XBAR Multi-Port Filter with Variable Diaphragm Thicknesses
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Solution Overview
Problem
Existing RF filters using acoustic wave resonators are not well-suited for higher frequencies and bandwidths required in future communications networks, particularly in 5G NR bands and Wi-Fi frequencies above 3 GHz.
Innovation Solution
The use of transversely-excited film bulk acoustic resonators (XBARs) with multiple diaphragm thicknesses and dielectric layers to achieve frequency separation between shunt and series resonators, enabling the design of high-frequency bandpass filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional acoustic wave resonators are used, then the filter structure is simple, but the frequency range is limited and cannot handle higher frequencies above 3 GHz
Solution Approach 1:
The resonator structure is segmented into multiple sections with different diaphragm thicknesses. Each section has a specific thickness (e.g., first section with thickness t1, second section with thickness t2) that enables different resonant frequencies, allowing the filter to operate at higher frequencies while maintaining a manageable structural complexity through modular design
Solution Approach 2:
The invention introduces thickness variation as an additional dimensional parameter to control resonant frequency. By varying the diaphragm thickness in different sections rather than relying solely on lateral dimensions, the filter achieves higher operating frequencies above 3 GHz without proportionally increasing the overall device footprint and structural complexity
2Adaptability or versatility
If multiple diaphragm thicknesses are used to achieve frequency separation, then frequency tuning capability is improved, but manufacturing complexity increases
Solution Approach 1:
Different sections of the resonator have locally optimized diaphragm thicknesses tailored to their specific frequency requirements. The first section has thickness t1 optimized for its resonant frequency, while the second section has thickness t2 optimized for its frequency, allowing each local region to contribute to the overall frequency tuning capability without requiring the entire structure to be redesigned
Solution Approach 2:
The invention changes the physical parameter of diaphragm thickness to achieve frequency separation and tuning. By systematically varying this parameter across different sections (t1, t2, etc.), the filter achieves enhanced adaptability and frequency tuning capability. The manufacturing complexity is managed by implementing these parameter changes through standardized fabrication processes that can handle multiple thickness levels
3Measurement precision
If dielectric layers are added for frequency control, then frequency precision is improved, but device complexity increases
Solution Approach 1:
Dielectric layers are introduced as intermediary elements between the metal electrodes and the substrate. These layers (with dielectric constants k1, k2, etc.) act as mediators that precisely control the resonant frequencies by adjusting the electrical field distribution and capacitance, thereby improving frequency precision without requiring direct modification of the resonator geometry
Solution Approach 2:
The filter structure employs composite material layers including metal electrodes, dielectric layers with specific constants, and piezoelectric substrates. This composite construction allows precise frequency control through the selection and combination of materials with different electrical and mechanical properties, achieving high frequency precision while managing overall device complexity through material rather than structural 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
This approach allows for the creation of RF filters that can effectively handle the higher frequencies and wider bandwidths needed for future communication systems, providing improved performance and tuning capabilities.
Implementation Method 1
a radio frequency or microwave signal applied between the two busbars excites an acoustic wave within the piezoelectric plate
Implementation Method 2
excites an acoustic wave within the piezoelectric plate
Implementation Method 3
the acoustic wave resonates at a resonant frequency determined by the thickness of the piezoelectric plate
Data Source
AI summary
Filter devices and methods are disclosed. A single-crystal piezoelectric plate is attached to substrate, portions of the piezoelectric plate forming a plurality of diaphragms spanning respective cavities in the substrate. A conductor pattern formed on the piezoelectric plate defines a low band filter including low band shunt resonators and low band series resonators and a high band filter including high band shunt resonators and high band series resonators. Interleaved fingers of interdigital transducers (IDTs) of the low band shunt resonators are disposed on respective diaphragms having a first thickness, interleaved fingers of IDTs of the high band series resonators are disposed on respective diaphragms having a second thickness less than the first thickness, and interleaved fingers of IDTs of the low band series resonators and the high band shunt resonators are disposed on respective diaphragms having thicknesses intermediate the first thickness and the second thickness.