Double Gated a-InGaZnO TFT Properties Based on Quantitative Defect Analysis and Computational Modeling

The device characteristics of amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) were investigated using both single-gate (SG) and double-gate (DG) structures. The DG a-IGZO TFT demonstrated improved subthreshold swing (SS) and mobility compared to the SG structure. Moreover, in both positive and negative bias stresses (NBSs), the threshold voltage variation in the DG structure was significantly reduced. Quantitative analysis of activation energy and defect density indicated an increase in shallow-level defects and a decrease in deep-level defects within the DG structure. Additionally, based on quantitative defect measurements, the density of state (DOS) in a-IGZO was adjusted according to the structure, and the device properties and electric field distribution were simulated through TCAD. In the DG structure, the electric field was concentrated at both gates, resulting in an increase in bulk electric field intensity. Due to the increase in electric field, the average electron density within the channel in the DG structure increased by a factor of seven compared to the SG structure. This increase in electron density contributed to the enhancement of SS, mobility, and drive current. Additionally, there was a reduction in electron drift in the vertical direction within the channel, leading to an improvement in the stability of the device.