Buried-Electrode Multilayer SAW Substrate for Wider RF Passbands

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Solution Overview

Problem

Existing lithium tantalate (LT) based multilayer piezoelectric substrate (MPS) SAW filters have a limited electromechanical coupling coefficient (k2) of around 12%, which is insufficient for achieving a wide passband with good insertion loss, and lithium niobate (LN) based MPS SAW filters have even lower k2 values.

Innovation Solution

The implementation of a multilayer piezoelectric substrate structure with embedded or partially buried interdigital transducer (IDT) electrodes, utilizing layers of lithium tantalate and lithium niobate, and incorporating a quartz substrate for temperature compensation, enhances the electromechanical coupling coefficient (k2) and quality factor (Q) while reducing size.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If lithium tantalate or lithium niobate based multilayer piezoelectric substrate SAW filters are used, then the device can be manufactured with existing materials and processes, but the electromechanical coupling coefficient (k2) is limited to around 12% or lower, which is insufficient for achieving a wide passband with good insertion loss

Engineering Contradiction:

Improveelectromechanical coupling coefficient (k2)VSAvoidpassband width and insertion loss performance

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent employs a composite piezoelectric substrate structure consisting of multiple layers with different materials (lithium tantalate and lithium niobate) and different orientations. This composite structure combines the advantages of each material to achieve a higher electromechanical coupling coefficient (k2) of up to 14%, enabling wide passband with good insertion loss while maintaining compatibility with existing manufacturing processes

Inventive Principle:

Principle #40Composite materials

2Reliability

If the piezoelectric layer thickness is increased to improve coupling coefficient, then k2 increases, but the device size and thickness increase

Engineering Contradiction:

Improveelectromechanical coupling coefficient (k2)VSAvoiddevice thickness and size

Core Design Contradiction:

ReliabilityVSLength of moving object

Solution Approach 1:

The patent resolves the thickness contradiction by transitioning from a single-layer structure to a multilayer structure with different orientations. The first piezoelectric layer is oriented at a first angle and the second layer at a second angle, creating a three-dimensional composite structure that achieves high k2 (up to 14%) without proportionally increasing overall device thickness, thus maintaining compact form factor

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Device complexity

If single-layer piezoelectric substrate is used to simplify device structure, then manufacturing is easier, but the electromechanical coupling coefficient (k2) is limited and cannot achieve wide passband with good insertion loss

Engineering Contradiction:

Improvedevice structure simplicityVSAvoidelectromechanical coupling coefficient (k2)

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent divides the piezoelectric substrate into multiple segments or layers, each with specific material composition and orientation angles. This segmentation allows each layer to contribute differently to the overall electromechanical coupling, achieving a composite k2 of up to 14% that exceeds what any single layer could provide, while maintaining a structured and manufacturable design

Inventive Principle:

Principle #1Segmentation

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 proposed structure increases k2 by up to 14% and maintains low insertion loss, providing a wider passband and improved performance in radio frequency filters.

Implementation Method 1

a layer of a first lithium-based piezoelectric material disposed on an upper surface of the quartz substrate, a layer of a second lithium-based piezoelectric material formed of a material different from the first lithium-based piezoelectric material disposed on an upper surface of the layer of the first lithium-based piezoelectric material

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

interdigital transducer electrodes disposed on an upper surface of the layer of the second lithium-based piezoelectric material

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS20250247069A1Multilayer piezoelectric substrate acoustic wave device including multiple piezoelectric material layers disposed on quartz substrate and utilizing buried electrodes

Publication Date: 2025.07.31 SKYWORKS SOLUTIONS INC

AI summary

Aspects and embodiments disclosed herein include a surface acoustic wave device comprising a quartz substrate, a layer of a first lithium-based piezoelectric material disposed on an upper surface of the quartz substrate, a layer of a second lithium-based piezoelectric material formed of a material different from the first lithium-based piezoelectric material disposed on an upper surface of the layer of the first lithium-based piezoelectric material, and interdigital transducer electrodes disposed on an upper surface of the layer of the second lithium-based piezoelectric material.