Electroluminescent display device having a plurality of low-refractive members

1. An electroluminescent display device comprising:

an overcoat layer on a substrate;

a plurality of low-refractive members formed of an inorganic matter and disposed on the overcoat layer;

a first electrode on the overcoat layer and the plurality of low-refractive members;

a bank layer disposed on the overcoat layer and the first electrode and including an opening configured to expose the first electrode;

an emitting layer disposed on the first electrode; and

a second electrode disposed on the emitting layer,

wherein each of the plurality of low-refractive members includes a first flat surface overlaid by the first electrode, a second flat surface below the first flat surface, the second flat surface having an area greater than that of the first flat surface and overlying the overcoat layer, the low-refractive member including first and second inclined surfaces extending between the first flat surface and the second flat surface, and

wherein a refractive index of each of the plurality of low-refractive members is lower than those of the overcoat layer and the first electrode.

2. The electroluminescent display device of claim 1 , wherein the first electrode is disposed to conform to the shape of the top surfaces of the plurality of low-refractive members and the overcoat layer, the first electrode including third and fourth inclined surfaces corresponding to the first and second inclined surfaces.

3. The electroluminescent display device of claim 2 , further comprising:

a light extraction member disposed between the third and fourth inclined surfaces and the emitting layer.

4. The electroluminescent display device of claim 1 , wherein an angle between the second flat surface and each of the first and second inclined surfaces is in a range of about 20° to 70°.

5. The electroluminescent display device of claim 1 , wherein:

the plurality of low-refractive members are disposed at a selected distance from each other, and

a ratio of a length of the first flat surface to a distance between the plurality of low-refractive members is in a range of about 0.3 to 5.

6. The electroluminescent display device of claim 1 , wherein a ratio of a thickness of the overcoat layer to a thickness of the plurality of low-refractive members is in a range of 0.3 to 1.

7. The electroluminescent display device of claim 3 , wherein the light extraction member and the bank layer are formed of the same material.

8. The electroluminescent display device of claim 1 , wherein each of the low-refractive members has a shape of a trapezoidal pyramid.

9. The electroluminescent display device of claim 1 , wherein each of the low-refractive members has a shape of a truncated cone.

10. The electroluminescent display device of claim 1 , wherein each of the low-refractive members has a shape of a truncated hexagonal pyramid.

11. The electroluminescent display device of claim 5 , wherein:

an average ratio of a length of the first flat surface to a distance between the plurality of low-refractive members is in a range of about 0.5 to 2.

12. The electroluminescent display device of claim 5 , wherein:

an average ratio of a length of the first flat surface to a distance between the plurality of low-refractive members is in a range of about 0.8 to 1.2.

13. The electroluminescent display device of claim 12 , wherein:

the ratio of a length of the first flat surface to a distance between the plurality of low-refractive members is less than 0.5 at some locations and greater than 2 at other locations.

14. The electroluminescent display device of claim 1 , wherein the first electrode is directly contacting the low refractive member.

15. The electroluminescent display device of claim 1 , wherein the first electrode is directly contacting the overcoat layer.