Display device utilizing a thin film encapsulation layer having a plurality of sub-layers

1. A display device comprising:

a display substrate comprising at least one step portion; and

a thin film encapsulation layer above the display substrate,

the thin film encapsulation layer comprising a buffer layer and a barrier layer above the buffer layer,

the buffer layer comprising a plurality of sub-layers and interfaces between the plurality of sub-layers, each one of the sub-layers comprising a first portion and a second portion between the first portion and the display substrate, a carbon content of each one of the sub-layers gradually increasing from the first portion toward the second portion,

a carbon content of the buffer layer changing at each of the interfaces in a thickness direction of the buffer layer, and

the interfaces comprising a curved surface changing from a concave shape to a convex shape toward a portion overlapping the step portion from an outer portion of the step portion, a distance between each of adjacent interfaces of the plurality of interfaces increases toward the display substrate in the outer portion of the step portion,

wherein the plurality of sub-layers comprise a silicon oxide comprising carbon and hydrogen, and

wherein each of the plurality of sub-layers comprises about 20 to about 50 atomic % of silicon, about 10 to about 40 atomic % of oxygen, and about 30 to about 60 atomic % of carbon based on a total number of atoms of the silicon, the oxygen, and the carbon.

2. The display device of claim 1 , wherein each of the plurality of sub-layers has a thickness from about 300 Å to about 10000 Å.

3. The display device of claim 1 , wherein an interval between two adjacent interfaces of the interfaces reduces toward a portion overlapping the step portion from the outer portion of the step portion.

4. The display device of claim 1 , wherein the buffer layer has a first thickness at a location spaced from the step portion and has a second thickness at a location overlapping the step portion, and wherein the second thickness is less than the first thickness and greater than or equal to 0.5 times the first thickness.

5. The display device of claim 1 , wherein an upper surface of the first portion forms an interface of the interfaces, and

wherein the first portion has a silicon content ratio greater than that of the second portion, and the first portion has a carbon content ratio less than that of the second portion.

6. The display device of claim 5 , wherein each of the plurality of sub-layers comprises about 30 to about 40 atomic % of the silicon, about 18 to about 28 atomic % of the oxygen, and about 40 to about 50 atomic % of the carbon based on a total number of atoms of the silicon, the oxygen, and the carbon.

7. The display device of claim 5 , wherein each of the plurality of sub-layers comprises about 33 to about 36 atomic % of the silicon, about 20 to about 23 atomic % of the oxygen, and about 42 to about 45 atomic % of the carbon based on a total number of atoms of the silicon, the oxygen, and the carbon.

8. The display device of claim 1 , wherein the display substrate comprises a base substrate and a display portion above the base substrate,

wherein the display portion comprises a plurality of display elements and a pixel-defining layer defining a light-emitting region of the plurality of display elements, and

wherein the at least one step portion comprises the pixel-defining layer.

9. The display device of claim 8 , further comprising a protective layer above the display portion, the protective layer comprising a same material as that of the buffer layer.

10. The display device of claim 9 , wherein each of the plurality of display elements comprises a first electrode, a second electrode, and an intermediate layer between the first and second electrodes, the intermediate layer comprising an organic emission layer, and

wherein the display substrate further comprises a capping layer between the first electrode and the protective layer, the capping layer having a refractive index greater than that of the protective layer.

11. The display device of claim 10 , wherein the protective layer has a refractive index from about 1.38 to about 1.5.

12. The display device of claim 9 , wherein the protective layer further comprises silicon carbide to which hydrogen is coupled.

13. The display device of claim 8 , wherein the thin film encapsulation layer is configured to seal the display portion,

wherein the barrier layer comprises a first barrier layer and a second barrier layer overlapping each other with the buffer layer therebetween, and

wherein the first and second barrier layers comprise an inorganic layer.

14. The display device of claim 13 , wherein the first and second barrier layers contact each other at an outer portion of the buffer layer.