Acoustic sensor and microphone
Provided is an acoustic sensor capable of improving an S/N ratio of a sensor without preventing reduction in size of the sensor. A diaphragm 43 as a movable electrode plate is formed on the top surface of a silicon substrate 42 . The diaphragm 43 has a rectangular form, and four corners and midsections of long sides of the diaphragm 43 are supported by anchors 46 . A displacement of the diaphragm 43 is minimal on a line D that connects between the anchors 46 at the midsections of the long sides. A displacement maximal point G, at which a displacement is maximal, is present on each side of the line D, and the line D extends in a direction intersecting with a line connecting between the displacement maximal points G.
1. An acoustic sensor, comprising:
a substrate having a hollow section;
a thin film-like diaphragm, arranged above the substrate so as to cover the hollow section;
a movable electrode plate, formed on the diaphragm;
a back plate, fixed to a top surface of the substrate so as to be opposed to the diaphragm; and
a fixed electrode plate, provided on the back plate in a position opposed to the movable electrode plate,
characterized in that
the diaphragm is supported along a periphery of the diaphragm on the substrate or the back plate by a plurality of supporting sections,
the diaphragm has points, at which a displacement amount is maximal at a time of vibration,
the plurality of supporting sections supports the periphery of the diaphragm on both sides of the diaphragm segmented by a line segment connecting between adjacent maximal points at which the displacement amount of the diaphragm is maximal, and
the plurality of supporting sections supports the periphery of the diaphragm in an area of the diaphragm between the adjacent maximal points.
2. The acoustic sensor according to claim 1 , wherein
the diaphragm has a plurality of outwardly extended beam sections, and
each beam section is supported by the supporting sections.
3. The acoustic sensor according to claim 1 , wherein the diaphragm has a rectangular form.
4. The acoustic sensor according to claim 3 , wherein the diaphragm is supported by the plurality of the supporting sections arranged in grid form.
5. The acoustic sensor according to claim 4 , wherein the diaphragm is supported by the supporting sections at four corners, and is further supported by the supporting sections located at an intermediate portion between the corners, and the intermediate portion is located on opposite sides of the rectangular form of the diaphragm.
6. The acoustic sensor according to claim 1 , wherein
the diaphragm is further supported by at least three supporting sections along a straight line intersecting with the line segment connecting between the adjacent maximal points at which the displacement amount of the diaphragm is maximal.
7. The acoustic sensor according to claim 1 , wherein the plurality of supporting sections is located on a straight line intersecting with the line segment connecting between the adjacent maximal points and distance between the plurality of supporting sections located on the straight line intersecting with the line segment is shorter than distance between two supporting sections located at opposite corners of the diaphragm.
8. The acoustic sensor according to claim 7 , wherein a whole perimeter of a periphery of the diaphragm is supported by the supporting sections provided on the substrate or the back plate.
9. The acoustic sensor according to claim 1 , wherein the diaphragm is divided by a slit.
10. The acoustic sensor according to claim 9 , wherein the slit is formed in the diaphragm on a line that connects between two of said supporting sections.
11. The acoustic sensor according to claim 9 , wherein a width of the slit is not larger than 10 μm.
12. The acoustic sensor according to claim 9 , wherein length of the slit is not smaller than a half of a diameter of the diaphragm.
13. The acoustic sensor according to claim 1 , wherein a void is formed between the diaphragm and the substrate in at least one place between adjacent supporting sections.
14. The acoustic sensor according to claim 1 , wherein an acoustic vibration reaches the diaphragm through the hollow section.
15. A microphone, provided with the acoustic sensor according to claim 1 ; and a circuit for processing a signal outputted from the acoustic sensor.