Abstract:
A laser inducted thermal imaging method includes preparing a donor element and a substrate; facing a transfer layer of the donor element to the substrate and then patterning the transfer layer onto the substrate; and annealing the patterned substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of Korean Patent Application No. 2004-68769, filed Aug. 30, 2004, the disclosure of which is hereby incorporated herein by reference in its entirety.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a laser induced thermal imaging method and, more particularly, to a laser induced thermal imaging method which includes controlling aerial atmosphere in a device and annealing a transfer layer. The present invention relates to a laser induced thermal imaging for manufacturing of an organic EL display device.  
         [0004]     2. Description of the Related Art  
         [0005]     Of plat panel display devices, an organic light emitting display(“OLED”) device has a response speed of less than 1 ms which is a high response speed, is low in power consumption, and has no viewing angle problem due to its self-emitting characteristic, and so has an advantage as a moving image medium regardless size of a device. Also, the OLED can be manufactured and a simplified manufacturing process based on the existing semiconductor process technique and thus it attracts public attention.  
         [0006]     The OLED display device is classified into a polymer type device using a wet-dry etching technique and a monomer device having a deposition technique according to its material and a process.  
         [0007]     Of methods of patterning a polymer or monomer light emitting layer, an ink jet printing method has a disadvantage in that a material of organic layers except the light emitting layer is restricted and a structure for the ink jet printing should be formed on a substrate. Also, in case of patterning the light emitting layer using the deposition process, it has a difficulty manufacturing a large-size device due to use of a metal mask.  
         [0008]     As an alternative technology of such a pattering method, a laser induced thermal imaging (“LITI”) has been recently developed.  
         [0009]     The LITI is a technique that a laser generated from a light source is converted to heat energy and a pattern forming material is transferred to an object substrate using the heat energy to form a pattern. For the sake of the LITI, a donor element on which a transfer layer is formed and a substrate which is a subject are required. In the LITI, a donor film covers the acceptor substrate, and the donor film and the substrate are fixed to a stage.  
         [0010]     The transfer layer is formed of an organic layer and has a characteristic of being so sensitive to oxygen and water vapor. That is, if the organic layer is exposed to oxygen and water vapor, life span of the organic layer is lowered or light emitting efficiency and life span are lowered if the organic layer includes a light emitting layer, thereby lowering life span and light emitting efficiency of the OLED.  
       SUMMARY OF THE INVENTION  
       [0011]     It is an object of the present invention to provide a laser induced thermal imaging (“LITI”) method which can improve life span and light emitting efficiency of an OLED by controlling an aerial atmosphere in a device during a LITI process.  
         [0012]     It is another object of the present invention to provide a LITI method which can improve life span and lightemitting efficiency of an OLED by annealing a transferred organic layer.  
         [0013]     A first aspect of the present invention provides a laser induced thermal imaging method, comprising: preparing a donor element and a substrate; facing a transfer layer of the donor element to the substrate and then patterning the transfer layer onto the substrate; and annealing the patterned substrate.  
         [0014]     A second aspect of the present invention provides a laser induced thermal imaging method, comprising: preparing a donor element and a substrate; facing a transfer layer of the donor element to the substrate and then patterning the transfer layer onto the substrate; and annealing the patterned substrate at an inert gas atmosphere.  
         [0015]     A third aspect of the present invention provides a laser induced thermal imaging method, comprising: preparing a donor element and a substrate; facing a transfer layer of the donor element to the substrate and then patterning the transfer layer onto the substrate, at an inert gas atmosphere; and annealing the patterned substrate at an inert gas atmosphere at an inert gas atmosphere.  
         [0016]     A forth aspect of the present invention provides a method of fabricating an organic light emitting display, comprising: forming a transfer layer on a donor element; forming arrays having thin film transistors, capacitors and lines on a substrate; forming pixel electrodes contacted each of the thin film transistors; patterning the transfer layer on the substrate after laminating the donor element and the substrate; annealing the patterned transfer layer; and forming a opposite electrode on the annealed transfer layer.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail preferred embodiments thereof with reference to the attached drawings in which:  
         [0018]      FIG. 1  is a flow chart illustrating a laser induced thermal imaging (“LITI”) process according to an embodiment of the present invention;  
         [0019]      FIG. 2  is a cross-sectional view illustrating the donor element;  
         [0020]      FIG. 3  is a cross-sectional view illustrating a unit pixel of the substrate having the predetermined layer formed thereon;  
         [0021]      FIG. 4  is a cross-sectional view illustrating a unit pixel formed by the LITI; and  
         [0022]      FIG. 5  is a graph illustrating a characteristic of the OLED according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. Like numbers refer to like elements throughout the specification.  
         [0024]      FIG. 1  is a flow chart illustrating a laser induced thermal imaging (“LITI”) process according to an embodiment of the present invention.  
         [0025]     Referring to  FIG. 1 , a donor element a having a transfer layer and a substrate b having a predetermined layer are prepared. The transfer layer of the donor element is located to face to the predetermined layer of the substrate, and then the transfer layer is patterned in a laser irradiating device to perform a laser induced thermal imaging process c. After the patterning, the donor element having the transfer layer is removed, and the substrate is annealed. After the annealing process, an organic layer or a counter electrode is formed on the substrate having the transfer layer and then sealed, thereby completing an OLED.  
         [0026]     FIGS.  2  to  4  are cross-sectional views illustrating respective steps of the LITI process according to the present invention.  
         [0027]      FIG. 2  is a cross-sectional view illustrating the donor element which is labeled at “a” in  FIG.1 .  
         [0028]     Referring to  FIG. 2 , the donor element  100  has a structure that a plurality of layers formed on a base substrate  110 . That is, the donor element includes the base substrate  110  and a light-to-heat converting layer  120  formed on the base substrate  110  and a transfer layer  140 .  
         [0029]     The base substrate  110  may be framed one and may have a flexible or hard material. If the base substrate  110  is too thin, it is difficult to handle, and if it is too thick, it may have a difficulty conveying a donor film due to its heavy weight. Preferably, a thickness of the base substrate  110  is in a range of 20 to 200 □.  
         [0030]     The light-to-heat converting layer  120  is formed on the base substrate  110 , and the transfer layer  140  is formed on the light-to-heat converting layer  140 .  
         [0031]     The light-to-heat converting layer  120  serves to convert a laser irradiated from the laser irradiating device to the heat energy, and the heat energy changes adhesive force between the transfer layer  140  and the light-to-heat converting layer  120  to thereby transfer the transfer layer  140  to the lower substrate.  
         [0032]     To prevent damage of a transfer material and effectively control the adhesive force of the donor film, a buffer layer  130  may be interposed between the light-to-heat converting layer  120  and the transfer layer  140 .  
         [0033]     The transfer layer  140  may be a light emitting layer of the OLED. The transfer layer  140  may be one selected from a group comprised of a hole injecting layer, a hole transporting layer, a hole blocking layer, and an electron injecting layer.  
         [0034]     The transfer layer  140  may be a monomer organic layer.  
         [0035]      FIG. 3  is a cross-sectional view illustrating a unit pixel of the substrate having the predetermined layer formed thereon which is labeled at “b” in  FIG. 1 .  
         [0036]     Referring to  FIG. 3 , a process of forming the predetermined layer on the substrate  210  may include forming a thin film transistor (“TFT”) E having a gate electrode  250 , a source electrode  270   a , and a drain electrode  270   b , forming a pixel electrode layer  290  connected to the TFT E, and forming a pixel defining layer  295 .  
         [0037]     In more detail, a semiconductor layer  230  is formed on the substrate  210 . In order to prevent impurities existing on the substrate  210  from flowing into the semiconductor layer  230 , a buffer layer  220  may be formed between the semiconductor layer  230  and the substrate  210 . A gate insulating layer  240  is formed on the semiconductor layer  230 , and the gate electrode  250  is formed on the gate insulating layer  240 . An interlayer insulator  260  is formed on the gate electrode  250  using a typical material, and contact holes are formed to expose source and drain regions of the semiconductor layer  230 . A conductive material layer is formed on the interlayer insulator  260  and patterned to form the source and drain electrodes  270   a  and  270   b  which are connected to the source and drain regions, respectively.  
         [0038]     A planarization layer  280  is formed above the substrate  210  having the source and drain electrodes  270   a  and  270   b , and a via hole is formed in the planarization layer  280  to expose a portion of the drain electrode  270   b . An inorganic passivation layer may be formed before forming the planarization layer  280  to protect the lower layers from humidity, impurities and a wet-etching process. A conductive material layer is deposited on the planarization layer  280  having the via hole and patterned to form the pixel electrode  290 . The pixel defining layer  290  is formed to expose a portion of the pixel electrode  290  to thereby define a region on which an organic layer in a unit pixel will be formed.  
         [0039]      FIG. 4  is a cross-sectional view illustrating a unit pixel formed by the LITI which is labeled at “c” in  FIG. 1 .  
         [0040]     A laser  600  is irradiated to a region to be patterned of the substrate  200  and the donor element  100 .  
         [0041]     Before forming the LITI process, the donor element  100  and the substrate  200  may be subjected to a lamination process. Due to the lamination process, the donor element  100  and the substrate  200  are fixed, and bubbles between the donor element  100  and the substrate  200  are removed by a pressurizing process for the lamination process. Therefore, it is preferred that the lamination process is performed.  
         [0042]     After irradiating the laser  600 , the adhesive force between the transfer layer  140   a  and the pixel electrode  290  becomes stronger than the adhesive force between the buffer layer  130  and the transfer layer  140 , the transfer layer  140   a  of the region irradiated by the laser  600  is separated from the buffer layer  130  and patterned, i.e., patterned onto the pixel electrode  290 . The patterned transfer layer  140   a  may be patterned into a stripe type or a delta type according to a type of a unit pixel.  
         [0043]     Patterning the transfer layer onto the substrate may be performed in a vacuum state of less than 10 −2  Torr. The transfer layer  140   a  may be a monomer organic layer.  
         [0044]     Since the patterning is performed in a vacuum state, it is possible to prevent contamination substances which may occur on the pixel electrode and the organic layer during the patterning process, thereby increasing life span of the organic layer including the light emitting layer.  
         [0045]     After the patterning process, the substrate  200  is removed from the donor film  100 .  
         [0046]     The transfer layer of the patterned substrate may be annealed.  
         [0047]     The annealing process may be performed at an inert gas atmosphere.  
         [0048]     It is preferred that the annealing process at inert gas atmosphere is performed after controlling density of water vapor to be less than 10 ppm. Also, it is preferred that the annealing process at inert gas atmosphere is performed after controlling oxygen density to be less than 50 ppm. It is because even though the device in which the annealing process is performed has an inert gas atmosphere, since it is difficult to perfectly keep out oxygen and water vapor coming in from an external portion, it is preferred to control an inflow amount of oxygen or water vapor in the device in which the annealing process is performed as described above.  
         [0049]     As another embodiment of the present invention, regardless of atmosphere during the process of patterning the transfer layer onto the substrate, the transfer layer of the patterned substrate may be annealed at an inert gas atmosphere. The transfer layer  140   a  may be a monomer organic layer.  
         [0050]     It is preferred that the annealing process at inert gas atmosphere is performed after controlling density of water vapor to be less than 10 ppm. Also, it is preferred that the annealing process at inert gas atmosphere is performed after controlling oxygen density to be less than 50 ppm.  
         [0051]     Due to the annealing process, inert gases such as argon and nitrogen which remains on the transferred organic layer are removed. Also, by controlling a partial pressure of oxygen and water vapor during the annealing process, a characteristic of the organic layer is more improved. Therefore, life span of the organic layer is increased, and a life span characteristic of the OLED is improved.  
         [0052]     As another embodiment of the present invention, the process of patterning the transfer layer onto the substrate may be performed at inert gas atmosphere. The transfer layer  140   a  may be a monomer organic layer.  
         [0053]     It is preferred that the patterning process at inert gas atmosphere is performed after controlling density of water vapor to be less than 10 ppm. Also, it is preferred that the patterning process at inert gas atmosphere is performed after controlling oxygen density to be less than 50 ppm. Therefore, by controlling a partial pressure of oxygen and water vapor during the patterning process, the pixel electrode and the organic layer on the substrate may be protected during the patterning process, whereby life span of the organic layer including the light emitting layer is increased.  
         [0054]     After the patterning process, the substrate  200  is removed from the donor film  100 .  
         [0055]     The substrate  200  on which the transfer layer  140   a  is formed may be annealed at an inert gas atmosphere.  
         [0056]     It is preferred that the annealing process at inert gas atmosphere is performed after controlling density of water vapor to be less than 10 ppm. Also, it is preferred that the annealing process at inert gas atmosphere is performed after controlling oxygen density to be less than 50 ppm.  
         [0057]     Due to the annealing process, inert gases such as argon and nitrogen which remains on the transferred organic layer are removed. Also, by controlling a partial pressure of oxygen and water vapor during the annealing process, a characteristic of the organic layer is more improved. Therefore, life span of the organic layer is increased, and a life span characteristic of the OLED is improved.  
         [0058]     In all of the above described thee embodiments, it is preferred that the process of annealing the transfer layer of the patterned substrate at inert atmosphere to protect the transfer layer is performed in a range of temperature of less than a glass transition temperature.  
         [0059]     A counter electrode is formed o the patterned organic layer and then sealed, thereby completing the OLED.  
         [0060]      FIG. 5  is a graph illustrating a characteristic of the OLED according to the present invention. The graph of  FIG. 5  shows a variation of illumination with respect to time.  
         [0061]     Referring to  FIG. 5 , “1” denotes a variation of luminance after performing the patterning process of the light emitting layer at a N 2  atmosphere and thereafter the annealing process, “2” denotes a variation of luminance after performing the patterning process of the light emitting layer in a vacuum state and thereafter the annealing process, and “3” denotes a variation of luminance after performing the patterning process of the light emitting layer in a normal aerial atmosphere and thereafter the annealing process. “4” and “5” denotes one which does not perform the annealing process, where “4” denotes one which patterns the light emitting layer at a normal aerial atmosphere.  
         [0062]     It can be seen that luminance characteristic of the OLEDs which have undergone the annealing process after the patterning of the light emitting layer is such that more than 50% of an initial luminance is maintained after 1,000 hours go by regardless of the atmosphere of the patterning process. That is, it can be seen that the light emitting layer which has undergone the annealing process is more improved in life span than the light emitting layer which has not undergone the annealing process.  
         [0063]     Performing the annealing process after the patterning process at a N 2  atmosphere is similar to in luminance characteristic to performing the patterning process in a vacuum state. Therefore, it can be seen that the OLED of the present invention has improved life span compared to the conventional OLED.  
         [0064]     As described above, the laser induced thermal image can protect the pixel electrode and the transferred organic layer from gases flowing into an inside of the device from an external portion by performing the patterning process in a vacuum state, and can also improve life span of the organic layer including the light emitting layer of the OLED manufactured is thereby.  
         [0065]     Also, by annealing the transferred organic layer regardless of the atmosphere of the pattering process, gases remaining on the transferred organic layer are removed, and by controlling a partial pressure of oxygen and water vapor during the annealing process, a characteristic of the organic layer can be more improved.  
         [0066]     Further, by performing the whole process of the patterning and the annealing at inert atmosphere and controlling a partial pressure of oxygen and water vapor, a life span characteristic of the organic layer can be more improved.  
         [0067]     Therefore, a life span characteristic of the OLED can be more improved.