Acoustic Reflection Layer Thickness Layout for Spurious Mode Separation
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Solution Overview
Problem
Elastic wave devices used in filters, such as those in cellular phones, often experience significant spurious emission around the frequency of the main mode, which can adversely affect filter characteristics.
Innovation Solution
The elastic wave device incorporates an acoustic reflection layer with three or more low-acoustic impedance layers and two or more high-acoustic impedance layers, where the film thickness of the layer closest to the piezoelectric layer is thinner than the others, increasing the difference between the main mode frequency and spurious emission frequency without impairing the main mode characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the film thickness of all low-acoustic impedance layers and high-acoustic impedance layers is made equal, then the manufacturing process is simplified, but spurious emission occurs around the main mode frequency affecting filter characteristics
Solution Approach 1:
The patent applies asymmetry by making the film thickness of at least one low-acoustic impedance layer different from the film thickness of other low-acoustic impedance layers, or making the film thickness of at least one high-acoustic impedance layer different from other high-acoustic impedance layers. This asymmetric thickness distribution in the acoustic reflection layer suppresses spurious emission around the main mode frequency while maintaining filter characteristics, resolving the contradiction between manufacturing simplicity and spurious emission suppression.
2Device complexity
If the acoustic reflection layer uses equal thickness layers, then the device complexity is reduced, but the reflectance is insufficient causing increased loss
Solution Approach 1:
The patent employs asymmetric film thickness design in the acoustic reflection layer, where at least one low-acoustic impedance layer or at least one high-acoustic impedance layer has a different thickness from others in the same group. This asymmetric configuration increases the reflectance of acoustic waves, thereby reducing energy loss without significantly increasing device complexity.
Solution Approach 2:
The patent changes the physical parameter of film thickness in the acoustic reflection layer by making at least one layer's thickness different from the others. This parameter variation optimizes the acoustic impedance distribution, enhancing reflectance and reducing energy loss while maintaining reasonable structural complexity.
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 enhances reflectance, reduces loss, and effectively separates the main mode frequency from spurious emission frequencies, thereby minimizing the adverse effects on filter characteristics.
Implementation Method 1
an acoustic reflection layer provided on the supporting substrate... The acoustic reflection layer includes three or more low-acoustic impedance layers; and two or more high-acoustic impedance layers
Implementation Method 2
a piezoelectric layer provided on the acoustic reflection layer... an interdigital transducer (IDT) electrode provided on the piezoelectric layer... a plate wave in S0 mode is used
Data Source
AI summary
An elastic wave device includes a supporting substrate, an acoustic reflection layer on the supporting substrate, a piezoelectric layer on the acoustic reflection layer, and an IDT electrode on the piezoelectric layer. The acoustic reflection layer includes three or more low-acoustic impedance layers and two or more high-acoustic impedance layers. At least one of a first relationship in which in which, a film thickness of a first low-acoustic impedance layer closest to the piezoelectric layer is thinner than a film thickness of a low-acoustic impedance layer closest to the first low-acoustic impedance layer, and a second relationship in which a film thickness of a first high-acoustic impedance layer closest to the piezoelectric layer is thinner than a film thickness of a high-acoustic impedance layer closest to the first high-acoustic impedance layer, is satisfied.