In this letter, we investigate the impact of the light illumination on the stability of indium–gallium–zinc oxide thin film transistors under positive gate-bias stress. The noticeable decrease in threshold voltage (Vt) shift more than 5.5 V under illuminated positive gate-bias stress indicates a superior reliability in contrast with the dark stress. The accelerated Vt recovery characteristic compared with dark recovery demonstrates that the charge detrapping effect was enhanced under illumination. Furthermore, the average effective energy barrier of charge trapping and detrapping was derived to verify that illumination can excite the trapped charges and accelerate the charge detrapping process.

This letter investigates the degradation mechanism of amorphous indium-gallium-zinc oxide thin-film transistors under gate-bias stress. The larger Vt shift under positive AC gate-bias stress when compared to DC operation indicates that an extra electron trapping mechanism occurs during rising/falling time during the AC pulse period. In contrast, the degradation behavior under illuminated negative gate-bias stress exhibits the opposite degradation tendency. Since electron and hole trapping are the dominant degradation mechanisms under positive and illuminated negative gate-bias stress, respectively, the different degradation tendencies under AC/DC operation can be attributed to the different trapping efficiency of electrons and holes.

This paper investigates the illuminated behaviors of InGaZnO thin film transistors with and without a SiO x passivation. For the passivated device, more interface states were generated during SiO x passivation layer deposition by plasma-enhanced-chemical-vapor-deposition. The enhanced trap-assisted photoexcited hole generation induces source side barrier lowering and causes an apparent subthreshold stretch-out phenomenon. However, for the unpassivated device, the fact that the threshold voltage shift in ambient oxygen is lower than in vacuum under light illumination suggests oxygen desorption and readsorption occurs simultaneously, which is consistent with the accelerated recovery rate in oxygen ambiance.Transparent oxide-based thin-film transistors ͑TFTs͒, such as amorphous InGaZnO ͑a-IGZO͒ TFTs, have considerable potential for their possible applications in flat, flexible, and transparent display devices because they offer high mobility, excellent uniformity, good transparency in visible light, and applicability for low-temperature process. 1-4 Although oxide-based TFTs have shown high performance, they have also demonstrated limitations such as instability under light illumination and in different ambient gas. Since most of the proposed uses of the a-IGZO TFT will expose the TFT to a backlight or ambient light during operation, it is necessary to investigate the electrical properties under light illumination and prevent the gas adsorption/desorption onto the exposed back channel layer. 5,6 Recently, many studies have discussed the behavior of ZnO based TFTs under light illumination and illuminated gate bias stress; 7,8 in addition, a passivation layer such as SiO x has been reported to exhibit a good resistance to ambient gas. 9 However, the impact of the SiO x passivation layer for light illumination has not been thoroughly studied, and is worthy of further investigation. In this letter, we investigate the instability under light illumination and discuss the illuminated mechanism for devices with and without a SiO x passivation layer formed by plasmaenhanced-chemical-vapor-deposition ͑PECVD͒. The experiment results suggest different mechanisms occur during illumination for the passivated and unpassivated devices. Furthermore, the illumination behavior of the unpassivated device was examined in vacuum and in O 2 ambiance to analyze the illuminated mechanism.Inverted coplanar a-IGZO TFTs were produced on glass substrate in this work. Briefly, the shaped Ti/Al/Ti ͑50/ 200/50 nm͒ gate electrodes were capped with 300-nm-thick SiO x gate dielectric. The source/drain electrodes were formed with dc-sputtered Ti/Al/Ti ͑50/200/50 nm͒ and then patterned by wet-etching. An active layer of 30-nm-thick a-IGZO film was deposited by a DC magnetron sputtering system using a target of In: Ga: Zn=1:1:1 in atomic ratio. Finally, the passivated device was capped with 200 nm SiO x layer by PECVD. Both the devices were annealed in an oven at 330°C for 2 h. In this work, the threshold voltage ͑V t ͒ is defined as the gate voltage ͑V...

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Amorphous In-Ga-Zn-O thin film transistors are expected to be adopted in the next-generation display industry. The most crucial challenges are to improve the reliabilities and instabilities to meet the criteria for practical applications. Reliability issues including gate-bias instability, hot-carrier effect, self-heating effect and light-induced instability in amorphous In-Ga-Zn-O thin film transistor are discussed in this article. Degradation behaviors corresponding to different effects are presented, and the dominant physical mechanisms are proposed to explain the observed phenomena. Moreover, verifications are addressed to support the proposed physical models.