Backlight unit using multi-cell light emitting diode
A backlight unit includes a backlight module with a printed circuit board including blocks and MJT LEDs disposed on the blocks, respectively and a backlight control module generating a signal for drive control of each of the blocks, wherein each of the blocks comprises at least one MJT LED, and the backlight control module includes a drive controller for On/Off control and dimming control of each of the blocks.
1. A backlight unit comprising:
a backlight module comprising:
a printed circuit board including blocks and multi junction technology light emitting diodes (MJT LEDs) disposed on the blocks, respectively; and
a backlight control module generating a signal for drive control of each of the blocks,
wherein:
each block comprises at least one MJT LED,
the backlight control module comprises a drive controller for On/Off control and dimming control of each block, and
each MJT LED comprises:
a first light emitting cell and a second light emitting cell disposed on a single growth substrate separated from each other, each of the first and second light emitting cells comprising: a lower semiconductor layer, an upper semiconductor layer disposed on the lower semiconductor layer, and an active layer disposed between the upper and lower semiconductor layers;
a first transparent electrode layer disposed on the first light emitting cell and electrically connected to the first light emitting cell;
an interconnection line electrically connecting the first light emitting cell to the second light emitting cell; and
an insulation layer insulating the interconnection line from a side surface of the first light emitting cell.
2. The backlight unit of claim 1 , wherein:
the backlight control module further comprises a drive power generator configured to supply a drive voltage to each block.
3. The backlight unit of claim 2 , wherein:
the drive controller is configured to independently detect and control a drive current for each block.
4. The backlight unit of claim 2 , wherein:
each block comprises an anode and a cathode; and
the anode and the cathode of each block are directly connected to the drive power generator and the drive controller, respectively.
5. The backlight unit of claim 2 , wherein:
the drive controller is configured to electrically connect or insulate the plurality of MJT LEDs from each other.
6. The backlight unit of claim 1 , wherein:
the drive controller is configured to perform dimming control with respect to each block through PWM control in response to the signal.
7. The backlight unit of claim 1 , wherein:
the number of blocks is M×N and the blocks are arranged in an M×N matrix, where M and N are natural numbers.
8. The backlight unit of claim 1 , wherein:
an upper surface of the lower semiconductor layer of the second light emitting cell comprises an exposed region exposed through the upper semiconductor layer and the active layer;
the interconnection line has a first connection portion for electrical connection to the first light emitting cell and a second connection portion for electrical connection to the second light emitting cell;
the first connection portion contacting the first transparent electrode layer; and
the second connection portion being electrically connected to the exposed region of the lower semiconductor layer of the second light emitting cell.
9. The backlight unit of claim 8 , wherein:
a portion of the first transparent electrode layer is connected to the second light emitting cell.
10. The backlight unit of claim 9 , wherein:
a portion of the first transparent electrode layer extends from an upper surface of the first light emitting cell to a side surface of the lower semiconductor layer of the second light emitting cell through a space between the first light emitting cell and the second light emitting cell.
11. The backlight unit of claim 10 , wherein:
a portion of the first transparent electrode layer disposed on the side surface of the lower semiconductor layer of the second light emitting cell has a larger width than a portion of the interconnection line disposed on the side surface of the lower semiconductor layer of the second light emitting cell.
12. The backlight unit of claim 10 , wherein:
a portion of the first transparent electrode layer disposed between the first light emitting cell and the second light emitting cell has a larger width than a portion of the interconnection line disposed between the first light emitting cell and the second light emitting cell.
13. The backlight unit of claim 9 , wherein:
the first transparent electrode layer is disposed between the second connection portion and the lower semiconductor layer of the second light emitting cell.
14. The backlight unit of claim 8 , wherein:
the first transparent electrode layer separates the interconnection line and the insulation layer from each other.
15. The backlight unit of claim 14 , wherein:
a portion of the insulation layer is disposed on a portion between the first light emitting cell and the second light emitting cell on the growth substrate.
16. The backlight unit of claim 8 , further comprising:
a current blocking layer disposed between the first light emitting cell and the first transparent electrode layer and separating a portion of the first transparent electrode layer from the first light emitting cell.
17. The backlight unit of claim 1 , further comprising:
field effect transistors (FETs); and
an FET controller configured to control On/Off functions of each of the FETs.
18. The backlight unit of claim 17 , wherein:
the number of FETs is the same as the number of MJT LEDs, and the FET controller is configured to control On/Off functions of each of the MJT LEDs through On/Off control of each of the FETs.
19. The backlight unit of claim 17 , wherein:
the number of FETs is the same as the number of blocks, and the FET controller is configured to control On/Off functions of each of the blocks through On/Off control of each of the FETs.
20. The backlight unit of claim 17 , wherein:
the FET controller is disposed in a drive IC, the drive IC comprising at least one of the FETs.
21. The backlight unit of claim 20 , wherein:
the number of FETs not included in the drive IC is less than the number of MJT LEDs.
22. The backlight unit of claim 20 , wherein:
the drive IC comprises all of the FETs.
23. The backlight unit of claim 20 , wherein:
the drive controller is disposed in the drive IC.
24. The backlight unit of claim 1 , further comprising:
an optical member covering each of the MJT LEDs,
wherein, assuming that major and minor axes of each of the MJT LEDs is a and b, respectively, light emitted through each of the optical members has a full width at half maximum greater than or equal to 0.6a and less than or equal to √{square root over (a 2 +b 2 )}.
25. The backlight unit of claim 24 , wherein:
light emitted through each of the optical members has a beam angle (θ Lens ), as represented by the Equation
θ
Lens
>
2
tan
-
1
(
FWHM
LED
2
OD
)
,
wherein FWHM LED is the full width at half maximum of light emitted from the MJT LED without the optical member and OD is a distance from a bottom surface of the MJT LED to a bottom surface of a diffusive plane.
26. The backlight unit of claim 24 , wherein a and b are the same.