Patent ID: 8742872

Claim:
A MEMS device comprising a substrate and a sealing membrane, wherein: a movable portion of beam structure which vibrates mechanically, and an electrode which is positioned close to the movable portion are provided between the substrate and the sealing membrane, and the movable portion and the electrode have a region where the movable portion and the electrode overlap each other with a gap in a direction perpendicular to a surface of the substrate, a first cavity and a second cavity which are separated by the electrode are formed between the substrate and the sealing membrane, the first cavity is positioned on a side of the movable portion in the direction perpendicular to the surface of the substrate when viewed from the electrode at the region where the movable portion and the electrode overlap, the second cavity is positioned on a side opposite to the movable portion in the direction perpendicular to the surface of the substrate when viewed from the electrode at the region where the movable portion and the electrode overlap, and B 1 /A 1≧1.0 in which A 1 is distance between an inner surface of a side wall A in contact with the electrode, of the first cavity, and a reference position O in the direction parallel to the surface of the substrate and perpendicular to the direction of the beam constituting the movable portion, B 1 is distance between an inner surface of a side wall B in contact with the electrode, of the second cavity, and the reference position O in the direction parallel to the surface of the substrate and perpendicular to the direction of the beam constituting the movable portion, and the reference position O is a position where the electrode is maximally displaced in the direction perpendicular to the surface of the substrate at a region where the electrode and the movable portion are faced to each other perpendicular to the surface of the substrate when force is exerted to the electrode in the direction perpendicular to the surface of the substrate.