XBAR RF Filter Structure for Wideband 5G Frequency Tuning
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Solution Overview
Problem
Existing RF filters using acoustic wave resonators are not well-suited for higher frequencies and bandwidths required by future communications networks, such as the 5G NR standard and WiFi bands at 5 GHz and 6 GHz, due to limitations in design and performance.
Innovation Solution
The use of transversely-excited film bulk acoustic resonators (XBARs) with specific piezoelectric materials and dielectric layers to achieve high piezoelectric coupling and frequency tuning, allowing for the design of filters capable of handling higher frequencies and wider bandwidths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional acoustic wave resonators are used, then the filter structure is simple and easy to manufacture, but the resonance frequency and bandwidth are limited and not suitable for higher frequencies above 3 GHz
Solution Approach 1:
The patent changes the fundamental operating parameters of the resonator by transitioning from surface acoustic wave (SAW) mode to bulk acoustic wave (BAW) mode in a transversely excited configuration. This parameter change enables operation at frequencies above 3 GHz while maintaining manufacturability through established semiconductor fabrication processes. The XBAR structure achieves higher resonance frequencies by utilizing bulk wave propagation rather than surface wave propagation, fundamentally altering the resonator's operational characteristics.
Solution Approach 2:
The invention employs composite material structures including piezoelectric films deposited on substrate plates, with multiple layers having different acoustic and electrical properties. The resonator comprises a piezoelectric plate bonded to a substrate, with interdigital transducers formed on the plate surface. This composite structure enables simultaneous optimization of mechanical support, acoustic wave propagation, and electrical excitation/detection functions, achieving high-frequency operation with controlled impedance and minimal losses.
2Adaptability or versatility
If the filter is designed for wider bandwidth, then the communication channel capacity increases, but the filter complexity and number of resonators required increases
Solution Approach 1:
The patent introduces tunability and adaptability to the filter design through variable capacitor configurations and adjustable matching networks. The filter can dynamically adjust its bandwidth and center frequency to accommodate different communication standards and channel requirements. This dynamic capability allows a single filter design to serve multiple bandwidth requirements without increasing physical complexity, as the electrical tuning mechanisms provide flexible adaptation.
Solution Approach 2:
The XBAR resonator design provides universal applicability across multiple frequency bands and communication standards. The resonator structure can be configured for different operating frequencies and bandwidths through geometric parameter adjustments rather than requiring fundamentally different resonator types. This multi-functionality reduces overall system complexity by using a single resonator platform for diverse communication requirements.
3Reliability
If higher resonance frequencies are achieved, then the filter performance for 5G NR bands improves, but the manufacturing precision and material quality requirements increase
Solution Approach 1:
The patent replaces mechanical adjustment and trimming mechanisms with precisely controlled deposition and lithography processes fabricated using standard semiconductor manufacturing techniques. The resonator dimensions, piezoelectric layer thicknesses, and electrode geometries are controlled through automated fabrication processes rather than mechanical post-processing. This substitution of mechanical systems with automated fabrication processes maintains high precision while improving manufacturability and consistency across production batches.
Solution Approach 2:
The invention optimizes material parameters such as piezoelectric coupling coefficients, acoustic velocity, and dielectric constants by selecting specific crystal orientations and material compositions. These parameter optimizations enable higher Q-factors and more stable resonance frequencies at operating frequencies above 3 GHz. The patent carefully controls material parameters through selective deposition conditions and thermal processing to achieve the required performance while maintaining compatibility with existing fabrication capabilities.
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 provide improved performance in RF filters by enabling high piezoelectric coupling and frequency tuning, facilitating the development of filters suitable for 5G NR bands N77, N79, and WiFi frequencies with reduced viscous losses and enhanced bandwidth.
Implementation Method 1
high piezoelectric coupling
Implementation Method 2
acoustic wave resonators
Data Source
AI summary
Filter devices are disclosed. A filter device includes a piezoelectric plate comprising a supported portion, a first diaphragm, and a second diaphragm. The supported portion is attached to a substrate and the first and second diaphragms spans respective cavities in the substrate. A first interdigital transducer (IDT) has interleaved fingers on the first diaphragm. A second interdigital transducer (IDT) has interleaved fingers on the second diaphragm. A first dielectric layer is between the interleaved fingers of the first IDT, and a second dielectric layer is between the interleaved fingers of the second IDT. A thickness of the first dielectric layer is greater than a thickness of the second dielectric layer. The piezoelectric plate and the first and second IDTs are configured such that radio frequency signals applied to first and second IDTs excite primary shear acoustic modes in the respective diaphragms.