Foldable window, display device including the same, and a method of manufacturing the window

1. A window comprising:

a substrate comprising a folding area, a non-folding area, an upper surface, and a lower surface, wherein the folding area is configured to fold about a folding axis; and

a plurality of groove patterns arranged in the folding area along a first direction crossing the folding axis, wherein each of the plurality of groove patterns comprises:

a bottom surface recessed from the upper surface of the substrate and substantially parallel to the upper surface of the substrate; and

a side surface, wherein each side surface of the plurality of groove patterns connects each bottom surface of the plurality of groove patterns to the upper surface of the substrate, and wherein the side surface comprises at least one curved surface.

2. The window of claim 1 , wherein each of the side surfaces of the plurality groove patterns, when the substrate is in a non-folded state, comprises:

a first surface; and

a second surface facing the first surface and more spaced apart from the folding axis in the first direction than the first surface is, and

wherein the first surface is inclined at a first angle with respect to the bottom surface, wherein the second surface is inclined at a second angle with respect to the bottom surface, and wherein each of the first angle and the second angle is equal to or greater than about 90 degrees and is equal to or smaller than about 140 degrees.

3. The window of claim 2 , wherein the first angles of each of the plurality of groove patterns are substantially the same as each other.

4. The window of claim 2 , wherein the plurality of groove patterns comprise two or more groove patterns having different the first angles from each other.

5. The window of claim 2 , wherein the second angles of each of the plurality of groove patterns are substantially the same as the first angles respectively facing the second angles.

6. The window of claim 2 , wherein at least one second angle of the second angles of the plurality of groove patterns are different from the first angles of the plurality of groove patterns.

7. The window of claim 2 , wherein the second angles of the plurality of groove patterns decrease as a distance between a groove pattern of the plurality of groove patterns and the folding axis decreases.

8. The window of claim 1 , wherein thicknesses from the lower surface of the substrate to the bottom surfaces of each of the plurality of groove patterns are the same as each other.

9. The window of claim 1 , wherein thicknesses from the lower surface of the substrate to the bottom surfaces of each of the plurality of groove patterns are equal to or greater than about 1 micrometer (μm) and equal to or smaller than about 30 micrometer (μm).

10. The window of claim 1 , wherein the bottom surfaces of each of the plurality of groove patterns have a width equal to or greater than about 4 μm.

11. The window of claim 1 , wherein the plurality of groove patterns are symmetrical with respect to the folding axis.

12. The window of claim 1 , wherein the plurality of groove patterns comprise a mesh pattern.

13. The window of claim 1 , wherein the lower surface of the substrate faces the folding axis when the substrate is in a folded state.

14. The window of claim 1 , further comprising a filling member disposed in the plurality of groove patterns.

15. A display device comprising:

a display module configured to fold and un-fold; and

a window disposed on the display module and configured to fold and un-fold, wherein the window includes:

a substrate comprising a folding area, a non-folding area, an upper surface, and a lower surface, wherein the folding area is configured to fold about a folding axis; and

a plurality of groove patterns arranged in the folding area along one direction crossing the folding axis, wherein each of the plurality of groove patterns comprises:

a bottom surface recessed from the upper surface of the substrate and substantially parallel to the upper surface of the substrate; and

a side surface, wherein each side surface of the plurality of groove patterns connects each bottom surface of the plurality of groove patterns to the upper surface of the substrate, and wherein the side surface comprises at least one curved surface.

16. A method of manufacturing a window, comprising:

providing a mother substrate in which a first line extending in a first direction is for forming a first groove pattern; and

forming the first groove pattern in areas of the mother substrate, wherein the forming of the first groove pattern comprises:

irradiating, with a first laser beam, first portions, of the mother substrate, overlapping the first line; and

providing an alkaline solution onto the first portions of the mother substrate to etch the first portions, and

wherein a refractive index of the first portions irradiated with the first laser beam is different from a refractive index of the mother substrate before being irradiated by the first laser beam, and the first portions irradiated with the first laser beam have a thickness smaller than a thickness of a second portion of the mother substrate not irradiated by the first laser beam.

17. The method of claim 16 , further comprising forming a second groove pattern, wherein the forming of the second groove pattern comprises:

providing a second line spaced apart from the first line and extending in the first direction on the mother substrate to form the second groove pattern;

irradiating, with a second laser beam, third portions and fourth portions of the mother substrate, wherein the third portions overlap the second line, and wherein the fourth portions are spaced apart from the third portions in a second direction crossing the first direction; and

providing the alkaline solution onto the third portions and the fourth portions to etch the third portions and the fourth portions, and

wherein the third and fourth portions irradiated with the second laser beam have a refractive index different from the refractive index of the second portion of the mother substrate not irradiated by the second laser beam, wherein the third and fourth portions irradiated with the second laser beam have a thickness smaller than the thickness of the second portion of the mother substrate not irradiated by the second laser beam, and the second groove pattern has a width greater than a width of the first groove pattern in the second direction.

18. The method of claim 17 , wherein the thickness of the third portions is substantially the same as the thickness of the fourth portions.

19. The method of claim 17 , wherein the thickness of the third portions is different from the thickness of the fourth portions.

20. The method of claim 16 , wherein the alkaline solution has a temperature equal to or greater than about 100 Celsius degrees and equal to or smaller than about 150 Celsius degrees.