Rounded IDT Electrodes for Low-Spur SAW Resonators

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Solution Overview

Problem

Multilayer piezoelectric substrate acoustic wave resonators suffer from non-linear spurious signals and reduced quality factor due to stress and strain concentrations in interdigital transducer (IDT) electrodes, which also increase the size of the acoustic wave filter.

Innovation Solution

The IDT electrodes are redesigned with rounded upper sides and varying sidewall configurations to reduce stress and strain concentrations, using metals with different densities for the upper and lower layers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional interdigital transducer (IDT) electrodes with sharp corners are used, then manufacturing is simpler, but stress and strain concentrations occur causing non-linear spurious signals and reduced quality factor

Engineering Contradiction:

Improvequality factorVSAvoidelectrode fabrication complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The IDT electrodes are designed with rounded upper sides instead of sharp corners. This curvature eliminates stress and strain concentrations at the electrode edges, thereby reducing non-linear spurious signals and maintaining high quality factor in multilayer piezoelectric substrate acoustic wave resonators.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The electrode structure employs different materials for upper and lower layers with varying densities, and applies rounding specifically to the upper sides where stress concentrations occur. This localized modification addresses the specific problem area without changing the entire electrode structure, optimizing performance where needed while maintaining manufacturing feasibility.

Inventive Principle:

Principle #3Local quality

2Volume of stationary object

If traditional IDT electrodes are used, then device structure is simpler, but stress concentrations increase filter size due to need for cascaded resonators

Engineering Contradiction:

Improvefilter sizeVSAvoidelectrode structure complexity

Core Design Contradiction:

Volume of stationary objectVSDevice complexity

Solution Approach 1:

Rounded electrode geometry reduces stress concentrations, which eliminates the need for cascaded resonators to compensate for non-linear effects. This single structural modification achieves both smaller filter size and reduced complexity compared to traditional designs requiring multiple cascaded stages.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The electrode design changes the geometric parameter of corner sharpness to rounded edges, and modifies material parameters by using different density metals for upper and lower layers. These parameter changes reduce stress concentrations and improve resonator performance, allowing compact filter design without cascaded stages.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If IDT electrodes with rounded upper sides are implemented, then non-linear spurious signals are reduced, but manufacturing precision requirements increase

Engineering Contradiction:

Improvesignal linearityVSAvoidelectrode shape control

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The rounded upper sides of IDT electrodes eliminate stress concentrations that cause non-linear spurious signals. Standard semiconductor fabrication techniques including photolithography and etching can achieve the required rounding with appropriate process control, balancing manufacturing precision requirements with performance benefits.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The electrode structure uses composite materials with different density metals for upper and lower layers. This composite approach allows the rounded geometry to be formed in the upper layer while the lower layer provides structural support, distributing the manufacturing precision requirements and achieving both signal linearity and fabricability.

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 design reduces non-linear spurious signals, enhances power durability, and maintains high quality factor without the need for cascaded resonators, resulting in a smaller filter size.

Implementation Method 1

multilayer piezoelectric substrate

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

interdigital transducer (IDT) electrodes disposed on an upper surface of the multilayer piezoelectric substrate

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS20260081580A1Multilayer piezoelectric substrate device with reduced nonlinear response and rounded interdigital transducer electrodes

Publication Date: 2026.03.19 SKYWORKS SOLUTIONS INC

AI summary

Aspects and embodiments disclosed herein include a surface acoustic wave resonator comprising a multilayer piezoelectric substrate and interdigital transducer (IDT) electrodes disposed on an upper surface of the multilayer piezoelectric substrate, the IDT electrodes having at least partially rounded upper sides.