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 200nm thick SiO₂ layer was used as a bottom-gate and a Au electrode with a 100nm thick SiO ₂ 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 (10⁵-10 ⁷) was at least one order of magnitude larger than that of the bottom-gate mode (10⁴-10⁶). Normalized transconductance, one of the key transistor parameters, was also drastically increased from 0.34νSνm^-1 for the bottom-gate to 2.4νSνm^-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.