AT-Cut Crystal Structure for Vibration Confinement and Low Impedance
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Solution Overview
Problem
The downsizing of AT-cut crystal units has made mechanical processing challenging, and existing manufacturing methods using photolithography and wet etching techniques face difficulties in achieving optimal structural configurations for connecting thick and thin portions, leading to suboptimal crystal impedance and frequency-temperature characteristics.
Innovation Solution
A crystal unit with an AT-cut crystal element featuring a planar rectangular shape, including a thick portion, first and second depressed portions, and end portions, where the dimensions from the first end portion to the second depressed portion satisfy the formula L=λ×(n/2±⅛), with specific angles and surface configurations to enhance vibration confinement and resonance frequency stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the crystal element is downsized to reduce device size, then the device becomes more compact, but mechanical processing becomes difficult and manufacturing precision deteriorates
Solution Approach 1:
The patent replaces mechanical processing with photolithography and wet etching techniques to manufacture the crystal element. This substitution enables precise fabrication of the depressed portions and thick portion structure at small scales where mechanical processing becomes infeasible, thereby maintaining manufacturing precision while achieving device downsizing.
Solution Approach 2:
The patent changes the manufacturing approach from mechanical to chemical/photo-based processes, and optimizes the dimensions of the depressed portions and thick portion according to specific formulas involving wavelength λ and natural number n. These parameter changes enable precise control of vibration confinement and resonance characteristics in downsized devices.
2Ease of manufacture
If the connecting part structure is simplified for ease of manufacture, then manufacturing becomes easier, but crystal impedance and frequency-temperature characteristics deteriorate
Solution Approach 1:
The patent introduces depressed portions with specific dimensions and shapes at localized regions of the crystal element. These local structural modifications create optimal vibration confinement and resonance characteristics in the connecting parts, improving crystal impedance and frequency-temperature characteristics while maintaining compatibility with photolithography manufacturing processes.
Solution Approach 2:
The patent adds vertical dimensionality by creating depressed portions that extend into the thickness direction of the crystal element. This three-dimensional structuring within the planar crystal substrate enables precise control of vibration modes and resonance characteristics without complicating the overall manufacturing process.
3Reliability
If the thick portion structure is optimized for low crystal impedance, then crystal impedance improves, but vibration confinement becomes insufficient and frequency-temperature characteristics worsen
Solution Approach 1:
The patent segments the crystal element structure by introducing depressed portions that divide the connecting parts between the thick portion and end portions. This segmentation creates distinct functional zones: the thick portion for low crystal impedance and the depressed portions for vibration confinement, thereby simultaneously achieving both objectives.
Solution Approach 2:
The patent optimizes the dimensions of the depressed portions according to specific formulas involving wavelength λ and natural number n. By carefully controlling the depth, width, and position of these depressed portions, the patent achieves optimal balance between vibration confinement and frequency-temperature characteristics while maintaining low crystal impedance.
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 reduces unnecessary vibrations, achieves a low crystal impedance value, and improves frequency-temperature characteristics by properly confining vibrations within the thick portion, resulting in a more stable and efficient crystal unit.
Implementation Method 1
a surface of the first depressed portion is depressed with a predetermined angle θa and subsequently bulged, and connected to the first end portion. The second depressed portion is a depressed portion disposed from the thick portion toward a side of the second end portion, and a surface of the second depressed portion is depressed with a predetermined angle θb and subsequently bulged, and connected to the second end portion.
Implementation Method 2
When a dimension from a distal end of the first end portion to an edge on a side of the second depressed portion of the thick portion is defined as L, the L satisfies a following formula (1). In the formula (1), n is a natural number, and λ is a wavelength of a flexure vibration that propagates along an X-axis of a crystal in the crystal unit, L=λ×(n/2±1⁄8)
Data Source
AI summary
A crystal unit includes an AT-cut crystal element that has a planar shape in a rectangular shape and a part as a thick portion. The crystal element includes a first end portion, a first depressed portion, the thick portion, a second depressed portion, and a second end portion in this order from a side of one short side, in viewing a cross section taken along a longitudinal direction near a center of the short side. The first depressed portion is a depressed portion disposed from the thick portion toward the first end portion side, depressed with a predetermined angle θa and subsequently bulged, and connected to the first end portion. The second depressed portion is a depressed portion disposed from the thick portion toward the second end portion side, depressed with a predetermined angle θb and subsequently bulged, and connected to the second end portion.