Multiple Transfer Gate Structure for Low-Noise Image Sensors

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Solution Overview

Problem

Existing image sensing devices face issues with residual photocharges accumulating in potential pockets under transfer gates, leading to noise and signal delay due to the formation of potential pockets, which restricts the increase of potential levels required for high-performance image sensing.

Innovation Solution

The implementation of a multiple transfer gate structure with a main transfer gate at the center and sub transfer gates at the boundary regions of the photoelectric conversion elements, allowing different potential levels to be applied, thereby minimizing the potential pocket effect and enhancing photocharge transfer efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a single transfer gate structure is used, then the device complexity is low, but residual photocharges accumulate in potential pockets causing noise and signal delay

Engineering Contradiction:

Improvephotocharge transfer efficiencyVSAvoidgate structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The transfer gate is divided into multiple gates (first transfer gate, second transfer gate, third transfer gate) positioned at different locations (center, first boundary region, second boundary region) of the photoelectric conversion element. Each gate can be independently controlled with different potential levels, allowing selective photocharge transfer while minimizing potential pocket formation and residual charge accumulation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different potential levels are applied to different transfer gates based on their local positions. The center transfer gate and boundary transfer gates receive different potential signals, optimizing photocharge extraction from different regions of the photoelectric conversion element and reducing the potential pocket effect in specific locations.

Inventive Principle:

Principle #3Local quality

2Productivity

If higher potential levels are applied to improve photocharge transfer, then transfer efficiency increases, but residual charge accumulation in potential pockets worsens

Engineering Contradiction:

Improvephotocharge transfer speedVSAvoidnoise from residual charges

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

By segmenting the transfer gate into multiple independently controllable gates, the system can apply optimized potential levels to each segment. This allows efficient photocharge transfer without uniformly high potential levels that would exacerbate residual charge accumulation, thereby reducing noise while maintaining transfer speed.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the potential level parameter differently for each transfer gate. By adjusting potential levels independently for center and boundary gates, the system optimizes transfer efficiency while controlling residual charge accumulation and associated noise.

Inventive Principle:

Principle #35Parameter changes

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 reduces noise and signal delay by allowing higher potential levels to be applied without significant residual charge accumulation, improving the overall performance and efficiency of photocharge transfer in image sensing devices.

Implementation Method 1

a photoelectric conversion element configured to generate photocharges in response to incident light

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

a transfer gate disposed to overlap with the photoelectric conversion element and configured to transmit the photocharges generated by the photoelectric conversion element to the floating diffusion region

Methodology Applied

Scientific EffectElectric field: Electric Field

Data Source

PatentUS11784200B2Image sensing device having multiple transfer gate structure

Publication Date: 2023.10.10 SK HYNIX INC

AI summary

An image sensing device includes a photoelectric conversion element configured to generate photocharges in response to incident light, a floating diffusion configured to temporarily store the photocharges generated by the photoelectric conversion element, and a transfer gate configured to transmit the photocharges generated by the photoelectric conversion element to the floating diffusion region. The transfer gate includes a main transfer gate disposed to overlap a center section of the photoelectric conversion element and configured to operate in response to a first transmission signal, and a sub transfer gate disposed to overlap a boundary region of the photoelectric conversion element and configured to operate in response to a second potential level different from the first potential level.