High-sensitivity and no-crosstalk pixel technology for embeddedCMOS image sensor |
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Authors: | Furumiya M Ohkubo H Muramatsu Y Kurosawa S Okamoto F Fujimoto Y Nakashiba Y |
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Affiliation: | ULSI Device Dev. Div., NEC Corp., Kanagawa; |
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Abstract: | A high-photosensitivity and no-crosstalk pixel technology has been developed for an embedded active-pixel CMOS image sensor, by using a 0.35-μm CMOS logic process. To increase the photosensitivity, we developed a deep p-well photodiode and an antireflective film, consisting of Si3N4 film, for the photodiode surface. To eliminate the high voltage required for the reset transistor in the pixel, we used a depletion-type transistor as the reset transistor. The reset transistor also operates as an overflow control gate, which enables antiblooming overflow when excess charge is generated in the photodiode by high-illumination conditions. To suppress pixel crosstalk caused by obliquely incident light, a double-metal photoshield was used, while crosstalk caused by electron diffusion in the substrate was suppressed by using the deep p-well photodiode. A 1/3-in 330-k-pixel active-pixel CMOS image sensor was fabricated using this technology. A sensitivity improvement of 110% for 550-nm incident light was obtained by using the deep p-well photodiode, while an improvement of 24% was obtained by using the antireflective film. The pixel crosstalk was suppressed to less than 1% throughout the range of visible light |
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