Investigation on the Doping Dependence of Solution-Processed Zinc Tin Oxide Thin Film and Thin-Film Transistors

Abstract

The effect of the tin (Sn) concentration in zinc tin oxide (ZTO) films fabricated using a spin-coating process and its effect on ZTO channel thin film transistors (TFTs) with various Sn concentrations were examined. Spin-coated ZTO films with various Sn concentrations were nanocrystalline and had high transmittance (>85%) in the visible region. As the Sn concentration increased, the carrier concentration and resistivity of the nanocrystalline ZTO (nc-ZTO) films ranged from 9.6 × 1014 cm−3 to 2.2 × 1016 cm−3 and from 1.5 × 103 Ω-cm to 1.6 × 102 Ω-cm, respectively. The nc-ZTO channel TFTs that were deposited as a function of Sn and Zn concentrations exhibited a subthreshold gate voltage swing (S) of 1.1–1.2 V decade−1, an on/off ratio of 105–106, a threshold voltage (Vth) of -0.8–1.7 V, and a μFE value of 2.4–2.6 cm2 V−1 s−1. The threshold voltage shift toward the negative gate bias as the Sn concentration in the nc-ZTO TFTs increased indicates the existence of sufficient charge carriers needed to form conductive channels.