The Stability of Oxide TFTs under Electrical Gate Bias and Monochromatic Light Illumination

Abstract

We have investigated a stability of oxide TFTs (IGZO) under electrical bias and monochromatic light illumination. Under -20 V gate bias, when 650 nm monochromatic illumination with intensity of 1 mW/cm 2 was radiated, threshold voltage (V th ) was shifted by about -1.55 V while V th was almost constant without illumination. Even though the photon energy of 650 nm is much smaller than optical band gap of oxide active layer (E opt~3 .0 eV), V th was changed due to generation of carriers through localized state. However, under positive gate bias of 20 V, V th was not changed with and without 650 nm light illumination. In terms of 300 nm wavelength light, V th was shifted positively under negative bias stress and negatively under positive bias stress. It is considered that light affected not only the active layer but also the gate insulator layer.

Role of Oxygen in Amorphous In-Ga-Zn-O Thin Film Transistor for Ambient Stability

“…Light irradiation with wavelengths ranging from 300 nm to 600 nm was used to illuminate the a-IGZO TFT, whose optical bandgap is about 3.2 eV, and sensitive to wavelengths below 400 nm. 15,24 slight change under visible-light illumination, while it decreases apparently under 350-nm UV light illumination. a-IGZO TFT devices with high annealing temperature had less V th shifts than those with lower annealing temperature under UV light illumination.…”