Parabolic behavior of solution processed ZnSnO device performances depending on Zn/Sn ratios

Thin film transistors (TFTs) with amorphous zinc tin oxide (ZTO) channel layer were fabricated by a simple and low-cost solution process, prepared by dissolving 0.2 M of zinc acetate dihydrate and tin chloride dihydrate in 20 mL of 2-methoxyethanol. All ZTO thin films showed amorphous phases and no impurities (no carbon and chlorine content) even at process temperature of 350 °C. As the Sn ratio in ZTO films increased, the values of saturated mobility (u_sat) and subthreshold gate swing (SS) exhibited a parabolic behavior in ZTO TFTs, depicting that the μ_sat and SS values were a maximum (3.4 cm²/V.s) and minimum (0.38 V/decade) at Zn/Sn∈=∈1 ratio. Interestingly, the x-ray absorption and X-ray photoemission spectroscopy revealed the origin of parabolic behavior, indicating not only to improve a charge transport in conduction bands but also to increase the Sn⁴⁺/Sn²⁺ ratio at the peak values (Sn/(Zn∈+∈Sn)∈=∈1).