Abstract:
An anti-reflective and anti-static multilayer structure for display device, comprising a glass substrate, and an ITO layer, a first Nb 2 O 5  layer, a first SiO 2  layer, a second Nb 2 O 5  layer and a second SiO 2  layer, which are successively formed on the glass substrate, achieves good film adhesive strength, solidity and enhanced photoreflectance.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an antireflective and anti-static multilayer structure for use in a display device; and, more particularly, to a five-layered anti-reflective and anti-static coating on a glass substrate with an improved adhesion coefficient and strength.  
         BACKGROUND OF THE INVENTION  
         [0002]    Recently, a thin film coating is widely applied to a surface of a display device in order to prevent generation of static electricity, block electromagnetic radiation and reduce the reflection of external light. Such a thin film is normally made of at least 2 layers and 2 kinds of materials; and in order to enhance electrical and optical properties thereof, a large number of layers formed of various materials can be employed for the manufacture thereof. The multilayer thin film of this type is also required to have appropriate mechanical properties of, e.g., adhesion coefficient and strength.  
           [0003]    Multilayer thin films for such purpose are generally fabricated by using various film forming techniques, such as spraying, deposition, coating, chemical deposition, and sputtering. The sputtering, which is one of the most generally employed film forming method, can be classified into one of a batch type sputtering, an inter-back sputtering and an in-line sputtering technique depending on the type of the way how loading and unloading substrates being carried out.  
           [0004]    In the batch type sputtering, a substrate is directly loaded in a coating chamber and a surface thereof is coated with a thin film therein.  
           [0005]    In the inter-back sputtering, a sub-chamber is provided for loading and unloading therethrough a substrate into and from a coating chamber in which the film formation is carried out.  
           [0006]    In the in-line sputtering, a loading chamber and an unloading chamber are provided next to a coating chamber. A substrate is loaded into the coating chamber via the loading chamber to be processed and then the processed substrate is unloaded from the coating chamber via the unloading chamber.  
           [0007]    In the field of manufacturing LCD and PDP, the above-described in-line sputtering technique is most widely used for coating a substrate surface with a SiO 2  layer and an ITO(Indium Tin Oxide) layer sequentially.  
           [0008]    A prior art multilayer thin film produced by the in-line sputtering scheme is normally  4  layered structure including an ITO layer formed on an ordinary glass substrate.  
           [0009]    [0009]FIG. 1 shows a conventional thin film having 4 layers, including an ITO layer  12 , a first SiO 2  layer  13 , a Nb 2 O 5  layer  14 , and a second SiO 2  layer  15  successively formed on a glass substrate  11 .  
           [0010]    The glass substrate  11  is normally composed of ordinary glass generally having an RMS(root mean square) roughness of 1.75˜2.09 Å and peak-to-valley surface roughness of 24.8˜40 Å. The thickness of the ITO layer  12 , the first SiO 2  layer  13 , the Nb 2 O 5  layer  14 , and the second SiO 2  layer  15  are respectively about 19 nm, 29 nm, 112 nm, and 90 nm.  
           [0011]    Such a prior art multilayer thin film having 4 layers suffers from weak adhesive strength between layers, so that it cannot withstand impacts of strength of 1.5 KgF/cm 2  more than approximately 150 times, wherein the strength for the film is tested in such a manner that a sample is placed on a balance and is pressed by a cotton wad having contact surface of 10 cm×1 cm to scale 15 KgF. Also, the light reflectance of such conventional film is as high as about 0.27%.  
         SUMMARY OF THE INVENTION  
         [0012]    It is, therefore, an object of the present invention to provide an anti-reflective and anti-static multilayer structure, for use in a display device, having 5 layers with an improved adhesion property, film strength, and light reflecting property.  
           [0013]    In accordance with the present invention, there is provided an anti-reflective and anti-static structure for a display device, comprising a glass substrate, and an ITO layer, a first Nb 2 O 5  layer, a first SiO 2  layer, a second Nb 2 O 5  layer, and a second SiO 2  layer successively formed in that order on the glass substrate. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiment given in conjunction with the accompanying drawings, in which:  
         [0015]    [0015]FIG. 1 schematically illustrates a prior art multi-layer structure; and  
         [0016]    [0016]FIG. 2 schematically exhibits a multilayer structure in accordance with the preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    [0017]FIG. 2 illustrates a multilayer thin film having 5 layers including an ITO layer  22 , a first Nb 2 O 5  layer  23 , a first SiO 2  layer  24 , a second Nb 2 O 5  layer  25 , and a second SiO 2  layer  26  successively grown in that order on a glass substrate  21  in accordance with the preferred embodiment of the present invention.  
         [0018]    In accordance with the preferred embodiment of the present invention, entire process is performed through the use of an in-line sputtering system. Particularly, the ITO layer  22  is formed by DC sputtering; and the Nb 2 O 5  layers  23 ,  25  and SiO 2  layers  24 ,  26  are formed by PEM(Plasma Emission Monitor) controlled MF(Mid Frequency) reactive sputtering. The entire process is performed in an environment whose temperature is kept at about 15˜400° C. DC sputtering is the process most often used for large area commercial coating applications and the PEM control is used to obtain high stability at high deposition rates of the processes, controlling by regulating the ratio of collision numbers between the sputtered metal particles and the admitted reactive gas.  
         [0019]    An ordinary glass, which is typically used for the glass substrate  11  in the prior art thin film forming process, may be used for the glass substrate  21 , but in order to obtain greater film strength and improved surface property of the thin film, a surface-treated glass is preferably used. The surface-treated glass is obtained by polishing the surface of an ordinary glass. In the preferred embodiment of the present invention, the surface-treated glass has RMS surface roughness of 6.14 Å and peak-to-valley surface roughness of 106 Å.  
         [0020]    The ITO layer  22  is deposited on the glass substrate  21  by DC sputtering using an ITO target in an atmosphere including argon(Ar) and oxygen with flow rates of 200 sccm and 3 sccm, respectively, for example. The thickness of the ITO layer  22  is preferably about 17 nm˜19 nm.  
         [0021]    The first Nb 2 O 5  layer  23  is deposited on the ITO layer  22  by PEM controlled reactive sputtering using a Niobium(Nb) target in an atmosphere including argon, and oxygen with flow rates of, e.g., about 80˜450 sccm and 120 sccm respectively. The thickness of the first Nb 2 O 5  layer  23  is preferably about 3 nm to 5 nm. In the preferred embodiment of the present invention, the first Nb 2 O 5  layer  23  having a thickness of about 3 nm and 5 nm is additionally deposited on the ITO layer  22 , in contrast to the prior art film forming method where the first SiO 2 layer  13  is directly provided on the ITO layer  12  as shown FIG. 1. The first Nb 2 O 5  layer  23  plays an essential role to enhance film strength.  
         [0022]    Thereafter, the first SiO 2  layer  24  having a thickness of about 28 nm to 29 nm is deposited on the first Nb 2 O 5  layer  23  by using a silicon target in an atmosphere including Ar and oxygen with flow rates of, e.g., 150˜400 sccm and 120 sccm, respectively.  
         [0023]    The second Nb 2 O 5  layer  25  is deposited on the first SiO 2  layer  24  by using a Nb target in the atmosphere as in the first Nb 2 O 5  layer  23 . The thickness of the second Nb 2 O 5  layer  25  is preferably about 112 nm.  
         [0024]    In a final step, the second SiO 2  layer  26  is deposited on the second Nb 2 O 5  layer  25  under the same condition as in the first SiO 2  layer  24 . The thickness of the second SiO 2  layer  26  is preferred to be approximately 90 nm.  
         [0025]    Accordingly, a multilayer structure having 5 layers as shown in FIG. 2 is constructed through the above-described processing steps. The thickness of each layer is optimized to provide the lowest possible reflection.  
         [0026]    The multilayer structure for display device having 5 layers on a glass substrate in accordance with the present invention is strong enough to sustain impacts of strength of 1.5 kgF/cm 2  more than 2000 times. Specifically, the prior thin film having 4 layers structure shown in FIG. 1 can withstand impacts of strength of 1.5 kgF/cm 2  only about 150 times as described above; but the inventive structure having 5 layers on a glass substrate is durable against impacts of strength of 1.5 KgF/cm 2  for more 1000 times even in the case where the ordinary glass is used as the substrate as in the prior art film, and has a superior durability to sustain against impacts of strength of 1.5 KgF/cm 2  for about 2000 times when the surface-treated glass is used as the glass substrate  21  as described above.  
         [0027]    That is, even when the glass substrate  21  is an ordinary glass, the 5 layered structure fabricated in accordance with the present invention can attain superior film strength compared to the conventional 4 layered film; and when the surface-treated glass is used as the glass substrate, the strength of the structure increases tremendously. And also, a thin film having the 5 layers structure of the present invention has a much improved optical property, i.e., a reduced photoreflectance of 0.13%, compared to the photoreflectance of 0.27% of the prior art 4 layered film structure.  
         [0028]    While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.