Suppressed Instability of a-IGZO Thin-Film Transistors Under Negative Bias Illumination Stress Using the Distributed Bragg Reflectors

Abstract

We suggest functional passivation layers in the form of a distributed Bragg reflector (DBR) composed of ZnS and LiF for transparent thin-film transistors (TFTs) to improve the stability under negative bias illumination stress (NBIS). The luminous transmittance of the DBR was 82.0% when the number of dyads was 3.5, and the thicknesses of ZnS and LiF were 42 and 85 nm, respectively. We applied the DBR to TFTs based on amorphous indium-gallium-zinc oxide without the degradation of electrical performance, such as the mobility, ON-OFF ratio, subthreshold swing, and V-ON. The luminous transmittance of the TFT with the DBR was measured as 71.6%. Delta V-ON of the TFT with the DBR was reduced to -1.119 V compared with that of the reference TFT, which is -3.261 V when a 1.25 MV/cm electric field was applied, and white light was illuminated during 3000 s. This confirms that the functional passivation layers suggested, in this paper, provide a solution to suppress the instability of TFTs in the NBIS and enhance the optical transmittance of transparent displays.