XBAR Filter Dielectric Layer Split for Spurious Mode Mitigation
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Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequency communications bands above 3 GHz, such as those proposed for future wireless communication systems, due to limitations in performance and design trade-offs.
Innovation Solution
The use of transversely-excited film bulk acoustic resonators (XBARs) with divided frequency-setting dielectric layers, which include a back-side dielectric layer to mitigate spurious modes and improve frequency separation between shunt and series resonators, enabling efficient excitation of primary shear acoustic modes and enhancing filter performance at higher frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acoustic wave resonators are used for RF filters, then the filters can operate at traditional frequencies, but they are not well-suited for higher frequency communications bands above 3 GHz due to performance limitations
Solution Approach 1:
The patent changes the operating parameters of the resonator by using transversely-excited film bulk acoustic resonators (XBARs) with specific piezoelectric materials and configurations optimized for high-frequency operation above 3 GHz, including millimeter wave frequencies up to 28 GHz
Solution Approach 2:
The patent employs composite material structures including piezoelectric films, frequency-setting dielectric layers, and metal electrodes to create resonators that achieve both high-frequency performance and reduced spurious modes through material property optimization
2Device complexity
If a single frequency-setting dielectric layer is used in XBARs, then the structure is simpler, but spurious modes are not effectively mitigated and frequency separation between shunt and series resonators is insufficient
Solution Approach 1:
The patent divides the frequency-setting dielectric layer into multiple separate layers with different dielectric constants and thicknesses, where each layer contributes to frequency separation and spurious mode mitigation, achieving better performance than a single equivalent layer
Solution Approach 2:
The patent applies different dielectric materials with specific properties to different locations and functions within the resonator structure, optimizing each layer's characteristics for its specific role in frequency control and spurious mode suppression
3Adaptability or versatility
If wider communication channel bandwidths are supported, then the filter can handle millimeter wave frequencies up to 28 GHz, but the design requirements and manufacturing precision demands increase
Solution Approach 1:
The patent enables dynamic bandwidth adjustment by configuring multiple resonators with different frequency responses and using electronic switching or tuning mechanisms to adapt the filter's passband width and center frequency for different communication standards and frequency bands
Solution Approach 2:
The patent achieves wide bandwidth operation by carefully controlling and optimizing multiple parameters including piezoelectric film thickness, dielectric layer dimensions, electrode geometry, and material properties to maintain performance across millimeter wave frequencies up to 28 GHz
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 with divided frequency-setting dielectric layers demonstrate improved electromechanical coupling and reduced spurious modes, allowing for the design of high-performance RF filters capable of handling wider communication channel bandwidths, including millimeter wave frequencies up to 28 GHz.
Implementation Method 1
a piezoelectric material layer bonded to a substrate
Implementation Method 2
acoustic wave resonators including surface acoustic wave (SAW) resonators, bulk acoustic wave (BAW) resonators
Data Source
AI summary
Methods of fabricating acoustic filters. A back-side frequency setting layer is formed on a surface of a substrate and/or a back surface of a piezoelectric plate. The piezoelectric plate is attached to the substrate with the back-side frequency setting layer sandwiched between the substrate and the piezoelectric plate. Portions of the piezoelectric plate and backside frequency setting layer form diaphragms spanning respective cavities in the substrate. A conductor pattern defining a plurality of acoustic resonators is formed on a front surface of the piezoelectric plate. Each of the acoustic resonators includes an interdigital transducer (IDT) with interleaved fingers disposed on a respective diaphragm. A front-side frequency setting layer is formed over the interleaved fingers and the front surface of the diaphragms of one or more shunt resonators. The back-side frequency setting layer is removed from the back surfaces of the diaphragms of one or more series resonators.