XBAR Oxide Strip Confinement for Higher-Q RF Filters
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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 communications networks, particularly in 5G NR standards for bands n77 and n79, and WiFi bands at 5 GHz and 6 GHz.
Innovation Solution
The use of transversely-excited film bulk acoustic resonators (XBARs) with oxide strip acoustic confinement structures (ACS) improves the performance of RF filters by enhancing the Bode Q factor, which is critical for achieving better frequency selectivity and reducing losses at band edges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acoustic wave resonators are used, then the filter structure is simple, but the Bode Q factor is insufficient for higher frequencies and wider bandwidths
Solution Approach 1:
The resonator structure is segmented by introducing oxide strip acoustic confinement structures that divide the acoustic field into confined regions. These oxide strips act as acoustic barriers that segment the propagation path, improving the Bode Q factor by reducing energy loss at band edges while maintaining a manageable structural complexity through modular placement.
Solution Approach 2:
The resonator employs composite material structures combining piezoelectric materials with oxide strip acoustic confinement layers. This composite approach enhances the Bode Q factor by leveraging the acoustic confinement properties of oxide materials to suppress unwanted modes and improve frequency selectivity, particularly for higher frequency applications.
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 oxide strip acoustic confinement structures utilize parameter changes in material properties (acoustic impedance, density) to achieve enhanced frequency selectivity. By carefully controlling the thickness, width, and position of oxide strips, the resonator achieves superior frequency discrimination without requiring excessively complex manufacturing processes.
Solution Approach 2:
The oxide strips serve as intermediary acoustic confinement elements between the interdigital transducer and the substrate. These intermediary structures mediate the acoustic field distribution, improving frequency selectivity by confining acoustic energy to desired regions while simplifying the overall fabrication through standardized oxide deposition processes.
3Adaptability or versatility
If existing resonator designs are used, then the device is suitable for current communication standards, but it cannot handle higher transmit powers and wider bandwidths required for future standards
Solution Approach 1:
The resonator design transitions to a dimensionally enhanced structure by incorporating vertical oxide strip confinement layers that add a third dimension to acoustic control. This dimensional enhancement enables the resonator to handle wider bandwidths and higher frequencies (including 5G n77, n79, and WiFi 5/6 GHz bands) while maintaining robust power handling capabilities through improved acoustic energy confinement.
Solution Approach 2:
The resonator structure achieves universality by being designed to operate across multiple frequency bands and communication standards. The oxide strip acoustic confinement structures provide multi-functional benefits including enhanced Bode Q factor, improved power handling, and adaptability to various bandwidth requirements, making the same resonator design suitable for both current and future communication standards.
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 incorporation of dielectric strip ACS in XBARs leads to increased maximum available gain at band edges, improved filter performance, and the ability to handle higher transmit powers, making them suitable for future communication standards.
Implementation Method 1
An interdigital transducer (IDT) generates a shear acoustic wave in a thin plate of piezoelectric material
Implementation Method 2
oxide strip acoustic confinement structures (ACS) improves the performance of RF filters by enhancing the Bode Q factor
Data Source
AI summary
Acoustic resonators, filters, and methods. An exemplary filter includes a piezoelectric layer plate supported by a substrate; and three or more diaphragms of the piezoelectric layer spanning a respective cavity. A conductor pattern on the layer 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. One or more of the resonators can have 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. Moreover, the first and second dielectric strips can be on a surface of the layer, have a first portion under the IDT fingers and have a second portion extending into a gap between the margins and the busbars.