Ferroelectric Multilayer BAW Resonators for Tunable Coupling
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Solution Overview
Problem
Conventional Bulk Acoustic Wave (BAW) resonators face challenges in achieving tunable electromechanical coupling coefficients without continuous electric power loss and bulkiness, as they require external components like capacitors and inductors to adjust coupling coefficients, leading to complex and costly filter modules.
Innovation Solution
A BAW resonator design featuring a multilayer transduction structure with ferroelectric materials whose polarization varies with an electric field, allowing for adjustable electromechanical coupling coefficients via DC bias voltage, which remains unchanged after voltage removal, eliminating continuous power loss and bulkiness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If external components like capacitors and inductors are used to adjust the electromechanical coupling coefficient, then the coupling coefficient can be tuned, but the filter module becomes bulky, costly, and complex
Solution Approach 1:
The patent changes the material parameter of the transduction layer from conventional piezoelectric material to ferroelectric material, which allows the electromechanical coupling coefficient to be tuned by applying a DC bias voltage that modifies the polarization state of the ferroelectric layer, eliminating the need for external capacitors and inductors
Solution Approach 2:
The patent uses a composite multilayer structure consisting of ferroelectric transduction layer combined with electrode layers and acoustic mirror layers, where the ferroelectric material provides tunable electromechanical coupling while the acoustic mirrors provide acoustic confinement, achieving both functionality and compactness
2Adaptability or versatility
If a DC bias voltage is continuously applied to tune the electromechanical coupling coefficient, then the coupling can be adjusted, but continuous electric power loss occurs due to leakage current
Solution Approach 1:
The patent applies a DC bias voltage during the fabrication process to set the desired polarization state and electromechanical coupling coefficient of the ferroelectric transduction layer before final device operation. Once the polarization is established, no continuous DC bias is needed during operation, eliminating continuous power loss while maintaining the tuned coupling coefficient
Solution Approach 2:
The patent utilizes the ferroelectric phase transition properties where the material can be switched between different polarization states by applying a DC field during fabrication. After the phase transition establishes the desired polarization, the material maintains its state without requiring continuous energy input, similar to how a magnet retains its magnetization after being magnetized
3Device complexity
If a single piezoelectric transduction layer is used, then the device structure is simple, but the electromechanical coupling coefficient cannot be tuned
Solution Approach 1:
The patent replaces the single piezoelectric transduction layer with a composite multilayer structure where at least one layer is made of ferroelectric material. This composite structure maintains the basic sandwich configuration (electrode-transduction layer-electrode) for simplicity while the ferroelectric material provides the tunable coupling capability through polarization control
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 enables tunable electromechanical coupling without continuous DC bias voltage, reducing power loss and module complexity, making the resonator more efficient and cost-effective.
Implementation Method 1
at least one of the transduction layers is formed of a first ferroelectric material, whose polarization will vary with an electric field across the first ferroelectric material
Data Source
AI summary
The present disclosure relates to a Bulk Acoustic Wave (BAW) resonator with tunable electromechanical coupling. The disclosed BAW resonator includes a bottom electrode, a top electrode, and a multilayer transduction structure sandwiched therebetween. Herein, the multilayer transduction structure is composed of multiple transduction layers, and at least one of the transduction layers is formed of a ferroelectric material, whose polarization will vary with an electric field across the ferroelectric material. Upon adjusting direct current (DC) bias voltage across the bottom electrode and the top electrode, an overall polarization of the multilayer transduction structure and an overall electromechanical coupling coefficient of the multilayer transduction structure are capable of being changed. Once the change of the overall electromechanical coupling coefficient of the multilayer transduction structure is completed, the overall electromechanical coupling coefficient of the multilayer transduction structure will remain unchanged after removing the DC bias voltage.