AT-Cut Crystal Element Geometry for Higher Crystal Impedance
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Solution Overview
Problem
Existing piezoelectric devices with AT-cut crystal elements have limitations in impedance improvement due to the etching process, which reduces the planar area and increases unnecessary vibrations, necessitating a more effective manufacturing method and design for enhanced crystal impedance (CI).
Innovation Solution
A piezoelectric device with an AT-cut crystal element featuring a quadrangular planar shape and side surfaces intersecting with the Z′-axis, including three specifically angled surfaces (first, second, and third surfaces) and approximately right-angled corner portions, secured with conductive adhesive, utilizing a photolithography and wet etching technique to optimize crystal impedance by reducing unnecessary vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a long-period etching process is used to form the crystal element surfaces, then the first to third surfaces with specific angles can be achieved, but the planar area of the crystal element is reduced due to excessive etching at corner portions
Solution Approach 1:
The patent applies preliminary action by forming a protective film on specific regions (corner portions and side surfaces) before the etching process. This protective film prevents excessive etching at these locations, allowing the main surfaces to be etched to the required angles while preserving the corner portions and maintaining the overall planar area of the crystal element.
2Manufacturing precision
If the planar area of the crystal element is reduced by etching, then the first to third surfaces can be formed, but the crystal impedance cannot be sufficiently improved
Solution Approach 1:
The protective film is applied in advance to prevent unwanted etching, ensuring that the crystal element maintains its planar area while still achieving the required surface angles. This resolves the contradiction by allowing proper surface configuration without sacrificing the area needed for high crystal impedance.
3Volume of moving object
If photolithography and wet etching techniques are used to achieve compact crystal unit, then the device size is reduced, but the etching process creates triangular regions at corner portions that reduce the crystal element area
Solution Approach 1:
The protective film is formed on corner portions and side surfaces before the wet etching process. This preliminary protection allows the photolithography and etching techniques to be used for device miniaturization while preventing the formation of triangular etched regions at the corners, thereby maintaining the full planar area of the crystal element.
4Reliability
If the crystal element has wide planar area for better CI, then the impedance can be improved, but the device cannot be sufficiently compact
Solution Approach 1:
By applying the protective film before etching, the crystal element can maintain its maximum planar area (improving CI) while the overall device size is kept compact through the use of photolithography and precise etching techniques. The protective film ensures that no area is lost to excessive etching, maximizing the crystal element area within the compact device footprint.
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 and manufacturing method result in improved crystal impedance (CI) by maintaining a wider planar area and reducing unnecessary vibrations, with corner angles and dimensions optimized to achieve a CI average value of 83.5Ω and standard deviation of 6.6Ω, surpassing conventional devices.
Implementation Method 1
a piezoelectric device, such as a crystal unit, a crystal controlled oscillator including the crystal unit
Data Source
AI summary
A piezoelectric device includes a container and an AT-cut crystal element. The AT-cut crystal element has at least one side surface intersecting with a Z′-axis of the crystallographic axis of the crystal constituted of three surfaces. The first surface is a surface equivalent to a surface formed by rotating the principal surface by 4°±3.5° with an X-axis of the crystal as a rotation axis. The second surface is a surface equivalent to a surface formed by rotating the principal surface by −57°±5° with the X-axis. The third surface is a surface equivalent to a surface formed by rotating the principal surface by −42°±5° with the X-axis. When two corner portions on a side of a second side opposed to the first side of the AT-cut crystal element are viewed in plan view, each of the two corner portions have an approximately right angle.