SM XBAR Resonator Structure for RF Filters Above 3 GHz
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Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequency communications bands above 3 GHz, such as those proposed for future wireless communication systems, as they fail to provide optimal performance in terms of insertion loss, rejection, isolation, power handling, linearity, size, and cost.
Innovation Solution
The development of solidly-mounted transversely-excited film bulk acoustic resonators (SM XBARs) that utilize a thin film conductor pattern on a piezoelectric plate with an interdigital transducer (IDT) and an acoustic Bragg reflector, capable of exciting shear-mode acoustic waves, which are particularly suited for frequencies above 3 GHz and are designed to improve filter performance in RF systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acoustic wave resonators are used for RF filters, then existing technologies can be maintained, but performance is not optimal for frequencies above 3 GHz in terms of insertion loss, rejection, isolation, power handling, linearity, size, and cost
Solution Approach 1:
The patent changes the fundamental operating parameters by transitioning from longitudinal acoustic waves to transverse shear-mode acoustic waves. This parameter change enables the resonator to operate effectively at higher frequencies (above 3 GHz) while improving multiple performance metrics simultaneously including insertion loss, rejection, isolation, power handling, and linearity. The transverse excitation mode fundamentally alters how acoustic energy is generated and propagated within the piezoelectric substrate.
Solution Approach 2:
The patent employs composite material structures including piezoelectric substrates (such as lithium niobate or lithium tantalate) combined with specific electrode configurations and acoustic Bragg reflectors. These composite structures are specifically designed to support and enhance transverse shear-mode acoustic waves, creating a resonator system that is optimized for high-frequency operation with improved performance characteristics that cannot be achieved with conventional single-material resonators.
2Productivity
If wider communication channel bandwidths are enabled, then system performance is improved, but device complexity increases
Solution Approach 1:
The patent segments the acoustic wave propagation path by introducing acoustic Bragg reflectors that create distinct resonant cavities. These reflectors divide the piezoelectric substrate into functional regions that support specific resonant modes, enabling the device to achieve wider bandwidth through multiple resonant frequencies while maintaining a relatively simple overall structure. The segmentation allows independent optimization of different frequency channels.
Solution Approach 2:
The transverse-excited film bulk acoustic resonator is designed with multi-functionality to handle multiple communication channels and frequency bands simultaneously. The resonator structure can support both series and shunt resonant modes, enabling it to function as different filter elements (series resonators, shunt resonators) within the same device, thereby achieving wide bandwidth communication capabilities without proportionally increasing device complexity.
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
SM XBARs effectively enhance RF filter performance by enabling wider communication channel bandwidths, improving system performance metrics like insertion loss, rejection, and power handling, while being compact and cost-effective, thus addressing the limitations of existing technologies for higher frequency applications.
Implementation Method 1
a piezoelectric plate with a thin film conductor pattern formed on a surface of the piezoelectric plate, the thin film conductor pattern including interdigital transducers (IDTs)
Implementation Method 2
an acoustic Bragg reflector
Data Source
AI summary
Resonator and filter devices and methods of fabrication. A resonator chip includes a substrate, a piezoelectric plate, and an acoustic Bragg reflector between the substrate and a back surface of the piezoelectric plate. A conductor pattern on a front surface of the piezoelectric plate includes a first plurality of contact pads and an interdigital transducer (IDT). The IDT and the piezoelectric plate are configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode within the piezoelectric plate. The acoustic Bragg reflector is configured to reflect the shear primary acoustic mode. An interposer has a second plurality of contact pads on a back surface. A seal connects a perimeter of the piezoelectric plate to a perimeter of the interposer. Each contact pad of the first plurality of contact pads is directly connected to a respective contact pad of the second plurality of contact pads.