Variable-Thickness SAW Structure for Multi-Band Filter Tuning

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Solution Overview

Problem

Multilayer piezoelectric substrate (MPS) surface acoustic wave (SAW) devices face challenges in achieving optimal electrical properties such as coupling factor k2 and temperature coefficient of frequency (TCF) across multiple frequency bands, due to the complexity of forming multiple acoustic wave elements in a single die with varying thicknesses and materials.

Innovation Solution

The implementation of a multilayer piezoelectric substrate with distinct regions of different thicknesses and a sloped acoustic obstruction structure between these regions, allowing for the formation of multiple acoustic wave elements with tailored electrical properties, including the use of lithium tantalate and lithium niobate layers, to enhance coupling factor k2 and maintain low loss and suitable TCF.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If multiple acoustic wave elements are formed in a single die with varying thicknesses and materials, then optimal electrical properties such as coupling factor k2 and temperature coefficient of frequency (TCF) across multiple frequency bands can be achieved, but the complexity of forming multiple acoustic wave elements increases

Engineering Contradiction:

Improveelectrical properties across multiple frequency bandsVSAvoidcomplexity of forming multiple acoustic wave elements

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The piezoelectric substrate is divided into multiple distinct regions (first region, second region, third region) with different thicknesses and material compositions. Each region is optimized for specific frequency bands, allowing multiple acoustic wave elements to be formed with tailored electrical properties without requiring a completely separate device for each band

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the piezoelectric substrate are assigned different local properties: the first region has a first thickness optimized for first frequency bands, the second region has a second thickness optimized for second frequency bands, and the third region provides a transition. This local differentiation enables optimal electrical properties across multiple bands while maintaining a single integrated device structure

Inventive Principle:

Principle #3Local quality

2Object-generated harmful factors

If a sloped acoustic obstruction structure is used between regions of different thicknesses, then unwanted reflections are minimized, but the manufacturing precision requirements increase

Engineering Contradiction:

Improveunwanted reflectionsVSAvoidprecision of sloped acoustic obstruction structure

Core Design Contradiction:

Object-generated harmful factorsVSManufacturing precision

Solution Approach 1:

The acoustic obstruction structure features a sloped or curved interface between regions of different thicknesses rather than a sharp angular transition. This gradual curvature reduces acoustic impedance mismatches and minimizes unwanted reflections at the boundaries between regions, though it does require precise manufacturing control to achieve the intended smooth transition

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Adaptability or versatility

If multiple piezoelectric layers with different materials are used, then coupling factor k2 is enhanced, but the difficulty of detecting and measuring increases

Engineering Contradiction:

Improvecoupling factor k2VSAvoidmeasurement complexity of multi-layer structure

Core Design Contradiction:

Adaptability or versatilityVSDifficulty of detecting and measuring

Solution Approach 1:

The piezoelectric substrate employs a composite structure with multiple layers of different piezoelectric materials (such as lithium niobate and lithium tantalate) with different thicknesses. This composite construction enhances the coupling factor k2 by leveraging the complementary properties of different materials, allowing optimization for specific frequency bands while maintaining a manageable measurement approach through standardized characterization methods

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

This approach enables improved electrical properties and reduced size for multi-band SAW filters, allowing for efficient signal separation across multiple frequency bands while minimizing unwanted reflections and maintaining robustness against dicing processes.

Implementation Method 1

a piezoelectric structure including a first region having a first thickness, a second region having a second thickness different from the first thickness, and a third region sloped between the first region and the second region; a first surface acoustic wave element positioned in the first region; and a second surface acoustic wave element positioned in the second region

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS20250007488A1Acoustic wave device with a variable thickness multi-layer piezoelectric structure

Publication Date: 2025.01.02 SKYWORKS SOLUTIONS INC

AI summary

A surface acoustic wave device is disclosed. The surface acoustic wave device can include a support substrate structure, a first piezoelectric layer over the support substrate structure, and a second piezoelectric layer over the first piezoelectric layer. The second piezoelectric layer has a first region with a first thickness and a second region with a second thickness different from the first thickness. The surface acoustic wave device can include a first acoustic wave element that is positioned in the first region, and a second acoustic wave element that is positioned in the second region.