Mobility Enhancement and Reliability Characterization of Back-Channel-Etch Amorphous InGaZnO TFT with Double Layers

The double layer (DL) TFT consists of an IGZO channel layer with no oxygen flow (NOF) and an IGZO barrier layer with oxygen flow (OF). The DL-TFT demonstrates the field-effect mobility of 19 cm2/V-s, which is 1.6X of the NOF and the OF singe-layer TFTs (SL-TFTs) at the overdrive voltage of 18V and the drain voltage of 0.1V. The conduction band difference between NOF and OF IGZO is 0.28 eV, which was obtained by Tauc method, X-Ray photoelectron spectroscopy (XPS), and Kevin probe force microscopy (KPFM). The carriers in the DL-TFT are confined in the NOF layer by quantum confinement, where the OF layer serves as the barrier to reduce the Coulomb scattering between the channel electrons and oxide charge, and the surface roughness scattering from the IGZO/oxide interface. The results of positive bias temperature instability (PBTI) show that the threshold voltage shift of the DL-TFT is between the individual SL-TFT, and the DL-TFT is close to the lower one of the two SL-TFTs.