Top-down ZnO nanowire field effect transistors for logic circuit applications

Abstract

ZnO nanowire transistors have shown a great potential in gas and chemical sensing, high power IC, short wavelength photodetector and light emitting applications. This is due to ZnO excellent semiconducting properties of high bulk mobility, large bandgap of 3.4eV and optical transparency from visible to mid-infra red spectrum. There are two approaches to realise ZnO nanowires; bottom-up and top-down. Bottom-up fabricated ZnO nanowire transistors exhibit a high mobility > 1000 cm2/V.s and large output drain current but device electrical performance is difficult to reproduce due to size variation and material quality. Therefore, a top-down fabrication approach is an attractive option since nanowire properties and size can be controlled by process parameters. In this work, we propose a top-down fabrication approach to produce nanowires using a combined photolithography, atomic layer deposition and anisotropic plasma etching technology. ZnO nanowires were fabricated on 150mm diameter SiO2-Si wafer with a dimension of 40nm x 38nm. The nanowires are made into field-effect transistors with a channel length from 1.3um to 18.6µm to study channel scaling. Preliminary electrical measurements give field-effect mobility of 0.5 cm2/V.s to 3 cm2/V.s and Ion/Ioff of 2×106. We anticipate mobility improvement by 3 times through passivation of the nanowire surface thanks to reduction of donor and surface traps with potential for logic circuits in display applications