CMOS Image Sensor Pixel Layout for Balanced Channel Saturation
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Solution Overview
Problem
In Complementary Metal-Oxide Semiconductor (CMOS) image sensors using RYYB or RWWB color filters, the red and blue pixels often remain unsaturated while the yellow or white pixels are saturated, leading to signal waste due to unequal light absorption across channels.
Innovation Solution
Incorporating a sub-wavelength pixel unit with photodiode columns of varying sizes and angles, ensuring equal light-receiving surfaces but unequal junction areas, allowing for different full well capacities across channels, thus enabling simultaneous saturation of all pixel types and optimizing light absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If RYYB or RWWB color filters are used to increase light absorption efficiency, then the overall light efficiency of the image sensor is improved, but the red and blue pixels remain unsaturated while yellow or white pixels become saturated, causing signal waste in the R and B channels
Solution Approach 1:
The patent applies local quality by making the light-receiving surfaces of different photodiode column units equal in area, while their junction areas differ. This localized differentiation allows each channel (R, G, B) to have optimized full well capacity matching its light absorption characteristics, enabling simultaneous saturation of all channels and eliminating signal waste in the R and B channels while maintaining high overall light efficiency.
2Ease of manufacture
If photodiode column units have equal light-receiving surface areas, then manufacturing simplicity is maintained, but channels with higher light absorption (Y/W) saturate before channels with lower light absorption (R/B), resulting in unequal signal utilization
Solution Approach 1:
The patent maintains equal light-receiving surface areas for manufacturing simplicity while introducing local quality differentiation through unequal junction areas. This allows the full well capacity of each channel to be independently optimized based on its light absorption characteristics, ensuring that all channels reach saturation simultaneously and maximizing signal utilization efficiency without complicating the manufacturing process.
3Device complexity
If all pixel types have the same full well capacity, then device structure is simplified, but pixels with higher light absorption saturate first, leaving other pixels unsaturated and wasting captured light information
Solution Approach 1:
The patent introduces local quality differentiation by setting different full well capacities for different pixel types based on their light absorption characteristics. Pixels with higher light absorption (Y/W channels) are assigned larger full well capacities, while pixels with lower light absorption (R/B channels) have smaller full well capacities. This optimized distribution allows all pixel types to reach saturation simultaneously, maximizing the utilization of captured light information while maintaining relatively simple device structure.
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 allows for full utilization of each channel's information, significantly improving the efficiency of the CMOS image sensor by ensuring all pixel types reach saturation simultaneously, reducing signal waste and enhancing image processing capabilities.
Implementation Method 1
The sub-wavelength pixel unit includes a first PD column unit corresponding to the first wavelength range, a second PD column unit corresponding to the second wavelength range, and a third PD column unit corresponding to a third wavelength range
Data Source
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AI summary
Disclosed in embodiments of the present invention are a CIS, an image processing method, and a storage medium. The CIS comprises a color filter and a sub-wavelength pixel unit. The color filter comprises a first filter unit corresponding to a first wavelength range, a second filter unit corresponding to a second wavelength range, and a third filter unit corresponding to a third wavelength range. The sub-wavelength pixel unit comprises a first photodiode (PD) pillar corresponding to the first wavelength range, a second PD pillar corresponding to the second wavelength range, and a third PD pillar corresponding to the third wavelength range. A first light-receiving surface corresponding to the first PD pillar, a second light-receiving surface corresponding to the second PD pillar and a third light-receiving surface corresponding to the third PD pillar have equal areas. A first junction area corresponding to the first PD pillar, a second junction area corresponding to the second PD pillar and a third junction area corresponding to the third PD pillar are not equal.