Symmetric XBAR Diaphragm With Back-Side Fingers for RF Filter Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequency communications bands above 3 GHz, as existing technologies face challenges in achieving optimal performance in terms of insertion loss, rejection, isolation, power handling, linearity, size, and cost for future wireless communication systems.
Innovation Solution
The development of Symmetric XBAR (Transversely-Excited Film Bulk Acoustic Resonator) structures with a symmetric diaphragm and back-side fingers to balance the mass of IDT fingers, which reduces spurious modes and enhances electromechanical coupling, power handling, and bandwidth, allowing for effective use in higher frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acoustic wave resonators are used for higher frequency bands above 3 GHz, then existing filter structures can be maintained, but performance in terms of insertion loss, rejection, isolation, power handling, linearity, and bandwidth deteriorates
Solution Approach 1:
The patent applies asymmetry by introducing a symmetric diaphragm structure with mass-balancing features. Specifically, a first mass balancing structure is added to the first diaphragm and a second mass balancing structure to the second diaphragm, creating an asymmetric mass distribution that balances the overall resonator mass. This resolves the contradiction by enabling conventional filter structures to achieve superior performance in higher frequency bands through controlled asymmetric mass balancing.
Solution Approach 2:
The patent changes physical parameters of the resonator structure, including adding mass balancing structures with specific densities and volumes, adjusting diaphragm thicknesses, and modifying cavity dimensions. These parameter changes optimize the resonator's electromechanical coupling and spurious mode characteristics, enabling reliable operation in higher frequency bands above 3 GHz while maintaining conventional filter architectures.
2Reliability
If mass balancing structures are added to the diaphragm, then spurious modes are reduced and electromechanical coupling is enhanced, but device complexity increases
Solution Approach 1:
The patent merges the mass balancing function with the existing diaphragm structure by integrating mass balancing structures directly into the diaphragm assembly. The first mass balancing structure is coupled to the first diaphragm and the second mass balancing structure to the second diaphragm, combining multiple functions (support, acoustic isolation, and mass balancing) into a unified structure. This reduces device complexity while achieving spurious mode reduction and enhanced electromechanical coupling.
3Power
If the resonator mass is balanced, then power handling and bandwidth are improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies local quality by positioning mass balancing structures at specific locations on the diaphragms rather than uniformly distributing mass. The first mass balancing structure is located on the first diaphragm and the second on the second diaphragm, with specific densities and volumes tailored to local mass distribution requirements. This localized approach achieves accurate mass balancing and improved power handling while reducing overall manufacturing precision requirements compared to uniform mass distribution methods.
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 symmetric XBAR design significantly reduces spurious modes over a wide frequency band, improves power handling, and increases electromechanical coupling, enabling the design of high-performance microwave and millimeter-wave filters with improved bandwidth and reduced spurious content.
Implementation Method 1
A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm
Implementation Method 2
back-side fingers to balance the mass of IDT fingers, which reduces spurious modes
Implementation Method 3
The Transversely-Excited Film Bulk Acoustic Resonator (XBAR) is an acoustic resonator structure for use in microwave filters
Data Source
AI summary
Acoustic resonator devices and filters are disclosed. An acoustic resonator includes a substrate having a surface. A back surface of a single-crystal piezoelectric plate is attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm spanning a cavity in the substrate. An interdigital transducer (IDT) is formed on a front surface of the piezoelectric plate with interleaved IDT fingers of the IDT disposed on the diaphragm. Back-side fingers are formed the back surface of the diaphragm. A pitch of the IDT fingers and a pitch of the back-side fingers are substantially equal.