Acoustic Reflection Film Structure for Suppressing Unwanted Waves
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Solution Overview
Problem
Acoustic wave devices often generate unwanted waves due to impedance characteristics degradation, which affects their performance in cellular phones and similar applications.
Innovation Solution
The acoustic wave device incorporates a multilayer acoustic reflection film with alternating low and high acoustic impedance layers, where the arithmetic average roughness of the layers differs, effectively reducing or preventing unwanted waves by confining energy on the piezoelectric body side and improving adhesion between layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple acoustic reflection layer is used, then device complexity is reduced, but unwanted waves are generated and impedance characteristics are degraded
Solution Approach 1:
The acoustic reflection layer is segmented into multiple thin films with alternating high and low acoustic impedance (first high acoustic impedance layer 3b, first low acoustic impedance layer 3a, second high acoustic impedance layer 3d, second low acoustic impedance layer 3c). This segmentation creates a more complex structure that effectively suppresses unwanted waves while maintaining impedance characteristics, resolving the contradiction between structural simplicity and performance reliability.
Solution Approach 2:
The acoustic reflection layer uses composite material structure with alternating high and low acoustic impedance layers. This composite approach combines materials with different acoustic properties (such as Pt for high impedance and SiO2 for low impedance) to achieve superior wave suppression and impedance control compared to single-material layers, thereby improving reliability without excessive complexity.
2Manufacturing precision
If acoustic impedance layers with uniform roughness are used, then manufacturing precision is improved, but unwanted waves propagate through the acoustic reflection film
Solution Approach 1:
Different acoustic impedance layers are given different local surface qualities through varying arithmetic average roughness values. The first high acoustic impedance layer (3b) has Ra1, the first low acoustic impedance layer (3a) has Ra2, the second high acoustic impedance layer (3d) has Ra3, and the second low acoustic impedance layer (3c) has Ra4, where at least one roughness value differs from others. This local quality differentiation disrupts unwanted wave propagation while maintaining controllable manufacturing precision for each individual layer.
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 significantly reduces unwanted waves, maintaining impedance characteristics and enabling accurate measurement of the piezoelectric film thickness, thus enhancing the device's performance and reliability.
Implementation Method 1
an acoustic reflection film provided on the supporting substrate, wherein the acoustic reflection film is a multilayer body including a plurality of acoustic impedance layers including a low acoustic impedance layer whose acoustic impedance is relatively low and a high acoustic impedance layer whose acoustic impedance is relatively high
Implementation Method 2
a piezoelectric body provided on the acoustic reflection film
Data Source
AI summary
An acoustic wave device includes a supporting substrate, an acoustic reflection film the supporting substrate, a piezoelectric thin film on the acoustic reflection film, and an interdigital transducer electrode the piezoelectric thin film. The acoustic reflection film includes acoustic impedance layers including therein first, second, third, and fourth low acoustic impedance layers and first, second, and third high acoustic impedance layers. The acoustic reflection film includes a first acoustic impedance layer and a second acoustic impedance layer, the first and second acoustic impedance layers each being one of the acoustic impedance layers, and the second acoustic impedance layer has an arithmetic average roughness different from that of the first acoustic impedance layer.