XBAR Electrode Geometry for Spurious Mode Suppression
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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 bandpass filters capable of handling higher transmit power and wider communication channel bandwidths.
Innovation Solution
The use of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with an irregular hexagon IDT finger cross-sectional shape, which enhances the Q-factor and reduces spurious modes, allowing for improved performance in high-frequency applications by optimizing the IDT finger geometry to minimize internal resonances and increase thermal and electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional IDT finger geometry is used, then manufacturing is simpler, but spurious modes increase and Q-factor decreases
Solution Approach 1:
The patent applies asymmetry by transitioning from conventional symmetric rectangular IDT finger cross-sections to asymmetric irregular hexagon cross-sections. This asymmetric geometry disrupts the symmetry of spurious acoustic modes, preventing their formation and improving the Q-factor of the resonator.
Solution Approach 2:
The patent changes geometric parameters of the IDT fingers by defining specific cross-sectional dimensions (widths w1, w2, w3 and heights h1, h2) that create the irregular hexagon shape. These parameter changes optimize the acoustic field distribution and eliminate spurious modes while maintaining manufacturability.
2Productivity
If wider bandwidth is implemented, then communication capacity increases, but filter design complexity increases
Solution Approach 1:
The patent utilizes parameter changes in the IDT finger geometry (irregular hexagon cross-section with optimized dimensions) to enhance the electromechanical coupling coefficient. This allows for wider bandwidth operation while maintaining manageable filter design complexity through improved fundamental mode performance.
3Speed
If higher frequency operation is implemented, then communication capacity increases, but spurious modes and losses increase
Solution Approach 1:
The asymmetric irregular hexagon cross-section prevents the formation of spurious acoustic modes that would otherwise be excited at higher frequencies. This geometric asymmetry decouples the fundamental resonant mode from spurious modes, reducing signal loss and improving reliability in high-frequency 5G NR applications.
Solution Approach 2:
The patent applies local quality optimization by creating regions of different acoustic impedance within the IDT finger structure through the irregular hexagon cross-section. This local variation in acoustic properties helps confine the fundamental mode while suppressing spurious mode propagation, reducing losses at high frequencies.
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 XBARs with irregular hexagon IDT fingers demonstrate improved frequency versus admittance characteristics, reducing spurious modes and increasing the Q-factor, thereby enhancing the performance of RF filters in high-frequency applications, particularly in the 5G NR frequency bands.
Implementation Method 1
The XBARs with irregular hexagon IDT fingers demonstrate improved frequency versus admittance characteristics, reducing spurious modes
Implementation Method 2
increasing the Q-factor, thereby enhancing the performance of RF filters in high-frequency applications
Implementation Method 3
optimizing the IDT finger geometry to minimize internal resonances and increase thermal and electrical conductivity
Data Source
AI summary
Acoustic resonators and filter devices, and method of making acoustic resonators and filter devices. An acoustic resonator includes a substrate having a surface and a piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm that spans a cavity in the substrate. An interdigital transducer (IDT) is formed on the front surface of the piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm. The interleaved fingers have an irregular hexagon cross-sectional shape.