Capacitive Micromachined Ultrasonic Transducer (CMUT) Made with SWCNTs/Parylene-C Composite Membranes

Traditional CMUTs are fabricated from silicon-based membranes. However, the poor flexibility and high cost of silicon-based membranes have resulted in low output pressure and high manufacturing costs for the fabricated CMUTs. Here, we report the feasibility of a type of single-walled carbon nanotubes (SWCNTs)/Parylene-C composite membrane for the fabrication of a CMUT. The innovative aspect of this method is the replacement of traditional silicon-based membranes with SWCNTs/Parylene-C composite membranes, which can simplify the process and reduce manufacturing costs. The SWCNTs/Parylene-C composite membrane has a Young’s modulus of 4.4 GPa and a surface resistivity of 29.6 Ω/sq. Prior to bonding, oxygen plasma treatment is performed on the SWCNTs/Parylene-C composite membrane and SU-8 surface to introduce functional groups such as hydroxyl and carboxyl, which aid in bonding. The resonance frequency of the fabricated CMUT is 2.108 MHz, and the quality factor is 52.6. The results suggest that the SWCNTs/Parylene-C composite membrane has potential for use in CMUT fabrication due to its excellent mechanical and electrical properties. The study provides a direction for the development of CMUTs with improved performance and may have significant applications in fields such as medical imaging and wearable health monitoring devices.