Planar light source device and liquid crystal display device having the same

A planar light source device includes a lower substrate, a cathode electrode a carbon nanotube, an upper substrate, a fluorescent layer, and an anode electrode. The cathode electrode is on the lower substrate. The carbon nanotube is electrically connected to the cathode electrode. The upper substrate faces the lower substrate. The fluorescent layer and the anode electrode are formed on the upper substrate. Therefore, the planar light source device generates light without using mercury.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Korean Patent Application No. 2005-59463, filed on Jul. 2, 2005, the disclosure of which is hereby incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a planar light source device and a liquid crystal display (LCD) device having the planar light source device. More particularly, the present invention relates to a field emission-type planar light source device, and an LCD device having the planar light source device.

2. Description of the Related Art

Various flat display panel devices, such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, organic light-emitting diode (OLED) devices, etc., have been developed to replace cathode ray tube (CRT) devices.

The LCD device that is widely used in various fields includes an LCD panel that has a thin-film transistor (TFT) substrate, a color filter substrate, and a liquid crystal layer interposed between the TFT substrate and the color filter substrate. The LCD panel is a non-emissive-type display element, and thus the LCD device requires a backlight unit that is disposed under the TFT substrate to supply the LCD panel with light. A liquid crystal of the liquid crystal layer varies arrangement in response to an electric field applied thereto, and thus a light transmittance of the liquid crystal layer is changed, thereby displaying an image having a predetermined gray-scale.

A light source of the backlight unit includes a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), a flat fluorescent lamp (FFL) that is a type of planar light source, etc. Each of the CCFL, EEFL, and FFL generates light using a plasma discharge. When a high voltage difference is applied to electrodes of the lamp, an electric field is formed between the electrodes to emit electrons. The electrons excite mercury molecules, and ultraviolet light is generated from the excited mercury molecules. A fluorescent layer changes the ultraviolet light into visible light so that the visible light exits the lamp. However, mercury is a pollutant and is restricted by environmental regulations. Thus, a light source that does not use mercury is required.

SUMMARY OF THE INVENTION

The present invention provides a field emission-type planar light source device.

The present invention also provides a liquid crystal display (LCD) device having the above-mentioned planar light source device.

A field emission-type planar light source device in accordance with one aspect of the present invention includes an emitter tip including a carbon nanotube and a cathode electrode having a charge transition rate of no more than about 10−6.1A/cm2.

A field emission-type planar light source device in accordance with another aspect of the present invention includes an emitter tip including a carbon nanotube, a gate electrode surrounding an upper portion of the emitter tip and a catalyst metal accelerating growth of the carbon nanotube on the gate electrode.

A field emission-type planar light source device in accordance with still another aspect of the present invention includes a lower substrate, a cathode electrode including at least two layers on the lower substrate, a carbon nanotube grown on the cathode electrode and an upper substrate facing the lower substrate, the upper substrate including a fluorescent material and a transparent electrode.

The cathode electrode may include a charge transition rate per unit area of no more than about 10−6.1A/cm2. The cathode electrode may have a double-layer structure including a lower cathode electrode layer and an upper cathode layer, and the lower cathode electrode layer may include substantially the same material as the gate electrode.

The gate electrode may include a material having a charge transition rate per unit area of no less than about 10−6.0A/cm2.

An LCD (LCD) device in accordance with one aspect of the present invention may include the planar light source device and an LCD panel on the planar light source device.

A frequency of a voltage applied to the gate electrode may be substantially the same as a driving frame frequency of the LCD panel or N times the driving frame frequency of the LCD panel, wherein N is an integer.

A method of manufacturing a planar light source device in accordance with one aspect of the present invention includes selectively growing a carbon nanotube on a cathode electrode of a lower substrate in a chamber.

A method of manufacturing a planar light source device in accordance with another aspect of the present invention is provided as follows. A cathode electrode including at least one layer is formed on a lower substrate. A gate electrode electrically insulated from the cathode electrode is formed on the cathode electrode. The cathode electrode is exposed through an opening of the gate electrode. A catalyst metal layer is formed on the gate electrode and the cathode electrode in the opening of the gate electrode. A carbon nanotube is grown on the cathode electrode in the opening of the gate electrode using the catalyst metal layer. An upper substrate including a fluorescent material and a transparent electrode is formed. The upper substrate faces the lower substrate.

The catalyst metal layer may be preprocessed under an ammonia atmosphere to form the catalyst metal layer.

The carbon nanotube may be formed under an atmosphere of a mixture of ammonia (NH3) gas and a hydrocarbon gas.

The planar light source device may be manufactured through a single photo process to form the gate electrode pattern.

An LCD device in accordance with one aspect of the present invention may be manufactured by forming an optical film on the planar light source device, and arranging an LCD panel on the optical film.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1is an exploded perspective view illustrating a liquid crystal display (LCD) device in accordance with one embodiment of the present invention.

Referring toFIG. 1, the LCD device1000includes an LCD panel200, an optical member300, and a planar light source device400. The optical member300is on a rear surface of the LCD panel200. The planar light source device400supplies the optical member300with light. The LCD panel200, the optical member300, and the planar light source device400are received between an upper chassis100and a lower chassis500.

The LCD panel200includes a thin-film transistor (TFT) substrate213, a color filter substrate223, a sealant, and a liquid crystal layer. The color filter substrate223faces the TFT substrate213. The TFT substrate213is combined with the color filter substrate223through the sealant. The liquid crystal layer is interposed between the TFT substrate213, the color filter substrate223, and the sealant. The liquid crystal layer of the LCD panel200typically is a non-emissive-type element so that the LCD device1000can employ the planar light source device400that is on the rear surface of the LCD panel200to supply light to the LCD panel200. A driving part250applying driving signals is on a side of the TFT substrate213.

The driving part250includes a flexible printed circuit board (FPC)260, a driving chip270, and a printed circuit board (PCB)280. The driving chip270is on the FPC260. The PCB280is electrically connected to the FPC260. The driving part250may include without limitation a chip-on-film (COF) structure, a tape carrier package (TCP) structure, or a chip-on-glass (COG) structure. Alternatively, the driving part250may be directly formed on the TFT substrate213with lines and pixels of the TFT substrate213.

The optical member300that is on the rear surface of the LCD panel200may include a base film, and an optical pattern that is formed on the base film. The optical member300may include without limitation a light-diffusion plate, a prism sheet, a recycling film, a transreflective film, a brightness enhancement film, or a dual brightness enhancement film.

The base film includes a transparent material, and is aligned substantially parallel with the LCD panel. The optical pattern may include a plurality of lenses formed on the base film facing the LCD panel200. Examples of the transparent material that can be used for the base film include without limitation polyethylene terephthalate (PET), polycarbonate (PC), and cyclo-olefin polymer (COP). These can be used alone or in a combination thereof. The optical pattern may include substantially the same material as the base film, and may be integrally formed with the base film. The optical pattern diffuses the light that is incident into the optical member300. The optical pattern may have a bead shape. The optical pattern may be formed on substantially the entire surface of the base film.

FIG. 2is a cross-sectional view illustrating a planar light source device in accordance with one embodiment of the present invention.

Referring toFIG. 2, the planar light source device400generates the light using a field emission effect. The planar light source device400includes a lower substrate10, and an upper substrate90that is combined with the lower substrate10to form an emission space. Each of the respective lower and upper substrates10and90include a transparent insulating material. Examples of the transparent insulating material that can be used for the respective lower and upper substrates10and90include without limitation glass and quartz.

A cathode electrode20is formed on the lower substrate10. The cathode electrode20may have a single-layer structure or may have a multilayer structure. The cathode electrode20may include a conductive material such as a metal.

A supporting portion30and a gate electrode40are formed on the lower substrate10. The supporting portion30is protruded toward a front portion of the lower substrate10. The gate electrode is on the supporting portion30. A plurality of grooves is formed on adjacent portions of the supporting portion30.

The cathode electrode20is partially exposed through the grooves. That is, a region corresponding to the gate electrode40, and an exposed region in which the cathode electrode20is partially exposed through an opening between adjacent portions of the gate electrode40, are defined on the lower substrate10. The cathode electrode20may be a metal layer formed on substantially the entire surface of the lower substrate10. In addition, the gate electrode40also may be a metal layer formed on substantially the entire surface of the supporting portion30. For example, the light generated from the planar light source device may be a white light, and the LCD panel200may display an image by using the white light emitted from the planar light source400.

The supporting portion30includes an insulating material. Examples of the insulating material that can be used for the supporting portion30include without limitation silicon oxide, silicon nitride, and organic material.

A plurality of carbon nanotubes50is formed as emitter tips in the grooves on the cathode electrode20. The carbon nanotubes50emit electrons based on a voltage that is received from the cathode electrode20. The carbon nanotubes50may grow on the cathode electrode20. Alternatively, the carbon nanotubes50may be formed on the cathode electrode20using a mixture of a carbon nanotube material and a high polymer.

The gate electrode40is on the supporting portion30. A height of the gate electrode40may be greater than that of the carbon nanotubes50.

The emission space between the respective lower and upper substrates10and90may be in a vacuum state, so that the planar light source device400may benefit from a spacer60to maintain a distance between the respective lower and upper substrates10and90.

An anode electrode80and a fluorescent layer70are formed on the upper substrate90, desirably in sequence. The anode electrode80includes a transparent conductive material to accelerate electrons emitted from the carbon nanotubes50. Examples of the transparent conductive material that can be used for the anode electrode80include without limitation indium tin oxide (ITO) and indium zinc oxide (IZO). The fluorescent layer70may include a plurality of phosphor particles. The fluorescent layer70generates light based on the electrons exciting the phosphor particles. The light generated from the fluorescent layer70may be a white light. InFIG. 2, red (R), green (G), and blue (B) fluorescent materials are mixed to form the fluorescent layer70, so that R, G, and B lights are mixed to form a white light including the three color types of red, green, and blue. Thus, the white light, including the three color types is emitted from the front surface of the planar surface light source. Alternatively, R, G, and B fluorescent portions may be spaced apart from each other by a substantially constant distance so that the planar light source device1000emits the light of the three color types. When the R, G, and B fluorescent portions are spaced apart from each other, the R, G, and B lights are mixed in a space between the planar light source device400and the LCD panel200.

Alternatively, the anode electrode80may be formed on an outer surface of the upper substrate90, and a protective layer is formed on the anode electrode80. Exemplary protective layers may include without limitation a silicon nitride layer, a silicon oxide layer, and a high polymer layer that transmits the light.

A voltage having a predetermined frequency may be applied to the gate electrode40. The carbon nanotubes50may emit electrons based on a voltage difference between the gate electrode40and the carbon nanotubes50. The electrons are accelerated by the voltage applied to the anode electrode80so that the electrons are impacted onto the fluorescent layer70. The frequency of the voltage fVgapplied to the gate electrode40may be substantially the same as a frame frequency fFpof the LCD panel200, or as a frequency several times higher than the frame frequency of the LCD panel200. That is, fV=nfF, for integer values of n from 1 to N, inclusively. In selected embodiments, the frame frequency of the LCD panel200may be substantially the same as the frequency of the voltage applied to the gate electrode40. For example, when the frame frequency of the LCD panel200is about 60 Hz or about 120 Hz, the frequency of the voltage applied to the gate electrode40may be about 60 Hz or about 120 Hz. In selected other embodiments the frequency of the voltage applied to the gate electrode40may be several times higher than about 60 Hz or about 120 Hz. When the frame frequency of the LCD panel200is synchronized with the frequency of the voltage applied to the gate electrode40, a black image may be inserted into a region between adjacent images. The inserted black image precisely defines a boundary between the adjacent images to improve image display quality of the LCD device1000.

In general, a voltage of a negative level is applied to the cathode electrode20, and a voltage of a positive level is applied to the gate electrode40and to the anode electrode80. A voltage difference is formed between the cathode electrode20and the gate electrode40so that the electric field is formed therebetween and effecting emission of electrons by the carbon nanotubes50. The electrons emitted from the carbon nanotubes50are accelerated toward the anode electrode80, by an electric field formed between the cathode electrode20and the anode electrode80.

FIGS. 3A to 5Care electron microscopic images showing carbon nanotubes on a cathode electrode, in accordance with one embodiment of the present invention.

Carbon nanotubes were grown on various cathode electrodes. The cathode electrode was formed on a substrate, and a catalyst metal was prepared on the substrate. The cathode electrode and the catalyst metal were preprocessed in a chamber, and the carbon nanotubes were grown. The catalyst metal was nickel (Ni). The cathode electrode and the catalyst metal were preprocessed in an ammonia atmosphere, for example, by ammonia plasma. The carbon nanotubes were grown using a plasma including a mixture of ammonia (NH3) and acetylene (C2H2). Examples of the catalyst metal that can be used for growing the carbon nanotubes include without limitation nickel (Ni), iron (Fe), and cobalt (Co). The substrate was a glass substrate, and the growing process was performed at a temperature of no more than about 500° C.

InFIGS. 3A to 3C, the cathode electrode ofFIG. 3A, the cathode electrode ofFIG. 3B, and the cathode electrode ofFIG. 3Crespectively include platinum (Pt), chromium (Cr), and tungsten (W). InFIGS. 4A to 4E, the cathode electrode ofFIG. 4A, the cathode electrode ofFIG. 4B, the cathode electrode of4C, the cathode electrode ofFIG. 4D, and the cathode electrode ofFIG. 4Erespectively include a molybdenum-tungsten (MoW) alloy, molybdenum (Mo), silver (Ag), copper (Cu), and aluminum (Al). InFIGS. 5A to 5C, the cathode electrodes ofFIG. 5AandFIG. 5Binclude a titanium-platinum (Ti—Pt) layered structure and a titanium-chromium (Ti—Cr) layered structure, respectively. InFIG. 5C, the cathode electrode includes titanium (Ti). InFIGS. 3A to 5C, the catalyst metal is nickel (Ni), with the cathode electrode being interposed between the glass and the nickel (Ni).

Table 1 represents a current density and a growth of the carbon nanotubes on a selected floating metal, such as the growth of carbon nanotubes shown inFIGS. 3A to 5C.

In Table 1, the metals are classified into a first group of metals having a charge transition rate of no less than about 10−6.0A/cm2, and a second group of metals and an alloy having a charge transition rate of no more than about 10−6.1A/cm2. The first group includes palladium (Pd), platinum (Pt), rhodium (Rh), iridium (Ir), nickel (Ni), iron (Fe), gold (Au), tungsten (W), and chromium (Cr). The second group includes silver (Ag), niobium (Nb), molybdenum (Mo), copper (Cu), tantalum (Ta), bismuth (Bi), aluminum (Al), titanium (Ti), and a molybdenum-tungsten (MoW) alloy.

An “X” entry in Table 1 indicates cases in which carbon nanotubes were not grown on the cathode electrode; a “O” entry in Table 1 indicates cases in which carbon nanotubes were grown on the cathode electrode; and a dashed entry (-) in Table 1 indicates cases in which the current density, the growth of the carbon nanotubes, or both, were not ascertainable.

In Table 1, the current density represents a variation in charge per unit area of a metal that was electrically floated, that is, an electric charge transition rate on a surface of a metal charged by a plasma gas. In Table 1, the current density is displayed on a log scale in units of A/cm2. For example, when the current density is about 10−3.0, the corresponding log scale of the current density is about −3.0.

InFIGS. 3A to 3C, the carbon nanotubes were not grown on the cathode electrode. However, inFIGS. 4A to 5C, the carbon nanotubes were grown on the cathode electrode.

Referring toFIGS. 5A and 5B, the layered structure of the cathode electrode ofFIG. 5Amay employ a lower metal layer of the first group, including without limitation, platinum (Pt) or chromium (Cr), and an upper metal layer of the second group including titanium (Ti). InFIG. 5C, the cathode electrode employed a layer of titanium (Ti). The carbon nanotubes were grown on the upper metal layer of the second group. In other words, the growth of the carbon nanotubes was independent from the lower metal layer, and was dependent on the upper metal layer.

FIGS. 6A to 6Dare electron microscopic images showing carbon nanotubes on a cathode electrode according to various source gas ratios in accordance with one embodiment of the present invention.

The carbon nanotubes were grown using a plasma including a mixture of ammonia (NH3) and a hydrocarbon gas. InFIGS. 6A to 6D, the hydrocarbon gas was acetylene (C2H2) gas.

Referring toFIGS. 6A to 6D, a volumetric ratio of the ammonia (NH3) to the acetylene (C2H2) gas was changed to test the growth of the carbon nanotubes. The volumetric ratio can be measured by the standard cubic centimeter (SCCM) unit, where one SCCM represents 1 cm3at 0° C. under one atmospheric pressure. In FIG.6A, a volumetric ratio of the ammonia (NH3) to the acetylene (C2H2) gas was about 1:1. InFIG. 6B, a volumetric ratio of the ammonia (NH3) to the acetylene (C2H2) gas was about 2:1. InFIG. 6C, a volumetric ratio of the ammonia (NH3) to the acetylene (C2H2) gas was about 4:1. InFIG. 6D, a volumetric ratio of the ammonia (NH3) to the acetylene (C2H2) gas was about 6:1. For example, the ratio of 2:1 represented two ammonia molecules and one acetylene (C2H2) molecule. When the volumetric ratio of the ammonia (NH3) to the acetylene (C2H2) gas was about 1:1 to about 4:1, the carbon nanotubes tended to grow. In particular, when the volumetric ratio of the ammonia (NH3) to the acetylene (C2H2) gas was about 2:1, the carbon nanotubes grew in a vertical direction.

FIGS. 7A and 7Bare electron microscopic images showing carbon nanotubes on a cathode electrode at various voltages, in accordance with one embodiment of the present invention. InFIG. 7A, a level of a plasma voltage was about 400 V. InFIG. 7B, the level of the plasma voltage was about 40 V.

Referring toFIGS. 7A and 7B, a height of the carbon nanotubes formed at the plasma voltage of about 40 V was smaller in a vertical direction than that of the carbon nanotubes formed at the plasma voltage of about 400 V. In particular, when the plasma voltage was about 400 V, the carbon nanotubes grew in the vertical direction at a greater height than when the plasma voltage was about 40 V. Thus, a plasma voltage of about 400 V or more may be desirable.

FIGS. 8 to 13are cross-sectional views illustrating a method of manufacturing a planar light source device in accordance with one embodiment of the present invention.

Referring toFIG. 8, a cathode electrode211is formed on a substrate2000. In particular, a lower cathode electrode layer205and an upper cathode electrode layer210are formed on the substrate2000, in sequence, to form the cathode electrode211. The upper cathode electrode layer210of the cathode electrode211includes a metal of a second group. Examples of the metal of the second group that can be used for the upper cathode electrode layer210include without limitation silver (Ag), lead (Pb), niobium (Nb), molybdenum (Mo), copper (Cu), tantalum (Ta), bismuth (Bi), aluminum (Al), and titanium (Ti). The second group may also include an alloy including without limitation, a molybdenum-tungsten (MoW) alloy. A current density of the second group typically is no more than about 106.1A/cm2. Desirably, substrate2000ofFIGS. 8-13can be a constituent element of the planar light source device400.

When the cathode electrode211has the double-layer structure including the lower cathode electrode layer205and the upper cathode electrode layer210, the lower cathode electrode layer205includes the metal of a first group or the second group, and the upper cathode electrode layer210includes the metal of the second group. For example, the lower cathode electrode layer205may include chromium (Cr), and the upper cathode electrode layer210may include titanium (Ti).

The lower cathode electrode layer205and the upper cathode electrode layer210may be formed through a sputtering method.

InFIG. 8, the cathode electrode211may be an integrally formed conductor so that the cathode electrode211may not have an isolated portion.

An insulating layer215, a gate electrode layer220and a photoresist layer225are formed on the lower substrate2000having the cathode electrode211, in sequence.

Referring toFIG. 9, the gate electrode layer220is patterned through a photolithography process. In particular, the photoresist layer225that is formed on the gate electrode layer220is exposed using an exposure unit. The photoresist layer225is developed to be patterned to form a photoresist pattern225′. The gate electrode layer220is partially etched using the photoresist pattern225′ as an etching mask. The gate electrode220′ includes the metal of the first group. Alternatively, the gate electrode220′ may include chromium (Cr) as shown inFIG. 8. The gate electrode220′ may also include substantially the same material as the lower cathode electrode205. When the gate electrode220′ includes substantially the same material as the lower cathode electrode205, manufacturing costs are decreased. Examples of an insulating material that can be used for the insulating layer215include an organic material, silicon oxide, silicon nitride, etc. These can be used alone of in a combination thereof.

The gate electrode220′ may be an integrally formed conductor so that the gate electrode220′ may not have an isolated portion. InFIGS. 1 and 9, the planar light source device generates light having uniform luminance, and does not include pixels that are independently driven.

Referring toFIG. 10, the insulating layer215is partially etched using the gate electrode220′ as an etching mask, so that the cathode electrode210is partially exposed. The insulating layer215may be dry etched or wet etched. When the insulating layer215is wet etched, the insulating layer215is isotropically etched so that a portion of the insulating layer215under a side of the gate electrode220′ is recessed, thereby forming an undercut.

Referring toFIG. 11, a catalyst metal layer227for the carbon nanotubes is formed on the lower substrate2000having the gate electrode220′, and the cathode electrode210is partially exposed through an opening between adjacent portions of the gate electrode220′. Examples of the catalyst metal that can be used form the catalyst metal layer227include nickel (Ni), iron (Fe), cobalt (Co), etc. The catalyst metal layer227may be formed through a sputtering method.

Referring toFIG. 12, the lower substrate2000having the catalyst metal layer227is preprocessed. The lower substrate2000is divided into a region in which a plurality of catalyst metal seeds227′ is formed and a region between adjacent catalyst metal seeds227′. For example, the lower substrate2000having the catalyst metal layer227is preprocessed using ammonia plasma. The catalyst metal seeds227′ function as seeds for growing carbon nanotubes.

Referring toFIG. 13, the carbon nanotubes230grow based on the catalyst metal seeds227′. In particular, the carbon nanotubes230grow using a plasma including a mixture of ammonia (NH3) and a hydrocarbon. The hydrocarbon may be acetylene (C2H2). The carbon nanotubes230grow on the metal of the second group, which corresponds to the catalyst metal seeds227′. Although the catalyst metal seeds227′ are on the metal of the first group, the carbon nanotubes230may not grow on the metal of the first group. Thus, inFIG. 13, the carbon nanotubes230only grow on the cathode electrode210in the region surrounded by the adjacent portions of the gate electrode225′.

The processes ofFIGS. 12 and 13may be performed in situ. That is, the processes may be performed in a chamber without being exposed to external air. In addition, the processes ofFIGS. 12 and 13may include one photo process.

An upper substrate having a transparent electrode and a fluorescent layer is combined with the lower substrate having the carbon nanotubes to form the planar light source device. A spacer may be formed between the upper substrate and the lower substrate.

InFIGS. 1 to 13, the planar light source device400is used for a backlight assembly of the LCD device1000. However, the planar light source device400may be used in various other fields, for example, as a generic lighting device.

According to the present invention, the field emission-type planar light source device, and the LCD device having the planar light source device, can generate light, for example, without using mercury.

This invention has been described with reference to the example embodiments. It is evident, however, that many alternative modifications and variations will be apparent to those having skill in the art in light of the foregoing description. Accordingly, the present invention embraces all such alternative modifications and variations as fall within the spirit and scope of the appended claims.