XBAR Matrix Filter Layout for Wideband High-Frequency RF
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Solution Overview
Problem
Existing RF filters are not well-suited for higher frequencies and bandwidths required by future communications networks, particularly in 5G NR and WiFi bands, and existing acoustic wave resonators like SAW and BAW devices struggle to meet these demands.
Innovation Solution
The use of Transversely-Excited Film Bulk Acoustic Resonator (XBAR) structures, which incorporate interdigital transducers on a thin piezoelectric diaphragm to excite shear primary acoustic waves, providing high electromechanical coupling and frequency capability, are integrated into matrix filters with specific resonator configurations to enhance performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional acoustic wave resonators (SAW, BAW) are used, then the filter structure is well-established and manufacturable, but the frequency capability and bandwidth are insufficient for future communications networks
Solution Approach 1:
The patent changes the fundamental operating parameters of the resonator by transitioning from longitudinal wave modes (BAW) or surface waves (SAW) to shear horizontal wave modes in a thin film. This parameter change enables the resonator to operate at higher frequencies with better performance characteristics required for future communications networks
Solution Approach 2:
The patent replaces the conventional acoustic wave mechanisms (SAW, BAW) with a new mechanically-based approach using transversely-excited film bulk acoustic resonators. This substitution provides high electromechanical coupling and enables operation at higher frequencies while maintaining manufacturability
2Productivity
If wider communication channel bandwidths are implemented, then the data rates and network capacity increase, but the frequency requirements increase to higher bands
Solution Approach 1:
The XBAR resonator design provides a universal solution that can operate across multiple frequency bands and communication standards. The resonator structure is designed to be adaptable to different frequency requirements, making it suitable for both current and future communications networks including 5G NR bands N77 and N79
3Speed
If high frequency operation is achieved, then the bandwidth capability improves, but the filter rejection and isolation characteristics become more difficult to maintain
Solution Approach 1:
The patent utilizes mechanical vibration principles by exciting shear horizontal acoustic waves in the thin film resonator. This mechanical vibration approach provides high electromechanical coupling that maintains sharp resonance characteristics, enabling good rejection and isolation even at high frequencies
Solution Approach 2:
The resonator employs a composite structure with a thin piezoelectric film deposited on a substrate, creating a film bulk acoustic resonator. This composite material approach enables high frequency operation while maintaining the mechanical properties needed for good rejection and isolation characteristics
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
XBAR resonators enable high-frequency and wide-bandwidth RF filters, offering improved performance in terms of bandwidth and frequency capability, suitable for 5G NR bands N77, N79, and WiFi frequencies, with enhanced rejection and isolation characteristics.
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. The IDT includes a first set of parallel fingers, extending from a first busbar and a second set of parallel fingers extending from a second busbar. The first and second sets of parallel fingers are interleaved. A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm.
Implementation Method 2
A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm. XBAR resonators provide very high electromechanical coupling and high frequency capability.
Data Source
AI summary
Radio frequency filters. A radio frequency filter includes a substrate attached to a piezoelectric plate, portions of the piezoelectric plate forming a plurality of diaphragms spanning respective cavities in the substrate. A conductor pattern formed on the piezoelectric plate includes a plurality of interdigital transducers (IDTs) of a respective plurality of resonators, interleaved fingers of each IDT disposed on a respective diaphragm of the plurality of diaphragms. The conductor pattern connects the plurality of resonators in a matrix filter circuit including a first sub-filter and a second sub-filter, each sub-filter comprising two or more resonators from the plurality of resonators.