Fluorine-controlled subgap states and negative bias illumination stability behavior in solution-processed InZnOF thin-film transistor

Abstract

The subgap density of states (DOS) in amorphous oxide semiconductor has strong influence on the stability of thin-film transistors (TFTs). Generally, the reduction in DOS is at the expense of the mobility of metal oxide TFTs. To solve the issue, a strategy of fluorine anion doping is proposed to control the subgap state of metal oxide. Using the strategy, the field-effect mobility and negative bias illumination stress (NBIS) stability of metal oxide TFTs are simultaneously improved. Solution-processed InZnOF-TFTs with AlZrOx gate insulator are fabricated. Extraction of DOS in InZnOF-TFTs is performed by measuring temperature-dependent electrical characteristics. The suppression behavior of oxygen vacancies by fluorine doping for InZnOF thin films is also investigated by XPS spectra. The subgap DOS and the oxygen vacancies of InZnOF films are significantly reduced by substituting O with F anion. Compared with the conventional InZnO thin-film transistor, the field-effect mobility of InZnOF-TFT is enhanced from 7.9 to 13.4 cm2/V s, while the threshold voltage shift is reduced from − 4.02 to − 1.81 V under the identical NBIS conditions. It implies a crucial role of F anion doping in improving the NBIS stability of metal oxide TFTs.