Single-Crystal BAW Resonator Structure for Above-5-GHz RF Filters
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Solution Overview
Problem
Conventional bulk acoustic wave resonators using polycrystalline piezoelectric thin films face degradation at frequencies above 5 GHz due to poor crystalline quality at thin thicknesses, limiting their performance in high-frequency applications.
Innovation Solution
The use of single crystalline or epitaxial piezoelectric thin films grown on compatible substrates, combined with advanced manufacturing processes, to create high-quality bulk acoustic wave resonators with enhanced performance and quality factor for RF filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polycrystalline piezoelectric thin films are used in bulk acoustic wave resonators, then the resonators can be manufactured with conventional processes, but the crystalline quality degrades at thin thicknesses required for frequencies above 5 GHz
Solution Approach 1:
The patent changes the fundamental parameter of crystal structure from polycrystalline to single crystal. This parameter change enables the material to maintain high crystalline quality at thin thicknesses (below 0.5 um) required for frequencies above 5 GHz, while still allowing conventional manufacturing processes to be used.
Solution Approach 2:
The patent employs a composite structure consisting of a single crystal piezoelectric layer grown on a patterned bottom electrode substrate. This composite approach combines the high crystalline quality of single crystal materials with the manufacturability of conventional electrode patterns, enabling high-frequency operation above 5 GHz.
2Speed
If the piezoelectric film thickness is reduced below 0.5 um to achieve higher frequencies, then the resonator frequency increases above 5 GHz, but the polycrystalline film quality degrades
Solution Approach 1:
The patent changes the crystal structure parameter from polycrystalline to single crystal, which fundamentally alters how the material behaves at thin thicknesses. This enables the film to maintain high crystalline quality even when thickness is reduced below 0.5 um to achieve frequencies above 5 GHz.
Solution Approach 2:
The patent replaces the conventional polycrystalline film deposition process with a single crystal growth process (such as epitaxial growth). This substitution of the material formation mechanism enables high-frequency operation by maintaining crystalline quality at the required thin thicknesses.
3Manufacturing precision
If single crystalline piezoelectric films are used, then high piezoelectric performance is maintained at thin thicknesses for frequencies above 5 GHz, but the manufacturing process becomes more complex
Solution Approach 1:
The patent segments the manufacturing process into distinct stages: first forming the bottom electrode pattern on a substrate, then growing the single crystal piezoelectric layer on this patterned surface. This segmentation allows the complex single crystal growth to be performed on a pre-prepared template, reducing overall process complexity.
Solution Approach 2:
The patent performs preliminary actions by first creating the bottom electrode pattern and preparing the substrate surface before initiating single crystal growth. This preliminary preparation provides a controlled template that guides the single crystal formation, simplifying what would otherwise be a highly complex process.
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
These single crystalline piezoelectric films maintain high piezoelectric performance even at thin thicknesses, enabling effective operation at frequencies above 5 GHz with improved quality factor and electro-mechanical coupling, addressing the limitations of polycrystalline films.
Implementation Method 1
single crystal piezoelectric material... high piezoelectric performance... electro-mechanical coupling
Implementation Method 2
electro-mechanical coupling... bulk acoustic wave resonators
Data Source
AI summary
A method and structure for single crystal acoustic electronic device. The device includes a substrate having an enhancement layer formed overlying its surface region, a support layer formed overlying the enhancement layer and an air cavity formed through a portion of the support layer. Single crystal piezoelectric material is formed overlying the air cavity and a portion of the enhancement layer. Also, a first electrode material coupled to the backside surface region of the crystal piezoelectric material and spatially configured within the cavity. A second electrode material is formed overlying the topside of the piezoelectric material, and a dielectric layer formed overlying the second electrode material. Further, one or more shunt layers can be formed around the perimeter of a resonator region of the device to connect the piezoelectric material to the enhancement layer.