1. 5.5 GHz film bulk acoustic wave filters using thin film transfer process for WLAN applications.
- Author
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Yang T, Gao C, Wang Y, Lin B, Zheng Y, Liu Y, Lei C, Sun C, and Cai Y
- Abstract
Wireless local area network (WLAN) has gained widespread application as a convenient network access method, demanding higher network efficiency, stability, and responsiveness. High-performance filters are crucial components to meet these needs. Film bulk acoustic resonators (FBARs) are ideal for constructing these filters due to their high-quality factor (Q) and low loss. In conventional air-gap type FBAR, aluminum nitride (AlN) is deposited on the sacrificial layer with poor crystallinity. Additionally, FBARs with single-crystal AlN have high internal stress and complicated fabrication process. These limit the development of FBARs to higher frequencies above 5 GHz. This paper presents the design and fabrication of FBARs and filters for WLAN applications, combining the high electromechanical coupling coefficient ( K t 2 ) of Al
0.8 Sc0.2 N film with the advantages of the thin film transfer process. An AlN seed layer and 280 nm-thick Al0.8 Sc0.2 N are deposited on a Si substrate via physical vapor deposition (PVD), achieving a full width at half maximum (FWHM) of 2.1°. The ultra-thin film is then transferred to another Si substrate by wafer bonding, flipping, and Si removal. Integrating conventional manufacturing processes, an FBAR with a resonant frequency reaching 5.5 GHz is fabricated, demonstrating a large effective electromechanical coupling coefficient ( k eff 2 ) of 13.8% and an excellent figure of merit (FOM) of 85. A lattice-type filter based on these FBARs is then developed for the Wi-Fi UNII-2 band, featuring a center frequency of 5.5 GHz and a -3 dB bandwidth of 306 MHz, supporting high data rates and large throughputs in WLAN applications., Competing Interests: Conflict of interest: The author declares no competing interests., (© 2024. The Author(s).)- Published
- 2024
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