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Conference Paper
The Highly Stable InGaZnO TFTs Deposited by High Density Plasma Sputtering
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- Authors
- S. H. Cho, C. -S. Hwang, Y. -S. Roh, J. -R. Lee, S. -B. Kim, S. J. Yoo, H. -O. Kim, O. -S. Kwon, E. -S. Park, S. -H. Ko Park
- Issue Date
- 2015-02
- Citation
- International Thin-Film Transistor Conference (ITC) 2015, pp.17-18
- Language
- English
- Type
- Conference Paper
- Abstract
- New sputtering method for the deposition of metal oxide semiconductor thin-film for large area electronic devices is suggested and demonstrated in InGaZnO Thin-Film Transistor (TFT) applications in this work. We employ the high density plasma (HDP) which can be operated in a very low pressure regime of 10 -4 ~ 10 -5 torr. Remarkably, our IGZO thin-films deposited by HDP sputtering are shown to be crystallized at an optimal oxygen partial pressure (P O2 ) even without thermal treatment over 500~600 o C at which IGZO thin-film starts to be crystallized [1], as demonstrated in X-ray diffraction patterns and transmission electron microscope image in Fig. 1(a) and Fig. 1(b), respectively. The XRD peak positions for crystalline and amorphous IGZO are in good agreement with the previous reports [1,2]. We fabricated the bottom gate, etch stopper TFTs as a test vehicle for device applications. The plasma enhanced chemical vapor deposition (PECVD) SiO2 was used for gate insulator and etch stop layer. The initial electrical characteristics and the turn-on voltage (Von) instability of TFTs were greatly affected by P O2 condition. As shown in Fig. 2, Fig. 3 and Fig. 4, at low P O2 for IGZO deposition, the Von was quite unstable under negative bias stress (NBS) or negative bias and illumination stress (NBIS), while that under positive gate bias stress (PBS) was stable. As Po 2 increases, the Von became extremely stable under PBS, NBS, and even NBIS conditions, with a slight degradation of field effect mobility from 14 cm 2 /Vs to 9 cm 2 /Vs. With further increase of P O2 , the Von instability induced by NBS was intact, but both PBS and NBIS instabilities were getting worse than those under optimal P O2 condition. We discuss the origin of NBS instability in view of migration of ionized oxygen vacancies naturally existing under oxygen deficient environment into the gate insulator interface and trapping thereafter by the gate electric field and ascribe the origin of PBS instability to the electron trapping under accumulation condition into the interface states near gate insulator/channel interface and charge injection thereafter into the gate dielectric bulk, especially aggravated by oxygen anion bombardment under oxygen-rich sputtering atmosphere [3,4]. Especially, it is suggested that the crystalline and dense structure of our IGZO film deposited by HDP sputtering at an optimal P O2 suppresses the stabilization of photo-ionized oxygen vacancies which needs the rearrangement of cation configuration around oxygen vacancy to expand the volume to accommodate the positive charge, which results in great enhancement of NBIS instability in metal oxide TFTs.
- KSP Keywords
- Accumulation condition, Bottom gate, Dense structure, Electrical characteristics, Electron microscope, Etch stop layer, Gate electric field, High density plasma(HDP), Highly stable, IGZO film, InGaZnO TFTs