{{\rm DS}}=3-24~{\rm V})$
. Owing to the additional positive polarization charge in the AlN passivation layer, the access resistance
$R_{s}$
in the GaN-on-Si HEMTs is significantly reduced while maintaining small parasitic gate-drain capacitance
$C_{{\rm gd}}$
, contributing to a high power-gain cutoff frequency
$f_{{\rm MAX}}$
of 182 GHz and a high Johnson's figure of merit of
${BV}_{{\rm DS}}\times f_{\,T}$
of
$6.43\times 10^{{12}}~{\rm V}/{\rm s}$
simultaneously. The accuracy of the RF performance is verified by a small signal modeling based on measured S-parameters.