Image Sensor Pixel Isolation Structure for Crosstalk Reduction

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Solution Overview

Problem

As CMOS image sensors increase in resolution, the reduced size of each pixel can lead to interference issues such as crosstalk, resulting in decreased image quality and accuracy due to characteristic deviations between pixels.

Innovation Solution

The image sensing device incorporates a device isolation structure with each unit pixel having a single photoelectric conversion element, a single floating diffusion region, and at least three transistors, arranged in a specific layout to minimize pixel interference, and includes a common floating diffusion node for electrical interconnection of certain unit pixels, allowing for adjustment of conversion gain while reducing characteristic deviations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the pixel size is reduced to increase resolution, then the number of pixels increases, but interference between pixels (crosstalk) occurs and image quality deteriorates

Engineering Contradiction:

Improvenumber of pixelsVSAvoidcrosstalk

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The pixel array is divided into multiple independently isolated unit pixels using device isolation structures. Each unit pixel contains its own photoelectric conversion element and floating diffusion region, physically separating adjacent pixels to prevent charge carrier diffusion and crosstalk while maintaining high pixel density for increased resolution

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Device isolation structures are introduced as intermediary elements between adjacent unit pixels. These isolation structures act as barriers that prevent harmful charge carrier diffusion from one pixel to another, enabling close pixel spacing without crosstalk and thus allowing higher resolution

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If the pixel size is reduced to increase resolution, then the number of pixels increases, but characteristic deviation between pixels increases and image accuracy decreases

Engineering Contradiction:

Improvenumber of pixelsVSAvoidimage accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

Each unit pixel is designed with identical local structure and composition, including the same photoelectric conversion element configuration, floating diffusion region geometry, and transistor arrangement. This uniformity ensures consistent photoelectric conversion characteristics across all pixels, minimizing characteristic deviation and maintaining high image accuracy even at increased resolution

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent optimizes specific parameters of the unit pixel structure, such as the size and shape of the floating diffusion region and the configuration of transistors, to achieve uniform photoelectric conversion characteristics. By carefully controlling these parameters, characteristic deviation between pixels is minimized while maintaining high pixel density

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If a shared pixel structure with electrically interconnected floating diffusion regions is used, then conversion gain can be adjusted, but pixel interference may occur

Engineering Contradiction:

Improveconversion gain adjustmentVSAvoidpixel interference

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The pixel structure is segmented into isolated unit pixels with individual floating diffusion regions, preventing charge carrier diffusion between adjacent pixels. This physical segmentation eliminates pixel interference while maintaining the ability to adjust conversion gain through transistor control within each isolated unit pixel

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The floating diffusion regions are equipped with control transistors that dynamically adjust the capacitance and electrical characteristics of each pixel. This dynamic control enables conversion gain adjustment while the isolated structure prevents interference, allowing versatile operation without sacrificing pixel independence

Inventive Principle:

Principle #15Dynamics

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 enhances the operational characteristics of the image sensing device by minimizing pixel deviation and improving image quality and accuracy, enabling high-quality imaging performance.

Implementation Method 1

CMOS image sensors include a photoelectric conversion element to generate charges from incident light received from outside

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS11227883B2Image sensing device having a shared pixel structure including MOS transistors

Publication Date: 2022.01.18 SK HYNIX INC

AI summary

An image sensing device is disclosed. The image sensing device includes a plurality of unit pixels arranged as an array of unit pixels in a first direction and a second direction perpendicular to the first direction, and a device isolation structure wherein each of the unit pixels is disposed in a region isolated from adjacent unit pixels and includes a single photoelectric conversion element, a single floating diffusion region, and at least three transistors. The single photoelectric conversion element, the single floating diffusion region, and the at least three transistors are located in a region isolated by the device isolation structure.