Current status and future challenge of oxide semiconductors

This paper describes my personal view on several hot issues in oxide semiconductors for AM-FPD applications. Topics to be discussed are origin and mechanism for negative bias illumination stress (NBIS) instability of a-IGZO-TFTs, impurity effects, down-sized TFTs and bipolar oxide TFTs. I propose a model for explaining the origin, depth distribution of the large subgap state density above the conduction band maximum. Importance of oxide semiconductors with a small indirect gap is addresses to realize c-MOS based on the band alignment of SnO which was demonstrated to operate as a bipolar TFT.