Effect of surface passivation on the electrical performance of AlGaN/GaN high-electron-mobility transistors with slant field plates fabricated using deep-UV lithography

AlGaN/GaN high-electron-mobility transistors (HEMTs) have been extensively applied for high power applications at high frequencies. To further improve the device performance, field plates and passivation layers are commonly integrated with the device technology. This paper is to investigate the effects of surface passivation thickness on the electrical performance of AlGaN/GaN HEMTs with slant field plates fabricated using deep-UV technology. As a benchmark, the device without nitride passivation exhibited a peak transconductance of 214 mS/mm and a breakdown voltage of 122 V with an output power of 5.0 W/mm at 8 GHz. For the passivated devices, it is observed that the existence of the silicon nitride passivation layer helps to improve the DC characteristics of the devices in terms of the lower drain current collapse, higher maximum DC transconductance, and higher maximum drain current. RF wise, the devices with passivation suffer from lower f_T and f_MAX due to the increase in the gate capacitances. However, an improvement of RF output power was observed for devices with passivation layer thickness up to 300 nm.