Thin-film transistors (TFTs) were fabricated using amorphous indium gallium zinc oxide (a-IGZO) channels by rf-magnetron sputtering at room temperature. The conductivity of the a-IGZO films was controlled from ∼10−3to10−6Scm−1 by varying the mixing ratio of sputtering gases, O2∕(O2+Ar), from ∼3.1% to 3.7%. The top-gate-type TFTs operated in n-type enhancement mode with a field-effect mobility of 12cm2V−1s−1, an on-off current ratio of ∼108, and a subthreshold gate voltage swing of 0.2Vdecade−1. It is demonstrated that a-IGZO is an appropriate semiconductor material to produce high-mobility TFTs at low temperatures applicable to flexible substrates by a production-compatible means.

High-performance and excellent-uniformity thin-film transistors (TFTs) having bottom-gate structures are fabricated using an amorphous indium-gallium-zinc-oxide (IGZO) film and an amorphous-silicon dioxide film as the channel layer and the gate insulator layer, respectively. All of the 94 TFTs fabricated with an area 1 cm 2 show almost identical transfer characteristics: the average saturation mobility is 14.6 cm 2 /(V-sec) with a small standard deviation of 0.11 cm 2 /(V-sec). A five-stage ring-oscillator composed of these TFTs operates at 410 kHz at an input voltage of 18 V. Pixel-driving circuits based on these TFTs are also fabricated with organic light-emitting diodes (OLED) which are monolithically integrated on the same substrate. It is demonstrated that light emission from the OLED cells can be switched and modulated by a 120-Hz ac signal input. Amorphous-IGZO-based TFTs are prominent candidates for building blocks of large-area OLED-display electronics.

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Five-stage ring oscillators (ROs) composed of amorphous In/Ga/Zn/O (a-IGZO) channel thin-film transistors (TFTs) with the channel lengths of 10 µm were fabricated on a glass substrate. The a-IGZO layer was deposited by RF magnetron sputtering onto the unheated substrate. The RO operated at 410 kHz (the propagation delay of 0.24 µs/stage), when supplied with an external voltage of +18 V. This is the fastest integrated circuit based on oxide-semiconductor channel TFTs to date that operates faster than the ROs using conventional hydrogenated amorphous silicon TFTs and organic TFTs.

We review the features of amorphous In‐Ga‐Zn‐O (a‐IGZO) thin‐film transistors (TFTs), as well as circuit operation based on these TFTs. We also report a novel TFT structure which improves environmental stability of the TFT operation by taking full advantage of the a‐IGZO properties, where a conventional PECVD a‐SiNX:H films serve not only as an effective barrier layer but also as a hydrogen source to form the coplanar source and drain.