Back-side illuminated optical stack optimized with a high refractive index micro-lens array for CMOS image sensors

Abstract

We simulate a simplified optical stack model with Lumerical FDTD over wide ranges of optical parameters: wavelength, 550 nm to 1.4 μm, and pixel array pitch, 1 to 10 μm. By increasing the lens and the planarization layer refractive indices from the usual 1.5 to 2, we study the improved lens focalization abilities, in terms of spot width, power, and depth below the micro-lens. We show an NIR wavelength range benefit from slightly increasing the optical stack index to 1.7 while visible wavelengths have less interest. Indeed, increasing the lens and planarization layer index enables thinner back-side illuminated optical stacks for higher quantum efficiencies and angular response improvement.