CMOS Image Sensor Pixel Architecture for Signal-to-Noise Ratio
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
CMOS image sensors face challenges in achieving optimal pixel characteristics due to differences in photoelectric conversion sensitivity among blue, green, and red light wavelengths, leading to inefficiencies in charge storage and image quality, particularly in environments with poor shooting conditions.
Innovation Solution
A solid-state image pickup unit is designed with distinct configurations for red, blue, and green pixels, where the green pixel has multiple charge storage sections arranged along the substrate's thickness direction to maximize saturation charge and sensitivity, allowing for better utilization of high sensitivity characteristics and improved signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If pixel transistors are shared among multiple pixels to reduce cell size, then pixel miniaturization is achieved, but the formation area of individual pixels is reduced
Solution Approach 1:
Multiple pixels (red, blue, and green pixels) share common pixel transistors including the transfer transistor and floating diffusion region section. This merging approach reduces the total number of transistors needed per pixel, enabling pixel miniaturization while maintaining necessary circuit functionality.
Solution Approach 2:
The shared pixel transistors serve multiple functions across different color pixels. The transfer transistor and floating diffusion region section are universally used by red, blue, and green pixels, allowing these components to perform the same charge transfer and signal conversion functions for multiple pixels simultaneously.
2Length of moving object
If the formation area of pixel transistors is reduced through sharing, then cell size decreases, but the formation area of photodiodes is limited
Solution Approach 1:
Each pixel type (red, blue, green) has its photodiode positioned at specific depths optimized for its wavelength. Green pixel photodiodes are located at intermediate depths where green light photoelectric conversion is most efficient, while red and blue photodiodes are positioned at depths optimized for their respective wavelengths. This local optimization allows each photodiode to maximize its effective area for its specific color function.
Solution Approach 2:
The patent utilizes the depth dimension (thickness direction) of the semiconductor substrate to differentiate photodiode positions. Instead of competing for surface area, photodiodes for different colors are arranged at different depths, with green pixel photodiodes positioned at intermediate depths between the front surface and the back surface, effectively using the third dimension to resolve area conflicts.
3Device complexity
If green pixels use single charge storage sections, then结构简单 (structure is simple), but saturation charge amount is limited and sensitivity is reduced
Solution Approach 1:
The green pixel charge storage section is divided into multiple segments positioned at different depths within the semiconductor substrate. These segmented storage sections work together to increase the total saturation charge amount while maintaining the functional simplicity of a unified green pixel response.
Solution Approach 2:
Multiple green charge storage sections are arranged in the depth direction (thickness direction) of the substrate rather than expanding horizontally. This vertical arrangement increases the total storage capacity for green light-generated charges without increasing the planar footprint of the green pixel, thereby improving sensitivity while maintaining compact 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 enhances the saturation charge capacity and sensitivity of the green pixel, leading to improved image quality and increased signal-to-noise ratio, effectively leveraging the high sensitivity of green pixels while minimizing waste of converted charge.
Implementation Method 1
a red charge storage section that is provided in the substrate and holds a charge obtained by performing photoelectric conversion on a light component with a red wavelength
Data Source
AI summary
A solid-state image pickup unit includes substrate; a red pixel including a red charge storage section; a blue pixel including a blue charge storage section; and a green pixel including a plurality of green charge storage sections, the red charge storage section and the blue charge storage section being provided in the substrate. Then, the plurality of green charge storage sections are arranged in the substrate along a thickness direction of the substrate.