XBAR Resonator Package With LTCC Interposer for Wideband RF Filtering
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Solution Overview
Problem
Current RF filters are not well-suited for higher frequency bands proposed for future communications networks, particularly for 5G cellular service and 5 GHz/6 GHz WiFi, requiring filters with wider bandwidth and improved performance at frequencies above 3 GHz.
Innovation Solution
The development of transversely-excited film bulk acoustic resonators (XBARs) using a thin film conductor pattern on a piezoelectric plate, with a substrate and interdigital transducer design that excites a bulk shear mode, enabling high-frequency and wide-bandwidth RF filtering capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional RF filters are used, then current frequency bands are supported, but they are not suitable for higher frequency bands (above 3 GHz) required for future communications networks
Solution Approach 1:
The patent changes the operating parameters of the resonator by using transversely-excited film bulk acoustic resonators (XBARs) with interdigital transducers that operate at higher frequencies (above 3 GHz, including 5G and WiFi bands). The resonator structure and excitation method are modified to achieve high-frequency operation with wide bandwidth capability
Solution Approach 2:
The patent replaces conventional RF filter mechanisms with acoustic wave-based XBAR resonators that use piezoelectric materials and acoustic wave propagation to achieve filtering functionality. This substitution enables high-frequency operation and wide bandwidth performance that conventional electrical filters cannot achieve
2Adaptability or versatility
If wider bandwidth filtering is implemented, then high-frequency communication requirements are met, but filter design complexity increases
Solution Approach 1:
The patent uses mechanically vibrating acoustic waves in piezoelectric materials to achieve wide bandwidth filtering. The XBAR resonators utilize bulk acoustic waves that propagate through the piezoelectric substrate, providing inherent wide bandwidth characteristics without requiring complex multi-resonator designs
Solution Approach 2:
The patent achieves wide bandwidth by changing the fundamental operating parameters of the resonator - using transverse excitation mode and bulk acoustic waves instead of surface waves, which inherently provides broader frequency response and reduced sensitivity to parameter variations
3Reliability
If piezoelectric coupling is increased, then high-frequency performance improves, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs self-aligned fabrication processes where the interdigital transducer fingers are automatically positioned using standard photolithography alignment marks on the piezoelectric substrate. The high piezoelectric coupling is achieved through this self-alignment mechanism, which reduces the need for ultra-precise manual positioning while maintaining high-frequency performance
Solution Approach 2:
The patent performs preliminary alignment mark formation on the piezoelectric substrate before depositing the interdigital transducer electrodes. This preliminary action establishes the reference framework that guides subsequent electrode patterning, ensuring high coupling efficiency without requiring extreme precision in the final electrode positioning steps
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
XBARs provide improved performance by achieving high piezoelectric coupling and reduced viscous losses, enabling the design of microwave and millimeter-wave filters with appreciable bandwidth and enhanced filtering capabilities for future communication systems.
Implementation Method 1
a thin film conductor pattern on a piezoelectric plate, with a substrate and interdigital transducer design that excites a bulk shear mode
Implementation Method 2
transversely-excited film bulk acoustic resonators (XBARs) ... excites a bulk shear mode, enabling high-frequency and wide-bandwidth RF filtering capabilities
Data Source
AI summary
Acoustic resonator devices and filters are disclosed. A piezoelectric plate is attached to a substrate, a portion of the piezoelectric plate forming a diaphragm spanning a cavity in the substrate. A first conductor pattern is formed on a surface of the piezoelectric plate. The first conductor pattern includes interleaved fingers of an interdigital transducer disposed on the diaphragm, and a first plurality of contact pads. A second conductor pattern is formed on a back surface of an interposer, the second conductor pattern including a second plurality of contact pads. The interposer has layers of a LTCC circuit card, at least one layer of the tape comprising printed conductors. A plurality of conductive balls directly bonds the first plurality of contact pads formed on the plate to respective contact pads of the second plurality of contact pads formed on the interposer.