Piezoelectric ultrasonic transducer and process

A piezoelectric micromechanical ultrasonic transducer (PMUT) comprising:

• a multilayer stack disposed on a substrate and including:
• an anchor structure disposed over the substrate;
• a piezoelectric layer stack disposed over the anchor structure;
• and
• a mechanical layer disposed proximate to the piezoelectric layer stack, the mechanical layer including a recess where the mechanical layer is locally thinned;
• wherein
• the piezoelectric layer stack is disposed over a cavity;
• and
• the mechanical layer, together with the piezoelectric layer stack, is supported by the anchor structure and forms a membrane over the cavity, the membrane being configured to undergo one or both of flexural motion and vibration when the PMUT receives or transmits ultrasonic signals.

An apparatus comprising:

• an array of piezoelectric micromechanical ultrasonic transducer (PMUT) sensors;
• and
• an acoustic coupling medium, wherein:
• at least one PMUT includes a multilayer stack disposed on a substrate and including an anchor structure disposed over the substrate, a piezoelectric layer stack disposed over the anchor structure and a cavity, and a mechanical layer disposed proximate to the piezoelectric layer stack, the mechanical layer sealing the cavity;
• the acoustic coupling medium is disposed above the piezoelectric layer stack;
• and
• the PMUT is configured to receive or transmit ultrasonic signals through the coupling medium.