Strain sensor and method of fabricating the same

1. A strain sensor, comprising:

an X-axis sensor formed on a flexible insulating substrate and responsible for sensing X-axis strain;

a Y-axis sensor formed on the flexible insulating substrate to be orthogonal to the X-axis sensor and responsible for sensing Y-axis strain;

a metal electrode formed on a region of the flexible insulating substrate where the X-axis sensor and the Y-axis sensor are not formed; and

an encapsulation layer formed on the X-axis sensor, the Y-axis sensor, and the metal electrode,

wherein the X-axis sensor and the Y-axis sensor have a metal-insulator heterostructure, and

wherein the X-axis sensor and the Y-axis sensor each comprise cracks therein.

2. The strain sensor according to claim 1 , wherein the metal-insulator heterostructure comprises first nanocrystals used as a metallic material and second nanocrystals used as an insulating material.

3. The strain sensor according to claim 2 , wherein a volume ratio of the first nanocrystals to the second nanocrystals is 38 to 18:62 to 82.

4. The strain sensor according to claim 2 , wherein the first nanocrystals or the second nanocrystals have a diameter of 5 nm to 15 nm.

5. The strain sensor according to claim 2 , wherein the first nanocrystals or the second nanocrystals comprise an organic ligand containing 1 to 3 carbon chains or an inorganic ligand.

6. The strain sensor according to claim 5 , wherein the organic ligand containing 1 to 3 carbon chains comprises at least one of 3-mercaptopropionic acid (MPA) and 1,2-ethanedithiol (EDT).

7. The strain sensor according to claim 5 , wherein the inorganic ligand comprises at least one of sulfide ion (S 2− ), chloride ion (Cl − ), bromide ion (Br − ), thiocyanate ion (SCN − ), iodide ion (I − ), disulfide ion (HS − ), telluride ion (Te 2− ), hydroxide ion (OH − ), tetrafluoroborate ion (BF 4 − ), and hexafluorophosphate ion (PF 6 − ).

8. The strain sensor according to claim 1 , wherein the encapsulation layer comprises at least one of SU-8, polydimethylsiloxane (PDMS), Ecoflex, poly(methyl methacrylate) (PMMA), and polyimide.

9. The strain sensor according to claim 1 , wherein the cracks are formed in the X-axis sensor and the Y-axis sensor so that the cracks are orthogonal to each other.

10. The strain sensor according to claim 2 , wherein the first nanocrystals comprise at least one of indium tin oxide (ITO), fluorine-doped tin oxide (FTO), and aluminum-doped zinc oxide (AZO).

11. The strain sensor according to claim 2 , wherein the second nanocrystals comprise at least one of zinc oxide (ZnO), silicon oxide (SiO 2 ), and aluminum oxide (Al 2 O 3 ).

12. The strain sensor according to claim 1 , wherein the metal electrode comprises at least one of a silver (Ag) nanowire, a copper (Cu) nanowire, an aluminum (Al) nanowire, a gold (Au) nanowire, a platinum (Pt) nanowire, a nickel (Ni) nanowire, a tungsten (W) nanowire, an iron (Fe) nanowire, a carbon nanotube (CNT), and graphene.

13. A strain sensor, comprising:

an X-axis sensor formed on a flexible insulating substrate and responsible for sensing X-axis strain;

a Y-axis sensor formed on the flexible insulating substrate to be orthogonal to the X-axis sensor and responsible for sensing Y-axis strain;

a metal electrode formed on a region of the flexible insulating substrate where the X-axis sensor and the Y-axis sensor are not formed; and

an encapsulation layer formed on the X-axis sensor, the Y-axis sensor, and the metal electrode,

wherein the X-axis sensor and the Y-axis sensor have a metal-insulator heterostructure, and

wherein the metal electrode comprises at least one of a silver (Ag) nanowire, a copper (Cu) nanowire, an aluminum (Al) nanowire, a gold (Au) nanowire, a platinum (Pt) nanowire, a nickel (Ni) nanowire, a tungsten (W) nanowire, an iron (Fe) nanowire, a carbon nanotube (CNT), and graphene.

14. A method of fabricating a strain sensor, comprising:

dispersing first nanocrystals and second nanocrystals in a solvent to prepare a sensing solution;

performing patterning using the sensing solution to form an X-axis sensor and a Y-axis sensor on a flexible insulating substrate so that the X-axis sensor and the Y-axis sensor are orthogonal to each other;

forming a metal electrode on a region of the flexible insulating substrate where the X-axis sensor and the Y-axis sensor are not formed;

forming cracks in the X-axis sensor and the Y-axis sensor; and

forming an encapsulation layer on the X-axis sensor in which cracks are formed, the Y-axis sensor in which cracks are formed, and the metal electrode.

15. The method according to claim 14 , wherein the X-axis sensor and the Y-axis sensor have a metal-insulator heterostructure.

16. The method according to claim 14 , wherein a volume ratio of the first nanocrystals to the second nanocrystals is 38 to 18:62 to 82.

17. The method according to claim 14 , wherein the performing further comprises replacing a first organic ligand formed on surfaces of the first nanocrystals and the second nanocrystals with a second organic ligand or an inorganic ligand.

18. The method according to claim 17 , wherein the first organic ligand contains 8 to 18 carbon chains.

19. The method according to claim 17 , wherein the second organic ligand contains 1 to 3 carbon chains.

20. The method according to claim 17 , wherein the inorganic ligand comprises at least one of sulfide ion (S 2− ), chloride ion (Cl − ), bromide ion (Br − ), thiocyanate ion (SCN − ), iodide ion (I − ), disulfide ion (HS − ), telluride ion (Te 2− ), hydroxide ion (OH − ), tetrafluoroborate ion (BF 4 − ), and hexafluorophosphate ion (PF 6 − ).