Migration of weakly bonded oxygen atoms in a-IGZO thin films and the positive shift of threshold voltage in TFTs

doi:10.1088/1674-1056/ac560f

Abstract Amorphous indium-gallium-zinc oxide (a-IGZO) thin films are prepared by pulsed laser deposition and fabricated into thin-film transistor (TFT) devices. In-situ x-ray photoelectron spectroscopy (XPS) illustrates that weakly bonded oxygen (O) atoms exist in a-IGZO thin films deposited at high O₂ pressures, but these can be eliminated by vacuum annealing. The threshold voltage (V_th) of the a-IGZO TFTs is shifted under positive gate bias, and the V_th shift is positively related to the deposition pressure. A temperature variation experiment in the range of 20 K-300 K demonstrates that an activation energy of 144 meV is required for the V_th shift, which is close to the activation energy required for the migration of weakly bonded O atoms in a-IGZO thin films. Accordingly, the V_th shift is attributed to the acceptor-like states induced by the accumulation of weakly bonded O atoms at the a-IGZO/SiO₂ interface under positive gate bias. These results provide an insight into the mechanism responsible for the V_th shift of the a-IGZO TFTs and help in the production of reliable designs.

Keywords: a-IGZO thin films weakly bonded O atoms threshold voltage shift

Received: 01 December 2021
Revised: 29 January 2022
Accepted manuscript online: 17 February 2022

PACS:	61.43.Dq	(Amorphous semiconductors, metals, and alloys)
	68.35.Fx	(Diffusion; interface formation)
	85.30.Tv	(Field effect devices)

Fund: Project supported by the National Natural Science Foundation of China (Grant Nos. 51771144 and 62104189), the Natural Science Foundation of Shaanxi Province, China (Grant Nos. 2021JC-06, 2019TD-020, and 2019JLM-30), the China Postdoctoral Science Foundation (Grant No. 2020M683483), and the Fundamental scientific research business expenses of Xi'an Jiaotong University (Grant No. XZY022020017).

Corresponding Authors: Fei Ma
E-mail: mafei@mail.xjtu.edu.cn

Cite this article:

Chen Wang(王琛), Wenmo Lu(路文墨), Fengnan Li(李奉南), Qiaomei Luo(罗巧梅), and Fei Ma(马飞)^† Migration of weakly bonded oxygen atoms in a-IGZO thin films and the positive shift of threshold voltage in TFTs 2022 Chin. Phys. B 31 096101

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Migration of weakly bonded oxygen atoms in a-IGZO thin films and the positive shift of threshold voltage in TFTs

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