AlN/GaN/InGaN Coupling-Channel HEMTs for Improved g m 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 ( ${f}_{\text {max}}$ ) of 80 GHz were obtained for 0.15- $\mu \text{m}$ gate-length transistors, both of which remain constant values across wide input voltage ( ${V}_{\text {GS}}$ ) 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 ${f}_{\text {max}}$ versus ${V}_{\text {GS}}$ profiles illustrate that the linearity characteristics of the CC-HEMT greatly improve with an increase in ${V}_{\text {DS}}$ . These results demonstrate the AlN/GaN/InGaN material system as a viable platform for high frequency requiring high-linearity applications.