Image Sensor Pixel Layout With Centered Detection Node Alignment
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Solution Overview
Problem
In solid-state imaging devices, the asymmetrical structure between large and small pixels leads to transfer defects and delays due to asymmetry in charge transfer, resulting in inconsistent sensitivity ratios and output linearity, which is disadvantageous for high saturation and maximum transfer performance.
Innovation Solution
The center of the detection node in some unit pixels is made coincident with the light receiving center of the photoelectric conversion unit, facilitating efficient charge transfer and reducing potential pocket formation, thereby improving saturation and transfer performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the transfer electrode is provided at the edge of the photoelectric conversion area, then the saturation charge amount can be increased, but the charge transfer time increases and transfer performance deteriorates
Solution Approach 1:
Instead of placing the transfer electrode at the edge of the photoelectric conversion area, the patent inverts the approach by positioning it at the center. This central placement creates a potential gradient that radiates outward to the edges, enabling faster charge collection while maintaining high saturation charge capacity. The center position allows charge to be collected from all directions simultaneously, reducing transfer time.
2Quantity of substance
If the transfer electrode is provided at the edge of the photoelectric conversion area, then the saturation charge amount can be increased, but potential pockets are created that trap charge
Solution Approach 1:
The patent inverts the conventional edge placement of transfer electrodes by positioning them at the center of the photoelectric conversion area. This prevents the formation of potential pockets that occur at edge positions, ensuring reliable charge transfer without trapping. The central electrode creates a uniform potential gradient that directs charge flow smoothly toward collection nodes.
3Adaptability or versatility
If asymmetrical structure is used between large and small pixels, then different sensitivities can be achieved, but transfer defects and delays occur
Solution Approach 1:
The patent applies local quality by making the detection node position adaptive to pixel type. Large pixels and small pixels both use central detection nodes, but the specific geometric parameters and potential distribution are optimized locally for each pixel size. This allows different sensitivities while maintaining consistent central-symmetric charge transfer paths, preventing transfer defects.
Solution Approach 2:
The patent uses controlled asymmetry in the potential distribution and electrode dimensions while maintaining central symmetry in position. The detection node structure and surrounding potential fields are asymmetrically optimized for large versus small pixels to achieve different sensitivities, but both remain centered to ensure reliable transfer.
4Quantity of substance
If the detection node is positioned away from the light receiving center, then the saturation charge amount can be increased, but sensitivity shading occurs
Solution Approach 1:
Instead of positioning detection nodes away from the light receiving center, the patent inverts this approach by placing them at the center. This central alignment ensures that the detection node is optimally positioned relative to the incident light distribution, achieving uniform sensitivity across the pixel array while maintaining high saturation charge capacity through optimized potential gradients.
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 high saturation and maximum transfer performance by aligning the detection node with the light receiving center, reducing sensitivity shading and improving signal-to-noise ratio in the structure including large and small pixels.
Implementation Method 1
a photoelectric conversion unit that photoelectrically converts incident light
Data Source
AI summary
Provided is a solid-state imaging device that allows high saturation and maximum transfer performance to be achieved. The solid-state imaging device includes a plurality of unit pixels arranged in a two-dimensional array. The plurality of unit pixels each includes a photoelectric conversion unit that photoelectrically converts incident light and a wiring layer stacked on a surface opposite to a light-incident side surface of the photoelectric conversion unit and having a detection node that detects charge stored at the photoelectric conversion unit. In at least some of the plurality of unit pixels, a center of the detection node is coincident with a light receiving center of the photoelectric conversion unit.