| 학회 | 한국재료학회 |
| 학술대회 | 2012년 가을 (11/07 ~ 11/09, 라카이샌드파인 리조트) |
| 권호 | 18권 2호 |
| 발표분야 | F. 광기능/디스플레이 재료(Optical Funtional and Display Materials) |
| 제목 | The effects of Al2O3 passivation with HfO2 as a buffer layer on a-IGZO TFTs |
| 초록 | During the past few years, ZnO-based semiconductors such as IGZO, SnGZO, and SnIZO have attracted great attention for their use as the active channel layer of thin film transistors(TFTs) for transparent devices, large area active matrix backplanes, and flexible appliances. ZnO-based TFTs offer various advantages including transparency in the visible light region, a high field effect mobility compared to amorphous silicon (a-Si) TFTs, and low processing temperatures. Despite their many merits, the electrical reliability of ZnO-based TFT devices remains a very important and critical issue. Recently, several studies have reported that exposure of the active channel layer to environmental conditions causes charge trapping, charge injection, and channel defect creation, leading to the electrical instability of ZnO-based TFTs. Passivation is one of the promising processes to protect the active channel layer from contamination caused by environmental conditions. However, exposure of the active channel layer to various reactant gases during the passivation process is unavoidable in the case of bottom-gate type TFTs. Namely, the passivation process can adversely affect the electrical properties and stability of TFTs under these conditions. In this study, we investigated the effects of a HfO2 buffer layer on Al2O3-passivated IGZO TFTs. Before applying the HfO2 buffer layer, single Al2O3 passivation layers deposited by two different ALD systems, thermal ALD and remote plasma ALD, were examined to determine the proper passivation process. As a result, hydrogen related defect states, formed during the thermal ALD process, led to the instability of the devices. Therefore we concluded that remote plasma ALD is a better passivation process than thermal ALD. Although ALD-derived Al2O3 passivation layers are known to act as an efficient diffusion barrier against the penetration of oxygen or water, some corrosion of Al2O3 layers can be formed. Therefore, we fabricated the Al2O3/HfO2 layer to enhance the protective effects of the passivation layer against the external environment. When applying the HfO2 buffer layer, the formation of HfAlxOy at the Al2O3/HfO2 interface reduces the water vapor transmission rate (WVTR) due to densification of the passivation layer. Consequently, by adding the HfO2 buffer layer, WVTR of the TFT was highly improved. Moreover, changes in the electrical characteristics can be prevented compared to both the non-passivated and Al2O3-passivated TFTs. |
| 저자 | Heewang Yang1, Hagyoung Choi2, Joohyun Park3, Seokyoon Shin4, Giyul Ham1, Sanghun Lee2, Hyeongtag Jeon3 |
| 소속 | 1Division of Materials Science and Engineering, 2Hanyang Univ., 3Seoul 133-791, 4Korea |
| 키워드 | atomic layer deposition; thin film transistors; passivation; IGZO; HfO2; Al2O3 |
