Light illumination stability of amorphous InGaZnO thin film transistors with sputtered AlO<i>_x</i>passivation in various thicknesses

Abstract

Light illumination stability of amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) passivated by sputtered AlOx thin films were investigated in this paper. Light wavelength and passivation-layer thickness were intentionally controlled to ascertain the related two physical mechanisms, i.e., electron–hole pair (EHP) generation and oxygen vacancy (VO) formation. A qualitative model was proposed to effectively compare and distinguish the above two mechanisms in thermal stability of a-IGZO TFTs with passivation layers. With light wavelength decreasing EHP generation became evident where the "threshold wavelength" was between 420 and 400 nm for the a-IGZO TFTs used in this study. Meanwhile, passivation-layer could significantly improve the stability of a-IGZO TFTs under long-wavelength light illumination by suppressing the escape of oxygen atoms to form VO in a-IGZO films. The "threshold thickness" of AlOx passivation-layer in our devices was estimated to be about 90 nm.