Optical Isolation Grid for Color Filter Crosstalk Reduction
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Solution Overview
Problem
Conventional color image sensors face challenges in focusing incident light due to smaller pixel cell sizes, leading to undesired crosstalk among color filters and pixel cells, which results in image noise and degraded image quality.
Innovation Solution
An optical isolation grid with sidewalls defining openings is disposed over the color filter array, aligning each opening with a corresponding color filter to isolate light and prevent leakage between filters, using a material with a lower refractive index than the microlenses to deflect light and reduce crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel cell sizes are reduced to increase resolution, then image sensor resolution is improved, but light focusing accuracy deteriorates leading to increased crosstalk
Solution Approach 1:
The patent introduces an optical isolation grid that segments the optical path into isolated regions. The grid includes multiple isolation structures positioned between adjacent color filters, creating separate optical channels for each pixel cell. This segmentation prevents light from one pixel cell from interfering with adjacent cells, thereby maintaining focusing accuracy even as pixel cell sizes are reduced for higher resolution.
Solution Approach 2:
The optical isolation grid acts as an intermediary element between the color filters and microlenses. The isolation structures with refractive indices different from the surrounding medium create optical barriers that mediate light propagation, directing light precisely to the intended pixel cell while blocking stray light from reaching adjacent cells.
2Productivity
If microlenses focus light through smaller pixel cells, then light focusing efficiency is improved, but crosstalk among color filters increases
Solution Approach 1:
The optical isolation grid segments the optical paths of adjacent color filters by introducing isolation structures between them. These structures create distinct optical zones that prevent light intended for one color filter from leaking into adjacent filters, thereby eliminating crosstalk while preserving the efficient light focusing capability of the microlenses.
Solution Approach 2:
The isolation structures are strategically positioned only at the boundaries between color filters where crosstalk occurs, rather than uniformly across the entire sensor. This localized approach maintains high light transmission efficiency in the center of each pixel cell while providing crosstalk suppression only where needed at the interfaces between adjacent filters.
3Volume of moving object
If pixel cell sizes are reduced, then image sensor miniaturization is achieved, but image quality deteriorates due to increased noise from crosstalk
Solution Approach 1:
By introducing an optical isolation grid with segmentation structures between pixel cells, the patent creates isolated optical channels that prevent crosstalk even when pixel cells are closely spaced. This allows the sensor to maintain miniaturization with small pixel cells while preserving image quality by eliminating the noise that would otherwise result from light leakage between adjacent cells.
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 optical isolation grid effectively reduces crosstalk between color filters and pixel cells, enhancing image quality by minimizing noise and improving light focusing efficiency.
Implementation Method 1
using a material with a lower refractive index than the microlenses to deflect light and reduce crosstalk
Data Source
AI summary
A color image sensor includes a plurality of pixel cells arranged in a pixel array. A plurality of color filters is arranged in a color filter array disposed over the pixel array. Each color filter is aligned with a corresponding underlying pixel cell. An optical isolation grid is disposed over the color filter array such that incident light is directed through the optical isolation grid prior to be being directed through the color filter array to the pixel array. The optical isolation grid includes a plurality of sidewalls arranged to define a plurality of openings in the optical isolation grid. Each opening is aligned with a corresponding color filter such that each color filter is optically isolated by the optical isolation grid to receive incident light only through a corresponding aligned one of the plurality of openings.