Fabrication of CMUT with T-shaped Cavities Using Anodic Bonding Process

Capacitive micromachined ultrasonic transducers (CMUT) are known for their high sensitivity, favorable impedance matching, broad bandwidth, and good biocompatibility, making them suitable for medical diagnostics, non-destructive testing, and 3D ultrasound gesture recognition. However, challenges such as high collapse voltages (≥100 V) and difficulties in enhancing both transmitting and receiving sensitivities limit their broader application. In this paper, we introduce a novel T-shaped cavity CMUT (T-CMUT) design that utilizes the electrostatic stiffness softening effect. By reducing the electrode spacing in the cavity’s peripheral region, we achieved a higher electric field intensity, resulting in decreased stiffness and improved piston-like deformation of the membrane. Additionally, we developed a fabrication process for T-CMUT using silicon-glass anodic bonding, addressing stringent surface roughness requirements and high preparation temperatures associated with traditional wafer direct bonding processes. The results indicate that the T-CMUT exhibit a 20.6% increase in transmission sensitivity and a 36.6% improvement in fractional bandwidth compared to conventional CMUTs.