Highly Stable, Crystalline InGaO Thin-Film Transistors by 7% Lanthanum Incorporation

The development of high-mobility metal oxide semiconductor (MOS) thin-film transistors (TFTs) is of increasing interest. It is well-known that increasing the indium (In) concentration in MOS enhances the crystal volume fraction and mobility. However, the high carrier concentration resulting from a high In content induces TFT depletion mode and degrades device stability. Here, we introduce the incorporation of lanthanum (La) cation into the high-In-containing indium-gallium oxide (InGaO) films grown by spray pyrolysis at a substrate temperature of 375 °C. As the La ratio increases from 3 to 20%, La-incorporated InGaO (LaInGaO) experiences an elevation in both mass density and optical bandgap, but its crystallinity degrades. The coplanar LaInGaO TFTs, optimized with a La ratio of 7%, exhibit an average threshold voltage (V_TH) of 0.01 V, field-effect mobility of 30.63 cm² V^-1 s^-1, and a subthreshold swing of 0.23 V dec^-1. Moreover, compared to pristine InGaO TFTs, the bias temperature and photostability of 7% LaInGaO TFTs have been enhanced, resulting in shifts of V_TH under positive and negative bias temperature stresses, as well as negative illumination bias stress conditions by 0.2, 0.1, and -1.6 V, respectively. Additionally, the gate driver circuit employing 7% LaInGaO TFTs demonstrates fast rising and falling times of 437.3 and 557.9 ns, respectively. Therefore, the highly reliable 7% LaInGaO TFTs grown by spray pyrolysis can be utilized for large-area, cost-effective TFT electronics.