We investigated the visible photon accelerated negative bias instability (NBI) in amorphous In–Ga–Zn–O (a-IGZO) thin film transistor (TFT). As reported in previous works, the rigid shift in transfer curves with insignificant changes in field-effect mobility and subthreshold swing was observed. On the other hand, there is substantial change in capacitance-voltage characteristics caused by created subgap states. The suggested nature of created states is the ionized oxygen vacancy (VO2+) by the combination of visible light and negative bias. The generated VO2+ states enhance the NBI under illumination as increased deep hole trapping centers. Furthermore, the photoexcitation of VO to stable VO2+ yields excess free carriers in conduction band. The increased carrier density also enhances the negative shift in turn-on voltage of a-IGZO TFT.

The gate bias dependence on the negative bias instability under illumination was examined. As the gate bias got more negative, dominant mechanism was changed from simple charge trapping to that accompanied by generation of subgap states. Degree of threshold voltage shift was not monotonously dependent on the magnitude of negative gate bias. It is strongly related with the corresponding instability modes for different gate bias regimes. The transition of instability mechanism depends on how much the gate bias stabilizes ionized oxygen vacancy states.

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Stoichiometric crystalline binary metal oxide thin films can be used as channel materials for transparent thin film transistors. However, the nature of the process used to fabricate these films causes most binary metal oxide thin films to be highly conductive, making them unsuitable for channel materials. We overcame this hurdle by forming stoichiometric ultra-thin (5 nm) crystalline In2O3 films by using a thermal atomic layer deposition method. Specifically, (3-(dimethylamino)propyl)dimethylindium was used as a liquid precursor and ozone as an oxygen source to grow In2O3 thin films at a high growth rate of 0.06 nm/cycle. Adjustment of the deposition processing temperature followed by annealing in an oxygen atmosphere enabled us to fully crystallize the film into a cubic bixbyite structure with the retained stoichiometry. The transparent crystalline ultra-thin In2O3-based bottom-gate thin film transistors showed excellent and statistically uniform switching characteristics such as a high Ion/Ioff ratio exceeding 107, a high linear mobility of 41.8 cm2/V s, a small subthreshold swing of 100 mV/dec, and a low hysteresis of 0.05 V. Our approach offers a straightforward scheme, which is compatible with oxide electronics, for fabricating a transparent metal oxide device without resorting to complicated oxide compositional strategies.

Organic-inorganic hybrid-type nonvolatile memory thin-film transistors using an organic ferroelectric gate insulator and an oxide semiconducting active channel are a very promising solution to the memory devices having both features of low-cost and high-performance, which are embeddable into the next-generation flexible and transparent electronics. In this paper, we discuss some important issues for this proposed device, such as device structure design, process optimization and memory array integration. Promising feasible applications and remaining technology issues to solve were also discussed.