High-f_ MAX High Johnson's Figure-of-Merit 0.2- μ m Gate AlGaN/GaN HEMTs on Silicon Substrate With AlN/ SiN_ x Passivation

This letter reports a 0.2-μ mgate AlGaN/GaN high-electron-mobility transistors (HEMTs) on an Si substrate passivated with anAlN/ SiN_ x(4/20 nm) stack layer. The 4-nm-thick AlN was grown by plasma-enhanced atomic-layer-deposition. TheAlN/ 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 resistanceRₛin the GaN-on-Si HEMTs is significantly reduced while maintaining small parasitic gate-drain capacitanceC_ gd, contributing to a high power-gain cutoff frequencyf_ MAXof 182 GHz and a high Johnson's figure of merit ofBV_ DS× f\,Tof6.43× 10^12~ V/ ssimultaneously. The accuracy of the RF performance is verified by a small signal modeling based on measured S-parameters.