Xu Jiashuai, Ren Zijun, Qian Fangsheng, Zheng Junyan, Yang Yansong
Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Hong Kong, China.
Microsyst Nanoeng. 2025 May 27;11(1):107. doi: 10.1038/s41378-025-00958-8.
This study presents a wafer-level sealed silicon cavity (SSC) microacoustic integration platform to address the limitations in the cavity Silicon-on-Insulator (C-SOI) wafers for the 5G/6G wireless communication system. The proposed SSC platform features an extremely smooth suspended membrane with adjustable thickness, flexible cavity shapes with high density, self-formed acoustic wave confinement steps, stable temperature coefficient of frequency (TCF), and highly integrated compatibility with complementary metal-oxide semiconductor (CMOS). A surface smoothing method based on wet oxidation for SSC wafers is presented, which achieves a root mean square (RMS) roughness on the cavity surface of 1.5 nm for the first time. Based on the presented SSC platform, an AlScN sealed cavity bulk acoustic wave resonator (S-BAR) is designed, fabricated, and characterized. The experimental results show that the asymmetric second-order (A2) Lamb mode of S-BAR is enhanced for higher frequency with a maximum piezoelectric coupling coefficient ( ) of 9.53%, a maximum quality factor (Q) of 439, and a TCF of -11.44 ppm/K. Different designs' piezoelectric coupling coefficient distribution is consistent with the theoretical prediction. The proposed smoothing process increases the S-BARs' quality factor by ~400%. The frequency shift caused by the temperature (absolute value of TCF) is reduced by 62% compared with the traditional AlScN thin film bulk acoustic wave resonator (without temperature compensation). The enhanced performances demonstrated the potential of SSC in the next-generation highly integrated RF communication systems.
本研究提出了一种晶圆级密封硅腔（SSC）微声学集成平台，以解决用于5G/6G无线通信系统的绝缘体上硅（C-SOI）晶圆中的局限性。所提出的SSC平台具有极其光滑的悬浮膜，其厚度可调、具有高密度的灵活腔形状、自形成的声波限制台阶、稳定的频率温度系数（TCF）以及与互补金属氧化物半导体（CMOS）的高度集成兼容性。提出了一种基于湿氧化的SSC晶圆表面平滑方法，该方法首次在腔表面实现了1.5nm的均方根（RMS）粗糙度。基于所提出的SSC平台，设计、制造并表征了一种AlScN密封腔体声波谐振器（S-BAR）。实验结果表明，S-BAR的非对称二阶（A2）兰姆模在更高频率下得到增强，最大压电耦合系数（ ）为9.53%，最大品质因数（Q）为439，TCF为-11.44ppm/K。不同设计的压电耦合系数分布与理论预测一致。所提出的平滑工艺使S-BAR的品质因数提高了约400%。与传统的AlScN薄膜体声波谐振器（无温度补偿）相比，温度引起的频率偏移（TCF的绝对值）降低了62%。增强的性能证明了SSC在下一代高度集成射频通信系统中的潜力。
