Hybrid BAW Resonator Structure for Higher Coupling at GHz Frequencies
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Solution Overview
Problem
Existing resonant structures face challenges in achieving high frequency operation with sufficient coupling coefficient, leading to limitations in remote measurement applications, particularly with volume wave solutions and composite structures.
Innovation Solution
A resonant structure with a piezoelectric transducer comprising two electrodes surrounding a piezoelectric layer, where one electrode is coated with an additional layer to optimize acousto-electric density, and a Bragg mirror is used to position the stress 'belly' within the piezoelectric layer, enhancing coupling performance and reducing overvoltage effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional body-wave resonators use thin piezoelectric plates to achieve high frequency operation, then frequency increases, but mechanical strength and reliability deteriorate due to excessive thinning
Solution Approach 1:
The patent employs a composite structure consisting of a piezoelectric layer deposited on a non-piezoelectric substrate. This composite configuration allows the use of extremely thin piezoelectric layers (a few micrometers) while the substrate provides mechanical support and strength. The substrate acts as a structural backbone that compensates for the weakness of thin piezoelectric films, enabling high-frequency operation without sacrificing mechanical integrity.
2Speed
If passive surface acoustic wave components are used to achieve frequency ranges exceeding one gigahertz, then frequency increases, but device size increases due to acoustic wavelength requirements
Solution Approach 1:
The patent utilizes a thin-film piezoelectric layer deposited on a substrate, creating a compact resonator structure. The thin-film configuration allows the device to achieve gigahertz frequencies while maintaining a small footprint, as the active piezoelectric layer thickness is on the order of micrometers rather than the millimeter-scale dimensions required by conventional bulk acoustic wave devices.
3Speed
If composite resonant structures use piezoelectric films on non-piezoelectric substrates, then frequency operation improves, but coupling coefficient decreases
Solution Approach 1:
The patent optimizes the coupling coefficient by carefully controlling the thickness of the piezoelectric layer and the properties of the substrate. By adjusting these parameters, the resonator achieves both high-frequency operation and sufficient electromechanical coupling. The piezoelectric layer thickness is specifically designed to maximize coupling while the substrate properties are selected to enhance the overall coupling coefficient, resolving the trade-off between frequency operation and coupling strength.
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 configuration significantly increases the coupling coefficient by a factor of 5 to 10, allowing for improved frequency operation and reduced insertion losses, making it suitable for remote measurement applications.
Implementation Method 1
through the inverse piezoelectric effect, a deformation of the plate 4
Implementation Method 2
Applying a radio frequency (RF) field across the terminals of the resulting dipole 2, 3 induces, through the inverse piezoelectric effect, a deformation of the plate 4
Implementation Method 3
body waves, often longitudinally polarized, simultaneously exhibiting very high propagation speeds and high piezoelectric coupling
Implementation Method 4
a Bragg mirror is used to position the stress 'belly' within the piezoelectric layer
Data Source
Figure 1~2C
Figure 2D~3
Figure 4~6
AI summary
A structure has a piezoelectric transducer (14) on a substrate (12) and comprising two conductive electrodes (16, 20) separated by a piezoelectric material layer (18), where the thickness (e18) of the layer is given by a specified relation. An additional layer (22) is placed on the surface of the electrode (20) opposite to the layer (18), where the thickness (e22) of the layer (22) is fixed for optimizing the acoustic-electric density inside the layer (18). Independent claims are also included for the following: (1) a frequency filter comprising a set of resonant structures; (2) a radio frequency transducer comprising an antenna associated to a resonant structure or to a frequency filter; and (3) the production of a hybrid bulk acoustic wave resonant structure.