Air-Gap FBAR Electrode Spacing to Suppress Lateral Wave Escape
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Solution Overview
Problem
Existing air-gap type film bulk acoustic resonators (FBARs) face challenges in achieving high quality factors due to mechanical anchor losses and limitations in miniaturization, which affect their resonance properties and ability to cover ultrahigh frequency bands.
Innovation Solution
The air-gap type FBAR design includes a substrate with an air-gap portion, a lower electrode with a polygonal plate shape surrounding the air-gap, a piezoelectric layer, and an upper electrode, featuring an air bridge structure that prevents lateral wave escape through structural resonance, optimizing the distance between electrode and air-gap boundaries to enhance the quality factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a membrane type FBAR is used to reduce dielectric loss, then power loss is reduced, but the device area increases and structural stability decreases
Solution Approach 1:
The device is divided into two main types: membrane type FBAR for low power loss applications and air-gap type FBAR for high stability applications. This segmentation allows each type to be optimized for its specific function without compromising the other.
Solution Approach 2:
The air-gap type FBAR extracts the piezoelectric layer from the substrate and suspends it in air, eliminating the need for a membrane structure. This extraction provides structural stability while maintaining low power loss through the air gap configuration.
2Reliability
If the lower electrode is extended to the substrate boundary to reduce mechanical anchor loss, then quality factor improves, but lateral waves escape and increase mechanical anchor loss
Solution Approach 1:
The lower electrode is designed with different extensions at different locations: it extends closer to the substrate boundary in regions where lateral wave escape is minimal (improving quality factor), while maintaining appropriate spacing in regions where lateral waves are more prevalent (reducing mechanical anchor loss). This local optimization of electrode positioning resolves the contradiction between improving quality factor and reducing mechanical anchor loss.
3Reliability
If distance between lower electrode and air-gap boundary is reduced to minimize mechanical anchor loss, then quality factor improves, but manufacturing precision becomes more difficult
Solution Approach 1:
Instead of using a fixed small distance between the lower electrode and air-gap boundary, the patent optimizes the distance parameter to a specific range that balances quality factor improvement with manufacturing feasibility. This parameter optimization allows achieving high quality factor while maintaining reasonable manufacturing precision requirements.
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 improves the quality factor of the FBAR, reducing insertion loss and enhancing filter skirt properties, enabling better performance across a wider frequency range, including ultrahigh frequencies.
Implementation Method 1
the FBAR generates resonance by depositing a piezoelectric film between both electrodes and causing a bulk acoustic wave
Implementation Method 2
an air bridge structure that prevents lateral wave escape through structural resonance
Data Source
AI summary
Disclosed is an air-gap type film bulk acoustic resonator (FBAR) including a substrate including an air-gap portion on a top surface, a lower electrode having a polygonal plate shape above the substrate and configured to surround a top of the air-gap portion, a piezoelectric layer formed above the lower electrode, and an upper electrode formed above the piezoelectric layer. Here, the lower electrode includes an electrode non-deposited area formed between one side plate boundary surface of the polygonal plate and one side air-gap boundary surface of the air-gap portion to expose one part of a top of the air-gap portion.