Acoustic Wave Device Bonding Layer Q-Value

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Solution Overview

Problem

The Q-value of acoustic wave devices is deteriorated when a piezoelectric material substrate is directly bonded to a polycrystalline ceramic supporting body, due to the generation of a fine amorphous layer along the bonding interface, causing acoustic wave leakage and reduced propagation efficiency.

Innovation Solution

A method involving the formation of an intermediate layer and a bonding layer with specific materials on the piezoelectric substrate, followed by direct bonding with a polycrystalline ceramic supporting body, using a neutralized beam for activation, to enhance the Q-value by suppressing wave propagation in the amorphous layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If direct bonding is performed between piezoelectric substrate and polycrystalline ceramic supporting body, then bonding strength is improved, but Q-value deteriorates due to acoustic wave leakage through amorphous layer

Engineering Contradiction:

Improvebonding strengthVSAvoidQ-value

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

A bonding layer made of crystalline ceramic material (alumina, mullite, or silicon nitride) is introduced as an intermediary between the piezoelectric substrate and the polycrystalline ceramic supporting body. This bonding layer serves dual purposes: it provides strong bonding through direct bonding while preventing acoustic wave leakage by blocking the formation of amorphous layers at the interface, thereby maintaining high Q-value.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The device structure employs a composite material system consisting of the piezoelectric substrate, the crystalline ceramic bonding layer, and the polycrystalline ceramic supporting body. This composite structure leverages the complementary properties of each material: the piezoelectric substrate for acoustic wave generation, the crystalline bonding layer for strong adhesion and acoustic isolation, and the supporting body for mechanical support and thermal management.

Inventive Principle:

Principle #40Composite materials

2Strength

If bonding temperature is increased to improve bonding strength, then bonding strength is improved, but cracks occur due to thermal expansion coefficient difference

Engineering Contradiction:

Improvebonding strengthVSAvoidcrack formation

Core Design Contradiction:

StrengthVSStability of the object's composition

Solution Approach 1:

The bonding process parameters are optimized to perform direct bonding at relatively low temperatures (room temperature to 200°C) using plasma treatment and pressure application. This parameter change avoids the high-temperature thermal mismatch issues while achieving sufficient bonding strength through surface activation and controlled bonding conditions.

Inventive Principle:

Principle #35Parameter changes

3Strength

If plasma activation method is used for bonding, then bonding strength is improved, but heating is required which causes thermal expansion issues

Engineering Contradiction:

Improvebonding strengthVSAvoidbonding temperature

Core Design Contradiction:

StrengthVSTemperature

Solution Approach 1:

Plasma treatment is applied partially and locally only to the bonding surfaces of the piezoelectric substrate and bonding layer, rather than heating the entire device structure. This localized surface activation provides sufficient bonding strength while minimizing thermal effects and avoiding thermal expansion coefficient mismatches in the bulk materials.

Inventive Principle:

Principle #16Partial or excessive action

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 Q-value of the acoustic wave device is significantly improved by effectively blocking wave propagation in the bonding layer and supporting body, leading to increased propagation intensity and reduced leakage.

Implementation Method 1

irradiating a neutralized beam onto a surface of the bonding layer to provide an activated surface; irradiating a neutralized beam onto a surface of a supporting body comprising a polycrystalline ceramic to provide an activated surface

Methodology Applied

Scientific EffectNeutralized beam activation: Ion Beam

Implementation Method 2

a piezoelectric material substrate... propagating a surface acoustic wave

Methodology Applied

Scientific EffectSurface acoustic wave propagation: Surface Acoustic Wave

Implementation Method 3

an acoustic wave device having a bonded body of a piezoelectric material substrate

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS11632093B2Acoustic wave devices and a method of producing the same

Publication Date: 2023.04.18 NGK INSULATORS LTD

AI summary

An acoustic wave device includes a piezoelectric material substrate, an intermediate layer on the piezoelectric material substrate and composed of one or more materials selected from the group consisting of silicon oxide, aluminum nitride and sialon. A bonding layer is on the intermediate layer and is composed of one or more materials selected from the group consisting of tantalum pentoxide, niobium pentoxide, titanium oxide, mullite, alumina, and a high resistance silicon and hafnium oxide. A supporting body is composed of a polycrystalline ceramic and is bonded to the bonding layer by direct bonding, and an electrode is on the piezoelectric material substrate.