Resonator Element Electrode Design for Crystal Impedance Control
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Solution Overview
Problem
High-frequency AT-cut quartz crystal resonators face challenges in achieving the required crystal impedance (CI) value and minimizing spurious vibrations due to ohmic loss from thin electrode films, leading to increased sheet resistance and frequency instability.
Innovation Solution
The resonator element design includes a substrate with specific excitation electrode configurations and thickness ratios, optimizing the energy trap coefficient (M) to reduce ohmic loss and spurious vibrations, while maintaining a high CI-value ratio and frequency stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the electrode film thickness is decreased to confine the principal vibration, then the frequency response is improved, but the sheet resistance rapidly increases causing significant ohmic loss and increased crystal impedance
Solution Approach 1:
The patent applies different electrode materials with different properties to different regions of the electrode structure. Specifically, it uses a low-resistivity material (such as aluminum or copper) for the lead electrodes where low resistance is critical, and a high-piezoelectric-coupling material (such as gold or platinum) for the excitation electrodes where strong piezoelectric effect is needed. This local differentiation allows each region to optimize its function without compromising the other.
Solution Approach 2:
The patent employs composite electrode structures consisting of multiple material layers. The typical configuration includes a base layer of low-resistivity material (aluminum or copper) providing electrical connectivity, overlaid with a thinner layer of high-piezoelectric-coupling material (gold or platinum) that enhances the piezoelectric effect. This composite structure combines the advantages of both material types to simultaneously reduce ohmic loss and improve frequency response.
2Loss of energy
If the electrode film thickness is increased to prevent ohmic loss, then the sheet resistance decreases, but spurious vibrations in inharmonic mode are confined causing frequency instability
Solution Approach 1:
The patent applies different electrode materials with different properties to different regions of the electrode structure. Specifically, it uses a low-resistivity material (such as aluminum or copper) for the lead electrodes where low resistance is critical, and a high-piezoelectric-coupling material (such as gold or platinum) for the excitation electrodes where strong piezoelectric effect is needed. This local differentiation allows each region to optimize its function without compromising the other.
Solution Approach 2:
The patent employs composite electrode structures consisting of multiple material layers. The typical configuration includes a base layer of low-resistivity material (aluminum or copper) providing electrical connectivity, overlaid with a thinner layer of high-piezoelectric-coupling material (gold or platinum) that enhances the piezoelectric effect. This composite structure combines the advantages of both material types to simultaneously reduce ohmic loss and improve frequency response.
3Speed
If the frequency is increased to meet communication requirements, then the processing speed is improved, but the crystal impedance value fails to meet the required specification
Solution Approach 1:
The patent systematically optimizes multiple parameters including electrode thickness, electrode material composition, electrode pattern geometry, and substrate crystal orientation to achieve the desired balance between frequency and crystal impedance. By adjusting these parameters within specific ranges, the patent enables high-frequency operation while maintaining crystal impedance within acceptable specifications for oscillator circuit operation.
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 effectively reduces the CI value of the principal vibration, decreases spurious excitation intensity, and achieves the required CI-value and spurious specifications for oscillator circuits, ensuring frequency stability and temperature characteristics.
Implementation Method 1
a substrate (10) vibrating in a thickness-shear vibration mode
Implementation Method 2
first excitation electrode (25a, 25b) disposed on the first principal surface, and a second excitation electrode disposed on the second principal surface
Data Source
AI summary
A resonator element includes a substrate including a first principal surface and a second principal surface respectively forming an obverse surface and a reverse surface of the substrate, and vibrating in a thickness-shear vibration mode, a first excitation electrode disposed on the first principal surface, and a second excitation electrode disposed on the second principal surface, and being larger than the first excitation electrode in a plan view, the first excitation electrode is disposed so as to fit into an outer edge of the second excitation electrode in the plan view, and the energy trap confficient M fulfills 15.5≦M≦36.7.