All-sputtered, flexible, bottom-gate IGZO/Al2O3 bi-layer thin film transistors on PEN fabricated by a fully room temperature process

Abstract

In this work, an innovative all-sputtered bottom-gate thin film transistor (TFT) using an amorphous InGaZnO (IGZO)/Al₂O₃ bi-layer channel was fabricated by fully room temperature processes on a flexible PEN substrate. A bi-layer channel consisting of 10 nm-thick IGZO and 3 nm-thick Al₂O₃ was clearly observed in high resolution TEM images. The chemical structure of IGZO was dependent on different sputtering modes (pulse-DC/DC/RF), which were investigated by XPS measurements. The ultrathin Al₂O₃ layer on IGZO showed a significant effect on enhancing the mobility, reducing the off-state current, and improving the gate-bias stability. As a result, the IGZO/Al₂O₃ bi-layer TFT eventually exhibited a saturation mobility of 18.5 cm² V⁻¹ s⁻¹, an I_on/I_off ratio of 10⁷, an on-state voltage of 1.5 V and a subthreshold swing of 0.27 V decade⁻¹, as well as good stability under NBS/PBS and bending strain. The fabrication of this TFT can be suitably transferred to large-size arrays or paper-like substrates, which is in line with the trend of display development.