Single Microhole per Pixel in CMOS Image Sensor with Enhanced Optical Sensitivity in Near-Infrared

TL;DR

This paper demonstrates that incorporating a single hole in CMOS photodiodes significantly enhances near-infrared optical sensitivity, achieving 70% absorption in silicon and reducing crosstalk through optimized trench design.

Contribution

It introduces a novel pixel design with a single hole that improves near-infrared sensitivity and compares various hole geometries for optimal performance.

Findings

Single-hole design increases optical efficiency by 4x in NIR.

Optimized trenches reduce crosstalk and allow minimal pixel separation.

Achieved 70% absorption in 3-micron silicon at NIR wavelengths.

Abstract

Silicon photodiode based CMOS sensors with backside-illumination for 300 to 1000 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 microns thick Si. It is 4x better than for the flat pixel. We compared different shapes and sizes of single holes and holes arrays. We have shown that a certain size and shape in single holes pronounce better optical efficiency enhancement. The crosstalk was successfully reduced with trenches between pixels. We optimized the trenches to achieve minimal pixel separation for 1.12 microns pixel.