Piezoelectric thin film elemental device, sensor and actuator

1. A piezoelectric thin film elemental device comprising: a piezoelectric thin film on a substrate, wherein the piezoelectric thin film has a (K 1−x Na x )NbO 3 thin film expressed by a compositional formula (K 1−x Na x )NbO 3 (0<x<1) with a perovskite structure, and a ratio of an out-of-plane directional lattice constant c to an in-plane directional lattice constant a of the thin film is in a range of 0.98≦c/a ≦1.01.

2. The piezoelectric thin film elemental device according to claim 1 , wherein when there are a plurality of (K 1−x Na x )NbO 3 (0<x <1) layers in the piezoelectric thin film, the ratio in at least the thickest same composition layer made of (K 1−x Na x )NbO 3 out of these plurality of layers is within the range of 0.98≦c/a ≦1.01.

3. The piezoelectric thin film elemental device according to claim 1 , wherein the (K 1−x Na x )NbO 3 thin film is preferentially-oriented in a (001) plane direction.

4. The piezoelectric thin film elemental device according to claim 1 , wherein the (K 1−x Na x )NbO 3 thin film is formed by an RF magnetron sputtering technique.

5. The piezoelectric thin film elemental device according to claim 1 , wherein at least one kind of Ta, Li, Sb is added to the (K 1−x Na x )NbO 3 thin film.

6. The piezoelectric thin film elemental device according to claim 1 , wherein the x, being a composition ratio of Na, is in a range of 0.3≦x ≦0.7.

7. The piezoelectric thin film elemental device according to claim 1 , wherein a tensile stress is added to in the piezoelectric thin film, and the ratio of the (K 1−x Na x )NbO 3 thin film is in a range of 0.980≦c/a ≦0.993.

8. The piezoelectric thin film elemental device according to claim 7 , wherein the piezoelectric thin film is provided on a stress relaxation layer with smaller lattice constant than that of the piezoelectric thin film.

9. The piezoelectric thin film elemental device according to claim 1 , wherein a compression stress is generated in the piezoelectric thin film, and the ratio of the (K 1−x Na x )NbO 3 thin film is in a range of 1.004≦c/a ≦1.010.

10. The piezoelectric thin film elemental device according to claim 9 , wherein the piezoelectric thin film is provided on a stress relaxation layer with larger lattice constant than that of the piezoelectric thin film.

11. The piezoelectric thin film elemental device according to claim 1 , wherein an electrode is formed between the substrate and the piezoelectric thin film.

12. The piezoelectric thin film elemental device according to claim 11 , wherein the electrode is formed of Pt or Au.

13. The piezoelectric thin film elemental device according to claim 12 , wherein the electrode formed of Pt is preferentially-oriented in a (111) plane direction.

14. The piezoelectric thin film elemental device according to claim 11 , wherein the electrode is formed by an RF magnetron sputtering technique.

15. The piezoelectric thin film elemental device according to claim 11 , wherein an adhesive layer is provided between the substrate and the electrode.

16. The piezoelectric thin film elemental device according to claim 1 , wherein the substrate is a silicon substrate.

17. The piezoelectric thin film elemental device according to claim 16 , wherein a SiO 2 film is formed on a surface of the silicon substrate.

18. The piezoelectric thin film elemental device according to claim 1 , wherein an electrode is formed on the piezoelectric thin film.

19. An actuator, comprising:

the piezoelectric thin film elemental device according to claim 1 ; and

a voltage applying means for applying voltage to the piezoelectric thin film of the piezoelectric thin film elemental device.

20. A sensor, comprising:

the piezoelectric thin film elemental device according to claim 1 ; and

a voltage detector for detecting voltage generated in the piezoelectric thin film of the piezoelectric thin film elemental device.