High- $f_{{\rm MAX}}$ High Johnson\´s Figure-of-Merit 0.2- $\mu{\rm m}$ Gate AlGaN/GaN HEMTs

This letter reports a 0.2- μm gate AlGaN/GaN high-electron-mobility transistors (HEMTs) on an Si substrate passivated with an AlN/SiN_x (4/20 nm) stack layer. The 4-nm-thick AlN was grown by plasma-enhanced atomic-layer-deposition. The AlN/SiN_x-passivated HEMTs exhibit a high maximum drain current of 930 mA/mm, an three-terminal OFF-state breakdown voltage (BV_DS) of 119 V, and a small threshold voltage shift of 130 mV in a wide drain bias range (V_DS=3-24 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_gd, contributing to a high power-gain cutoff frequency f_MAX of 182 GHz and a high Johnson´s figure of merit of BV_DS × f T of 6.43 × 10¹² V/s simultaneously. The accuracy of the RF performance is verified by a small signal modeling based on measured S-parameters.