Double BAW Resonator Layer Ratios for Higher Quality Factor
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Solution Overview
Problem
Acoustic resonators in mobile communication devices, particularly bulk acoustic wave (BAW) resonators, face challenges in achieving a high quality factor due to internal losses, which affect the performance of filters and oscillators by increasing insertion loss and phase noise.
Innovation Solution
The design of a double thin film bulk acoustic resonator (DBAR) with optimized electrode and piezoelectric layer thicknesses, along with specific structural modifications such as air-bridges and acoustic termination elements, is employed to suppress eigenmodes and reduce coupling between modes, thereby enhancing the quality factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single piezoelectric layer resonator is used, then the device structure is simple, but the quality factor is limited due to internal losses
Solution Approach 1:
The resonator is divided into two separate piezoelectric layers (first and second piezoelectric layers) with different thicknesses, allowing each layer to contribute differently to the acoustic resonance. This segmentation enables independent optimization of each layer's thickness to suppress eigenmodes and reduce internal losses, thereby improving the quality factor while managing device complexity
Solution Approach 2:
The patent optimizes the thickness parameters of the piezoelectric layers and electrode layers to specific ratios. By changing these dimensional parameters, the resonator achieves suppressed eigenmodes and reduced coupling between modes, which directly improves the quality factor without requiring fundamentally different device architecture
2Reliability
If electrode and piezoelectric layer thicknesses are optimized, then the quality factor improves by up to 50%, but the manufacturing precision requirements increase
Solution Approach 1:
The patent specifies optimized thickness ratios for piezoelectric layers and electrode layers that maximize quality factor improvement. These parameter optimizations are designed to provide up to 50% improvement in quality factor while establishing clear manufacturing specifications for achieving the desired performance
Solution Approach 2:
Different regions of the resonator structure (different layers) are assigned different thicknesses and material properties optimized for their specific functions. The first and second piezoelectric layers have different thicknesses tailored to suppress specific eigenmodes, allowing each local region to contribute optimally to the overall quality factor
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 results in a significant improvement of the quality factor, reducing internal losses and improving the performance of RF and microwave filters and oscillators by up to 50% compared to baseline designs.
Implementation Method 1
If an electric field is applied between first electrode 11 and second electrode 13 of acoustic resonator 10, the reciprocal or inverse piezoelectric effect will cause acoustic resonator 10 to mechanically expand or contract
Implementation Method 2
whenever the thickness d of piezoelectric layer 12 and of the top and bottom electrodes equals an odd (1, 3, 5 . . . ) integer multiple of half the wavelength λ of the acoustic waves, resonance states and/or acoustic resonance vibrations will occur
Data Source
AI summary
A device includes: a first electrode having a first electrode thickness; a first acoustic propagation layer disposed on the first electrode, the first piezo-electric layer having a first acoustic propagation layer thickness; a second electrode having a second electrode thickness; a second piezo-electric layer disposed on the first electrode, the second piezo-electric layer having a second acoustic propagation layer thickness; and a third electrode having a third electrode thickness, wherein the second electrode thickness is between 1.15 and 1.8 times the first electrode thickness. The first and third electrode thicknesses may be equal to each other, and the first and second piezo-electric layer thicknesses may be equal to each other. The first and third electrodes may be connected together to provide two acoustic resonators in parallel with each other.