SAW Resonator Mass Loading Strip With Buffer Layer for Transverse Modes

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Solution Overview

Problem

Piezoelectric MEMS resonators, particularly surface acoustic wave (SAW) resonators, face challenges in suppressing transverse modes, which affect the accuracy and stability of oscillators and filters by causing passband ripples and limited rejection, due to the presence of strong transverse modes near the passband.

Innovation Solution

Incorporating a mass loading strip with a high density material, such as a molybdenum layer, buried in a silicon dioxide temperature compensation layer, and a buffer layer with a coefficient of thermal expansion between the mass loading strip and the temperature compensation layer to prevent void formation and enhance transverse mode suppression.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a mass loading strip with high density material is used to suppress transverse modes, then transverse mode suppression is improved, but void formation occurs at the interface between the mass loading strip and temperature compensation layer

Engineering Contradiction:

Improvetransverse mode suppressionVSAvoidvoid formation

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

A buffer layer is introduced between the mass loading strip and the temperature compensation layer to act as an intermediary. This buffer layer has a coefficient of thermal expansion that is greater than the temperature compensation layer but less than the mass loading strip, creating a gradient that prevents void formation while maintaining effective transverse mode suppression.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The coefficient of thermal expansion parameter is strategically modified by introducing a buffer layer with intermediate CTE value. This parameter gradient (buffer layer CTE between mass loading strip CTE and temperature compensation layer CTE) resolves the interface compatibility issue and prevents void formation.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If a buffer layer is added to prevent void formation, then manufacturing precision is improved, but device complexity increases

Engineering Contradiction:

Improvevoid formation preventionVSAvoidlayer structure

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The buffer layer is applied locally only at the critical interface between the mass loading strip and temperature compensation layer, rather than throughout the entire device. This targeted approach improves manufacturing precision at the specific problem location while minimizing overall device complexity.

Inventive Principle:

Principle #3Local quality

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 effectively suppresses transverse modes, improving the performance of SAW resonators by minimizing void formation and maintaining the integrity of the acoustic wave propagation, thereby enhancing the accuracy and stability of filters and oscillators.

Implementation Method 1

a buffer layer with a coefficient of thermal expansion between the mass loading strip and the temperature compensation layer to prevent void formation

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

Incorporating a mass loading strip with a high density material, such as a molybdenum layer, buried in a silicon dioxide temperature compensation layer

Methodology Applied

Scientific EffectDensity gradient effect: Density Gradient

Implementation Method 3

Piezoelectric MEMS resonators can process electrical signals using mechanically vibrating structures

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS20230344406A1Acoustic wave device having mass loading strip with thermal expansion compensation buffer layer

Publication Date: 2023.10.26 SKYWORKS SOLUTIONS INC

AI summary

An acoustic wave device is disclosed. The acoustic wave device can include a piezoelectric layer, an interdigital transducer electrode formed with the piezoelectric layer, a temperature compensation layer over the interdigital transducer electrode. The interdigital transducer electrode includes a bus bar and fingers that extend from the bus bar. The fingers each includes an edge portion and a body portion. The acoustic wave device can include a mass loading strip overlaps the edge portions of the fingers. The acoustic wave device can include a portion of the temperature compensation layer is positioned between the mass loading strip and the piezoelectric layer. The acoustic wave device can include a buffer layer that is disposed at least partially between the mass loading strip and the temperature compensation layer. The buffer layer can have a coefficient of thermal expansion greater than a coefficient of thermal expansion of the temperature compensation layer and less than a coefficient of thermal expansion of the mass loading strip.