Symmetric XBAR Filter Layout for 5G Power and Bandwidth
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Solution Overview
Problem
Current RF filters, particularly those using acoustic wave resonators, are not well-suited for higher frequency communications bands such as 5G NR, which requires bandpass filters capable of handling higher transmit power and wider channel bandwidths, especially in frequency ranges like 3300 MHz to 4200 MHz and 4400 MHz to 5000 MHz, and millimeter wave frequencies.
Innovation Solution
The development of transversely-excited film bulk acoustic resonators (XBARs) with a symmetric layout, utilizing a thin film conductor pattern on a Z-cut piezoelectric plate, such as lithium niobate, to create a high-power band-pass filter capable of operating effectively in these higher frequency ranges, leveraging a primary acoustic mode that minimizes viscous losses and achieves high piezoelectric coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional acoustic wave resonators are used in RF filters, then the filters can operate at traditional frequency bands, but they cannot handle higher transmit power and wider channel bandwidths required for 5G NR frequency bands
Solution Approach 1:
The patent changes the operating parameters by using transversely-excited film bulk acoustic resonators (XBARs) with a symmetric layout on Z-cut lithium niobate, operating in the shear horizontal mode. This configuration enables the resonators to function effectively at 5G NR frequency bands (3300-4200 MHz and 4400-5000 MHz) while handling higher transmit power levels, thus resolving the contradiction between power handling capability and performance reliability in higher frequency bands
2Adaptability or versatility
If conventional RF filters are used, then they can maintain simple structure, but they cannot achieve enhanced bandwidth and power handling capabilities required for 5G NR
Solution Approach 1:
The patent divides the filter structure into multiple XBAR resonators with symmetric layout, where each resonator is independently designed to operate at specific 5G NR frequency bands. This segmentation allows the filter to achieve enhanced bandwidth and power handling capabilities through the combined performance of multiple resonators, while each individual resonator maintains a relatively simple structure
Solution Approach 2:
The patent uses a composite structure combining thin film conductor pattern on Z-cut lithium niobate piezoelectric plate. This composite material approach enables the resonators to achieve both the required bandwidth and power handling capabilities for 5G NR while maintaining structural efficiency
3Reliability
If existing filters are used in 5G NR frequency bands, then manufacturing can be simplified, but insertion loss and rejection characteristics are insufficient for high-power applications
Solution Approach 1:
The patent optimizes the resonator parameters including the symmetric layout configuration, Z-cut lithium niobate orientation, and shear horizontal mode operation to achieve superior insertion loss and rejection characteristics. These parameter changes improve reliability for high-power 5G NR applications while maintaining compatibility with standard semiconductor manufacturing processes
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
XBARs provide improved performance in high-power RF filters, enabling efficient operation in 5G NR frequency bands with enhanced bandwidth and power handling capabilities, reducing insertion loss and improving rejection characteristics, thus addressing the limitations of existing filters in higher frequency communications.
Implementation Method 1
a transversely-excited film bulk acoustic resonator (XBAR) including an interdigital transducer (IDT) formed over a cavity in the substrate, where the IDT includes a first plurality of interdigitated fingers extending from a first busbar and a second plurality of interdigitated fingers extending from a second busbar
Implementation Method 2
High performance RF filters for present communication systems commonly incorporate acoustic wave resonators including surface acoustic wave (SAW) resonators, bulk acoustic wave (BAW) resonators, film bulk acoustic wave resonators (FBAR), and other types of acoustic resonators
Data Source
AI summary
There are disclosed acoustic resonators and radio frequency filter devices. A back surface of a single-crystal piezoelectric plate is attached to a surface of a substrate except for portions of the piezoelectric plate forming a plurality of diaphragms, each of which spans a respective cavity in the substrate. A conductor pattern is formed on the front surface, the conductor pattern including interdigital transducers (IDTs) of one or more pairs of sub-resonators, each pair consisting of two sub-resonators. The IDT of each sub-resonator includes interleaved fingers disposed on a respective diaphragm. The piezoelectric plate and the IDTs are configured such that respective radio frequency signals applied to each IDT excite respective shear primary acoustic modes in the respective diaphragms. The two sub-resonators of each pair of sub-resonators are positioned symmetrically about a central axis.