SH-Mode Elastic Wave Filter Structure for Spurious Mode Suppression
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Solution Overview
Problem
Conventional surface elastic wave devices experience spurious emission in high frequency bands due to excitation of parasitic resonance modes, which adversely affect attenuation characteristics and signal integrity in mobile communication equipment.
Innovation Solution
An elastic wave device with a piezoelectric layer and a carrier substrate having specific crystal orientations and thicknesses, where the piezoelectric layer is between 0.15λ and 1.5λ thick, and the carrier substrate is oriented to reduce unnecessary vibrations of SV and vertical L-modes, thereby minimizing spurious emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the piezoelectric layer thickness is increased to improve Q value and confine elastic wave, then the Q value is improved, but parasitic resonance modes are excited causing spurious emission in high frequency band
Solution Approach 1:
The patent applies parameter changes by precisely controlling the piezoelectric layer thickness within the range of 0.15λ to 1.5λ and selecting specific crystal orientations for the carrier substrate. This parameter optimization allows the device to maintain high Q value while suppressing parasitic resonance modes that cause spurious emission in the high frequency band.
Solution Approach 2:
The patent implements local quality by selecting specific crystal orientations for different regions of the carrier substrate to reduce unnecessary vibrations. By tailoring the acoustic anisotropy properties of the substrate in specific orientations, the device confines the desired surface elastic wave while suppressing parasitic modes locally.
2Ease of manufacture
If conventional surface elastic wave device structure is used, then manufacturing is simple, but spurious emission occurs in high frequency band affecting attenuation characteristics
Solution Approach 1:
The patent maintains ease of manufacture by using a conventional layered structure of piezoelectric layer on carrier substrate, but improves attenuation characteristics through parameter optimization. The specific thickness range (0.15λ to 1.5λ) and crystal orientation selection enhance performance without fundamentally changing the manufacturing process or structure.
3Object-generated harmful factors
If piezoelectric layer thickness is adjusted to reduce spurious emission, then spurious emission is reduced, but Q value deteriorates
Solution Approach 1:
The patent resolves this contradiction by identifying an optimal parameter range for piezoelectric layer thickness (0.15λ to 1.5λ) rather than using a single fixed value. This parameter range allows the device to simultaneously achieve low spurious emission and high Q value, overcoming the trade-off present in conventional designs.
Solution Approach 2:
The patent uses a composite structure combining piezoelectric material layer with a carrier substrate of specific acoustic anisotropy. This composite approach allows the piezoelectric layer to generate strong surface waves (high Q) while the anisotropic substrate confines the waves and suppresses parasitic modes (low spurious emission).
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 effectively reduces spurious emissions in high frequency bands while maintaining high Q values and electromechanical coupling coefficients, enhancing signal quality and filter performance.
Implementation Method 1
a piezoelectric layer formed from a piezoelectric material
Implementation Method 2
the carrier substrate has an acoustic anisotropy, and is arranged in a crystal orientation that reduces unnecessary vibrations of an SV mode and a vertical L-mode
Data Source
AI summary
An elastic wave device that excites main vibration of an SH mode includes a piezoelectric layer formed from a piezoelectric material, a carrier substrate, and an IDT electrode formed on the piezoelectric layer. When a wavelength of an elastic wave, which is determined by an electrode cycle P of the IDT electrode, is represented by λ, the piezoelectric layer has a thickness of 0.15λ or more and 1.5λ or less. The carrier substrate has an acoustic anisotropy, and is arranged in a crystal orientation that reduces unnecessary vibrations of an SV mode and a vertical L-mode.