Acoustic wave device having mass loading strip with buffer layer

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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 and difficulties in effectively using mass loading strips without void formation in temperature-compensated SAW (TCSAW) resonators.

Innovation Solution

Incorporating a mass loading strip with a high density, such as a molybdenum layer, buried in a silicon dioxide temperature compensation layer, and using 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 is used to suppress transverse modes, then transverse mode suppression is improved, but void formation occurs 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 as an intermediary between the mass loading strip and the temperature compensation layer. This buffer layer fills the void space and provides adhesion, eliminating the harmful void formation while maintaining the mass loading strip's transverse mode suppression function. The buffer layer acts as a mediator that resolves the conflict between achieving effective mass loading and preventing void formation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The structure employs composite materials by combining the mass loading strip (high density material like molybdenum), the buffer layer (adhesive material), and the temperature compensation layer (silicon dioxide). This composite structure leverages the complementary properties of each material: the mass loading strip provides transverse mode suppression, the buffer layer prevents void formation and ensures adhesion, and the temperature compensation layer provides thermal stability.

Inventive Principle:

Principle #40Composite materials

2Reliability

If a high density mass loading strip is used, then transverse mode suppression is improved, but adhesion between layers deteriorates

Engineering Contradiction:

Improvetransverse mode suppressionVSAvoidadhesion

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The buffer layer serves as an adhesive intermediary between the high density mass loading strip and the temperature compensation layer. It provides the necessary bonding strength that the mass loading strip material alone cannot provide, ensuring reliable adhesion while preserving the mass loading strip's transverse mode suppression capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The multi-layer composite structure combines materials with different properties: the mass loading strip provides high density for transverse mode suppression, while the buffer layer provides adhesive properties to ensure strong bonding between the mass loading strip and temperature compensation layer, resolving the adhesion weakness of high density materials.

Inventive Principle:

Principle #40Composite materials

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 in TCSAW resonators, improving the performance of acoustic wave filters by minimizing void formation and maintaining the integrity of the resonator's frequency response.

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

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

Methodology Applied

Scientific EffectMass loading:

Implementation Method 3

Piezoelectric MEMS resonators can process electrical signals using mechanically vibrating structures

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS20230344407A1Acoustic wave device having mass loading strip with 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. A thickness of the buffer layer can be at least one forth a thickness of the mass loading strip. The buffer layer can be disposed at least partially between a bottom side, a top side, and a side wall of the mass loading strip and the temperature compensation layer.