Piezoelectric device
In a piezoelectric device, when viewed in a direction perpendicular to one main surface, an outer shape of a recess is a polygonal shape or a circular shape. When n represents a number of sides of the polygonal shape, r represents a radius of a circumscribed circle of an imaginary regular polygon including n sides with a length identical to a length of a shortest of the sides, and d represents a maximum thickness of a membrane portion, which is located above the recess, of a multilayer portion, r≤197.7 dn −0.6698 when 3≤n≤7, and r≤52.69 d when 8≤n or when the outer shape of the recess is a circular shape.
1 . A piezoelectric device comprising:
a base portion including one main surface and another main surface located on an opposite side from the one main surface, and including a recess in the one main surface; and
a multilayer portion stacked on a side of the base portion where the one main surface is located so as to cover the recess from above; wherein
the multilayer portion includes, at least above the recess, a single-crystal piezoelectric layer and a pair of electrode layers through which a voltage is applied to the single-crystal piezoelectric layer;
the single-crystal piezoelectric layer curves convexly in the direction perpendicular to the one main surface towards the base portion above the recess;
an outer shape of the recess is a polygonal shape or a circular shape when viewed in a direction perpendicular to the one main surface; and
when n represents a number of a plurality of sides of the polygonal shape, r represents a radius of a circumscribed circle of an imaginary regular polygon including n sides with a length identical to a length of a shortest side among the plurality of sides, and d represents a maximum thickness of a membrane portion, which is located above the recess, of the multilayer portion:
r≤197.7 dn −0.6698 is satisfied when 3≤n≤7; and
r≤52.69 d is satisfied when 8≤n or when the outer shape of the recess is a circular shape.
2 . The piezoelectric device according to claim 1 , wherein the outer shape of the recess is rectangular or substantially rectangular.
3 . The piezoelectric device according to claim 1 , wherein
the base portion is provided with a hole that penetrates from a bottom of the recess to the other main surface; and
a diameter of the hole is about 140 μm or less when viewed in a direction perpendicular to the one main surface.
4 . The piezoelectric device according to claim 1 , wherein a pressure inside the recess is a negative pressure.
5 . The piezoelectric device according to claim 1 , wherein a width of an opening of the recess is smaller than a width of a bottom portion of the recess.
6 . The piezoelectric device according to claim 1 , wherein a width of an opening of the recess is equal to a width of a bottom portion of the recess.
7 . The piezoelectric device according to claim 1 , wherein a width of an opening of the recess is larger than a width of a bottom portion of the recess.
8 . The piezoelectric device according to claim 1 , wherein an inside of the recess is sealed.
9 . The piezoelectric device according to claim 1 , wherein a pressure inside the recess is atmospheric pressure.
10 . The piezoelectric device according to claim 1 , wherein a pressure inside the recess is a positive pressure.
11 . The piezoelectric device according to claim 1 , wherein the base portion includes silicon.
12 . The piezoelectric device according to claim 1 , wherein the single-crystal piezoelectric layer is flat at portions not above the recess.
13 . The piezoelectric device according to claim 1 , wherein a hole extends vertically through the single-crystal piezoelectric layer.
14 . The piezoelectric device according to claim 13 , wherein the hole is above the one main surface of the base portion and not above the recess.
15 . The piezoelectric device according to claim 1 , wherein the single-crystal piezoelectric layer includes lithium tantalate or lithium niobate.
16 . The piezoelectric device according to claim 15 , wherein the single-crystal piezoelectric layer has a uniform polarization state.
17 . The piezoelectric device according to claim 1 , wherein the multilayer portion curves convexly towards the other main surface above the recess.
18 . The piezoelectric device according to claim 1 , further comprising an intermediate layer including a lower surface located above the recess and curving convexly towards the other main surface.
19 . The piezoelectric device according to claim 18 , wherein the intermediate layer includes SiO 2 .
20 . A piezoelectric device comprising:
a base portion including one main surface and another main surface located on an opposite side from the one main surface, and including a recess in the one main surface; and
a multilayer portion stacked on a side of the base portion where the one main surface is located so as to cover the recess from above; wherein
the multilayer portion includes, at least above the recess, a single-crystal piezoelectric layer and a pair of electrode layers through which a voltage is applied to the single-crystal piezoelectric layer;
the multilayer portion curves convexly in the direction perpendicular to the one main surface towards the other main surface above the recess;
an outer shape of the recess is a polygonal shape or a circular shape when viewed in a direction perpendicular to the one main surface; and
when n represents a number of a plurality of sides of the polygonal shape, r represents a radius of a circumscribed circle of an imaginary regular polygon including n sides with a length identical to a length of a shortest side among the plurality of sides, and d represents a maximum thickness of a membrane portion, which is located above the recess, of the multilayer portion:
r≤197.7 dn −0.6698 is satisfied when 3≤n≤7; and
r≤52.69 d is satisfied when 8≤n or when the outer shape of the recess is a circular shape.