Room temperature fabricated high performance IAZO thin film transistors with dual-active-layer structure and sputtered Ta2O5 gate insulator

The room temperature fabrication of amorphous oxide semiconductor thin film transistors (TFTs) is essential for their applications in flexible electronics due to the low glass-transition temperatures of flexible substrates. High performance In-Al-Zn-O (IAZO) TFTs with a homogeneous dual-active-layer structure are successfully fabricated at room temperature. The electrical properties including bias and illumination stabilities of the as-fabricated devices are investigated. The sputtered bilayer IAZO films are firstly prepared on SiO2/p+-Si substrates with different bottom (low-oxygen)/top (high-oxygen) layer thicknesses. When the thicknesses of the bottom/top layers are 20/10 nm, IAZO TFT exhibits the best overall performance and highest negative-bias-illumination stability, including a high saturation-mobility (12.05 cm2 V−1 s−1) and a small threshold-voltage-shift (− 0.73 V). Then, in order to reduce the operating-voltage and meet the requirements of low temperature fabrication for flexible IAZO TFTs, a 70-nm-thick room-temperature-sputtered Ta2O5 film is employed to be the gate insulator. The performance of IAZO TFTs with Ta2O5 is greatly improved, especially the saturation-mobility (19.56 cm2 V−1 s−1) and subthreshold-swing (81 mV dec−1). They also exhibit outstanding bias and illumination stabilities as compared to the IAZO TFTs using SiO2. The largest threshold-voltage-shifts under positive-bias-illumination (5 V) and laser-illumination (450 nm) stresses are only − 0.78 and 0.05 V, respectively.