Piezoelectric Resonator Bragg Ring for Parasitic Mode Suppression
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Solution Overview
Problem
Conventional quartz crystal and ceramic resonators are not suitable for high-frequency and miniaturized products due to their large volume and low frequency, and they suffer from parasitic modes that cause phase fluctuations and ripple waves in the frequency response, affecting their performance.
Innovation Solution
A resonator design incorporating a silicon substrate, a bottom electrode, a piezoelectric layer, a top electrode, and a Bragg reflecting ring with alternating high and low acoustic impedance layers, which suppresses parasitic modes by reflecting clutter waves and improving the frequency response curve.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional quartz crystal or ceramic resonators are used, then the resonator structure is simple, but the volume is large and frequency is low, making them unsuitable for high-frequency and miniaturized products
Solution Approach 1:
The patent changes the physical parameters of the resonator by using piezoelectric thin film materials with specific piezoelectric coefficients and configuring multiple reflecting rings with different acoustic impedances, enabling high-frequency operation in a miniaturized structure
Solution Approach 2:
The patent employs composite material structures including piezoelectric thin film layers, metal electrodes, and multiple reflecting rings made of different materials (first reflecting material, second reflecting material) with different acoustic impedances to achieve both miniaturization and high-frequency performance
2Object-generated harmful factors
If the piezoelectric layer has piezoelectric coefficients in multiple directions, then the resonator can generate acoustic waves, but parasitic modes are generated causing phase fluctuation and ripple waves in the frequency response
Solution Approach 1:
The patent converts the harmful parasitic acoustic waves into beneficial reflected waves by using the alternating high and low acoustic impedance layers of the reflecting rings to reflect clutter waves back toward the center, canceling out parasitic modes and improving phase stability
Solution Approach 2:
The patent introduces reflecting rings as intermediary structures between the piezoelectric layer and the surrounding environment, which mediate the acoustic wave propagation by reflecting clutter waves and preventing them from causing parasitic modes
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 Bragg reflecting ring effectively cancels out parasitic modes, smoothing the phase angle and enhancing the overall performance of the resonator by reducing filtering and improving the frequency response curve.
Implementation Method 1
The Bragg reflecting ring comprising a Bragg high-resistivity layer and a Bragg low-resistivity layer alternately arranged along the radial direction of the Bragg reflecting ring, an acoustic impedance of the Bragg high-resistivity layer being greater than an acoustic impedance of the Bragg low-resistivity layer
Implementation Method 2
Bragg reflecting ring being formed on a side of the piezoelectric layer connected to the top electrode and surrounding the top electrode
Implementation Method 3
The frequency generated by the resonator has the characteristics of good stability and good anti-interference performance... Film bulk acoustic resonator (FBAR) manufactured by utilizing the longitudinal wave resonance which is excited along the thickness direction of a piezoelectric thin film material
Data Source
AI summary
A resonator includes a silicon substrate, a bottom electrode stacked on a portion of the silicon substrate, a piezoelectric layer covering the bottom electrode and another portion of the silicon substrate, a top electrode stacked on the piezoelectric layer, and a Bragg reflecting ring. The Bragg reflecting ring is formed on a side of the piezoelectric layer connected to the top electrode and surrounds the top electrode. The Bragg reflecting ring includes a Bragg high-resistivity layer and a Bragg low-resistivity layer alternately arranged along the radial direction of the Bragg reflecting ring. An acoustic impedance of the Bragg high-resistivity layer is greater than an acoustic impedance of the Bragg low-resistivity layer. The Bragg reflecting ring forms reflection surfaces to reflect the laterally propagating clutter waves, thereby suppressing the parasitic mode in the working frequency band, improving the frequency response curve of the resonator and the overall performance of the resonator.