XBAR Ladder Filter Structure for 5G Band Frequency Separation
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Solution Overview
Problem
Existing RF filters are not well-suited for the higher frequencies and bandwidths required by future communications networks, particularly in 5G NR and Wi-Fi bands, due to limitations in frequency separation and performance of current acoustic wave resonators.
Innovation Solution
The use of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with specific diaphragm thicknesses and dielectric layers to achieve the necessary frequency separation and performance in ladder filter architectures, utilizing shear acoustic modes for improved electromechanical coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional acoustic wave resonators (SAW, BAW, FBAR) are used, then the filters can operate at current communication frequencies, but they cannot achieve the higher frequencies and bandwidths required for future 5G NR and Wi-Fi bands
Solution Approach 1:
The patent changes the fundamental operating parameters of the resonator by transitioning from surface acoustic wave (SAW) or bulk acoustic wave (BAW) modes to transverse electric (TE) mode resonators. This parameter change enables operation at higher frequencies (3 GHz to 30 GHz and beyond) while achieving the required frequency separation and bandwidth performance for 5G NR and Wi-Fi bands that conventional resonators cannot provide
2Adaptability or versatility
If existing acoustic resonator technologies are used, then the filter structure is relatively simple, but they are not well-suited for higher frequencies and bandwidths proposed for future communications networks
Solution Approach 1:
The patent replaces conventional mechanical acoustic wave propagation mechanisms (SAW, BAW, FBAR) with a transverse electric mode resonator system that uses dielectric resonators and waveguide structures. This substitution enables the system to achieve the required adaptability for future communication bands (5G NR n77, n79, Wi-Fi 6E, millimeter wave) while maintaining a manageable structural complexity through standardized resonator designs
3Productivity
If wider communication channel bandwidths are implemented, then higher data rates are achieved, but frequency separation and rejection performance become more difficult to maintain
Solution Approach 1:
The patent transitions from two-dimensional surface acoustic wave propagation to three-dimensional transverse electric mode resonance within dielectric resonators. This dimensional change provides additional degrees of freedom for frequency control and separation, enabling the maintenance of precise frequency separation and rejection performance even when implementing wider communication channel bandwidths for higher data rates
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 high-frequency capability and improved frequency separation, enabling effective filtering in 5G NR and Wi-Fi bands with reduced spurious modes and enhanced performance parameters.
Implementation Method 1
A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm
Implementation Method 2
XBAR resonators provide very high electromechanical coupling and high frequency capability
Data Source
AI summary
A bandpass filter is provided that includes a ladder filter circuit having series and shunt transversely-excited film bulk acoustic resonators (XBARs). The series XBAR includes a lithium niobate piezoelectric layer; and a front side dielectric layer that comprises a silicon oxide between interleaved fingers of an interdigital transducer of the series XBAR disposed on the lithium niobate piezoelectric layer of the series XBAR. Similarly, the shunt XBAR includes a lithium niobate piezoelectric layer; and a front side dielectric layer that comprises a silicon oxide between interleaved fingers of an interdigital transducer of the shunt XBAR disposed on the lithium niobate piezoelectric layer of the shunt XBAR.