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

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 x 10(14) cm(-3) to 2.2 x 10(16) cm(-3) and from 1.5 x 10(3) Omega-cm to 1.6 x 10(2) Omega-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 10(5)-10(6), a threshold voltage (V-th) of -0.8-1.7 V, and a mu(FE) value of 2.4-2.6 cm(2) 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.