High-transmission and low-voltage CMUTs based on annular electrode and membrane groove configuration

Capacitive micromachined ultrasonic transducers (CMUTs) are considered promising alternatives to traditional transducers owing to their compact size, high electromechanical coupling coefficient, and ease of integration with circuits. However, their limited transmission performance and high operating voltage hinder applications in advanced fields such as, intracavitary ultrasonography, portable ultrasound imaging, human–machine interfaces, and long-term non-destructive testing. This study presents an innovative CMUTs design through a combination of annular electrodes and membrane grooves. The annular electrodes partially adjust the membrane stiffness with electrostatic stiffness softening effect, while the grooves release stress in the membrane edge and convert the fully clamped membrane boundary into a hinge-like boundary. By leveraging these effects, this combined configuration achieves synergistic improvement in multiple performances metrics, especially, enhancing transmission amplitude and reducing collapse voltage. Finite elemental analysis is used to evaluate the influence of annular electrodes and grooves on crucial performance parameters. These results reveal maximum increases of 327%, 23%, 305% and 17% in average displacement, electromechanical coupling coefficient, transmitting vibration amplitude and receiving sensitivity, respectively, while maximum reduction of 19% in collapse voltage. Comprehensive analysis indicates that an optimal annular electrode coverage of 40% to 70%, along with a groove-to-post ratio of 90%, delivers superior overall performances. Moreover, the fabricated CMUTs chips are used to validate performance improvements with the structural design. The proposed CMUTs exhibit low collapse voltage, high transmission performance, and a simple membrane structure, demonstrating great promise for advanced ultrasound applications.