Capacitive sensor, acoustic sensor and microphone
A diaphragm is arranged on the upper surface of a silicon substrate so as to cover a chamber in the silicon substrate. Multiple anchors are provided on the upper surface of the silicon substrate, and the lower surfaces of corner portions of the diaphragm are supported by the anchors. Also, a fixed electrode plate is provided above the diaphragm with an air gap therebetween. In a view from a direction perpendicular to the upper surface of the silicon substrate, the entire length of the outer edge of the diaphragm located between adjacent anchors is located outward of a line segment that circumscribes the edges of the adjacent anchors on the side distant from the center of the diaphragm. Also, one or two or more through-holes are formed in the diaphragm in the vicinity of the anchors.
1. A capacitive sensor comprising:
a substrate having a cavity that is open at least at an upper surface;
a vibrating electrode plate formed above the substrate so as to cover an upper portion of the cavity;
a plurality of anchors that are arranged with a gap in an outer peripheral portion of the vibrating electrode plate and enable the vibrating electrode plate to be fixed to a stationary member; and
a fixed electrode plate arranged so as to oppose the vibrating electrode plate,
wherein in a view from a direction perpendicular to an upper surface of the substrate, an entire length of an outer edge of the vibrating electrode plate located between adjacent anchors is located outward of a tangent that circumscribes edges of the adjacent anchors on a side distant from a center of the vibrating electrode plate, and
one or two or more openings are provided in regions of the vibrating electrode plate that are in a vicinity of the anchors.
2. The capacitive sensor according to claim 1 , wherein the openings are provided at positions separated from positions of the anchors by an amount equal to or twice the size of the anchors.
3. The capacitive sensor according to claim 1 , wherein the openings are slits or through-holes that vertically penetrate the vibrating electrode plate.
4. The capacitive sensor according to claim 1 , wherein a portion of an outer peripheral edge of each of the openings that has a longest perpendicular distance from a line segment that connects an anchor in a vicinity of the opening and a center of the vibrating electrode plate is curved.
5. The capacitive sensor according to claim 3 , wherein the openings are slits shaped as an open ring.
6. The capacitive sensor according to claim 5 , wherein the slits are interrupted on a central side of the vibrating electrode plate.
7. The capacitive sensor according to claim 5 , wherein a gap between ends of each of the slits in an interrupted portion of the slit is smaller than a longest perpendicular distance from a line segment that connects an anchor in a vicinity of the slit and a center of the vibrating electrode plate to an outer peripheral edge of the slit.
8. The capacitive sensor according to claim 5 , wherein an end portion of each of the slits is curved toward an interior of a region surrounded by the slit.
9. The capacitive sensor according to claim 5 , wherein regions surrounded by the slits are blocked by a portion of the vibrating electrode plate.
10. The capacitive sensor according to claim 1 , wherein in the view from the direction perpendicular to the upper surface of the substrate, the opening has a shape symmetrical with respect to a straight line connecting the anchor and a center of the vibrating electrode plate.
11. The capacitive sensor according to claim 1 , wherein a plurality of openings provided in a region in a vicinity of one anchor are arranged in a periphery of the one anchor.
12. The capacitive sensor according to claim 1 , wherein the openings in the vibrating electrode plate are provided at locations that are not overlapped with the cavity in the view from the direction perpendicular to the upper surface of the substrate.
13. The capacitive sensor according to claim 1 ,
wherein the stationary member is the substrate, and
the vibrating electrode plate is fixed on the substrate via the anchors.
14. The capacitive sensor according to claim 13 , wherein the vibrating electrode plate and the substrate are electrically conductive by a conductive portion that penetrates an interior of an anchor.
15. The capacitive sensor according to claim 1 ,
wherein a back plate is formed on the substrate so as to cover the vibrating electrode plate,
the stationary member is the back plate, and
the vibrating electrode plate is fixed to a lower surface of the back plate via the anchors.
16. The capacitive sensor according to claim 1 ,
wherein the stationary member is the fixed electrode plate, and
the vibrating electrode plate is fixed to the fixed electrode plate via the anchors.
17. The capacitive sensor according to claim 1 , wherein the vibrating electrode plate is shaped as a rectangle.
18. An acoustic sensor employing the capacitive sensor according to claim 1 ,
wherein a plurality of acoustic holes for allowing passage of acoustic vibration is formed in the back plate and the fixed electrode plate.
19. The acoustic sensor according to claim 18 , wherein the acoustic holes located above the openings have a smaller opening area than the acoustic holes located in a central portion of the back plate.
20. A microphone comprising the acoustic sensor according to claim 18 and a circuit portion that amplifies a signal from the acoustic sensor and outputs the amplified signal to the outside.