Piezoelectric element and method for manufacturing the same
View Patent ↗A piezoelectric element includes a substrate, and a lower electrode layer, a piezoelectric layer, and an upper electrode layer sequentially formed on the substrate. The substrate has a linear thermal expansion coefficient higher than that of the piezoelectric layer, and the piezoelectric layer includes a polycrystalline body having an in-plane stress in a compressive direction. Thus, the piezoelectric element realizes the piezoelectric layer having a high orientation in a polarization axis direction, high proportionality of a displacement amount with respect to an applied voltage, and a large absolute value of the displacement amount.
1. A piezoelectric element comprising:
a substrate;
a lower electrode layer formed on the substrate;
a piezoelectric layer formed on the lower electrode layer; and
an upper electrode layer formed on the piezoelectric layer, wherein
the lower electrode layer includes a conductive oxide crystalline body,
the substrate has a linear thermal expansion coefficient higher than that of the piezoelectric layer, and
the piezoelectric layer is a polycrystalline body having an in-plane compressive stress.
2. The piezoelectric element according to claim 1 , wherein
the piezoelectric layer is formed by a chemical solution deposition method.
3. The piezoelectric element according to claim 1 , wherein
the substrate has fracture toughness higher than that of the piezoelectric layer.
4. The piezoelectric element according to claim 1 , wherein
the lower electrode layer is a perovskite type.
5. The piezoelectric element according to claim 1 , wherein
a difference between a lattice constant of a main oriented surface of the lower electrode layer and a lattice constant of a main oriented surface of the piezoelectric layer is within ±10%.
6. The piezoelectric element according to claim 1 , wherein
the piezoelectric layer includes a perovskite oxide ferroelectric body provided such that a surface vertical to the substrate is preferentially oriented in a polarization axis direction, and a surface parallel to the substrate is randomly oriented.
7. The piezoelectric element according to claim 1 , wherein
the substrate includes a metal material.
8. The piezoelectric element according to claim 1 , wherein
a highly conductive layer having resistivity lower than that of the lower electrode layer is formed under the lower electrode layer.
9. The piezoelectric element according to claim 1 , wherein
the substrate has a rough surface.
10. The piezoelectric element according to claim 1 , wherein
a surface state of the substrate has a surface roughness Ra of 90 nm or more.
11. The piezoelectric element according to claim 1 , wherein
a piezoelectric layer is further formed on a second surface opposed to a first surface across the substrate having the lower electrode layer, and the piezoelectric layer
the substrate has a linear thermal expansion coefficient higher than that of the piezoelectric layer on the second surface, and the piezoelectric layer on the second surface includes a polycrystalline body having an in-plane stress.
12. The piezoelectric element according to claim 11 , wherein
the piezoelectric layer on the second surface is formed on the second surface through the lower electrode layer.