Multi-mode Bulk Acoustic Wave Resonator Design
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Solution Overview
Problem
Conventional solidly-mounted BAW resonators are fragile and require sophisticated deposition and etching processes, limiting their ability to simultaneously operate in multiple non-harmonically-related acoustic modes, such as thickness shear and thickness extensional modes, which are essential for multi-band communication filters and bio-sample analyses.
Innovation Solution
A BAW resonator design featuring a hexagonal crystal structure with a plurality of electrodes positioned about the crystal, allowing it to resonate in at least two non-harmonically-related operational modes, including thickness shear and thickness extensional modes, using an acoustic reflector with alternating layers of materials to support both modes within the gigahertz range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional SMR configuration is used with c-axis oriented ZnO, then the device can operate in single mode (TSM or TEM), but it cannot simultaneously operate in multiple non-harmonically-related modes
Solution Approach 1:
The patent designs a universal BAW resonator structure that can operate in multiple acoustic modes (TSM, TEM, and hybrid modes) simultaneously. The key is using c-axis oriented ZnO crystal structure with specifically designed electrode configurations that can excite different modes. The reflector stack is designed with acoustic impedance values that support multiple modes, making the device multi-functional without requiring separate devices for each mode.
Solution Approach 2:
The patent employs dynamic mode selection through electrode configuration. By applying electrical excitation in different orientations (parallel or orthogonal to c-axis) and using different electrode patterns (interdigitated, coplanar, etc.), the same physical device can dynamically switch between or simultaneously operate in TSM, TEM, and hybrid modes, providing adaptability without structural changes.
2Measurement precision
If thinner piezoelectric films are used to achieve higher mass sensitivity, then sensitivity increases, but the device becomes very fragile
Solution Approach 1:
The patent uses composite material structure with c-axis oriented ZnO piezoelectric film deposited on acoustic Bragg reflectors. The reflector structure provides mechanical support and robustness to the thin piezoelectric film, while the film itself maintains its high mass sensitivity. The composite structure allows the thin film to function effectively without being mechanically fragile.
Solution Approach 2:
The patent applies different material properties to different parts of the device. The piezoelectric film is kept thin for high sensitivity, while the acoustic Bragg reflector layer provides mechanical strength. The electrode structures are designed with specific local configurations to provide both electrical functionality and mechanical support where needed, balancing sensitivity and robustness locally throughout the device.
3Reliability
If different electrode and reflector designs are used for TSM and TEM, then each mode can be optimized, but separate devices are needed for each mode
Solution Approach 1:
The patent merges the functionality of separate TSM-optimized and TEM-optimized devices into a single BAW resonator. The acoustic Bragg reflector stack is designed with specific acoustic impedance values that are optimized to reflect both TSM and TEM waves effectively. Multiple electrode configurations can be implemented on the same device to excite different modes, combining the capabilities of multiple devices into one.
Solution Approach 2:
The patent segments the electrode structure into multiple independent electrode sets that can be activated selectively. Different electrode patterns (interdigitated electrodes for TSM, coplanar electrodes for TEM) are designed on the same substrate, allowing the device to be segmented functionally rather than requiring separate physical devices for each mode.
4Adaptability or versatility
If inclined/tilted c-axis growth of ZnO is used to achieve both TSM and TEM operation, then multi-mode operation is possible, but the membrane structures become inherently fragile in GHz range
Solution Approach 1:
Instead of using inclined/tilted c-axis growth as the primary approach, the patent inverts the approach by using substantially c-axis oriented ZnO growth with the electrode configurations and reflector design adapted to enable multi-mode operation. This inversion maintains the mechanical integrity of the c-axis oriented film while achieving multi-mode capability through electromagnetic and acoustic field design rather than crystal orientation manipulation.
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 durable and manufacturable BAW resonators capable of operating in multiple modes, enhancing their robustness and versatility for applications like multi-band communication filters and bio-sensing, while maintaining efficiency in both liquid and vapor sensing.
Implementation Method 1
Hexagonal crystals structures serving as piezoelectric thin films, such as zinc oxide ("ZnO") and aluminum nitride ("AlN"), have been used to make film BAW resonators
Implementation Method 2
In SMRs, the piezoelectric film is deposited on top of an acoustic Bragg reflector
Implementation Method 3
The frequency at which a BAW resonator resonates is inversely proportional to the thickness of the device
Data Source
AI summary
The various embodiments of the present disclosure relate generally bulk-acoustic-wave resonators. An exemplary embodiment of the present invention provides a bulk-acoustic-wave resonator comprising an acoustic reflector, a substantially c-axis oriented hexagonal crystal structure, and a plurality of electrodes. The crystal structure is solidly-mounted to the acoustic reflector. The bulk-wave resonator resonates in at least two non-harmonically-related operational modes.