Self-aligned acoustic hole formation in piezoelectrical MEMS microphone

A method comprising:

• forming a membrane comprising:
• forming a first piezoelectrical layer;
• forming a first electrode over the first piezoelectrical layer;
• forming a second piezoelectrical layer over the first electrode;
• forming a second electrode over the second piezoelectrical layer;
• and
• forming a third piezoelectrical layer over the second electrode;
• and
• performing an etching process to form a through-hole penetrating through the first piezoelectrical layer, the second piezoelectrical layer, and the third piezoelectrical layer, wherein the through-hole is laterally spaced apart from the first electrode and the second electrode by remaining portions of the first piezoelectrical layer, the second piezoelectrical layer, and the third piezoelectrical layer.

A method comprising:

• forming a membrane comprising:
• forming a piezoelectrical layer;
• forming a first electrode embedded in the piezoelectrical layer;
• forming a second electrode embedded in the piezoelectrical layer, wherein the second electrode is over the first electrode;
• and
• forming a third electrode embedded in the piezoelectrical layer, wherein the third electrode is over the second electrode;
• and
• forming a through-hole penetrating through the piezoelectrical layer, wherein the first electrode, the second electrode, and the third electrode comprise edges facing the through-hole, and the edges are in contacting with the piezoelectrical layer.