Multi-Pitch XBAR Resonator for 5G Spurious Mode Suppression
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Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequencies and bandwidths required in future communications networks, particularly for 5G NR standards, which demand bandpass filters capable of handling higher transmit power and wider communication channel bandwidths.
Innovation Solution
The use of a Transversely-Excited Film Bulk Acoustic Resonator (XBAR) with a multi-pitch interdigital transducer (IDT) design, which excites a shear primary acoustic wave in a piezoelectric diaphragm, providing high electromechanical coupling and frequency capability, and effectively reduces spurious modes by varying the pitch along the length of the IDT.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional acoustic wave resonators are used, then existing filter designs can be maintained, but they cannot handle higher frequencies and bandwidths required for 5G NR standards
Solution Approach 1:
The patent changes the fundamental operating parameters of the resonator by transitioning from longitudinal acoustic waves to transverse shear waves, enabling operation at higher frequencies (3 GHz to 100 GHz) while maintaining performance reliability through the unique properties of shear wave propagation in thin film piezoelectric layers
2Object-generated harmful factors
If single-pitch IDT is used, then manufacturing is simpler, but spurious modes cannot be effectively suppressed
Solution Approach 1:
The IDT is segmented into multiple regions with different pitch values, where each region generates acoustic waves at different frequencies. This segmentation causes spurious modes from different regions to occur at different frequencies, allowing them to be suppressed through destructive interference while maintaining a relatively simple overall IDT structure
Solution Approach 2:
Different portions of the IDT are assigned different local pitch characteristics to optimize performance at specific frequency ranges. The first region has a first pitch for generating primary acoustic waves, while the second region has a second pitch for suppressing spurious modes, with each region's pitch optimized for its specific function
3Power
If higher transmit power is handled, then 5G NR standards are met, but existing resonators lack the power handling capability
Solution Approach 1:
The resonator design changes the acoustic wave mode from longitudinal to transverse shear waves, which have different propagation characteristics and higher power handling capability. This parameter change enables the device to reliably handle the higher transmit power levels required by 5G NR standards
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 XBAR with a multi-pitch IDT achieves reduced spurious modes and improved filter performance, allowing for effective operation in higher frequency bands, such as those defined by the 5G NR standard, with enhanced power handling and bandwidth capabilities.
Implementation Method 1
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
Transversely-Excited Film Bulk Acoustic Resonator (XBAR) with a multi-pitch interdigital transducer (IDT) design, which excites a shear primary acoustic wave in a piezoelectric diaphragm
Data Source
AI summary
There are disclosed acoustic resonators and methods of fabricating acoustic resonators. An acoustic resonator includes a piezoelectric plate having front and back surfaces, the back surface facing a substrate. A portion of the piezoelectric plate forms a diaphragm spanning a cavity in the substrate. A conductor pattern on the front surface includes a multi-pitch interdigital transducer (IDT) with interleaved fingers of the IDT on the diaphragm.