Elastic Wave Resonator Bus Bar Layout to Prevent Film Cracks
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Solution Overview
Problem
Conventional elastic wave devices face challenges in reducing size while maintaining high Q value and preventing cracks in the piezoelectric film, particularly due to the concentration of pressure at corner portions of bus bars within the cavity portion.
Innovation Solution
The elastic wave device incorporates a support substrate with a recessed portion forming a cavity, a piezoelectric film of lithium niobate or tantalate, and electrode bus bars with curved or protruding pressure relaxation portions at their corners, which are located inside the cavity to alleviate pressure on the film, allowing for reduced size without compromising the Q value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the number of electrode fingers is reduced to reduce device size, then the device size is reduced, but the Q value is reduced
Solution Approach 1:
The invention transitions from using plate waves (two-dimensional propagation in the piezoelectric film plane) to using bulk waves in thickness slip mode (three-dimensional wave propagation through the film thickness). This dimensional change allows the resonator to achieve high Q values with fewer electrode fingers, thereby reducing device size while maintaining performance.
Solution Approach 2:
The invention changes the wave propagation mode parameter from plate wave to bulk wave in thickness slip mode. This parameter change fundamentally alters the resonance characteristics, enabling the system to achieve high Q values with a reduced number of electrode fingers, thus resolving the contradiction between device size and Q value.
2Volume of moving object
If bus bar corner portions are located above the cavity portion to reduce device size, then the device size is reduced, but cracks occur in the piezoelectric film at the corner portions
Solution Approach 1:
The invention introduces a recessed portion in the support substrate as an intermediary structure. This recessed portion positions the bus bar corner portions over the cavity rather than directly over the piezoelectric film, thereby mediating the stress distribution and preventing crack formation while enabling compact device design.
Solution Approach 2:
The invention creates a localized recessed portion under the bus bar corner portions, providing different structural qualities in different regions. The area under the bus bar corners has a recessed support substrate to prevent cracking, while other areas maintain the normal structure, thus locally addressing the stress concentration problem.
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 increases the Q value and prevents cracks in the piezoelectric film by distributing pressure more evenly, enabling size reduction without propagation loss or structural damage.
Implementation Method 1
a piezoelectric film made of lithium niobate or lithium tantalate, which is laminated on the first main surface of the support substrate... The elastic wave device uses a bulk wave in a thickness slip mode
Data Source
AI summary
An elastic wave device includes a piezoelectric film laminated on a first main surface of a support substrate including a recessed portion open to a first main surface. A cavity portion including the recessed portion is defined by the support substrate and the piezoelectric film. An electrode is on the piezoelectric film. The electrode includes first and second bus bars, a first electrode finger connected to the first bus bar, and a second electrode finger connected to the second bus bar. The first and second bus bars include corner portions inside the cavity portion when viewed in plan view. A curved portion as a pressure relaxation portion to relax pressure on the piezoelectric film at at least one of the corner portions of the first and second bus bars is provided between the corner portion and an outer edge of the cavity portion.