In this paper we will report on the optical performances of submicron planar lensless pixels arranged in the 2 x 2 Bayer cell configuration, the basic element of CMOS colour image sensors. The 2D microlens array placed in front of each pixel in commercial devices has been replaced by a 2D array of submicron holes realised on a thin metal film. Each pixel has been designed to present a lightpipe inside its structure acting as an optical waveguide that confines the light up to photodiode surface. This pixel design is fully compatible with large scale industry production since its fabrication involves only standard lithographic and etching procedures. Simulations of the light propagation inside the lensless pixel has been performed by using full 3D electromagnetic analysis. In this way it was possible to determine the optical performances of the Bayer cell in terms of the normalized optical efficiency and crosstalk effects between adjacent pixels that result to be up to 30% and a factor 10, respectively, better than those ones obtained for the microlens counterpart. The significant increase of the achievable values of the normalized optical efficiency and crosstalk can foresee the possibility to reduce the pixel size down to 1 μm, i.e., beyond the limit imposed by the diffraction effects arising in microlens equipped pixel.
"Optical Performances of Lensless Sub-2micron Pixel for Application in Image Sensors," Progress In Electromagnetics Research B,
Vol. 31, 1-14, 2011. doi:10.2528/PIERB11032306
1. Huo, Y., C. C. Fesenmaier, and P. B. Catrysse, "Microlens performance limits in sub-2μm pixel CMOS image sensors," Optics Express, Vol. 18, No. 6, 5861-5872, 2010. doi:10.1364/OE.18.005861
2. Hsu, T. H., Y. K. Fang, D. N. Yaung, S. G. Wuu, H. C. Chien, C. S. Wang, J. S. Lin, C. H. Tseng, S. F. Chen, C. S. Lin, and C. Y. Lin , "Dramatic reduction of optical crosstalk in deep-submicrometer CMOS imager with air gap guard ring," IEEE Electron Dev. Lett., Vol. 25, No. 6, 375-377, 2004. doi:10.1109/LED.2004.828995
3. Swain, P. K. and D. Cheskis, "Back-illuminated image sensors come to the forefront," Photonics Spectra, Issue August, 2008.
4. Dragoi, V., A. Filbert, S. Zhu, and G. Mittendorfer, "CMOS wafer bonding for back-side illuminated image sensors fabrication," 11th International Conference on Electronic Packaging Technology & High Density Packaging, 27-30, August 2010. doi:10.1109/ICEPT.2010.5582379
5. Lezec, H. J., A. Degiron, E. Devaux, R. A. Linke, L. Martin-Moreno, F. J. Garcia-Vidal, and T. W. Ebbesen, "Beaming light from a subwavelength aperture," Science, Vol. 297, 820-822, 2002. doi:10.1126/science.1071895
6. Verslegers, L., P. B. Catrysse, Z. Yu, J. S. White, E. S. Barnard, M. L. Brongersma, and S. Fan, "Planar lenses based on nanoscale slit arrays in a metallic film," Nanoletters, Vol. 9, No. 1, 235-238, 2009.
7. Shi, H., C. Wang, C. Du, X. Luo, X. Dong, and H. Gao, "Beam manipulating by metallic nano-slits with variant witdths," Optics Express, Vol. 13, No. 18, 6815-6820, 2005. doi:10.1364/OPEX.13.006815
8. Ma, C. and Z. Liu, "A super resolution metalens with phase compensation mechanism," Appl. Phys. Lett., Vol. 96-1833103, 2010. doi:10.1063/1.3427199
9. Gambino, J., B. Leidy, J. Adkisson, M. Jaffe, R. J. Rassel, J. Wynne, J. Ellis-Monaghan, T. Hoague, D. Meatyard, S. Mongeon, and T. Kryzak, "CMOS Imager with copper wiring and lightpipe," International Electron Device Meeting, IEDM'06, Technical Digest, San Francisco, USA, December 2006.
10. Fesenmaier, C. C., Y. Huo, and P. B. Catrysse, "Optical confinement methods for continued scaling of CMOS image sensor pixels," Optics Express, Vol. 16, No. 25, 20457-20470, 2008. doi:10.1364/OE.16.020457
11. Weiland, T., "A discretization method for the solution of Maxwell's equations for six component fields," Electron. Commun., Vol. 31, 116, 1977.
12. Clemens, M. and T. Weiland, "Discrete electromagnetism with the finite integration technique ," Progress In Electromagnetics Research, Vol. 32, 65-87, 2001. doi:10.2528/PIER00080103
14. Palik, E. D., Handbook of Optical Constants of Solids, Academic Press, 1998.
15. Vial, A. and T. Laroche, "Comparison of gold and silver dispersion law suitable for FDTD simulations," Applied Physics B, Vol. 93, No. 1, 139-143, 2008. doi:10.1007/s00340-008-3202-4
16. Ebbesen, T. W., H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, "Extraordinary optical transmission through sub-wavelength hole arrays," Nature, Vol. 391, 667-669, February 1998. doi:10.1038/35570
17. Ghazi, G. and M. Shahabadi, "Modal analysis of extraordinary transmission through an array of subwavelength slits," Progress In Electromagnetics Research, Vol. 79, 59-74, 2008. doi:10.2528/PIER07092402
18. Nakamura, J., Image Sensors and Signal Processing for Digital Still Cameras, Chapter 5, Taylor and Francis Group, Boca Raton, USA , 2006.
19. Agranov, G., V. Berezin, and R. H. Tsai, "Crosstalk and microlens study in a color CMOS image sensor," IEEE Trans. Electron Dev., Vol. 50, No. 1, 4-11, January 2003. doi:10.1109/TED.2002.806473
20. Onozawa, K., K. Toshikiyo, T. Yogo, M. Ishii, K. Yamanaka, T. Matsuno, and D. Ueda , "A MOS image sensor with a digital-microlens," IEEE Trans. Electron Dev., Vol. 55, No. 4, 986-991, April 2008. doi:10.1109/TED.2008.917331