Two-Layer XBAR Electrodes for 5G RF Filter Selectivity
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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 defined in the 5G NR standard, particularly for bands n77 and n79, which require improved performance to handle higher transmit power and wider channel bandwidths.
Innovation Solution
The development of transversely-excited film bulk acoustic resonators (XBARs) with optimized IDT finger cross-sectional shapes, such as pedestal and wedding cake-like configurations, to enhance frequency response and reduce spurious modes, allowing for the design of high-performance band-pass filters capable of operating in frequencies up to 40 GHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional RF filters using acoustic wave resonators are used, then existing technology can be maintained, but they are not well-suited for higher frequency communications bands (5G NR bands n77 and n79) with improved power handling and bandwidth requirements
Solution Approach 1:
The patent changes the operating parameters by designing XBAR resonators specifically for higher frequency bands (3.3-5.0 GHz for n77 and 4.4-5.0 GHz for n79). The resonator dimensions, electrode configurations, and acoustic wave properties are optimized for these higher frequencies while maintaining power handling capability through the specific XBAR structure with vertically propagating acoustic waves.
Solution Approach 2:
The patent employs composite material structures in the XBAR resonator design, including piezoelectric substrates with specific crystal orientations, metal electrode layers, and potentially multiple functional layers. This composite structure enables simultaneous achievement of high frequency operation and power handling by combining materials with complementary properties.
2Adaptability or versatility
If RF filters are designed for wider channel bandwidths, then bandwidth requirement is met, but frequency selectivity and spurious mode reduction become more challenging
Solution Approach 1:
The patent applies local quality optimization by designing specific electrode finger patterns and configurations in different regions of the XBAR resonator. The interdigital transducer (IDT) electrodes are configured with specific pitch, width, and overlap ratios to locally control the acoustic wave generation and propagation, enabling wide bandwidth while maintaining frequency selectivity through localized electromagnetic and acoustic field distribution.
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 frequency selectivity and reduced spurious modes, enabling the creation of RF filters that meet the demanding requirements of 5G communication bands, including n77 and n79, with enhanced power handling and bandwidth, thus addressing the limitations of existing technologies.
Implementation Method 1
A radio frequency (RF) filter is a two-port device configured to pass some frequencies and to stop other frequencies
Implementation Method 2
transversely-excited film bulk acoustic resonators (XBARs) with optimized IDT finger cross-sectional shapes
Data Source
AI summary
An acoustic resonator device, filter devices, and methods of making the same. An acoustic resonator device includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces, where the back surface is attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm that spans a cavity in the substrate. The device further includes an interdigital transducer formed on the front surface of the piezoelectric plate, where interleaved fingers of the IDT disposed on the diaphragm are configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the diaphragm. The interleaved fingers include a first layer adjacent the diaphragm and a second layer over the first layer, the second layer having a narrower width than the first layer.