Piezoelectric device
In a piezoelectric device, a layered portion includes, at a position at least above a recess, a single crystal piezoelectric layer and a pair of electrode layers to apply voltage to the single crystal piezoelectric layer. At least a portion of the pair of electrode layers includes a lower electrode layer extending along a surface of the single crystal piezoelectric layer, the surface being closer to a base. The lower electrode layer is present only inside the recess.
1. A piezoelectric device comprising:
a base including:
a first principal surface and a second principal surface positioned opposite to the first principal surface; and
a recess at the first principal surface; and
a layered portion provided on the first principal surface of the base so as to cover the recess from above; wherein
the layered portion includes, at a position at least above the recess, a single crystal piezoelectric layer and a pair of electrode layers to apply voltage to the single crystal piezoelectric layer;
at least a portion of the pair of electrode layers includes a lower electrode layer;
the lower electrode layer extends along a surface of the single crystal piezoelectric layer, the surface being closer to the base; and
the lower electrode layer is present only inside the recess.
2. The piezoelectric device according to claim 1 , wherein
the base includes a protrusion protruding into the recess from a bottom of the recess; and
the protrusion includes a top surface that is in contact with the lower electrode layer.
3. The piezoelectric device according to claim 2 , wherein
the single crystal piezoelectric layer has a hole extending therethrough from the first principal surface to the second principal surface at a position above the lower electrode layer;
extended wiring is provided in the hole and is electrically connected to the lower electrode layer; and
when the hole is viewed in a direction orthogonal to the first principal surface, the hole entirely overlaps the top surface of the protrusion.
4. The piezoelectric device according to claim 3 , wherein a portion of the lower electrode layer positioned between the hole and the top surface of the protrusion is thicker than a portion of the lower electrode layer that applies voltage to the single crystal piezoelectric layer.
5. The piezoelectric device according to claim 3 , wherein a portion of the lower electrode layer is positioned under the hole extending through the single crystal piezoelectric layer and covers the hole from below.
6. The piezoelectric device according to claim 1 , wherein the single crystal piezoelectric layer is made of lithium tantalate, lithium niobate, or rock crystal.
7. The piezoelectric device according to claim 1 , wherein the recess has a shape of a circle, an oval or a polygon.
8. The piezoelectric device according to claim 1 , wherein a width of an opening of the recess is smaller than a width of a bottom of the recess.
9. The piezoelectric device according to claim 1 , wherein a width of an opening of the recess is equal to a width of a bottom of the recess.
10. The piezoelectric device according to claim 1 , wherein a width of an opening of the recess is larger than a width of a bottom of the recess.
11. The piezoelectric device according to claim 1 , wherein an interior of the recess is sealed.
12. The piezoelectric device according to claim 1 , wherein an interior of the recess is under negative pressure.
13. The piezoelectric device according to claim 1 , wherein an interior of the recess is under atmospheric pressure.
14. The piezoelectric device according to claim 1 , wherein an interior of the recess is under positive pressure.
15. The piezoelectric device according to claim 1 , wherein a portion of the single crystal layer is above the recess.
16. The piezoelectric device according to claim 1 , wherein at least a portion of the pair of electrode layers includes an upper electrode layer on an upper surface of the single crystal piezoelectric layer above the recess.
17. The piezoelectric device according to claim 16 , wherein the lower electrode layer is positioned in an upper region in the recess so as to oppose at least a portion of the upper electrode layer with the single crystal piezoelectric layer being interposed therebetween.
18. The piezoelectric device according to claim 1 , wherein the pair of electrode layers includes only lower electrode layers.
19. The piezoelectric device according to claim 1 , wherein the pair of electrode layers includes only a pair of comb-shaped electrode layers.
20. The piezoelectric device according to claim 1 , wherein the single crystal piezoelectric layer includes a first hole above a first of the pair of electrode layers and a second hole above a second of the pair of electrode layers.