Breakdown Voltage Enhancement in ScAlN/GaN High-Electron-Mobility Transistors by High-k Bismuth Zinc Niobate Oxide

ScAlN/GaN dielectric superjunction high-electron-mobility transistors (HEMTs) with high-
${k}$
passivation layer Bi
_1.5
Zn
_1.0
Nb
_1.5
O
₇
(BZN) are demonstrated for enhancement of breakdown voltage. The BZN thin film deposited by RF magnetron sputtering has a dielectric constant of 192 after postdeposition annealing at 400 °C for 10 min. The HEMT with
${L}_{g} =200$
nm and
${L}_{\text {sd}} = 2.0\,\,\mu \text{m}$
has a maximum current density of 1.98 A/mm, a maximum transconductance of 0.52 S/mm, and a threshold voltage of
${V}_{\text {th}} = -3$
V. With the use of SiN/BZN/SiN sandwiched passivation layer, the average value of breakdown voltage is improved from 68.9 to 121.5 V, due to the reduction of the peak electrical field between the gate and the drain. The device has a cutoff frequency (
${f}_{T}{)}$
and maximum oscillation frequency (
${f}_{\text {max}}{)}$
of 59 and 69 GHz, respectively. Overall, the devices exhibit a significantly higher breakdown voltage with essentially the same
${f}_{T}$
and
${f}_{\text {max}}$
values. Pulse measurements suggest that SiN/BZN/SiN has a similar passivation effect in comparison with devices passivated by a SiN-only layer. This work demonstrates that high current and high breakdown voltage can be achieved simultaneously on semiconductor heterostructures with a high sheet charge density by integration of high-
${k}$
dielectrics.