Capacitive micromachined ultrasonic transducer with driving voltage over 100 V and vibration durability over 1011 cycles

A capacitive micromachined ultrasonic transducer (CMUT) was fabricated using a standard 0.25-mum CMOS backend-of-line process. By adopting the planarization of dielectric material between the upper and lower electrodes by chemical mechanical polishing (CMP), we achieved a time-dependent dielectric breakdown (TDDB) lifetime exceeding 10 years at a DC stress voltage of 192 V. In the case of DC and AC voltage driving, we found degradation of the dielectric at the center of a membrane for the first time. By optimally controlling the driving voltage, membrane vibrations over 10¹¹ cycles were accomplished without dielectric degradation.