Capacitive Substrate Coupling of Row-Column-Addressed 2-D CMUT Arrays

Row-column-addressed CMUT arrays suffer from low receive sensitivity of the bottom elements due to a capacitive coupling to the substrate. The capacitive coupling increases the parasitic capacitance. A simple approach to reduce the parasitic capacitance is presented, which is based on depleting the semiconductor substrate. To reduce the parasitic capacitance by 8 0 % the bulk doping concentration should be at most 10(12) cm-(3). Experimental results show that the parasitic capacitance can be reduced by 8 7 % by applying a substrate potential of 6 V relative to the bottom electrodes. The depletion of the semiconductor substrate can be sustained for at least 10 minutes making it applicable for row-column-addressed CMUT arrays for ultrasonic imaging. Theoretically the reduced parasitic capacitance indicates that the receive sensitivity of the bottom elements can be increased by a factor of 2.1.