Millimeter-Wave Power AlGaN/GaN HEMT Using Surface Plasma Treatment of Access Region

Recess gate AlGaN/GaN millimeter-wave power high-electron-mobility transistors (HEMTs) with N
₂
O plasma treatment on access region have been fabricated. A thin oxide layer formed on the gate region leads to the gate leakage current at least three orders of magnitude lower than that of conventional recess gate HEMT, which results a ultralow off-state current of 9.4×10
^-7
mA/mm accompanied by an on/off ratio of over 10
⁸
, and a suppressed current collapse of about 4% due to a simultaneous plasma treatment on the gate-source and the gate-drain regions. The forward and the reverse gate-bias stress measurements show that the increment in gate current is within an order of magnitude, indicating an excellent stability of the thin oxide layer. The large signal measurement shows that the HEMT with SiN passivation can yield an output power density of 6 W/mm associated with a peak power-added efficiency (PAE) of 46.8% and a gain of 6.8 dB (V
_ds
= 25 V), and an output power density of 4.3 W/mm with a PAE of 59.4% and a gain of 6.6 dB (V
_ds
= 15 V), respectively, at 30 GHz. The small signal measurement shows that the HEMT without SiN passivation can yield f
_T
and f
_max
of 85 and 274 GHz, respectively.