Patent Publication Number: US-2009227074-A1

Title: Method of manufacturing display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority from Korean Patent Application No. 10-2008-0020088, filed in the Korean Intellectual Property Office on Mar. 4, 2008, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to a method for manufacturing a display device. 
     (b) Description of the Related Art 
     Various types of display devices have been introduced to the market. Among these various types of display devices, the liquid crystal display (LCD) has been reduced in size and weight, and the performance thereof has been improved, due in large part to the rapid development of semiconductor technology. The liquid crystal display continues to receive attention as a most important type of display device. 
     Lately, there has arisen a strong demand for a flexible and compact display device. 
     Accordingly, a display device, with an improved level of integration, having a driver integrated circuit (IC) chip directly mounted on an edge portion of a substrate has been developed and has been used. Also, a flexible display device using a substrate made of plastic material has been developed. 
     However, there are many technical difficulties in mounting a driver IC chip directly on a substrate made of a plastic material. The driver IC chip is generally mounted directly on a substrate by means of an anisotropic conductive film (ACF). 
     When the driver IC chip is mounted directly on the substrate made of a plastic material, pads on the substrate, which are electrically connected to the driver IC chip, may be seriously cracked or damaged due to pressure and temperature that are generated while mounting the driver IC chip. 
     The above information disclosed in this background section is intended only for enhancement of understanding of the background of the invention and therefore it may contain information that is not part of the prior art. 
     SUMMARY OF THE INVENTION 
     An exemplary embodiment of the present invention provides a method for manufacturing a display device. In the method, a carrier substrate is provided, and a plastic substrate is formed on the carrier substrate. A thin film transistor, a pixel electrode, and a contact pad are formed on the plastic substrate. A driver integrated circuit (IC) chip is mounted on the plastic substrate to be electrically connected with the contact pad, and the plastic substrate then is separated from the carrier substrate. 
     A sacrificial layer may be formed on the carrier substrate before the plastic substrate is formed. 
     The plastic substrate may be separated from the carrier substrate by removing the sacrificial layer. 
     Laser radiation may be applied to the sacrificial layer to remove the sacrificial layer. 
     The plastic substrate may be formed by coating a plastic material on the carrier substrate. 
     The plastic substrate may be separated from the carrier substrate by removing a part of the plastic substrate, the part of the plastic substrate being adjacent to the carrier substrate. 
     A part of the plastic substrate may be removed by applying laser radiation to the part of the plastic substrate. 
     The plastic substrate may be separated from the carrier substrate through a temperature difference generated by heating or cooling the plastic substrate and the carrier substrate. 
     The carrier substrate may be made of glass. 
     The plastic substrate may be made of a material including a polymer having excellent heat resistance, including one of polyimide (PI), polyamide (PA), polyethylene terephthalate (PET), fiber-reinforced polymers (FRP), polycarbonate, polyethersulfone (PES), polyarylate (PAR), and polyethylene naphthalate (PEN). 
     The mounting of a driving IC chip on the plastic substrate may include: forming an anisotropic conductive film (ACF) on the contact pad; disposing the driver IC chip on the anisotropic conductive film; and electrically connecting the contact pad to the driver IC chip by applying heat and pressure thereto. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a liquid crystal display device manufactured according to exemplary embodiments of the method of manufacture of the present invention. 
         FIG. 2  is a cross-sectional view of  FIG. 1  taken along the line II-II. 
         FIGS. 3 to 6  are cross-sectional views sequentially illustrating a method for manufacturing a display device according to a first exemplary embodiment of the present invention. 
         FIG. 7  is a cross-sectional view illustrating a method for manufacturing a display device according to a second exemplary embodiment of the present invention. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS INDICATING PRIMARY ELEMENTS IN THE DRAWINGS 
       100 : first display panel 
       101 : thin film transistor 
       110 : first substrate member 
       124 : gate electrode 
       128 : gate pad 
       130 : gate insulating layer 
       140 : semiconductor layer 
       165 : source electrode 
       166 : drain electrode 
       170 : passivation layer 
       180 : pixel electrode 
       185 : contact pad 
       200 : second display panel 
       210 : second substrate member 
       220 : light blocking member 
       230 : color filter 
       250 : overcoat layer 
       280 : common electrode 
       300 : liquid crystal layer 
       310 : first alignment layer 
       320 : second alignment layer 
       400 : anisotropic conductive film 
       500 : driver IC chip 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The present invention is described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would understand, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. 
     In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like reference numerals designate like elements throughout the specification. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. 
     In the accompanying drawings, a display device having an amorphous silicon (a-Si) thin film transistor (TFT) formed through five mask processes is schematically shown as an exemplary embodiment of the present invention. A pixel denotes a minimum unit for displaying an image. However, a thin film transistor may be formed in various forms in the present invention and is not limited to those forms used in exemplary embodiments described in the specification. 
     To clearly explain the present invention, portions having no connection to the explanation are omitted, and the same or similar constituent elements are designated with the same reference numerals throughout the specification. 
     For various exemplary embodiments, constituent elements having the same constitution are designated with the same reference numerals and explained representatively in the first exemplary embodiment. In other exemplary embodiments, only constituent elements that are different from those in the first exemplary embodiment are described. 
     A display device manufactured according to exemplary embodiments of the present invention will be described with reference to  FIG. 1  and  FIG. 2 . 
     As shown in  FIG. 1 , a display device  900  includes a first display panel  100 , a second display panel  200 , a liquid crystal layer  300  (shown in  FIG. 2 ), and a driver integrated circuit (IC) chip  500 . The second display panel  200  has a smaller surface area than that of the first display panel  100 . An overlapping region of the first display panel  100  and the second display panel  200  is referred to as a display area D. An area of the first display panel  100 , which is not overlapped by the second display panel, is referred to as a non-display area N. The driver IC chip  500  is directly mounted on the first display panel  100  in the non-display area N. 
     With reference to  FIG. 2 , the structure of the display device  900  is described in terms of sequentially formed layers. 
     First, a structure of the first display panel  100  is described. 
     The first display panel  100  includes a plastic substrate  110  that is made of a material including a polymer having excellent heat resistance, such as polyimide (PI), polyamide (PA), polyethylene terephthalate (PET), fiber-reinforced polymers (FRP), polycarbonate, polyethersulfone (PES), polyarylate (PAR), and polyethylene naphthalate (PEN). However, the material of the plastic substrate  110  is not limited to these polymers. Any other material may be used if the material has excellent heat resistance to allow thin film processes to be performed on the plastic substrate  110 . Hereinafter, the plastic substrate  110  may be referred to as a first substrate member. 
     A gate wiring pattern having a plurality of gate electrodes  124  is formed on the first substrate member  110 . Although not shown, the gate wiring pattern may further include a plurality of gate lines connected to the gate electrodes  124 , and a plurality of first storage electrode lines. The gate wiring pattern further includes gate pads  128 , formed in the non-display area N, and connected to the gate lines. 
     The gate wiring pattern, including the gate electrodes  124  and the gate pads  128 , is formed in a gate level conductive layer which may include a metal such as Al, Ag, Cr, Ti, Ta, Mo, or alloys thereof. Although the gate level conductive layer is shown as a single layer in  FIG. 4 , the gate level conductive layer may include multiple layers, for example, a metal layer made of Cr, Mo, Ti, Ta, or alloys thereof, which have excellent physicochemical characteristics, and a layer that includes an Al series or Ag series metal having low resistivity. In addition to these metals, the gate level conductive layer may be made of various other metals or conductors. It is preferable, when the gate level conductive layer includes multiple layers, that etch patterning be performed under the same etch conditions for each of the multiple layers. 
     A gate insulating layer  130  is formed on the gate wiring pattern and on the first substrate member  110 . The gate insulating layer  130  may be made of silicon nitride (SiNx), for example. 
     A semiconductor layer  140  is formed on the gate insulation layer  130  at predetermined regions above the gate electrodes  124 . The semiconductor layer includes a semiconductor such as silicon and may be amorphous silicon. Ohmic contacts  155  and  156  are formed on the semiconductor layer  140 . The ohmic contacts may include a metal silicide or heavily doped N-type silicon. 
     A data wiring pattern is formed in a data level conductive layer deposited on the gate insulating layer  130  and on the semiconductor layer  140 . The data wiring pattern includes a plurality of source electrodes  165  each source electrode  165  having a region that overlaps an ohmic contact  155  which overlaps a portion of a gate electrode  124 , and a plurality of drain electrodes  166  separated from the source electrodes  165 , each drain electrode  166  having a region that overlaps an ohmic contact  156  which overlaps a portion of a gate electrode  124 . Although not shown, the data wiring pattern may further include a plurality of data lines that cross the gate lines, a plurality of second storage electrode lines overlapping first storage electrodes, and data pads formed on the non-display area N and connected to the data lines. 
     Like the gate level conductive layer, the data level conductive layer is made of a conductive material such as chromium, molybdenum, aluminum, or alloys thereof, and may be formed as a single layer or as multiple layers. 
     Each semiconductor layer  140  includes a region which overlaps the gate electrode  124 , a region which is overlapped by the source electrode  165 , and a region which is overlapped by the drain electrode  166 . The gate electrode  124 , the source electrode  165 , and the drain electrode  166  become three electrodes of a thin film transistor  101 . The semiconductor layer  140  between the source electrode  165  and the drain electrode  166  becomes a channel region of the thin film transistor  101 . The structure of the thin film transistor  101  is not limited to the structure shown in  FIG. 2 . The thin film transistor  101  may have various well-known structures within a range that allows those skilled in the art to easily modify it. 
     Ohmic contacts  155  and  156  are formed between the semiconductor layer  140  and the source electrode  165  and the drain electrode  166 , respectively, to reduce contact resistance therebetween. The ohmic contacts  155  and  156  are made of silicide or amorphous silicon doped with an n-type impurity at a high concentration. 
     A passivation layer  170  is deposited on the data wiring pattern and on the gate insulating layer. The passivation layer  170  is formed by plasma enhanced chemical vapor deposition (PECVD) and is made of a low dielectric constant insulating material such as a-Si:C:O or a-Si:O:F, an inorganic insulating material such as silicon nitride or silicon oxide, or, alternatively, an organic insulating material. 
     A plurality of pixel electrodes  180  and a plurality of contact pads  185  are formed on the passivation layer  170 . The pixel electrodes  180  and the contact pads  185  may be made of a transparent conductor such as indium tin oxide (ITO) or indium zinc oxide (IZO), or, alternatively, may be made of an opaque conductor such as aluminum (Al). 
     The passivation layer  170  includes a plurality of first contact holes  171  for exposing portions of the drain electrodes  166  and second contact holes  172  for exposing portions of the gate pads  128  and data pads (not shown). The pixel electrodes  180  are electrically connected to the drain electrodes  166  through the first contact holes  171 . Also, the contact pads  185  are electrically connected to the gate pads  128  and the data pads (not shown) through the second contact holes  172 . 
     Second, a structure of the second display panel  200  is described. 
     The second display panel  200  includes a second substrate member  210 . Like the first substrate member  110 , the second substrate member  210  may be made of a plastic material. However, the second substrate member  210  is not limited to a plastic material. The second substrate member  210  may be formed of various insulating materials such as glass, quartz, or ceramic. However, if the second substrate member  210  is made of a flexible material as well as the first substrate member  110 , the practical use range of the display device  900  may be expanded, thereby further improving the overall utility of the display device  900 . Therefore, it is preferable that the second substrate member  210  be a plastic substrate as well as the first substrate member  110 . 
     A light blocking member  220  is formed on the second substrate member  210 . The light blocking member  220  includes openings facing the pixel electrodes  180  of the first display panel  100 , and blocks light from leaking through a gap between adjacent pixels. Here, a pixel is a minimum unit used for displaying an image. The light blocking member  220  is also formed at locations corresponding to the thin film transistors  101  in order to block external light from entering the semiconductor layers  140  of the thin film transistors  101 . 
     In order to block light, the light blocking member  220  may be made of a photosensitive organic material having an opaque pigment, or may include a metal layer. The opaque pigment may be carbon black or titanium oxide. 
     Color filters  230  having three primary colors are sequentially disposed on the second substrate member  210  in the openings formed in the light blocking member  220 . Here, colors of the color filters  230  are not limited to three primary colors. The color filters  230  may be variously constituted with at least one primary color. Although a boundary of each color filter  230  is located on the light blocking member  220 , the present invention is not limited thereto. Edges of adjacent color filters  230  may be overlapped with each other to block leaked light like the light blocking member  220 . In the latter configuration, the light blocking member  220  disposed along the boundaries of pixels may be omitted. 
     An overcoat layer  250  is formed on the light blocking member  220  and the color filters  230 . Such an overcoat layer  250  may be omitted. The overcoat layer  250  protects the color filters  230  and smoothes the surface thereof. 
     A common electrode  280  is formed on the overcoat layer  250 . An electric field is formed between the common electrode and the pixel electrode  180 . The common electrode  280  is made of a transparent conductor such as ITO or IZO. 
     The structures of the first display panel  100  and the second display panel  200  are not limited to the above-described structures and are not limited to the structures shown in the accompanying drawings. The first display panel  100  and the second display panel  200  may have various well-known structures within a range that allows those skilled in the art to modify them. For example, the color filter may be formed on the first display panel instead of the second display panel. 
     The liquid crystal layer  300  includes a plurality of liquid crystal molecules, and is disposed between the first display panel  100  and the second display panel  200 . The liquid crystal layer  300  may include various types of liquid crystal molecules according to a driving method of the display device  900 , such as vertically aligned liquid crystal molecules, horizontally aligned liquid crystal molecules, and blue-phase liquid crystal molecules. 
     Also, the display device  900  further includes a first alignment layer  310  formed on the pixel electrode  180  and a second alignment layer  320  formed on the common electrode  280 . The first alignment layer  310  and the second alignment layer  320  align liquid crystal molecules of the liquid crystal layer  300 . 
     The driver IC chip  500  is directly mounted on the first display panel  100 , and is electrically connected to the contact pads  185 . Here, the driver IC chip  500  and the contact pads  185  are electrically connected to each other through an anisotropic conductive film (ACF)  400 . The driver IC chip  500  includes a main body  510  and terminals  520 . The anisotropic conductive film (ACF)  400  includes an adhesive layer  420  and conductive balls  410  disposed in the adhesive layer  420 . The contact pads  185  on the first display panel  100  are electrically connected to the terminals  520  of the driver IC chip  500  through the conductive balls  410  of the anisotropic conductive film (ACF)  400 . 
     As described above, the level of integration of the display device  900  may be increased while the flexibility of a plastic substrate is sustained by directly mounting the driver IC chip  500  on the first substrate member  110  which is a plastic substrate. 
     Hereinafter, a method for manufacturing a display device according to a first exemplary embodiment of the present invention is described with reference to  FIG. 3  to  FIG. 6 . 
     First, as shown in  FIG. 3 , a carrier substrate  700  made of generally-used glass is provide and prepared. Preparation of the carrier substrate  700  may include cleaning the carrier substrate  700 . A sacrificial layer  112  is formed on the carrier substrate  700 . The plastic substrate  110  is formed on the sacrificial layer  112  by coating a plastic material on to the sacrificial layer  112 . 
     The plastic substrate  110  is made of material including a polymer having excellent heat resistance, such as polyimide (PI), polyamide (PA), polyethylene terephthalate (PET), fiber-reinforced polymers (FRP), polycarbonate, polyethersulfone (PES), polyarylate (PAR), and polyethylene naphthalate (PEN). The material of the plastic substrate  110  is not limited to these polymers. Any other material may be used if the material has excellent heat resistance sufficient to allow thin film processes to be performed on the plastic substrate  110 . Hereinafter, the plastic substrate  110  may be referred to as the first substrate member. The sacrificial layer  112  and the first substrate member  110  are formed on the carrier substrate  700  by doubly coating a polymer material on the carrier substrate  700 . Here, the first substrate member  110  and the sacrificial layer  112  are substantially made of similar materials. However, the first substrate member  110  and the sacrificial layer  112  are formed to react differently to laser light or to a high temperature. 
     As shown in  FIG. 4 , the first display panel  100  is completed by providing the elements of the first display panel shown in  FIG. 2  on the plastic substrate  110 . Here, the thin film transistors  101  and the pixel electrodes  180  are formed in a display area D, and the contact pads  185  are formed in a non-display area N. Also, the second display panel  200  is independently manufactured and is disposed opposite and facing the first display panel  100 . A liquid crystal layer  300  is disposed between the first display panel  100  and the second display panel  200 . 
     As shown in  FIG. 5 , a driver IC chip  500  is directly mounted on the first display panel  100  including the first substrate member  110  which is a plastic substrate to electrically connect the driver IC chip  500  with the contact pads  185 . Here, an anisotropic conductive film (ACF)  400  is used. That is, the anisotropic conductive film  400  electrically connects the terminals  520  of the driver IC chip  500  to the contact pads  185 . That is, in the method for connecting the contact pads  185  to the driver IC chip  500  using the anisotropic conductive film  400 , the anisotropic conductive film  400  is formed on the contact pads  185 , and the driver IC chip  500  is disposed on the anisotropic conductive film  400 . Then, the contact pads  185  and the driver IC chip  500  are electrically connected to each other by applying heat and pressure. 
     High temperature and pressure are applied to the first substrate member  110  while mounting the driver IC chip  500  on the first substrate member  110  using the anisotropic conductive film  400  in order to electrically connect the driver IC chip  500  and the contact pads  185 . Since the first substrate member  110  is a plastic substrate, the first substrate member  110  is fragile at such applied high temperature and pressure. Therefore, the contact pads  185  formed on the first substrate member  110  may be damaged while mounting the driver IC chip  500 . 
     However, the weakness of the first substrate member  100  at elevated temperature and pressure is compensated by supporting the first substrate member  110  which is a plastic substrate on the carrier substrate  700  made of glass or other suitable material. 
     Therefore, in accordance with the method of the present invention the driver IC chip  500  is stably mounted on the first substrate member  110  which is a plastic substrate. 
     Then, as shown in  FIG. 6 , the sacrificial layer  112  is removed by applying radiation from a laser onto the sacrificial layer  112  through the carrier substrate  700 . That is, the first substrate member  110  is separated from the carrier substrate  700  by removing the sacrificial layer  112 . The application of the laser radiation to the sacrificial layer  112  is indicated in  FIG. 6  by the vertical arrows. 
     In  FIG. 2 , the completed display device  900  including the first display panel  100  with the driver IC chip  500  stably mounted on the first substrate member  110  which is a plastic substrate, the second display panel  200 , and the liquid crystal layer  300 , is shown after the carrier substrate  700  has been separated from the first display panel. 
     As described above, the driver IC chip  500  can be stably mounted on the first substrate member  110 , which is a plastic substrate, based on the manufacturing method according to the first exemplary embodiment of the present invention. Therefore, a display device in which a driver IC chip is mounted on a flexible plastic substrate can be manufactured while sustaining the flexibility thereof. 
     A method for manufacturing a display device according to a second exemplary embodiment of the present invention is described with reference to  FIG. 7 . 
     First, a carrier substrate  700  made of a generally-used glass substrate is provided and prepared. Then, a plastic substrate  110  is formed on the carrier substrate  700  by coating a plastic material on the carrier substrate  700 . Here, the plastic substrate  110  is referred to as a first substrate member. The first substrate member  110  is formed without a sacrificial layer. 
     Then, a first display panel  100  is manufactured by forming the elements shown in  FIG. 2 , or equivalent elements, on the first substrate member  110 . Also, a second display panel  200  is independently manufactured and disposed opposite the first display panel  100  to face each other. In this process, a liquid crystal layer  300  may be disposed between the first display panel  100  and the second display panel  200 . 
     Then, a driver IC chip  500  is directly mounted on the first substrate member  110  using an anisotropic conductive film  400  to electrically connect the driver IC chip  500  and the contact pads  185 . 
     As indicated by the vertical arrows in  FIG. 7 , laser radiation is applied through the carrier substrate  700  to the first substrate member  110  that is a plastic substrate. This application of the laser radiation to the first substrate member  110  causes the first substrate member  110  to separate from the carrier substrate  700 . A thin portion of the first substrate member may be eliminated by the laser light. As described above, the first substrate member  110  is separated from the carrier substrate  700  and the process of separation may include removing a part of the first substrate member  110 . 
     As shown in  FIG. 2 , a display device  900  having the driving IC chip  500  directly mounted on the first display panel  100  including the first substrate member  110  made of the plastic substrate is manufactured. 
     Using the manufacturing method according to the second embodiment, the driver IC chip  500  can be stably attached to a first display panel  100  that includes the first substrate member  110  made of the plastic substrate. Therefore, a more integrated and flexible display device can be manufactured. 
     The present invention is not limited to the method including a step of using a laser. Alternatively the first substrate member  110  may be separated from the carrier substrate  700  through a temperature difference generated by heating or cooling the first substrate member  110  made of the plastic substrate and the carrier substrate  700 . 
     Since the methods for separating substrates by heating or cooling the substrates are well known to those skilled in the art, a detail description thereof is omitted. 
     Embodiments of the present invention provide a display device having a driver IC chip stably mounted on a flexible plastic substrate. 
     Also, embodiments of the present invention provide a method for manufacturing a display device having a driver IC chip stably mounted on a flexible plastic substrate. 
     While this invention has been described in connection with what is presently considered to be practical 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.