Acoustic Wave Layer Stack for Lower Energy Loss and Higher Q
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Solution Overview
Problem
Conventional acoustic wave devices experience significant loss of acoustic wave energy due to its concentration on both the piezoelectric film and dielectric film, leading to inefficient energy transfer and reduced Q factor.
Innovation Solution
The acoustic wave device incorporates a high-acoustic-velocity member, a low-acoustic-velocity film, a piezoelectric layer, and a dielectric film, where the IDT electrode is on the piezoelectric layer, the high-acoustic-velocity member is opposite to the piezoelectric layer, the low-acoustic-velocity film is between them, and the dielectric film covers the IDT electrode, with a Young's modulus of the dielectric film being higher than that of the low-acoustic-velocity film to minimize energy loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a dielectric film is disposed to cover the IDT electrode on a high-acoustic-velocity support substrate, then the device structure is completed and functional, but acoustic wave energy concentrates on both the piezoelectric film and dielectric film causing increased energy loss
Solution Approach 1:
The device segments the acoustic wave propagation path by introducing a low-acoustic-velocity film as a distinct layer between the high-acoustic-velocity support substrate and the piezoelectric film. This segmentation creates separate functional zones: the low-acoustic-velocity film confines acoustic energy to prevent its concentration in the dielectric film, while the dielectric film maintains its protective and insulating functions. The segmentation of energy confinement and structural protection into different layers resolves the contradiction by preventing energy loss without requiring complex material compositions.
Solution Approach 2:
The low-acoustic-velocity film acts as an intermediary layer that mediates between the high-acoustic-velocity support substrate and the piezoelectric film. This intermediary layer has acoustic velocity characteristics that are lower than both adjacent layers, creating acoustic impedance mismatches that confine acoustic wave energy within the piezoelectric film and prevent it from propagating into the dielectric film. The intermediary layer thus protects the system from energy loss while maintaining the necessary structural configuration.
2Reliability
If acoustic wave energy concentrates on the dielectric film, then the device can be simplified, but viscosity loss increases reducing the Q factor
Solution Approach 1:
The invention applies local quality by creating a specific acoustic velocity profile across different layers: the low-acoustic-velocity film has deliberately reduced acoustic velocity compared to both the support substrate and the piezoelectric film. This localized variation in acoustic velocity creates acoustic confinement zones that direct energy specifically where needed (in the piezoelectric film) and prevent it from entering regions where it would cause loss (the dielectric film). The local quality modification of acoustic velocity in the intermediate layer resolves the contradiction by controlling energy distribution spatially.
3Loss of energy
If the dielectric film has low Young's modulus, then it is easier to manufacture, but acoustic wave energy is not effectively confined leading to increased loss
Solution Approach 1:
The invention changes the critical parameter of Young's modulus for the dielectric film, specifying that it should have a Young's modulus of 70 GPa or more. This parameter change transforms the dielectric film from a compliant material that would allow acoustic energy propagation into a rigid material that effectively confines acoustic energy. The parameter specification resolves the contradiction by prioritizing energy confinement performance over manufacturing ease, though it does provide guidance for material selection within the high-Young's-modulus category.
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 reduces acoustic wave energy loss and enhances the Q factor by concentrating energy on the low-acoustic-velocity medium and increasing the Young's modulus of the dielectric film, thereby decreasing viscosity loss and improving frequency-temperature characteristics.
Implementation Method 1
An acoustic velocity of a bulk wave propagating through the low-acoustic-velocity film is lower than the acoustic velocity of a bulk wave propagating through the piezoelectric layer
Implementation Method 2
a piezoelectric film is disposed on the low-acoustic-velocity film. On an upper surface of this piezoelectric film, the IDT electrode is disposed
Implementation Method 3
A Young's modulus of the dielectric film is larger than a Young's modulus of the low-acoustic-velocity film
Data Source
AI summary
In an acoustic wave device, an IDT electrode is located on a piezoelectric layer. A high-acoustic-velocity member is positioned on an opposite side of the piezoelectric layer from the IDT electrode. An acoustic velocity of a bulk wave propagating through the high-acoustic-velocity member is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer. A low-acoustic-velocity film is provided between the high-acoustic-velocity member and the piezoelectric layer. An acoustic velocity of a bulk wave propagating through the low-acoustic-velocity film is lower than the acoustic velocity of the bulk wave propagating through the piezoelectric layer. A dielectric film is located on the piezoelectric layer so as to cover the IDT electrode. In the acoustic wave device, a Young's modulus of the dielectric film is larger than a Young's modulus of the low-acoustic-velocity film.