Subthreshold Characteristics of AlGaN/GaN MIS-FinFETs with Controlling Threshold Voltages

Abstract

AlGaN/GaN metal-insulator-semiconductor field-effect transistors with fin structures (AlGaN/GaN MIS-FinFETs) were fabricated and characterized by changing fin width and using different dielectric layers. The FinFET with 20 nm-thick SiO2 dielectric layer exhibits a very small subthreshold swing (SS) of 56 mV/decade. However, the threshold voltage of the device is too low to ensure low off-state leakage current (at the gate voltage of 0 V), even though the fin width of the device is reduced to 30 nm, which would not meet the requirement for low standby power consumption. On the other hand, the FinFET with a 10 nm-thick Al2O3 dielectric layer and a much wider fin width of 100 nm shows normally-off operation with a threshold voltage of 0.8 V, SS of 63 mV/dec, and very low off-state current of 1 nA/mm. When the fin width is reduced to 40 nm, the threshold voltage of the FinFET is increased to 2.3 V and the SS is decreased to 52 mV/decade. These excellent switching performances convince us that the FinFETs might be promising either for low voltage logic or for efficient power switching applications. The observed SS values, which are smaller than the theoretical Boltzmann limit (60 mV/decade), can be explained by the concept of the voltage-dependent effective channel width.