Membrane Acoustic Wave Structure for Ripple and Q Stability
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Solution Overview
Problem
There is a demand for acoustic wave devices with a membrane structure that can reduce ripple, as existing devices face challenges in minimizing ripple while maintaining effective resonance characteristics and Q values, especially when reducing device size.
Innovation Solution
The acoustic wave device incorporates a piezoelectric layer with a gap portion on the element substrate and a ground electrode on the mounting substrate, which overlaps the functional electrode, allowing for the reduction of ripple by stabilizing the potential and minimizing propagation loss, even when the number of electrode pairs is reduced for size reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the number of electrode pairs is reduced to minimize device size, then device area is reduced, but ripple increases and resonance characteristics deteriorate
Solution Approach 1:
The device is segmented into distinct functional regions: a membrane region with the piezoelectric layer and IDT electrode for acoustic wave generation, and a separate ground electrode region on the mounting substrate. This segmentation allows the ground electrode to be positioned independently to provide electrical stability without occupying the active acoustic region, enabling size reduction while maintaining resonance characteristics.
Solution Approach 2:
The mounting substrate acts as an intermediary between the element substrate and the external environment. By placing the ground electrode on the mounting substrate rather than directly on the element substrate, the patent creates an intermediate electrical reference that stabilizes potential without interfering with the acoustic wave propagation in the piezoelectric layer, thus reducing ripple while maintaining compact dimensions.
2Reliability
If reflectors are added to improve resonance characteristics, then Q value is improved, but device complexity and size increase
Solution Approach 1:
The ground electrode on the mounting substrate serves multiple functions simultaneously: it provides electrical grounding, stabilizes the potential of the functional electrode, reduces ripple, and acts as a reference for acoustic wave propagation. This multi-functionality eliminates the need for separate reflector structures that would otherwise be required to achieve similar resonance stabilization, thereby reducing device complexity while maintaining high Q values.
3Area of moving object
If a membrane structure is implemented to reduce device size, then device area is reduced, but ripple increases due to potential instability
Solution Approach 1:
The ground electrode on the mounting substrate creates an equipotential reference plane that stabilizes the electrical potential across the membrane structure. By providing this stable reference, the patent prevents potential fluctuations that would otherwise cause ripple in the acoustic signal, enabling the use of compact membrane structures without sacrificing signal quality.
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 ripple and maintains good resonance characteristics and a high Q value, even when the device size is minimized, by eliminating the need for reflectors and reducing propagation loss, thus enhancing the acoustic wave device's performance.
Implementation Method 1
an acoustic wave element includes a piezoelectric layer made of lithium niobate or lithium tantalate
Implementation Method 2
maintains good resonance characteristics and a high Q value
Data Source
AI summary
An acoustic wave device includes an element substrate, a piezoelectric layer, a functional electrode on the piezoelectric layer, and a mounting substrate. The element substrate includes a gap portion at a position overlapping at least a portion of the functional electrode as seen in a lamination direction of the element substrate and the piezoelectric layer, and the mounting substrate includes a ground electrode at a position overlapping the functional electrode in the lamination direction.