High-fMAX high Johnson's figure-of-merit 0.2-μ m gate algan/gan HEMTs on silicon substrate with AlN}/SiNx passivation

This letter reports a 0.2-&mu ; m gate AlGaN/GaN high-electron-mobility transistors (HEMTs) on an Si substrate passivated with an AlN/SiNx (4/20 nm) stack layer. The 4-nm-thick AlN was grown by plasma-enhanced atomic-layer-deposition. The AlN/SiNx-passivated HEMTs exhibit a high maximum drain current of 930 mA/mm, an three-terminal OFF-state breakdown voltage BVDS of 119 V, and a small threshold voltage shift of 130 mV in a wide drain bias range VDS=3-24 V. Owing to the additional positive polarization charge in the AlN passivation layer, the access resistance Rs in the GaN-on-Si HEMTs is significantly reduced while maintaining small parasitic gate-drain capacitance Cgd, contributing to a high power-gain cutoff frequency fMAX of 182 GHz and a high Johnson's figure of merit of VDS× fT of 6.43\times 10 12 V/s simultaneously. The accuracy of the RF performance is verified by a small signal modeling based on measured S-parameters. © 2014 IEEE