XBAR Resonator Structure With Etch-Stop Layer for High-Frequency RF Filters
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Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequency communications bands, such as those proposed for future wireless networks, due to limitations in performance parameters like insertion loss, rejection, and power handling.
Innovation Solution
The development of a transversely-excited film bulk acoustic resonator (XBAR) with an etch-stop layer and bonding layer, which enhances the performance of RF filters by improving the structural integrity and etching processes, allowing for effective operation in higher frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acoustic wave resonators are used, then they work well at lower frequencies, but they cannot achieve satisfactory performance at higher frequency bands (up to 28 GHz)
Solution Approach 1:
The patent changes the structural parameters of the resonator by introducing an etch-stop layer with specific material composition and thickness, and modifying the bonding layer configuration, to enable operation at higher frequencies up to 28 GHz while maintaining performance characteristics
Solution Approach 2:
The patent uses composite material structures including the etch-stop layer made of specific materials positioned between the piezoelectric plate and substrate, combined with bonding layers, to create a resonator that achieves both high-frequency operation and mechanical stability
2Ease of manufacture
If the piezoelectric plate is directly bonded to the substrate, then the structure is simple, but the etching process damages the piezoelectric plate
Solution Approach 1:
The patent introduces an etch-stop layer as an intermediary component between the piezoelectric plate and the substrate. This layer protects the piezoelectric plate from etching damage while allowing the etching process to proceed to form acoustic wave cavities, thus preserving manufacturing simplicity without compromising plate integrity
3Device complexity
If no etch-stop layer is used, then the manufacturing process is simpler, but spurious modes increase and acoustic wave propagation efficiency decreases
Solution Approach 1:
The patent optimizes the parameters of the etch-stop layer including its thickness, material composition, and positioning to minimize spurious modes and maximize acoustic wave propagation efficiency. The layer acts as an acoustic mirror that reflects unwanted waves, reducing energy loss without requiring complex multi-layer structures
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 XBAR design improves the performance of RF filters by maintaining low insertion loss and high rejection across wider frequency bands, enabling efficient operation in frequencies up to 28 GHz, thus supporting future wireless communication systems.
Implementation Method 1
a piezoelectric layer 510 made of a piezoelectric material
Implementation Method 2
an etch-stop layer 550 disposed between the piezoelectric layer 510 and the substrate 520
Implementation Method 3
a bonding layer 522 between the etch-stop layer 550 and the substrate 520
Data Source
AI summary
Acoustic resonator devices and methods are disclosed. An acoustic resonator device includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces. A bonding layer is formed on the surface of the substrate. An etch-stop layer is sandwiched between the bonding layer and the back surface of the single crystal piezoelectric plate. A portion of the single crystal piezoelectric plate and the etch-stop layer, but not the bonding layer, forms a diaphragm spanning a cavity in the substrate. An interdigital transducer (IDT) is formed on the front surface of the single-crystal piezoelectric plate with interleaved fingers of the IDT disposed on the diaphragm. The etch-stop layer is impervious to an etch process used to form the cavity.