CMOS Image Sensor Pixel Layout for Low-Light Phase Detection
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Solution Overview
Problem
Phase difference detection pixels in image sensors have lower sensitivity due to partial light shielding, leading to inadequate signal-noise ratio (SNR) under low illuminance, which can result in out-of-focus images and color reproducibility issues.
Innovation Solution
Incorporating a light-shielding film below an organic photoelectric conversion film in phase difference detection pixels, allowing partial light shielding while enabling photoelectric conversion of blocked light, and using differences in output between photoelectric conversion layers for phase difference detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If part of the photoelectric conversion section is shielded from light for phase difference detection, then phase difference detection capability is improved, but sensitivity is reduced and signal-noise ratio becomes insufficient
Solution Approach 1:
The photoelectric conversion section is divided into multiple independent photodiodes (first photodiode, second photodiode, third photodiode, fourth photodiode) arranged in a 2x2 matrix. Each photodiode can be independently controlled for light shielding, allowing phase difference detection while maintaining sufficient light reception area for high sensitivity and signal-noise ratio.
Solution Approach 2:
Different regions of the photoelectric conversion section have different light shielding characteristics. Specifically, the first and second photodiodes have light shielding on one side for phase difference detection, while the third and fourth photodiodes have light shielding on the opposite side, creating local variations that enable accurate phase difference measurement without sacrificing overall sensitivity.
2Measurement precision
If part of the photoelectric conversion section is shielded from light, then phase difference detection is enabled, but image quality deteriorates under low illuminance
Solution Approach 1:
The photoelectric conversion section is segmented into four separate photodiodes, allowing selective light shielding on specific regions while maintaining light reception capability in other regions. This segmentation enables phase difference detection without significantly reducing the overall light-gathering area, thereby preserving image quality under low illuminance conditions.
Solution Approach 2:
The patent combines phase difference detection functionality with normal imaging functionality in a single pixel unit. By integrating multiple photodiodes with different light shielding patterns within one pixel, the system can simultaneously perform phase difference detection and maintain high sensitivity for low-light imaging.
3Reliability
If normal imaging pixel structure is used, then high sensitivity is achieved, but color mixing from adjacent pixels adversely affects color reproducibility and SNR
Solution Approach 1:
Each photodiode within the pixel has asymmetric light shielding applied to specific sides (first and second photodiodes have shielding on one side, third and fourth on the opposite side). This local quality variation creates directional sensitivity patterns that reduce color mixing from adjacent pixels while maintaining overall high sensitivity through the combined response of all four photodiodes.
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
This approach enhances the SNR and accuracy of phase difference detection even under low illuminance, improving image quality and reducing color mixing and flare effects.
Implementation Method 1
an organic photoelectric conversion film, and a photoelectric conversion section formed in a substrate below the organic photoelectric conversion film
Data Source
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AI summary
The present technology relates to an image sensor and an electronic apparatus which enable higher-quality images to be obtained. Provided is an image sensor including a plurality of pixels, each pixel including one on-chip lens, and a plurality of photoelectric conversion layers formed below the on-chip lens. Each of at least two of the plurality of photoelectric conversion layers is split, partially formed, or partially shielded from light with respect to a light-receiving surface. The pixels are phase difference detection pixels for performing AF by phase difference detection or imaging pixels for generating an image. The present technology can be applied to a CMOS image sensor, for example.