Search

We investigated the effects of the passivation layer on the characteristics of amorphous InGaZnO4 thin-film transistors (a-InGaZnO TFTs) by comparing AlOx film by thermal atomic layer deposition (TALD-AlOx) with SiOx film by plasma enhanced chemical vapor deposition (PECVD-SiOx). The PECVD-SiOx TFTs before and after final annealing exhibited conductive and hump characteristics, respectively. In contrast, both TALD-AlOx TFTs before and after final annealing exhibited enhancement characteristics. From secondary ion mass spectroscopy analysis, we found that TALD-AlOx effectively suppresses H injection into the underneath of the a-InGaZnO layer compared with PECVD-SiOx. We believe such suppression of H injection leads to the enhancement characteristics of TALD-AlOx TFTs. On the other hand, the conductive and hump characteristics of PECVD-SiOx TFTs may be attributed to a higher concentration of H injected into the a-InGaZnO layer and ion bombardment due to PECVD. From these results, we argue that plasma-free TALD-AlOx is effective for achieving good characteristics in a-InGaZnO TFTs. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0231507jss] All rights reserved.

Amorphous In-Ga-Zn-O thin-film transistors (a-IGZO TFTs) have attracted considerable attention as an alternative device for conventional amorphous silicon (a-Si) TFTs. The features of this material are a low fabrication temperature less than 200 ◦ C, and preferable electronic properties such as higher field-effect mobility and lower threshold voltage (Vth) compared with those of a-Si TFTs. Such desirable performances also enable us to design peripheral circuits for displays. Furthermore, a-IGZO TFTs are regarded as a prospective material for “transparent electronics”, because of their wide bandgap of ∼3.2 eV. 1‐4 On the other hand, several papers have reported that aIGZO TFTs showed poor stability against electrical stresses. 5‐7 Since reliability is an issue for the realization of next-generation displays utilizing oxide semiconductors in transparent electronics, a deeper understanding of a-IGZO and its problems are necessary. The influence of hydrogen concentration in silicon nitride (SiNx) gate insulators (GIs) on the electrical stability of a-IGZO TFTs has been actively discussed. 8‐10 Lee et al. reported that the hydrogen in SiNx film strongly induced threshold voltage shift (�V th) due to the generation of shallow charge-trapping sites for electrons. 11 Their results lead us to expect that lower hydrogen content in the gate insulator will provide quite stable TFTs. In this study, we propose a fluorinated SiNx film utilizing SiF4 and N2 as source gasses unlike conventional film fabricated with SiH4/NH3 and investigated the electrical properties of a-IGZO TFT by applying positive biased stress (PBS). In order to discuss effect on reliability of hydrogen and fluorine in the GIs, we prepared several kindsofSiNx filmswithcontrollingtheconcentrationofhydrogenand fluorine. Thermally-oxidized SiO2 gate insulator was also evaluated for comparison.

We have investigated thermal distribution of an amorphous InSnZnO thin-film transistor (TFT) under voltage stress by using thermal imaging system. To clarify an influence of only self-heating phenomenon on reliability, we have focused on a channel scale dependence of heating. As the result, heating effect were strongly depended on channel scale and showed two types of dependences on channel length and width. When positive bias stress was applied to TFT, severe threshold voltage shift and high heating temperature were observed for wider TFT. Moreover, reliability under voltage stress was seems to be affected by accumulation of heating in wider TFT. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigate the influence of polymer passivation on amorphous Indium Gallium Zinc Oxide (a-IGZO) TFT reliability. We made photosensitive siloxane passivation layer on bottom-gate type a-IGZO TFTs with SiO 2 /Si substrate. For photosensitive materials, contact holes can be formed by UV photolithography technique without plasma etching process, leading to serious damage to the channel layer. The samples with and without passivation layer were tested in terms of the stability during the positive bias stress (PBS; V gs = 20 V) for 1000 sec. The stability of a-IGZO TFTs was improved by using the photo-sensitive siloxane passivation layer.

Amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) having several metals, namely Ag, Ti, and Mo, as the source and drain electrodes were characterized. TFTs with Ti and Mo electrodes showed drain current–gate voltage characteristics without fluctuation. However, TFTs with Ag electrodes indicated a low noisy on-state current at a large channel length under a low drain–source voltage condition. The source and drain resistances [R s/d (Ω)] of the TFTs with each of the three metals were calculated from the I DS–V GS characteristics. The R s/d values of the Ag, Ti, and Mo samples reached 4 × 104, 2 × 104, and 1 × 104 Ω, respectively. This implies that a spatial potential barrier exists at the a-IGZO/Ag interface and that the resistance of the potential barrier changes with the application of gate voltage.

The electronic structures of amorphous indium gallium zinc oxide (a-IGZO) on a SiO2 layers before and after annealing were observed by constant final state X-ray photoelectron spectroscopy (CFS-XPS) and X-ray adsorption near-edge structure spectroscopy (XANES). From the results of angle-resolved CFS-XPS, the change in the electronic state was clearly observed in the a-IGZO bulk rather than in the a-IGZO/SiO2 interface. This suggests that the electronic structures of the a-IGZO bulk strongly affected the thin-film transistor characteristics. The results of XANES indicated an increase in the number of tail states upon atmospheric annealing (AT). We consider that the increase in the number of tail states decreased the channel mobility of AT samples.