Cavity edge insulator extension in CMUT cell for high ultrasound power transmission

As an ultrasonic transducer in medical imaging diagnostics, capacitive micro-machined ultrasonic transducers (CMUTs) have various advantages over conventionally used piezoelectric transducers, such as superior image quality and feasibility of circuit integration. CMUTs must be operated by applying not only high AC driving voltage (V
_AC
) but also high DC bias voltage (V
_DC
) to generate enough ultrasound power especially in the case of tissue harmonic imaging (THI). Applying high V
_DC
results in high electromechanical coupling constant required for THI, however, that causes electric breakdown between the top and bottom electrodes at the edge of the cavity where electric field concentrates. In this research, we propose a novel CMUT cell structure which has long breakdown lifetime against high V
_DC
at the edge of the cavity.