Piezoelectric device
In a piezoelectric device, a piezoelectric driving portion includes layers and is directly or indirectly supported by a base portion. The piezoelectric driving portion includes a piezoelectric layer, an upper electrode layer, and a lower electrode layer. The upper electrode layer is disposed on the upper side of the piezoelectric layer. The lower electrode layer faces at least a portion of the upper electrode layer with the piezoelectric layer interposed therebetween. The piezoelectric driving portion includes a through groove extending through the piezoelectric driving portion in the vertical direction, so that a pair of inner side surfaces are provided. The pair of inner side surfaces each include a first small-width portion in which the width of the through groove decreases in a downward direction from an upper end surface of the piezoelectric layer.
1. A piezoelectric device comprising:
a base portion; and
a piezoelectric driving portion directly or indirectly supported by the base portion and including a plurality of layers; wherein
the piezoelectric driving portion includes a piezoelectric layer, an upper electrode layer on an upper side of the piezoelectric layer, and a lower electrode layer facing at least a portion of the upper electrode layer with the piezoelectric layer interposed between the lower electrode layer and the upper electrode layer;
the piezoelectric driving portion includes a through groove extending through the piezoelectric driving portion in a vertical direction, so that a pair of inner side surfaces are provided;
the pair of inner side surfaces each include a first small-width portion in which a width of the through groove decreases in a downward direction from an upper end surface of the piezoelectric layer; and
the width of the through groove decreases in a varying manner from an upper end of the through groove toward a lower end of the through groove in the vertical direction.
2. The piezoelectric device according to claim 1 , wherein
the piezoelectric driving portion is indirectly supported by the base portion and is positioned above the base portion; and
the piezoelectric driving portion does not overlap the base portion.
3. The piezoelectric device according to claim 1 , wherein
the piezoelectric layer includes first corner portions each of which is contiguous to the upper end surface of the piezoelectric layer and each of which defines at least a portion of one of the first small-width portions; and
each of the first corner portions is curved obliquely upward in a convex manner.
4. The piezoelectric device according to claim 1 , wherein the piezoelectric layer includes first inclined portions each of which is contiguous to the upper end surface of the piezoelectric layer and each of which defines at least a portion of one of the first small-width portions.
5. The piezoelectric device according to claim 1 , wherein
the piezoelectric driving portion includes an active layer below the lower electrode layer and the piezoelectric layer; and
each of the pair of inner side surfaces includes a second small-width portion in which the width of the through groove decreases in the downward direction from an upper end surface of the active layer.
6. The piezoelectric device according to claim 3 , wherein
the piezoelectric driving portion includes an active layer positioned below the lower electrode layer and the piezoelectric layer;
each of the pair of inner side surfaces includes a second small-width portion in which the width of the through groove decreases in the downward direction from an upper end surface of the active layer;
the active layer includes second corner portions each of which is contiguous to the upper end surface of the active layer and each of which defines at least a portion of one of the second small-width portions;
each of the second corner portions is curved obliquely upward in a convex manner; and
a radius of curvature of each of the first corner portions and a radius of curvature of each of the second corner portions are different from each other.
7. The piezoelectric device according to claim 1 , wherein
the piezoelectric layer is made of a single-crystal piezoelectric material; and
an axial direction of a polarization axis of the single-crystal piezoelectric material is inclined with respect to a lamination direction of the piezoelectric driving portion.
8. The piezoelectric device according to claim 7 , wherein the axial direction of the polarization axis of the single-crystal piezoelectric material is not perpendicular or substantially perpendicular to the lamination direction of the piezoelectric driving portion.
9. The piezoelectric device according to claim 1 , wherein a thermal expansion coefficient of the piezoelectric layer in the lamination direction of the piezoelectric driving portion and a thermal expansion coefficient of the piezoelectric layer in a planar direction are different from each other.
10. The piezoelectric device according to claim 1 , wherein the piezoelectric layer includes a hole extending through the piezoelectric layer and being positioned above the base portion.
11. The piezoelectric device according to claim 1 , wherein the piezoelectric layer is made of lithium tantalate or lithium niobate.
12. The piezoelectric device according to claim 10 , wherein a portion of the lower electrode layer is positioned below the hole.
13. The piezoelectric device according to claim 1 , wherein the lower electrode layer is connected to the piezoelectric layer via an etching stop layer.
14. The piezoelectric device according to claim 1 , wherein the lower electrode layer is made of Pt, Ni, or Au.
15. The piezoelectric device according to claim 1 , further comprising an intermediate layer in contact with a lower surface of the lower electrode layer and a portion of the piezoelectric layer not covered by the lower electrode layer.
16. The piezoelectric device according to claim 15 , wherein the intermediate layer is made of SiO 2 .