Abstract:
A method of forming a spacer for a liquid crystal display (LCD) device is disclosed. To form the spacer, an ink jet injection nozzle is aligned over a substrate on which unit pixels are arranged in a matrix. After aligning the nozzle, first dispensing spacers are dispensed from the injection nozzle with a certain gap so that at least one unit pixels is interposed between the spacers. Subsequently, the nozzle is moved and second dispensing spacers are dispensed by the nozzle at each of the unit pixels formed between the first spacers. This is repeated until the spacer is formed at all unit pixels. The spacer contains a ball spacer and a volatile liquid, which is vaporized during dispensing. The ink jet injection method prevents adjacent spacers from interfering with each other during formation.

Description:
TECHNICAL FIELD  
       [0001]     The present application relates to a spacer forming method, and more particularly, to a ball spacer forming method using an ink jet injection method.  
       BACKGROUND  
       [0002]     As various mobile electronic devices including a mobile phone, a PDA or a notebook computer are being developed, demands for light, thin, short and small flat panel display devices that can be applied to the mobile electronic devices are increasing. As a result, research for flat panel display devices such as an LCD (Liquid Crystal Display), PDP (Plasma Display Panel), an FED (Field Emission Display), a VFD (Vacuum Fluorescent Display) is actively ongoing. Of these displays, the LCD is the most prevalent because of its implementation in mass-production techniques, ease of a driving unit, and high picture quality.  
         [0003]     The LCD device comprises an array substrate that unit pixels are arranged in a matrix form, a color filter substrate facing the array substrate for displaying colors in natural colors, and a liquid crystal layer contained between the two substrates.  
         [0004]     The array substrate and the color filter substrate are bonded to each other by a sealant at edges thereof, and a cell gap is formed therebetween. The cell gap between the array substrate and the color filter substrate is maintained by a spacer.  
         [0005]     The spacer serves to maintain a cell gap between an upper substrate and a lower substrate of an LCD panel, and may be divided into a ball spacer and a column spacer (or a pattern spacer) according to a spacer forming method.  
         [0006]     The ball spacer is formed on the upper substrate or the lower substrate by a dispensing minute ball shapes along the substrate. The column spacer, on the other hand, is formed by exposing and developing of a photosensitive layer.  
         [0007]     A method of forming the ball spacer includes a wet dispensing method, in which the spacer is mixed with alcohol, etc. and then dispensed, or a dry dispensing method for dispensing only the spacer. The dry dispensing method includes an electrostatic dispensing method using static electricity, or an electrostatic discharge dispensing method using an injection pressure of gas. Generally, the electrostatic discharge dispensing method is mainly applied to the LCD panel susceptible to static electricity.  
         [0008]     A spacer is formed easily by the dispensing method of ball spacer. However, the dispensing method has disadvantages that a spacer is not formed at a desired position and a forming density of a spacer is not uniform.  
         [0009]     By the dispensing method, a spacer may be formed in a unit pixel portion thus to decrease an aperture ratio, or dispensed spacers may be lumped to each other thus to cause problems with the screen.  
         [0010]     On the other hand, the column spacer is formed by a photo mask process. Accordingly, a forming position of the column spacer may be freely controlled, and a density and a shape of the spacer may be freely controlled. However, due to the photo process, an amount of a photosensitive material coated on a substrate to form a spacer is wasted thus increasing production cost and environment pollution. Also, an expensive mask is used and several additional processes have to be performed for the photo process.  
       BRIEF DESCRIPTION  
       [0011]     By way of introduction only, in one embodiment a spacer forming method comprises: aligning an ink jet injection nozzle over a substrate on which unit pixels are arranged in a matrix form; first dispensing spacers with a predetermined distance so that at least one unit pixels may be interposed between the spacers; and second dispensing spacers between the first dispensed spacers.  
         [0012]     The foregoing brief description is merely a summary of embodiment(s) of the present disclosure and is in no manner intended to limit the scope of the invention recited in the claims. Further aspects of the disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.  
         [0014]     In the drawings:  
         [0015]      FIG. 1  is a sectional view showing a liquid crystal display (LCD) panel according to one embodiment of the present invention;  
         [0016]      FIG. 2  is a plan view showing a color filter substrate according to one embodiment of the present invention;  
         [0017]      FIG. 3  is a plan view showing an array substrate according to one embodiment of the present invention; and  
         [0018]      FIGS. 4A  to  4 C are detail descriptions of showing a spacer forming method according to one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0019]     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0020]     A liquid crystal display (LCD) panel comprises an upper substrate and a lower substrate attached to each other, and liquid crystal contained therebetween. In the LCD panel, a cell gap between the upper substrate and the lower substrate is maintained uniformly by a spacer. The spacer is formed at a precise position using an ink jet dispensing method.  
         [0021]     As the LCD panel becomes larger, more minute spacers of a high density are formed in order to maintain a cell gap of the LCD panel uniformly. As the density of the spacers increases, the chances of aggregation likewise increase due to a narrow dispensing distance therebetween. The ink jet dispensing method is capable of forming spacers having a high density and capable of preventing the spacers from being aggregated.  
         [0022]     The spacer forming method comprises dispensing spacers between unit pixels separated by at least one unit pixel therebetween, and after hardening the spacer, dispensing other spacers at each unit pixel formed between the first spacers, thereby forming spacers at each unit pixel.  
         [0023]     The first dispensed spacers dispensed before the second dispensing are hardened after being dried, thus reducing aggregation of the second dispensed spacer to the first dispensed spacer and thereby easily forming the spacers at a precise position. If the disposed spacers are relatively large and the unit pixel is small, adjacent spacers disposed at the unit pixels easily adhere and aggregate to each other when the spacers are dispensed. As disclosed herein, however, since first spacers dispensed are separated by at least one unit pixel and the second spacers are dispensed between the first dispensed spacers, the first and second dispensed spacers are not likely to adhere or aggregate.  
         [0024]     Hereinafter, a structure of the present LCD panel will be explained with reference to  FIGS. 2 and 3 . Also, a method for forming a spacer by an ink jet method either on an upper substrate or on a lower substrate constituting the LCD panel will be explained with reference to  FIGS. 4A  to  4 C.  
         [0025]      FIG. 1  is a sectional view showing a liquid crystal display (LCD) panel according to the present invention.  
         [0026]     As shown, a liquid crystal display (LCD) panel  100  comprises a TFT array substrate  120 , a color filter substrate  110 , and a liquid crystal layer  140  contained between the TFT array substrate  120  and the color filter substrate  110 .  
         [0027]     On the TFT array substrate  120 , a TFT  150  and a storage capacitor are formed as one pair. The TFT  150  drives the unit pixels. The storage capacitor maintains a signal applied to the unit pixel for a certain time.  
         [0028]     The TFT array substrate  120  comprises a gate electrode  151 , a gate insulating layer  122  for insulating the gate electrode  151 , a semiconductor layer  152  formed on the gate insulating layer  122  and constituting an active layer including TFT channel and source/drain regions, an ohmic contact layer  153  for ohmic-contacting the semiconductor layer  152  to source/drain electrodes  154  and  155 , and the source/drain electrodes  154  and  155  for receiving data signals.  
         [0029]     The source/drain electrodes  154  and  155  are protected by a passivation layer  123 . On the passivation layer  123 , a pixel electrode  156  for applying an electric field to the liquid crystal layer  140  is formed. The pixel electrode  156  is connected to the drain electrode  155  thus receiving data signals.  
         [0030]     The storage electrode  160  forms a capacitor with the pixel electrode  156  formed thereon, thereby maintaining data signals applied to the TFT for a certain time.  
         [0031]     The color filter substrate  110  facing the TFT array substrate  120  may be constructed as a color filter layer (not shown) is formed on a transparent substrate  111  and a common electrode  112  for applying an electric field to liquid crystal is formed on the color filter layer. The common electrode  112  may be constituted with a transparent electrode such as ITO, etc.  
         [0032]     Referring to  FIG. 2 , a plan view of a color filter substrate, the upper substrate of a present LCD panel will be explained. A color filter substrate  201  includes a plurality of sub color filters  202   a (Red),  202   b (Green), and  202   c (Blue) arranged in a matrix. The Red, Green, and Blue sub color filters  202   a,    202   b,  and  202   c  constitute one unit pixel  202 .  
         [0033]     The sub color filters  202   a,    202   b,  and  202   c  are spaced from each other uniformly, and a black matrix layer  203  for preventing light leakage from occurring between the sub color filters  202   a,    202   b,  and  202   c  is formed between the sub color filters  202   a,    202   b,  and  202   c.    
         [0034]     Although not shown, a common electrode is also formed on the color filter layer. The common electrode and the pixel electrode  156  of the array substrate  120  are used to apply an electric field to the liquid crystal  140 .  
         [0035]     In a non-high resolution LCD panel of 15 inches, the sub color filter  202   a,    202   b,  and  202   c  formed in the sub unit pixel generally has a horizontal size of approximately 100 μm and a vertical size of approximately 200 to 300 μm. Therefore, the sub color filters  202   a,    202   b,  and  202   c  are arranged to each other with a gap of approximately 100 μm. For a high resolution LCD panel, the size of the unit pixel decreases.  
         [0036]      FIG. 3  is a plan view showing an array substrate  301  facing the color filter substrate  201 . Referring to  FIG. 3 , on the array substrate  301 , a plurality of gate lines  302  and a plurality of data lines  303  perpendicular to the gate lines  302  are formed to define unit pixels  310 . The unit pixels  310  are arranged on the array substrate  301  in a matrix.  
         [0037]     The unit pixel  310  is provided with a thin film transistor  320  as a switching device which is respectively connected to the gate lines  302  and the data lines  303 . A drain electrode of the thin film transistor  320  is connected to a pixel electrode  330  of each unit pixel thus to receive data signals.  
         [0038]     The unit pixels of the array substrate  301  respectively correspond to the sub color filters  202   a,    202   b,  and  202   c  of the color filter substrate  201 . When the two substrates  201 ,  301  are attached to each other, the unit pixels  310  drive liquid crystal  140  contained between the color filter substrate  201  and the array substrate  301  as the pixel electrode  330  of the array substrate  301  and the common electrode of the color filter substrate  201  form an electric field therebetween.  
         [0039]     A constant cell gap is maintained between the color filter substrate  201  and the array substrate  301  using a spacer. The constant cell gap permits a uniform picture quality to be implemented. The spacer is formed by a simple ink jet method that is capable of controlling a dispensing position of a spacer.  
         [0040]     In the ink jet injection method, a volatile solvent including ball spacers is dispensed onto a substrate, and the solvent is volatilized to form a spacer. For a high resolution LCD panel, a gap distance between sub unit pixels is decreased. However, it is difficult to fabricate injection ports of an ink jet injection nozzle dispensing spacers with such a small uniform gap distance between the sub unit pixels. Also, even if the injection ports having a minute gap distance are fabricated, dispensed spacers that are melted in a solvent may be aggregated to each other to form inferior spacers. That is, as the solvent spreads onto the unit pixel and the spacer is formed at the unit pixel, an aperture ratio is decreased or a stain remains on the unit pixel after the solvent is volatilized.  
         [0041]     Therefore, the present invention provides a spacer forming method using an ink jet method capable of forming a spacer at each unit pixel and capable of preventing the spacers from being adhered to each other in fabrication of a high resolution LCD panel.  
         [0042]     In the present invention, a first spacer dispensing is performed with a wide gap distance between spacers, and then a second spacer dispensing is performed between the first dispensed spacers to prevent the adhesion of the spacers.  
         [0043]     The first dispensed spacer is scarcely adhered to the second dispensed spacer since a volume of the dispensed solvent including first spacers is volatilized and the first spacers are hardened before the second spacers are dispensed.  
         [0044]     Hereinafter, a spacer forming method using an ink jet injection method according to the present invention will be explained with reference to  FIGS. 4A  to  4 C.  
         [0045]     In the present invention, a spacer may be dispensed either on the color filter substrate or on the array substrate. As shown, the spacer is dispensed on the color filter substrate.  
         [0046]     Referring to  FIG. 4A , an ink jet injection nozzle  430  is arranged on a color filter substrate  400  with a constant gap. The ink jet injection nozzle  430  has a bar shape and is provided with a plurality of injection ports.  
         [0047]     The uniform gap distance between the injection ports may correspond to at least every two sub pixels or three sub pixels. That is, if length of the sub pixel 100 μm, the gap distance between the injection ports of the nozzle  430  may be about 200 μm or 300 μm. However, the gap distance between the injection ports is not limited to the above size, but may be constructed in various manners.  
         [0048]     The ink jet injection nozzle  430  is aligned above the color filter substrate  400 . A first spacer dispensing is then performed.  
         [0049]     A spacer  420  contains a ball spacer melted in a volatile solvent such as alcohol, etc. The spacer  420  is dropped onto the color filter substrate  400  in a mixed state between the solvent and the ball spacer. The spacer  420  is dropped at a region where a black matrix is formed except a unit pixel region in order not to decrease an aperture ratio of the unit pixel. Therefore, one first dispensed spacer is formed on the color filter substrate with a uniform gap distance corresponding to at least every two sub pixels.  FIG. 4A  shows that one spacer is dispensed every three sub pixels according to one embodiment of the present invention.  
         [0050]     Since the dropped spacer  420  includes a volatile solvent, the spacer is volatilized upon being dropped. Therefore, after the volatile solvent is volatilized only the ball spacer remains. As the result, the dropped spacer has a very small volume.  
         [0051]     The ink jet injection nozzle  430  disperses a spacer  420  onto a first line  410   a  of the sub color filter, and then moves with a predetermined distance in a Y direction. Then, the spacer  420  is dropped onto a second line  410   b  of the sub color filter. Then, the spacer  420  is dropped onto a third line  410   c  of the sub color filter.  
         [0052]     When moving in the Y-direction, the ink jet injection nozzle may move with a distance corresponding to at least two sub pixels and then spacers may be dropped.  
         [0053]     However, in the preferred embodiment, a vertical length of the sub pixel is sufficiently long such that spacers dropped in the vertical direction are not adhered to each other and spacers are formed at every line by an ink jet injection method.  
         [0054]     As shown in  FIG. 4A , a first spacer dispensing is performed every three sub pixels, as shown, the 3n th  column  420   a.  The ink jet injection nozzle  430  is moved in an X direction with a uniform gap distance (the gap corresponding to a horizontal length of the sub unit pixel) thereby to perform a second spacer dispensing.  
         [0055]     As shown in  FIG. 4B , a second spacer dispensing is performed between the first spacers formed by the first spacer dispensing.  
         [0056]     The first dispensed spacer has a very small volume since the solvent thereof has been volatilized and it has been hardened, and is not adhered to the second dropped spacer including a solvent.  
         [0057]     The second dispensing is performed at of the sub pixel regions between the spacers formed by the first dispensing. Referring to  FIG. 4B , the second dispensing is performed at every three column, that is, the 3n+1 th  column  420   b  of the sub pixels arranged in a matrix form. The ink jet injection nozzle  430  is moved in the Y direction by the vertical length of the sub pixels, and then the second dispensing is performed on the entire substrate.  
         [0058]     The ink jet injection nozzle  430  is moved in the X direction by the horizontal length of the sub pixels, and then a third dispensing is performed on the entire substrate. The third dispensing is performed in the same manner as the first dispensing and the second dispensing at the 3n+2 th  column  420   c  of the sub pixels.  
         [0059]     As the result, at least one ball spacer is formed at every sub unit pixel on the color filter substrate of the LCD panel. Accordingly, in fabricating a high resolution LCD panel in which the sub unit pixels are arranged with a minute gap, spacers can be formed on each sub unit pixel by an economical and easy ink jet method. Also, the adjacent spacers do not interfere with each other and thus do not adhere to each other due to the minute pixels.  
         [0060]     As aforementioned, in the present invention, a spacer can be formed at a desired position by an ink jet injection method. The ink jet injection method is more economical when compared with a column spacer forming method, and can form a spacer at a precise position when compared with a ball spacer forming method by an injection method. Also, at the time of forming spacers at each sub pixel arranged with a minute gap, the adjacent spacers do not interfere with each other and thus do not adhere to each other. Accordingly, picture quality problems such as stain are not generated on the LCD panel.  
         [0061]     As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.