Backlight unit

1. A backlight unit comprising:

a circuit board;

at least one light emitting diode chip disposed on the circuit board;

at least one reflector disposed on the light emitting diode chip; and

at least one light diffuser covering the light emitting diode chip and the reflector,

wherein the light diffuser comprises a cavity corresponding to the light emitting diode chip and the reflector disposed inside the light diffuser,

the light emitting diode chip comprising:

a substrate;

a light emitting structure disposed at a lower side of the substrate;

a transparent electrode layer disposed at a lower surface of the light emitting structure;

a first electrode pad electrically connected to a first conductivity type semiconductor layer of the light emitting structure;

a second electrode pad electrically connected to a second conductivity type semiconductor layer of the light emitting structure; and

a reflective layer formed to cover at least a portion of a lower side of the light emitting structure.

2. The backlight unit according to claim 1 ,

wherein the reflector is a DBR (Distributed Bragg Reflector) comprising at least a first layer and a second layer, each of the first layer and the second layer including SiO2, TiO2, SiN, or TiN.

3. The backlight unit according to claim 1 ,

wherein the reflector further comprises a first, a second and a third reflector to reflect at least a fraction of light emitted through un upper surface of the light emitting diode chip.

4. The backlight unit according to claim 1 ,

wherein the light diffuser comprises a transparent material.

5. The backlight unit according to claim 1 ,

wherein the light diffuser comprises a convex portion on an upper surface of thereof.

6. The backlight unit according to claim 5 ,

wherein the convex portion protrudes in an upward direction.

7. The backlight unit according to claim 1 ,

wherein the light diffuser has a semispherical structure.

8. The backlight unit according to claim 1 ,

wherein the light diffuser has a parabolic structure.

9. The backlight unit according to claim 8 ,

wherein the parabolic structure has a greater height than a width in a cross-section thereof.

10. The backlight unit according to claim 5 ,

wherein the convex portion has different radii of curvature along a light emission location of the convex portion.

11. The backlight unit according to claim 1 ,

wherein a light exit surface of the light diffuser has a flat structure.

12. The backlight unit according to claim 1 ,

wherein the reflective layer comprises an insulation layer including a single layer or multilayer DBR.

13. The backlight unit according to claim 1 ,

further comprising a housing which is open at an upper side thereof and contains the circuit board, the light emitting diode chip, the reflector and the light diffuser therein.

14. The backlight unit according to claim 1 ,

further comprising a wavelength conversion sheet disposed on the light diffuser.

15. The backlight unit according to claim 14 ,

wherein the wavelength conversion sheet converts wavelengths of light emitted from the light diffuser and emits white light.

16. The backlight unit according to claim 1 , wherein the reflector is a DBR (Distributed Bragg Reflector) comprising at least one set of two different layers, each layer including SiO2, TiO2, SiN, or TiN; and

the set of two different layers are stacked once or repeatedly on or above another set of two different layers.

17. The backlight unit according to claim 2 , wherein the DBR further comprises a third layer including SiO2, TiO2, SiN, or TiN; and

the first and the second layers are stacked once or repeatedly on or above another set of the first and the second layers.

18. The backlight unit according to claim 17 , wherein another set of the first and the second layers further includes the third layer.