3 March 2008 Mitigation of pixel scaling effects in CMOS image sensors
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Proceedings Volume 6817, Digital Photography IV; 681706 (2008) https://doi.org/10.1117/12.766045
Event: Electronic Imaging, 2008, San Jose, California, United States
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.
© (2008) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Christian C. Fesenmaier, Peter B. Catrysse, "Mitigation of pixel scaling effects in CMOS image sensors", Proc. SPIE 6817, Digital Photography IV, 681706 (3 March 2008); doi: 10.1117/12.766045; https://doi.org/10.1117/12.766045
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