Multilayer Piezoelectric Substrate for Side Leakage Suppression

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Solution Overview

Problem

Conventional multilayer piezoelectric substrates (MPSs) used in acoustic wave devices suffer from side leakage and transverse mode suppression, which degrade the performance of surface acoustic wave (SAW) devices.

Innovation Solution

The implementation of a multilayer piezoelectric substrate with first and second high impedance portions positioned outside the active region of the interdigital transducer (IDT), extending in the direction of acoustic wave propagation. These high impedance portions can be air gaps or made from materials like silicon nitride, silicon, diamond, aluminum nitride, etc., and are configured to confine acoustic waves within the substrate.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional multilayer piezoelectric substrates are used in acoustic wave devices, then the device structure is simple and manufacturing is easy, but side leakage and transverse modes occur which degrade device performance

Engineering Contradiction:

Improvedevice performanceVSAvoidsubstrate structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The substrate structure is segmented into multiple functional layers: a first substrate layer, a second substrate layer with different acoustic impedance, and an interdigital transducer layer. This segmentation creates distinct acoustic impedance boundaries that suppress side leakage and transverse modes, thereby improving device performance without excessive complexity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The second substrate layer is positioned specifically beneath the active region of the interdigital transducer where acoustic wave generation occurs. This localized configuration provides targeted suppression of side leakage and transverse modes at the critical region while maintaining overall structural simplicity

Inventive Principle:

Principle #3Local quality

2Reliability

If slanted IDT structures are used to reduce transverse modes and side leakage, then device performance improves, but additional space is required leading to larger device size

Engineering Contradiction:

Improvedevice performanceVSAvoiddevice size

Core Design Contradiction:

ReliabilityVSArea of moving object

Solution Approach 1:

Instead of modifying the IDT electrode geometry in the planar dimension (slanted structures), the solution introduces a vertical dimension by stacking multiple substrate layers with different acoustic impedances. This dimensional transition allows performance improvement through vertical acoustic impedance management rather than horizontal space expansion

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Reliability

If high impedance portions are added to confine acoustic waves, then side leakage is reduced and Q factor is maintained, but the manufacturing process becomes more complex

Engineering Contradiction:

ImproveQ factorVSAvoidsubstrate fabrication

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The invention changes the acoustic impedance parameter by selecting materials with different acoustic properties for the first and second substrate layers. This parameter change creates the high impedance boundary needed to confine acoustic waves and maintain Q factor, while the material selection allows for compatibility with existing semiconductor manufacturing processes

Inventive Principle:

Principle #35Parameter changes

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 effectively reduces side leakage and suppresses transverse modes, thereby enhancing the performance of SAW devices by maintaining a high Q factor and electromechanical coupling coefficient without increasing the device size.

Implementation Method 1

first and second high impedance portions included within the multilayer piezoelectric substrate, the first and second high impedance portions each positioned outside the active region of the interdigital transducer and extending in the direction of propagation of the acoustic wave to be generated by the interdigital transducer

Methodology Applied

Scientific EffectAcoustic wave reflection: Reflection

Implementation Method 2

a layer of piezoelectric material having a lower surface disposed on an upper surface of a layer of a dielectric material

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS12278614B2Multilayer piezoelectric substrate with reduced side leakage and transverse mode suppression

Publication Date: 2025.04.15 SKYWORKS SOLUTIONS INC

AI summary

An acoustic wave device, a method of manufacture of the same, and a radio frequency filter including the same. The acoustic wave device comprises a multilayer piezoelectric substrate (MPS) including a layer of piezoelectric material having a lower surface disposed on an upper surface of a layer of a dielectric material having a lower surface disposed on an upper surface of a carrier substrate. An interdigital transducer (IDT) is disposed on the multilayer piezoelectric substrate and includes an active region configured to generate an acoustic wave. First and second high impedance portions are included within the multilayer piezoelectric substrate, the first and second high impedance portions each positioned outside the active region of the interdigital transducer and extending in the direction of propagation of the acoustic wave to be generated by the interdigital transducer. The first and second high impedance portions reduce side leakage and suppress transverse modes.