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Proceedings Paper

Mitigation of pixel scaling effects in CMOS image sensors
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Paper Abstract

Over the last decade, the pixels that make up CMOS image sensors have steadily decreased in size. This scaling has two effects: first, the amount of light incident on each pixel decreases, reducing the photodiode signal and making optical efficiency, i.e., the collection of each photon, more important. Second, spatial optical crosstalk increases because diffraction comes into play when pixel size approaches the wavelength of visible light. To counter these two effects, we have investigated and compared three methods for guiding incident light from the microlens down to the photodiode. Two of these techniques rely on total internal reflection (TIR) at the boundary between dielectric media of different refractive indices. The first involves filling the central pixel area with a high-index dielectric material, while in the second approach, material between the pixels is removed and air is used as a low-index cladding. The third method uses reflection at a metal-dielectric interface to confine the light. Simulations were performed using commercial finite-difference time-domain (FDTD) software on a realistic 1.75 μm pixel model for on-axis as well as angled incidence. We evaluate the optical efficiency and spatial crosstalk performance of these methods compared to a reference pixel and examine the influence of several design parameters.

Paper Details

Date Published: 3 March 2008
PDF: 13 pages
Proc. SPIE 6817, Digital Photography IV, 681706 (3 March 2008); doi: 10.1117/12.766045
Show Author Affiliations
Christian C. Fesenmaier, Stanford Univ. (United States)
Peter B. Catrysse, Stanford Univ. (United States)

Published in SPIE Proceedings Vol. 6817:
Digital Photography IV
Jeffrey M. DiCarlo; Brian G. Rodricks, Editor(s)

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