Solid-State Image Sensor Floating Diffusion Capacitance Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional solid-state image capturing devices face a challenge in reducing the capacitance of the floating diffusion layer while maintaining or increasing the transfer path width, which affects the efficiency of carrier transfer and conversion gain.
Innovation Solution
The device incorporates a first conductivity type well, a second conductivity type diffusion layer, and a third conductivity type well, with specific electrode formations and insulating films to reduce the capacitance of the floating diffusion layer, allowing for wider transfer paths without compromising carrier transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the transfer path width is increased to improve carrier transfer efficiency, then the transfer efficiency is improved, but the capacitance of the floating diffusion layer increases which reduces conversion gain
Solution Approach 1:
The floating diffusion layer is divided into multiple regions with different conductivity types (first 2nd-conductivity type diffusion layer and second 2nd-conductivity type diffusion layer). This segmentation allows the first region to serve as the main accumulation area with larger area for high conversion gain, while the second region acts as an extension that reduces overall capacitance effects, enabling the transfer path width to be increased without proportionally increasing the capacitance that limits conversion gain.
Solution Approach 2:
Different regions of the floating diffusion layer are assigned different conductivity types and functions. The first 2nd-conductivity type diffusion layer has higher doping concentration and serves as the primary accumulation region, while the second 2nd-conductivity type diffusion layer has lower doping concentration and serves to extend the structure. This local differentiation allows optimization of each region's properties to simultaneously achieve high transfer efficiency and maintain conversion gain.
2Reliability
If the capacitance of the floating diffusion layer is reduced to increase conversion gain, then the conversion gain is improved, but the transfer path width must be reduced which decreases carrier transfer efficiency
Solution Approach 1:
By segmenting the floating diffusion layer into multiple conductivity type regions, the patent achieves reduced effective capacitance while maintaining sufficient accumulation area. The first 2nd-conductivity type diffusion layer provides the main accumulation function with optimized capacitance, while the second 2nd-conductivity type diffusion layer extends the structure to maintain transfer path width, thus improving conversion gain without sacrificing transfer efficiency.
Solution Approach 2:
The patent changes the doping concentration parameter between different regions: the first 2nd-conductivity type diffusion layer has higher doping concentration to reduce capacitance and improve conversion gain, while the second 2nd-conductivity type diffusion layer has lower doping concentration to maintain carrier transfer efficiency. This parameter differentiation resolves the contradiction between conversion gain and transfer efficiency.
3Reliability
If the capacitance of the floating diffusion layer is reduced regardless of transfer path width, then conversion gain is improved while maintaining transfer efficiency, but the device structure becomes more complex
Solution Approach 1:
The patent merges the floating diffusion layer with the transfer path structure by forming the second 2nd-conductivity type diffusion layer as an extension of the first 2nd-conductivity type diffusion layer. This merging allows the floating diffusion layer to serve dual functions: maintaining conversion gain through optimized capacitance in the first region and maintaining transfer efficiency through the extended structure in the second region, without requiring completely separate structures.
Solution Approach 2:
The multi-region floating diffusion layer structure serves multiple functions simultaneously: the first 2nd-conductivity type diffusion layer provides high conversion gain through optimized capacitance, while the second 2nd-conductivity type diffusion layer provides carrier transfer pathway extension. This multi-functionality allows the single integrated structure to achieve both high conversion gain and high transfer efficiency without requiring additional separate components.
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 reduces the capacitance of the floating diffusion layer, enhancing carrier transfer efficiency and conversion gain, while simplifying the manufacturing process and reducing costs.
Implementation Method 1
carriers generated in a photodiode due to photoelectric conversion
Data Source
AI summary
An aspect of the invention is a solid-state image capturing device that includes a P-type well 12, an N-type low concentration diffusion layer 18 formed in the P-type well 12, a P-type surface diffusion layer 16 formed on a surface of the N-type low concentration diffusion layer 18, and a P-type high concentration well 15 formed in a boundary region between a side surface of the N-type low concentration diffusion layer 18 and the P-type well 12.