Patent ID: 8067811

Claim:
An acoustic transducer comprising: a semiconductor substrate; a movable electrode formed above the semiconductor substrate; a fixed electrode formed above the semiconductor substrate; a first insulating film provided between the semiconductor substrate and a portion of the movable electrode; and a second insulating film provided between the semiconductor substrate and a portion of the fixed electrode, wherein: the semiconductor substrate, the first insulating film and the movable electrode comprise a first MIS structure, the semiconductor substrate, the second insulating film and the fixed electrode comprise a second MIS structure, an interface charge having a first polarity is present at an interface between the semiconductor substrate and at least one of the first insulating film and the second insulating film, the semiconductor substrate has, as majority carriers, carriers having a second polarity different from the first polarity, and the interface charge having the first polarity is present in the first insulating film in a vicinity of the interface between the semiconductor substrate and the first insulating film.