Global Shutter Pixel Stack With Light-Shielded Storage Node
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Solution Overview
Problem
Active pixel sensors struggle with low fill factor and high sensitivity to parasitic light when attempting to implement global shutter functionality, leading to image distortion and reduced sensitivity, especially for non-perpendicular or long-wavelength light sources.
Innovation Solution
A pixel design featuring a stacked sensing and storage layer configuration with a light shield between the layers, where the storage node is shielded from radiation, and a common floating diffusion region shared between the layers, improving charge transfer and reducing parasitic light sensitivity, while maintaining a compact and high fill factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a light shield is added between sensing and storage layers, then parasitic light sensitivity is reduced, but device complexity increases
Solution Approach 1:
The patent introduces a light shield layer positioned between the sensing layer and storage layer, utilizing the vertical dimension to block parasitic light paths. This spatial arrangement in the z-direction effectively shields the storage node from parasitic light generated in the sensing layer without affecting the main optical path from the lens through the sensing element.
Solution Approach 2:
The light shield acts as an intermediary element that selectively blocks harmful parasitic light while allowing the normal imaging light to pass through. It mediates between the sensing layer and storage layer, preventing direct interaction between parasitic light and the storage node, thus reducing sensitivity to parasitic light without requiring fundamental changes to the sensor architecture.
2Reliability
If storage node is completely depleted, then charge transport is improved and leakage current is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by adjusting the depletion voltage of the storage node to achieve complete depletion. By controlling the voltage parameter applied to the storage node, the system ensures that no residual charge remains, which improves charge transport completeness and reduces leakage current. This parameter control approach allows for reliable operation while managing manufacturing tolerances.
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 solution enables active pixel sensors to achieve global shutter functionality with improved fill factor and reduced parasitic light sensitivity, allowing for distortion-free imaging of moving objects without increasing sensor area or reducing sensitivity.
Implementation Method 1
Digital imaging uses sensing elements which generate charge carriers upon light impinging
Implementation Method 2
The stack further comprises a light shield at least between the sensing layer and at least the storage node of the storage layer, so the storage node is shielded from radiation
Data Source
AI summary
A pixel for a global shutter pixel array includes a sensing layer and a storage layer. The sensing layer has a sensing element adapted to provide charges upon receiving radiation and a floating diffusion region for receiving charges from the sensing element. The storage layer has at least one storage node for receiving charges from the sensing layer's floating diffusion region and storing the charges. The sensing layer and storage layer form a stack of layers, the sensing layer covering at least the storage node of the storage layer, and the stack has a light shield between the sensing layer and the storage node of the storage layer, so the storage node is shielded from impinging radiation. The storage node is between two transfer gates. The storage node and its surrounding gates are provided between the first floating diffusion region and a second floating diffusion region.