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.
Highlights
AlGaN/GaN-based high electron mobility transistors (HEMTs) are very promising for high power and high-frequency applications due to their wide bandgap, large critical electric field, and high saturation velocity [1,2,3,4]
AlGaN/GaN metal-insulator-semiconductor field-effect transistors with fin structures (MIS-FinFETs) have been widely investigated to achieve better gate controllability and higher device linearity, compared with conventional planar HEMTs, which results in a great reduction of off-state leakage current (IOFF ), suppression of drain induced barrier lowering (DIBL), and improvement of subthreshold swing (SS) [5,6,7,8,9,10]
It is worth noting that the threshold voltage (VTH ) of the MIS-FinFET increases as the fin width (Wfin ) decreases due to the lateral depletion of 2-dimensional electron gas (2DEG) channel by sidewall gate and eventually the device can show a normally-off operation when the Wfin is reduced to a few tenths of a nanometer [11,12], without adapting additional process methods, such as recessed gate, P-GaN gate, thin AlGaN barrier layer, and cascode structure, usually applied to conventional planar HEMTs [13,14,15,16]
Summary
AlGaN/GaN-based high electron mobility transistors (HEMTs) are very promising for high power and high-frequency applications due to their wide bandgap, large critical electric field, and high saturation velocity [1,2,3,4]. Our previous work demonstrated that AlGaN/GaN MIS-FinFETs with Wfin of around 30 nm can show normally-off operation, and extremely low IOFF as well as small SS (smaller than theoretical Boltzmann limit of < 60 mV/decade) [17]. (12 off-angle to m-plane), were characterized for the same purpose
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