Thickness-Shear Acoustic Wave Structure for High-Frequency Linearity

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Solution Overview

Problem

Conventional surface acoustic wave devices face challenges in increasing frequency and maintaining linearity due to harmonic distortion and intermodulation distortion, particularly with materials like LiTaO3 and silicon oxide.

Innovation Solution

The acoustic wave device employs a bulk wave of thickness-shear primary mode using a silicon substrate with a lithium niobate or lithium tantalate piezoelectric layer, featuring a trap region and electrode configuration where the distance between electrode center lines is less than half the thickness of the piezoelectric layer, enhancing frequency handling and linearity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional surface acoustic wave device structure is used, then device operation is achieved, but frequency increase is limited and linearity degrades due to harmonic distortion and intermodulation distortion

Engineering Contradiction:

ImprovelinearityVSAvoidharmonic distortion and intermodulation distortion

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent changes the fundamental operating mode from surface acoustic wave to bulk acoustic wave (thickness-shear mode), and modifies the electrode configuration parameter by setting the distance between electrode center lines to less than half the piezoelectric layer thickness. These parameter changes eliminate the harmful distortion mechanisms while maintaining device functionality.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Instead of using the conventional surface acoustic wave propagation mode, the patent inverts the approach by utilizing bulk acoustic wave propagation in the thickness-shear mode. This fundamental inversion of the wave mode eliminates the distortion issues inherent in surface wave devices.

Inventive Principle:

Principle #13The other way round (Inversion)

2Speed

If frequency is increased in conventional devices, then higher frequency operation is attempted, but linearity degrades due to distortion

Engineering Contradiction:

ImprovefrequencyVSAvoidlinearity

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent achieves higher frequency operation by transitioning to bulk wave thickness-shear mode and adjusting the electrode spacing parameter (distance between center lines less than half the piezoelectric layer thickness). These parameter changes enable frequency increases while preserving linearity, unlike conventional surface wave devices where frequency increases cause distortion.

Inventive Principle:

Principle #35Parameter changes

3Volume of moving object

If electrode pairs are reduced to miniaturize the device, then device size decreases, but Q value becomes insufficient

Engineering Contradiction:

Improvedevice sizeVSAvoidQ value

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The patent changes the wave propagation mode from surface acoustic wave to bulk acoustic wave in thickness-shear mode. This parameter change fundamentally alters the Q value characteristics, allowing the device to maintain sufficient Q value even with reduced electrode pairs, thereby enabling miniaturization without sacrificing performance.

Inventive Principle:

Principle #35Parameter changes

4Ease of manufacture

If conventional materials (silicon oxide, LiTaO3) are used, then device manufacturing is straightforward, but frequency increase is limited and linearity degrades

Engineering Contradiction:

Improvematerial availabilityVSAvoidfrequency and linearity performance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent changes the operational parameters by using bulk acoustic wave thickness-shear mode instead of surface acoustic wave mode, and by configuring the electrode distance to be less than half the piezoelectric layer thickness. These parameter changes enable the conventional materials to achieve higher frequencies and better linearity, resolving the contradiction between ease of manufacture and performance.

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 allows for higher frequency operation while improving linearity and maintaining a sufficient Q value, even with reduced electrode pairs, and reduces charge movement, thereby enhancing the device's performance.

Implementation Method 1

A material of the piezoelectric layer is lithium niobate or lithium tantalate. The acoustic wave device uses a bulk wave of a thickness-shear primary mode

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

The acoustic wave device further includes a trap region in the silicon substrate

Methodology Applied

Scientific EffectCharge trapping:

Data Source

PatentUS11621688B2Acoustic wave device

Publication Date: 2023.04.04 MURATA MFG CO LTD

AI summary

An acoustic wave device includes a piezoelectric layer and first and second electrodes. The first and second electrodes face each other in a direction intersecting with a thickness direction of the piezoelectric layer. The acoustic wave device uses a bulk wave of a thickness-shear primary mode. A material of the piezoelectric layer is lithium niobate or lithium tantalate. The piezoelectric layer is on a first main surface of the silicon substrate. The acoustic wave device further includes a trap region on a side of a second main surface of the piezoelectric layer.