Piezoelectric Resonator Frequency Adjustment via Electrode Overlay
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Solution Overview
Problem
Existing methods for adjusting the frequency of piezoelectric resonators face challenges due to inaccuracies in positioning metallic films, leading to spurious responses and depolarization of the substrate, especially as resonator sizes decrease and structures become finer.
Innovation Solution
A method involving the formation of first electrodes on a piezoelectric substrate to trap vibration, followed by measuring the frequency, determining the required thickness of a metallic film, and forming a second electrode to overlay on the first, allowing for precise adjustment without precise positioning, thereby preventing depolarization and enhancing measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a metallic film is formed on vibrating electrodes by a dry process to adjust frequency, then the resonant frequency can be adjusted accurately in small increment units, but it is difficult to accurately position the metallic film to the vibrating electrodes, making frequency adjustment difficult
Solution Approach 1:
The patent applies preliminary action by forming a metallic film on the entire piezoelectric substrate before patterning the vibrating electrodes. This allows the metallic film to be deposited uniformly across the substrate surface before the electrode pattern is defined, eliminating positioning difficulties that would arise from attempting to deposit metal only on pre-formed small electrodes. The frequency adjustment is then achieved by controlling the overall film thickness rather than by precise spatial positioning.
Solution Approach 2:
The patent segments the metallic film formation process into two distinct stages: first, forming a continuous metallic film layer on the entire substrate; second, patterning this film to create the vibrating electrode structure. This segmentation separates the film deposition process from the electrode pattern definition, allowing each process to be optimized independently and avoiding the positioning problems that would result from attempting to combine them.
2Ease of manufacture
If the piezoelectric substrate is covered with a metallic mask except for the portion on which vibrating electrodes are formed, then a metallic material can be attached by vapor deposition or sputtering, but accurate positioning of the metallic mask to the vibrating electrodes remains difficult
Solution Approach 1:
The patent inverts the conventional approach by not using a mask to define where metal should be deposited, but instead forming a continuous metallic film and then using etching to remove material where it is not needed. This inversion of the masking approach eliminates the need for precise mask positioning, as the continuous film ensures uniform coverage and the etching process defines the final electrode pattern without requiring alignment.
3Ease of manufacture
If etching resist ink is applied onto the overall surface of the piezoelectric substrate except for the portion on which vibrating electrodes are disposed, then a metallic material can be attached by vapor deposition or sputtering, but variations in the application quantity of ink are large, resulting in low concentration of frequency adjustment
Solution Approach 1:
The patent replaces the mechanical/chemical process of applying etching resist ink with a vapor deposition or sputtering process that forms a metallic film directly. This substitution eliminates the variability inherent in ink application methods, providing a more controlled and concentrated means of frequency adjustment through precise control of film thickness rather than through variable ink coverage.
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 approach enables accurate frequency adjustment with uniform electrode thickness, reducing spurious responses and preventing substrate depolarization, thus improving the precision and reliability of piezoelectric resonator manufacturing.
Implementation Method 1
piezoelectric resonator in which vibrating electrodes are disposed on both surfaces of a piezoelectric substrate and piezoelectric vibration is trapped between the vibrating electrodes
Implementation Method 2
a metallic film, for example, a metallic thin film, having a predetermined thickness is formed on each vibration electrode by a dry process
Data Source
AI summary
A method of manufacturing a piezoelectric resonator includes forming first electrodes larger than vibrating electrodes in an area D1 including the vibrating electrodes on obverse and reverse surfaces of a piezoelectric substrate, and measuring the resonant frequency fr1 of a resonator including the first electrodes. The thickness of a metallic thin film required for frequency adjustment is determined based on the measured resonant frequency. Then, second electrodes formed of the metallic thin film having the determined thickness are formed in an area D2 including at least the vibrating electrodes of the piezoelectric substrate. By removing unnecessary portions of the first and second electrodes, a pattern of the resulting vibrating electrodes is formed. Thus, high-accuracy frequency adjustment can be achieved without the need for complicated positioning.