Semiconductor device and method of forming the same

A method of forming a semiconductor device, comprising:

• providing a first semiconductor structure that comprises a first microelectromechanical system (MEMS) structure over a first substrate, wherein the first MEMS structure comprises a first flexible membrane and a first cavity between the first substrate and the first flexible membrane, and the first flexible membrane is configured to vibrate at a first frequency;
• providing a second semiconductor structure that comprises a second MEMS structure on a second substrate, wherein the second MEMS structure comprises a second flexible membrane overlying a second cavity of the second substrate, and the second flexible membrane is configured to vibrate at a second frequency;
• bonding the second semiconductor structure to the first semiconductor structure, wherein the second MEMS structure is vertically stacked above the first MEMS structure;
• and
• electrically connecting the second MEMS structure to an interconnect structure over the first substrate.

A method of forming a semiconductor device, comprising:

• providing an integrated circuit (IC) structure that comprises an interconnect structure over a first substrate;
• forming a first microelectromechanical system (MEMS) structure over the IC structure, wherein the first MEMS structure comprises a first flexible membrane and a first cavity between the first substrate and the first flexible membrane, and the first MEMS structure is coupled to an IC device on the first substrate;
• providing a second substrate with a second MEMS structure, wherein the second MEMS structure comprises a second flexible membrane overlying a second cavity of the second substrate;
• and
• bonding the second substrate to a conductive layer over the interconnect structure, and the second MEMS structure stacked above the first MEMS structure, wherein the second cavity is positioned between the second flexible membrane and the first flexible membrane.