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Description:

The degradation of field-effect mobility with decreasing channel thickness in amorphous In-Ga-Zn-O thin-film transistors (a-IGZO TFTs) remains a critical issue with a controversial origin. Here, we propose that the mobility degradation in very thin a-IGZO TFTs originates from a defective surface layer. Simulated results reveal that the degradation is primarily governed by the broadening of unoccupied tail states below the conduction band minimum. These large tail state densities arise from enhanced structural disorder created by sputter-deposition process. As the channel thickness decreases, this defective layer becomes dominant in carrier transport. The presence of surface defect layer was revealed by hard X-ray photoelectron spectroscopy combined with ex situ wet etching. Removal of the surface defective layer by the etching led to the restoration of the mobility of the 5 nm channel thickness from 13.7 to 28.5 cm2/V·s at 2 MV/cm, which is comparable to the thick TFTs.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: a-IGZO, mobility, TFT, surface defects

Date published: 2026-05-22

Publisher: Institute of Electrical and Electronics Engineers (IEEE)

Journal:

• IEEE Electron Device Letters (ISSN: 07413106) vol. 47 issue. 7 p. 1394-1397

Funding:

• Ministry of Education, Culture, Sports, Science and Technology JPMXP1122683430
• JSPS KAKENHI JP23K19266
• JSPS KAKENHI JP24K17753
• Samsung IO250530-13006-01

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1109/led.2026.3695312

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Updated at: 2026-08-25 14:17:04 +0900

Published on MDR: 2026-08-25 16:27:38 +0900