Normally-Off GaN Power Device Based on Stack AlGaN Barrier Structure and P-Type NiO Gate Electrode

In this study, we propose a novel normally-off AlGaN/GaN HFET based on stack AlGaN barrier structure and p-type NiO gate. The residual thin AlGaN barrier (with low Al content) is adopted to alleviate mobility degradation. Besides, p-type conductive NiO formed by thermal oxidation at 500 °C was used as gate electrode, which contribute to the positive shift of threshold voltage. Combining NiO gate and thin barrier structure, normally-off device with a threshold voltage of +1.1 V is realized. Temperature dependent transfer characteristics show that the normally-off device presents good thermally stability within the temperature range from 25 to 150 °C.

Investigation of AlGaN/GaN HFET and VO2 Thin Film Based Deflection Transducers Embedded in GaN Microcantilevers

The static and dynamic deflection transducing performances of piezotransistive AlGaN/GaN heterojunction field effect transistors (HFET) and piezoresistive VO2 thin films, fabricated on GaN microcantilevers of similar dimensions, were investigated. Deflection sensitivities were tuned with the gate bias and operating temperature for embedded AlGaN/GaN HFET and VO2 thin film transducers, respectively. The GaN microcantilevers were excited with a piezoactuator in their linear and nonlinear oscillation regions of the fundamental oscillatory mode. In the linear regime, the maximum deflection sensitivity of piezotransistive AlGaN/GaN HFET reached up to a 0.5% change in applied drain voltage, while the responsivity of the piezoresistive VO2 thin film based deflection transducer reached a maximum value of 0.36% change in applied drain current. The effects of the gate bias and the operation temperature on nonlinear behaviors of the microcantilevers were also experimentally examined. Static deflection sensitivity measurements demonstrated a large change of 16% in drain-source resistance of the AlGaN/GaN HFET, and a similarly high 11% change in drain-source resistance in the VO2 thin film, corresponding to a 10 μm downward step bending of the cantilever free end.