XBAR Resonator Plate Thickness and Multi-Pitch IDT for Spurious Mode Control
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Solution Overview
Problem
Current RF filters, particularly those using acoustic wave resonators, are not well-suited for higher frequencies and wider bandwidths required in future communication networks, such as the 5G NR standard, which necessitates the development of more effective transversely-excited film bulk acoustic resonators (XBARs) capable of handling higher power and providing improved frequency selectivity and reduced spurious modes.
Innovation Solution
The design of transversely-excited film bulk acoustic resonators (XBARs) with optimized electrode thickness, pitch, and dielectric layer thickness, utilizing materials like lithium niobate, and incorporating features such as periodic etched holes and multi-mark interdigital transducers to minimize spurious modes and enhance thermal conductivity, allowing for efficient heat dissipation and improved performance at higher frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional acoustic wave resonators are used, then existing RF filter performance is maintained, but they are not suitable for higher frequencies and wider bandwidths required in 5G NR
Solution Approach 1:
The patent changes the fundamental operating parameters of the resonator by transitioning from longitudinal to transverse excitation mode, enabling operation at higher frequencies (3 GHz to 100 GHz) required for 5G NR. The XBAR structure with interdigital transducers creates shear horizontal waves that propagate transversely through the piezoelectric plate, fundamentally altering the frequency-response characteristics to meet 5G requirements
Solution Approach 2:
The invention employs composite material structures including piezoelectric plates (lithium niobate, lithium tantalate, gallium nitride) combined with metal interdigital transducers and dielectric layers. This composite approach enables both high-frequency operation and efficient thermal management, addressing the reliability requirement for 5G NR applications
2Power
If higher power handling is achieved, then power capacity increases, but thermal management becomes more challenging
Solution Approach 1:
The patent introduces thermal management intermediaries including heat sink structures, thermally conductive substrates, and cooling channels that act as mediators between the high-power resonator elements and the environment. These intermediaries facilitate efficient heat transfer while maintaining the high power handling capability of the XBAR device
Solution Approach 2:
The invention replaces conventional thermal management approaches with advanced heat dissipation mechanisms including phonon engineering in piezoelectric materials, thermal conduction through specialized substrate structures, and potentially active cooling systems, substituting passive thermal management with more effective thermal control mechanisms
3Measurement precision
If spurious modes are reduced, then frequency selectivity improves, but resonator design complexity increases
Solution Approach 1:
The patent applies local quality optimization by carefully designing the local geometry of interdigital transducer fingers, their spacing, and the piezoelectric plate thickness in specific regions to suppress spurious modes. By optimizing local structural parameters rather than redesigning the entire resonator, frequency selectivity is improved while managing design complexity
Solution Approach 2:
The invention employs dynamic design elements such as variable finger spacing, non-uniform electrode patterns, and adjustable biasing mechanisms that allow the resonator to dynamically suppress spurious modes while maintaining primary resonance performance. This dynamic approach enables frequency selectivity improvement without permanently increasing 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
The optimized XBARs demonstrate enhanced performance in terms of reduced spurious modes, increased power handling, and improved frequency selectivity, making them suitable for high-frequency applications like 5G NR, while maintaining low thermal impedance and efficient heat removal.
Implementation Method 1
A time-varying electric field generated by an interdigital transducer (IDT) disposed on the piezoelectric plate excites a shear horizontal acoustic wave in the piezoelectric plate
Data Source
AI summary
Acoustic resonators and filter devices. An acoustic resonator including a piezoelectric plate having front and back surfaces, a portion of the piezoelectric plate forming a diaphragm, and a conductor pattern on the front surface, the conductor pattern including an interdigital transducer (IDT), fingers of the IDT on the diaphragm. A thickness between the front and back surfaces is greater than or equal to 200 nm and less than or equal to 1000 nm. The IDT comprises a first portion having a first pitch and a first mark and a second portion having a second pitch and a second mark not equal to the first pitch and first mark.