Abstract:
The invention prevents moisture infiltration into a pixel region and improves reliability of an organic EL display device. A plurality of pixels is disposed in a matrix on a device substrate to form a pixel region. Each of the pixels in the pixel region is provided with an organic EL element and a driving transistor for driving the organic EL element. Furthermore, organic interlayer insulating films are formed on the driving transistor and under the organic EL element. The device substrate and a sealing substrate are attached with a sealing member disposed on a peripheral region of the pixel region. The organic interlayer insulating films are separated by a separating region provided between the sealing member and the pixel region.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to an organic EL (electroluminescent) display device, particularly to an organic EL display device in which a plurality of pixels is disposed on a device substrate to form a pixel region and each of the pixels has an organic EL element and a driving transistor for driving the organic EL element. 
   2. Description of the Related Art 
   In recent years, an organic EL display device using organic EL elements has been receiving attention as a new display device to replace a CRT or an LCD. For example, research and development of an EL display device having thin film transistors (hereafter, referred to as TFTs) as switching elements for driving the organic EL elements are being pursued. 
     FIG. 7  is a partial plan view of such an organic EL display device, and  FIG. 8  is a cross-sectional view thereof. A pixel region  200  is disposed on a device glass substrate  100 , and a horizontal drive circuit  250  and a vertical drive circuit  260  serving as a drive circuit are disposed on a periphery of the pixel region  200 . The vertical drive circuit  260  supplies a gate signal Gn as a pixel selecting signal to each of the pixels in the pixel region  200 . The horizontal drive circuit  250  supplies a display signal Dm to each of the pixels in the pixel region  200  based on a horizontal scanning signal. Each of the vertical and horizontal drive circuits is configured of shift resistors. 
   The plurality of pixels is disposed in a matrix in the pixel region  200 .  FIG. 7  shows a pixel GS only. A structure of this pixel GS will be explained as follows. A gate signal line  201  supplying the gate signal Gn and a drain signal line  202  supplying the display signal Dm intersect each other. An organic EL element  203 , a driving TFT  204  for driving the organic EL element  203 , and a pixel selecting TFT  205  for selecting the pixel GS are disposed on a periphery of an intersection of these signal lines. 
   A drain  204   d  of the driving TFT  204  is supplied with positive power supply voltage PVdd. A source  204   s  of the driving TFT  204  is connected with an anode of the organic EL element  203 . A gate of the pixel selecting TFT  205  is connected with the gate signal line  201 , and supplied with the gate signal Gn from the gate signal line  201 . A drain of the pixel selecting TFT  205  is connected with the drain signal line  202 , and supplied with the display signal Dm from the drain signal line  202 . A source of the pixel selecting TFT  205  is connected with a gate of the driving TFT  204 . 
   The organic EL element  203  includes an anode, a cathode, and an emissive layer formed between the anode and the cathode. The cathode is supplied with negative power supply voltage CV. 
   Furthermore, the gate of the driving TFT  204  is connected with a storage capacitor  206 . That is, one electrode of the storage capacitor  206  is connected with the gate of the driving TFT  204 , and another electrode thereof is connected with a storage capacitor electrode  207 . The storage capacitor  206  stores the display signal Dm applied to the gate of the driving TFT  204  through the pixel selecting TFT  205  for a field period by storing electric charge corresponding to the display signal Dm. 
   Operation of the EL display device having the above-described structure will be described. Here, the driving TFT  204  is of P-channel type, and the pixel selecting TFT  205  is of N-channel type. 
   When the gate signal Gn is high level for a predetermined horizontal period, the pixel selecting TFT  205  turns on. Then, the display signal Dm is applied from the drain signal line  202  to the gate of the driving TFT  204  through the pixel selecting TFT  205 . According to the display signal Dm supplied to the gate, conductance between the source and the drain of the driving TFT  204  changes. A drive current corresponding to the changed conductance is supplied to the organic EL element  203  through the driving TFT  204 , thereby exiting the organic EL element  203 . 
   The organic EL element  203  degrades its characteristics by absorbing moisture. Therefore, as shown in  FIG. 8 , the above-described device glass substrate  100  and the sealing glass substrate  300  are attached to each other by using sealing resin  301  made of, for example, an epoxy resin. Furthermore, a concave portion  302  is formed on a surface of the sealing glass substrate  300 , which is on the side facing the device glass substrate  100 , and a desiccant layer  303  is attached on a bottom of the concave portion  302 . This technology is disclosed in the Japanese Patent Application Publication No. 2002-175029. 
   As shown in  FIGS. 7 and 8 , an organic interlayer insulating film  208  is formed on and covers the driving TFT  204 . The source  204   s  of the driving TFT  204  is connected with the anode of the organic EL element  203  through a contact hole provided in this organic interlayer insulating film  208 . The organic interlayer insulating film  208  has appropriate characteristics as an interlayer insulating film, since it can be formed thick with its low stress and permittivity, and also costs low. On the other hand, however, the organic interlayer insulating film  208  has an adverse characteristic, i.e., high moisture transmittance. 
   Therefore, moisture infiltrating through the sealing resin  301  from outside of the organic EL display device partially reaches the pixel region  200  through this organic interlayer insulating film  208 , thereby degrading the characteristics of the organic EL element  203 . 
   SUMMARY OF THE INVENTION 
   In an organic EL display device of the invention, a plurality of pixels is disposed in a matrix on a device substrate to form a pixel region. Each of the pixels in the pixel region is provided with an organic EL element and a driving transistor for driving the organic EL element. Furthermore, organic interlayer insulating films are formed on the driving transistor and under the organic EL element. The device substrate and a sealing substrate are attached with a sealing member disposed on a peripheral region of the pixel region. The organic interlayer insulating films are separated by a separating region provided between the sealing member and the pixel region. Accordingly, even when moisture is infiltrated from outside to the organic interlayer insulating film through the sealing resin, the moisture filtration stops at the separating region and the moisture is prevented from infiltrating into the pixel region. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partial plan view of an organic EL display device of a first embodiment of the invention. 
       FIG. 2  is a cross-sectional view of the organic EL display device of the first embodiment of the invention along A—A line shown in  FIG. 1 . 
       FIG. 3  is a partial cross-sectional view along A—A line in  FIG. 1  showing a pixel region and its peripheral region of the organic EL display device of the first embodiment of the invention. 
       FIG. 4  is a partial cross-sectional view along A—A line in  FIG. 1  showing a pixel region and its peripheral region of an organic EL display device of a second embodiment of the invention. 
       FIG. 5  is a partial cross-sectional view along A—A line in  FIG. 1  showing a pixel region and its peripheral region of an organic EL display device of a third embodiment of the invention. 
       FIG. 6  is a partial cross-sectional view along A—A line in  FIG. 1  showing a pixel region and its peripheral region of an organic EL display device of a fourth embodiment of the invention. 
       FIG. 7  is a partial plan view of an organic EL display device of a conventional art. 
       FIG. 8  is a cross-sectional view of the organic EL display device of the conventional art. 
       FIG. 9  is a partial cross-sectional view along A—A line in  FIG. 1  of a modified organic EL display device of the first embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An embodiment of the invention will be described with reference to the drawings in detail.  FIG. 1  is a partial plan view of an organic EL display device of a first embodiment of the invention, and  FIG. 2  is a cross-sectional view thereof. Note that the same numerals are provided to the same components as those of  FIGS. 7 and 8 , and the descriptions of the components will be omitted. 
   Organic interlayer insulating films  216 A and  216 B are formed on a driving TFT  204 , and a drain of a driving TFT  204  is connected with an anode of an organic EL element  203  through a contact hole provided in the organic interlayer insulating film  216 B. The organic interlayer insulating films  216 A and  216 B are made of an acrylic resin, for example. 
   The organic interlayer insulating films  216 A and  216 B are separated by a separating region S provided between sealing resin  301  and a pixel region  200 . That is, the organic interlayer insulating film  216 B covers the pixel region  200 , and the organic interlayer insulating film  216 A covers a peripheral region of the pixel region  200 , extending to an edge of the device substrate  100 . The organic interlayer insulating films  216 A and  216 B are not formed in the separating region S. 
   Furthermore, a horizontal drive circuit  250  and a vertical drive circuit  260  are disposed on the periphery of the pixel region  200 , and the separating region S is disposed between the horizontal drive circuit  250  and the pixel region  200  and between the vertical drive circuit  260  and the pixel region  200 . The sealing resin  301  is interposed between the device substrate  100  and the sealing substrate  300 , and disposed in a region including the horizontal drive circuit  250  and the vertical drive circuit  260  as shown in  FIG. 1 . The edge of the organic interlayer insulating films  216 A may be covered by the sealing resin  301  as shown in  FIG. 9 . 
   Thus, in this embodiment, the organic interlayer insulating films  216 A and  216  B are separated by the separating region S provided between the sealing resin  301  and the pixel region  200 . Therefore, even when moisture is infiltrated from outside to the organic interlayer insulating film  216 A on the periphery of the pixel region  200  through the sealing resin  301 , the moisture filtration stops at the separating region S and the moisture does not infiltrate into the organic interlayer insulating film  216 B on the side of the adjacent pixel region  200 . 
   Furthermore, as shown in  FIG. 2 , moisture entering a space between the device substrate  100  and the sealing substrate  300  through the sealing resin  301  and so on is absorbed by the desiccant layer  303 . This prevents moisture infiltration into the organic EL element  203  in the pixel region  200  and degrading of characteristics thereof. 
   Next, a structure of the pixel region  200  and its peripheral region will be described in more detail.  FIG. 3  is a partial cross-sectional view showing the driving TFT  204  of one of the pixels GS in the pixel region  200  and its peripheral region. The driving TFT  204  and the organic EL element  203  are formed on a transparent insulating substrate  100  made of a silica glass or a non-alkali glass. The driving TFT  204  is formed by laminating an active layer  211  formed by poly-crystalizing an amorphous silicon film by irradiation of laser beams, a gate insulating film  212  laminated with an SiO 2  film and an SiN film in this order, and a gate electrode  213  made of metal having a high melting point such as Cr (chromium) and Mo (molybdenum), in this order. The active layer  211  is provided with a channel, a source  204   s , and a drain  204   d , the source  204   s  and the drain  204   d  being disposed on each side of the channel. 
   An first interlayer insulating film  214  laminated with an SiO 2  film, an SiN x  film and an SiO 2  film in this order is formed on the whole surfaces of the gate insulating film  212  and the active layer  211 . A drain electrode  215  is formed by filling with a metal such as Al (aluminum) a contact hole provided correspondingly to the drain  204   d . This drain electrode  215  is connected with a driving power supply PVdd. A source electrode  217  is formed by filling with a metal such as Al a contact hole provided correspondingly to the source  204   s.    
   Furthermore, a protection film  230  made of an SiN film and an organic interlayer insulating film  216 B as a second interlayer insulating film are formed on a whole surface. This organic interlayer insulating film  216 B is formed with the contact hole in a position corresponding to the source  204   s  of the driving TFT  204 . A transparent electrode made of ITO (indium tin oxide), i.e., an anode layer  218  of the organic EL element  203 , is formed on the organic interlayer insulating film  216 B, being in contact with the source electrode  217  through the contact hole. This anode layer  218  is formed in each of the pixels GS, being isolated as an island. 
   Furthermore, a third interlayer insulating film  219  is formed on a periphery of the anode layer  218 , being removed above the anode layer  218 . The organic EL element  203  is formed by laminating the anode layer  218 , a hole transport layer  220 , an emissive layer  221 , an electron transport layer  222 , and a cathode layer  223  in this order. 
   On the other hand, in the peripheral region, the gate insulating film  212  and the first interlayer insulating film  214  in the pixel region  200  extend to the peripheral region of the transparent insulating substrate  100 , and a drain signal line  202  is formed on the first interlayer insulating film  214 . The drain signal line  202  is formed of Al or Al alloy, and covered with the protection film  230 . 
   The organic interlayer insulating films  216 A and  216 B are formed on the protection film  230  formed on the drain signal line  202 . The organic interlayer insulating film  216 B extends from the pixel region  200  to this peripheral region, and the organic interlayer insulating films  216 A and  216 B are separated by the separating region S. An end of the sealing resin  301  is on the organic interlayer insulating film  216 A. The separating region S has a width enough to prevent moisture infiltrated from the sealing resin  301  from infiltrating further into the adjacent organic interlayer insulating film  216 B through the organic interlayer insulating film  216 A, for example, 5 μm or larger. 
   Next, a second embodiment of the invention will be described. Although the end of the sealing resin  301  is positioned on the organic interlayer insulating film  216 A in the first embodiment, the end of the sealing resin  301  is positioned inside the separating region S between the organic interlayer insulating films  216 A and  216 B in this embodiment as shown in  FIG. 4 . In this structure, too, the end of the sealing resin  301  is kept off from the organic interlayer insulating film  216 B on the side of the pixel region  200  by a predetermined distance d 1 , so that moisture infiltrating in the sealing resin  301  can be prevented from infiltrating further into the organic interlayer insulating film  216 B. 
   Next, a third embodiment of the invention will be described. Although the drain signal line  202  is formed of a single layer of Al in the first and second embodiments as shown in  FIGS. 3 and 4 , the drain wiring  202  in this embodiment is formed of upper wiring  202 A made of Al, and lower wiring  202 B disposed across the first interlayer insulating film  214  from the upper wiring  202 A as shown in  FIG. 5 . 
   That is, the lower wiring  202 B is formed in the same process step as the gate electrode  213  of the driving TFT  204 , and made of a same material as the gate electrode  213 . Contact holes are formed in both ends of the first interlayer insulating film  214  on the lower wiring  202 B, and the upper wiring  202 A is connected with both ends of the lower wiring  202 B through these contact holes. The separating region S between the organic interlayer insulating films  216 A and  216 B is located on the first interlayer insulating film  214  formed on the lower wiring  202 B, and the organic interlayer insulating films  216 A and  216 B cover the upper wiring  202 A. 
   This configuration is employed because the drain signal line  202  is not covered with the thick organic interlayer insulating films  216 A and  216 B at the separating region S in the case where the drain signal line  202  is formed of a single layer of Al as in the first and second embodiments. In this structure of the first and second embodiments, when the anode layer  218  is etched to partially remain at a predetermined region, the drain signal line  202  therebelow may be damaged by etching the protection film  230 . In this embodiment, the upper wiring  202 A is bypassed to the lower wiring  202 B at the separating region S, and the upper wiring  202 A is covered with the upper interlayer insulating films  216 A and  216 B, so that the drain signal line  202  can be prevented from receiving such etching damage. 
   Next, a fourth embodiment of the invention will be described. Although the end of the sealing resin  301  is positioned on the organic interlayer insulating film  216 A in the third embodiment, the end of the sealing resin  301  is positioned inside the separating region S between the organic interlayer insulating films  216 A and  216 B in this embodiment as shown in  FIG. 6 . In this structure, too, the end of the sealing resin  301  is kept off from the organic interlayer insulating film  216 B on the side of the pixel region  200  by a predetermined distance d 2 , so that moisture infiltrating in the sealing resin  301  is prevented from infiltrating into the organic interlayer insulating film  216 B. 
   Although the separating region S for separating the organic interlayer insulating films  216 A and  216 B is provided in the above-described embodiments, the invention is not limited to such interlayer insulating films. The invention can be applied to an organic insulating film for other use, for example, an organic insulating film to be used as a protection film or a planarization insulating film, and prevent moisture infiltration by the similarly provided separating region. 
   Furthermore, although the organic interlayer insulating film  216 A is disposed under the almost the whole surface of the sealing resin  301  in the above embodiments, the invention does not necessarily have such a structure. As described above, the organic interlayer insulating film  216 A has a function of protecting wiring such as the drain signal line  202  from etching damage when the anode layer  218  in the pixel region is etched. That is, the organic interlayer insulating film  216 A is not necessarily formed in a region having no wiring made of Al or Al alloy such as the drain signal line  202 . Therefore, the organic interlayer insulating film  216 A can be patterned in accordance with wiring designs. In this case, although the patterned organic interlayer insulating film  216 A is disposed under the sealing resin  301 , a separating region having a predetermined width or distance d 1  is provided between the organic interlayer insulating film  216 B and the organic interlayer insulating film  216 A or the sealing resin  301 . 
   Still furthermore, a glass is used as a material of the sealing substrate  300  in the above embodiments, the invention is not limited to such a material and can employ plastic or non-transparent materials. However, it is preferable that the material has a high adhesion to the sealing resin. 
   Although the organic EL display device of bottom emission type is exemplified for description of the above embodiments, the invention can be applied to an organic EL display device of top emission type.