SAW Resonator Conductive Strip for Hyperbolic Mode Suppression

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Solution Overview

Problem

Piezoelectric MEMS resonators, particularly surface acoustic wave (SAW) resonators, face challenges in suppressing transverse modes, which lead to accuracy and stability issues in oscillators and filter performance due to severe passband ripples and limited rejection.

Innovation Solution

Incorporating a high-density metal strip buried in the temperature compensation layer of SAW resonators, such as silicon dioxide, to create a piston mode that cancels out transverse wave vectors, thereby suppressing hyperbolic modes without degrading the quality factor (Q) or electromechanical coupling coefficient (k2).

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional SAW resonator structure is used, then device simplicity is maintained, but transverse modes cannot be suppressed leading to passband ripples and limited rejection

Engineering Contradiction:

Improvefilter performanceVSAvoidresonator structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The resonator structure is segmented by introducing a conductive strip that divides the electrode regions into distinct zones (first electrode region, second electrode region, and third electrode region). This segmentation creates different acoustic impedance zones that suppress transverse modes while maintaining overall device functionality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The conductive strip acts as an intermediary element between the first and second electrode regions. It serves as a mediator that controls acoustic wave propagation, preventing transverse mode formation while allowing longitudinal modes to pass through, thus improving filter performance without requiring complete structural redesign.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If mass loading strip is added to suppress hyperbolic modes, then filter passband insertion loss characteristics improve, but device complexity increases

Engineering Contradiction:

Improvefilter passband insertion loss characteristicsVSAvoidresonator structure

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The conductive strip is merged with the existing electrode structure, forming an integrated design where the strip serves dual purposes: it is both part of the electrical conduction path and the mass loading element for mode suppression. This merging reduces the need for separate components and simplifies the overall manufacturing process.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The conductive strip performs multiple functions simultaneously: it acts as an electrical conductor, a mass loading element for suppressing hyperbolic modes, and a structural component that defines the electrode regions. This multi-functionality improves filter performance while minimizing the increase in device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If conductive strip is introduced to create piston mode, then transverse wave vectors are canceled suppressing hyperbolic modes, but manufacturing complexity increases

Engineering Contradiction:

Improvemode suppressionVSAvoidresonator fabrication

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The conductive strip allows for controlled changes in acoustic impedance and mass distribution across the resonator. By adjusting the strip's width, position, and electrical properties, the piston mode is created to cancel transverse wave vectors, achieving effective mode suppression while maintaining compatibility with standard fabrication processes.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The conductive strip introduces local variations in mass and electrical properties at specific positions within the resonator structure. These localized changes create the necessary conditions for piston mode formation and transverse mode suppression without requiring global structural modifications, thereby easing manufacturing.

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 hyperbolic modes, improving filter passband insertion loss characteristics and maintaining admittance performance, thus enhancing the stability and accuracy of SAW resonators.

Implementation Method 1

surface acoustic wave (SAW) resonators

Methodology Applied

Scientific EffectSurface Acoustic Wave: Surface Acoustic Wave

Implementation Method 2

Piezoelectric MEMS resonators can process electrical signals using mechanically vibrating structures

Methodology Applied

Scientific EffectPiezoelectric Effect: Piezoelectric Effect

Data Source

PatentUS11848658B2Acoustic wave resonator with mass loading strip for suppression of hyperbolic mode

Publication Date: 2023.12.19 SKYWORKS SOLUTIONS INC

AI summary

Aspects of this disclosure relate to an acoustic wave resonator with hyperbolic mode suppression. The acoustic wave resonator can include a piezoelectric layer, an interdigital transducer electrode, a temperature compensation layer, and a mass loading strip. The mass loading strip can be a conductive strip. The mass loading strip can overlap edge portions of fingers of the interdigital transducer electrode. A layer of the mass loading strip can have a density that is at least as high as a density of a material of the interdigital transducer electrode. The material of the interdigital transducer can impact acoustic properties of the acoustic wave resonator.