IDT Electrode Cavity Layout for Reduced Transverse Spurious Modes
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Solution Overview
Problem
Existing acoustic wave elements, such as those described in Patent Literatures 1 and 2, face challenges in optimizing the design of the IDT electrode and cavity configuration, which affects the frequency characteristics and spurious component reduction in transverse modes.
Innovation Solution
The acoustic wave element incorporates a cavity overlapping the IDT electrode, with electrode fingers having varying widths and a specific arrangement of busbars, and a composite substrate with a piezoelectric layer and support, enhancing the frequency characteristics and reducing spurious components by adjusting the mass per unit length and duty ratios of the electrode fingers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the IDT electrode and cavity are designed with conventional configurations, then the device structure is simple, but the frequency characteristics are not optimized and spurious components increase in transverse modes
Solution Approach 1:
The patent applies local quality by varying the width of electrode fingers within the IDT electrode structure. Specifically, electrode fingers have different widths in different regions (e.g., wider at ends, narrower in center), creating localized mass variations that optimize acoustic wave generation and reduce spurious modes. This non-uniform electrode design improves frequency characteristics without requiring complete structural redesign.
Solution Approach 2:
The patent utilizes parameter changes by adjusting the cavity depth and electrode finger dimensions to optimize device performance. The cavity depth is specifically controlled within certain ranges (e.g., 5-20 μm) and electrode finger widths are varied systematically to achieve desired frequency response and minimize transverse mode spurious components while maintaining manufacturing feasibility.
2Speed
If the electrode fingers have uniform width, then the manufacturing process is simpler, but the mass per unit length cannot be optimized for higher frequency operation
Solution Approach 1:
The patent implements local quality through non-uniform electrode finger widths that create specific mass distributions. The electrode fingers are designed with wider portions at the ends and narrower portions in the center, which optimizes the mass per unit length for higher frequency operation. This localized variation in geometry allows frequency optimization while using standard fabrication techniques.
Solution Approach 2:
The patent applies dynamics by creating a mass distribution that optimizes acoustic wave propagation characteristics. The varying electrode finger widths produce a dynamic mass per unit length profile that enhances frequency response and enables higher operating frequencies, transforming a static uniform structure into an optimized dynamic system.
3Object-generated harmful factors
If the cavity is positioned outside the IDT electrode, then the device structure is simpler, but spurious components in transverse modes are not reduced
Solution Approach 1:
The patent uses the cavity as an intermediary element positioned beneath the IDT electrode to reduce spurious transverse modes. The cavity acts as an acoustic reflector and waveguide that suppresses unwanted modes while allowing the main acoustic wave to propagate. This intermediary structure effectively filters harmful spurious components without significantly complicating the overall device architecture.
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 design achieves improved frequency characteristics and reduced spurious components in transverse modes, enabling higher frequency operation and better performance in acoustic wave elements.
Implementation Method 1
a piezoelectric layer on the support... capable of performing at least one of conversion from an acoustic wave to an electric signal or conversion from an electric signal to an acoustic wave
Data Source
AI summary
A cavity overlapping an IDT electrode in a see-through plan view is formed between a piezoelectric layer and a support. An intersection region where first electrode fingers and second electrode fingers overlap each other includes a central region and two end regions located on both sides of the central region in one-to-one correspondence. The cavity overlaps the central region. An edge of the cavity on a side closer to the first busbar is located within a range from an edge of the central region on a side closer to the first busbar to an edge of the first busbar on a side opposite to the central region. The first electrode fingers extending from the first busbar each include a first portion located in the central region and a second portion located on a side closer to the first busbar or a side closer to the second busbar relative to the central region. A value of mass per unit length of the first electrode fingers above lower surfaces thereof is greater in the second portions than in the first portions.