Piezoelectric Thin-Film Resonator Mass Element Acoustic Impedance
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Solution Overview
Problem
Conventional piezoelectric thin-film resonators face issues with energy dissipation of transverse waves and increased intensity of standing waves due to changes in acoustic impedance, leading to reduced electromechanical coupling coefficients and spike-like losses in filter applications.
Innovation Solution
A piezoelectric thin-film resonator design that includes a mass element on the upper electrode at the edge of the resonant portion, creating a sloped boundary with increased acoustic impedance, which confines transverse-mode waves and prevents standing wave intensification by strategically placing the mass element to minimize its impact on the resonator's perimeter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the acoustic impedance of the portion surrounding the resonant portion is made smaller than that of the resonant portion, then transverse-mode waves can propagate more easily, but energy dissipation increases and leakage occurs
Solution Approach 1:
The patent applies local quality by creating a specific acoustic impedance distribution: the resonant portion has lower acoustic impedance while the surrounding portion has higher acoustic impedance. This localized differentiation prevents transverse wave leakage by creating an acoustic barrier at the boundary, while maintaining optimal conditions for thickness vibration within the resonant portion. The acoustic impedance is controlled through material selection and geometric design of the resonant and surrounding portions.
2Object-generated harmful factors
If a uniform layer with different acoustic characteristics is added around the resonant portion, then transverse wave leakage is prevented, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent merges the resonant portion and surrounding portion into a single integrated structure made of the same piezoelectric material, eliminating the need for separate acoustic barrier layers. The acoustic impedance difference is achieved through geometric design and material density variations rather than adding distinct functional layers, thereby reducing device complexity and manufacturing steps while still preventing transverse wave leakage.
Solution Approach 2:
The patent changes physical parameters (acoustic impedance, density, geometric dimensions) of the piezoelectric material in different regions to achieve the desired acoustic barrier effect. By adjusting these parameters within the same material system, the patent avoids adding complex multi-layer structures while still effectively preventing transverse wave propagation to the surrounding area.
3Object-generated harmful factors
If mass elements are added to the edge of the upper electrode, then acoustic impedance increases and transverse wave leakage is prevented, but the resonator's perimeter is affected
Solution Approach 1:
The patent applies local quality by strategically placing mass elements only at specific locations where transverse wave leakage is most problematic, rather than uniformly distributing them around the entire perimeter. This localized approach prevents wave leakage at critical boundaries while minimizing the impact on the overall resonator area and maintaining the electromechanical coupling coefficient.
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 prevents energy dissipation of transverse waves, suppresses standing wave intensity, and reduces spike-like losses, thereby enhancing the filtering characteristics and communication quality in mobile devices.
Implementation Method 1
a piezoelectric film 103 is sandwiched by an upper electrode 101 and a lower electrode 102, and a region defined by the upper electrode 101 and the lower electrode 102 which are opposed to each other acts as an actual resonator
Implementation Method 2
the apparent acoustic impedance of the piezoelectric film 103 gradually decreases toward the nonresonant portion R2... the acoustic impedance of the perimeter of the resonator is greater than the acoustic impedance of an exciting portion
Data Source
AI summary
There is provided a piezoelectric thin-film resonator including a substrate, a lower electrode disposed on the substrate, a piezoelectric film disposed on the lower electrode, an upper electrode disposed on the piezoelectric film in such a manner that a portion of the upper electrode is opposed to the lower electrode, and a mass element disposed on the upper electrode in a portion of an edge of the region of the upper electrode in which the upper electrode and the lower electrode are opposed to each other.