FBAR Air Bridge Resonator for Lateral Energy Loss Reduction
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Solution Overview
Problem
Current film bulk acoustic resonators (FBARs) face challenges in reducing electrode loss and achieving high quality factors due to mechanical anchor losses and energy escape in the lateral direction, limiting their performance in high-frequency applications.
Innovation Solution
The acoustic resonator incorporates an air bridge structure with a piezoelectric layer terminated by an etching area, forming air bridges and cavities to prevent lateral energy escape and reduce mechanical anchor losses, while the second electrode is designed with inclined surfaces and V- or U-shapes to cover termination surfaces and enhance conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a membrane type FBAR structure is used, then dielectric loss and power loss are reduced, but device area increases and structural stability decreases
Solution Approach 1:
The device is segmented into distinct functional regions: a first electrode extending beyond the piezoelectric layer to form a first air bridge area, and a second electrode configured to form a second air bridge area. This segmentation allows the electrodes to extend into regions where they do not overlap with the piezoelectric layer, reducing dielectric loss while containing the active resonant region to a smaller effective area.
Solution Approach 2:
The electrode structures are designed to extend in the lateral dimension beyond the piezoelectric layer boundaries, creating air bridge areas that reduce dielectric loss. The first electrode has a first end that extends beyond the piezoelectric layer, and the second electrode has a second end that extends beyond the piezoelectric layer, utilizing the lateral dimension to reduce loss without increasing the vertical footprint.
2Loss of energy
If a membrane type FBAR structure is used, then dielectric loss is reduced, but structural stability decreases causing yield reduction
Solution Approach 1:
The electrode structures are segmented into regions that overlap with the piezoelectric layer and regions that extend beyond it. The first electrode includes a first overlapping area with the piezoelectric layer and a first air bridge area where it extends beyond. This segmentation allows the structure to maintain stability in the overlapping region while reducing power loss in the extended air bridge region.
Solution Approach 2:
Different regions of the electrode structures have different functional qualities: the overlapping areas provide mechanical support and electrical connection with stable piezoelectric coupling, while the extended air bridge areas reduce dielectric loss and power loss. The first electrode has an inclined termination surface in the air bridge area, and the second electrode has corresponding inclined surfaces, creating local structural variations that optimize both stability and loss reduction.
3Quantity of substance
If the piezoelectric layer extends beyond the electrode overlapping area, then more piezoelectric material is utilized, but mechanical anchor loss increases
Solution Approach 1:
The harmful mechanical anchor loss is extracted and isolated by confining the piezoelectric layer to a specific region that does not extend beyond the electrode overlapping areas. The piezoelectric layer is positioned between the first and second electrodes such that its lateral dimensions are contained within the regions where electrodes provide support, preventing energy leakage into the substrate while still utilizing sufficient piezoelectric material for effective resonance.
Solution Approach 2:
The electrode structures are designed with inclined termination surfaces that extend beyond the piezoelectric layer before it is terminated. This preliminary extension creates air bridge areas that prevent mechanical energy from coupling into the substrate, acting as a preliminary barrier against mechanical anchor loss before the piezoelectric layer ends. The inclined surfaces of the first and second electrodes provide gradual termination that reduces stress concentration and prevents energy leakage.
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 effectively prevents piezoelectric layer operation outside the active area, reduces stress, and improves the quality factor at resonance points by minimizing energy loss, enabling better performance in high-frequency applications.
Implementation Method 1
an FBAR filter is formed by depositing zinc oxide (ZnO), aluminum nitride (AlN), or the like which is a piezoelectric-dielectric material on silicon (Si) or gallium arsenide (GaAs) which is a semiconductor substrate using an RF sputtering method and causes resonation due to a piezoelectric property
Implementation Method 2
the piezoelectric layer and the first electrode include an overlapping area that corresponds to a first end and a second end of the first cavity, the first electrode has a termination surface formed as an inclined surface of a first acute angle θ1 outside the overlapping area with respect to the second end of the first cavity, the piezoelectric layer is formed to include a first air bridge area that has a second cavity and is formed between the piezoelectric layer and the first electrode
Data Source
AI summary
Provided is an acoustic resonator including: a substrate including a first cavity; a first electrode formed above the substrate; a piezoelectric layer formed on one surface of the first electrode; and a second electrode formed on one surface of the piezoelectric layer, wherein the first electrode and the piezoelectric layer include an overlapping area that corresponds to a first end and a second end of the first cavity, the first electrode has a termination surface formed as an inclined surface of a first acute angle θ1 outside the overlapping area with respect to the second end of the first cavity, the piezoelectric layer is formed to include a first air bridge area that has a second cavity and is formed between the piezoelectric layer and the first electrode in a vertical direction and between the second end of the first cavity and the termination surface in a horizontal direction.