Elastic Wave Resonator Structure for Moisture-Resistant Frequency Stability
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Solution Overview
Problem
Elastic wave devices experience moisture penetration through etching windows and spaces, leading to frequency fluctuations and reliability issues due to insufficient moisture resistance.
Innovation Solution
The design includes a supporting substrate with a recessed portion, a piezoelectric thin film covering the recessed portion, an IDT electrode facing the space, an intermediate layer with alternating acoustic impedance layers, and a cover member covering the through holes to prevent moisture ingress, enhancing moisture resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a space is formed on the supporting body side of the piezoelectric thin film to enable IDT electrode operation, then the elastic wave device can function properly, but moisture penetrates into the IDT electrode unit through the etching window and space, causing frequency fluctuation and reliability issues
Solution Approach 1:
The patent implements a multi-layer nested structure where the piezoelectric thin film is positioned over a recessed portion of the supporting substrate, creating a nested configuration that defines a protected space. This nesting approach allows the IDT electrode to face the space while being protected from moisture penetration, resolving the contradiction between functionality and moisture resistance.
Solution Approach 2:
The patent introduces an intermediate layer as a mediator between the piezoelectric thin film and the IDT electrode structure. This intermediate layer acts as a barrier that prevents moisture from reaching the IDT electrode through the space, while still allowing the device to function properly. The intermediary element resolves the contradiction by providing protection without compromising the operational space.
2Volume of moving object
If the piezoelectric thin film is made thinner to reduce device size, then the device becomes more compact, but the energy confinement capability of the elastic wave is reduced
Solution Approach 1:
The patent applies local quality by creating a recessed portion in the supporting substrate with specific depth and dimensions. This localized structural modification enhances the energy confinement capability in the specific region where the piezoelectric thin film is positioned, allowing thinner films to maintain adequate energy confinement through optimized local geometry rather than requiring uniform thickness throughout.
Solution Approach 2:
The patent transitions from considering only the thickness dimension of the piezoelectric film to incorporating the vertical dimension of the recessed portion in the supporting substrate. By utilizing this additional dimensional space, the device achieves compact size while maintaining energy confinement capability through the three-dimensional geometry of the recessed structure rather than relying solely on film thickness.
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
The solution effectively confines elastic wave energy and prevents moisture penetration, resulting in stable frequency operation and improved reliability of the elastic wave devices.
Implementation Method 1
an intermediate layer including a pair of main surfaces opposite to each other, the intermediate layer being provided on the other one of the main surfaces of the piezoelectric thin film... the intermediate layer is an acoustic reflecting layer that includes a plurality of acoustic impedance layers
Implementation Method 2
a piezoelectric thin film including a pair of main surfaces opposite to each other, the piezoelectric thin film being provided on the supporting substrate
Data Source
AI summary
An elastic wave device includes a supporting substrate including an upper surface including a recessed portion, a piezoelectric thin film on the supporting substrate to cover the recessed portion of the supporting substrate, an IDT electrode on a main surface of the piezoelectric thin film, the main surface being adjacent to the supporting substrate, and an intermediate layer on a main surface of the piezoelectric thin film, the main surface being remote from the supporting substrate. A space is defined by the supporting substrate and the piezoelectric thin film. The IDT electrode faces the space. Through holes are provided in the piezoelectric thin film and the intermediate layer to extend from a main surface of the intermediate layer to the space, the main surface being remote from the piezoelectric thin film. The elastic wave device further includes a cover member on the intermediate layer and covering opening ends of the through holes.