Elastic Wave Layer Stack for Acoustic Confinement and High Q
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Solution Overview
Problem
Elastic wave devices face significant propagation loss and inability to effectively confine surface acoustic waves, leading to low Q factors due to energy leakage into dielectric substrates, limiting frequency enhancement and acoustic wave confinement.
Innovation Solution
Incorporating a low-acoustic-velocity film and a high-acoustic-velocity film between the piezoelectric film and the supporting substrate, with the low-acoustic-velocity film made of silicon oxide and the high-acoustic-velocity film made of materials like aluminum nitride, to confine energy and enhance the Q factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a hard dielectric layer is formed between the dielectric substrate and the piezoelectric film to increase acoustic velocity, then the frequency of the surface acoustic wave device can be increased, but there is considerable propagation loss and surface acoustic waves cannot be effectively confined within the piezoelectric thin film, causing energy to leak into the dielectric substrate and resulting in a low Q factor
Solution Approach 1:
The device is segmented into multiple functional layers: a low-acoustic-velocity film (first dielectric layer) directly beneath the piezoelectric film to confine surface acoustic waves, and a high-acoustic-velocity film (second dielectric layer) beneath the low-acoustic-velocity film to increase the overall acoustic velocity. This segmentation allows independent optimization of wave confinement and velocity enhancement, resolving the contradiction between increasing frequency and reducing propagation loss.
2Speed
If a hard dielectric layer is formed between the dielectric substrate and the piezoelectric film to increase acoustic velocity, then the frequency of the surface acoustic wave device can be increased, but energy of the surface acoustic wave device leaks into the dielectric substrate, resulting in a low Q factor
Solution Approach 1:
The device structure is divided into distinct functional zones: the low-acoustic-velocity film serves as a confinement layer to prevent energy leakage into the substrate, while the high-acoustic-velocity film provides velocity enhancement. This segmentation enables simultaneous achievement of high Q factor through effective confinement and high frequency through velocity enhancement.
Solution Approach 2:
The low-acoustic-velocity film acts as an intermediary layer between the piezoelectric film and the high-acoustic-velocity film, creating an acoustic impedance mismatch that confines surface acoustic waves within the piezoelectric film and prevents energy leakage into the substrate, thereby maintaining high Q factor while allowing the high-acoustic-velocity film to enhance overall acoustic velocity.
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 confines elastic wave energy, reducing propagation loss and increasing the Q factor, while also improving temperature characteristics and band width ratio, allowing for higher frequency operation and better acoustic wave confinement.
Implementation Method 1
some portion of energy of an elastic wave propagating in the piezoelectric film is distributed into the low-acoustic-velocity film and the high-acoustic-velocity supporting substrate
Implementation Method 2
an IDT electrode disposed on a surface of the piezoelectric film
Data Source
AI summary
An elastic wave device includes a supporting substrate, a high-acoustic-velocity film stacked on the supporting substrate and in which an acoustic velocity of a bulk wave propagating therein is higher than an acoustic velocity of an elastic wave propagating in a piezoelectric film, a low-acoustic-velocity film stacked on the high-acoustic-velocity film and in which an acoustic velocity of a bulk wave propagating therein is lower than an acoustic velocity of a bulk wave propagating in the piezoelectric film, the piezoelectric film is stacked on the low-acoustic-velocity film, and an IDT electrode stacked on a surface of the piezoelectric film.