Acoustic Wave Filter Layering to Suppress Bulk Wave Reflection
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Solution Overview
Problem
The reduction in thickness of acoustic wave element substrates leads to deterioration of filter characteristics due to the influence of bulk waves, making it challenging to achieve higher integration in acoustic wave modules.
Innovation Solution
The use of a layered structure with a comb-shaped filter electrode on the acoustic wave element substrate, a first insulator layer covering one surface, and a second insulator layer laminated on top, where the propagation speeds and densities of the layers are selected to prioritize wave attenuation, reducing the impact of unwanted bulk waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the thickness of the acoustic wave element substrate is reduced to achieve higher integration, then the height of the module is reduced, but the filter characteristics deteriorate due to bulk wave reflection
Solution Approach 1:
A resin layer is introduced as an intermediary substance between the acoustic wave element substrate and the module substrate. This resin layer acts as a mediator that absorbs and attenuates bulk waves, preventing their reflection back into the acoustic wave element substrate. The resin layer has acoustic impedance specifically designed to be lower than that of the acoustic wave element substrate, creating an acoustic mismatch that reduces bulk wave propagation and reflection, thereby maintaining filter characteristics even when the substrate thickness is reduced.
Solution Approach 2:
The invention converts the harmful effect of bulk wave reflection into a beneficial outcome by using the same bulk waves that cause deterioration as a means to identify and address the problem. By understanding that bulk waves reflect at the interface between the acoustic wave element substrate and module substrate, the invention deliberately introduces a resin layer that absorbs these bulk waves, transforming the harmful reflection into a controlled energy dissipation mechanism that protects the filter characteristics.
2Adaptability or versatility
If multiple acoustic wave element substrates are stacked to achieve higher integration, then the functionality is enhanced, but the height reduction goal cannot be met due to bulk wave generation in each substrate
Solution Approach 1:
When multiple acoustic wave element substrates are stacked, resin layers are introduced as intermediaries between each substrate. These resin layers serve as acoustic buffers that prevent bulk wave generation and propagation in each individual substrate. By placing resin layers between the stacked substrates, bulk waves are absorbed at each interface, preventing the cumulative height increase that would otherwise result from adding multiple substrates with their associated bulk wave effects.
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 approach effectively reduces or prevents characteristic deterioration, allowing for a thinner acoustic wave element substrate while maintaining good filter performance and enabling higher integration in acoustic wave modules.
Implementation Method 1
Assuming that propagation speeds of the acoustic wave in the pass band in the acoustic wave element substrate, the first insulator layer, and the second insulator layer are denoted by V0, V1, and V2, respectively, and densities of the acoustic wave element substrate, the first insulator layer, and the second insulator layer are denoted by ρ0, ρ1, and V2×ρ2>V0×ρ0>V1×ρ1 is satisfied
Implementation Method 2
the influence of a bulk wave W12 propagating in the substrate and reflecting at a rear surface of the acoustic wave element substrate 512 in contact with the resin is not negligible
Implementation Method 3
V0×ρ0>V1×ρ1>V2×ρ2 is satisfied
Data Source
AI summary
An acoustic wave device includes an acoustic wave element substrate, filter electrodes on a first surface of the acoustic wave element substrate, a first insulator layer covering a second surface of the acoustic wave element substrate, and a second insulator layer laminated on the first insulator layer and sandwiching the first insulator layer between the second insulator layer and the acoustic wave element substrate. The products of propagation speeds of an acoustic wave in those layers and densities of those layers satisfy a predetermined relationship.