CMOS Image Sensor Pixel Structure 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 under low illuminance and potential focus issues, as well as color mixing problems affecting image quality.
Innovation Solution
The image sensor incorporates phase difference detection pixels with split or partially shielded photoelectric conversion layers, including organic photoelectric conversion films and light-shielding films, to enhance sensitivity and accuracy, and imaging pixels with organic photoelectric conversion layers to correct for color mixing and light exposure.
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 under low illuminance
Solution Approach 1:
The photoelectric conversion section is divided into multiple independent photodiodes (first photodiode and second photodiode), each capable of independent operation. This segmentation allows the system to use only the unshielded photodiode for signal generation under low illuminance conditions, thereby maintaining sufficient sensitivity and signal-noise ratio while still enabling phase difference detection when needed.
Solution Approach 2:
The system dynamically selects which photodiode to use based on lighting conditions. Under low illuminance, the unshielded photodiode is activated for optimal sensitivity. Under sufficient lighting, the shielded photodiode configuration is used for accurate phase difference detection. This dynamic adaptation resolves the contradiction between detection accuracy and sensitivity.
2Measurement precision
If photoelectric conversion layers are split or partially shielded for phase difference detection, then detection accuracy is improved, but color mixing from adjacent pixels adversely affects color reproducibility and SNR
Solution Approach 1:
The harmful effect of color mixing is extracted and isolated to specific shielded regions. The light-shielding film is strategically positioned to block stray light from adjacent pixels that would cause color mixing, while leaving the primary light-receiving areas open. This extraction of the harmful factor protects the photoelectric conversion sections without compromising detection accuracy.
Solution Approach 2:
Different regions of the pixel structure are assigned different functions: the central region is optimized for light reception and photoelectric conversion, while peripheral regions are shielded to prevent color mixing from adjacent pixels. This local differentiation of quality and function simultaneously achieves accurate phase difference detection and eliminates color mixing artifacts.
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 configuration enables higher-quality images by improving sensitivity and accuracy of phase difference detection and color correction, even under low light conditions, and reduces color mixing artifacts.
Implementation Method 1
The organic photoelectric conversion film can photoelectrically convert light partially blocked out by the light-shielding film
Data Source
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.