US Patent 9344805 Micro-electromechanical system microphone

A capacitive micro-electromechanical system (MEMS) microphone includes a semiconductor substrate having an opening that extends through the substrate. The microphone has a membrane that extends across the opening and a back-plate that extends across the opening. The membrane is configured to generate a signal in response to sound. The back-plate is separated from the membrane by an insulator and the back-plate exhibits a spring constant. The microphone further includes a back-chamber that encloses the opening to form a pressure chamber with the membrane, and a tuning structure configured to set a resonance frequency of the back-plate to a value that is substantially the same as a value of a resonance frequency of the membrane.