Combined Effects of Light Illumination and Various Bottom Gate Length on the Instability of Via-Contact-Type Amorphous InGaZnO Thin-Film Transistors

Abstract

This paper utilizes electrical analyses and a study of physical mechanisms to investigate metal gate structure-dependent performance in amorphous InGaZnO (a-IGZO) thin-film transistors. The effects of different shielding areas between the IGZO layer and metal gate are investigated. In devices with shorter metal gate lengths, an abnormal rise in capacitance at the off-state in capacitance–voltage ( ${C}-{V}$ ) characteristic curves can be observed. This can be attributed to the stronger electric field induced by the edge of the metal gate under bias sweep when the metal gate length is shorter than the IGZO layer length. Light illumination measurements indicate a negative shift in threshold voltage and an increase in subthreshold-leakage current regardless of relative metal gate length. Moreover, negative threshold voltage shift becomes more severe with a more obvious hump in ${C}-{V}$ characteristic curves under back-light illumination of a shorter width device, a phenomenon which has been verified by simulation.