Abstract:
Organic light emitting diode display device including a substrate covered by a cover which has a plane surface delimited along the external perimeter thereof. The plane surface of the cover is provided with a protuberance. The substrate is provided with a stack of layers, the stack of layers including at least the following layers in succession in the following order starting from the substrate: at least one anode; an insulating layer; a spacer layer which has a first exclusion area in a first area; an active hole injection layer, an active hole transport layer and an active electron transport layer; a cathode layer which has a second exclusion area. The protuberance of the cover is joined to the layer with which the protuberance is in contact, a hole, whose diameter is smaller than the geometrical dimensions of the protuberance, being made in the protuberance and through the substrate.

Description:
[0001]    This application claims priority from European Patent Application No. 12192033.4 filed Sep. 11, 2012, the entire disclosure of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention concerns a method of manufacturing a display device using organic light emitting diodes known as OLEDs. The present invention also concerns a display device with light emitting diodes obtained by implementing this method, in addition to a timepiece comprising a display device of this type. 
       BACKGROUND OF THE INVENTION 
       [0003]    The present invention concerns OLED display devices. More specifically, the present invention concerns display devices known as passive matrix organic light emitting diodes or PMOLEDs. In PMOLED display devices, lighting is controlled by means of anodes and cathodes which are disposed in strips perpendicular to each other and powered separately. Although less energy efficient than active matrix light emitting diodes, also known as AMOLEDs, PMOLED display devices are less complex to make than AMOLED display devices and consequently were the first to be mass marketed. 
         [0004]    Compared to other types of display devices such as liquid crystal cells, OLED display devices have very interesting advantages such as a very rapid response time, improved colour rendering, better contrast or even less directive emissivity, thus offering a broader angle of vision. Compared to liquid crystal display devices, another decisive advantage of OLED display devices is that they do not require backlighting. However, one drawback of OLED display devices is their sensitivity to air and moisture. 
         [0005]    Very succinctly summarised, a PMOLED display device includes a base substrate, for example made of glass, on which anodes are structured in parallel strips. These anodes are made of a transparent, electrically conductive material such as indium tin oxide also known as ITO. After the indium tin oxide layer has been deposited on the glass substrate and the anodes have been structured, there is deposited in succession an insulating layer, whose purpose is to separate the line electrodes and column electrodes from each other, and a separation layer whose role is to create a space between the anodes and the cathodes to be deposited. The actual active layers, of which there are three, are then deposited: a hole injection layer, a hole transport layer and an electron transport layer. Finally, a layer of conductive material such as aluminium is deposited, in which the cathodes are structured. The resulting structure is covered with a cover which is bonded onto the edge of the base substrate. A moisture trap may be arranged in the volume left vacant by the cover. 
         [0006]    As mentioned above, OLED display devices have a certain number of very interesting advantages for use, for example, in portable electronic objects, such as wristwatches. However, in the particular field of horology, those skilled in the art have been confronted by a problem, which, to the Applicant&#39;s knowledge, has not yet been resolved. This problem is connected to the combined use, in a timepiece, of a digital OLED display device and an analogue display device which conventionally includes a set of hour and minute hands. Indeed, in that case, the OLED display device is on the watch dial and the hour and minute hands move above the OLED display device. The hour and minute hands are carried by a set of concentric arbours which must necessarily pass through the OLED display device. However, since the active layers and the cathode layer of an OLED display device are very sensitive to air and moisture, it is not possible to envisage piercing the OLED display device for the arbours carrying the hour and minute hands to pass therethrough, since this would place the moisture-sensitive layers of the OLED display device in direct contact with the atmosphere. 
       SUMMARY OF THE INVENTION 
       [0007]    Consequently, it is an object of the present invention to provide an OLED display device in which a hole may be made for the arbours carrying the hour and minute hands to pass through. 
         [0008]    The present invention therefore concerns a light emitting diode display device, said display device including a substrate covered by a cover which has a plane surface delimited along the external perimeter thereof by an edge, via which the cover is secured to the substrate, the plane surface of the cover being provided with an outgrowth or protuberance which extends in the direction of the substrate, the substrate being provided with a stack of layers, said stack of layers comprising at least the following layers which succeed each other in the following order starting from the substrate: 
         [0009]    at least one anode layer; 
         [0010]    an insulating coating; 
         [0011]    a spacer layer which has a first exclusion area in a first area which is located plumb with the protuberance; 
         [0012]    an active hole injection layer; 
         [0013]    an active hole transport layer; 
         [0014]    an active electron transport layer; 
         [0015]    a cathode which has a second exclusion area in a second area which is located plumb with the protuberance; 
         [0016]    the protuberance of the cover being joined to the layer with which the protuberance is in contact, a hole, whose diameter is smaller than the geometrical dimensions of the protuberance, being made in the protuberance, and said hole also passing through the substrate. 
         [0017]    As a result of these features, the present invention provides an OLED type display device which can be completely traversed by a hole through which, in the preferred example embodiment of the invention, a set of concentric arbours respectively carrying an hour hand and a minute hand are intended to pass. In fact, the protuberance of the cover, in which the hole is made for the hour and minute hand arbours to pass through, is totally sealed against moisture and oxygen, so that the active layers and the cathode layer of the OLED display device according to the invention are not liable to be damaged. To achieve this result, the present invention teaches providing an exclusion area in the spacer layer and in the cathode layer plumb with the protuberance of the cover. In other words, at the location of these exclusion areas, the materials used to deposit the spacer layer and the cathode layer are omitted. Indeed, after performing several tests, it was realised that if the spacer layer and the cathode layer remain at the place where the protuberance of the cover comes into contact with the active layers of the OLED display device, these cathode and spacer layers experience delamination when the hole is made in the protuberance of the cover, which results in the irreversible destruction of the OLED display device. Finally, it was noted that the quality of the bond between the protuberance and the substrate is much higher when the cathode and spacer layers are not present. 
         [0018]    The present invention also concerns a method of manufacturing an OLED display device, said method including the steps consisting in: 
         [0019]    taking a substrate and a cover which has a plane surface delimited along the external periphery thereof by an edge, via which the cover is intended to be secured to the substrate, the plane surface of the cover being provided with a protuberance, which extends in the direction of the substrate; 
         [0020]    depositing in succession on the substrate at least one anode layer and an insulating coating; 
         [0021]    then depositing a spacer layer in which a first exclusion area is arranged in a first area which will be located plumb with the protuberance of the cover once the cover is secured to the substrate; 
         [0022]    depositing an active hole injection layer, an active hole transport layer and an active electron transport layer in that order; 
         [0023]    depositing a cathode layer in which a second exclusion area is arranged in a second area which will be plumb with the protuberance of the cover once the cover is secured to the substrate, and 
         [0024]    joining the cover to the substrate, then making a hole, whose diameter is smaller than the geometrical dimensions of the protuberance, in the protuberance of the cover and in the substrate. 
         [0025]    According to a complementary feature of the method of the invention, the spacer layer, respectively the cathode layer, is deposited in two successive steps by means of a first mask, in which there is arranged a first aperture corresponding to a first portion of the spacer layer, respectively of the cathode layer, to be deposited, said first mask at least partially concealing an area of the substrate so as to form, in the spacer layer, respectively in the cathode layer, an exclusion area, which will be plumb with the protuberance once the cover is secured to the substrate; and by means of a second mask, which has a second aperture corresponding to a second portion of the spacer layer, respectively of the cathode layer, to be deposited, said second mask concealing if necessary the remainder of the area of the substrate, so as to form in the spacer layer, respectively in the cathode layer, the rest of the exclusion area which will be located plumb with the protuberance once the cover is secured to the substrate, the second aperture of the second mask being complementary to the first aperture of the first mask so that the combination of the first aperture and the second aperture corresponds to the desired spacer layer, respectively the cathode layer. 
         [0026]    The present invention also concerns a timepiece comprising a light emitting diode display device in which a hole is made for an hour hand arbour and a minute hand arbour to pass through. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    Other features and advantages of the present invention will appear more clearly from the following detailed description of one embodiment of an OLED display device according to the invention, this example being given solely by way of non-limiting illustration with reference to the annexed drawing, in which: 
           [0028]      FIG. 1A  is a perspective view of a glass substrate on which a conductive indium tin oxide layer and a chromium layer have been deposited in succession. 
           [0029]      FIG. 1B  is a similar view to that of  FIG. 1A , showing the step of structuring the chromium layer. 
           [0030]      FIG. 1C  illustrates the step of structuring the conductive indium tin oxide layer. 
           [0031]      FIG. 1D  illustrates the deposition of an insulating layer. 
           [0032]      FIG. 1E  illustrates the structuring of the insulating layer so as to delimit the matrix display pixels. 
           [0033]      FIG. 1F  illustrates the deposition of the separation layer. 
           [0034]      FIG. 1G  illustrates the structuring of the separation layer. 
           [0035]      FIGS. 1H ,  1 I and  1 J respectively illustrate the deposition of the active hole injection, hole transport and electron transport layers. 
           [0036]      FIG. 1K  illustrates the deposition of the cathode layer. 
           [0037]      FIG. 2  is a cross-section of an organic light emitting diode display device according to the invention. 
           [0038]      FIG. 3  is a schematic view of a wristwatch fitted with an OLED display device according to the invention. 
           [0039]      FIGS. 4A ,  4 B and  4 C are top views of the first and second masks used for the vapour deposition of the spacer layer and of the cathode layer. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    The present invention proceeds from the general inventive idea which consists in providing an organic light emitting diode display device in which it is possible to make a hole for the arbours of hour and minute hands, for example, to pass through. It is known that it is impossible to make a hole straight into an OLED display device since this would place the active layers of the OLED display device in contact with the atmosphere and destroy them. To overcome this problem, the present invention teaches arranging an exclusion area in the spacer layer and in the cathode layer deposited on the substrate of the organic light emitting display device. In other words, at the location of these exclusion areas, the materials used to deposit the spacer layer and the cathode layer are omitted. The exclusion areas are located plumb with an protuberance provided in the bottom face of a cover which will cover the OLED display device at the end of manufacture. The hole for the arbours of the hour and minute hands is made in the protuberance and in the cover. This operation is made possible by the absence of the spacer layer and the cathode layer at the place where the protuberance comes into contact with the substrate. It was in fact realised that when the spacer layer and the cathode layer are present, these layers are subject to delamination when the hole is made in the protuberance of the cover. Further, the adhesion of the protuberance to the substrate is much better when the spacer and cathode layers are omitted. Having reached the conclusion that the spacer and cathode layers had to be omitted from the protuberance area, a method had to be found for depositing these layers in the desired manner. For this purpose, the present invention teaches depositing the spacer layer, respectively the cathode layer, in two successive steps, using two distinct masks, the first of which comprises a first aperture corresponding to a first portion of the spacer layer, respectively of the cathode layer, to be deposited, said first mask concealing all or part of the area of the substrate where it is desired to create the exclusion area; and the second of which comprises a second aperture which is the complement of the first aperture arranged in the first mask and which, if necessary, conceals the rest of the area of the substrate where it is desired to create the exclusion area. Finally, the invention concerns a portable object, such as a timepiece, comprising a light emitting diode display device in which a hole is made for an hour hand arbour and a minute hand arbour to pass through. 
         [0041]    The various steps of the method for making a light emitting diode display device or OLED display device according to the invention are described below. 
         [0042]      FIG. 1A  is a perspective view of a substrate  1 , for example made of glass, on the surface of which a first conductive layer  2  and a second conductive layer  4  have been deposited in succession. The first conductive layer  2  is for example made of indium tin oxide, better known as ITO, and the second conductive layer  4  is for example made of chromium. 
         [0043]    In  FIG. 1B , the second conductive layer  4  has been practically removed from the entire surface by photolithography and chemical etching. Chromium remains only on contact pads  6  where the presence of this material improves electrical conduction. 
         [0044]      FIG. 1C  illustrates the step of structuring anodes  8 . These anodes  8  take the form of parallel strips and are obtained by photolithography and chemical etching of the first conductive ITO layer  2 . 
         [0045]      FIG. 1D  illustrates the step of depositing an insulating layer  10  over ITO anodes  8 . As seen upon examining  FIG. 1E , insulating layer  10  is structured in lines  12  and columns  14  so as to delimit conductive areas  16  which will form the display pixels of the OLED display device of the invention. 
         [0046]    In  FIG. 1F , a layer of spacer material  18  is deposited in uniform thickness over substrate  1 . The function of this layer of spacer material  18  is to separate anodes  8  from the cathode which will be structured in a subsequent step of the method. It is seen that, substantially at the centre of substrate  1 , the spacer material has not been deposited so as to create an exclusion area  20  located plumb with an outgrowth or protuberance provided in the bottom face of a cover which, as will be seen in detail below, will cover the OLED display device of the invention at the end of manufacture. 
         [0047]    In  FIG. 1G , the spacer layer has been structured to form spacers  22 , which, in the example shown in the drawing, extend parallel to each other in a generally perpendicular direction to anodes  8 . 
         [0048]    In  FIGS. 1H ,  1 I and  1 J, the active layers of the OLED display device of the invention are deposited one after the other, namely a hole injection layer  24 , a hole transport layer  26  and an electron transport layer  28 . These three layers  24 ,  26  and  28  are deposited in a non-selective manner over the entire surface of substrate  1 . 
         [0049]    Finally, as shown in  FIG. 1K , a layer  30  which will form the cathode of the OLED display device of the invention, is deposited on substrate  1 . This cathode layer  30  is obtained by evaporating an electrically conductive material, such as, in a non limiting manner, aluminium. It may also be a mixture of aluminium and calcium or a barium and silver alloy. It is seen that, substantially at the centre of substrate  1 , cathode material  30  has not been deposited so as to create an exclusion area  32  located plumb with an outgrowth or protuberance  32  provided in the bottom face of a cover which, as will be seen in detail below, will cover the OLED display device of the invention at the end of manufacture. 
         [0050]    Reference will now be made to  FIG. 2  which is a cross-section of an organic light emitting diode display device according to the invention. Designed as a whole by the general reference numeral  34 , the OLED display device of the invention includes substrate  1  over which the indium tin oxide or ITO anode layer  8 , insulating layer  10  and spacer layer  18  have been deposited in succession. According to the invention, this layer of spacer material  18  is omitted at the place where exclusion area  20  is located. It will be recalled that exclusion area  20  is located plumb with an outgrowth or protuberance  36 , which extends in the direction of substrate  1  and which is arranged in the plane surface  38  of a cover  40  which covers OLED display device  34  of the invention at the end of manufacture. 
         [0051]    The method of manufacturing OLED display device  34  of the invention continues with the non-selective deposition of the active layers of the OLED display device of the invention, namely a hole injection layer  24 , a hole transport layer  26  and an electron transport layer  28 . The manufacturing method ends with the deposition of cathode layer  30 . According to the invention, this cathode layer  30  is omitted from the place where exclusion area  32  is located. It will be recalled that exclusion area  32  is located plumb with protuberance  36  which is arranged in the plane surface  38  of cover  40  which will cover OLED display device  34  of the invention at the end of manufacture. 
         [0052]    Finally, OLED display device  34  is hermetically sealed by means of cover  40 . Cover  40  has an edge  42 , along the external periphery of the plane surface  38  thereof, via which cover  40  is secured, by means of an adhesive film  44 , to substrate  1 . Protuberance  36 , arranged in plane surface  38  of cover  40 , extends in the direction of substrate  1  in the area where exclusion areas  20  and  32  are arranged in spacer layer  18  and cathode layer  30 . Consequently, protuberance  36  is in virtually direct contact with substrate  1 , only separated therefrom by anode layer  8  and by active layers  24 ,  26  and  28 , which are very thin. A thin adhesive film  46  enables protuberance  36  to be bonded to substrate  1 . 
         [0053]    According to the invention, a hole  48 , whose diameter is smaller than the geometrical dimensions of protuberance  36 , is made in protuberance  36 . Hole  48  also traverses substrate  1 . As a result of this feature, the present invention provides an OLED display device in which a through hole is made without placing the active layers and the cathode layer in contact with moisture and oxygen. 
         [0054]      FIG. 3  is a schematic diagram of a wristwatch fitted with an OLED display device  34  according to the invention. In the example shown, OLED display device  34  acts as the dial of watch  50  and a hole  48 , which passes through OLED display device  34  and substrate  1 , is advantageously used for the passage of two concentric arbours  52  and  54  respectively carrying an hour hand  56  and a minute hand  58 . 
         [0055]      FIGS. 4A and 4B  are top views of the first and second masks  60  and  62  used for the vapour deposition of spacer layer  18  and cathode layer  30 . According to the invention, spacer layer  18  and cathode layer  30  are deposited in two successive steps using first and second masks  60  and  62 . Therefore, first mask  60  comprises a first aperture  60   a  corresponding to a first portion of the spacer layer  18 , respectively of the cathode layer  30 , to be deposited. First mask  60  also comprises a first cover portion  60   b  for concealing all or part of the area of substrate  1  where it is desired to create exclusion areas  20 ,  32 . Subsequently, the second mask  62  comprises a second aperture  62   a  which is the complement of the first aperture  60   a  arranged in the first mask  60  and which, if necessary, includes a second cover portion  62   b  which is the complement of first cover portion  60   b  and which conceals the rest of the area of substrate  1  where it is desired to create exclusion areas  20  and  32 . Finally,  FIG. 4C  shows that the joining of the first and second masks  60  and  62  enables the external contour of spacer layer  18  and of cathode layer  30  to be delimited with exclusion areas  20  and  32  at the centre of said two layers  18  and  30 . It will be clear that  FIG. 4C  is not an illustration of a step of the manufacturing method of the OLED display device of the invention, but it merely demonstrates that, placed end-to-end, the two masks  60  and  62  have perfectly complementary shapes which delimit the contour of spacer layer  18  and cathode layer  30  with the exclusion area at the centre. 
         [0056]    It goes without saying that this invention is not limited to the embodiment that has just been described and that various simple modifications and variants can be envisaged by those skilled in the art without departing from the scope of the invention as defined by the annexed claims. It will be clear, in particular, that although it was mentioned above that the protuberance provided in the bottom face of the cover is located substantially at the centre of the OLED display device of the invention, it goes without saying that this protuberance may be located at any location on the bottom face of the cover.