XBAR Resonator Structure With Dielectric Decoupling for 5G 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 by future communication networks, such as the 5G NR standard which includes bands n77 and n79.
Innovation Solution
The use of a Transversely-Excited Film Bulk Acoustic Resonator (XBAR) with a decoupling dielectric layer between the IDT fingers and the piezoelectric diaphragm to reduce acoustic coupling, allowing for improved performance at higher frequencies and wider bandwidths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional acoustic wave resonators are used, then the filter structure is simple, but the frequency capability and bandwidth are insufficient for 5G communications
Solution Approach 1:
The resonator is segmented into distinct functional layers: IDT fingers for electrical excitation, decoupling dielectric layer for acoustic isolation, and piezoelectric membrane for resonance. This segmentation allows each layer to be optimized independently for high-frequency operation while managing complexity through modular design
Solution Approach 2:
A decoupling dielectric layer is introduced as an intermediary between the IDT fingers and the piezoelectric membrane. This intermediate layer reduces unwanted acoustic coupling while allowing electrical signals to pass through, enabling higher frequency operation without excessive structural complexity
2Reliability
If acoustic coupling between IDT fingers and piezoelectric membrane is strong, then electromechanical coupling is high, but acoustic energy loss increases at higher frequencies
Solution Approach 1:
The decoupling dielectric layer is applied selectively in specific regions between the IDT fingers and piezoelectric membrane to control acoustic coupling locally. This localized approach maintains necessary electromechanical coupling while reducing acoustic energy loss at high frequencies in critical areas
3Productivity
If wider bandwidth is achieved through higher frequencies, then communication capacity increases, but filter performance deteriorates
Solution Approach 1:
The filter employs composite material structure combining different dielectric materials with complementary properties: one layer provides acoustic decoupling while another provides electrical coupling. This composite approach enables simultaneous achievement of wide bandwidth and high filter performance at 5G frequencies
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 decoupling dielectric layers enhances the frequency capability and bandwidth of RF filters, enabling them to effectively handle the higher frequency communications bands defined in the 5G NR standard.
Implementation Method 1
a decoupling dielectric layer between the IDT fingers and the piezoelectric diaphragm to reduce acoustic coupling
Implementation Method 2
Transversely-Excited Film Bulk Acoustic Resonator (XBAR) with a decoupling dielectric layer between the IDT fingers and the piezoelectric diaphragm
Data Source
AI summary
Acoustic resonator devices and filters are disclosed. An acoustic resonator includes a substrate and a piezoelectric plate supported by the substrate. A portion of the piezoelectric plate suspended across a cavity in the substrate forms a diaphragm. A decoupling dielectric layer is on a front surface of the diaphragm. An interdigital transducer (IDT) has interleaved fingers on the decoupling dielectric layer over the diaphragm. The IDT and piezoelectric plate are configured such that a radio frequency signal applied to the IDT excites shear acoustic waves in the diaphragm.