Mesa AT-Cut Crystal Element Layout for Low Impedance Miniaturization
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Solution Overview
Problem
The demand for reducing the size of crystal vibration elements while minimizing their crystal impedance (CI) has increased, as smaller elements tend to have larger CI, posing a challenge in achieving both size reduction and low impedance.
Innovation Solution
A crystal vibration element with an AT cut crystal blank featuring a mesa part and a thinner outer circumferential part, paired with excitation and extraction electrodes, where the distance between the pad and mesa parts is optimized within specific ranges relative to the resonance frequency and thickness, ensuring the element's length is less than 1000 μm and resonance frequencies are maintained at 37.4 MHz or 27.12 MHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the size of crystal vibration element is reduced, then the miniaturization requirement is satisfied, but the crystal impedance becomes larger
Solution Approach 1:
The crystal blank is divided into two distinct parts: a mesa part with larger thickness and an outer circumferential part with smaller thickness. This segmentation allows the vibration element to maintain a compact overall size while the mesa part provides sufficient volume to keep crystal impedance low, thus resolving the contradiction between miniaturization and impedance control.
Solution Approach 2:
Different parts of the crystal blank are given different thicknesses to serve different functions. The mesa part has larger thickness optimized for vibration characteristics and low impedance, while the outer circumferential part has smaller thickness to reduce overall size. This local differentiation allows simultaneous achievement of miniaturization and impedance control.
2Reliability
If the distance between pad part and mesa part is increased, then the vibration characteristics are improved, but the available space is reduced
Solution Approach 1:
The distance y between the pad part and mesa part is optimized within a specific range (0.03 ≤ y/t ≤ 0.06 where t is the thickness of the mesa part). By controlling this parameter within the optimal range, the patent achieves good vibration characteristics while maintaining compact dimensions, thus resolving the contradiction between vibration performance and space utilization.
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 allows for the realization of crystal vibration elements and devices with reduced size and low crystal impedance, achieving CI values less than 100Ω, thereby enhancing design flexibility and practicality.
Implementation Method 1
an AT cut crystal blank including a mesa part and an outer circumferential part which is thinner than the mesa part and surrounds the mesa part, a pair of excitation electrodes provided on the two major surfaces of the mesa part
Implementation Method 2
a pair of extraction electrodes including pad parts provided at the end parts of the crystal blank in the longitudinal direction on one major surface of the outer circumferential part and connected to the pair of excitation electrodes
Data Source
AI summary
A vibration element includes a crystal blank, a pair of excitation electrodes, and pair of extraction electrodes. The crystal blank is an AT cut crystal blank including a mesa part and an outer circumferential part which is thinner than the mesa part and surrounds the mesa part. The pair of excitation electrodes is provided on the two major surfaces of the mesa part. The pair of extraction electrodes include pad parts which are provided at the end parts of the crystal blank in the longitudinal direction on one major surface of the outer circumferential part and are connected to the pair of excitation electrodes. The length in the longitudinal direction of the crystal blank is less than 1000 μm. When the resonance frequency is F (MHz) and t=1670/F, the distance “y” (μm) between each of the pad parts and the mesa part satisfies 0.048F+1.18<y/t<0.097F+0.36.