Micro-electromechanical system device and method of forming the same

A true wireless stereo earphone, comprising a micro-electromechanical structure, wherein the micro-electromechanical structure comprises:

• a micro-electromechanical substrate, comprising a first surface and a second surface opposite to the first surface, wherein the micro-electromechanical substrate comprises a first semiconductor layer, an insulating layer and a second semiconductor layer from bottom to top, and the insulating layer is in direct contact with both the first semiconductor layer and the second semiconductor layer to construct a silicon-on-insulator substrate;
• a cavity disposed in the micro-electromechanical substrate, penetrating through the first semiconductor layer, the insulating layer and the second semiconductor layer;
• an interconnection structure disposed on the first surface of the micro-electromechanical substrate, over the cavity, wherein the interconnection structure comprises a suspended region, one of the two opposite ends of the suspended region directly connects to the micro-electromechanical substrate and another one of the two opposite ends of the suspended region disconnect to the micro-electromechanical substrate;
• and
• a proof mass disposed in the cavity and connected to the suspended region of the interconnection structure, close to and misaligned with the another one of the two opposite ends of the suspended region, the proof mass having a thickness which is ¼-⅛ of a thickness of the micro-electromechanical substrate.