Acoustic wave device
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Solution Overview
Problem
Existing acoustic wave devices used as filters often experience deterioration in filter characteristics due to the occurrence of spurious modes outside the pass band.
Innovation Solution
An acoustic wave device with a multilayer structure comprising a high-acoustic-velocity support substrate, a low-acoustic-velocity film with different density portions, and a piezoelectric layer, where the acoustic velocity of the bulk waves propagates through these layers in a specific manner to reduce or prevent spurious modes by confining energy effectively on the piezoelectric layer side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a multilayer body with high-acoustic-velocity support substrate, low-acoustic-velocity film, and piezoelectric film is used, then the Q factor increases, but spurious modes occur outside the pass band causing filter characteristic deterioration
Solution Approach 1:
The low-acoustic-velocity film is divided into two portions with different densities: a first portion with density ρ1 and a second portion with density ρ2 (where ρ1 < ρ2). This local quality variation creates different acoustic impedance characteristics in different regions of the film, allowing suppression of spurious modes while maintaining the high Q factor benefit of the multilayer structure.
Solution Approach 2:
The invention changes the density parameter within the low-acoustic-velocity film by creating a gradient or stepped density distribution (ρ1 in the first portion, ρ2 in the second portion). This parameter change modifies the acoustic wave propagation characteristics, effectively suppressing spurious modes that would otherwise occur in a uniform density film while preserving the desired filter performance.
2Reliability
If the low-acoustic-velocity film has uniform density, then the structure is simple, but spurious modes occur that deteriorate filter characteristics
Solution Approach 1:
Rather than making the entire film complex, only a specific portion (the second portion adjacent to the piezoelectric film) has different density characteristics. This localized complexity is sufficient to suppress spurious modes without requiring the entire film structure to be complex, thus achieving the desired effect with minimal added complexity.
Solution Approach 2:
The low-acoustic-velocity film is constructed as a composite structure with two portions having different densities (ρ1 and ρ2). This composite approach allows the film to exhibit both the simplicity of a single-material construction in the first portion and the spurious-mode-suppressing properties of a complex structure in the second portion, effectively combining benefits while minimizing drawbacks.
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
Significantly reduces or prevents the occurrence of spurious modes outside the pass band, enhancing the filter characteristics by increasing the Q factor and improving phase characteristics through controlled density differences in the low-acoustic-velocity film.
Implementation Method 1
an acoustic velocity of a bulk wave propagating through the high-acoustic-velocity support substrate is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer, an acoustic velocity of a bulk wave propagating through the low-acoustic-velocity film is lower than an acoustic velocity of a bulk wave propagating through the piezoelectric layer
Implementation Method 2
a piezoelectric layer provided on the low-acoustic-velocity film; and an IDT electrode provided on the piezoelectric layer
Data Source
AI summary
An acoustic wave device includes a high-acoustic-velocity support substrate, a low-acoustic-velocity film provided on the high-acoustic-velocity support substrate, a piezoelectric layer provided on the low-acoustic-velocity film, and an IDT electrode provided on the piezoelectric layer. An acoustic velocity of a bulk wave propagating through the high-acoustic-velocity support substrate is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer. An acoustic velocity of a bulk wave propagating through the low-acoustic-velocity film is lower than an acoustic velocity of a bulk wave propagating through the piezoelectric layer. The low-acoustic-velocity film has a first portion and a second portion that is located closer to the high-acoustic-velocity support substrate than the first portion. The first and second portions include the same or similar materials. A density in the first portion of the low-acoustic-velocity film and a density in the second portion of that are different.