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Oxide semiconductors are promising semiconducting materials for next‐generation thin‐film transistors (TFTs). The role of the cations should be considered in the design of oxide semiconductors suitable for various applications. Ga has been widely used as a carrier suppressor in oxide semiconductors; however, research has recently been conducted to replace it with Al, which is cheaper and forms a stronger bond with O. Deposition using plasma‐enhanced atomic layer deposition (PEALD) is very useful for controlling the composition of the cations in an oxide semiconductor. In this study, an InAlZnO (IAZO) semiconductor was deposited using super‐cycle PEALD for the first time. Al2O3 (AO), AlZnO (AZO), and InAlO (IAO) as Al doping layers in IAZO are evaluated. Considering its electrical characteristics and stability, AZO is selected as the optimal Al doping layer. The IAZO thin film and TFT characteristics according to the Al doping method are examined through the role of the cations and H concentration. In addition, the Al concentration is controlled by adjusting the number of cycles in super‐cycle PEALD. As the Al concentration decreased, the mobility increased; however, the stability degraded significantly, which is induced by the increase in oxygen vacancies. Finally, the high‐Al IAZO system using AZO successfully showed overall excellent properties including mobility over 10 cm2 V−1 s, and outstanding stability under 0.1 V, which are greatly improved compared to previously reported IAZO TFTs. [ABSTRACT FROM AUTHOR]

We report the effect of a rapid thermal annealing process (RTP) on the electrical properties of an aluminum-doped indium zinc tin oxide (Al-IZTO) thin film transistor (TFT) with a back-channel etched (BCE) structure. First, the RTP temperatures were varied from 250 to 350 °C, and their effect on Al-IZTO TFT was investigated. The 250 °C RTP produced the best transfer characteristics (subthreshold swing = 0.11 V/dec, hysteresis = −0.25 V, and mobility = 26.42 cm2 V−1s−1), and as the temperature increased, the TFTs showed slightly degraded properties in hysteresis and subthreshold swing. Through the transmission line method (TLM), the channel shortening effect and contact properties according to the annealing temperature were studied. The reliability against a negative gate bias stress under illumination (NBIS) was also analyzed. At high RTP temperature (>300 °C), stability under NBIS was considerably improved, and the 350 °C RTP device showed turn-on voltage shift of −1.7 V. The microwave photoconductivity decay (μ-PCD) method revealed that the RTP effectively reduced shallow localized states, which enhanced the NBIS stability at high temperature. Finally, the RTP was compared with the conventional furnace process at the same temperature in terms of transfer characteristics and uniformity. Even with a much shorter process time for the RTP, Al-IZTO TFTs exhibited similar or better transfer properties and uniformity to or than the furnace annealing. [ABSTRACT FROM AUTHOR]

We report highly stable and high mobility aluminum-doped indium zinc tin oxide (AIZTO) thin-film transistor with field effect mobility larger than 30 cm2/Vs in the bottom gate, etch-stopper structure. The electrical instabilities against positive gate bias stress, negative gate bias stress, and negative gate bias under illumination stress are investigated.. [ABSTRACT FROM AUTHOR]

Abstract: We fabricated amorphous indium gallium zinc oxide thin film transistors (TFTs) in a top gate structure on a glass substrate. We investigated the effect of drain bias on the instability of the device. Although the device showed highly stable characteristics under both positive and negative gate bias stress, it showed significant degradation in the transfer characteristics under drain bias stress. The degradation phenomena are somewhat similar to those of negative gate bias illumination stress (NBIS). In the case of NBIS, degradation mechanisms have been confused between two kinds of illustrations, one of which is hole trapping in the gate insulator and the other is an increase of electron density in the active layer. Our experimental results revealed that the degradation mechanism of drain bias stress is closer to the latter mechanism of NBIS in amorphous oxide TFTs. [Copyright &y& Elsevier]

Abstract: We investigated the stability of amorphous InGaZnO (a-IGZO) thin film transistor (TFT) under pulsed gate bias stress with light illumination, and compared that with DC bias stress. In the case of DC gate bias stress, a-IGZO TFT showed considerable degradation only when the negative gate voltage was applied under light illumination. For the pulsed gate bias stress, we constructed a voltage square wave with a bi-level of −20V and 0V and also made variations in the time duration of −20V level in a cycle. Although the accumulated time duration of applying −20V in the pulsed gate bias stress was the same with that of DC −20V stress, the degradation was much reduced compared with DC bias stress. On the basis of the experimental results, we propose possible degradation mechanisms related with the role of subgap states. [Copyright &y& Elsevier]

Abstract: In this study, we investigated the electrical characteristics and the stability of amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) from the viewpoint of active layer composition. Active layers of TFTs were deposited by r.f. sputtering. Two kinds of sputtering targets, which have different compositional ratios of In:Ga:Zn, were used to make variations in the active layer composition. All the fabricated IGZO TFTs showed more excellent characteristics than conventional amorphous silicon TFTs. However, in accordance with the Ga content, IGZO TFTs showed somewhat different electrical characteristics in values such as the threshold voltage and the field effect mobility. The device stability was also dependent on the Ga content, but had trade-off relation with the electrical characteristics. [Copyright &y& Elsevier]