Film Bulk Acoustic Resonator Interdigital Frame for Parasitic Wave Reflection
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Solution Overview
Problem
Conventional film bulk acoustic resonators suffer from low quality factor due to the excitation of transverse parasitic acoustic waves, which carry away energy from the resonant region.
Innovation Solution
The film bulk acoustic resonator incorporates an interdigital protrusion frame on the top electrode, which reflects transverse Rayleigh-Lamb waves by utilizing the difference in acoustic impedance, thereby reducing energy leakage and enhancing the quality factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional film bulk acoustic resonator structure is used, then the device can be easily fabricated with MEMS technology, but transverse parasitic acoustic waves are excited causing low quality factor
Solution Approach 1:
The patent converts the harmful transverse parasitic acoustic waves into beneficial reflected waves by designing the interdigital protrusion frame with specific dimensions. The protrusion frame's width and spacing are optimized to reflect Rayleigh-Lamb waves back into the resonant region, transforming the energy that would otherwise be lost into useful acoustic energy that enhances the quality factor.
Solution Approach 2:
The patent applies local quality by adding the interdigital protrusion frame only at specific locations around the resonant region's perimeter, rather than modifying the entire structure. The protrusion frame is positioned strategically where it can most effectively reflect transverse waves, with specific width and spacing parameters optimized for the local acoustic field distribution.
2Device complexity
If the resonator structure is simplified, then fabrication is easier, but energy leakage occurs reducing the quality factor
Solution Approach 1:
The patent segments the acoustic wave reflection function into discrete interdigital protrusion elements rather than using a continuous complex structure. The protrusion frame is divided into multiple segments with specific spacing, where each segment contributes to reflecting transverse waves. This segmented approach achieves effective wave confinement while maintaining structural simplicity and ease of fabrication.
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 interdigital protrusion frame effectively increases the reflection efficiency of transverse Rayleigh-Lamb waves, leading to improved resistance and quality factor at anti-resonant frequencies, and reduces the peeling residue issue during the peeling process.
Implementation Method 1
When a radio frequency electrical signal is applied to the top electrode and the bottom electrode in work, under an action of the inverse piezoelectric effect, the piezoelectric films generate mechanical vibrations in a longitudinal direction and form bulk acoustic waves
Implementation Method 2
Under an action of the piezoelectric effect, these bulk acoustic waves are converted into electrical signals, in which an electrical signal converted from bulk acoustic waves with resonant frequencies has the greatest strength
Implementation Method 3
the interdigital protrusion frame effectively increases the reflection efficiency of transverse Rayleigh-Lamb waves by utilizing the difference in acoustic impedance
Data Source
AI summary
The present application provides a film bulk acoustic resonator, including a substrate, an acoustic reflection structure arranged on one side of the substrate, a bottom electrode stacked on one side of the acoustic reflection structure, a piezoelectric film covered on the bottom electrode and a top electrode stacked on a side of the piezoelectric film away from the bottom electrode. An interdigital protrusion frame is provided on a side of the top electrode away from the piezoelectric film, and the interdigital protrusion frame includes a first protrusion frame and a second protrusion frame arranged at intervals. The first protrusion frame and the second protrusion frame respectively extend toward each other and overlap each other to form at least a pair of interdigital structures, and each of the interdigital structures includes two forks spaced apart by a preset distance along an overlapping direction.