Piezoelectric element, piezoelectric device, and method of manufacturing piezoelectric element
A piezoelectric element includes a plurality of vibration regions that are separated from each other by a slit, and the slit is formed to have a tapered portion that is tapered from a first surface of the vibration regions on an opposite side to a support to a second surface opposite to the first surface. An electrode film is positioned inside than the slit when being viewed from a normal direction orthogonal to the first surface, and an angle formed by a side surface of the tapered portion in the vibration region and a surface parallel to the first surface is in a range of 39 to 81 degrees.
1 . Piezoelectric element comprising:
a support; and
a vibrating portion configured to output a pressure detection signal in accordance with a pressure, wherein
the vibrating portion includes a piezoelectric film disposed on the support and made of scandium aluminum nitride, and an electrode film connected to the piezoelectric film to generate electric charges by deformation and to extract the electric charges generated,
the vibrating portion is configured to have a support region supported by the support, and a plurality of vibration regions connected to the support region and floating from the support,
the plurality of vibration regions are separated from each other by a slit,
the slit has a tapered portion that is tapered from a first surface of the vibration regions on an opposite side to the support, to a second surface opposite to the first surface,
the electrode film is positioned in the vibration region such that the electrode film is not exposed at the tapered portion of the slit when being viewed from a normal direction that is orthogonal to the first surface, and
an angle defined by a side surface of the tapered portion in the vibration region and a surface parallel to the first surface is in a range of 39 to 81 degrees.
2 . The piezoelectric element of claim 1 , wherein
the angle defined by the side surface of the tapered portion and the surface parallel to the first surface is 63 degrees or less.
3 . The piezoelectric element of claim 1 , wherein
the angle defined by the side surface of the tapered portion and the surface parallel to the first surface is 45 degrees or more.
4 . The piezoelectric element of claim 1 , wherein
the slit is configured to have the tapered portion provided on a side of the first surface of the vibration region and a constant width portion provided on a side of the second surface and having a constant width, and
the tapered portion and the constant width portion are connected to each other.
5 . The piezoelectric element of claim 1 , wherein
the slit has a tapered shape in which a width of the slit is narrowed from the support region toward an opposite end of the vibration region opposite to the support region.
6 . The piezoelectric element of claim 1 , wherein
the vibration region and the electrode film are arranged in a state of point symmetry with respect to a center portion of the vibration region in the normal direction to the first surface of the vibration region opposite to the support.
7 . The piezoelectric element of claim 6 , wherein
the vibration region has a first region adjacent to the support region, and a second region different from the first region,
the piezoelectric film is made of a material having a hexagonal crystal structure, and
the electrode film is divided by six electrode film slits, and has a hexagonal virtual shape connecting predetermined locations in the electrode film slits of the first region, when being viewed from the normal direction.
8 . The piezoelectric element of claim 6 , wherein
the support has a support substrate and an insulation film disposed on the support substrate and on which the vibrating portion is disposed,
the support substrate and the insulation film are configured to have a recess for floating the vibration region,
the support substrate is made of a silicon substrate, and
an outline of the vibration region has a regular octagonal shape when being viewed from the normal direction.
9 . The piezoelectric element of claim 1 , wherein
an outline of the vibration region has a polygonal shape when being viewed from the normal direction to the first surface of the vibration region opposite to the support, and
at least one of the electrode film and the vibration region has a polygonal shape with a corner, and the corner is positioned at a different portion from a virtual line connecting opposite corners of the outline of the vibration section.
10 . A piezoelectric device comprising:
a casing; and
a piezoelectric element disposed in the casing, the piezoelectric element includes a support, and a vibrating portion configured to output a pressure detection signal in accordance with a pressure, wherein
the vibrating portion includes a piezoelectric film disposed on the support and made of scandium aluminum nitride, and an electrode film connected to the piezoelectric film to generate electric charges by deformation and to extract the electric charges generated,
the vibrating portion is configured to have a support region supported by the support, and a plurality of vibration regions connected to the support region and floating from the support,
the plurality of vibration regions are separated from each other by a slit,
the slit has a tapered portion that is tapered from a first surface of the vibration regions on an opposite side to the support, to a second surface opposite to the first surface,
the electrode film is positioned in the vibration region such that the electrode film is not exposed at the tapered portion of the slit when being viewed from a normal direction that is orthogonal to the first surface,
an angle defined by a side surface of the tapered portion in the vibration region and a surface parallel to the first surface is in a range of 39 to 81 degrees,
the casing includes a mounted member on which the piezoelectric element is mounted, and a lid portion fixed to the mounted member in a state of accommodating the piezoelectric element in the casing, and
the casing has a through hole communicating with an outside and introducing an atmospheric pressure therein.
11 . The piezoelectric device of claim 10 , wherein
when a space within the casing which is different from a pressure receiving surface space positioned between the through hole and the vibrating portion is defined as a back space, an acoustic compliance of the back space is designated as Cb, and a thickness of the vibration region is designated as h, an average slit width that is an average of widths of the slit along a thickness direction is designated as ga, an air resistance is designated as μ, and a slit length along the side surface of the vibration region of the slit is designated L, the slit length satisfies a following formula
L
≤
3
×
μ
×
h
×
40
π
×
Cb
2
×
ga
3
.
Formula
12 . The piezoelectric device of claim 11 , wherein
the piezoelectric element has the support mounted on the mounted member via a joining member, and has an outline of a polygonal shape with corner portions when being viewed from the normal direction of the first surface opposite to the support in the vibration region, and
the joining member is arranged at a portion different from the corner portions in the normal direction.
13 . The piezoelectric device of claim 12 , wherein
the joining member has an outline of a polygonal shape with corner portions when being viewed from the normal direction, and the corner portions of the joining member are positioned on a different portion from a virtual line connecting opposite corner portions in the outline of the piezoelectric element.
14 . The piezoelectric device of claim 12 , wherein
the mounted member has a protrusion provided at a portion where the joining member is arranged, and
the joining member is arranged on the protrusion.