Boron indium oxide (BIO) is studied for thin-film transistor (TFT) channel layer applications. Sputtered BIO thin films exhibit an amorphous phase over a wide range of B2O3/In2O3 ratios and remain amorphous up to 500 degrees C. The band gap decreases linearly with decreasing boron content, whereas device performance generally improves with decreasing boron content. The best amorphous BIO TFT exhibits a field-effect mobility of 10 cm(2) V-1 s(-1), turn-on voltage of 2.5 V, and sub-threshold swing of 0.72 V/dec. Decreasing the boron content to 12.5% leads to a polycrystalline phase, but further increases the mobility up to 20-40 cm(2) V-1 s(-1). TCAD simulation results suggest that the reason for higher performance after increasing the anneal temperature from 200 to 400 degrees C is due to a lower defect density in the subbandgap region of the BIO channel layer. (C) 2017 Elsevier Ltd. All rights reserved.