XBAR Matrix Filter Split-Die Layout for Wideband RF Filtering
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Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequencies and wider bandwidths required in future communication networks, such as those defined in the 5G NR standard, particularly for bands n77, n79, and millimeter wave frequencies, due to limitations in design and manufacturing methods.
Innovation Solution
The development of Transversely-Excited Film Bulk Acoustic Resonator (XBAR) matrix filters with split die sub-filters, which utilize a thin film conductor pattern on a piezoelectric plate with interleaved IDT fingers and different thicknesses of piezoelectric plate portions on separate substrates, allowing for high electromechanical coupling and reduced static capacitance, enabling effective filtering across higher frequency ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional acoustic wave resonators are used, then the filter structure is simple, but the frequency range is limited and bandwidth is narrow
Solution Approach 1:
The filter is divided into multiple sub-filters, each handling a specific frequency band. Each sub-filter contains resonators with specific electromechanical coupling coefficients designed for particular frequency ranges, allowing the overall filter to cover a wide bandwidth while maintaining structural simplicity through modular design
Solution Approach 2:
Different resonators within the filter are assigned different electromechanical coupling coefficients according to their specific frequency requirements. Resonators for lower frequency bands have different coupling characteristics than those for higher frequency bands, optimizing performance for each local frequency range while contributing to the overall wide bandwidth
2Adaptability or versatility
If resonator structures are enlarged to handle higher frequencies, then the frequency range improves, but the device area increases
Solution Approach 1:
The electromechanical coupling coefficient of resonators is adjusted as a key parameter to enable high-frequency operation without increasing physical size. By optimizing the coupling coefficient through material selection and structural design, the resonators achieve higher frequency responses while maintaining compact dimensions, directly addressing the contradiction between frequency capability and device area
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 matrix filters provide improved performance by achieving wider frequency ranges and reduced capacitance, enabling efficient filtering in high-frequency bands without the need for large resonator structures, thus addressing the limitations of existing technologies in handling higher frequencies and bandwidths.
Implementation Method 1
a piezoelectric plate with a back surface attached to different substrates and portions of the plate forming diaphragms spanning cavities in the substrates
Implementation Method 2
Interleaved fingers of IDTs are on the diaphragms. The different thickness portions of the piezoelectric plates may be on different substrates of different die
Data Source
AI summary
A radio frequency filter includes at least a first sub-filter and a second sub-filter connected in parallel between a first port and a second port. Each of the sub-filters has a piezoelectric plate having front and back surfaces, the back surface attached to a substrate, and portions of the piezoelectric plate forming diaphragms spanning respective cavities in the substrate. A conductor pattern is formed on the front surface of the plate, the conductor pattern includes interdigital transducers (IDTs) of a respective plurality of resonators, with interleaved fingers of each IDT disposed on a respective diaphragm of the plurality of diaphragms. A thickness of the portions of the piezoelectric plate of the first sub-filter is different from a thickness of the portions of the piezoelectric plate of the second sub-filter.