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Monolithic Fabrication of Film Bulk Acoustic Resonators above Integrated Circuit by Adhesive- Bonding-Based Film Transfer
- Citation Author(s):
- Submitted by:
- Abhay Kochhar
- Last updated:
- Fri, 05/20/2022 - 10:42
- DOI:
- 10.21227/H2GM18
- Research Article Link:
- License:
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Abstract
An integration process for the fabrication of thin film bulk acoustic wave resonator (FBAR) above the CMOS IC is proposed. An adhesive-bonding-based film transfer technique is utilized to transfer high resistivity Si film onto a CMOS chip. Benzocyclobutene (BCB) is used as an adhesive film. It is a heat resistive polymer and processes of temperature up to 300 C are allowed on it. The CMOS is protected by BCB and thus is not damaged by plasma and chemical treatments. The transferred Si film offers flat and stable surface which is utilized for the deposition of ruthenium, aluminum nitride & aluminum to fabricate the FBAR structure. Finally, Si underneath the active device area is sacrificially etched to fabricate the air gap type FBAR. In this paper, we present the fabrication process and discuss important issues related to the fabrication.
Conclusion: A monolithic FBAR-CMOS integration process for VCO application was developed. A CMOS IC was delivered from a commercial CMOS foundry in a form of full 8 inch wafer, but the die area except our device was laser-erased and had a very rough surface. After the surface was roughly planarized, a high resistivity monocrystalline Si film was transferred onto a CMOS wafer by BCB adhesive bonding. This process provides a smooth surface suitable for FBAR fabrication without any intensive polishing on CMOS wafers. On it, a FBAR structure was fabricated and the transferred Si under the active FBAR area was sacrificially etched to create the air gap. The fabrication process was completed in this study, during which some process-related problems were found. In this paper, the problems were discussed and the solutions were provided. The described process techniques should be useful for a variety of CMOS-MEMS integration devices as well as AlN acoustic devices.
