Single-Crystal BAW Resonator Structure for Low Acoustic Loss
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Solution Overview
Problem
Conventional bulk acoustic wave resonators constructed with poly-crystalline piezoelectric thin films, such as AlN, have lower electromechanical coupling coefficients and Q-factors, leading to compromised performance and power handling capabilities, particularly in thin film configurations.
Innovation Solution
The development of a bulk acoustic resonator with a piezoelectric layer comprising single-crystalline or polycrystalline materials epitaxially grown or physically deposited on a surrogate substrate, followed by removal of the substrate, and integrated with a support structure featuring a cavity or acoustic mirror to enhance energy confinement and reduce leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If poly-crystalline piezoelectric thin films are deposited via PVD techniques, then the manufacturing process is simple and cost-effective, but the electromechanical coupling coefficient and Q-factor are significantly lower
Solution Approach 1:
The patent changes the crystalline structure parameter of the piezoelectric film from poly-crystalline to single-crystalline by using epitaxial growth techniques instead of PVD, achieving higher electromechanical coupling coefficients and Q-factors while maintaining manufacturing feasibility
Solution Approach 2:
The patent introduces a surrogate substrate as an intermediary to grow high-quality single-crystalline piezoelectric films that would be difficult to grow directly on the final device substrate, enabling better film quality while maintaining processability
2Ease of manufacture
If poly-crystalline piezoelectric thin films are used, then the fabrication process is straightforward, but the Q-factor is lower leading to higher acoustic loss
Solution Approach 1:
The patent changes the crystalline structure parameter from poly-crystalline to single-crystalline, which fundamentally reduces acoustic loss and increases Q-factor while maintaining fabrication feasibility through epitaxial growth methods
3Volume of moving object
If thin piezoelectric film configurations are used, then the device size is reduced, but power handling capability is compromised due to degraded thermal conductivity
Solution Approach 1:
The patent changes the thermal conductivity parameter by using single-crystalline piezoelectric films instead of poly-crystalline films, as single-crystalline structures have superior thermal conductivity that enables better power handling in thin-film configurations
Solution Approach 2:
The patent uses composite structures including acoustic mirrors and support structures in conjunction with the single-crystalline piezoelectric film to enhance overall device performance and power handling capability while maintaining compact size
4Reliability
If single-crystalline piezoelectric films are grown epitaxially on surrogate substrate, then electromechanical coupling coefficient and Q-factor are improved, but the manufacturing complexity increases
Solution Approach 1:
The patent uses a surrogate substrate as an intermediary to grow single-crystalline piezoelectric films, which simplifies the manufacturing process by enabling controlled epitaxial growth and facilitating subsequent film transfer to the final device substrate
Solution Approach 2:
The patent segments the manufacturing process into distinct stages: growing the piezoelectric film on the surrogate substrate, transferring the film to the device substrate, and completing the device fabrication, which makes the complex process more manageable and scalable
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 resonator with improved electromechanical coupling coefficients and Q-factors, offering better performance and minimal dispersion loss, while being cost-effective and suitable for mass production.
Implementation Method 1
When an oscillating electrical signal is applied between the top and bottom electrodes, the piezoelectric thin film layer converts the oscillating electrical signal into bulk acoustic waves
Implementation Method 2
The support structure includes a cavity or an acoustic mirror adjacent the first electrode to reduce leakage of acoustic energy from the stack into the support structure
Implementation Method 3
the piezoelectric layer includes one or more single crystalline or polycrystalline piezoelectric materials epitaxially grown or physically deposited from the second side to the first side on a surrogate substrate
Implementation Method 4
Piezoelectric thin film materials used for bulk acoustic wave devices include AlN, ZnO thin films for small bandwidth applications and ScAlN or PZT films for wide bandwidth applications. Currently, BAW resonators are normally constructed by depositing piezoelectric (e.g., AlN) thin films via physical vapor deposition (PVD) techniques such as sputter deposition
Data Source
AI summary
A single-crystal bulk acoustic wave resonators with better performance and better manufacturability and a process for fabricating the same are described. A low-acoustic-loss layer of one or more single-crystal and/or poly-crystal piezoelectric materials is epitaxially grown and/or physically deposited on a surrogate substrate, followed with the formation of a bottom electrode and then a support structure on a first side of the piezoelectric layer. The surrogate substrate is subsequently removed to expose a second side of the piezoelectric layer that is opposite to the first side. A top electrode is then formed on the second side of the piezoelectric layer, followed by further processes to complete the BAW resonator and filter fabrication using standard wafer processing steps. In some embodiments, the support structure has a cavity or an acoustic mirror adjacent the first electrode layer to minimize leakage of acoustic wave energy.