Stress sensor

1. A stress sensor comprising:

a stress detection layer including a laminated body including a first magnetic layer, a first non-magnetic layer, and a second magnetic layer that are laminated; wherein

the first magnetic layer and the second magnetic layer have mutually different magnetoelastic coupling constants;

one of the first magnetic layer and the second magnetic layer is a strain-insensitive layer with an absolute value of the magnetoelastic coupling constant of about 0.5 MJ/m 3 or less, and another one of the first magnetic layer and the second magnetic layer is a strain-sensitive layer with an absolute value of the magnetoelastic coupling constant that is larger than the value of the strain-insensitive layer; and

a relative angle of magnetization between the first magnetic layer and the second magnetic layer varies depending on a stress externally applied thereto, and a strain direction is detected by a change in electrical resistance according to a direction of the stress externally applied.

2. The stress sensor according to claim 1 , wherein one of the first magnetic layer and the second magnetic layer is a strain-insensitive layer, and an absolute value of the magnetoelastic coupling constant is about 0.1 MJ/m 3 or less.

3. The stress sensor according to claim 1 , wherein the absolute value of the magnetoelastic coupling constant of the strain-sensitive layer is about 1 MJ/m 3 or more.

4. The stress sensor according to claim 1 , wherein the magnetization directions of the first magnetic layer and the second magnetic layer are parallel or substantially parallel, or antiparallel or substantially antiparallel to each other in an initial state where no stress is applied.

5. The stress sensor according to claim 1 , wherein the stress detection layer further includes another laminated body including one or more structures each defined by a second non-magnetic layer and a third magnetic layer that are laminated.

6. The stress sensor according to claim 1 , further comprising a substrate to support the stress detection layer.

7. The stress sensor according to claim 6 , wherein the substrate is a flexible substrate.

8. The stress sensor according to claim 5 wherein each of the first, second, and third magnetic layers is made of metallic magnetic materials.

9. The stress sensor according to claim 8 , wherein each of the first, second, and third magnetic layers includes one material selected from a group of Fe, Co, Ni, and alloys including Fe, Co, or Ni.

10. The stress sensor according to claim 5 , wherein the first and second non-magnetic layers are metals or insulators.

11. The stress sensor according to claim 7 , wherein the flexible substrate is made of polyester, polycarbonate, or polyimide.

12. The stress sensor according to claim 1 , further comprising a base layer on which the stress detection layer is disposed.

13. The stress sensor according to claim 12 , wherein the base layer is made of Pt, Cu, Ta, or Au.

14. The stress sensor according to claim 1 , further comprising a protective layer disposed on the stress detection layer.

15. The stress sensor according to claim 14 , further comprising electrodes disposed on the protective layer.

16. The stress sensor according to claim 1 , further comprising electrodes disposed on opposite side surfaces of the stress detection layer.

17. The stress sensor according to claim 14 , wherein the protective layer is defined by an insulator.

18. The stress sensor according to claim 17 , wherein the insulator is made of one of silicon oxide, silicon nitride, aluminum oxide, or magnesium oxide.

19. The stress sensor according to claim 12 , further comprising:

a protective layer disposed on the stress detection layer;

an electrode disposed on the protective layer; and

another electrode disposed on the base layer.

20. The stress sensor according to claim 1 , wherein a thickness of the first non-magnetic layer is about 5 nm or less.