Sandwiched XBAR Resonator Structure for Third-Harmonic RF Filtering
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Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequencies and bandwidths required in future communication networks, particularly for 5G NR standards, as they face challenges in achieving broad band filters due to insufficient resonator coupling and spurious modes at higher harmonic frequencies.
Innovation Solution
The development of sandwiched Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with IDT electrodes embedded in a dielectric layer between two piezoelectric plates, which suppresses spurious modes and provides high coupling into third harmonic modes, enabling the creation of 15 GHz bandpass filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional acoustic wave resonators are used for higher frequency operations, then frequency capability is improved, but resonator coupling becomes insufficient and spurious modes increase
Solution Approach 1:
The resonator structure is segmented into multiple layers including a piezoelectric substrate, a dielectric layer, and a metal layer with specific acoustic impedance. This segmentation allows each layer to be optimized for its specific function, enabling high-frequency operation with improved resonator coupling and reduced spurious modes
Solution Approach 2:
The patent changes the acoustic impedance parameter of the resonator structure by introducing a metal layer with specific acoustic impedance between the piezoelectric substrate and the load. This parameter change enables the resonator to operate at higher frequencies while maintaining strong coupling and suppressing spurious modes
2Speed
If conventional acoustic wave resonators are used for higher frequency operations, then frequency capability is improved, but spurious mode interference increases
Solution Approach 1:
A dielectric layer is introduced as an intermediary between the piezoelectric substrate and the metal layer. This intermediary layer helps to suppress spurious modes by controlling the acoustic wave propagation and reducing unwanted resonances, while still allowing the resonator to operate at high frequencies
Solution Approach 2:
The acoustic impedance of the resonator structure is modified by adding the metal layer with specific acoustic impedance. This parameter change suppresses spurious modes by creating acoustic barriers that prevent unwanted wave propagation, while maintaining high-frequency operation
3Productivity
If bandwidth is increased for future communication networks, then communication capacity is improved, but filter design becomes more difficult
Solution Approach 1:
The resonator structure is designed to be multi-functional, serving both as a high-frequency resonator and as a broadband filter element. The specific acoustic impedance metal layer and dielectric layer configuration enables the resonator to provide both frequency selection and broadband filtering capabilities, simplifying overall filter design for high-capacity communication networks
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
This solution allows for the design of high-frequency bandpass filters with improved resonator coupling and reduced spurious mode interference, effectively addressing the limitations of existing technologies in handling higher frequency ranges.
Implementation Method 1
An XBAR resonator comprises an interdigital transducer (IDT) formed on a thin floating layer, or diaphragm, of a single-crystal piezoelectric material. A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm.
Implementation Method 2
RF filters typically require many design trade-offs to achieve, for each specific application, the best compromise between performance parameters such as insertion loss, rejection, isolation, power handling, linearity, size and cost. High performance RF filters for present communication systems commonly incorporate acoustic wave resonators
Data Source
AI summary
A filter device has a first piezoelectric plate spanning a first and second cavity of a substrate. A first and second interdigital transducer (IDT) are on a front surface of the first piezoelectric plate over the first and second cavity. A dielectric layer is formed on the first piezoelectric plate and covers the first IDT and second IDT. A second piezoelectric plate is bonded to a front surface of the dielectric layer over the first cavity and the second cavity. A second dielectric layer is formed on a front surface of the second piezoelectric plate over the first cavity but not over the second cavity. The thickness of the dielectric layer, the first piezoelectric plate and the second piezoelectric plate can be selected to tune a shunt resonator over the first cavity and a series resonator over the second cavity.