Bulk Wave Resonator Layout for Precise Frequency Trimming
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Solution Overview
Problem
Existing piezoelectric bulk wave devices face challenges in accurately adjusting frequencies due to uneven shapes of frequency adjustment films, leading to variations in thickness that hinder precise frequency adjustment.
Innovation Solution
A piezoelectric bulk wave device design featuring a support substrate with a hollow portion, a piezoelectric layer, IDT electrodes, and a frequency adjustment film with via holes and wiring electrodes, where the thickness of the piezoelectric layer is optimized relative to the center-to-center distance between electrode fingers, allowing for precise frequency adjustment by grinding the frequency adjustment film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a frequency adjustment film is provided on the piezoelectric substrate to adjust frequency, then frequency adjustment capability is improved, but the film's uneven shape causes thickness variations that deteriorate frequency adjustment precision
Solution Approach 1:
The device is divided into functionally distinct layers: the piezoelectric substrate for wave generation, the frequency adjustment film for frequency control, and the hollow portion for mechanical support and stress management. This segmentation allows each component to be optimized independently, with the frequency adjustment film focusing solely on frequency control without being compromised by structural requirements.
Solution Approach 2:
The hollow portion is strategically positioned to overlap with the IDT electrode in plan view, creating a localized region with different mechanical properties. This local structural modification allows the frequency adjustment film to maintain uniform thickness in critical areas while the hollow portion provides overall support, resolving the contradiction between frequency adjustment precision and manufacturing feasibility.
2Adaptability or versatility
If the frequency adjustment film thickness is adjusted to achieve desired frequency, then frequency tuning range is improved, but thickness variations in directions other than the lamination direction deteriorate adjustment accuracy
Solution Approach 1:
The hollow portion introduces a vertical dimension (depth) to the support structure, allowing frequency adjustment through controlled thickness variation of the frequency adjustment film in the lamination direction while maintaining uniformity in lateral dimensions. This dimensional approach enables precise frequency tuning without compromising adjustment accuracy.
3Reliability
If via holes and wiring electrodes are added to connect busbars, then electrical connectivity is improved, but device structure complexity increases
Solution Approach 1:
The frequency adjustment film serves multiple functions: it adjusts the operating frequency of the device, provides a substrate for via holes and wiring electrodes, and maintains mechanical stability. By integrating these functions into a single component, the patent reduces overall device complexity while ensuring reliable electrical connectivity between the IDT electrode and external terminals.
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
Enables high-accuracy frequency adjustment in piezoelectric bulk wave devices, improving their performance in high-frequency applications by ensuring uniform thickness adjustments and reducing complexity in manufacturing processes.
Implementation Method 1
A bulk wave in the thickness-shear mode is excited by applying an alternating-current voltage between the electrodes
Data Source
AI summary
A piezoelectric bulk wave device includes a support including a support substrate, a piezoelectric layer on the support and including first and second principal surfaces, an IDT electrode on the first principal surface and including a pair of comb-shaped electrodes each including electrode fingers and a busbar connecting the electrode fingers, and a frequency adjustment film on the second principal surface and overlapping at least a portion of the IDT electrode. The support includes a hollow portion overlapping at least a portion of the IDT electrode. d/p is less than or equal to about 0.5. Via holes are provided to the piezoelectric layer and the frequency adjustment film. Wiring electrodes are provided in the via holes and on the frequency adjustment film and electrically connected to the busbars of the comb-shaped electrodes.