Single Microhole per Pixel in CMOS Image Sensors With Enhanced Optical Sensitivity in Near-Infrared

Silicon photodiode-based CMOS sensors with backside-illumination for 300-1100 nm wavelength range were studied. We showed that a single hole in the photodiode increases the optical efficiency of the pixel. In near-infrared wavelengths, the enhancement allows 70% absorption in a 3 μm thick Si. It is 4× better than that for the flat pixel. We compared different shapes and sizes of single hole and hole arrays. We have shown that a certain size and shape in single hole-based pixels contribute to stronger enhancement of optical efficiencies. The crosstalk was successfully reduced by employing trenches between pixels. We optimized the dimensions of the trenches to achieve minimal pixel separation for 1.12 μm pixels.