BAW Resonator Ferroelectric Multilayers for Bias-Free Coupling Tuning
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Solution Overview
Problem
Conventional Bulk Acoustic Wave (BAW) resonators have fixed electromechanical coupling coefficients, making it challenging to design low-loss filters with steep slopes, leading to bulky, costly, and complex filter modules, and existing solutions with voltage-tunable coefficients suffer from continuous electric power loss due to DC bias voltage requirements.
Innovation Solution
A BAW resonator design featuring a multilayer transduction structure with ferroelectric materials whose polarization varies with an electric field, allowing for tunable electromechanical coupling coefficients without continuous DC bias voltage, using materials like scandium aluminum nitride with box-shaped polarization-electric field curves, and incorporating piezoelectric layers with non-varying polarization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional piezoelectric transduction layer is used with fixed electromechanical coupling coefficient, then the resonator structure is simple and easy to manufacture, but the filter module becomes bulky and complex when external components are added to adjust coupling
Solution Approach 1:
The transduction layer is segmented into multiple sub-layers with different piezoelectric coefficients, allowing each layer to contribute differently to the overall electromechanical coupling. This segmentation enables tunable coupling characteristics while maintaining a compact integrated structure without external adjustment components.
Solution Approach 2:
The patent uses composite transduction structures combining multiple piezoelectric materials with different properties (e.g., AlN, ScAlN, PZT) in a single integrated layer. This composite approach enables continuous tuning of the electromechanical coupling coefficient by adjusting material composition ratios, eliminating the need for external tuning components.
2Adaptability or versatility
If external capacitors and inductors are used to adjust electromechanical coupling coefficient, then the desired coupling values are achieved, but the filter module becomes bulky and costly
Solution Approach 1:
The tuning function previously requiring external capacitors and inductors is merged directly into the transduction layer itself. By incorporating multiple piezoelectric sub-layers with different coupling coefficients, the resonator achieves adjustable electromechanical coupling internally, eliminating external tuning components and reducing overall filter module volume.
Solution Approach 2:
The multilayer transduction structure serves multiple functions simultaneously: it provides the primary piezoelectric transduction function while also enabling continuous tuning of the electromechanical coupling coefficient. This multi-functionality eliminates the need for separate tuning components, reducing both volume and cost.
3Loss of energy
If ferroelectric material with box-shaped P-E curve is used, then tunable electromechanical coupling is achieved without continuous DC bias, but the manufacturing precision requirements increase
Solution Approach 1:
The patent changes the material parameter from conventional piezoelectric to ferroelectric material with box-shaped P-E curve. This parameter change enables the material to maintain stable polarization states at different DC bias voltages, allowing tuning of electromechanical coupling without continuous power consumption, as the ferroelectric hysteresis loop provides stable state retention.
Solution Approach 2:
The ferroelectric material utilizes its characteristic phase transition behavior and hysteresis loop properties to maintain stable polarization states. The box-shaped P-E curve indicates distinct stable states that can be switched and maintained without continuous energy input, enabling lossless tuning of electromechanical coupling characteristics.
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
Enables tunable electromechanical coupling coefficients without continuous electric power loss, maintaining desired values after removing the DC bias voltage, thus reducing bulk and cost while enhancing filter performance.
Implementation Method 1
at least one of the plurality of transduction layers is formed of a first ferroelectric material, whose polarization will vary with an electric field across the first ferroelectric material
Implementation Method 2
at least one of the transduction layers is formed of a piezoelectric material, whose polarization does not vary with an electric field across the piezoelectric material
Implementation Method 3
an overall polarization of the multilayer transduction structure and an overall electromechanical coupling coefficient of the multilayer transduction structure are capable of being changed
Data Source
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AI summary
The present disclosure relates to a Bulk Acoustic Wave, BAW, resonator with tunable electromechanical coupling. The disclosed BAW resonator (30) includes a bottom electrode (32), a top electrode (34), and a multilayer transduction structure (36) sandwiched therebetween. Herein, the multilayer transduction structure is composed of multiple transduction layers (38_1, .... 38_N), 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 (32) and the top electrode (34), an overall polarization of the multilayer transduction structure (36) 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.