High RF performance improvement using surface passivation technique of AlGaN/GaN HEMTs at K‐band application

A surface passivation technique of high electron mobility transistor (HEMT) devices is reported. The passivated HEMT device has a much higher RF performance of F T and F max than a non‐passivated one. The AlGaN/GaN HEMT has a short gate length of 0.15 µm using an E‐beam lithography system and very low ohmic contact resistance of 1.3 × 10 −6 Ωcm −2 using a rapid thermal processing alloy system. In addition, to protect the active layer from the surface trap, an SiO 2 thin film passivation process is applied by the plasma‐enhanced chemical vapour deposition system. The fabricated AlGaN/GaN HEMT exhibits a maximum drain current of 900 mA/mm and a maximum transconductance of 320 mS/mm. In particular, this device produces excellent RF performance of small‐signal characteristics, such as a current gain cut‐off frequency ( f T ) of 55 GHz and maximum oscillation frequencies ( f max ) of 130 GHz.