Thin-Film Piezoelectric Resonator Gaps for Lower Acoustic Energy Loss
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Solution Overview
Problem
Traditional bulk acoustic wave resonators suffer from energy loss due to direct transmission of acoustic waves to electrodes, residual stress at the piezoelectric thin film and electrode interface, and temperature-dependent frequency shifts, which affect the performance and yield of RF filters.
Innovation Solution
A thin film piezoelectric acoustic wave resonator design featuring a first and second gap between the piezoelectric plate body and electrodes, with an isolation cavity surrounding the periphery, and a connecting bridge between the piezoelectric plate body and substrate, allowing for reduced energy loss through reflection and improved temperature stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the piezoelectric plate body is made thinner to achieve higher resonant frequency, then the resonant frequency is improved, but the proportion of bulk acoustic wave energy dissipation increases
Solution Approach 1:
A suspended mass is introduced as an intermediary element between the piezoelectric plate body and the electrodes. This suspended mass acts as a mediator that couples the piezoelectric plate to the electrodes mechanically while minimizing acoustic wave transmission to the electrodes, thereby reducing energy dissipation while maintaining high resonant frequency
Solution Approach 2:
The direct mechanical connection between the piezoelectric plate body and the electrodes is removed. By suspending the piezoelectric plate body rather than directly contacting it with electrodes, the harmful acoustic wave transmission path is extracted from the system, reducing energy loss to the electrodes
2Reliability
If the area of the piezoelectric plate body and electrodes is increased, then the resonant frequency response is improved, but the proportion of consumed bulk acoustic wave increases
Solution Approach 1:
The suspended mass serves as a mediator that allows larger electrode areas to be used for improved frequency response while preventing excessive acoustic wave transmission. The intermediary structure enables the electrodes to be larger without proportionally increasing energy dissipation
3Device complexity
If direct contact between electrodes and piezoelectric thin film is maintained for simple structure, then device complexity is reduced, but residual stress and interface reflection cause energy loss
Solution Approach 1:
The suspended mass acts as an intermediary mechanical coupling element between the piezoelectric plate body and the electrodes. This intermediary structure reduces residual stress at the interfaces and minimizes acoustic wave reflection, thereby reducing energy loss while maintaining structural simplicity
Solution Approach 2:
The direct contact interface between the piezoelectric plate and electrodes is segmented into two separate interfaces: one between the piezoelectric plate and suspended mass, and another between the suspended mass and electrodes. This segmentation reduces stress concentration and acoustic wave reflection at each interface
4Ease of manufacture
If traditional FBAR structure is used, then manufacturing process is simplified, but acoustic wave transmission to electrodes causes quality factor reduction
Solution Approach 1:
The suspended mass is introduced as a mediator that can be integrated into the existing FBAR manufacturing process. This intermediary element improves the quality factor by reducing acoustic wave transmission to electrodes while maintaining compatibility with standard manufacturing techniques
Solution Approach 2:
The suspended mass is implemented as a thin film structure that can be deposited using standard thin film fabrication techniques. This flexible thin film approach allows the suspended mass to be integrated into the FBAR structure without requiring complex manufacturing processes
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 design minimizes energy loss by reflecting acoustic waves back into the piezoelectric plate body, enhancing the quality factor and reducing parasitic effects, while also providing temperature compensation to maintain frequency stability across varying temperatures.
Implementation Method 1
Acoustic wave resonators based on piezoelectric induction are divided into a surface acoustic wave resonator (SAWR) and a bulk acoustic wave resonator (BAWR)
Implementation Method 2
the bulk acoustic wave elastic vibration will naturally be transmitted to the upper electrode plate R30 and the lower electrode plate R50 and be propagated outwards along the upper electrode plate R30 and the lower electrode plate R50
Implementation Method 3
Under the action of the alternating electric field generated by the upper and lower electrode plates, bulk acoustic wave elastic vibration in a longitudinal direction R1 and a transverse direction R2 will be generated
Implementation Method 4
The thickness of the piezoelectric plate body, electrode or dielectric layer and the sound velocity therein change with the temperature change, so the resonant frequency of the piezoelectric acoustic wave resonator changes with the temperature change
Data Source
AI summary
A thin film piezoelectric acoustic wave resonator and a manufacturing method therefor, and a filter. The thin film piezoelectric acoustic wave resonator includes: a first base, an upper electrode, a piezoelectric plate body, a lower electrode and an isolation cavity. The upper electrode, the piezoelectric plate body and the lower electrode are arranged on an upper surface of the first base and are stacked sequentially from top to bottom. The upper electrode, the piezoelectric plate body and the lower electrode have an overlapping region in a direction perpendicular to the surface of the piezoelectric plate body, in which a first gap is formed between the piezoelectric plate body and the upper electrode, and a second gap is formed between the piezoelectric plate body and the lower electrode. The isolation cavity surrounds the periphery of the piezoelectric plate body and connects the first and second gaps together. At least one connecting bridge is arranged between the piezoelectric plate body and the base.