Capacitive sensor, acoustic sensor and microphone

A capacitive sensor comprising:

• a substrate having a cavity that is open at least at an upper surface;
• a diaphragm formed above the substrate so as to cover an upper portion of the cavity;
• a fixed electrode plate arranged opposite to the diaphragm;
• and
• a plurality of leg pieces partially separated from the diaphragm by slits such that the plurality of leg pieces are surrounded by the diaphragm and are partially connected to the diaphragm;
• and
• a plurality of anchors which are projected from a lower surface of a back plate formed on the fixed electrode plate at positions corresponding to the leg pieces;
• wherein
• the plurality of leg pieces are not fixed to the substrate,
• the plurality of leg pieces are not fixed to the back plate,
• in a state in which the capacitive sensor is not operated, the diaphragm with the plurality of leg pieces is placed on the substrate, and
• in a state in which the capacitive sensor is operated, the plurality of leg pieces are respectively supported by the plurality of anchors, with electrostatic attraction force between the fixed electrode plate and the diaphragm.