Fabrication and electrical characteristics of dual-gate ZnO nanorod metal-oxide semiconductor field-effect transistors

We fabricated dual-gate ZnO nanorod metal - oxide semiconductor field-effect transistors(MOSFETs) where a Si substrate with a 200 nm thick SiO2 layer was used as a bottom-gate and a Au electrode with a 100 nm thick SiO2 layer was used as a top-gate. From current - voltage characteristic curves of the nanorod MOSFETs, the top-gate mode operation exhibited significantly enhanced device characteristics compared with the bottom-gate case. A switch current ON/OFF ratio of the top-gate mode (10(5) - 10(7)) was at least one order of magnitude larger than that of the bottom-gate mode (10(4) - 10(6)). Normalized transconductance, one of the key transistor parameters, was also drastically increased from 0.34 mu S mu m(-1) for the bottom-gate to 2.4 mu S mu m(-1) for the top-gate mode. The enhanced device performance can be explained in terms of geometric field enhancement and the resulting efficient gating effect for the top-gate mode geometry.