Design, Fabrication, and Characterization of Aluminum Scandium Nitride-Based Thin Film Bulk Acoustic Wave Filter

• Published in: Journal of microelectromechanical systems Vol. 32; no. 3; pp. 1 - 8
• Main Authors: Zou, Yang, Cai, Yao, Gao, Chao, Luo, Tiancheng, Liu, Yan, Xu, Qinwen, Wang, Yaxin, Nian, Laixia, Liu, Wenjuan, Soon, Jeffrey Bo Woon, Sun, Chengliang
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.06.2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acoustic waves; Acoustics; Aluminum; aluminum scandium nitride; Bandwidth; Bandwidths; Bulk acoustic wave devices; Electromagnetic wave filters; Film bulk acoustic resonators; Film bulk acoustic wave filter; high frequency; Insertion loss; Lattices; Molybdenum; Nitrides; Optical filters; Resonant frequencies; Resonant frequency; Resonator filters; Resonators; Scandium; Thickness; Thin films; Topology; wide bandwidth
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2023.3263187

The demand for filters with a large fractional bandwidth, up to 5%, still puts a great challenge to the typical aluminum nitride (AlN) thin films-based bulk acoustic wave (BAW) filters in an acoustic-only approach. This paper presents the design, fabrication, and characterization of film bulk acoustic wave resonator (FBAR) and filters using aluminum scandium nitride (Al<inline-formula> <tex-math notation="LaTeX">_{0.8}</tex-math> </inline-formula>Sc<inline-formula> <tex-math notation="LaTeX">_{0.2}</tex-math> </inline-formula>N) thin films. The fundamental thickness-mode resonance of the FBAR is measured at 4.235 GHz with an excellent effective electromechanical coupling factor (<inline-formula> <tex-math notation="LaTeX">K_{eff}^{2})</tex-math> </inline-formula> of 14%. The filters employ a modified structure with additional<inline-formula> <tex-math notation="LaTeX">\vphantom{^{\int}}</tex-math> </inline-formula> molybdenum (Mo) layers formed on the connection strips between each adjacent resonator. The proposed filtering topologies including ladder topology, lattice topology, and ladder-lattice topology are constructed. Results show that the modified connection strips can decrease the magnitude impedance at series resonant frequency and improve the insertion loss (IL) of the filters. The fabricated ladder filter demonstrates a high center frequency of 4.25GHz, low IL of 1.804 dB, wide bandwidth of 189 MHz, and out-of-band rejection of 30 dB, holding a great potential for the 5G wideband applications. 2022-0201