XBAR Electrode Thickness and Pitch Tuning 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
1Reliability
If conventional acoustic wave resonators are used, then existing technology is maintained, but frequency selectivity and power handling for 5G NR are insufficient
Solution Approach 1:
The patent optimizes specific parameters of the XBAR including electrode thickness (0.5-2.0 times the piezoelectric layer thickness), pitch (0.5-2.0 times the piezoelectric layer thickness), and dielectric layer thickness to enhance frequency selectivity and enable 5G NR applications. These parameter adjustments transform the resonator performance to meet higher frequency and bandwidth requirements.
2Power
If higher power handling is implemented, then power capability increases, but thermal management becomes more challenging
Solution Approach 1:
The patent introduces a dielectric layer as an intermediary thermal management component between the piezoelectric layer and the substrate. This dielectric layer with optimized thickness serves as a thermal pathway that facilitates heat dissipation from the interdigital transducer, enabling high power handling while controlling thermal impedance through its material properties and geometric configuration.
3Use of energy by moving object
If electrode dimensions are increased to improve coupling, then spurious modes increase
Solution Approach 1:
The patent establishes specific parameter relationships where electrode thickness is maintained between 0.5-2.0 times the piezoelectric layer thickness and electrode pitch is maintained between 0.5-2.0 times the piezoelectric layer thickness. These constrained parameter ranges optimize electromechanical coupling through the piezoelectric layer while simultaneously suppressing spurious modes by preventing excessive electrode dimensions that would excite unwanted acoustic resonances.
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 frequency selectivity, reduced spurious modes, and improved power handling capabilities, making them suitable for high-frequency applications like 5G NR, while maintaining low thermal impedance and efficient heat removal, thus addressing the limitations of existing technologies.
Implementation Method 1
an interdigital transducer (IDT) formed on a surface of a piezoelectric plate
Implementation Method 2
acoustic resonator structure for use in microwave filters
Implementation Method 3
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
Data Source
AI summary
Acoustic resonators and filter devices. An acoustic resonator includes 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 of the interleaved fingers is greater than or equal to 0.85 times a thickness of the piezoelectric plate and less than or equal to 2.5 times the thickness of the piezoelectric plate. 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.