CMOS Image Sensor Pixel Shielding for PDAF Sensitivity Uniformity
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Solution Overview
Problem
Existing image sensors with a PDAF structure do not adequately address the sensitivity difference between pixels, leading to potential bright spots and image quality issues.
Innovation Solution
A light detection element with a pixel array unit that includes phase difference detection pixels and normal pixels, featuring an image-height-dependent light shielding portion to adjust sensitivity differences by varying the width or shape of light shielding films based on image height.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a PDAF structure with shared on-chip lens is used for phase difference detection pixels, then phase detection capability is improved, but sensitivity difference between pixels occurs leading to bright spots and image quality degradation
Solution Approach 1:
The patent applies local quality by providing different light shielding portions for different pixel groups based on their location in the pixel array. Specifically, pixel groups adjacent to phase difference detection pixels receive light shielding portions with different characteristics (width, shape, or opening ratio) compared to other pixel groups, thereby locally adjusting the optical characteristics to compensate for sensitivity differences caused by the PDAF structure.
Solution Approach 2:
The patent changes physical parameters of the light shielding portions, specifically the width, shape, or opening ratio, to adjust the amount of light reaching different pixel groups. By varying these parameters based on the pixel group's position relative to phase difference detection pixels, the patent equalizes the sensitivity across all pixels while maintaining the PDAF functionality.
2Manufacturing precision
If light shielding portions are added to pixel groups adjacent to phase difference detection pixels, then sensitivity difference is suppressed, but device complexity increases
Solution Approach 1:
The patent segments the light shielding portions into different types based on their location and function. By dividing the pixel array into distinct groups (those adjacent to phase difference detection pixels versus others), the patent applies simplified light shielding structures only where needed, rather than uniformly across the entire array, thereby reducing overall device complexity while maintaining sensitivity uniformity.
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 suppresses sensitivity differences between pixels, preventing bright spots and enhancing image quality by correcting sensitivity ratios and intra-color differences, thereby improving overall image capture performance.
Implementation Method 1
a light shielding portion provided for each of the pixel groups constituted by the normal pixels, including surrounding pixels disposed around the phase difference detection pixels, the light shielding portion differing in width or shape depending on the image height
Data Source
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AI summary
The present disclosure relates to a light detection element that can suppress a sensitivity difference between pixels in an image sensor having a PDAF structure. The light detection element of the present disclosure includes a pixel array unit formed by an arrangement of pixels that constitute, for every n × n pixels, a pixel group including color filters of the same color, two or more phase difference detection pixels adjacent to each other, the two or more phase difference detection pixels being provided in place of some of normal pixels arranged in the pixel array unit, and a light shielding portion provided for each of the pixel groups constituted by the normal pixels, including surrounding pixels disposed around the phase difference detection pixels, the light shielding portion differing in width or shape depending on an image height. The present disclosure is applicable to, for example, a CMOS image sensor.