FBAR Cavity Structure With Boundary Protrusions for Lateral Wave Loss
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Solution Overview
Problem
Current cavity-type film bulk acoustic resonators face issues such as lateral wave loss, insufficient structural strength, and low quality factor (Q), which hinder their ability to meet the performance requirements of high-frequency radio frequency systems.
Innovation Solution
A film bulk acoustic resonator design featuring a carrier substrate with a support layer enclosing a cavity, a piezoelectric stacked structure, and protrusions at the boundary of the effective resonance region to prevent lateral acoustic wave leakage and enhance structural strength, along with a method for fabricating this resonator that includes forming protrusions on the electrodes and piezoelectric layer and patterning a support layer to create a cavity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a cavity-type structure is used in film bulk acoustic resonator, then the resonator can be fabricated with integrated electrodes and piezoelectric layer, but lateral wave loss occurs and quality factor cannot be further improved
Solution Approach 1:
The patent extracts the harmful lateral acoustic waves from the effective resonance region by introducing acoustic reflectors that reflect these waves back into the resonance region, thereby preventing energy loss and improving quality factor while maintaining the integrated cavity structure
Solution Approach 2:
The patent introduces acoustic reflectors as intermediary structures between the piezoelectric layer and the cavity walls. These reflectors act as mediators that manage acoustic wave propagation, reflecting lateral waves back into the resonance region and preventing them from causing energy loss
2Volume of moving object
If the resonator structure is made thinner to reduce size, then the device footprint is reduced, but structural strength becomes insufficient
Solution Approach 1:
The patent segments the resonator structure into distinct functional layers including support layer, acoustic reflectors, piezoelectric layer, and electrode structures. This segmentation allows each component to be optimized independently, enabling thin overall structure while maintaining structural strength through properly designed support and reflective elements
Solution Approach 2:
The patent employs composite material structures with multiple layers having different acoustic and mechanical properties. The support layer provides mechanical strength, while acoustic reflectors provide acoustic functionality. This composite approach enables the resonator to achieve both reduced thickness and sufficient structural strength
3Loss of energy
If protrusions are added at the boundary of effective resonance region to prevent lateral wave leakage, then quality factor is improved, but device complexity increases
Solution Approach 1:
The patent merges the acoustic reflector structures with the existing electrode and support layer structures. By integrating the reflectors into the boundary regions of the cavity, the design prevents lateral wave leakage without requiring completely separate additional components, thereby improving quality factor while limiting the increase in device complexity
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 proposed design effectively prevents lateral wave leakage and improves the quality factor of the resonator, enhancing its structural strength and yield, thereby supporting high-performance radio frequency systems.
Implementation Method 1
The piezoelectric film layer is configured to generate vibration under an alternating electric field; the vibration excites the bulk acoustic wave propagating along the thickness direction of the piezoelectric film layer
Implementation Method 2
such acoustic wave may be reflected back from the interface between the air and each of two film electrodes, and then be reflected back and forth inside the film layer to form an oscillation
Data Source
AI summary
The present disclosure provides a film bulk acoustic resonator and a method for fabricating the film bulk acoustic resonator. The resonator includes a carrier substrate; a support layer bonded on the carrier substrate, where the support layer encloses a first cavity exposing the carrier substrate; a piezoelectric stacked structure covering the first cavity, where the piezoelectric stacked structure includes a first electrode, a piezoelectric layer, and a second electrode which are stacked sequentially from a bottom to a top; and protrusions disposed at a boundary of an effective resonance region, where the protrusions are disposed on an upper surface or a lower surface of the piezoelectric stacked structure; or a part of the protrusions is disposed on the upper surface of the piezoelectric stacked structure, and another part of the protrusions is disposed on the lower surface of the piezoelectric stacked structure.