New manufacturing method for capacitive ultrasonic transducers with monocrystalline membrane

A new method to manufacture Capacitive Micromachined Ultrasonic Transducers (eMUT) combining a wafer bonding and a sacrificial layer processes is introduced. Devices with monocrystalline silicon membranes over a polysilicon electrode have been manufactured. The process is highly reliable and shows an excellent homogeneity all over the 200 mm wafer. From impedance measurements in air of a monocell test device biased under 140 V, a resonance at 8.0 MHz and an electromechanical coupling coefficient of 45% have been found. Underwater pulse-echo experiments are presented demonstrating a large bandwidth of the device of about 130%.