Surface Engineering of Polycrystalline Silicon for Long-Term Mechanical Stress Endurance Enhancement in Flexible Low-Temperature Poly-Si Thin-Film Transistors.
The surface morphology in polycrystalline silicon (poly-Si) film is an issue regardless of whether conventional excimer laser annealing (ELA) or the newer metal-induced lateral crystallization (MILC) process is used. This paper investigates the stress distribution while undergoing long-term mechanical stress and the influence of stress on electrical characteristics. Our simulated results show that the nonuniform stress in the gate insulator is more pronounced near the polysilicon/gate insulator edge and at the two sides of the polysilicon protrusion. This stress results in defects in the gate insulator and leads to a nonuniform degradation phenomenon, which affects both the performance and the reliability in thin-film transistors (TFTs). The degree of degradation is similar regardless of bending axis (channel-length axis, channel-width axis) or bending type (compression, tension), which means that the degradation is dominated by the protrusion effects. Furthermore, by utilizing long-term electrical bias stresses after undergoing long-tern bending stress, it is apparent that the carrier injection is severe in the subchannel region, which confirms that the influence of protrusions is crucial. To eliminate the influence of surface morphology in poly-Si, three kinds of laser energy density were used during crystallization to control the protrusion height. The device with the lowest protrusions demonstrates the smallest degradation after undergoing long-term bending.
Bo-Wei
BW
Chen
Advanced Optoelectronics Technology Center, National Cheng Kung University, Tainan 701 Taiwan, Republic of China.
Ting-Chang
http://orcid.org/0000-0002-5301-6693
TC
Chang
Kuan-Chang
KC
Chang
Yu-Ju
YJ
Hung
Shin-Ping
SP
Huang
Hua-Mao
HM
Chen
Po-Yung
PY
Liao
Yu-Ho
YH
Lin
Hui-Chun
HC
Huang
Hsiao-Cheng
HC
Chiang
Chung-I
CI
Yang
Yu-Zhe
YZ
Zheng
Ann-Kuo
AK
Chu
New Display Process Research Division, AU Optronics Company, Limited , Taoyuan 300, Taiwan.
Hung-Wei
HW
Li
New Display Process Research Division, AU Optronics Company, Limited , Taoyuan 300, Taiwan.
Chih-Hung
CH
Tsai
New Display Process Research Division, AU Optronics Company, Limited , Taoyuan 300, Taiwan.
Hsueh-Hsing
HH
Lu
Industrial Technology Research Institute , 195 Section 4, Chung Hsing Road, Hsinchu 31040, Taiwan.
Terry Tai-Jui
TT
Wang
Industrial Technology Research Institute , 195 Section 4, Chung Hsing Road, Hsinchu 31040, Taiwan.
Tsu-Chiang
TC
Chang
LTPS TFTs; foldable electronics; long-term mechanical bending; polycrystalline silicon protrusion; surface engineering