Research on Graded Channel AlGaN/GaN MISHEMT for High Linearity Applications

In order to achieve high linearity operation of $\mathbf{G a N}$ based power amplifiers, this paper designed the graded channel AlGaN/GaN MISHEMT with the gate length of $0.2 \mu \mathrm{~m}$ and $\mathbf{6 n m}$ Al2 O3 gate dielectric based on the Silvaco TCAD tool. The designed graded MISHEMT exhibited flat transconductance ($g_{m}$) profile, which increases the gate voltage swing (GVS) of the device from 3.5 V to 6.3 V compared to the HEMT with conventional channel structure, reduced $g_{m}$ derivatives and demonstrated nearly steady current gain cutoff frequency $f_{T}$ and maximum oscillation frequency $f_{\text {max }}$ as a function of gate voltage. The Al composition in the designed graded channel MISHEMT linearly graded from upward to downward of the device, inducing threedimensional charge distribution (3DEG). Combined with Al2 O3 gate dielectric, it suppressed $g_{m}$ roll off while expanded the gate bias range of the device. The $f_{\mathrm{T}}$ and $f_{\text {max }}$ of the Graded-MISHEMT are $\mathbf{3 4. 1} \mathrm{GHz}$ and 65.9 GHz at the gate voltage $V_{G S}=0.7 \mathrm{~V}$, respectively. While the Graded-MISHEMT can obtain flatter frequency-gate voltage profile in a wide gate voltage range. These results indicated the great potential of the graded channel MISHEMT for high linearity amplifier applications.