XBAR Ladder Filter Layout for Wideband 5G and Wi-Fi RF Signals
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Solution Overview
Problem
Existing RF filters using acoustic wave resonators are not well-suited for higher frequencies and wider bandwidths required in future communication systems, particularly for 5G NR and Wi-Fi bands.
Innovation Solution
The use of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with specific design features such as interleaved IDT fingers, dielectric layers, and varying pitch and mark ratios to achieve the necessary frequency selectivity and bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional acoustic wave resonators (SAW, BAW, FBAR) are used, then the filters work at lower frequencies, but they cannot achieve the higher frequencies and wider bandwidths required for 5G NR and Wi-Fi bands
Solution Approach 1:
The patent changes the fundamental operating parameters of the resonator by transitioning from surface acoustic waves to bulk acoustic waves with transverse excitation. This parameter change enables operation at higher frequencies (3 GHz to 100 GHz range) while maintaining the desired filter performance for 5G and Wi-Fi applications
Solution Approach 2:
The patent replaces conventional acoustic wave mechanisms (SAW, traditional BAW, FBAR) with a new transverse-excited bulk acoustic wave mechanism. This substitution of the underlying physical mechanism enables the resonator to achieve both high frequency capability and wide bandwidth performance required for modern communication systems
2Adaptability or versatility
If the filter bandwidth is increased to support wider communication channels, then higher frequency bands are required, but existing resonator technologies cannot handle these frequencies effectively
Solution Approach 1:
The patent modifies key resonator parameters including the interdigital transducer finger pitch, diaphragm thickness, and piezoelectric material properties to enable operation at higher frequencies while maintaining wide bandwidth. The transverse excitation mode specifically allows the resonator to achieve both high frequency and wide bandwidth simultaneously
Solution Approach 2:
The patent employs dynamic design elements such as varying the pitch and mark ratios of the interdigital transducer fingers across different regions of the resonator. This dynamic variation in geometric parameters allows the filter to achieve wide bandwidth while operating at the required high frequencies for 5G and Wi-Fi bands
3Speed
If XBAR resonators are used to achieve high frequency capability, then spurious modes may be generated, but these need to be minimized to maintain performance
Solution Approach 1:
The patent applies local quality control by carefully designing the interdigital transducer with specific pitch and mark ratio variations in different regions. This local optimization of the transducer geometry suppresses spurious modes while maintaining the desired high frequency operation and wide bandwidth characteristics
Solution Approach 2:
The patent converts the potential harmful effect of spurious modes by using the same transverse excitation mechanism that generates high frequency capability to also suppress unwanted modes. The specific geometry and excitation pattern transform what could be harmful spurious responses into beneficial filter characteristics
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
XBAR filters provide high electromechanical coupling and frequency capability, enabling effective filtering for 5G NR and Wi-Fi bands while minimizing spurious modes and maintaining performance across the desired frequency range.
Implementation Method 1
A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm
Implementation Method 2
The IDT includes a first set of parallel fingers, extending from a first busbar and a second set of parallel fingers extending from a second busbar. The first and second sets of parallel fingers are interleaved. A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm
Implementation Method 3
The XBAR is an acoustic resonator structure for use in microwave filters... 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 with at least one shunt transversely-excited film bulk acoustic resonators (XBAR) and at least one series XBAR. Each of the XBARs includes a diaphragm having an LN-equivalent thickness greater than or equal to 360 nm, and each of the XBARs includes a diaphragm having an LN-equivalent thickness less than or equal to 375 nm.