Advanced technologies of FBAR for tuning effective electromechanical coupling coefficient

• Published in: Applied physics letters 2024-01, Vol.124 (1)
• Main Authors: Qu, Yuanhang, Liu, Yan, Gu, Xiyu, Wei, Min, Chen, Xiang, Huang, Xiaoming, Liu, Zesheng, Ding, Jiaqi, Wen, Zhiwei, Cai, Yao, Liu, Wenjuan, Guo, Shishang, Sun, Chengliang
• Format: Article
• Language: English
• Subjects: Acoustic waves; Applied physics; Bulk acoustic wave devices; Coupling coefficients; Piezoelectric films; Resonant frequencies; Tuning
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/5.0185078

The film bulk acoustic wave resonator (FBAR) is one of the most popular devices in the radio frequency field. Numerous researchers are simultaneously working to develop an effective electromechanical coupling coefficient ( k eff 2) tuning technology, aiming to meet the diverse bandwidth requirements of the 5 G era. Based on a traditional FBAR process, this work prepares several different devices and then analyzes the four factors that influence k eff 2 from the perspective of process, material, and design. The pillar structure achieves the largest k eff 2 tuning range of 2.84% (33 MHz). The composite piezoelectric film can tune the overall resonant frequency in a wide range, and its k eff 2 tuning range is 1.75% (12.5 MHz). The area effect tunes the fs in a small range, ultimately achieving a k eff 2 tuning range of 1.16% (11 MHz). Film stress regulation achieves k eff 2 tuning range of 2.73% (30 MHz), but it has the greatest difficulty. The integration of various k eff 2 tunable methods has important guiding significance for the design of FBAR filters in the future.