Acoustic Wave Stack Sealing Against Moisture-Induced Piezoelectric Cracking
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Solution Overview
Problem
Acoustic wave devices face issues with moisture ingress into the low acoustic velocity film, leading to stress application on the piezoelectric film, which can result in cracking or peeling during heat treatment, such as during mounting or sealing.
Innovation Solution
The acoustic wave device incorporates a cover film that covers the entire or substantial side surface of the silicon oxide film, preventing moisture from entering and reducing stress on the piezoelectric layer, while the wiring electrode extends from the piezoelectric layer to the resin layer, enhancing heat dissipation and reducing the risk of breakage and peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the low acoustic velocity film is formed of silicon oxide and disposed on the support substrate, then the acoustic wave device can be manufactured with conventional processes, but moisture in air or moisture in the insulating layer may enter the low acoustic velocity film, causing stress application to the piezoelectric film during heat treatment
Solution Approach 1:
A cover film is introduced as an intermediary layer between the silicon oxide film and the external environment (moisture). This cover film prevents moisture from reaching the silicon oxide film, thereby eliminating the source of stress that would otherwise be applied to the piezoelectric film during heat treatment, while allowing the device to be manufactured using conventional processes
2Reliability
If the insulating layer is formed of a resin and disposed around the multilayer body, then the device can be sealed and protected, but moisture in the insulating layer may enter the low acoustic velocity film and cause stress application to the piezoelectric film
Solution Approach 1:
The cover film serves as a protective intermediary that blocks moisture from the resin insulating layer from reaching the silicon oxide film. This allows the device to maintain the benefits of resin sealing while preventing moisture contamination of the acoustic wave structure
Solution Approach 2:
A thin film cover is applied over the silicon oxide film to create a moisture barrier. This flexible thin film structure effectively seals the underlying layers against moisture ingress from the surrounding resin insulating layer, preventing the harmful effects of moisture on the piezoelectric film
3Ease of manufacture
If heat treatment is applied during mounting or sealing, then the device can be sealed with resin, but moisture in the low acoustic velocity film is removed by heat, applying stress to the piezoelectric film and causing cracking or peeling
Solution Approach 1:
The cover film is applied in advance to prevent moisture from entering the silicon oxide film before heat treatment occurs. By eliminating the moisture source beforehand, the subsequent heat treatment process does not cause moisture removal from the film, thereby preventing stress application and maintaining the integrity of the piezoelectric film during sealing
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 or prevents breakage and peeling of the piezoelectric layer, ensuring the device's reliability and performance by minimizing moisture-induced stress and maintaining acoustic wave energy confinement within the piezoelectric layer.
Implementation Method 1
a cover film that covers the entire or substantially the entire side surface of the silicon oxide film
Implementation Method 2
a piezoelectric layer that is provided on the silicon oxide film and that includes a first principal surface and a second principal surface opposite to each other, an excitation electrode provided on at least one of the first principal surface and the second principal surface of the piezoelectric layer
Implementation Method 3
a wiring electrode that is electrically connected to the excitation electrode and that extends from the piezoelectric layer to the resin layer
Data Source
AI summary
An acoustic wave device includes a support substrate having a central region and a surrounding region located around the central region, a silicon oxide film that is located in the central region directly or indirectly and that has a side surface, a piezoelectric layer that is provided on the silicon oxide film and that has a first principal surface and a second principal surface, an excitation electrode provided on at least one of the first principal surface and the second principal surface, a cover film provided to cover the entire side surface of the silicon oxide film, a resin layer that is provided in the surrounding region and that is provided to cover the side surface of the silicon oxide film from above the cover film, and a wiring electrode that is electrically connected to the excitation electrode and that extends from the piezoelectric layer to the resin layer.