XBAR Resonator Orientation for Low-Drift RF Filter Frequency
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Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequencies and wider bandwidths required in future communication networks, such as the 5G NR standard, which includes bands like n77, n79, and millimeter wave frequencies, due to significant temperature frequency dependence and performance limitations.
Innovation Solution
The use of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with specific piezoelectric material orientations, like rotated Y-cut lithium niobate or lithium tantalate, to optimize piezoelectric coupling and reduce temperature coefficient of frequency (TCF), enabling improved frequency stability and performance in high-frequency band-pass filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional acoustic wave resonators (SAW, BAW, FBAR) are used in RF filters, then the filters can operate at current frequencies, but they exhibit significant temperature frequency dependence and cannot handle higher frequencies and wider bandwidths required for future communication networks
Solution Approach 1:
The patent changes the cut orientation parameter of the piezoelectric substrate from traditional Z-cut to rotated Y-cut (specifically 63-degree rotated Y-cut). This parameter change fundamentally alters the temperature coefficient of frequency characteristics, enabling the resonator to achieve both high frequency stability and adaptability to higher frequencies and wider bandwidths required for 5G and future communication networks
Solution Approach 2:
The patent employs a composite structure combining specifically oriented piezoelectric material (rotated Y-cut lithium niobate or lithium tantalate) with interdigital transducers and electrode configurations. This composite approach leverages the unique properties of the rotated cut material to achieve superior temperature compensation and extended frequency range compared to traditional single-material resonators
2Reliability
If piezoelectric material orientation is optimized to reduce temperature coefficient of frequency, then frequency stability improves, but device complexity increases due to precise cutting and manufacturing requirements
Solution Approach 1:
The patent specifies a precise cut orientation parameter (63-degree rotated Y-cut) that optimizes the temperature coefficient of frequency. While this requires precise manufacturing, the standardized nature of this specific angle allows for repeatable production processes. The benefit of achieving ultra-low TCF (temperature coefficient of frequency) justifies the manufacturing precision requirements, especially for high-performance applications like 5G infrastructure
Solution Approach 2:
The patent applies different orientations and configurations to different components within the resonator structure. The piezoelectric substrate is cut at a specific rotated Y-angle, while the interdigital transducers and electrodes are configured with specific geometric parameters. This local optimization of quality parameters achieves overall superior temperature stability while managing manufacturing complexity through component-specific design
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 reduced temperature frequency dependence, enhancing the performance of RF filters by achieving wider bandwidths and improved frequency stability, particularly in the 5G NR frequency bands, with reduced temperature coefficient of frequency values compared to traditional Z-cut designs.
Implementation Method 1
a piezoelectric plate made of a rotated Y-cut piezoelectric material... A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm
Implementation Method 2
Transversely-Excited Film Bulk Acoustic Resonators (XBARs)... excites a shear primary acoustic wave in the piezoelectric diaphragm... capable of handling the transmit power
Data Source
AI summary
Acoustic resonator devices and filters. An acoustic resonator includes a substrate having a surface and a lithium niobate plate. A back surface of the lithium niobate plate is attached the substrate except for a portion of the lithium niobate plate forming a diaphragm that spans a cavity in the substrate. An interdigital transducer (IDT) is formed on a front surface of the lithium niobate plate such that interleaved fingers of the IDT are disposed on the diaphragm. The IDT and the lithium niobate plate configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode within the diaphragm. Euler angles of the lithium niobate plate are [0°, β, 0°], where β is greater than or equal to 40° and less than or equal to 70°.