Piezoelectric Resonator Shield Electrode Layout for Stable Frequency
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Solution Overview
Problem
Piezoelectric resonator devices with a sandwich structure face challenges in shielding due to the absence of a package lid and increased parasitic capacitance when shield electrodes are used, leading to frequency variability and adjustment difficulties.
Innovation Solution
Incorporating shield electrodes in the internal space of the piezoelectric resonator device, connected to a fixed potential, and patterning them to match the excitation electrodes, reduces parasitic capacitance and prevents capacitive coupling, while openings in the shield electrodes prevent contact with excitation electrodes during impacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shield electrodes are disposed among the layers of the package to prevent capacitive coupling, then characteristic variations are reduced, but the number of layers is increased which deteriorates the thin structure
Solution Approach 1:
The shield electrode is integrated into the existing package structure by forming it on the outer surface of the piezoelectric resonator plate, merging the shielding function with the resonator plate structure itself rather than adding separate shield layers among the package layers
Solution Approach 2:
The shield electrode is positioned on the outer surface of the piezoelectric resonator plate, utilizing the surface dimension rather than adding layers in the thickness direction, thus maintaining the thin structure while providing shielding
2Reliability
If a metal plate lid is used to create a shield structure, then capacitive coupling is prevented, but the package lid is absent in sandwich structure making this approach inapplicable
Solution Approach 1:
The shielding function is extracted from the package lid (which is absent in sandwich structure) and transferred to the piezoelectric resonator plate itself, allowing shielding without requiring a metal plate lid
Solution Approach 2:
The piezoelectric resonator plate serves multiple functions: it provides the resonating structure and simultaneously serves as the base for the shield electrode, making the shielding approach compatible with sandwich structure that lacks a separate lid
3Reliability
If shield electrodes are connected to ground potential to prevent characteristic variations, then potential change shielding is achieved, but parasitic capacitance increases making frequency adjustment difficult
Solution Approach 1:
The shield electrode is positioned locally on the outer surface of the piezoelectric resonator plate, creating a localized shielding effect that reduces parasitic capacitance compared to extensive ground planes, while still providing adequate protection against potential changes
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 effectively reduces characteristic variations and allows for easier frequency control by minimizing parasitic capacitance and preventing defects from electrode contact, maintaining the thin structure advantage of the sandwich design.
Implementation Method 1
a piezoelectric resonator plate (2) including a first excitation electrode (221) formed on a first main surface (211) of a substrate (2), and a second excitation electrode (222) formed on a second main surface (212) of the substrate (2)
Implementation Method 2
When capacitive coupling occurs between the excitation electrodes/wiring inside the package and board mounting terminals outside the package, the piezoelectric resonator device is affected by potential change in the board mounting terminals
Data Source
AI summary
A crystal oscillator includes: a crystal resonator plate having a first excitation electrode and a second excitation electrode. A first sealing member covers the first excitation electrode of the crystal resonator plate. A second sealing member covers the second excitation electrode of the crystal resonator plate. An internal space is formed by bonding the first sealing member to the crystal resonator plate and the second sealing member to the crystal resonator plate, and seals a vibrating part of the crystal resonator plate. First and second shield electrodes are connected to a fixed potential (e.g. GND potential) in the internal space.