Transfer Wiring Light Shielding for CMOS Image Sensor Crosstalk

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Solution Overview

Problem

In back surface irradiation type CMOS solid-state image pickup apparatuses, finer pixel sizes lead to increased capacitive coupling between wirings, causing potential variations in transfer gates, which result in charge leakage from photodiodes, degrading image quality by increasing variation in saturation signal amounts between pixels.

Innovation Solution

The implementation of transfer wirings arranged in parallel with uniform opening widths, overlapped by different wirings in a wiring layer, forms a light shielding structure that equalizes coupling capacitance and suppresses hot carrier light emission, thereby stabilizing the potential variation of transfer gates and reducing signal variation between pixels.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If pixel size is reduced to achieve finer resolution, then image resolution is improved, but capacitive coupling between wirings increases causing potential variation in transfer gates

Engineering Contradiction:

Improveimage resolutionVSAvoidpotential stability of transfer gate

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

A light shielding structure is introduced as an intermediary element between transfer wirings to block capacitive coupling and hot carrier light. This mediator prevents the harmful interaction between adjacent wirings while maintaining the fine pixel size for high resolution imaging.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The light shielding function is extracted from the transfer wiring structure itself and implemented as a separate dedicated component. This allows the transfer wiring to focus on signal transmission while the light shielding structure handles the capacitive coupling and hot carrier light issues independently.

Inventive Principle:

Principle #2Taking out (Extraction)

2Quantity of substance

If interval between adjacent wirings is reduced to increase pixel density, then pixel density is improved, but capacitive coupling between wirings increases causing charge leakage

Engineering Contradiction:

Improvepixel densityVSAvoidcapacitive coupling and charge leakage

Core Design Contradiction:

Quantity of substanceVSObject-generated harmful factors

Solution Approach 1:

The light shielding structure serves as a physical intermediary between closely spaced wirings, blocking the capacitive coupling effect that causes charge leakage. This enables higher pixel density without sacrificing signal integrity.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The light shielding structure, originally designed to block light, is utilized to also block capacitive coupling and hot carrier light. This converts a single-function component into a multi-functional solution that addresses multiple harmful effects simultaneously.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Reliability

If additional light shielding structures are added to block hot carrier light, then image quality is improved, but device complexity increases

Engineering Contradiction:

Improveimage qualityVSAvoidwiring structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The light shielding structure is designed to perform multiple functions: blocking visible light, blocking hot carrier light, and reducing capacitive coupling between wirings. This multi-functionality eliminates the need for separate structures for each purpose, reducing overall device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

Multiple protective functions (light shielding, hot carrier light blocking, capacitive coupling reduction) are merged into a single integrated light shielding structure. This consolidation simplifies the device architecture while maintaining image quality.

Inventive Principle:

Principle #5Merging (Combining)

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 approach enhances image quality by equalizing saturation signal amounts between pixels and preventing hot carrier light from entering photodiodes, resulting in improved image capture performance without the need for additional light shielding structures.

Implementation Method 1

the transfer wirings and the different wirings form a light shielding structure in the pixel region

Methodology Applied

Scientific EffectLight shielding: Absorption (EM radiation)

Implementation Method 2

when an interval between adjacent wirings becomes smaller as the pixel size becomes finer, capacitive coupling between the wirings does not become negligible

Methodology Applied

Scientific EffectCapacitive coupling: Capacitance

Data Source

PatentUS9806120B2Solid-state image pickup apparatus and electronic apparatus

Publication Date: 2017.10.31 SONY GROUP CORP

AI summary

A solid-state image pickup apparatus includes a pixel region in which a plurality of pixels each including a photoelectric conversion element are arranged, transfer wirings formed on the pixel region in parallel to each other with uniform opening widths, and different wirings formed in a wiring layer above the transfer wirings. At least a part of the different wirings is overlapped with the transfer wirings on a plan position. The transfer wirings and the different wirings form a light shielding structure in the pixel region.