High mobility amorphous InSnO thin film transistors via low-temperature annealing

In this article, we fabricated amorphous InSnO thin film transistors (TFTs) with exceedingly high mobility and low thermal budget. The device is annealed only at a low temperature of 150 °C, a field-effect mobility (⁠$μFE$⁠) of 70.53 cm²/V s, a subthreshold swing of 0.25 V/decade, an on/off current ratio over 10⁸, and a reasonable threshold voltage shift under negative bias stress. The influence of thermal annealing on amorphous InSnO TFTs was investigated by systematically analyzing the crystallization, surface morphology, internal chemical state, and energy band relationship of the InSnO thin film. Amorphous InSnO films deposited at room temperature have a sparse and porous loose structure, which has carrier scattering caused by poor film quality, resulting in low mobility and few free carriers in the film. With the increase in the annealing temperature, the In and Sn metal cations are further oxidized, increasing the carrier concentration in the film and forming a dense M–O–M network when annealed at 150 °C. With the further increase in the annealing temperature, a large number of thermally excited free electrons make the device appear metal like conductivity. This paper expands the research on a high electron concentration InSnO material as the active layer and promotes the development of amorphous oxide semiconductors in high mobility and flexible TFTs.