Complementary metal oxide semiconductor (CMOS) ultrasonic transducers and methods for forming the same

An apparatus, comprising:

• a semiconductor wafer having a complementary metal oxide semiconductor (CMOS) integrated circuit;
• an electrode;
• an insulating material having a cavity formed at least partially therein;
• a conductive membrane contacting the insulating material, sealing the cavity and having a first side proximate the cavity and a second side distal the cavity, wherein the electrode, cavity, and conductive membrane together define, at least in part, an ultrasonic transducer, with the cavity being between the electrode and the conductive membrane;
• a conductive contact coupling the electrode to the CMOS integrated circuit;
• and
• a conductive plug embedded in the insulating material and terminating on the first side of the conductive membrane proximate the cavity without extending through the conductive membrane such that a surface of the conductive plug forms at least part of a bonding interface between the first side of the conductive membrane and the insulating material, the conductive plug electrically connecting the conductive membrane to the CMOS integrated circuit,
• wherein the electrode and the conductive plug are electrically isolated from each other, and
• wherein the apparatus lacks an electrode that is on the second side of the conductive membrane and that overlies the cavity.