Fabrication and characterization of a new capacitive micromachined ultrasonic transducer (cMUT) using polysilicon as membrane and sacrificial layer material

This paper presents a new type of capacitive micromachined ultrasonic transducer (cMUT) using polysilicon for the membrane as well as for the sacrificial layer. Further features are the structured metallic bottom electrode, a silicon oxide isolation layer and a low stress polysilicon membrane combined with a defined electrically doped area. Moreover, the device is completely fabricated using surface micromachining technology. This technology has been applied to fabricate 1D cMUT arrays for operation in fluids in the range of 5 - 15 MHz. the characterization of the fabricated cMUTs have been performed by using optical LDV measurements of the membrane deflection in air using CW mode, LDV measurements in water burst operation mode and acoustic field measurements in water using hydrophone.