Silicon-nanocrystal-based photosensor integrated on low-temperature polysilicon panels

• Published in: Journal of the Society for Information Display 2008-07, Vol.16 (7), p.777-786
• Main Authors: Chiang, Wen-Jen, Lin, Chrong-Jung, King, Ya-Chin, Cho, An-Thung, Peng, Chia-Tien, Chao, Chih-Wei, Lin, Kun-Chih, Gan, Feng-Yuan
• Format: Article
• Language: English
• Subjects: LTPS display-panel-embedded photosensor; LTPS photosensor; silicon-nanocrystal-based photosensor; TFT photodetector
• ISSN: 1071-0922; 1938-3657
• DOI: 10.1889/1.2953485

— A photodetector using a silicon‐nanocrystal layer sandwiched between two electrodes is proposed and demonstrated on a glass substrate fabricated by low‐temperature poly‐silicon (LTPS) technology. Through post excimer‐laser annealing (ELA) of silicon‐rich oxide films, silicon nanocrystals formed between the bottom metal and top indium thin oxide (ITO) layers exhibit good uniformity, reliable optical response, and tunable absorption spectrum. Due to the quantum confinement effect leading to enhanced phonon‐assisted excitation, these silicon nanocrystals, less than 10 nm in diameter, promote electron‐hole‐pair generation in the photo‐sensing region as a result resembling a direct‐gap transition. The desired optical absorption spectrum can be obtained by determining the thickness and silicon concentration of the deposited silicon‐rich oxide films as well as the power of post laser annealing. In addition to obtaining a photosensitivity comparable to that of the p‐i‐n photodiode currently used in LTPS technology, the silicon‐nanocrystal‐based photosensor provides an effective backlight shielding by the bottom electrode made of molybdenum (Mo). Having a higher temperature tolerance for both the dark current and optical responsibility and maximizing the photosensing area in a pixel circuit by adopting a stack structure, this novel photosensor can be a promising candidate for realizing an optical touch function on a LTPS panel.