Monday, October 04, 2021

Holes vs Pyramids

W&W Sens Device together with Universities of California at Davis and Santa Cruz publishes paper "Optimization of CMOS image sensors with single photon-trapping hole per pixel for enhanced sensitivity in near-infrared" by E. Ponizovskaya Devine, Ahasan Ahamed, Ahmed S. Mayet, Soroush Ghandiparsi, Cesar Bartolo-Perez, Lisa McPhillips, Aly F. Elrefaie, Toshishige Yamada, Shih-Yuan Wang, and M Saif Islam.

"The optimization of silicon photodiode-based CMOS sensors with backside-illumination for 300-1000 nm wavelength range was studied. It was demonstrated that a single hole on a photodiode increases the optical efficiency of the pixel in near-infrared wavelengths. A hole with optimal dimensions enhanced optical absorption by 60% for a 3 μm thick Si photodiode, which is 4 orders better than that for comparable flat photodiodes. We have shown that there is an optimal size and depth of the hole that exhibits maximal absorption in blue, green, red, and infrared. Crosstalk was successfully reduced by employing thin trenches between pixels of 1.12 μm^2 in size."

Although the labels on the following figures seem to be off, the general conclusion is clear: NIR sensitivity is a little bit better with holes, but visible is significantly worse:

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