SM-XBAR Filter Structure Using Multiple Piezoelectric Thicknesses
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Solution Overview
Problem
Existing RF filters using acoustic wave resonators are not well-suited for higher frequencies and wider bandwidths required by future communications networks, such as the 5G NR standard which includes bands n77 and n79 operating at frequencies between 3300 MHz and 5000 MHz.
Innovation Solution
The use of transversely-excited film bulk acoustic resonators (XBARs) and solidly-mounted transversely-excited film bulk acoustic resonators (SM-XBARs) with interdigital transducers and acoustic Bragg reflectors, which provide high electromechanical coupling and frequency capability, enabling the design of RF filters suitable for high-frequency communications bands.
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 achieve the higher frequencies and wider bandwidths 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) that operate in shear mode, enabling higher frequency operation (3300-5000 MHz) compared to conventional resonators. This parameter change in excitation mode and acoustic wave type directly addresses the frequency capability requirement for 5G networks
Solution Approach 2:
The patent employs composite material structures including piezoelectric films deposited on substrates with acoustic Bragg reflectors, creating a solidly-mounted configuration (SM-XBAR). This composite structure enables both high frequency operation and wide bandwidth performance by combining the piezoelectric effect with acoustic reflection principles
2Ease of manufacture
If single piezoelectric plate thickness is used, then manufacturing is simplified, but frequency separation between shunt and series resonators cannot be achieved
Solution Approach 1:
The patent applies different piezoelectric plate thicknesses to different functional regions: thicker plates for shunt resonators and thinner plates for series resonators. This local differentiation in thickness enables precise frequency separation between shunt and series modes while maintaining a relatively simple single-layer manufacturing process
Solution Approach 2:
The piezoelectric plate is segmented into regions of different thicknesses corresponding to different resonator types. This segmentation allows independent optimization of shunt and series resonator frequencies through selective thickness control during the deposition or thinning process
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 and SM-XBARs enable the creation of high-performance RF filters that can effectively handle the higher frequencies and wider bandwidths needed for future communications systems, improving system performance by enabling larger cell sizes, longer battery life, higher data rates, and greater network capacity.
Implementation Method 1
a piezoelectric material having parallel front and back surfaces
Implementation Method 2
an acoustic Bragg reflector sandwiched between the surface of the substrate and the back surface of the piezoelectric plate
Data Source
AI summary
A filter device is provided that includes a piezoelectric layer having a first portion having a first thickness and a second portion having a second thickness less than the first thickness; an acoustic multilayer reflector attached to the piezoelectric layer; and a conductor pattern on the first portion and the second portion of the piezoelectric layer. The conductor pattern includes a first IDT with interleaved fingers on the first portion, and a second IDT with interleaved fingers on the second portion. At least a portion of interleaved fingers of the second IDT has a width that is greater than or equal to 0.2 times a pitch of the second IDT and less than or equal to 0.3 times the pitch of the second IDT.