KR20090123669A - Backlighting unit employing polarized light source - Google Patents

Abstract

PURPOSE: A BLU(Backlight Unit) selecting a polarized light source emitting polarized light is provided to reduce the entire power consumption of an LCD(Liquid Crystal Display) module by reducing the loss of the light by reflective polarized DBEF(Double Brightness Enhancement Film). CONSTITUTION: LED(Light Emitting Device) packages comprises three or more non-polar or semi- polar LED chips(77a, 77b, 77c). Non-polar or semi- polar LED chips respectively include the LED chip emitting the blue light, and the LED chip emitting the green light and the LED chip emitting the red light. Non-polar or semi- polar LED chip comprises a nitride semiconductor layer of the GaN on the GaN substrate.

Description

BACKLIGHTING UNIT EMPLOYING POLARIZED LIGHT SOURCE}

The present invention relates to a backlight unit, and more particularly, to a backlight unit for irradiating polarized light to a liquid crystal display panel by employing a polarized light source.

Passive display devices, such as liquid crystal displays, can reflect or absorb ambient sunlight or room light to produce an image. Thus, ambient sunlight or room light is required to view the displayed image. However, there is a problem in that the displayed image cannot be viewed when the intensity of ambient sunlight or room light is not sufficient to illuminate a liquid crystal display (LCD) panel. As an alternative to this problem, a back light unit (BLU) for backlighting the display panel is generally employed.

The backlight unit includes a light source such as an incandescent lamp, a fluorescent lamp or a light emitting diode (LED). The light emitted from the light source illuminates the LCD panel to realize the image. On the other hand, LED is often used as a backlight light source due to its excellent color reproduction, and it is expected to increase its use in the future as it is environmentally friendly.

1 is a schematic diagram showing a conventional LCD module incorporating an LED light source.

Referring to FIG. 1, a conventional LCD module includes an LCD panel 10 and a backlight unit 20. The LCD panel 10 includes a liquid crystal layer 15 between the upper substrate 11 and the lower substrate 13, and also the upper polarizing film 17 and the lower substrate positioned on the upper substrate 11. (13) a lower polarizing film 19 positioned below. In general, the upper polarizing film 17 and the lower polarizing film 19 are disposed such that the polarization directions are perpendicular to each other. Meanwhile, the backlight unit 20 includes LEDs 23 as a light source, and a diffuser plate 25 and a brightness enhancement film (BEF) for mixing light emitted from the light sources 23. It includes. In addition, the backlight unit may further include a dual brightness enhancement film (DBEF).

The LEDs 23 may be arranged on a substrate (not shown), such as a printed circuit board, to form an array, and the LEDs 23 may include red, green and blue LEDs or may include white LEDs. Can be. These LEDs are regularly arranged on a printed circuit board to constitute an LED module, and a plurality of LED modules may be used to backlight the LCD panel 10. The reflective film 21 is positioned below the light exit surface of the LEDs 23 to reflect the light emitted from the LEDs to the upper side.

Light L emitted from the LEDs 23 and then passed through the diffusion plate 25, the BEF 27, and the DBEF 29 is incident on the LCD panel 10. The lower polarizing film 19 polarizes the light L, and the polarized light is incident on the liquid crystal layer. Light incident on the liquid crystal layer is incident on the upper polarizing film by maintaining the polarization direction or rotating 90 degrees according to the arrangement of the liquid crystal layer. Thereafter, the light maintaining the polarization direction is shielded by the upper polarizing film 17, and the light rotated 90 degrees passes through the upper polarizing film 17 to realize an image.

That is, according to the prior art, the light emitted from a light source such as an LED is firstly polarized using the lower polarizing film 19, and the direction of the polarized light is controlled using the liquid crystal layer 15, and again the upper polarizing film ( 17) to implement the image by the second polarization. Thus, since this prior art uses the first polarized light using the lower polarizing film 19, most of the light emitted from the light source (about 50%) is shielded by the lower polarizing film 19 and lost. As the light passes through the various films and many layers including the polarizing film, the light that makes up the final image is less than 10% of the total light. In addition, the use of BEF and DBEF, lower and upper polarizing films thickens the LCD panel and backlight unit.

Meanwhile, a reflective polarized DBEF film (Vikuiti ^™ DBEF) has been developed and used to reduce light loss and reduce overall power consumption. The reflective polarized DBEF film passes polarized light (eg, P wave) in one direction among light incident on the DBEF film and reflects polarized light (eg, S wave) in the other direction. The light reflected by the reflective polarization DBEF film is reflected back from the reflective film 21, and the DBEF film passes the polarization in one direction of the reflected light and reflects the polarization in the other direction again. That is, the reflective polarization DBEF film may increase the utilization of light by using both reflection and polarization. However, because light loss occurs when light is reflected, the DBEF film has a limit in reducing light loss. In addition, the reflective polarization DBEF film has a disadvantage of high manufacturing cost.

SUMMARY OF THE INVENTION An object of the present invention is to provide a backlight unit capable of reducing total power consumption by reducing light loss.

Another object of the present invention is to provide a backlight unit capable of reducing the thickness of the LCD panel and / or backlight unit.

Another object of the present invention is to provide a backlight unit for an LCD module capable of realizing an image without using a lower polarizing film and / or a reflective polarizing DBEF film.

In order to solve the above problems, the present invention provides a backlight unit employing a polarized light source. The backlight unit emits light onto a liquid crystal display panel, and includes a light emitting diode package including at least three non-polar or semi-polar LED chips each emitting light having a different wavelength. Include.

The liquid crystal display panel may include an upper substrate, a lower substrate, a liquid crystal layer positioned between the upper substrate and the lower substrate, and an upper polarizing film positioned on the upper substrate, wherein the backlight unit is disposed under the lower substrate. And irradiates polarized light onto the lower substrate.

Here, the non-polar light emitting diode is distinguished from a polar light emitting diode including a compound semiconductor layer grown in the c-axis direction, and includes a compound semiconductor layer grown on the m-plane or a-plane. And non-polar as well as semi-polar light emitting diodes.

In addition, the nonpolar light emitting diode includes a GaN-based nitride semiconductor layer such as GaN, InGaN, AlGaN, AlInGaN. The nitride semiconductor light emitting diode may emit light in an ultraviolet ray and visible light region by adjusting a composition ratio thereof.

Unlike the polar light emitting diode, the non-polar light emitting diode exhibits the characteristic of emitting polarized light, as reported in the Japanese Journal of Applied Physics, Vol 46, No. 42, 2007, pp. L1010-L1012. have.

Therefore, the present invention can extract polarized light from the light source by using the non-polar light emitting diode as a light source, and accordingly the lower polarizing film (19 of FIG. 1) or the reflective polarization DBEF ( 29) can be removed.

Meanwhile, the nonpolar light emitting diode may emit some unpolarized light. In this case, in order to polarize the non-polarized light, the liquid crystal display panel may further include a lower polarizing film positioned between the lower substrate and the backlight unit. However, since the ratio of the unpolarized light is relatively low, the lower polarizing film may have a lower polarization degree and a higher transmittance than the upper polarizing film.

In general, the polarization degree of the polarizing film used in the LCD module is 98 to 100%, the transmittance is 40 to 50%. However, since the light emitted from the non-polar light emitting diode has a high ratio of already polarized light, the lower polarizing film used in the embodiments of the present invention may have a polarization degree of 70 to 90%, and a transmittance of 60 to 80%. Can have

The at least three chips may include a light emitting diode chip that emits blue light, a light emitting diode chip that emits green light, and a light emitting diode chip that emits red light, and white light may be realized by these chips.

The LED package may include at least two non-polar or semi-polar LED chips and a polar light emitting diode chip that emit light having different wavelengths, respectively. For example, the at least two chips may include a light emitting diode chip emitting blue light and a light emitting diode chip emitting green light, and the polarity light emitting diode chip may include a light emitting diode chip emitting red light. The red light emitting diode chip may be formed of a nitride semiconductor, but is not limited thereto and may be formed of a GaAlInP series compound semiconductor.

The polarization light emitting diode chip emits unpolarized light, and in this case, to polarize the unpolarized light, the liquid crystal display panel may include a lower polarizing film positioned between the lower substrate and the backlight unit. . However, since the ratio of the unpolarized light is relatively low, the lower polarizing film may have a lower polarization degree and a higher transmittance than the upper polarizing film.

According to embodiments of the present invention, by adopting a polarized light source it is possible to reduce the light loss by the conventional polarizing film or reflective polarization DBEF, thus reducing the overall power consumption of the LCD module. In addition, the lower polarizing film and / or the reflective polarizing DBEF film can be removed to reduce the thickness of the LCD panel and / or backlight unit.

Hereinafter, with reference to the accompanying drawings will be described embodiments of the present invention; The following embodiments are provided as examples to ensure that the spirit of the present invention can be fully conveyed to those skilled in the art. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. In the drawings, widths, lengths, thicknesses, and the like of components may be exaggerated for convenience. Like numbers refer to like elements throughout.

2 is a schematic diagram illustrating an LCD module having a backlight unit according to an embodiment of the present invention.

Referring to FIG. 2, the LCD module includes an LCD panel 50 and a backlight unit 60. The LCD panel 50 is positioned on the upper substrate 51, the lower substrate 53, the liquid crystal layer 55 positioned between the upper substrate 51 and the lower substrate 53, and the upper substrate 51. An upper polarizing film 57. In addition, the LCD panel 50 may include a lower polarizing film 59 positioned below the lower substrate 13.

Meanwhile, the backlight unit 60 includes non-polar LED packages 63 as a light source, and a diffuser plate 65 and a brightness enhancement film for mixing light emitted from the light sources 63. (brightness enhancement film; BEF, 67).

The LED packages 63 may be arranged on a substrate (not shown) such as a printed circuit board to form an array, and the LED packages 63 may include red, green, and blue LED chips. . These LED packages are regularly arranged on a printed circuit board to constitute an LED module, and a plurality of LED modules can be used to backlight the LCD panel 50. The reflective film 61 may be positioned under the light emitting surface of the LED packages 63 to reflect the light emitted from the LEDs toward the upper side. The reflective film 61 may be formed on a printed circuit board on which LED packages are arranged. The LED packages 63 include nonpolar light emitting diode chips. The LED package 63 on which the non-polar LED chips are mounted will be described later in detail with reference to FIG. 4.

Non-polar light emitting diodes are distinguished from polar light emitting diodes comprising a compound semiconductor layer grown in the c-axis direction. For example, by growing a GaN-based nitride semiconductor layer such as GaN, InGaN, AlGaN, or AlInGaN on the m-plane or a-plane of a GaN substrate, there is no spontaneous polarization or piezoelectrice polarization. Alternatively, a semipolar light emitting diode can be manufactured.

In addition, the light emitting diode using the nitride semiconductor may be manufactured to emit light of a wavelength required in the ultraviolet to visible region by adjusting the composition ratio of the nitride semiconductor.

A nonpolar gallium nitride-based light emitting diode device having a polarization ratio of 0.80 has been reported in the Journal of the Korean Society for Applied Physics (Vol. 46, No. 42, 2007, pp. L1010-L1012). It can be further increased by improving the crystallinity of the layer, polishing the sidewalls of the light emitting diode chip, and the like.

Meanwhile, light L emitted from the LED packages 63 and passing through the diffusion plate 65 and the BEF 67 is incident on the LCD panel 50. At this time, since the ratio of the polarized light of the light (L) is relatively high, the polarization degree of the lower polarizing film 59 may be lower than the prior art. That is, the polarization degree of the lower polarizing film 59 may be relatively lower than the polarization degree of the upper polarizing film 57, and thus, the transmittance of the lower polarizing film 59 may be relatively increased to reduce light loss. have.

In general, a polarization degree of 98 to 100% is required for the polarizing film used in the LCD panel, and thus the transmittance does not exceed about 40 to 50%. However, in this embodiment, for example, a polarizing film having a polarization degree of 70 to 90% and a transmittance of 60 to 80% can be used as the lower polarizing film 59.

The light transmitted through the lower polarizing film 59 is incident on the liquid crystal layer, and the light incident on the liquid crystal layer is incident on the upper polarizing film by maintaining the polarization direction or rotating 90 degrees according to the arrangement of the liquid crystal layer. The image is realized by being shielded or passed by this upper polarizing film 57.

According to this embodiment, the light loss due to the polarizing film can be reduced without using a DBEF film such as the conventional reflective polarizing DBEF. Therefore, the manufacturing cost of the LCD panel can be reduced, and also the thickness of the backlight unit can be reduced. In addition, the transmittance of the lower polarizing film may be increased to further reduce light loss.

Meanwhile, when the polarization ratio of the light emitted from the nonpolar LED packages 63 is relatively high, the lower polarizing film 59 may also be removed.

3 is a schematic diagram illustrating an LCD module having a backlight unit according to another embodiment of the present invention.

Referring to FIG. 3, the LCD module according to the present embodiment includes the backlight unit 60 as described with reference to FIG. 2. In addition, the LCD module includes an LCD panel 70, wherein the LCD panel 70 includes an upper substrate 51, a lower substrate 53, a liquid crystal layer 55, and the like as described with reference to FIG. 2. An upper polarizing film 57. However, the LCD panel 70 is different from the LCD panel 50 of FIG. 2 in that a lower polarizing film is not used.

That is, when the polarization ratio of the light emitted from the non-polar LED packages 63 is relatively high, both the lower polarizing film 59 and the DBEF can be removed, and thus the thickness of the LCD panel 70 can be made smaller. have.

In the embodiments of the present invention, it has been described that the diffusion plate 65 and the BEF 67 are used, but these may also be removed. For example, by arranging the LED packages 63 at narrow intervals on the plane, high brightness plane light can be realized by the LED packages 63, thereby eliminating the diffuser plate and the BEF.

4 is a cross-sectional view illustrating an example of a light emitting diode package 63 that may be employed in embodiments of the present invention.

Referring to FIG. 4, the light emitting diode package has a package body 71. The package body is formed to have a recess, and lead terminals 73 are exposed in the recess. In addition, the side wall of the recess may be formed to be inclined at a predetermined angle.

The lead terminals 73 extend outside to protrude out of the package body 71. Lead terminals 73 protruding to the outside are connected to the printed circuit board and electrically connected to an external power source. The lead terminals 73 may be bent from outside to enable surface mounting.

Meanwhile, the heat sink 75 may be mounted on the lower portion of the package body 71. The heat sink is mounted to easily dissipate heat generated from the LED chips 77a, 77b, and 77c to the outside. The heat sink 75 may have a base portion and a protrusion protruding upward from the center portion of the base portion. The protrusion is inserted into the package body and exposed to the recess. The heat sink may be inserted into the through hole of the package body after forming the package body 71 having the through hole. Alternatively, the heat sink 75 may be mounted on the package body 71 by placing the lead terminals 73 and the heat sink 75 and forming a package body using an insert molding technique. The heat sink 75 may be electrically insulated from the lead terminals 73, but may be electrically connected to one of the lead terminals.

At least three LED chips 77a, 77b, and 77c emitting light of different wavelengths are mounted on the heat sink 75. The LED package may implement white light by including at least three LED chips 77a, 77b, and 77c that emit light having different wavelengths.

The LED chips 77a, 77b, and 77c may be non-polar or semi-polar light emitting diode chips. For example, the LED chips 77a, 77b, and 77c may be nonpolar or semipolar light emitting diode chips that emit blue light, green light, and red light, respectively. The non-polar light emitting diode chip may be made of a nitride semiconductor of GaN, InGaN, AlGaN, or AlGaInN, and may be formed by growing on the m-side or a-side of a GaN substrate.

In contrast, the LED chips 77a, 77b, and 77c may include general polarity LED chips that are not nonpolar or semipolar light emitting diode chips. For example, the LED chip 77c may be a polar LED chip emitting red light, and the LED chips 77a and 77b may be nonpolar or semipolar light emitting diode chips emitting light of different wavelengths. The polar LED chip emitting red light may be manufactured of a nitride semiconductor or a GaInAlP series compound semiconductor. The LED chips 77a and 77b may be light emitting diode chips of a nitride semiconductor series emitting blue light and green light, respectively.

Each of the LED chips 77a, 77b, and 77c includes two electrodes to be connected to an external power source. The electrodes may be located on the same side or opposite sides of the chip. The electrodes of the LED chips are electrically connected to the lead terminals 73 in various ways. For example, the electrodes may be electrically connected to the lead terminal through an adhesive, or may be connected to the lead terminal through a bonding wire (not shown). For example, in the case of an LED chip having electrodes formed on the same side, it may be electrically connected to lead terminals through two bonding wires. Alternatively, when the electrodes are located on opposite sides of one another, one electrode may be electrically connected to one lead terminal through a bonding wire, and the other electrode may be electrically connected to the heat sink 75 through a conductive adhesive. Can be. At this time, the heat sink 75 is electrically connected to another lead terminal through a bonding wire or directly.

The molding member 79 may be positioned on the LED chips 77a, 77b, and 77c. The molding member 79 may be formed of an epoxy resin or a silicone resin, and may be formed of a single layer or multiple layers. Meanwhile, a lens 83 may cover the LED chips 77a, 77b, 77c and the molding member 79, and the lens may have various shapes. For example, a top emitting LED according to aspects of the present invention. In order to implement, the lens may have the shape of a convex lens, as shown. At this time, the curvature of the lens is determined according to the required orientation angle. The lens 83 may be omitted by forming the molding member 79 in a lens shape.

In the present embodiment, the light emitting diode package includes mainly the LED chips 77a, 77b, 77c emitting blue light, green light, and red light, but the LED chips emitting light of various colors, for example, It may include a yellow LED chip, a cyan LED chip or an amber LED chip.

1 is a schematic view for explaining a liquid crystal display module according to the prior art.

2 is a schematic diagram illustrating a liquid crystal display module having a backlight unit according to an embodiment of the present invention.

3 is a schematic view illustrating a liquid crystal display module having a backlight unit according to another embodiment of the present invention.

4 is a cross-sectional view for explaining an example of a non-polar light emitting diode package that can be used in embodiments of the present invention.

Claims (6)

In the backlight unit for irradiating light to the liquid crystal display panel, A backlight unit comprising a light emitting diode package comprising at least three non-polar or semi-polar LED chips each emitting light of a different wavelength. The backlight unit of claim 1, wherein the nonpolar or semipolar light emitting diode chip comprises a gallium nitride-based nitride semiconductor layer grown on an m-plane or a-plane of a GaN substrate. The backlight unit of claim 1, wherein the at least three nonpolar or semipolar light emitting diode chips include a light emitting diode chip emitting blue light, a light emitting diode chip emitting green light, and a light emitting diode chip emitting red light. In the backlight unit for irradiating light to the liquid crystal display panel, A backlight unit comprising a light emitting diode package comprising at least two non-polar or semi-polar LED chips and a polar light emitting diode chip each emitting light of different wavelengths. The method according to claim 4, The non-polar or semi-polar light emitting diode chip includes a gallium nitride-based nitride semiconductor layer grown on the m-plane or a-plane of the GaN substrate. The method according to claim 4, The at least two non-polar or semi-polar light emitting diode chips include a light emitting diode chip emitting blue light and a light emitting diode chip emitting green light, wherein the polarity light emitting diode chip is a light emitting diode chip emitting red light.

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