Electrostatic membranes for sensors, ultrasonic transducers incorporating such membranes, and manufacturing methods therefor

A method for making capacitive micromachined ultrasonic transducer devices for ultrasonic transducer use, said method comprising:

• providing a silicon wafer substrate;
• depositing a silicon oxide layer on a top surface of said substrate so as to provide dielectric insulation between the substrate and further components;
• providing a bottom electrode on the silicon oxide layer;
• providing a sacrificial layer over the bottom electrode, said sacrificial layer being comprised of a high lateral etching rate columnar structured oxide;
• providing a low stress silicon nitride membrane on said sacrificial layer using a low pressure chemical vapor deposition process;
• removing sacrificial material from selected sites of said sacrificial layer to form cavities for cells;
• depositing an oxide layer as a sealing material using a physical vapor deposition process and under vacuum conditions so as to preserve said cavities;
• and
• providing a top electrode layer over said silicon nitride membrane.