Piezoelectric Resonator Acoustic Isolation Spurious Mode Suppression
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Solution Overview
Problem
Piezoelectric resonators face challenges in suppressing both long-wavelength and short-wavelength spurious modes, with existing designs being difficult to miniaturize and having inadequate analysis of short-wavelength spurious radiation, leading to suboptimal planar shapes that affect filter layout and chip size.
Innovation Solution
A piezoelectric resonator structure featuring a vibrating region with a substantial polygon or rectangle shape, where the peripheral portion has a smaller thickness than the central portion, and is acoustically isolated from the substrate, utilizing a gap or sound reflecting layer, with waveform edges that scatter and cancel out undesired wave components, thereby suppressing spurious modes across various wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the vibrating region is acoustically isolated from the substrate, then spurious wave generation is suppressed, but device complexity increases due to additional acoustic isolation structures
Solution Approach 1:
The patent introduces an acoustic isolation layer as an intermediary element between the vibrating region and the substrate. This layer acts as a mediator that blocks acoustic energy transmission, preventing spurious waves from propagating into the substrate while maintaining the functional integrity of the resonator.
Solution Approach 2:
The patent extracts the acoustic isolation function from the substrate itself and implements it through a separate dedicated layer. This separation allows the substrate to maintain its primary structural role while the acoustic isolation layer specifically addresses spurious wave suppression, making the overall system more modular and manageable.
2Volume of moving object
If the planar shape of the vibrating region is optimized for miniaturization, then device size is reduced, but spurious mode suppression becomes inadequate
Solution Approach 1:
The patent applies different geometric characteristics to different regions of the vibrating structure. The central portion has one set of dimensional characteristics optimized for resonance, while the peripheral portion has different dimensional characteristics optimized for spurious mode suppression. This local differentiation allows simultaneous optimization of both miniaturization and spurious mode rejection.
Solution Approach 2:
The patent employs asymmetric thickness distribution within the vibrating region, with the central portion having a different thickness than the peripheral portion. This asymmetric design creates different acoustic impedances in different regions, which helps suppress spurious modes while maintaining compact overall dimensions.
3Object-generated harmful factors
If the peripheral portion thickness is reduced relative to the central portion, then long-wavelength spurious modes are suppressed, but manufacturing precision requirements increase
Solution Approach 1:
The patent divides the vibrating region into distinct segments - a central portion and a peripheral portion - with clearly defined thickness differences. This segmentation allows each region to be independently controlled during manufacturing, making the thickness variation more manageable and less prone to cumulative errors.
Solution Approach 2:
The patent addresses the thickness control challenge by introducing a radial dimension variation. Instead of controlling thickness uniformly across the entire vibrating region, the thickness is varied as a function of radial distance from the center, creating a gradient structure that is more tolerant to manufacturing variations.
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 both long-wavelength and short-wavelength spurious modes, improves resonant frequency characteristics, and facilitates miniaturization while maintaining suitable filter bandwidth and ripple suppression.
Implementation Method 1
piezoelectric resonator elements each including a pair of electrode films with a piezoelectric film are supported on substrates so as to be acoustically isolated from the substrates and operating in a thickness-extensional vibration mode
Implementation Method 2
with waveform edges that scatter and cancel out undesired wave components, thereby suppressing spurious modes across various wavelengths
Implementation Method 3
a piezoelectric resonator in which a vibrating region including a pair of conductive layers with a piezoelectric layer provided therebetween is supported so as to be acoustically isolated from a substrate
Data Source
AI summary
A piezoelectric resonator and a piezoelectric thin-film filter including the piezoelectric resonator. The piezoelectric resonator includes a piezoelectric layer disposed between a pair of conductive layers to form a vibrating region. Outer edges of the vibrating region each have a waveform. The vibrating region includes a peripheral portion extending along the outer edges of the planar shape and having a relatively small thickness; and a central portion extending inside the peripheral portion and having a relatively large thickness. The piezoelectric resonator is thus capable of suppressing long-wavelength spurious modes and short-wavelength spurious modes.