Composite BAW Resonator Structure for Low Trimming Sensitivity
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Solution Overview
Problem
Bulk acoustic wave (BAW) resonators face challenges in trimming sensitivity, which makes it difficult to achieve precise frequency control due to high sensitivity to layer thickness changes, especially at higher frequencies, leading to increased complexity and cost in manufacturing high-frequency filters.
Innovation Solution
The implementation of a composite layered structure with alternately formed high and low acoustic impedance layers, specifically with thicknesses that are odd integral multiples of a quarter wavelength, reduces trimming sensitivity and enhances immunity to environmental changes, allowing for improved frequency trimming and reduced manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the resonator operates at higher frequencies with thinner film layers, then the frequency operation capability is improved, but the trimming sensitivity increases significantly making frequency control difficult
Solution Approach 1:
The patent applies composite materials by introducing a distributed acoustic impedance structure consisting of multiple layers with alternating high and low acoustic impedance materials. This composite structure is designed to reduce the trimming sensitivity of the resonator by distributing the acoustic energy more effectively across the film layers, thereby enabling high-frequency operation (5 GHz and above) while maintaining controllable frequency trimming despite the reduced thickness of individual layers
2Measurement precision
If the film layers are made thinner to achieve higher resonant frequencies, then the frequency is improved, but the trimming sensitivity increases to 250 kHz/Å making frequency distribution control extremely challenging
Solution Approach 1:
The patent segments the acoustic impedance structure into multiple thin layers with alternating high and low acoustic impedance materials. This segmentation approach distributes the acoustic energy across many interfaces, reducing the sensitivity of the overall resonant frequency to thickness variations in any single layer. The segmented structure enables precise frequency control even when individual layers are extremely thin, addressing the challenge of high trimming sensitivity at 5 GHz and above
3Device complexity
If conventional single-layer structures are used, then the device complexity is low, but the immunity to environmental change and aging effects is poor
Solution Approach 1:
The patent employs composite materials with alternating high and low acoustic impedance layers to create a distributed acoustic impedance structure. This composite design provides multiple acoustic reflection interfaces that are less sensitive to environmental changes and aging effects compared to conventional single-layer structures. The multi-layer composite structure improves reliability by distributing stress and acoustic energy across multiple interfaces, reducing the impact of any single layer's degradation over time
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 approach significantly reduces trimming sensitivity, facilitating the fabrication of high-frequency filters with lower manufacturing costs and improved product yield by minimizing the impact of layer thickness variations on resonant frequency.
Implementation Method 1
When an RF electric signal is applied across the two electrodes 14a and 14b, the resonator body is mechanically extended and contracted due to the piezoelectric effect and an acoustic wave is excited in the structure 10
Implementation Method 2
The acoustic wave propagates parallel to the applied electric field and is reflected at the interfaces of the electrodes 14a and 14b and air to form the resonance
Data Source
AI summary
In one aspect of the invention, the acoustic wave resonator includes a resonator structure having a first electrode, a piezoelectric layer formed on the first electrode, and a second electrode formed on the piezoelectric layer, and a composite layered structure associated with the resonator structure such that the immunity of the acoustic wave resonator to environmental change and aging effects is improved, the trimming sensitivity is substantially minimized, and/or dispersion characteristics of the acoustic wave resonator is optimized.