XBAR Ladder Filter Thickness Split for 5 GHz Wi-Fi Bandwidth
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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 communication networks, particularly for 5G NR and Wi-Fi bands, as they struggle to provide the necessary frequency selectivity and bandwidth without degrading performance with spurious modes.
Innovation Solution
The use of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with specific piezoelectric plate thicknesses and dielectric layers to adjust resonance and anti-resonance frequencies, combined with a ladder filter architecture, to create band-pass filters capable of handling higher frequencies and bandwidths, such as those in the 5 GHz Wi-Fi band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acoustic wave resonators (SAW, BAW, FBAR) are used for higher frequency communications, then device compatibility is maintained, but frequency selectivity and bandwidth performance degrade due to spurious modes
Solution Approach 1:
The patent changes the operating mode parameters from longitudinal/acoustic waves to transverse shear acoustic waves. This parameter change in wave propagation mode eliminates spurious modes while maintaining high frequency selectivity, directly resolving the contradiction between reliability and harmful factors
Solution Approach 2:
The patent substitutes the conventional acoustic wave mechanism with a transverse shear wave mechanism in a thin film piezoelectric layer. This mechanical substitution eliminates the spurious modes inherent in conventional resonators while achieving superior frequency selectivity for 5G and Wi-Fi applications
2Productivity
If higher frequency bands are used to increase bandwidth, then communication capacity improves, but filter performance degrades due to spurious modes and reduced frequency selectivity
Solution Approach 1:
The patent changes the fundamental operating parameters by using transverse shear acoustic waves instead of conventional acoustic waves. This enables the filter to achieve both high bandwidth (supporting 5G n77, n79, and Wi-Fi 5/6 GHz bands) and high frequency selectivity simultaneously, resolving the contradiction between productivity and reliability
Solution Approach 2:
The patent employs a thin film piezoelectric layer with controlled thickness (50-200 nm) that dynamically responds to RF signals at higher frequencies. The transverse shear wave mode provides superior frequency discrimination at these higher bands, enabling both wide bandwidth and high selectivity
3Measurement precision
If piezoelectric plate thickness is increased to adjust resonance frequency, then frequency tuning is achieved, but spurious modes are generated that degrade filter performance
Solution Approach 1:
The patent changes the thickness parameter to a thin film range (50-200 nm) and combines it with transverse shear wave operation. This parameter combination enables precise resonance frequency tuning for different 5G and Wi-Fi bands while the transverse mode inherently suppresses spurious modes, resolving the contradiction between measurement precision and harmful factors
Solution Approach 2:
The patent creates local quality control by using a thin film piezoelectric layer with specific thickness and transverse shear wave confinement. This localized structural quality enables frequency tuning while suppressing spurious modes that would otherwise be generated in thicker plates
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 enables the design of RF filters with improved frequency selectivity and bandwidth, reducing spurious modes and enhancing filter performance for 5G NR and Wi-Fi applications by precisely tuning the resonance and anti-resonance frequencies of XBARs, ensuring effective signal transmission and rejection.
Implementation Method 1
a thin film piezoelectric layer 50 nm to 200 nm thick formed on a substrate
Implementation Method 2
acoustic resonators including surface acoustic wave (SAW) resonators, bulk acoustic wave (BAW) resonators, film bulk acoustic wave resonators (FBAR)
Data Source
AI summary
A 5 GHz Wi-Fi bandpass filter includes a ladder filter circuit with two or more shunt transversely-excited film bulk acoustic resonators (XBARs) and two or more series XBARs. Each of the two or more shunt XBARS includes a diaphragm having an LN-equivalent thickness greater than or equal to 360 nm, and each of the two or more series XBARS includes a diaphragm having an LN-equivalent thickness less than or equal to 375 nm.