Amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) invented only one decade ago are now being commercialized for active-matrix liquid crystal display (AMLCD) backplane applications. They also appear to be well positioned for other flatpanel display applications such as active-matrix organic light-emitting diode (AMOLED) applications, electrophoretic displays, and transparent displays. The objectives of this contribution are to overview AOS materials design; assess indium gallium zinc oxide (IGZO) TFTs for AMLCD and AMOLED applications; identify several technical topics meriting future scrutiny before they can be confidently relied upon as providing a solid scientific foundation for underpinning AOS TFT technology; and briefly speculate on the future of AOS TFTs for display and non-display applications. Keywords-Oxide electronics, amorphous oxide semiconductor (AOS), thin-film transistor (TFT), flat-panel displays, indium gallium zinc oxide (IGZO), active-matrix liquid crystal display (AMLCD), active-matrix organic light-emitting diode (AMOLED)

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We report on the development of low‐temperature gate dielectric materials for zinc indium oxide (ZIO) thin‐film transistors (TFTs). Several films, including ALD HfO2 and PECVD SiNx (deposited at 175°C and 150°C, respectively), yield good TFT performance. Bias stress‐induced threshold shift for HfO2 is quite small, however does not follow conventional trends associated with hydrogenated amorphous Si (a‐Si:H) TFTs; PECVD SiNx conversely, shows bias stress characteristics that conform reasonably to a model appropriate for a‐Si:H devices.

An indium–gallium–zinc oxide or a zinc–tin oxide thin‐film transistor (TFT) fabricated when the relative humidity in the laboratory is less than 50% is found to exhibit good electrical performance, with an abrupt, distortion‐free transfer curve and a turn‐on voltage close to 0 V. In contrast, when such an amorphous oxide semiconductor (AOS) TFT is fabricated at a relative humidity greater than 50%, its “as‐fabricated” electrical performance is very poor, typically characterized by a large amount of hysteresis, a strongly negative turn‐on voltage, and a kink‐like distortion in the subthreshold region of its transfer curve. However, the electrical performance of such a poor‐quality TFT is observed to improve over time, if it is simply stored in the dark at room temperature without being subjected to electrical stress. This recovery usually requires weeks (months) for an unpassivated (passivated) AOS TFT. Recovery is tentatively ascribed to the gradual removal of moisture from the AOS TFT channel layer.

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