Shared-Filter Pixel Layout for Higher-SNR Image Sensors
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Solution Overview
Problem
Current image sensors face challenges in enhancing image quality due to limitations in pixel design and signal processing, particularly in the arrangement of photodiodes and color filters, which affect the accumulation and output of electric charges.
Innovation Solution
The proposed image sensor design includes a pixel group with a first, second, and third photodiode under a shared color filter, each with a floating diffusion and a source follower transistor, where the metal layer extends to receive pixel signals, enabling improved charge accumulation and signal processing through analog and digital binning operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple photodiodes are arranged under a shared color filter to improve charge accumulation, then the signal-to-noise ratio is improved, but the device complexity increases
Solution Approach 1:
Multiple photodiodes (first, second, and third photodiodes) are arranged under a shared color filter, merging their charge accumulation functions. The floating diffusions and column lines are also shared among multiple pixels, reducing redundant structures while improving signal-to-noise ratio through combined charge accumulation.
Solution Approach 2:
The color filter serves multiple photodiodes simultaneously, making it a universal component. The floating diffusion regions are shared by multiple pixels, and column lines serve multiple pixels, enabling multi-functionality that improves measurement precision without proportional increases in device complexity.
2Manufacturing precision
If floating diffusions are shared among multiple pixels to reduce device complexity, then manufacturing precision is improved, but coupling capacitance increases
Solution Approach 1:
While floating diffusions are shared, the pixel structure is segmented into distinct photodiode regions with individual color filters. The column lines are extended in the second direction to separate signal paths, segmenting the capacitance coupling while maintaining shared floating diffusion benefits for manufacturing precision.
Solution Approach 2:
The column lines extend in a second direction that intersects with the first direction of photodiode arrangement. This dimensional change separates the signal readout paths spatially, reducing coupling capacitance between adjacent pixels while maintaining the shared floating diffusion structure for manufacturing precision.
3Measurement precision
If column lines are extended to intersect with photodiode arrangement direction to reduce coupling capacitance, then signal quality is improved, but device complexity increases
Solution Approach 1:
The extended column lines serve multiple functions: they collect signals from multiple pixels, extend in the second direction to reduce coupling capacitance, and maintain electrical connection to readout circuits. This multi-functionality improves signal quality without requiring separate structures for each function.
Solution Approach 2:
Multiple column lines are merged into extended conductive structures that span across multiple pixel rows. The metal layers are combined to form continuous column lines that serve multiple pixels, reducing the number of separate components while improving signal quality through reduced coupling capacitance.
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 design enhances image quality by optimizing charge accumulation and signal processing, leading to improved signal-to-noise ratio and reduced coupling capacitance, thereby increasing the overall performance of the image sensor.
Implementation Method 1
Each of the pixels may include, for example, a photodiode (PD). The photodiode may serve to convert incident light into electrical signals.
Implementation Method 2
a first floating diffusion configured to accumulate electric charges generated by the first photodiode, a second floating diffusion configured to accumulate electric charges generated by the second photodiode, a third floating diffusion configured to accumulate electric charges generated by the third photodiode
Data Source
AI summary
An image sensor includes a pixel group. The pixel group includes a first color filter, first to third photodiodes below the first color filter such that the first color filter overlaps each of the first to third third photodiodes in a vertical direction, wherein the first to third photodiodes are arranged in a first direction perpendicular to the vertical direction, first to third floating diffusions configured to accumulate electric charges generated by the first to third photodiodes, respectively, a source follower transistor configured to output a first pixel signal based on the electric charges accumulated in at least one of the first to third floating diffusions, and a first metal layer configured to receive the first pixel signal from the source follower transistor, wherein the first metal layer extends in a second direction intersecting the first direction, wherein the first to third floating diffusions are arranged in the first direction.