Image Sensor Vertical Charge Storage Well for Global Shutter
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Solution Overview
Problem
Modern image sensors face challenges in achieving high-speed and high-resolution performance in low-light conditions due to issues with fill-factor degradation and parasitic electron-hole pair contamination, particularly in global shutter applications, where existing solutions either compromise on fill-factor or suffer from reduced quantum efficiency.
Innovation Solution
The implementation of a pump gate structure and vertical charge storage well in image sensors, where the storage well blocks incident light and shields the storage region from backside illumination, maintaining high fill-factor while enhancing conversion gain and reducing read noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel size is reduced to achieve higher resolution, then the resolution is improved, but the photosensitivity and dynamic range are degraded
Solution Approach 1:
The patent introduces a vertical charge storage well extending from the backside surface toward the frontside surface, moving the charge storage function from a lateral plane to a vertical dimension. This allows the photodiode active area to remain large for high photosensitivity while the vertical well provides additional charge storage capacity, effectively decoupling the trade-off between pixel size and photosensitivity.
Solution Approach 2:
The charge storage function is segmented into two parts: the photodiode depletion region for initial charge collection and the extended vertical storage well for additional charge capacity. This segmentation allows each region to be optimized independently - the photodiode for light sensitivity and the storage well for charge capacity - resolving the contradiction between small pixel size and high photosensitivity.
2Adaptability or versatility
If a storage node is added to enable global shutter function, then the global shutter capability is improved, but the fill-factor is reduced due to parasitic electron-hole pair contamination
Solution Approach 1:
The patent extracts the charge storage function from the traditional lateral storage node and relocates it to a vertical storage well. This removes the storage node structure that blocks incident light and causes parasitic electron-hole pair generation, thereby maintaining high fill-factor while preserving global shutter capability.
Solution Approach 2:
By moving charge storage from a lateral storage node to a vertical well extending through the substrate, the patent eliminates the need for a light-blocking storage node structure. The vertical well allows charge storage without interfering with incident light paths, thus maintaining high fill-factor while enabling global shutter operation.
3Productivity
If the storage region is positioned closer to the frontside surface to improve charge transfer, then the charge transfer efficiency is improved, but the quantum efficiency is reduced due to backside illumination interference
Solution Approach 1:
Instead of moving the storage region toward the frontside surface as conventional approaches do, the patent inverts the approach by extending the storage well vertically from the backside surface upward. This allows the storage function to be positioned optimally for both charge transfer and protection from backside illumination interference.
Solution Approach 2:
The patent resolves the contradiction by transitioning from a lateral positioning approach to a vertical dimension approach. The storage well extends vertically from the backside, allowing charge to be collected efficiently from the photodiode while the vertical structure naturally shields the stored charge from backside illumination interference, maintaining high quantum 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
This configuration enables high-speed global-shutter image sensors with improved low-light performance and reduced read noise, maintaining high fill-factor and conversion gain, suitable for applications like scientific imaging and augmented reality.
Implementation Method 1
the storage well blocks incident light and shields the storage region from backside illumination
Implementation Method 2
a pump gate structure situated between the storage well and the frontside surface
Data Source
AI summary
Disclosed herein are image apparatuses comprising a frontside surface, a backside surface, a storage region (e.g., a storage node or a floating diffusion node), the storage region being situated closer to the frontside surface than to the backside surface, a storage well situated between the backside surface and the storage region, and a doping region situated between the storage region and the storage well. An impurity type of the doping region is opposite an impurity type of the storage well. A lateral area of the storage well is greater than or equal to a lateral area of the storage region, and no portion of a lateral perimeter of the storage region extends outside of a lateral perimeter of the storage well.