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 back chamber 45 is vertically opened in a silicon substrate 42 . A thin film-like diaphragm 43 to serve as a movable electrode plate is formed on the top surface of the substrate 42 so as to cover the back chamber 45 . The back plate 48 is fixed to the top surface of the substrate 42 so as to cover the diaphragm 43 , and a fixed electrode plate 49 is provided on the under surface of the back plate 48 . Further, the diaphragm 43 is divided into a plurality of areas by the slit 47 , and the respective plurally divided diaphragms 43 a, 43 b and the fixed electrode plate 49 constitute a plurality of parallelly connected capacitors (acoustic sensing sections 60 a, 60 b ).
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 the 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, wherein
the diaphragm and the movable electrode plate are substantially divided by a slit into a plurality of areas, and a plurality of parallelly connected capacitors are configured by the respective divided movable electrode plates and the fixed electrode plate.
2. The acoustic sensor according to claim 1 , wherein the slit is formed in a position passing through a maximal displacement place of the diaphragm.
3. The acoustic sensor according to claim 1 , wherein the respective areas of the diaphragm divided by the slit respectively have the maximal displacement places with the slit provided therebetween.
4. The acoustic sensor according to claim 1 , wherein the slit is located on a line segment connecting any two supporting places out of supporting places of the diaphragm.
5. The acoustic sensor according to claim 1 , wherein the slit is partially interrupted, and the respective areas of the diaphragm, which are located on both sides of the slit with the slit provided therebetween, are partially connected to each other through the interrupted portion of the slit.
6. The acoustic sensor according to claim 1 , wherein a width of the slit is not larger than 10 μm.
7. The acoustic sensor according to claim 1 , wherein a length of the slit is not smaller than a half of a distance across length of the diaphragm in an extending direction of the slit.
8. The acoustic sensor according to claim 1 , wherein the diaphragm has a circular form.
9. The acoustic sensor according to claim 1 , wherein the diaphragm has a rectangular form.
10. The acoustic sensor according to claim 1 , wherein an edge of the diaphragm is supported by the substrate or the back plate at a plurality of supporting places, and a void is provided in at least one place between the adjacent supporting places out of the supporting places.
11. The acoustic sensor according to claim 1 , wherein an acoustic vibration reaches the diaphragm through the hollow section.
12. A microphone, comprising:
an acoustic sensor according to claim 1 ; and
a circuit for processing a signal outputted from the acoustic sensor.