Patent ID: 7194905

Claim:
An acceleration sensor for detecting acceleration in three orthogonal directions, comprising: an electrode substrate pair including two electrode substrates each having fixed electrodes arranged on one surface thereof, the fixed electrodes on one electrode substrate being opposed to the fixed electrodes on the other electrode substrate; a diaphragm held between said electrode substrate pair by spacers providing a predetermined distance from the said electrode substrate pair to said diaphragm, said diaphragm acting as a movable electrode; and a weight mounted on said diaphragm with the center of gravity of said weight coinciding with the center of said diaphragm; wherein the acceleration in three orthogonal directions along a first axis, a second axis and a third axis, the first axis extending through the center of gravity of said weight and perpendicular to said electrode substrates, is detected based on variations in capacitance between said fixed electrodes and said movable electrode; wherein said weight is formed to have an umbrella-like shape including a cylindrical shaft portion, and a disk-like main portion having a larger diameter than said shaft portion; wherein said fixed electrodes on each of said electrode substrates include an annular, first fixed electrode extending around said first axis and having a larger diameter than said shaft portion, and second fixed electrodes and third fixed electrodes that are two parts each of an annular electrode having a larger diameter than said first fixed electrode, and divided by dividing axes forming 45 degrees with said second axis and said third axis; wherein each of said electrode substrates has an electret layer formed to cover surfaces of said fixed electrodes, at least one of said electrode substrates defines, centrally thereof, a through hole having a diameter larger than a diameter of said shaft portion and smaller than an inside diameter of said first fixed electrode; wherein said main portion of said weight is located outside said electrode substrate pair having said second electrodes and said third electrodes opposed to each other, respectively; wherein said shaft portion of said weight extends through said through hole, and is connected to said diaphram; and wherein said fixed electrodes are formed on a surface of each of said electrode substrates without protruding or sinking therefrom.