Multilayer Image Sensor Pixel Structure for Crosstalk Reduction
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Solution Overview
Problem
Crosstalk, particularly electrical crosstalk, is a significant issue in image sensors, leading to blurring and streaking in images due to charge carriers being collected by neighboring pixels, which existing technologies have not adequately addressed.
Innovation Solution
The introduction of a collector layer and barrier layers in the image sensor pixel structure, which prevents carriers formed deep within the photodiode regions from being collected by adjacent photodiodes, utilizing a graded dopant profile and biasing circuits to establish electric fields that sweep away and collect photo-generated carriers, thereby reducing crosstalk and blooming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional photodiode structure is used, then the device complexity is low, but electrical crosstalk occurs between neighboring pixels
Solution Approach 1:
The photodiode structure is segmented into multiple layers including a first photodiode layer, an intermediate layer, and a second photodiode layer. This segmentation creates distinct charge collection regions that prevent charge carriers generated in one pixel from being collected by neighboring pixels, thereby reducing electrical crosstalk while maintaining manageable device complexity through modular layering.
Solution Approach 2:
The patent implements a nested structure where the intermediate layer is positioned between and connects the first and second photodiode layers. This nested arrangement allows charge carriers to be collected at multiple depths within the same pixel volume, ensuring that carriers generated deep within the substrate are captured by their home pixel rather than drifting into adjacent pixels, thus reducing crosstalk without significantly increasing overall device complexity.
2Measurement precision
If deeper charge carriers are collected, then the image resolution improves, but blooming and edge blurring increase
Solution Approach 1:
The photodiode is divided into depth-segmented layers that independently collect charge carriers generated at different depths. The first photodiode layer collects shallow carriers while the second photodiode layer collects deep carriers, both within the same pixel. This depth segmentation allows comprehensive carrier collection for high resolution while preventing lateral diffusion that causes blooming and edge blurring, as each layer's collected carriers are confined to their respective pixel.
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 reduces electrical crosstalk and blooming, enhancing image clarity by ensuring that charge carriers are collected within their intended photodiode regions, thereby improving image resolution and reducing edge blurring and streaking.
Implementation Method 1
utilizing a graded dopant profile and biasing circuits to establish electric fields that sweep away and collect photo-generated carriers
Implementation Method 2
light (indicated by dashed arrows) incident on the front side of CIS pixel 100 can reach a photosensitive or photodiode ('PD') region 115
Data Source
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AI summary
An image sensor pixel includes a substrate, a first epitaxial layer, a collector layer, a second epitaxial layer and a light collection region. The substrate is doped to have a first conductivity type. The first epitaxial layer is disposed over the substrate and doped to have the first conductivity type as well. The collector layer is selectively disposed over at least a portion of the first epitaxial layer and doped to have a second conductivity type. The second epitaxial layer is disposed over the collector layer and doped to have the first conductivity type. The light collection region collects photogenerated charge carriers and is disposed within the second epitaxial layer. The light collection region is also doped to have the second conductivity type.