Self-Compensation Effect of Photo-Bias Instabilities in a-InGaZnO Thin-Film Transistors Induced by Unique Ion Migration

The a-InGaZnO (a-IGZO) thin-film transistors (TFTs) in elevated-metal metal-oxide (EMMO) architecture was found to exhibit high stability against photo-bias stresses. In contrast to the common photo-enhanced degradation, an abnormal self-compensation effect of photo-bias instabilities was first observed for amorphous oxide semiconductor (AOS) TFTs. By analyzing the defect states and element distributions in both channel and source/drain (S/D) regions, the unique migration of thermally generated metal interstitials in a-IGZO S/D was clarified to be the origin. More specifically, the positive bias stress (PBS)-induced negative shift of threshold voltage (
${V}_{\text{th}}$
) originates from the ionization of positive metal ions near the backchannel, while these positively charged ions can be compensated by the illumination-excited electrons, resulting in photo-stable AOS TFTs. This also provides a flexible way to implement the electrically stable depletion-mode AOS TFTs.