IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Thin Films Monday Sessions
       Session TF-MoP

Paper TF-MoP8
Degradation Mechanisms of Low-Temperature Poly-Si Thin-Film Transistors with PECVD TEOS Oxide

Monday, October 29, 2001, 5:30 pm, Room 134/135

Session: Multilayers and Thin Film Characterization Poster Session
Presenter: H.W. Zan, National Chiao Tung University, Taiwan
Authors: H.W. Zan, National Chiao Tung University, Taiwan
P.S. Shih, National Chiao Tung University, Taiwan
T.C. Wu, National Chiao Tung University, Taiwan
T.C. Chang, National Sun Yat-Sen University, Taiwan
C.Y. Chang, National Chiao Tung University, Taiwan
D.Z. Peng, National Chiao Tung University, Taiwan
Correspondent: Click to Email
For being applied on low temperature poly-Si AMLCD, we fabricate poly-Si TFTs with PECVD TEOS oxide as gate insulator. It is found that the output characteristics of our devices are well enough with mobility as 37 cm2/V.s and quite low leakage current. However, due to the high density of trap states localized within the grain boundaries, the electric fields across the grain boundaries near the drain side are considerably high even under moderate biases. The hot-carrier effects are therefore more pronounced in poly-Si TFTs than in MOSFETs. To investigate the reliability issues of poly-Si TFTs, we carefully apply several kinds of electrical stresses on our devices and study their degradation phenomena. Two different degradation mechanisms can be concluded. For the stress under linear region, stress-induced defects are located in the whole gate insulator and are uniformly distributed from source to drain. These defects are positive fixed oxide charges and the acceptor-type interface states in the upper half of the band gap. It is also noted that the degradation degree depends on the magnitude of gate current and the electric field across the gate oxide. For stress under saturation region, however, additional defects near the drain side are generated. This asymmetric degradation phenomenon is attributed to the presence of avalanche-generated carriers. These defects could be acceptor-type interface states in the upper half of the bandgap and donor-type interface states in the lower half of the bandgap. In addition, stress under saturation region produces severer degradation than that under linear region.