Design and Modeling of CMUTs With T-Shape Cavities for Low Working Voltage, High Ultrasound Transmission and Reception

Low-voltage, high-performance capacitive micromachined ultrasonic transducers (CMUTs) are in urgent demand for portable ultrasound imaging and human–machine interfaces. However, most existing CMUTs exhibit superior comprehensive performance due to conflicting requirements in their structural design, which constrains their practical applications. This article proposes a novel CMUT with T-shape cavities to achieve synergistic enhancement of multiple key performances by harnessing the electrostatic stiffness softening effect (ESSE). The unique T-shape cavity design features a smaller electrode distance in the peripheral area compared to the central area, which produces a higher electric field intensity and thus a larger membrane stiffness drop in the peripheral area of the vibrating membrane through the corresponding enhancement of ESSE. This special stiffness adjustment strategy ultimately enables the entire membrane to produce piston-like deformation, significantly improving both the maximum and average membrane deformation, and contributing to enhancement in operation voltage, transmitting and receiving sensitivities, electromechanical coupling coefficient, and so on. The finite element method (FEM) is employed to investigate the device’s performance. Compared to conventional CMUTs, T-CMUTs reduce collapse voltage by 36.2%, with transmitting/receiving sensitivities and electromechanical coupling coefficient improved by 56.1%, 62.6%, and 76.0% under the same bias ratios. Furthermore, these parameters improve by 371.0%, 516.0%, and 618.4% at the same bias voltages. An analysis of the stress distribution of the membrane further verifies the underlying mechanism of the T-shape cavity in enhancing device performance. In addition, the foreseeable simplicity and feasibility in consistent fabrication endow the proposed CMUTs with significant potential for practical application.