Solidly Mounted 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, such as those proposed for future wireless communication systems, which require improved performance to support wider channel bandwidths and higher frequencies beyond the current LTE specification.
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 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 be integrated into RF filters for communications systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional acoustic wave resonators are used, then the filter works for current LTE frequency bands, but the filter performance degrades for higher frequency bands above 3 GHz
Solution Approach 1:
The patent changes the fundamental operating parameters of the resonator by transitioning from longitudinal wave modes to transverse shear wave modes. This parameter change enables the resonator to operate effectively at higher frequencies above 3 GHz while maintaining filter performance, thus resolving the contradiction between frequency band adaptability and high-frequency reliability
Solution Approach 2:
The patent substitutes the conventional longitudinal acoustic wave mechanism with a transverse shear wave mechanism. This mechanical substitution fundamentally alters how acoustic energy is generated and propagated, enabling superior performance at higher frequency bands while maintaining compatibility with standard filter architectures
2Productivity
If the resonator supports higher frequencies and wider bandwidths, then communication system performance improves, but the device complexity increases
Solution Approach 1:
The resonator structure is segmented into distinct functional layers: piezoelectric substrate, piezoelectric film, conductor pattern, and acoustic reflector. This segmentation allows each component to be optimized independently for high-frequency operation while maintaining overall structural simplicity, enabling wide bandwidth support without proportionally increasing device complexity
Solution Approach 2:
The resonator design achieves multi-functionality by simultaneously providing high-frequency operation, wide bandwidth support, and efficient acoustic confinement within a single integrated structure. The transverse shear wave mode inherently provides both the frequency extension and the acoustic confinement needed, reducing the need for additional complex components
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 SM XBARs provide enhanced performance for RF filters, enabling better frequency selectivity and power handling, making them suitable for higher frequency bands, thereby improving communication system performance by supporting wider bandwidths and higher data rates.
Implementation Method 1
a piezoelectric plate with a thin film conductor pattern formed on a surface of the piezoelectric plate including interdigital transducers configured to excite shear acoustic waves in the piezoelectric plate
Implementation Method 2
an acoustic Bragg reflector sandwiched between a surface of the substrate and the back surface of the piezoelectric plate
Data Source
AI summary
Methods of fabricating resonator and filter devices. A first conductor pattern formed on a front surface of a 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. An acoustic Bragg reflector is between a substrate and a back surface of the piezoelectric plate, the acoustic Bragg reflector configured to reflect the shear primary acoustic mode. A second conductor pattern including a second plurality of contact pads is formed on a back surface of the interposer. The first plurality of contact pads is directly connected to respective contact pads of the second plurality of contact pads. A perimeter of the acoustic resonator chip is sealed to a perimeter of the interposer.