Abstract

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 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text{th}}$ </tex-math></inline-formula> ) 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.

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