Semiconductor ultrasonic transducer device and methods of formation

A semiconductor device, comprising:

• a sensing electrode above a substrate and between a plurality of isolation trenches;
• a plurality of portions of a first dielectric layer on the sensing electrode;
• a portion of a second dielectric layer on the sensing electrode and on the plurality of portions of the first dielectric layer;
• a portion of a third dielectric layer on the portion of the second dielectric layer;
• and
• an actuation membrane above the third dielectric layer,
• wherein the actuation membrane and the third dielectric layer are spaced apart by a cavity.

A method, comprising:

• forming, on a semiconductor device, a layer stack including alternating metal layers and metal nitride layers;
• removing portions of the layer stack to form a sensing electrode from the layer stack;
• forming a first dielectric layer on the sensing electrode;
• forming a second dielectric layer on the first dielectric layer;
• forming a third dielectric layer on the second dielectric layer;
• remove first portions of the third dielectric layer such that second portions of the third dielectric layer remain over the sensing electrode;
• deposit additional material of the third dielectric layer to form a contact pedestal structure over the sensing electrode;
• and
• bond an actuation membrane to the semiconductor device.