Numerical study of a Fresnel zone plate based lens for a 2 μm × 2 μm CMOS image sensor pixel

Fresnel zone plate (FZP) topology is proposed to be used as the lens media for the light concentration in a 2 μm × 2 μm CMOS (complementary metal oxide semiconductor) image sensor pixel. According to the pixel size scaling, the width of each ring of the FZP becomes smaller than the incident light’s wavelength. Rayleigh-Sommerfeld diffraction theory is used to analyze dielectric scattering effects on the interfaces. Both the analytical and finite difference time domain (FDTD) numerical simulations agree on the focal distance of 2.7 μm. Moreover, angular response and crosstalk of the final CMOS image sensor (CIS) are calculated and analyzed. It is shown that the FZP based pixel has lower crosstalk at angles above 19°, compared with similar microlens (μlens) based pixels. Furthermore, wider response is observed in comparison with the μlens based pixels.