Piezoelectric thin-film element, piezoelectric sensor and vibration generator
View Patent ↗A piezoelectric thin-film element includes a substrate, a lower electrode layer formed on the substrate, a piezoelectric thin-film layer that is formed on the lower electrode layer and includes potassium sodium niobate having a perovskite structure represented by the composition formula of (K 1-x Na x )NbO 3 (0.4≦x≦0.7), and an upper electrode layer formed on the piezoelectric thin-film layer. The piezoelectric thin-film layer is formed such that a value of (Ec − +Ec + )/2 is not less than 10.8 kV/cm and a value of (Pr − +Pr + )/2 is not more than −2.4 μC/cm 2 where Ec − and Ec + are intersection points of a polarization-electric field hysteresis loop and the x-axis indicating an electric field and Pr − and Pr + are intersection points of the polarization-electric field hysteresis loop and the y-axis indicating polarization.
1. A piezoelectric thin-film element, comprising:
a substrate;
a lower electrode layer formed on the substrate;
a piezoelectric thin-film layer that is formed on the lower electrode layer and comprises potassium sodium niobate including a perovskite structure represented by a composition formula of (K 1-x Na x )NbO 3 (0.4≦x≦0.7); and
an upper electrode layer formed on the piezoelectric thin-film layer,
wherein the piezoelectric thin-film layer is formed such that a value of (Ec − +Ec + )/2 is not less than 10.8 kV/cm and a value of (Pr − +Pr + )/2 is not more than −2.4 μC/cm 2 , where Ec − and Ec + are intersection points of a polarization-electric field hysteresis loop and an x-axis indicating an electric field and Pr − and Pr + are intersection points of the polarization-electric field hysteresis loop and a y-axis indicating polarization.
2. The piezoelectric thin-film element according to claim 1 , wherein the piezoelectric thin-film layer has a relative permittivity of not more than 490.
3. The piezoelectric thin-film element according to claim 1 , wherein piezoelectric displacement in the piezoelectric thin-film layer without polarization treatment occurs in a contraction direction in a case of applying a positive electric field to the upper electrode layer and occurs in an elongation direction in a case of applying a negative electric field to the upper electrode layer.
4. The piezoelectric thin-film element according to claim 1 , wherein a substrate temperature during formation of the piezoelectric thin-film layer is in a range of 420° C. to 480° C.
5. The piezoelectric thin-film element according to claim 1 , wherein a substrate temperature during formation of the piezoelectric thin-film layer is in a range of 420° C. to 520° C., and the formed piezoelectric thin-film layer is subjected to heat treatment at 410° C. to 500° C.
6. The piezoelectric thin-film element according to claim 1 , wherein the piezoelectric thin-film layer comprises a pseudo-cubic crystal or a tetragonal crystal having a perovskite structure and preferentially oriented to a (001) plane direction, and a rate of orientation in the (001) plane direction is not less than 95%.
7. The piezoelectric thin-film element according to claim 1 , wherein the piezoelectric thin-film layer is subjected to stress in a compression direction from the lower electrode layer or the substrate.
8. The piezoelectric thin-film element according to claim 1 , wherein the lower electrode layer comprises Pt preferentially oriented to a (111) plane direction.
9. A piezoelectric sensor, comprising the piezoelectric thin-film element according to claim 1 .
10. A vibration generator, comprising the piezoelectric thin-film element according to claim 1 .
11. The piezoelectric thin-film element according to claim 1 , wherein the substrate comprises a silicon-on-insulator substrate.
12. The piezoelectric thin-film element according to claim 1 , wherein the substrate comprises a Si substrate including a surface oriented to a (100) plane direction.
13. The piezoelectric thin-film element according to claim 12 , further comprising:
an adhesive layer disposed between the Si substrate and the lower electrode layer.
14. The piezoelectric thin-film element according to claim 13 , wherein the adhesive layer comprises one of Ti, TiO, and TiO 2 .
15. The piezoelectric thin-film element according to claim 1 , wherein the lower electrode layer comprises one of Pt, Au, and Al.
16. The piezoelectric thin-film element according to claim 1 , further comprising:
an adhesive layer disposed between the substrate and the lower electrode layer.
17. The piezoelectric thin-film element according to claim 16 , wherein the adhesive layer comprises one of Ti, TiO, and TiO 2 .
18. The piezoelectric thin-film element according to claim 1 , wherein the upper electrode layer includes a circular electrode.
19. The piezoelectric thin-film element according to claim 18 , wherein the upper electrode layer comprises one of Pt, Au, and Al.
20. The piezoelectric thin-film element according to claim 1 , wherein the upper electrode layer comprises one of Pt, Au, and Al.