XBAR Oxide Strip Confinement for Wideband RF Filter Selectivity
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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 by future communications networks, such as the 5G NR standard bands n77 and n79.
Innovation Solution
The use of transversely-excited film bulk acoustic resonators (XBARs) with buried oxide strip acoustic confinement structures, which enhance the Bode Q factor and improve the frequency selectivity of RF filters, enabling them to handle higher frequencies and wider bandwidths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If existing acoustic wave resonators are used, then the filter structure is simple, but the frequency range is limited and bandwidth is narrow
Solution Approach 1:
The resonator is divided into multiple functional layers including piezoelectric film, acoustic confinement structures, and substrate layers. This segmentation allows each layer to be optimized for specific functions, enabling higher frequency operation and wider bandwidth while maintaining manufacturability through standardized fabrication processes for each layer
Solution Approach 2:
The resonator employs composite material structures combining piezoelectric materials with acoustic confinement materials of different acoustic impedances. This composite approach creates acoustic mirrors that reflect specific frequency ranges, extending the operational frequency range and bandwidth without requiring complete structural redesign
2Manufacturing precision
If acoustic confinement structures are added to enhance Bode Q factor, then frequency selectivity improves, but manufacturing complexity increases
Solution Approach 1:
The acoustic confinement structures utilize controlled variations in acoustic impedance through material selection and layer thickness control. By adjusting these parameters during fabrication, high frequency selectivity and Bode Q factor are achieved using standard thin-film deposition techniques, avoiding the need for complex post-fabrication assembly
Solution Approach 2:
Mechanical acoustic confinement achieved through physical barriers and complex geometries is replaced with acoustic mirror structures formed by material property variations. This substitution enables precision frequency control through material science rather than mechanical design, simplifying the manufacturing process while maintaining high frequency selectivity
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
The implementation of XBARs with buried oxide strip acoustic confinement structures significantly improves the Bode Q factor and frequency selectivity of RF filters, making them suitable for high-frequency applications such as 5G NR bands n77 and n79, while minimizing losses at band edges.
Implementation Method 1
a thin plate of piezoelectric material bonded to a substrate
Implementation Method 2
buried oxide strip acoustic confinement structures, which enhance the Bode Q factor
Data Source
AI summary
Acoustic resonators, filters, and methods. A filter includes a piezoelectric plate supported by a substrate; and three or more diaphragms of the piezoelectric plate spanning a respective cavity in the substrate. A conductor pattern on the plate has interdigital transducers (IDTs) of three or more acoustic resonators. Each IDT has two sets of interleaved fingers extending from two busbars respectively. Overlapping portions of the fingers define an aperture of each acoustic resonator. Sometimes, each of the resonators has two dielectric strips that overlap the IDT fingers in first and second margins of the aperture and that extend into first and second gaps between the first and second margins and the busbars. Other times, the first and second dielectric strips are on the front surface of the plate, have a first portion under the IDT fingers and have a second portion extending into a gap between the margins and the busbars.