Air-Gap FBAR Electrode Frame Structure for Higher Quality Factor
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Solution Overview
Problem
Conventional air-gap type film bulk acoustic resonators (FBARs) face mechanical anchor loss issues due to high mechanical energy loss, which decreases the quality factor and limits their performance in RF communication applications.
Innovation Solution
The air-gap type FBAR design incorporates a piezoelectric layer formed to conform to the edges of the resonator, with a first electrode frame having an open ring structure on the lower electrode and a second electrode frame positioned on the upper electrode, strategically spaced to reduce anchor loss and enhance the quality factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional air-gap type FBAR structure is used, then the device can be manufactured with simplified process, but mechanical anchor loss is high which decreases the quality factor
Solution Approach 1:
The device is segmented into distinct functional regions: a resonator region containing the piezoelectric layer and electrodes, and a ground electrode region separated by an air gap. This segmentation isolates the mechanical vibration to the resonator region, preventing energy loss to the substrate and improving the quality factor while maintaining manufacturability through standard semiconductor processes
Solution Approach 2:
An air gap is introduced as an intermediary element between the resonator structure and the ground electrode/substrate. This air gap acts as a mechanical isolator that prevents direct contact and energy transfer to the substrate, thereby reducing mechanical anchor loss without complicating the manufacturing process
2Reliability
If the piezoelectric layer is extended beyond the air gap portion, then the quality factor is improved by reducing anchor loss, but the device area increases
Solution Approach 1:
The piezoelectric layer is selectively extended only in the radial direction beyond the air gap portion, while maintaining compact dimensions in other directions. This localized extension optimizes the quality factor by reducing anchor loss at critical interfaces without proportionally increasing the overall device area, achieving improved performance with minimal area penalty
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 effectively reduces mechanical anchor loss, thereby improving the quality factor and performance of the FBAR, leading to better insertion loss and skirt characteristics in RF filters.
Implementation Method 1
The resonance of the FBAR filter arises from the piezoelectric characteristics of the piezoelectric material used therein. More particularly, the FBAR filter includes a piezoelectric film disposed between two electrodes, and generates bulk acoustic waves to induce resonance.
Data Source
AI summary
An air-gap type film bulk acoustic resonator (FBAR) is provided. The air-gap type FBAR includes a substrate which comprises an air gap portion having a substrate cavity formed in a top surface, a lower electrode formed on the substrate, a piezoelectric layer which is formed on the lower electrode and has one side forming an edge portion in the vicinity of a virtual edge according to vertical projection of the air gap portion, an upper electrode formed on the piezoelectric layer, a first electrode frame which comprises an open ring structure in plane, the open ring structure surrounding a part of a periphery of the piezoelectric layer on the lower electrode, and a second electrode frame positioned on the upper electrode and adjacent to an open portion of the open ring structure.