Image Sensor Auxiliary Electrodes Mitigate Thermal Stress

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Solution Overview

Problem

Direct conversion-type image sensors experience delamination or cracking of the photoconductive layer due to thermal stress, leading to reduced adhesion between the photoconductive layer and the substrate, which decreases the reliability and charge collection efficiency of the image sensor.

Innovation Solution

The introduction of auxiliary electrodes made of metal materials between the photoconductive layer and the substrate, which extend to the edge parts of pixel areas and form a Schottky contact, enhances the adhesion strength and reduces thermal stress, thereby preventing delamination or cracking.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If vacuum evaporation is performed at high process temperature to form the photoconductive layer, then the photoconductive layer can be successfully formed, but thermal stress occurs between the substrate and photoconductive layer causing delamination or cracking

Engineering Contradiction:

Improvephotoconductive layer formation qualityVSAvoidadhesion strength between photoconductive layer and substrate

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

An auxiliary electrode layer is introduced as an intermediary between the substrate and the photoconductive layer. This auxiliary electrode acts as a buffer that absorbs thermal stress during the vacuum evaporation process, preventing direct stress transmission between the substrate and photoconductive layer, thereby avoiding delamination and cracking while maintaining successful photoconductive layer formation

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The structure employs a composite multi-layer configuration consisting of substrate, auxiliary electrode, and photoconductive layer. This composite structure distributes thermal stress across different materials with varying thermal expansion coefficients, reducing the overall stress concentration at any single interface and improving adhesion reliability

Inventive Principle:

Principle #40Composite materials

2Device complexity

If the photoconductive layer is formed directly on the substrate, then the structure is simple, but adhesion strength is degraded due to thermal stress causing delamination or cracking

Engineering Contradiction:

Improvestructure simplicityVSAvoidadhesion strength between photoconductive layer and substrate

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The auxiliary electrode serves as a mediating layer between the substrate and photoconductive layer, absorbing thermal stress and preventing direct stress transmission. This intermediary structure improves adhesion reliability without significantly complicating the overall device architecture

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The introduction of the auxiliary electrode changes the physical and thermal parameters of the layered structure, creating a gradient in thermal expansion properties that reduces stress concentration. This parameter modification allows the system to withstand high process temperatures during photoconductive layer formation

Inventive Principle:

Principle #35Parameter changes

3Reliability

If auxiliary electrodes are formed between the photoconductive layer and substrate, then adhesion strength is increased and thermal stress is reduced, but the device complexity increases

Engineering Contradiction:

Improveadhesion strength between photoconductive layer and substrateVSAvoidnumber of layers and components

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The auxiliary electrode performs multiple functions simultaneously: it serves as an adhesion promoter between substrate and photoconductive layer, acts as a thermal stress buffer during vacuum evaporation, and provides electrical connection functionality. This multi-functionality justifies the additional layer by delivering multiple benefits from a single structural addition

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 solution increases the adhesion strength between the photoconductive layer and the substrate, improving the reliability and charge collection efficiency of the image sensor by minimizing current leakage and defects such as delamination or cracking.

Implementation Method 1

Each of the auxiliary electrodes may be formed of a metal material to form a Schottky contact with the photoconductive layer

Methodology Applied

Scientific EffectSchottky contact:

Data Source

PatentUS9923021B2Image sensor

Publication Date: 2018.03.20 RAYENCE

AI summary

There is provided an image sensor including: a plurality of first electrodes respectively formed within a plurality of pixel areas, the pixel areas being formed on a substrate; a protection layer formed on an upper surface of the substrate and including a plurality of contact holes respectively exposing the first electrodes of the pixel areas; a plurality of auxiliary electrodes respectively contacting with the first electrodes through the contact holes and extending to an upper surface of the protection layer of the pixel area; a photoconductive layer formed on both the first electrodes and on the auxiliary electrodes; and a second electrode formed on the photo conductive layer.