Reflective IDT Layout for Compact SAW Resonators

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Solution Overview

Problem

There is a need for surface acoustic wave (SAW) devices with reduced size while maintaining good performance characteristics, particularly in RF communication systems, as conventional SAW filters are large and have limitations in size reduction without compromising quality factors.

Innovation Solution

The use of interdigital transducers (IDTs) arranged between reflective structures on a piezoelectric material, where the reflective structures comprise reflective IDTs configured to have a phase difference with the IDT, allowing for reduced size without impacting device performance, by effectively confining and reflecting acoustic waves within a resonant cavity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If conventional reflective structures (gratings) are used in SAW devices, then the device achieves adequate acoustic wave reflection, but the device dimensions become large

Engineering Contradiction:

Improvedevice dimensionsVSAvoidquality factor

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The patent changes the fundamental parameters of the reflective structure by transitioning from conventional gratings to reflective IDTs with specific electrode configurations. The reflective IDTs use interdigitated electrode fingers with controlled spacing and positioning to achieve acoustic wave reflection through piezoelectric coupling, enabling size reduction while maintaining quality factor performance

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the mechanical grating structure with an electromechanical reflective IDT system. Instead of relying purely on physical grating geometry for reflection, the invention uses piezoelectric transduction where electrical signals applied to interdigitated electrodes generate acoustic waves that reflect off the piezoelectric material, achieving reflection with reduced physical dimensions

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Volume of moving object

If the size of SAW devices is reduced, then the device becomes more compact for modern RF systems, but the quality factor and performance characteristics deteriorate

Engineering Contradiction:

Improvedevice sizeVSAvoidperformance characteristics

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The patent applies local quality by creating distinct functional zones within the device: the reflective IDTs are positioned at specific locations to provide strong acoustic wave reflection, while the IDT is positioned optimally between them for efficient transduction. This localized optimization of structure and material properties maintains high quality factor despite overall device size reduction

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The reflective IDTs serve multiple functions: they act as reflective boundaries for acoustic wave confinement, provide electrical connections to the piezoelectric material, and contribute to the overall resonant cavity formation. This multi-functionality allows compact design without sacrificing performance

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 enables SAW devices with reduced dimensions compared to conventional designs, maintaining high quality factors and performance characteristics, such as low insertion loss and broad bandwidth, suitable for RF communication systems.

Implementation Method 1

Acoustic wave devices include a piezoelectric material in contact with one or more electrodes. Piezoelectric materials acquire a charge when compressed, twisted, or distorted, and similarly compress, twist, or distort when a charge is applied to them.

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

The reflective structures may include reflective IDTs that are configured to have a phase difference with the IDT to reflect and confine acoustic waves in the piezoelectric material.

Methodology Applied

Scientific EffectAcoustic wave reflection: Reflection

Implementation Method 3

Surface acoustic wave (SAW) devices, such as SAW resonators and SAW filters, are used in many applications such as radio frequency (RF) filters.

Methodology Applied

Scientific EffectSurface acoustic wave generation: Surface Acoustic Wave

Data Source

PatentUS11621691B2Reflective structures for surface acoustic wave devices

Publication Date: 2023.04.04 QORVO US INC

AI summary

Interdigital transducer (IDT) and reflective structure arrangements for surface acoustic wave (SAW) devices are disclosed. Representative SAW devices are described herein with reduced overall size while maintaining good quality factors. In certain embodiments, a SAW device may include an IDT arranged between reflective structures on a piezoelectric material. The reflective structures may include reflective IDTs that are configured to have a phase difference with the IDT to reflect and confine acoustic waves in the piezoelectric material. In certain embodiments, the reflective structures may be electrically connected to at least one of an input signal or an output signal. In this manner, the reflective structures may be configured with reduced size as compared to conventional reflective structures such as gratings, thereby providing a SAW device with reduced dimensions without a negative impact on device performance.