Composite diaphragms having balanced stress

A microphone assembly, comprising:

• a base;
• an enclosure disposed on the base;
• an acoustic transducer configured to generate an electrical signal responsive to acoustic activity, the acoustic transducer comprising:
• a transducer substrate defining an aperture therein,
• a diaphragm disposed on the transducer substrate, the diaphragm comprising:
• a diaphragm inner portion disposed over the aperture such that an outer edge of the diaphragm inner portion is located radially inwards of a rim of the aperture, the diaphragm inner portion having a first stress, and
• a diaphragm outer portion extending radially from the outer edge of the diaphragm inner portion to at least the rim of the aperture, the diaphragm outer portion having a second stress different from the first stress;
• and
• a back plate disposed on the transducer substrate spaced apart from the diaphragm;
• and
• an integrated circuit electrically coupled to the acoustic transducer and configured to receive the electrical signal from the acoustic transducer.

A method of forming a diaphragm assembly, comprising:

• providing a transducer substrate defining an aperture therethrough;
• forming a diaphragm outer portion on the transducer substrate over the aperture;
• and
• forming a diaphragm inner portion over the aperture coupled to the diaphragm outer portion such that an outer edge of the diaphragm inner portion is located radially inwards of a rim of the aperture and the diaphragm outer portion extends radially from the outer edge of the diaphragm inner portion to at least the rim of the aperture,
• wherein the diaphragm inner portion has a first stress and the diaphragm outer portion has a second stress different from the first stress.