Investigation of the Effect of Different SiN_x Thicknesses on the Characteristics of AlGaN/GaN High-Electron-Mobility Transistors in Ka-Band

The effect of different SiN_x thicknesses on the performance of AlGaN/GaN high-electron-mobility transistors (HEMTs) was investigated in this paper. The current, transconductance (G_m), cut-off frequency (f_T), maximum oscillation frequency (f_max), power performance, and output third-order intercept point (OIP3) of devices with three different SiN_x thicknesses (150 nm, 200 nm, and 250 nm) were measured and analyzed. The DC measurements revealed an increase in both the drain-source current (I_DS) and G_m values of the device with increasing SiN_x thickness. The S-parameter measurement results show that devices with a higher SiN_x thickness exhibit improved f_T and f_max. Regarding power performance, thicker SiN_x devices also improve the output power density (P_out) and power-added efficiency (PAE) in the Ka-band. In addition, the two-tone measurement results at 28 GHz show that the OIP3 increased from 35.60 dBm to 40.87 dBm as the SiN_x thickness increased from 150 nm to 250 nm. The device’s characteristics improved by appropriately increasing the SiN_x thickness.