Columnated Backside Illumination Light Guide for CMOS Imagers
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Solution Overview
Problem
CMOS imager devices suffer from optical cross-talk, leading to image blurring, reduced contrast, degraded spatial resolution, color mixing, and image noise, particularly as pixel sizes decrease and longer wavelengths penetrate deeper into the silicon structure, causing light to be reflected or refracted away from intended photoconversion devices.
Innovation Solution
Incorporating a light guide formed within a dielectric material and over an antireflective material with specific refractive indices, positioned to direct light columnated to the photoconversion device, reducing optical cross-talk between pixels by selecting materials where the refractive index of the light guide is greater than or equal to the antireflective material, and both are greater than the dielectric material, thereby minimizing light reflection and refraction to adjacent pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel size is reduced to increase pixel density, then productivity and imaging coverage are improved, but optical cross-talk increases causing image degradation
Solution Approach 1:
A light guide structure is introduced as an intermediary component between the optical lens and the photoconversion device. This light guide redirects strayed light back to the intended photoconversion device, effectively mediating the optical path to prevent cross-talk while allowing smaller pixel sizes to be used without sacrificing image quality.
2Loss of energy
If antireflective coating is applied to reduce reflection, then light transmission is improved, but refraction still causes light to stray to adjacent pixels
Solution Approach 1:
The light guide acts as an intermediary optical element that receives light after it passes through the antireflective coating. It captures light that would otherwise be refracted away and redirects it to the correct photoconversion device, addressing the refraction problem that the antireflective coating alone cannot solve.
Solution Approach 2:
The refractive index of the light guide material is specifically selected to be higher than that of the surrounding dielectric material. This parameter change enables the light guide to effectively capture and redirect strayed light through total internal reflection, preventing cross-talk while maintaining the benefits of the antireflective coating.
3Length of stationary object
If longer wavelengths are used for imaging, then penetration depth into silicon is improved, but refraction and reflection increase causing more cross-talk
Solution Approach 1:
The light guide serves as a mediator for longer wavelength light, which penetrates deeper into the silicon structure. By providing a controlled optical path with appropriate refractive index matching, the light guide captures and redirects deeply penetrating light that would otherwise be refracted or reflected to adjacent pixels, thereby reducing cross-talk for long wavelength imaging.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces optical cross-talk, enhancing image clarity, contrast, and spatial resolution while maintaining sensitivity, particularly effective at longer wavelengths by ensuring light is directed accurately to the intended photoconversion device, thereby improving overall image quality.
Implementation Method 1
the refractive index of the light guide is greater than or equal to the antireflective material, and both are greater than the dielectric material, thereby minimizing light reflection and refraction to adjacent pixels
Implementation Method 2
minimizing light reflection and refraction to adjacent pixels
Data Source
AI summary
Imager devices, systems including the imager devices and methods of forming the imager devices are provided. The imager device has a substrate with first and second opposing sides. The imager also includes an array of imager pixels at the first side of the substrate, each including a photoconversion device. An antireflective material is on the second side of the substrate and a dielectric material is over the antireflective material. A light guide material is disposed within a plurality of openings in the dielectric material and optically aligned with a respective photoconversion device.