Shared-Pixel Imaging Sensor Layout for Optical Symmetry
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Solution Overview
Problem
In surveillance cameras and mobile device solid-state imaging devices, pixel sharing structures compromise conversion efficiency and optical symmetry, making it challenging to maintain high performance under low illuminance conditions.
Innovation Solution
A solid-state imaging device design that includes a photoelectric conversion unit, a floating diffusion portion, an amplification transistor, and a conversion-efficiency adjustment transistor, with transistors such as reset and selection transistors shared among pixels to maintain high conversion efficiency and optical symmetry in a pixel sharing system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If transfer transistors are placed facing each other to share a floating diffusion portion in a pixel sharing structure, then the area covered by non-photodiode components is reduced and the number of pixels per unit area increases, but the optical symmetry is broken and conversion efficiency deteriorates
Solution Approach 1:
The patent applies asymmetry by intentionally placing the shared floating diffusion portion off-center relative to the photodiodes, and by positioning transfer transistors asymmetrically. This asymmetric design allows the floating diffusion to be optimally positioned for electrical connection while maintaining optical symmetry through careful layout of the photodiode active areas around the shared component.
Solution Approach 2:
The patent merges multiple floating diffusion portions into a single shared floating diffusion that serves multiple pixels. This consolidation reduces the total area occupied by floating diffusion structures and their associated transistors, allowing more photodiode area while maintaining conversion efficiency through proper electrical isolation and capacitance control.
2Productivity
If the distance between floating diffusion portion and amplification transistor is increased to accommodate more sharing pixels, then the number of sharing pixels increases, but the floating diffusion wire length increases and diffusion capacitance increases, causing conversion efficiency to decrease
Solution Approach 1:
The patent transitions from a one-dimensional linear arrangement to a two-dimensional planar layout where the floating diffusion portion is positioned centrally and connects to multiple photodiodes in different directions. This dimensional change allows shorter connection paths and reduces wire length while accommodating more sharing pixels through spatial optimization.
Solution Approach 2:
The patent changes the physical parameters of the floating diffusion structure, including its size, shape, and position, to optimize the balance between capacitance and connectivity. By adjusting these parameters, the design achieves lower diffusion capacitance and shorter wire lengths while supporting multiple sharing pixels, thereby maintaining conversion efficiency.
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
The design achieves high conversion efficiency similar to non-sharing systems while maintaining optical symmetry and reducing sensitivity variations among pixels, even in sharing configurations.
Implementation Method 1
a photodiode in which pixels arranged in a pixel region are photoelectric conversion units
Data Source
AI summary
There are provided a solid-state imaging device and an electronic apparatus that can enhance the conversion efficiency to a degree similar to that of a non-sharing pixel and can maintain the optical symmetry also in a case where sharing between pixels is performed. The solid-state imaging device includes a plurality of pixels arranged in a matrix, and each of the plurality of pixels includes: a photoelectric conversion unit configured to photoelectrically convert incident light; a floating diffusion portion in which signal charge generated by the photoelectric conversion unit is stored; an amplification transistor configured to amplify a potential corresponding to an amount the signal charge stored in the floating diffusion portion, and output a pixel signal corresponding to the amplified potential; and a conversion-efficiency adjustment transistor configured to adjust a conversion efficiency of the signal charge stored in the floating diffusion portion. At least a part of the plurality of pixels forms sharing pixels, and a transistor other than the amplification transistor and the conversion-efficiency adjustment transistor is shared by a plurality of pixels forming the sharing pixels.