BAW Resonator Edge Frames With Slanted Cuts for Acoustic Loss
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Solution Overview
Problem
Bulk acoustic wave resonators experience energy loss due to parasitic lateral acoustic waves generated at the resonator edges, which reduces the quality factor and efficiency of the device.
Innovation Solution
The implementation of a raised metal edge frame with slanted cuts around the periphery of the active region in the bulk acoustic wave resonator, which minimizes energy loss by preventing direct propagation of acoustic waves through the cuts, and the use of trenches and recessed edge frames to create an air gap and impedance mismatch, thereby confining lateral mode waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a traditional straight-edge frame is used, then the manufacturing is simple, but acoustic energy loss through edges is high
Solution Approach 1:
The edge frame is divided into multiple segments with cuts that create discrete reflection points for lateral acoustic waves. The frame is segmented into vertical portions and slanted portions, with gaps between segments that prevent direct wave propagation while maintaining structural integrity. This segmentation approach reduces acoustic energy loss by at least 75% compared to traditional straight-edge frames.
Solution Approach 2:
The edge frame incorporates slanted portions that are angled relative to the vertical portions, creating a non-linear geometry that deflects lateral acoustic waves. The slanted cuts and angled portions redirect acoustic energy away from the active region rather than allowing straight-line propagation, effectively using geometric curvature to manage wave paths.
2Loss of energy
If the edge frame is made with slanted cuts and gaps, then acoustic energy loss is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The edge frame is divided into multiple segments with cuts that create discrete reflection points for lateral acoustic waves. The frame is segmented into vertical portions and slanted portions, with gaps between segments that prevent direct wave propagation while maintaining structural integrity. This segmentation approach reduces acoustic energy loss by at least 75% compared to traditional straight-edge frames.
Solution Approach 2:
The edge frame geometry is optimized with specific slant angles and gap dimensions that balance acoustic performance with manufacturability. The slanted portions are angled at specific angles relative to the vertical portions, and the gaps between segments are dimensioned to effectively block lateral wave propagation while accommodating manufacturing tolerances.
3Reliability
If trenches and recessed edge frames are added to create air gaps, then lateral mode wave confinement is improved, but device complexity increases
Solution Approach 1:
The solution introduces vertical dimensionality with trenches extending into the substrate and recessed portions of the edge frame at different heights. This multi-level structure creates air gaps that provide acoustic isolation between the active region and the substrate, effectively confining lateral mode waves. The vertical stacking of structural elements at different elevations provides superior wave confinement compared to planar designs.
Solution Approach 2:
Air gaps created by the trenches and recessed edge frame portions serve as intermediary acoustic isolation layers between the active region and the substrate. These air gaps act as acoustic barriers that prevent direct mechanical coupling and reduce parasitic lateral wave propagation, improving resonator 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 significantly reduces acoustic energy loss through the edges, enhancing the quality factor and overall performance of the resonator by at least 75% compared to traditional straight-edge frames.
Implementation Method 1
the piezoelectric thin film converts the electrical energy of the signal into mechanical energy (or acoustic energy), resulting in longitudinal or shear waves propagating through the stack
Implementation Method 2
each respective cut of the one or more cuts is at a respective location along the periphery of the active region and is slanted with reference to a direction of extension of the edge frame at the respective location so as to reduce loss of acoustic energy in the active region through the respective cut
Implementation Method 3
the use of trenches and recessed edge frames to create an air gap and impedance mismatch, thereby confining lateral mode waves
Data Source
AI summary
A bulk acoustic wave (BAW) resonator includes a substrate, a stack over the substrate and including a piezoelectric layer disposed between two electrode layers, and one or more edge frames. The one or more edge frames can be a raised metal frame extending parallel to a periphery of an active region of the stack and has one or more slanted cuts such that the edge frame does not form a closed loop and loss of acoustic energy in the active region through the one or more cuts is reduced, minimized or prevented. Alternatively or additionally, the one or more edge frames include a recessed edge frame in the form of a trench in the piezoelectric layer extending parallel to a boundary of the active region, and may further include a second edge frame formed on the first electrode and embedded in the piezoelectric layer.