Acoustic resonator
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Solution Overview
Problem
Existing bulk acoustic resonators, such as XBARs, face challenges due to the fragility of submicron-thick Lithium Niobate membranes, limited piezo-coupling, and poor power-handling capabilities due to low thermal conductivity and bulk acoustic wave radiation.
Innovation Solution
The proposed solution involves a thin-film bulk acoustic resonator with a piezoelectric membrane attached to a solid, high-thermal-conductivity substrate, utilizing embedded vertical electrodes and an intermediate layer to enhance piezo-coupling and reduce acoustic coupling with the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a suspended piezoelectric membrane is used to achieve acoustic isolation, then bulk acoustic wave radiation is reduced, but the device becomes fragile and difficult to manufacture
Solution Approach 1:
A thin intermediate layer is introduced between the piezoelectric membrane and the substrate. This intermediate layer acts as an acoustic barrier that prevents bulk acoustic wave radiation into the substrate while providing mechanical support to the membrane, eliminating the need for complex suspension structures and cavity formations.
Solution Approach 2:
The piezoelectric membrane is directly bonded to the substrate through a thin intermediate layer, merging the acoustic isolation function with the mechanical support function. This eliminates the separate suspension structure and cavity formation processes, simplifying fabrication while maintaining acoustic isolation.
2Speed
If the piezoelectric membrane is made very thin to achieve resonance, then power handling capability deteriorates due to low thermal conductivity
Solution Approach 1:
The thin intermediate layer serves as a thermal interface that conducts heat away from the thin piezoelectric membrane to the substrate, enabling the membrane to be made very thin for high-frequency resonance while maintaining good power handling capability through enhanced heat evacuation.
3Reliability
If vertical electrodes are used to generate horizontal electric field, then piezo-coupling is enhanced, but device complexity increases
Solution Approach 1:
Vertical electrodes are used to generate horizontal electric field through the piezoelectric membrane, utilizing the vertical dimension to achieve horizontal field components that enhance piezo-coupling. This dimensional approach simplifies the electrode configuration while improving coupling efficiency.
4Strength
If the piezoelectric membrane is directly attached to the substrate, then mechanical robustness is improved, but acoustic coupling increases reducing quality factor
Solution Approach 1:
A thin intermediate layer is introduced between the piezoelectric membrane and substrate. This layer is thin enough to provide mechanical support and robustness but acts as an acoustic barrier to prevent bulk acoustic wave radiation into the substrate, thereby maintaining high quality factor.
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 configuration results in a robust device with improved power handling, increased piezo-coupling, and a higher quality factor, capable of operating effectively in the 5 GHz frequency range.
Implementation Method 1
use suspended piezoelectric crystalline membranes, such as Lithium Niobate (LN) of sub-micron thickness with a horizontal electric field to generate an A1 mode resonance
Implementation Method 2
the high thermal conductivity substrate provides a heat evacuation path below the piezoelectric membrane
Implementation Method 3
generate an A1 mode resonance with displacement in horizontal direction
Data Source
AI summary
An acoustic resonator is provided. The acoustic resonator may comprise a substrate, a piezoelectric membrane attached to the substrate, and a plurality of electrodes. The piezoelectric membrane presents a plurality of grooves, wherein two adjacent grooves define a ridge in between them. Each electrode is placed in a respective groove. Each electrode comprises two lateral parts, each lateral part covering at least partially a respective lateral wall of the groove.