XBAR IDT Narrow-Gap Layout for Spurious Mode Suppression
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Solution Overview
Problem
Existing RF filters using acoustic wave resonators are not well-suited for higher frequencies and wider bandwidths required by future communications networks, particularly in bands above 3 GHz such as n77 and n79, and millimeter wave frequencies.
Innovation Solution
The development of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with narrow gaps between busbars and ends of interdigital transducer (IDT) fingers, which reduces spurious modes and improves admittance performance, enabling effective operation at higher frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional acoustic wave resonators are used, then existing filter designs can be maintained, but they are not well-suited for higher frequencies and wider bandwidths required by future communications networks
Solution Approach 1:
The patent changes the fundamental operating parameters of the resonator by transitioning from longitudinal to transverse acoustic wave excitation. This parameter change enables the resonator to operate effectively at higher frequencies (above 3 GHz) and wider bandwidths, directly addressing the adaptability requirement for future communications networks while maintaining reliability through the inherent properties of transverse wave propagation in thin films
2Manufacturing precision
If standard gap distances between busbars and IDT fingers are used, then manufacturing is simpler, but spurious modes are generated that degrade admittance performance
Solution Approach 1:
The patent applies local quality by creating a non-uniform gap structure where the gap between busbars and IDT fingers is specifically reduced at critical locations. This localized modification of the gap distance at the busbar-IDT interface suppresses spurious modes and improves admittance performance without requiring changes to the entire resonator structure, thus balancing manufacturing feasibility with performance enhancement
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 with narrow busbar-electrode gaps demonstrate improved performance by reducing spurious modes and enhancing admittance, making them suitable for high-frequency applications such as 5G NR bands and millimeter wave communications.
Implementation Method 1
An IDT 130 includes a first busbar 132, a second busbar 134, and a plurality of interleaved fingers 136 formed on the surface of the piezoelectric plate 110
Implementation Method 2
XBAR resonators provide very high electromechanical coupling and high frequency capability
Implementation Method 3
A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm
Data Source
AI summary
An acoustic resonator has a piezoelectric plate attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm spanning a cavity in the substrate. An interdigital transducer (IDT) formed on the plate has interleaved fingers on the diaphragm with first parallel fingers extending from a first busbar and second parallel fingers extending from a second busbar of the IDT. A distance between the interleaved fingers defines an IDT pitch. The IDT has a gap distance between the ends of the first plurality of parallel fingers and the second busbar, and between the ends of the second plurality of parallel fingers and the first busbar; and the gap distance is less than ⅔ times the IDT pitch.