Image Sensor Extra Transfer Gate Floating Diffusion

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Solution Overview

Problem

Conventional image sensors face challenges in achieving high signal-to-noise ratio and low dark current characteristics, particularly in low illumination modes, due to limitations in charge transfer and dark current management.

Innovation Solution

The image sensor design incorporates multiple floating diffusion regions and extra transfer gates, allowing for operation in both high and low illumination modes by selectively activating or deactivating transfer transistors, which improves charge transfer efficiency and reduces dark current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional image sensors use standard transfer gates and floating diffusion regions, then device complexity is low, but signal-to-noise ratio and dark current characteristics deteriorate in low illumination modes

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoiddevice complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The pixel block is divided into multiple unit pixels, each with its own floating diffusion region. Additionally, a shared extra floating diffusion region is introduced that can receive photo-charges from multiple unit pixels through extra transfer gates. This segmentation allows independent operation in different modes, improving signal-to-noise ratio by enabling selective charge transfer to appropriate diffusion regions.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The extra floating diffusion region and extra transfer gates are designed to serve multiple functions: they can operate independently for low illumination mode imaging, or work in conjunction with unit pixel floating diffusion regions for high illumination mode. This multi-functionality allows the same hardware structure to adapt to different lighting conditions, improving reliability across varying environments.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If extra transfer gates and floating diffusion regions are added to improve charge transfer efficiency, then signal-to-noise ratio improves, but device complexity increases

Engineering Contradiction:

Improvecharge transfer efficiencyVSAvoiddevice complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Multiple unit pixels share common structures including the extra floating diffusion region and extra transfer gates. This merging approach allows charge transfer paths to be combined, improving charge transfer efficiency by providing multiple routes for photo-charge collection while reducing redundant components. The shared structures enable coordinated operation across the pixel block.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The extra transfer gates are designed with controllable conductivity states, allowing dynamic switching between different charge transfer modes. In low illumination mode, the extra transfer gates can be activated to transfer charges to the extra floating diffusion region. In high illumination mode, they can be deactivated or operate in conjunction with unit pixel transfer gates, providing adaptive charge transfer efficiency.

Inventive Principle:

Principle #15Dynamics

3Productivity

If transfer gates are used to control photo-charge transfer, then charge transfer efficiency improves, but dark current increases

Engineering Contradiction:

Improvecharge transfer efficiencyVSAvoiddark current

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The extra floating diffusion region acts as an intermediary charge collection point that receives photo-charges from multiple unit pixels through extra transfer gates. This intermediary structure provides an additional charge transfer pathway that is optimized for low illumination conditions, improving charge transfer efficiency while the selective activation of extra transfer gates minimizes dark current generation compared to continuously active gates.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 design enhances the image sensor's ability to capture high-quality images in low light conditions by minimizing charge loss and dark current, resulting in improved signal-to-noise ratio and precise image capturing.

Implementation Method 1

Each unit pixel includes a block of adjacent photodiodes that detect incident light to produce photo-generated charges

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS10818710B2Image sensor including an extra transfer gate and an extra floating diffusion region

Publication Date: 2020.10.27 SK HYNIX INC

AI summary

An image sensor may include a pixel array including different pixel blocks where a pixel block includes a block of adjacent unit pixels each unit responsive to light to produce photo-generated charges, a floating diffusion region disposed at a center of each unit pixel to receive the photo-generated charges, and transfer gates formed between the floating diffusion region and the unit pixel to control the transfer of the photo-generated charges. Each the pixel block may include an extra floating diffusion region at a center of the pixel block to interface with each of the adjacent unit pixels with the pixel block to photo-generated charges from each of the adjacent unit pixels and extra transfer gates that are formed between the extra floating diffusion region and the adjacent unit pixels to control the transfer of the photo-generated charges from the adjacent unit pixels to the extra floating diffusion region.