Method of making a piezoelectric MEMS diaphragm microphone

A method of making a radiofrequency module, comprising:

• forming or providing a printed circuit board that includes a substrate layer;
• forming or providing one or more piezoelectric microelectromechanical systems diaphragm microphones via a process comprising (a) oxidizing a top surface and a bottom surface of a substrate to form a top oxidation layer and a bottom oxidation layer, (b) forming or applying two or more piezoelectric film layers over the top surface of the substrate so that each of the two or more piezoelectric film layers have a predefined residual stress that substantially cancel each other out, the two or more piezoelectric film layers defining a substantially flat diaphragm structure with substantially zero residual stress, (c) forming or applying one or more electrodes over the two or more piezoelectric film layers, and (d) etching the bottom oxidation layer and substrate to form an opening in the substrate that allows sound pressure to travel through the opening to deflect the diaphragm structure;
• and
• mounting the one or more piezoelectric microelectromechanical systems diaphragm microphones on the printed circuit board.