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Bias Stress Stability of Asymmetric Source-Drain a-Si:H Thin Film Transistors

Published online by Cambridge University Press:  01 February 2011

Kwang-Sub Shin
Affiliation:
luke@emlab.snu.ac.kr, Seoul National University, School of Electrical Engineering, San 56-1, Sillim-dong, Gwanak-gu, Seoul, 151-742, Seoul, N/A, N/A, Korea, Republic of
Jae-Hoon Lee
Affiliation:
jhlee@emlab.snu.ac.kr, Seoul National University, School of Electrical Engineering, San 56-1, Sillim-dong, Gwanak-gu, Seoul, 151-742, Seoul, N/A, N/A, Korea, Republic of
Won-kyu Lee
Affiliation:
wklee@emlab.snu.ac.kr, Seoul National University, School of Electrical Engineering, San 56-1, Sillim-dong, Gwanak-gu, Seoul, 151-742, Seoul, N/A, N/A, Korea, Republic of
Sang-Geun Park
Affiliation:
psg97@emlab.snu.ac.kr, Seoul National University, School of Electrical Engineering, San 56-1, Sillim-dong, Gwanak-gu, Seoul, 151-742, Seoul, N/A, N/A, Korea, Republic of
Min-Koo Han
Affiliation:
mkh@snu.ac.kr, Seoul National University, School of Electrical Engineering, San 56-1, Sillim-dong, Gwanak-gu, Seoul, 151-742, Seoul, N/A, N/A, Korea, Republic of
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Abstract

The threshold voltage (VT) degradation of asymmetric source-drain a-Si:H TFTs due to the electrical stress has been investigated. In the absence of a drain bias (VG=15V, VD=0V), the threshold voltage (VT) shifts of asymmetric TFTs were similar to that of symmetric TFT. However, in the presence of drain bias (VG=15V, VD=20V), the VT shifts of asymmetric TFTs were less than symmetric TFT. The VT shifts of ‘L’ and ‘J’ shaped TFT were 0.29V, 0.24V respectively, while the VT shift of ‘I’ shaped TFT was 0.42V.

The less VT degradation of the asymmetric source-drain a-Si:H TFT compared with the symmetric TFT may be explained by the defect creation model. Since the actual drain width of asymmetric TFT is longer than symmetric TFT at the same W/L ratio, the charge depletion due to the drain bias is larger than that of the asymmetric TFT. Due to the less carrier concentration in the channel, the asymmetric a-Si:H TFT shows the less VT degradation compared with the symmetric TFT.

Type
Research Article
Copyright
Copyright © Materials Research Society 2006

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