Shared-FD Image Sensor Layout for High Conversion Gain

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Solution Overview

Problem

Existing image sensors with share-pixel structures face challenges in maintaining high conversion gain, arrangement efficiency, and pixel transistor size due to increased complexity and metal wiring layers.

Innovation Solution

The image sensor incorporates a deep trench isolation (DTI) structure with inner and outer DTI components, a floating diffusion region, and transfer gates to improve pixel arrangement and reduce metal wiring, while maintaining a share-pixel configuration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of moving object

If a share-pixel structure is adopted to reduce pixel size, then the pixel size is reduced, but the conversion gain and arrangement efficiency decrease

Engineering Contradiction:

Improvepixel sizeVSAvoidconversion gain

Core Design Contradiction:

Area of moving objectVSManufacturing precision

Solution Approach 1:

The pixel is divided into two separate photodiodes arranged side-by-side, with each photodiode having its own transfer gate. This segmentation allows independent charge transfer control while maintaining a compact layout, resolving the contradiction between small pixel size and adequate conversion gain by optimizing the spatial arrangement of segmented components.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The photodiodes are arranged side-by-side in a planar configuration rather than stacking vertically, utilizing the two-dimensional layout space efficiently. This dimensional arrangement allows multiple photodiodes to coexist within a small pixel area while maintaining sufficient area for charge transfer operations, thus improving both pixel size reduction and conversion gain.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Area of moving object

If a share-pixel structure is adopted to reduce pixel size, then the pixel size is reduced, but the arrangement efficiency decreases

Engineering Contradiction:

Improvepixel sizeVSAvoidarrangement efficiency

Core Design Contradiction:

Area of moving objectVSProductivity

Solution Approach 1:

Adjacent pixels share common floating diffusion regions and transfer gates, merging functional elements across pixel boundaries. This merging reduces redundant structures and improves arrangement efficiency by allowing multiple photodiodes to utilize shared components, thus enabling higher density packing while maintaining functional performance.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The transfer gates and floating diffusion regions serve multiple functions: they transfer charge from individual photodiodes, act as charge storage nodes, and enable shared readout pathways. This multi-functionality reduces the number of dedicated components per pixel, improving arrangement efficiency while maintaining small pixel size.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Device complexity

If traditional pixel structures are used, then the structure is simple, but the number of metal wiring layers increases

Engineering Contradiction:

Improvestructure simplicityVSAvoidmetal wiring layers

Core Design Contradiction:

Device complexityVSQuantity of substance

Solution Approach 1:

The charge transfer function is extracted from the metal wiring layer and implemented through dedicated transfer gates made from polysilicon or other semiconductor materials. This extraction eliminates the need for complex metal wiring to transfer charge between photodiodes and readout circuits, reducing the number of metal wiring layers while maintaining structural simplicity.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Electrical charge transfer that would traditionally require metal interconnects is replaced by a semiconductor-based transfer mechanism using gated structures. This substitution uses the electric field control capability of semiconductor gates instead of physical metal wiring, reducing metal layer requirements while maintaining functional simplicity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 conversion gain, increases arrangement efficiency, and allows for larger pixel transistors, while reducing the number of metal wiring layers, thus addressing the limitations of existing share-pixel image sensors.

Implementation Method 1

two photodiodes (PDs) arranged side-by-side in a first direction

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS20250107255A1Image sensor

Publication Date: 2025.03.27 SAMSUNG ELECTRONICS CO LTD

AI summary

An image sensor includes pixels, each including two photodiodes arranged side-by-side in a first direction, a deep trench isolation structure, a floating diffusion region, and transfer gates. The deep trench isolation structure includes an inner structure that extends in a second direction perpendicular to the first direction and that separates the two PDs of pixel from each other in the first direction, and an outer structure that extends in the first and second directions and that separates the pixels from each other in the first and second directions. The floating diffusion region is arranged between a center portion of the outer structure extending in the first direction and an edge of the inner structure. The transfer gates are disposed adjacent to the floating diffusion region such that one or more transfer gates are disposed on each photodiode. For each pixel, the two photodiodes share the floating diffusion region.