Acoustic Wave Filter Stack for Suppressing Bulk-Wave Spurious Modes
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Solution Overview
Problem
Current acoustic wave devices face challenges in reducing spurious emissions, which are high-frequency unwanted signals that interfere with the primary acoustic wave response, due to the reflection of bulk waves at the boundaries between different layers in the device structure.
Innovation Solution
The introduction of a high acoustic velocity film (boundary layer) between the temperature compensation film and the support substrate, and an intermediate layer with a lower Q factor than the boundary layer, helps to confine the acoustic wave within the piezoelectric and temperature compensation films, reducing spurious emissions by inhibiting the propagation of bulk waves to the support substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a high acoustic velocity film (boundary layer) is provided between the temperature compensation film and the support substrate, then spurious emissions are reduced, but the acoustic wave propagation is still affected by bulk wave reflection at layer boundaries
Solution Approach 1:
An intermediate layer with acoustic velocity lower than the boundary layer but higher than the temperature compensation film is introduced between the boundary layer and the temperature compensation film. This intermediate layer acts as a mediator that gradually transitions the acoustic impedance, reducing bulk wave reflection and improving acoustic wave propagation stability while maintaining the spurious emission reduction effect of the boundary layer.
2Object-generated harmful factors
If multiple layers are added to reduce spurious emissions, then spurious response is suppressed, but device structure becomes more complex
Solution Approach 1:
The acoustic velocity parameter is strategically varied across different layers to achieve spurious response suppression. The boundary layer has high acoustic velocity, the intermediate layer has medium acoustic velocity, and the temperature compensation film has low acoustic velocity. This parameter gradient design effectively suppresses spurious response while keeping the structural complexity manageable through a systematic three-layer approach.
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 reduces spurious emissions while maintaining the main response characteristics, as demonstrated by simulations showing a decrease in spurious response without compromising the main response magnitude, thereby improving the overall performance of the acoustic wave device.
Implementation Method 1
a temperature compensation film interposed between the support substrate and the piezoelectric layer and having a temperature coefficient of an elastic constant opposite in sign to a temperature coefficient of an elastic constant of the piezoelectric layer
Implementation Method 2
a boundary layer interposed between the support substrate and the temperature compensation film, an acoustic velocity of a bulk wave propagating through the boundary layer being higher than an acoustic velocity of a bulk wave propagating through the temperature compensation film
Implementation Method 3
an intermediate layer interposed between the support substrate and the boundary layer and having a Q factor less than a Q factor of the boundary layer
Implementation Method 4
a piezoelectric layer provided over the support substrate; a pair of comb-shaped electrodes disposed on the piezoelectric layer, each of the pair of comb-shaped electrodes including electrode fingers that excite an acoustic wave
Data Source
AI summary
An acoustic wave device includes a support substrate, a piezoelectric layer provided over the support substrate, comb-shaped electrodes disposed on the piezoelectric layer, each of the comb-shaped electrodes including electrode fingers exciting an acoustic wave, a temperature compensation film interposed between the support substrate and the piezoelectric layer and having a temperature coefficient of an elastic constant opposite in sign to that of the piezoelectric layer, a boundary layer interposed between the support substrate and the temperature compensation film, an acoustic velocity of a bulk wave propagating through the boundary layer being higher than an acoustic velocity of a bulk wave propagating through the temperature compensation film and being lower than an acoustic velocity of a bulk wave propagating through the support substrate, and an intermediate layer interposed between the support substrate and the boundary layer and having a Q factor less than a Q factor of the boundary layer.