CMOS Imaging Pixel Layout for Higher Saturation Charge
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Solution Overview
Problem
In back-illuminated CMOS image sensors, the saturation signal charge amount of photodiodes in phase difference detection pixels is limited, necessitating improvements to enhance detection capabilities.
Innovation Solution
A solid-state imaging element with a matrix arrangement of light receiving pixels, each including a pair of photoelectric conversion units, a shared floating diffusion, and separation regions. The first separation region surrounds the photodiodes, while the second separation region is disposed between them, extending from the semiconductor surface to increase the photodiode volume and saturation signal charge capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If photodiodes are arranged in phase difference detection pixels with shared floating diffusion, then device integration is improved, but saturation signal charge amount is reduced
Solution Approach 1:
The pixel is divided into multiple photodiodes (first and second photodiodes) that share a common floating diffusion region. This segmentation allows multiple photoelectric conversion units to be integrated within a single pixel structure while maintaining their individual photoelectric conversion capabilities, thereby resolving the contradiction between device integration and charge storage capacity.
Solution Approach 2:
The first separation region extends in the depth direction (from light incident surface toward the opposite surface) rather than only in the planar direction. This three-dimensional extension allows the separation region to effectively isolate photodiodes while preserving lateral space for charge storage, enabling both high integration and sufficient saturation charge amount.
2Quantity of substance
If photodiode volume is increased to improve saturation charge amount, then detection capability is improved, but pixel area is increased
Solution Approach 1:
Instead of increasing photodiode volume solely through lateral expansion, the first separation region extends in the depth direction of the semiconductor substrate. This vertical extension provides effective isolation while preserving lateral space, allowing photodiodes to maintain sufficient volume for charge storage without increasing the overall pixel footprint.
Solution Approach 2:
The separation regions are strategically positioned only where needed for isolation and charge management, rather than uniformly throughout the entire pixel structure. This localized approach minimizes the space occupied by separation structures while ensuring proper photodiode isolation and charge collection, thereby maintaining high photodiode volume efficiency within the pixel area.
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 signal charge amount and layout efficiency of photodiodes, improving the dynamic range and SN ratio in phase difference detection pixels without reducing photodiode volume or increasing manufacturing complexity.
Implementation Method 1
a pair of photoelectric conversion units, and a first separation region and a second separation region... The pair of photoelectric conversion units is disposed adjacent to each other and has a shared floating diffusion
Data Source
AI summary
A solid-state imaging element having an array of light receiving pixels is disclosed. A light receiving pixel includes a pair of photoelectric conversion units, a first separation region, and a second separation region. The pair of photoelectric conversion units is disposed adjacent to each other and has a shared floating diffusion (FD). The first separation region surrounds the pair of photoelectric conversion units. The second separation region is disposed between the pair of photoelectric conversion units. The first separation region has a rectangular shape in plan view and extends from a surface on the opposite side to a light incident surface of the semiconductor layer toward the light incident surface. The second separation region is disposed along a diagonal line of the first separation region extends from the surface on the opposite side to the light incident surface of the semiconductor layer toward the light incident surface.