Patent Application
20100141115
This application claims priority to and the benefit of Korean Patent Application No. 10-2008-0124092, filed in the Korean Intellectual Property Office, on Dec. 8, 2008, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a light emission device and a display device using the same as a light source. More particularly, the present invention relates to a light emission device having a high cathodoluminescence luminous efficiency and a display device using the same as a light source.
2. Description of the Related Art
A device, which can emit light out of the device, can be referred to as a light emission device. In addition, a light emission device may have a front substrate on which a phosphor layer and an anode electrode are formed and a rear substrate on which electron emission regions and driving electrodes are formed. The peripheries of the front and rear substrates are bonded together by a sealing member to form a sealed interior space, and then the interior space is exhausted, thereby forming a vacuum vessel.
Typically, driving electrodes of the light emission device include cathode electrodes and gate electrodes. In one embodiment, the gate electrodes are located on the cathode electrodes and are formed in a direction crossing the cathode electrodes. Electron emission regions are formed at the crossing regions of the cathode electrodes and the gate electrodes.
In another embodiment, the driving electrodes can have a comb pattern and include cathode and gate electrodes that are alternatively arranged. Here, the electron emission region is disposed on the side of the corresponding cathode electrodes facing the corresponding gate electrode.
The light emission device has a plurality of pixels by associating the cathode electrodes with the gate electrodes. Set (or predetermined) driving voltages are applied to the cathode electrodes and the gate electrodes to control the amount of output (or emission) current (or electrons) of the electron emission regions per pixel. As such, the light emission device controls the luminance of the phosphor layer per pixel. Here, the light emission device can be used as a light source in a display device having a non-self-emission display panel such as a liquid crystal display panel.
A metal reflective layer may be disposed on one surface of the phosphor layer formed on the front substrate. The metal reflective layer reflects the visible light emitted to the rear substrate from among the visible light emitted from the phosphor layer toward the front substrate side to increase the luminance of the light emitting surface. The metal reflective layer can also be referred to as a metal back layer. In order to further improve the cathode luminescence (CL) efficiency of the phosphor layer, there is a need to improve the reflective efficiency of the metal reflective layer.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.
Aspects of embodiments of the present invention are directed toward a light emission device and a display device using the same as a light source having a high cathode luminescence efficiency.
Other aspects of embodiments of the present invention are directed toward a light emission device capable of improving the cathode luminescence efficiency of the phosphor layer by improving reflectivity of a reflective layer, and a display device using the light emission device as a light source.
The aspects of the embodiments of the present invention are not limited to the above described aspects.
According to an embodiment of the present invention, a light emission device is provided to include: a first substrate and a second substrate facing each other with a vacuum region therebetween; an electron emission region at a surface of the first substrate facing the second substrate; a driving electrode at the surface of the first substrate and for controlling an amount of electrons emitted from the electron emission region; an anode at a surface of the second substrate facing the first substrate; a phosphor layer on one surface of the anode and for receiving at least a portion of the electrons emitted from the electron emission region; and a reflective layer covering the phosphor layer, wherein the reflective layer includes a first reflective layer including Al and a second reflective layer including Ag.
The reflective layer is provided by covering the phosphor layer with the first reflective layer and covering the first reflective layer with the second reflective layer, or by covering the phosphor layer with the second reflective layer and covering the second reflective layer with the first reflective layer.
According to another embodiment of the present invention, provided is a display device including the light emission device and a display panel disposed to receive light emitted from the light emission device.
Other specific characteristics of exemplary embodiments of the present invention are described in the following detailed description.
Here, the light emission device according to an embodiment of the present invention improves the reflectivity of the reflective layer, so as to provide a phosphor with an improved cathode luminescence efficiency.
The accompanying drawings, together with the specification, illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain the principles of the present invention.
In the following detailed description, only certain exemplary embodiments of the present invention are shown and described, by way of illustration. As those skilled in the art would recognize, the invention may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Also, in the context of the present application, when an element is referred to as being “on” another element, it can be directly on the another element or be indirectly on the another element with one or more intervening elements interposed therebetween. Like reference numerals designate like elements throughout the specification.
Exemplary embodiments of the present invention will hereinafter be described in more detail. However, these embodiments are only exemplary, and the present invention is not limited thereto.
According to a first embodiment of the present invention, provided is a light emission device including: a first substrate and a second substrate arranged to face each other with a vacuum region therebetween; an electron emission region disposed at a surface of the first substrate facing the second substrate (hereafter also referred to as the inside surface of the first substrate); a driving electrode disposed at the inside surface of the first substrate and for controlling the amount of electrons emitted by the electron emission region; an anode electrode disposed at a surface of the second substrate facing the first substrate (hereafter also referred to as the inside surface of the second substrate); a phosphor layer formed on one surface of the anode electrode to receive at least a portion of the electrons emitted from the electron emission region; and a reflective layer covering the phosphor layer. The reflective layer includes a first reflective layer including Al and a second reflective layer including Ag.
According to one embodiment, the reflective layer is formed by covering the phosphor layer with the first reflective layer and covering the first reflective layer with the second reflective layer, or by covering the phosphor layer with the second reflective layer and covering the second reflective layer with the first reflective layer. In other words, the light emission device includes the anode electrode, the phosphor layer on the anode electrode, the first reflective layer on the phosphor layer, and the second reflective layer on the first reflective layer in order, or includes the anode electrode, the phosphor layer on the anode electrode, the second reflective layer on the phosphor layer, and the first reflective layer on the second reflective layer in order.
In addition, the light emission device may include a reflective space between the phosphor layer and the reflective layer. The reflective space may be formed by providing an intermediate film on the phosphor layer during the manufacturing process and removing the intermediate film during the baking process. That is, a composition including an organic solvent and a resin capable of being removed during the baking process is coated on the phosphor layer to provide an intermediate film, and then a reflective layer is formed on the intermediate film. During the following baking process, the resin and the organic solvent are removed to provide the reflective space. When a process for forming the intermediate film is performed, it is possible to improve the adhesive strength of the reflective layer, to decrease the roughness of the phosphor layer, and to increase the smoothness, and thereby the reflectivity is improved. The resin may be prepared by mixing at least one of ethylcellulose, nitrocellulose, an acryl-based resin, and the like, and the organic solvent may be prepared by mixing texanol, terpineol, butyl carbitol, and/or the like.
The first reflective layer may be formed by any suitable process for forming an Al reflective layer, and representative examples thereof may include Al thermal evaporation, Al lamination, Al lacquering, Al sputtering, and/or the like.
According to an embodiment of the present invention, the first reflective layer has a thickness between 200 and 3000 Å. In one embodiment, when the first reflective layer has a thickness of less than 200 Å, the reflectivity is deteriorated. In another embodiment, when the first reflective has a thickness that is more than 3000 Å, the transmission efficiency of electrons is deteriorated.
In one embodiment, the second reflective layer is formed by spray-coating a metal composition including an Ag salt, an additive, and a solvent on one surface of the phosphor layer or one surface of the first reflective layer and drying the same.
According to one embodiment, the Ag salt is selected from the group consisting of Ag-nitrates, Ag-chlorides, Ag-acetates, and combinations thereof.
In addition, the additive may be prepared by mixing at least one of a dispersing agent or a reducing agent. The dispersing agent may be a quadribasic acid such as ethylenediamine tetraacetic acid, and the reducing agent may be selected from the group consisting of NaBH4, hydrazine, ethylamine, and combinations thereof.
According to one embodiment, the additive selected from the group consisting of a dispersing agent, a reducing agent, and combinations thereof and a metal are mixed at a weight ratio of 0.25:1 to 2:1. In one embodiment, when the additive includes both the dispersing agent and the reducing agent, a metal, a dispersing agent, and a reducing agent are mixed at a weight ratio of 1:0.25:0.5 to 1:1:1.
The solvent may be selected from the group consisting of H2O, Na4OH, NaOH, and combinations thereof.
In the composition, the metal salt between 5 and 20 wt % may be used, and the additive between 5 and 20 wt % may be used. When the dispersing agent and the reducing agent are used together as an additive, the mixing ratio may be suitably adjusted.
The drying process may be performed at a temperature between 100 and 450° C. In one embodiment, the drying process is performed at a temperature between 400 and 450° C. to reduce (or prevent) the generation of a remaining gas during the vacuum sealing process.
The Ag ion in the Ag salt is reduced to Ag during the drying process and provides a second reflective layer, so the second reflective layer has Ag in a nano-size to provide a dense and uniform thickness. In addition, the dispersing agent, the reducing agent, and the like that are used as an additive are removed during the following baking process, so they are not present in the final light emission device.
According to one embodiment, the second reflective layer has a thickness between 200 and 3000 Å. In one embodiment, when the second reflective layer has a thickness that is less than 200 Å, the reflective efficiency is deteriorated. In another embodiment, when the second reflective layer has a thickness that is more than 3000 Å, the electron transmission efficiency is deteriorated.
The reflective layer of the light emission device includes fine holes for transmitting an electron beam and reflects the visible light emitted toward the first substrate from the phosphor layer, to the second substrate side, so as to improve the luminance of the light emitting surface.
The phosphor layer may be formed with a white phosphor, which is a mixture of red phosphor, green phosphor, and blue phosphor. The red phosphor is selected from the group consisting of Y2O3:Eu, Y2O2S:Eu, SrTiO3:Pr, and combinations thereof, and the green phosphor is selected from the group consisting of Y2SiO5:Tb, Gd2O2S:Tb, ZnS:(Cu,Al), ZnSiO4:Mn, Zn(Ga,Al)2O4:Mn, SrGa2S4:Eu, and combinations thereof. In addition, the blue phosphor is selected from the group consisting of ZnS:(Ag,Al), Y2SiO5:Ce, BaMgAl10O17:Eu, and combinations thereof. According to one embodiment, in the phosphor layer, the red phosphor, the green phosphor, and the blue phosphor are mixed in a weight ratio of 15:30:24 to 30:60:45. In one embodiment, when the mixing ratio of red phosphor, green phosphor, and blue phosphor is within the above described range, and it is applied to the light emission device and the light emission device is used for a light source of a display device to provide white light, the light generated from the light-emission device can have an improved luminance and suitable color coordinates for transmitting by the display panel.
Hereinafter, an embodiment of a light emission display 100 having a reflective layer 36 and 38 with a first reflective layer 36 and a second reflective 38 is illustrated with reference to
The light emission device 100 includes a first substrate 12 and a second substrate 14 arranged to face each other with a vacuum region (or a predetermined distance) therebetween. At the edge portion (or the edge) of the first substrate 12 and the second substrate 14, a sealing member 16 is disposed to join the substrates 12 and 14 together. The vacuum region is evacuated to a degree of vacuum of about 10−6 Torr, so a vacuum panel 18, including the first substrate 12, the second substrate 14, and the sealing member 16, is provided.
A region defined by the first substrate 12, the second substrate 14, and the sealing member 16 can be partitioned into an effective region that contributes to emission of visible light and a non-effective region surrounding the effective region. An electron emitting unit 20 for emitting electrons is in the effective region defined by the first substrate 12, and a light emitting unit 22 for emitting visible light is in the effective region defined by the second substrate 14.
The electron emission unit 20 includes an electron emission region 24 and driving electrodes for controlling the amount of emission current of the electron emission region 24. The driving electrodes include cathode electrodes 26 forming a stripe pattern along a first direction (e.g., the y axis direction in
The gate electrodes 30 and the insulation layer 28 have openings 301 and 281 at every crossing region of the cathode and gate electrodes 26 and 30 to expose a part of the surfaces of the cathode electrodes 26. The electron emission region 24 is formed on the cathode electrode 26 inside the opening 281 of the insulation layer. The electron emission region 24 may include any suitable material selected from the group consisting of materials that emit electrons by applying an electric field under vacuum, for example carbon nanotubes, graphite, graphite nanofiber, diamond-shaped carbon, fullerene, silicon nano-wire, and combinations thereof.
One crossing region overlapping the cathode electrode 26 and the gate electrode 30 may correspond to one pixel area of the light emission device 100, or two or more crossing regions may correspond to one pixel area of the light emission device 100.
The light emitting unit 22 includes an anode electrode 32, a phosphor layer 34 disposed on one surface of the anode electrode 32, and a reflective layer 36 and 38 covering the phosphor layer 34. The anode electrode 32 is formed with a transparent conductive material, such as indium tin oxide (ITO), to maintain the phosphor layer 34 in a high potential state when it is applied with a high voltage (anode voltage) of 5 kV or more, and to transmit the visible light emitted from the phosphor layer 34.
The reflective layer 36 and 38 reflects the visible light emitted to the first substrate 12, toward the second substrate 14 side, so as to increase the luminance of the light emission surface. On the other hand, the anode electrode 32 may be omitted, and the reflective layer 36 and 38 is then applied with the anode voltage to play the role of an anode electrode.
The phosphor layer 34 may be composed of white phosphor, which is a mix of red phosphor, green phosphor, and blue phosphor.
As shown in
Also, as shown in
As shown in
Referring to
Transparent pixel electrodes 76, each of which is driven and/or controlled by the TFT 62 per subpixel, are disposed on the surface of the lower substrate 64 facing the upper substrate 68, and transparent common electrodes 78 are disposed on the surface of the upper substrate 68 facing the lower substrate 64. The color filter layer 66 includes a red filter layer 66R, a green filter layer 66G, and a blue filter layer 66B, each of which is disposed for a subpixel.
When the TFT 62 of a certain subpixel turns on, an electric field is formed between the pixel electrode 76 and the common electrode 78. The electric field changes the alignment angle of liquid crystal molecules, thereby changing the light transmission. The display panel 60 controls the luminance and the light emitting color per pixel through such process.
Reference number 80 in
Referring to
For convenience, pixels of the display panel 60 are defined as first pixels and pixels of the light emission device 100 are defined as second pixels. The first pixels corresponding to one second pixel are called a first pixel group.
The light emission device 100 may be driven by a process including: {circle around (1)} detecting the highest gray level among gray levels of the first pixels for forming the first pixel group with a signal control part for controlling the display panel 60; {circle around (2)} determining and/or calculating the gray level required to emit light in the second pixel depending upon the detected highest gray level to convert it to digital data; {circle around (3)} producing a driving signal of the light emission device 100 by using the digital data; and {circle around (4)} applying the produced driving signal to the driving electrode of the light emission device 100.
In one embodiment, the driving signal of the light emission device 100 includes a scan driving signal and a data driving signal. In one embodiment, the driving electrode includes the cathode electrode 26 and the gate electrode 30 as described above. In one embodiment, for example, the gate electrode 30 is applied with the scan driving signal, and the cathode electrode 26 is applied with the data driving signal.
A scan printed circuit board assembly (PBA) and a data printed circuit board assembly (PBA) for driving the light emission device 100 can be disposed at the rear surface of the light emission device 100. According to an embodiment of the present invention, reference number 84 in
As mentioned above, when the image is expressed in the first pixel group corresponding to the second pixel of the light emission device 100, it is synchronized with the first pixel group to emit light of a set (or predetermined) gray level. In other words, the light emission device 100 provides high luminous light to a bright region in the screen expressed by the display panel 60, but it provides low luminous light to a dark region. Accordingly, the display device 200 according to the embodiment of
The following examples illustrate the present invention in more detail. However, the present invention is not limited by these examples.
A reflective layer was prepared by plating Cr on a glass substrate.
A reflective layer was prepared by sputtering Al on a glass substrate.
A reflective layer is prepared by depositing Ag on a glass substrate.
A composition was prepared by mixing AgNO3, a dispersing agent of ethylenediamine tetraacetic acid, and a reducing agent of hydrazine in a ratio of 20:10:20 wt % in a Na4OH solvent. The composition was spray-coated on a glass substrate and dried at 400° C. to provide a reflective layer.
A reflective layer was prepared with stainless steel on a glass substrate in accordance with the Super Mirror method.
The reflective layers obtained from Example 1 and Comparative Examples 1 to 4 were measured to determine reflectance, and the results are shown in
As shown in Table 1 and
It is understood that the reflectivity of Comparative Example 3 in which the reflective layer was formed by the Ag deposition process and the reflectivity of Comparative Example 4 in which the reflective layer was formed with the stainless steel in accordance with the Super Mirror method were substantially less than that of Example 1.
A 1000 Å-thick Al first reflective layer was prepared by depositing Al on one surface of an intermediate film formed on a white phosphor layer having a structure shown in
A reflective layer was prepared in accordance with the same procedure as in Example 1, except that the Ag second reflective layer was prepared by the deposition process.
The reflective layers obtained from Example 2 and Comparative Example 5 were measured to determine cathode luminescence efficiency, and the results are shown in the following Table 2.
As shown in Table 2, compared to the CL efficiency of the Al reflective layer, the case in which the Al reflective layer was prepared by the deposition process and coated by the spray process had much better CL efficiency.
The present invention is not limited to the embodiments illustrated with the drawings and tables, but can be fabricated into various modifications and equivalent arrangements included within the spirit and scope of the appended claims by a person who is ordinarily skilled in this field. Therefore, the aforementioned embodiments should be understood to be exemplary but not limiting the present invention in any way.
While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2008-0124092 | Dec 2008 | KR | national |
