Shared Floating Diffusion Layout for Low-Noise Image Sensors
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Solution Overview
Problem
Conventional image sensors face challenges with increased fixed pattern noise and reduced conversion gain due to longer metal wiring lengths connecting floating diffusion regions, which affects pixel size miniaturization and image quality.
Innovation Solution
The image sensor design shares floating diffusion regions through the silicon region of the substrate, reducing the length of metal wiring connecting them, and optimizing the angle and arrangement of these connections to minimize noise while maintaining high conversion gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the degree of integration of the image sensor increases, then the size of each pixel decreases, but the length of metal wiring connecting floating diffusion regions increases
Solution Approach 1:
The patent utilizes the vertical dimension by forming floating diffusion regions at different depths within the substrate. Multiple floating diffusion regions are positioned at different vertical levels, and metal wirings connect these regions by traversing through the vertical dimension, thereby reducing the horizontal wiring length and enabling higher integration without increasing pixel area.
Solution Approach 2:
The patent implements a nested structure where floating diffusion regions are positioned within vertically stacked layers. The metal wirings are routed through intermediate layers to connect nested floating diffusion regions, allowing compact arrangement of multiple pixels while minimizing wiring length through efficient spatial utilization.
2Length of stationary object
If the length of metal wiring connecting floating diffusion regions increases, then fixed pattern noise increases
Solution Approach 1:
By connecting floating diffusion regions through the vertical dimension rather than extending horizontally, the patent significantly reduces metal wiring length. This vertical routing approach minimizes the wiring length that would otherwise contribute to fixed pattern noise, while still enabling connection between multiple floating diffusion regions in highly integrated pixels.
3Length of stationary object
If the length of metal wiring connecting floating diffusion regions increases, then conversion gain decreases
Solution Approach 1:
The patent employs vertical stacking to position floating diffusion regions at different depths, with metal wirings connecting them through the vertical dimension. This approach maintains short wiring lengths that preserve signal strength and conversion gain, while accommodating multiple floating diffusion regions within a compact pixel area for high integration.
Data Source
AI summary
An image sensor, including a shared pixel including two sub pixels of a 1X2 structure and sharing a floating diffusion region on each of the two sub pixels through a metal wiring, unit pixels surrounding the floating diffusion region, within the shared pixel, separated from each other by front-side deep trench isolation, and each including a photodiode, a transfer transistor adjacent to the floating diffusion region and on each of the unit pixels, a reset transistor and a selection transistor on a first unit pixel located in a first quadrant among the unit pixels, a conversion gain transistor on a second unit pixel located in a second quadrant among the unit pixels, and a source follower transistor on a third unit pixel located in a third quadrant and a fourth unit pixel located in a fourth quadrant among the unit pixels.