Characterization of Unpassivated-Solution-Processed Zinc--Tin Oxide Thin Film Transistors

We have studied the bias stress and environment stability effects of transparent bottom-gate, bottom contact spin-coated zinc--tin oxide (ZTO) thin-film transistors (TFT). Various ratios of zinc to tin ($\text{Zn}:\text{Sn}= 2:1$, $1:1$, and $1:2$) were used for TFT fabrication. The linear mobilities of the TFTs with $\text{Zn}:\text{Sn}= 2:1$, $1:1$, and $1:2$ are 2.27, 6.77, and 0.44 cm 2 V -1 s -1 respectively. The on/off drain current ratio is $10^{8}$ for $\text{Zn}:\text{Sn}= 2:1$. However, the off-current increases by more than 5 orders in 7 days, which appears to be due to the adsorption of oxygen and water molecules. The TFTs are stable under negative bias stress for more than 10,000 s, but they show a large threshold shift under positive bias stress.