Storage Node Light Shield Structure for Global Shutter Light Leakage
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Solution Overview
Problem
Global shutter CMOS image sensors face issues with parasitic light leakage, which contaminates stored charges and leads to unwanted artifacts, compromising image quality.
Innovation Solution
A light-shielding structure made of metal or suitable material is implemented, extending into the substrate to encircle and protect the memory node, preventing stray light from reaching the storage region and associated signal processing elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light-shielding structure is introduced to block parasitic light from reaching the storage node, then image quality and global shutter efficiency are improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The light-shielding structure is segmented into multiple functional regions: a first light-shielding structure covering the storage node, a second light-shielding structure covering the transfer gate, and a third light-shielding structure covering the reset gate. This segmentation allows each region to independently address specific light leakage paths, improving image quality while maintaining manageable device complexity through modular design.
Solution Approach 2:
Different light-shielding structures are positioned at specific locations where light leakage problems occur most severely: over the storage node, transfer gate, and reset gate. Each structure has optimized dimensions and positions tailored to its local requirements, such as the first light-shielding structure extending deeper into the substrate than the second and third structures, providing targeted protection where needed most.
2Object-affected harmful factors
If the light-shielding structure extends deeper into the substrate, then parasitic light contamination is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The light-shielding structure is divided into segments with different depths: the first light-shielding structure extends to a first depth, while the second and third light-shielding structures extend to a second depth that is less than the first depth. This segmentation allows deeper shielding where most critical (over the storage node) while reducing manufacturing complexity at less critical locations.
Solution Approach 2:
The light-shielding structures extend to sufficient depths to effectively block parasitic light, with the first structure extending deeper than strictly necessary for minimal protection, ensuring complete elimination of light contamination. This excessive action compensates for variations in manufacturing tolerances and ensures reliable performance.
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 solution effectively minimizes light leakage, enhancing the global shutter efficiency of the image sensor and improving image quality by shielding the memory node and signal processing regions from parasitic light.
Implementation Method 1
a shield formed over the storage node which inhibits light from reaching the storage node
Data Source
AI summary
A pixel of an image sensor includes: a semiconductor material substrate; a photosensitive region formed in the substrate, the photosensitive region generating photo-induced electrical charge in response to illumination with light; a storage node formed in the substrate proximate to the photosensitive region, the storage node selectively receiving and storing photo-induced electrical charge generated by the photosensitive region; and a shield formed over the storage node which inhibits light from reaching the storage node, the shield including an extension which protrudes into the substrate and surrounds an outer periphery of the storage node.