WO2011083414A1

WO2011083414A1 - A method of manufacturing an oled device

Info

Publication number: WO2011083414A1
Application number: PCT/IB2011/050011
Authority: WO
Inventors: Holger Schwab
Original assignee: Koninklijke Philips Electronics N.V.; Philips Intellectual Property & Standards Gmbh
Priority date: 2010-01-05
Filing date: 2011-01-04
Publication date: 2011-07-14
Also published as: TW201138180A

Abstract

The invention describes a method of manufacturing an OLED device (1), which method comprises applying a first electrode (3) onto a carrier (2); applying an active layer (4) onto the first electrode (3) such that the active layer (4) essentially uniformly covers the first electrode (3); applying a second electrode (5) to the active layer (4) such that the second electrode (5) essentially uniformly covers the active layer (4); and exposing an access area (30) of the first electrode (3) in an opening (31), which opening (31) is made by removing a region (50) of the second electrode (5) and a corresponding underlying region (40) of the active layer (4) such that the first electrode (3) is electrically accessible through the opening (45). The invention also describes an OLED device (1) comprising a first electrode (3) applied onto a carrier (2); an active layer (4) applied onto the first electrode (3) such that the active layer (4) initially entirely covers the first electrode (3); a second electrode (5) applied onto the active layer (4) such that the active layer (5) initially entirely covers the second electrode (4); and an access area (30) for electrical access to the first electrode (3) within an opening in the second electrode (5), which opening comprises a removed region (50) of the second electrode (5) and a corresponding removed region (40) of the active layer (4), characterized in that the first electrode (3) is electrically isolated from the second electrode (5) only by the active layer (4) and/or free space (51).

Description

A METHOD OF MANUFACTURING AN OLED DEVICE

FIELD OF THE INVENTION

The invention describes a method of manufacturing an OLED device. The invention further describes such an OLED device.

BACKGROUND OF THE INVENTION

An organic light-emitting diode (OLED) device is manufactured by building up a series of layers, usually comprising an active or organic layer sandwiched between an anode and a cathode. The organic or functional layer, which may in fact comprise several layers, is often collectively referred to as the 'active layer', since it is in this active layer that light is generated when a current flows from the anode to the cathode. For OLEDs used in flat displays or illumination devices, the anode and cathode are generally accessed from the same side of the device, for example from the light-emitting side. Therefore, a first stage comprises creating electrically separated patterns of a conductive coating on a carrier such as glass. The required pattern, which comprises both anode and cathode areas, can be created by using subtractive methods like photo lithography, laser ablation, etc. where parts of the conductive coating are removed in certain areas. In a next stage, the functional or active layers - usually comprising small-molecule organic material - are deposited by thermal evaporation in vacuum. The deposition of the organic material in certain areas must be restricted, for example by use of a shadow mask, so that at least the cathode contacts are not coated, and the anode contacts are also usually protected from the coating. In a next step, the cathode is deposited, usually also in a vacuum thermal evaporation process. Again, a shadow mask must be used to ensure that the cathode and the anode are not short-circuited. Since the coated areas for the organic layer and the cathode are different, a different set of masks must be used in both processes. During deposition, the shadow masks become coated with material. Since high precision shadow masks are expensive, and since the shadow masks must either be replaced or cleaned after the deposition steps, this type of manufacturing method is costly. Furthermore, the shadow masks must be very precisely aligned to avoid the risk of short-circuiting the electrodes. After completion of the organic and cathode deposition processes, the device must be encapsulated to protect the organic layer from moisture. This encapsulation can be carried out in various ways. For example, a glass cover lid can be applied to the device using glue with low water permeability. In another approach, the outer surface of the device can be coated with a suitable film applied in a further deposition step. To allow electrical access to the cathode and anode, these must both extend beyond the sealing line, usually on different sides of the device. However, the fact that the electrodes protrude on two or more sides of the device means that these parts of the device effectively comprise non-emitting surface areas, which may well be undesirable in various applications.

The small size of prior art OLEDs is largely a result of the limited conductivity of the anode material. These need to be kept small so that they are not noticeable and also so that as much light as possible can leave the device. However, since these elements carry all the current for the entire OLED area, the realistic device size is effectively constrained. The largest practicable OLED device area which can be achieved by state of the art manufacturing techniques, without using metal grid lines or other measures to enhance conductivity of the anode, is limited to about 5 cm x 5 cm. To obtain a device with a larger total emitting area, either a metal mesh needs to be incorporated, or a number of devices can be 'tiled'. However, the additional non-emitting area taken up by the electrodes between the individual 'tiles' means that the tiling is not seamless. Neighbouring devices are separated by the area taken up by the electrodes, and this non-emitting area is easily noticeable. Again, this drawback limits the applications for which such OLED devices would be useful.

In an approach to improve the ratio between emitting and non-emitting area, i.e. to allow the encapsulation to extend to the edges of the device, the 'top' electrode (usually the cathode) is contacted through the encapsulation, for example by metal feed through the cover-lid (using the accepted convention, the terms 'top' and 'bottom' refer respectively to the cover-lid and substrate sides of an OLED). In order to also contact the anode from the top side a connection between the anode and electrically conductive layers on the cover lid through the cathode must be established. These conductive layers in the cover lid can then be contacted from the back side for example by electrical feed through in the lid similar to the cathode contact. The most convenient way to create a connection between anode and the cover lid is to have raised metal contacts already on the substrate before the vapour deposition processes are carried out. The conductive material of the structure or 'via' should be surrounded by insulating material to avoid a short circuit between it and the cathode. Using state of the art manufacturing technology during vapour deposition of the organic layers and cathode layer, one or more shadow masks must be used to protect the metal contacts from being coated. Such a deposition process requires a high degree of precision in order to satisfy the quality criteria of the final product. Furthermore, since the shadow masks are also coated with material during the vapour deposition steps and need to be cleaned before each use, or replaced, their use adds to the overall cost of manufacture. The vias made in this way are relatively large, so that such an OLED is really not practicable for decorative and lighting purposes in which an uninterrupted homogenous emitting surface is desired.

It is therefore an object of the invention to provide an improved method of manufacturing an OLED device, circumventing the problems described above.

SUMMARY OF THE INVENTION

This object is achieved by the method of claim 1 of manufacturing an OLED device, and by the OLED device of claim 9.

According to the invention, the method of manufacturing an OLED device comprises the steps of applying a first electrode onto a carrier, applying an active layer onto the first electrode such that the active layer essentially uniformly covers the first electrode, and subsequently applying a second electrode to the active layer such that the second electrode essentially uniformly covers the active layer. The method further comprises the step of exposing an access area of the first electrode in an opening, which opening is made by removing a region of the second electrode and a corresponding region of the active layer such that the first electrode is electrically accessible through the opening.

Here, the processing steps can be carried out in any appropriate sequence. For example, in a particularly straightforward technique, the first electrode, active layer, and second electrode can first be applied, and the cavities can then be created by removing regions of the second electrode and corresponding underlying regions of the active layer ablated to expose access areas on the first electrode. In an alternative approach, a cavity can be created in a two-step process. In a first step, the active layer can be applied to the first electrode, and regions of the active layer, corresponding to the locations of future vias, are subsequently excised or ablated to expose access areas on the first electrode. Then, in a second step, the second electrode is applied to the active layer, and regions of the second layer above the underlying removed regions of the active layer are also removed to expose the access areas again.

Such a means of accessing the first electrode is usually called a 'via'. Here, a via is made by removing a region of the second electrode and an underlying region of the active layer. Since these regions can be very small, the vias can be nearly invisible, so that an

OLED manufactured using this method can be suitable for large-area applications that require high emission homogeneity.

Since the first electrode layer can be easily accessed electrically through openings in the 'top' layer, and any number of these openings can be distributed about the second electrode layer, this means that the OLED device manufactured using the method according to the invention advantageously exhibits a high brightness homogeneity, i.e. there is effectively no difference in brightness between different regions of the emitting surface.

Most advantageously, the method according to the invention of manufacturing

OLED device does not require any costly or time-consuming complex shadow masks when applying the layers within the future emitting area of the OLED device, so that a device made using this method can be considerably cheaper than a comparable prior art device.

According to the invention, the OLED device comprises a first electrode applied onto a carrier, an active layer applied onto the first electrode such that the active layer initially entirely covers the first electrode, and a second electrode applied onto the active layer such that the active layer initially entirely covers the second electrode. The expression

"applied to initially entirely cover" means that, within the confines of the future emitting area of the OLED, a layer is applied to entirely and homogenously cover the preceding layer. The

OLED device according to the invention further comprises an access area for electrical access to the first electrode within an opening in the second electrode, which opening comprises a removed region of the second electrode and a corresponding removed region of the active layer through which the first electrode can be accessed, and wherein the first electrode is electrically isolated from the second electrode only by the active layer and/or free space.

The OLED device according to the invention can have an emitting area much greater than that which can be achieved by the prior art manufacturing techniques in which the anode and cathode are both accessed from an edge of the device. Since the maximum emitting OLED area can be made extremely large, and is effectively only limited by the manufacturing equipment used, a large OLED can be achieved without tiling or metal shunt lines and mesh lines on the substrate side. Such a large OLED device with homogenous light quality may be suitable for a wide variety of applications for which prior art OLED devices cannot be used. However, since the OLED device according to the invention does not require large contact areas on the sides of the device, an essentially seamless tiling is possible, so that an even larger device could be assembled by tiling several such OLED devices to give an array.

The dependent claims and the subsequent description disclose particularly advantageous embodiments and features of the invention.

The access area on the first electrode can be exposed in a number of ways, depending on the structure of the first electrode. In a preferred embodiment of the invention, the first electrode, the active layer and the second electrode are all essentially planar, and the thickness of each layer is in the order of 100 nm. In such an approach, the three layers can be particularly simply and economically applied, since no shadow masks are involved.

Preferably in such cases, but without restricting the invention in any way, the step of exposing the access area comprises creating a cavity extending between the second electrode and the first electrode. Using the techniques according to the invention, which will be explained in detail below, access areas with a surface area in the order of 100 μιη can be obtained.

Once the cavity has been created to expose the access area, an electrically conductive via can be introduced into the cavity. Again, this can be done in a number of ways. In one preferred embodiment of the invention, this is done by constructing an electrically conductive plug in the cavity to electrically extend the first electrode at least to the level of the second electrode. For example, one or more droplets of electrically conductive viscous liquid such as an electrically conductive glue or ink, a silver paste, etc., can be dropped into the cavity. The size of the droplets is preferably in the order of a few tens of micrometers. Spreading can be limited by proper formulation of the paste, glue or ink. The surface tension of the chosen liquid and the physical separation between the droplet and the second electrode is sufficient to prevent an overspill of material. Preferably, the properties of the conductive material used allow a 'mound' to form, which may extend to the level of the second electrode. This mound may even protrude slightly above the second electrode, since an overall 'flatness' of the top level is sufficient, and an unevenness in the range of a few micrometers is tolerable.

Depending on the choice of electrically conductive liquid, the mound or via can be allowed to harden simply by leaving it to dry. A focused heat source such as a laser or full area light source such as infrared lamp with specific wavelengths could alternatively be used to harden the material. In another preferred embodiment of the method according to the invention, a silver paste is used to form the electrically conductive plug, and the method comprises performing thermal annealing on the electrically conductive plug. For example, once the cover lid is in place, the paste can simply be heated locally using a suitable laser. The molten metal will then spread to wet a corresponding region on the surface of the cover lid.

In a further preferred embodiment of the invention, the first electrode layer comprises a number of additional raised contact points or 'studs' preferably dimensioned to extend through the active layer, effectively extending the surface of the first electrode, and the step of removing a region of the second electrode layer and a corresponding region of the active layer to expose an access area of the first electrode layer comprises at least partially exposing at least one of the contact points by removing a region of the second electrode and an underlying region of the active layer.

In both of the techniques described above, any suitable technique can be applied to remove the region of the second electrode and the underlying active layer region to expose the access area. For example, these regions could be removed using sticky tape or by an appropriate mechanical removal technique. Alternatively, the region of the active layer can be removed by thermal release after removing the region of the second electrode. In a particularly preferred embodiment of the invention, however, the step of exposing an access area comprises directing a laser light beam at the region of the second electrode layer and the corresponding underlying region of the active layer to ablate material in those regions. This technique is particularly preferred, since a very precise and rapid ablation can be achieved by using a beam of laser light.

Since the energy in a pulse of laser light is distributed over the pulse duration, the depth of material that can be ablated will depend on the laser used, and the laser process parameters. For relatively low-power pulses, a region of the second electrode can be laser- ablated in a first step, and then the region of the active layer can be ablated in a second step. In a preferred embodiment of the invention, however, the laser light beam comprises optical pulses with a duration of up to 10 ps, so that energy density is sufficiently high to ablate both layers in one step. These pulses may by applied to ablate the two layers above the access area, while shorter pulses are used to ablate a 'ring' of the second electrode around the hole in the active layer, thus forming a kind of active layer 'terrace' or 'platform' around the access area. This 'terrace' increases the physical separation between the electrical plug (formed in a later step as described above) and the second electrode. If picoseconds lasers are used, both metal and active layer materials are transferred into the gas phase and can easily be removed or extracted by suction. If lasers with longer pulse duration are used, particles freed form the second electrode metal layer can also be removed by suction. In case of the organic material in the active layer, the addition of oxygen to the atmosphere during ablation allows the organic material to be converted to gaseous compounds which can also easily be removed by suction.

The laser ablation technique allows the creation of extremely small cavities through the OLED device layers. Using currently available laser technology, the minimum size of the vias is only governed by the minimum laser spot size. Spot sizes of 10 μιη to 20 μιη can be achieved. Cavities (and the enclosed vias) are essentially invisible to the naked eye, so that an OLED device with vias of these dimensions essentially presents a

homogenous emitting area. Even though the vias themselves may not be transparent, the small feature size of the vias is sufficient to ensure that they will not be perceived as a distortion in the overall OLED device. Regardless of whether conductive plugs are inserted into one or more cavities, or whether the first electrode is treated to comprise one or more raised studs, in each case the 'top' surface of such an element can be regarded as an electrical extension of the first electrode.

Since the organic material used in the active layer must be protected from moisture, the method according to the invention also preferably includes the step of applying a hermetic seal - i.e. completely watertight - to enclose at least the active layer. The seal can be in the form of a cover lid of metal, glass, coated plastic, or any suitable material. Usually, a border along the outer edges of the substrate is left free, i.e. is not coated with any electrode or organic material. A glue can then be applied to this edge when the cover lid is applied to seal in the layers. This border, outside the emitting area of the OLED, can easily be kept free of unwanted deposits, for example by protecting it with a straightforward outline mask when the electrode and organic layers are applied, by using sticky tape to remove the unwanted material, or any other appropriate technique.

The OLED device can be manufactured using the usual materials, which will be known to the skilled person. For example, the carrier can comprise a glass substrate; the first electrode can act as anode and be made of a transparent conducting oxide such as aluminium doped zinc oxide (ZnO) or indium tin oxide (ITO) or a highly ductile transparent conductive polymer such as Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) PEDOT:PSS; the second electrode can act as cathode and be made of any suitable conductor such as aluminium; and the active layer can comprise one or more organic semiconductor materials chosen for their light-emitting properties. Such an OLED device will emit only though the anode and glass carrier. Alternatively, the OLED device could be realized to be essentially transparent, for example by using a transparent material for the cathode and using a transparent cover lid.

The OLED device according to the invention comprises at least one opening in the second electrode to an access area on the first electrode, so that the first electrode can be electrically accessed from above, and wherein the diameter of such an opening comprises at most 300 μιη, more preferably at most 200 μιη, and most preferably at most 100 um.

Preferably, the OLED device according the invention comprises an array of such openings to access areas on the first electrode, wherein neighbouring openings for the vias are spatially separated by a distance of, for example, 5 mm measured between the centres of the openings. The distance between neighbouring openings (and therefore also the distance between neighbouring vias) may depend on several parameters, for example on the dimensions and therefore the current-carrying capacity of the vias, on the brightness requirements of the OLED device, etc. Since each opening can contain a via, the OLED device according to the invention preferably comprises a corresponding array of vias to access areas of the first electrode. By creating small vias, an unwanted contact between these and the second electrode can be avoided. Therefore, in a particularly preferred embodiment of the invention, the diameter of a via comprises at most 30 um, more preferably at most 20 μιη, and most preferably at most 10 um.

In an OLED device according to the invention, the removed region of the second electrode is preferably larger than the removed region of the active layer, and the region of the active layer that is to be removed lies within the region of the second electrode that will be removed, such that, after creation of the opening, the access area on the first electrode is physically separate from, and therefore electrically isolated from, the second electrode.

In a further preferred embodiment of the invention of the OELD device according to the invention, the first electrode layer is augmented by at least one raised element, preferably an array of raised elements, such as studs or pins realized so that they will extend into the active layer applied in a subsequent step, and wherein an access area, after removal of the second electrode region and active layer region, comprises a surface of a raised element exposed in the opening.

In one preferred embodiment of the OLED device according to the invention, the opening comprises a cavity, extending through the second electrode and through the active layer to the access area on the first electrode, realized to contain or hold an electrically conductive via for electrically accessing the first electrode through the opening in the second electrode.

The second electrode, on the surface of OLED device, can easily be connected to a voltage source. To carry current to the vias and therefore to the first electrode, an electrical connection is required which does not come into contact with the second electrode. Therefore, in a particularly preferred embodiment of the invention, the cover lid comprises an electrically conductive material. To prevent unwanted contact between the cover lid and the cathode, a layer of free space can be left between the cathode and the cover lid. Alternatively, an isolating layer can be placed between the cover lid and the cathode, with appropriate openings to expose the cover lid inside surface in those regions that coincide with the vias.

In an alternative embodiment of the invention, the cover lid comprises at least one raised electrically conductive via positioned according to a corresponding opening in the second electrode and realized to extend through the cavity to the access area to electrically access the first electrode when the cover lid is put into place, so that an electrical connection can be made between the cover lid (and therefore a voltage supply connected to these) and the first electrode. Preferably, the cover lid comprises an array of raised electrically conductive vias of small dimensions corresponding to an array of cavities dimensioned accordingly in the OLED device layers, giving access to the first electrode on the carrier of the device.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the present invention will become apparent from the following detailed descriptions considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention.

Fig. 1 shows the steps in a first prior art method of manufacturing an OLED device;

Fig. 2 shows a prior art OLED device;

Fig. 3 shows the steps in a second prior art method of manufacturing an OLED device; Fig. 4 shows the steps of manufacturing an OLED device using a first method according to the invention;

Fig. 5 shows an elevation view into an access area on a partially completed OLED device of Fig. 4;

Fig. 6 shows an electrically conductive plug in a cavity of the partially completed OLED device of Fig. 4;

Fig. 7 shows a cover lid stud in a cavity of the partially completed OLED device of Fig. 4;

Fig. 8 shows a side view of the partially completed OLED device of Fig. 7 with a cover lid raised to show a number of contact studs;

Fig. 9 shows the steps of manufacturing an OLED device using a second method according to the invention;

Fig. 10 shows an embodiment of an OLED device according to the invention. In the diagrams, like numbers refer to like objects throughout. Elements of the diagrams are not necessarily drawn to scale, particularly the OLED device layer thicknesses.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. 1 shows the steps in a prior art method of manufacturing an OLED device. Here, a carrier 2, for example glass or plastic, is coated with a two separate areas 20, 21 of a transparent conducting material, for example a layer of doped zinc oxide (ZnO), indium tin oxide (ITO), PEDOT:PSS, or any other suitable conductive material in a first step (I). The areas 20, 21 must be isolated from each other since one of the areas will later be the cathode and the other area will be the anode. Assuming this device will be a bottom-emitting OLED, the carrier forms the front of the device and the cathode will form a top surface.

Therefore, it is assumed that the anode is the larger area 20. Contact areas 20', 21 ' are applied to the electrode areas 20, 21. Since the contact areas 20', 2Γ must remain uncoated by organic material, these regions must be masked during the subsequent deposition step. To this end, a shadow mask Mi is put into place as shown in the next step (II). Assuming the shadow mask Mi is precisely held in place, only the desired areas will be coated with the active layer material 22, as shown in stage (III) and indicated by the dashed lines. In a next stage (IV), another shadow mask M₂ is put in place before the cathode 23 is applied in stage (V). The second shadow mask M₂ is required to keep the anode contact area 20' electrically isolated from the cathode 23. For the sake of simplicity, only those relevant parts of the masks that block the vapour are indicated here. After the layers 23 have been applied, the anode 20 can be accessed from contact area 20', and the cathode 23 is simply the top-most surface, and anode 20 and cathode 23 are electrically separated. In this and the following diagram, a cross-section of only a small part of such an OLED construction is shown, and it is to be understood that the carrier, electrode layers etc. can extend by an appropriate amount in each case.

To complete the device, it is encapsulated, for example by gluing a glass lid into place. A finished prior art device 20 is shown in Fig. 2, which illustrates the cathode contact area 2Γ, the anode contact area 20', the emitting area 23, and a sealing rim 24. The contact areas are necessary because of the low current-carrying capability of this type of structure. Even with such contact areas 20', 2 , the maximum device size is limited to at most 5 cm by 5 cm if no additional metal shunt lines are applied onto the anode coating 20. For various purposes, large emitting areas are desired which can be only be achieved by tiling several of these individual encapsulated devices. However, because of the relatively large surface area of the contact areas 20', 2 , such prior art OLEDs 20 cannot be tiled in a seamless manner, owing to the relatively large non-emitting bands between the emitting areas.

Another prior art method of manufacture is illustrated with the aid of Fig. 3, in which studs are used to electrically access the bottom electrode from the surface of the device in order to obtain a larger emitting area. Here, a carrier 2 is coated with a first electrode layer 40 or anode 40 in stage (I). A raised stud 41 is applied to the anode 40 in stage (II). Then, a shadow mask M₃ is put into place in stage (III) to 'protect' the areas within the dashed lines before depositing the active layer 42 in stage (IV). The second electrode 43 is then applied onto the active layer 42 in stage (V), again avoiding the raised contact 41 of the first electrode layer 40. In this prior art method, to isolate the contact 41 of the cathode 40 from the anode 43, an insulating ring 45 is introduced between the stud 41 and the active layer 42 and anode layer 43 in stage (VI). While a larger overall emitting area can be obtained in this manner, the use of the complex shadow mask M₃ and the alignment tolerances between the mask and the studs makes the manufacturing of such devices impractical. In practice, therefore, such devices are not suitable for applications such as decorative lighting in which a homogenous emitting area is required.

Fig. 4 shows the steps of manufacturing an OLED device using the first method according to the invention. Here, a carrier 2 which can be glass or plastic is successively coated with planar layers - a first electrode 3 in stage (I), an active layer 4 in stage (II), and a second electrode 5 in stage (III). No shadow masks are required, since there are no critical areas to avoid, making the deposition easy and fast. In a next step (IV), a beam of laser light L is directed at a point on the 'top layer' to ablate a region 50 of the second electrode 5 and an underlying region 40 of the active area 4, so that an access area 30 is exposed on the first electrode 3. Free space now occupies the removed regions 40, 50. The access area 30 is effectively the bottom of a pit or cavity 31, as shown in Fig. 5, which gives a view 'into' such a cavity 31. This diagram shows the access area 30 surrounded by a rim or terrace of the active area 4, which is in turn surrounded by the top layer or second electrode 5. The dimensions of such a cavity 31 can be exceedingly small, and will to a large extent depend on the laser used. Good results in metal and organic ablation can be achieved using a frequency-doubled Nd:YAG laser with a pulse length in the tens of microseconds and a frequency of 532nm. With such a set-up, the metal region 50 is first ablated before proceeding to ablate the organic region 40. Even better results can be obtained with a shorter pulse length in the region of tens of picoseconds, since the increased pulse energy of the laser beam L makes it possible to remove both metal region 50 and organic region 40 in a single process step.

The cavity 31 can be used in a number of further techniques to provide electrical access to the first electrode 3. In one approach according to the invention, shown in Fig. 6, an electrically conductive viscous liquid 6 is dropped in a subsequent stage V into the cavity 31 , where it spreads to fill the hole in the active layer 4. Such a liquid 6 may be a silver paste or conductive glue, chosen for its conductive and viscous properties. The material deposited in this way into the cavity 31 hardens of its own accord, or can be thermally annealed as required, to give contact point 66 or via 66 in stage VI by means of which the first electrode 3 can be electrically accessed through the top layer 5. The contact point 66, extending the first electrode 3, is isolated from the second electrode 5 by free space 51 surrounding the contact point 66 in an annular manner. Although only one such contact point 66 is shown in the diagram, the skilled person will appreciate that any number of such small vias can be made, depending on the application for which the device is to be used.

In another approach, shown in Fig. 7, instead of building up a contact point with a viscous conductive liquid as described above, an electrically conductive stud 77 is lowered into the cavity 31 instead in stage V. Such a stud 77 can be part of a cover lid 7 which is applied to encapsulate the finished device. The cover lid 7 can be of metal, so that the anode can be supplied with a current by means of the cover lid 7 and the studs 77. To ensure that the cathode 5 is not touched by the cover lid 7, sufficient free space can be left between these, or the cover lid 7 can be given an insulating coating 71 as shown here. Again, the cover lid can have any number of such tiny studs 77, arranged to coincide with the cavities 31. The cover lid 7 and its studs 77 can be made of any suitable material. For example, the studs 77 and the cover lid 7 can be made of a metal such as aluminium. In order to guarantee good mechanical and electrical contact, the studs should preferably be made from conductive glue or metal paste which, by annealing or hardening, form reliable contacts between the first electrode and the cover lid. Here also, the removed region of the second electrode 5 is so large to leave a ring of free space 51 around the stud 77, thus isolating the stud 77 (and therefore also the first electrode 3) from the second electrode 5. To supply the cathode 5 with current, another region of the cover lid 7 can have a suitable opening through which the cathode 5 can be contacted electrically. Such means of electrically contacting the cathode 5 through the cover lid 7 are known and need not be explained in any detail here.

Fig. 8 shows a side view - greatly simplified and exaggerated - of a partially completed OLED device with such a cover lid 7. Here, the cover lid 7 is raised at one corner to show a number of studs 77, each arranged to coincide with a number of cavities 31. When the cover lid 7 is put into place, the contact pins 77 or studs 77 fit into the cavities 31 and make contact with the first electrode 3. Of course, the cover lid 7 may be of a rigid material, and it is only shown to be 'bent back' in the diagram for the purposes of illustration.

Fig. 9 shows the steps of manufacturing an OLED device using a second method according to the invention. Here, the first electrode 3 is applied in a continuous planar layer in stage (I), and a raised contact 33 is applied to the electrode 3 in stage (II), effectively extending the first electrode 3. In subsequent stages (III) and (IV), an active organic layer 4 and a second electrode 5 are applied. Here, no shadow masks are used, so that the active layer 4 and the second electrode 5 also cover the stud 33. In a laser ablation step (V), a region 50 of the second electrode 5 and a region 40 of the active layer 4, which regions 40, 50 coated the top of the stud 33, are removed to expose an access area 30 of the first electrode 3 on the stud 33, as shown in the finished stage (VI). Since the active area 4 also coated the sides of the stud 33, and this 'coating' was not removed in the ablation step (V), the stud 33 is effectively electrically isolated from the second electrode layer 5, so that an additional insulating ring as described in Fig. 3 for the prior art technique is not required here.

Fig. 10 shows a plan view of an embodiment of an OLED device 1 according to the invention, viewed through the transparent carrier in this case. The entire emitting area 10 was initially built up using homogenous layers as described in the above, leaving a surrounding edge 91 free, and openings were then created to accommodate a plurality of vias 33, 66, 77. Regardless of the technique used to create the electrical vias 33, 66, 77, these can be made exceedingly small and can be arranged in an even distribution throughout, so that a homogenous brightness can be achieved by the device, and a greater degree of brightness also, since the current-carrying capacity of the electrodes is greatly increased by the conductive vias 33, 66, 77. Here, the vias 33, 66, 77 are shown as circular regions in the emitting area 10, but in reality the vias 33, 66, 77, being only in the order of tens of μιη in diameter, would not be visible to the naked eye. Also, the device size can be much larger than the largest realistic prior art OLED device size. In effect, the dimensions of the OLED device according to the invention are only limited by the manufacturing equipment used to apply the layers and to complete the encapsulation. Furthermore, since the lateral contact areas known from the prior art are not required here, the surrounding edges 91 of the device can be realized to be very narrow (in the order of 100 μιη), allowing an essentially seamless tiling of many such devices.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art from a study of the drawings, the disclosure, and the appended claims. For the sake of clarity, it is to be understood that the use of "a" or "an" throughout this application does not exclude a plurality, and "comprising" does not exclude other steps or elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A method of manufacturing an OLED device (1), which method comprises

- applying a first electrode (3) onto a carrier (2);

- applying an active layer (4) onto the first electrode (3) such that the active layer (4) essentially uniformly covers the first electrode (3);

- applying a second electrode (5) to the active layer (4) such that the second electrode (5) essentially uniformly covers the active layer (4); and

- exposing an access area (30) of the first electrode (3) in an opening (31), which opening (31) is made by removing a region (50) of the second electrode (5) and a corresponding region (40) of the active layer (4) such that the first electrode (3) is electrically accessible through the opening (45).

2. A method according to claim 1, wherein the step of exposing the access area (30) comprises creating a cavity (31) extending between the second electrode (5) and the first electrode (3).

3. A method according to claim 1 or claim 2, which method comprises the step of placing an electrically conductive plug (6) into the cavity (31) and onto the access area (30) to electrically extend the first electrode (3) to the level of the second electrode (5).

4. A method according to any of the preceding claims, comprising the step of performing thermal annealing on the electrically conductive plug (6) to give an electrically conductive via (66) to the first electrode (3).

5. A method according to any of the preceding claims, wherein the first electrode layer (3) comprises an additional raised element (33), and the step of removing a region (50) of the second electrode (5) and a corresponding region (40) of the active layer (4) to expose an access area (30) of the first electrode (3) comprises at least partially exposing a surface of the raised element (33) to give an electrically conductive via (66) to the first electrode (3).

6. A method according to any of the preceding claims, wherein the step of exposing an access area (30) comprises directing a laser light beam (L) at the region (50) of the second electrode (5) and the corresponding region (40) of the active layer (4) to ablate material in those regions (40, 50).

7. A method according to any of the preceding claims, wherein the laser light beam (L) comprises optical pulses with a duration of up to 10 ps.

8. A method according to any of the preceding claims, comprising the step of applying a hermetic seal (8) to enclose at least the active layer (4).

9. An OLED device (1) comprising

- a first electrode (3) applied onto a carrier (2);

- an active layer (4) applied onto the first electrode (3) such that the active layer (4) initially entirely covers the first electrode (3);

- a second electrode (5) applied onto the active layer (4) such that the active layer (5) initially entirely covers the second electrode (4); and

- an access area (30) for electrical access to the first electrode (3) within an opening in the second electrode (5), which opening comprises a removed region (50) of the second electrode (5) and a corresponding removed region (40) of the active layer (4);

characterized in that the first electrode (3) is electrically isolated from the second electrode (5) only by the active layer (4) and/or free space (51).

10. An OLED device (1) according to claim 9, wherein the removed region (50) of the second electrode (5) is larger than the removed region (40) of the active layer (4) such that the access area (30) on the first electrode (3) is electrically isolated from the second electrode (5).

11. An OLED device (1) according to claim 9 or claim 10, wherein the first electrode (3) comprises at least one raised element (33), preferably an array of raised elements (33), realized to extend into the active layer (4) applied onto the first electrode (3), and wherein an access area (30) comprises a surface of a raised element (33) exposed in the opening.

12. An OLED device (1) according to any of claims 9 to 11, wherein the opening comprises a cavity (31) extending through the second electrode (5) and through the active layer (4) to the access area (30) on the first electrode (3), which cavity (31) is realized to contain an electrically conductive via (33, 77) for electrically accessing the first electrode (3) through the opening (31) in the second electrode (5).

13. An OLED device (1) according to any of claims 9 to 12, comprising a cover lid (7) applied onto the second electrode (5), which cover lid (7) comprises a raised electrically conductive via (77) positioned according to a corresponding cavity (31) and realized to extend through the cavity (31) to the access area (30) to electrically access the first electrode (3).

14. An OLED device (1) according to any of claims 9 to 13, wherein the OLED device (1) comprises an array of vias (33, 66, 77) to access areas (30) of the first electrode (3), and wherein the diameter of a via (33, 66, 77) comprises at most 30 μιη, more preferably at most 20 μιη, and most preferably at most 10 μιη.