Display device comprising cover window including density control area

1 . A display device, comprising:

a display panel; and

a cover window including a density control area and located corresponding to a transmission direction of light emitted from the display panel,

wherein a refractive index of the density control area is gradually changed through a plurality of voids disposed in the density control area,

wherein the density control area comprises:

an upper region comprising a top surface of the cover window and comprising a first plurality of voids among the plurality of voids,

a middle region disposed below the upper region and comprising a second plurality of voids among the plurality of voids, and

a lower region disposed below the middle region and comprising a third plurality of voids among the plurality of voids,

wherein the refractive index of the density control area gradually increases from the upper region to the lower region of the density control area,

wherein the upper region, the middle region, and the lower region are monolithic, and

wherein one of the first plurality of voids and one of the second plurality of voids, which are located at an interface between the upper region and the middle region, are combined to form a void.

2 . The display device of claim 1 , wherein the density control area is located adjacent to the top surface of the cover window opposite to a bottom surface of the cover window facing the display panel.

3 . The display device of claim 2 , wherein the plurality of voids decrease in size or number per unit area from the upper region to the lower region of the density control area.

4 . The display device of claim 3 , wherein a top side of the density control area in the upper region of the density control area has a first density, and a difference between a refractive index of the top surface of the density control area and a refractive index of an air layer located outside the cover window is equal to or less than a first predetermined threshold.

5 . The display device of claim 4 , wherein a lower side of the density control area in the lower region of the density control area has a second density greater than the first density, and a difference between a refractive index of the bottom surface of the density control area and a refractive index of a glass forming the cover window is equal to or less than a second predetermined threshold.

6 . The display device of claim 1 , wherein the plurality of voids has a particle diameter of 400 nm or less.

7 . The display device of claim 1 , wherein the density control area has a depth of 50 nm to 800 nm.

8 . The display device of claim 1 , wherein glass modifier cations of the density control area are removed in the cover window.

9 . The display device of claim 8 , wherein the glass modifier cations include alkali metals and alkaline earth metals.

10 . The display device of claim 1 , wherein one of the second plurality of voids and one of the third plurality of voids, which are located at an interface between the middle region and the lower region, are combined to form a void.

11 . A display device, comprising:

a display panel; and

a cover window including a density control area and located on an image displaying surface of the display panel,

a plurality of voids provided in the density control area, so that a refractive index of the density control area gradually changes from a first refractive index to a second refractive index, from a first side of the density control area to a second side of the density control area opposite to the first side, the first side is a side of the density control area that is in contact with a medium surrounding the display device,

wherein a difference between the first refractive index and a refractive index of a material constituting the cover window is less than or equal to a first predetermined threshold,

wherein a difference between the second refractive index and a refractive index of the medium is less than or equal to a second predetermined threshold,

wherein the density control area comprises:

an upper region comprising the first side of the density control area and comprising a first plurality of voids among the plurality of voids,

a middle region disposed below the upper region and comprising a second plurality of voids among the plurality of voids,

a lower region disposed below the middle region and comprising the second side of the density control area, the lower region comprising a third plurality of voids among the plurality of voids,

wherein the refractive index of the density control area gradually increases from the upper region to the lower region of the density control area,

wherein a size of the second plurality of voids is greater than a size of the third plurality of voids, and the size of the second plurality of voids is smaller than a size of the first plurality of voids.

12 . The display device of claim 11 , wherein the medium includes air.

13 . The display device of claim 11 , wherein the upper region, the middle region, and the lower region are monolithic, and

wherein one of the first plurality of voids and one of the second plurality of voids, which are located at an interface between the upper region and the middle region, are combined to form a void.

14 . The display device of claim 13 , wherein one of the second plurality of voids and one of the third plurality of voids, which are located at an interface between the middle region and the lower region, are combined to form a void.