Anodically Bonded CMUT with a Two-Layer Bottom Electrode for Increased Reliability and Reduced Parasitic Capacitance

This paper introduces a new fabrication process variation for improving the reliability and performance of capacitive micromachined ultrasonic transducers by using a two-layer bottom electrode on a glass substrate. This structure decouples the active gap from the gap at the interconnects allowing for thicker nitride in the sealing area. A larger gap at the interconnects decreases their parasitic capacitance, and thicker sealing nitride decreases the effects of charging and can prevent dielectric breakdown.