XBAR Resonator Crystal Orientation for Lower Temperature Drift
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Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequencies and bandwidths required in future communications networks, particularly for 5G NR standards, due to significant temperature coefficient of frequency (TCF) variations affecting their performance.
Innovation Solution
The use of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with specifically oriented piezoelectric materials like lithium niobate and lithium tantalate, where the Euler angle β is optimized to reduce the temperature coefficient of frequency (TCF), thereby minimizing frequency dependence on temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional acoustic wave resonators are used for higher frequency communications, then frequency capability is improved, but temperature coefficient of frequency (TCF) variations increase
Solution Approach 1:
The patent applies parameter changes by optimizing the Euler angle β of the piezoelectric crystal to specific ranges (40°-67° for lithium niobate, 30°-40° for lithium tantalate) to minimize the temperature coefficient of frequency. This angular parameter optimization allows the resonator to maintain stable frequency characteristics across temperature variations while operating at higher frequencies required for 5G communications
Solution Approach 2:
The patent employs composite material structures combining piezoelectric materials (lithium niobate or lithium tantalate) with specific crystal orientations and acoustic wave propagation modes. This composite approach integrates material selection with structural configuration to achieve both high frequency capability and reduced temperature sensitivity
2Reliability
If Euler angle β is optimized to reduce TCF, then temperature stability is improved, but device complexity increases
Solution Approach 1:
The patent transforms the complex temperature compensation problem into a manageable parameter optimization task by identifying specific Euler angle ranges. This converts a potentially complex iterative design process into a more straightforward parameter selection approach, where manufacturers can directly target specific angle ranges to achieve desired temperature stability
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 RF filters with improved temperature stability, achieving reduced TCF values by 8% to 24% compared to prior designs, enhancing performance and compatibility with higher frequency bands like 5G NR's n77, n79, and millimeter wave communications.
Implementation Method 1
The use of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with specifically oriented piezoelectric materials like lithium niobate and lithium tantalate
Implementation Method 2
acoustic resonators and filters with reduced temperature coefficient of frequency
Data Source
AI summary
Acoustic resonator devices and filters. An acoustic resonator includes a substrate and a lithium niobate plate. A back surface of the lithium niobate plate faces the substrate. A portion of the lithium niobate plate forms a diaphragm that spans a cavity in the substrate. An interdigital transducer (IDT) is on a front surface of the lithium niobate plate such that interleaved fingers of the IDT are on the diaphragm. The IDT and the lithium niobate plate are 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°.