Light Guiding Grid for CMOS Image Sensor Crosstalk Reduction
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Solution Overview
Problem
CMOS image sensors with sinking micro-lenses face challenges in reducing light crosstalk between adjacent photo sensors, which degrades the signal-to-noise ratio (SNR) at low illumination due to incident light passing through color filters near gaps between neighboring photo sensors.
Innovation Solution
A light guiding grid structure with intersecting grid lines and rounded corners is implemented, where the primary grid width and diagonal grid width are optimized to prevent light from passing between adjacent photo sensors, using materials like metal and dielectric, with a thickness ranging from 50 nm to 500 nm, to block unwanted light and reduce crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light guiding grid is implemented to block light between photo sensors, then light crosstalk is reduced and SNR is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The light guiding grid is segmented into multiple discrete lines positioned between adjacent photo sensors. Each grid line acts as an independent light-blocking element, collectively forming a comprehensive barrier against crosstalk while maintaining modular simplicity in design and fabrication
Solution Approach 2:
The light guiding grid serves as an intermediary structure positioned between the color filter array and photo sensors. This intermediate layer specifically addresses light crosstalk without interfering with the primary optical path from color filters to corresponding photo sensors, thereby improving SNR while preserving normal imaging function
2Object-affected harmful factors
If grid lines are made thicker to block more light, then crosstalk prevention is improved, but light loss to photo sensors increases
Solution Approach 1:
The grid lines are positioned with precise local control to block light only in the specific regions between adjacent photo sensors where crosstalk occurs. The grid structure provides localized light blocking exactly where needed, without affecting the optical path to the intended photo sensors, thus preventing crosstalk while minimizing light loss
Solution Approach 2:
The grid line width is optimized to a specific parameter range that provides sufficient light blocking capability to prevent crosstalk while maintaining adequate light transmission to photo sensors. This parameter optimization balances the competing requirements of crosstalk prevention and light transmission efficiency
3Manufacturing precision
If a light guiding grid is added to prevent crosstalk, then image quality is improved, but manufacturing processes become more complex
Solution Approach 1:
The light guiding grid fabrication is merged with the existing photolithography processes used for color filter array formation. By integrating the grid structure creation into the established manufacturing workflow, the additional complexity is minimized while achieving the desired image quality improvement through precise light blocking
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 grid structure effectively blocks light between photo sensors, enhancing the signal-to-noise ratio (SNR) by preventing crosstalk and maintaining image quality while allowing sufficient light to reach the intended photo diodes, thus improving the performance of CMOS image sensors.
Implementation Method 1
the grid structure effectively blocks light between photo sensors, enhancing the signal-to-noise ratio (SNR) by preventing crosstalk
Data Source
AI summary
A light guide grid can include a grid structure having a plurality of intersecting grid lines, each grid line having a width w, and a plurality of openings for photosensor elements between intersecting grid lines. The grid structure has a diagonal grid width between two adjacent ones of the plurality of openings in a diagonal direction. The diagonal grid width has a value exceeding approximately √3 w. An image sensor can include a light guide grid having a grid structure as described above and further include a micro-lens such as a sinking micro-lens and a color filter. A method of fabricating a light guide grid can include forming a grid above at least one photo sensor, the grid having intersecting grid lines of width w and a diagonal grid width in a diagonal direction having a value exceeding approximately √3 w.