Doubly Rotated Crystal Resonator With Elliptical Mesa Vibration Control
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Solution Overview
Problem
Doubly-rotated crystal resonators face issues with unwanted responses in contour and flexure modes, leading to sudden frequency changes and variations in crystal impedance due to temperature changes, which are difficult to mitigate using techniques from AT-cut crystal resonators.
Innovation Solution
A crystal resonator design featuring a crystal element with specific rotational axes and elliptical mesa portions on its principal surfaces, where the excitation electrodes are formed to reduce unwanted vibrations and stabilize crystal impedance across temperature ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a doubly-rotated cut crystal element is used to achieve good thermal shock property and zero temperature coefficient at high temperature, then thermal stability is improved, but unwanted responses in contour mode and flexure mode combine with the main vibration causing sudden frequency change and crystal impedance variation
Solution Approach 1:
The patent introduces dummy electrodes at specific locations on the crystal element to locally suppress unwanted contour and flexure mode vibrations. By placing these dummy electrodes at predetermined positions (such as at the periphery or at specific distances from the center), the invention selectively dampens harmful vibration modes without affecting the main vibration mode, thus resolving the contradiction between thermal stability and frequency stability
Solution Approach 2:
The dummy electrodes act as intermediary elements that mediate between the crystal element's thermal properties and its vibration characteristics. These electrodes serve as a bridge to control unwanted vibrations caused by temperature changes, allowing the crystal resonator to maintain both thermal shock resistance and frequency stability simultaneously
2Ease of manufacture
If AT-cut crystal resonator techniques are applied to doubly-rotated crystal resonator, then manufacturing is simplified, but the unwanted response cannot be reduced because the vibration modes are different
Solution Approach 1:
The patent changes the approach from using AT-cut specific techniques to a more generalizable solution by introducing dummy electrodes with specific geometric parameters (position, size, shape) optimized for doubly-rotated crystal elements. This parameter-based approach allows effective suppression of unwanted vibrations in doubly-rotated crystal resonators while maintaining manufacturing feasibility
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
The proposed design effectively reduces unwanted responses and stabilizes crystal impedance, minimizing frequency changes and impedance variations, especially at high temperatures, thereby enhancing the thermal stability of the crystal resonator.
Implementation Method 1
a crystal resonator that includes a crystal element and excitation electrodes
Implementation Method 2
Elliptical mesa portions or elliptical inverted mesa portions are formed on the respective principal surfaces
Data Source
AI summary
A crystal resonator includes a crystal element and excitation electrodes. The crystal element has a pair of principal surfaces parallel to an X′-axis and a Z′-axis. The X′-axis is an axis of rotating an X-axis as a crystallographic axis of a crystal in a range of 15 degrees to 25 degrees around a Z-axis as a crystallographic axis of the crystal. The Z′-axis is an axis of rotating the Z-axis in a range of 33 degrees to 35 degrees around the X′-axis. The excitation electrodes are formed on the respective principal surfaces of the crystal element. Elliptical mesa portions or elliptical inverted mesa portions are formed on the respective principal surfaces. The mesa portions project from outer peripheries of the principal surfaces. The inverted mesa portions are depressed from the outer peripheries of the principal surfaces.