SAW Filter IDT Electrode Adhesion via Metal Oxide Mediator

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Solution Overview

Problem

Surface acoustic wave (SAW) filters face challenges with frequency variation due to temperature changes, adhesion issues between copper electrode layers and lithium niobate substrates, and difficulties in patterning fine line-widths, which affect the stability and performance of the filters.

Innovation Solution

A SAW filter device structure is developed with a first layer comprising metal or metal oxide layers under the inter-digital transducer (IDT) electrode, a second layer of metal oxide covering the IDT electrode, and an overlay layer of silicon oxide, which enhances adhesion and prevents copper diffusion, allowing for uniform and fine line-width patterning.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If a copper electrode layer is formed on a lithium niobate substrate, then low resistance is achieved, but adhesion between the electrode layer and substrate deteriorates

Engineering Contradiction:

ImproveresistanceVSAvoidadhesion

Core Design Contradiction:

Loss of energyVSStrength

Solution Approach 1:

A first layer comprising metal or metal oxide is introduced between the copper electrode layer and the lithium niobate substrate. This intermediate layer serves as a mediator that enhances adhesion between the copper electrode and substrate while preventing copper diffusion into the substrate, thereby resolving the contradiction between achieving low resistance and maintaining strong adhesion.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Loss of energy

If copper electrode layer is used, then low resistance is achieved, but copper metal atoms diffuse easily causing oxidation

Engineering Contradiction:

ImproveresistanceVSAvoidoxidation resistance

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The first layer acts as a diffusion barrier that prevents copper metal atoms from migrating into the lithium niobate substrate. This intermediate barrier layer maintains the low resistance property of the copper electrode while preventing oxidation by blocking copper diffusion, thus resolving the contradiction between electrical conductivity and oxidation resistance.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Stability of the object's composition

If overlay layer of silicon oxide is formed, then frequency variation due to temperature is reduced, but adhesion between overlay layer and electrode layer deteriorates

Engineering Contradiction:

Improvefrequency stabilityVSAvoidadhesion

Core Design Contradiction:

Stability of the object's compositionVSStrength

Solution Approach 1:

The first layer comprising metal or metal oxide serves as an intermediary between the lithium niobate substrate and the silicon oxide overlay layer. This intermediate layer enhances adhesion between the overlay layer and the electrode structure while allowing the silicon oxide to maintain its function of reducing frequency variation with temperature changes.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Manufacturing precision

If fine line-width patterning is attempted, then precision is improved, but manufacturing difficulty increases due to copper diffusion

Engineering Contradiction:

Improveline-width uniformityVSAvoidpatterning difficulty

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The first layer acts as a diffusion barrier that prevents copper metal atoms from migrating during the patterning process. This intermediate layer enables fine line-width patterning with high precision by preventing copper diffusion that would otherwise complicate the manufacturing process and degrade pattern fidelity.

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

The solution improves adhesion between layers, prevents copper oxidation and migration, and ensures smooth surface acoustic wave transmission, reducing frequency variation with temperature changes and enabling high-performance SAW filters with low resistance.

Implementation Method 1

there is a need to develop a structure capable of preventing copper metal ions from moving to the LiNbO3 wafer substrate

Methodology Applied

Scientific EffectDiffusion barrier: Diffusion Barrier

Implementation Method 2

the overlay layer includes silicon oxide (SiO2), which is a material that varies a propagation speed of the surface acoustic wave (SAW), depending on temperature, to decrease a frequency variation depending on temperature

Methodology Applied

Scientific EffectSurface acoustic wave propagation: Surface Acoustic Wave

Implementation Method 3

there is a need to develop a structure capable of preventing copper metal from oxidizing and migrating

Methodology Applied

Scientific EffectOxidation prevention: Oxidation

Data Source

PatentUS10587243B2Saw filter device and method of manufacturing the same

Publication Date: 2020.03.10 SAMSUNG ELECTRO MECHANICS CO LTD

AI summary

A surface acoustic wave (SAW) filter device includes: a first layer disposed on a substrate; an inter-digital transducer (IDT) electrode layer disposed on the first layer; a second layer covering the IDT electrode layer and the first layer; and an overlay layer covering the second layer, wherein the first layer includes any one or any combination of any two or more of a metal layer, a metal oxide layer, and an oxide layer.