Piezoelectric Resonator Electrode Layout for Stable Resonant Frequency
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Solution Overview
Problem
In MEMS vibrators, variations in resonant frequency occur due to charging of the insulator layer, which affects the vibration and frequency stability, as Coulomb forces influence the resonator's vibration.
Innovation Solution
A resonator design with a protective film facing the piezoelectric film, where a conductive film is exposed in a specific region and connected to the lower electrode through a connection electrode, minimizing the overlap area with the upper electrode to reduce the impact of voltage on the insulator layer and conductive layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a mass portion including an insulator layer and conductive layer is formed on the MEMS vibrator for frequency adjustment, then the resonant frequency can be adjusted, but the insulator layer becomes charged and generates Coulomb force that influences vibration and causes variations in resonant frequency
Solution Approach 1:
The patent extracts the harmful charged insulator layer from the vibration region by providing a separate protective film that faces the piezoelectric film. The mass portion is configured so that its insulator layer does not overlap with the piezoelectric film in the thickness direction, preventing charge accumulation in the vibration path while maintaining frequency adjustment capability through the protective film structure.
Solution Approach 2:
The protective film acts as an intermediary between the piezoelectric film and the external environment. It provides a controlled interface that allows voltage application for frequency adjustment while preventing direct charging of the piezoelectric film, thus mediating between the need for frequency tuning and vibration stability.
2Manufacturing precision
If voltage is applied to the insulator layer or conductive layer on the resonator, then frequency adjustment is achieved, but the Coulomb force generated affects the vibration characteristics
Solution Approach 1:
The patent removes the insulator layer from the direct vibration path by configuring the mass portion such that its insulator layer is positioned separately from the piezoelectric film. This extraction prevents Coulomb force generation in the vibration region while maintaining the ability to apply voltage to the protective film for frequency adjustment.
Solution Approach 2:
The patent applies different properties to different regions: the protective film region allows voltage application for frequency adjustment, while the vibration region (piezoelectric film) is protected from charging. This local differentiation enables frequency tuning without harmful Coulomb forces in the critical vibration area.
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 design effectively suppresses the influence of voltage on the resonator's vibration, stabilizing the resonant frequency and improving the vibration characteristics by reducing electric field interference.
Implementation Method 1
a piezoelectric film provided between the upper electrode and the lower electrode, having a main surface facing the upper electrode, and that is configured to vibrate the vibration portion in a predetermined vibration mode when a voltage is applied between the upper electrode and the lower electrode
Implementation Method 2
When the MEMS vibrator vibrates in a state in which the insulator layer on the MEMS vibrator is charged, Coulomb force is generated due to electric charges in the insulator layer, thereby influencing vibration of the resonator
Data Source
AI summary
A resonator includes a vibration portion with upper and lower electrodes with a piezoelectric film disposed therebetween. Moreover, a protective film is provided to face the piezoelectric film with the upper electrode interposed therebetween and is exposed in a first region in the vibration portion. A conductive film is provided to face the piezoelectric film with the protective film interposed therebetween and is exposed in a second region that is adjacent to the first region in the vibration portion. A connection electrode is formed in the protective film to electrically connect the conductive film to the lower electrode. The upper electrode is formed such that an area of a region overlapping the conductive film is equal to or smaller than half of a total area of the conductive film and/or avoids the region overlapping the conductive film.