XBAR Resonator Oxide Strip Layout for Lower Anti-Resonance Loss
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Solution Overview
Problem
Current RF filters face challenges in achieving low loss near the anti-resonance frequency, which affects their performance in wireless communication systems, particularly at higher frequency bands.
Innovation Solution
The implementation of a transversely-excited film bulk acoustic resonator (XBAR) design that includes a substrate, a piezoelectric plate with a diaphragm spanning a cavity, interdigital transducers (IDTs), dielectric strips overlapping IDT fingers, and dummy fingers extending between neighboring IDT fingers, which helps in reducing acoustic energy leakage and improving performance near anti-resonance frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional IDT design is used, then the structure is simple, but acoustic energy leakage occurs near anti-resonance frequency causing high insertion loss
Solution Approach 1:
The IDT structure is segmented into three distinct parts: conventional IDT fingers for primary acoustic excitation, dielectric strips positioned adjacent to the fingers to confine acoustic energy, and dummy fingers extending from busbars to further reduce energy leakage. This segmentation allows each component to address specific aspects of energy loss independently while working together to achieve overall low insertion loss.
Solution Approach 2:
Dielectric strips are introduced as intermediary elements between the IDT fingers and the surrounding environment. These strips act as acoustic energy confiners that prevent energy leakage without directly interfering with the primary acoustic wave generation function of the IDT fingers, thus reducing insertion loss while maintaining structural clarity.
2Reliability
If dielectric strips and dummy fingers are added to reduce acoustic energy leakage, then insertion loss is reduced, but the device complexity increases
Solution Approach 1:
The dielectric strips and dummy fingers are strategically positioned only in specific locations where acoustic energy leakage is most problematic - adjacent to IDT fingers and extending from busbars into the aperture region. This localized approach improves reliability near anti-resonance frequencies without adding complexity across the entire device structure.
Solution Approach 2:
The IDT structure combines multiple material types with different acoustic properties: conductive materials for IDT fingers and busbars, dielectric materials for the strips, and piezoelectric substrate materials. This composite approach allows each material to be optimized for its specific function while working together to achieve superior overall performance and reliability.
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
This design enhances the Bode Q factor and admittance of the XBAR, leading to reduced insertion loss and improved filter performance across the desired frequency range, particularly around anti-resonance frequencies, thereby improving the overall efficiency of RF filters.
Implementation Method 1
a piezoelectric plate supported by the substrate
Implementation Method 2
an interdigital transducer (IDT) at the piezoelectric plate. The IDT includes interleaved IDT fingers extending from first and second busbars respectively
Implementation Method 3
acoustic resonator with a wide oxide strip and dummy fingers used in combination to achieve lower loss near the anti-resonance frequency of the XBARs
Implementation Method 4
one or more dielectric strips, each of the dielectric strips overlapping at least a portion of each of the IDT fingers and extending into a gap between a margin of the aperture and a corresponding one of the first busbar or the second busbar
Data Source
AI summary
An acoustic resonator includes a substrate, a piezoelectric plate supported by the substrate, and a diaphragm. The resonator further includes an interdigital transducer (IDT) having interleaved IDT fingers extending from first and second busbars respectively. Overlapping portions of the interleaved IDT fingers define an aperture of the acoustic resonator. The resonator further includes one or more dielectric strips, each of the one or more dielectric strips overlapping at least a portion of the IDT fingers and extending into a gap between a margin of the aperture and a corresponding one of the first busbar or the second busbar. The resonator further includes one or more dummy fingers, each of the dummy fingers extending from one of the first busbar or the second busbar at a position between neighboring IDT fingers and extending into the gap toward one of the one or more dielectric strips.