AlN/GaN/InGaN Coupling-Channel HEMTs for Improved gm and Gain Linearity

In this article, we report on the effective transconductance ( g
_m
) and gain linearity improvement of submicrometer gate AlN-barrier-based transistors using GaN/InGaN coupling-channel structures. The fabricated AlN/GaN/InGaN coupling-channel high electron mobility transistor (CC-HEMT) showed flat g
_m
profile, greatly reduced g
_m
derivatives, and constant dynamic source resistance compared with an AlN/GaN HEMT using the same fabrication process. The highest extrinsic current gain cutoff frequency ( f
_T
) of 55 GHz and the maximum oscillation frequency ( f
_max
) of 80 GHz were obtained for 0.15- μm gate-length transistors, both of which remain constant values across wide input voltage ( V
_GS
) of 4 V. Moreover, a significant theoretical OIP3 value boost by 7.1 dB has been observed using the CC-HEMT as compared to the AlN/GaN HEMT. The superior linearity performance of the CC-HEMT can be attributed to the strong channel-to-channel coupling effect. The drain bias-dependence of g
_m
, f
_T
, and f
_max
versus V
_GS
profiles illustrate that the linearity characteristics of the CC-HEMT greatly improve with an increase in V
_DS
. These results demonstrate the AlN/GaN/InGaN material system as a viable platform for high frequency requiring high-linearity applications.