WO2011007297A2

WO2011007297A2 - Method for producing structured conductive layers

Info

Publication number: WO2011007297A2
Application number: PCT/IB2010/053121
Authority: WO
Inventors: Christoph Rickers; Holger Schwab; Soeren Hartmann
Original assignee: Koninklijke Philips Electronics N.V.; Philips Intellectual Property & Standards Gmbh
Priority date: 2009-07-16
Filing date: 2010-07-08
Publication date: 2011-01-20
Also published as: WO2011007297A3

Abstract

The invention relates to the production of a structured layer (2) having electrically conductive regions (2a), particularly the production of a structured transparent OLED electrode. The method starts with producing an initial layer (2') of an electrically conductive material, which is then rendered electrically insulating outside the intended conductive regions (2a). Thus the shape of the initial layer with for example a smooth surface (S) is preserved. Rendering the conductive material locally insulating can be achieved by irradiating and/or heating it locally (3 a) to change its chemical composition or crystalline structure. Moreover, dopants may locally (3b) be added by diffusion processes and/or by plasma printing.

Description

METHOD FOR PRODUCING STRUCTURED CONDUCTIVE LAYERS

FIELD OF THE INVENTION

The invention relates to a method for the production of a structured layer having electrically conductive regions, particularly of a layer that serves as a structured OLED electrode. Moreover, it relates to an OLED device comprising such a structured layer.

BACKGROUND OF THE INVENTION

The US 2006/0061266 Al discloses an organic light emitting display with a plurality of pixel electrodes on a transparent substrate. The edges of the pixel electrodes are covered with an insulating material to avoid breakpoints.

SUMMARY OF THE INVENTION

Based on this background it was an object of the present invention to provide alternative means for generating a structured electrically conductive layer, particularly a layer that may be used as an electrode in OLED devices.

This object is achieved by a method according to claim 1 and an OLED device according to claim 2. Preferred embodiments are disclosed the dependent claims.

According to its first aspect, the invention relates to a method for the production of a structured layer having at least one electrically conductive region. In this context, the "structuring" of a layer shall generally be defined as any (intentional) deviation from a homogenous spatial distribution of some characteristic property, here of the electrical conductivity. The layer typically has the form of a planar or curved sheet with a height that is comparatively small with respect to its width and length. The structuring of the layer may in general occur with respect to any of its three dimensions; in many cases, the structuring occurs however with respect to the layer's large dimensions (width and length), while the layer is substantially uniform in the direction of its (small) height. The method of the invention comprises the following steps: Producing an "initial layer" of an electrically conductive material. This initial layer will have substantially the same shape and size as the desired structured layer, but not yet a structure of electrical conductivity.

Rendering the conductive material of the aforementioned initial layer electrically insulating (somewhere or everywhere) outside the at least one intended conductive region. In this context, a material with a specific resistance below about 6 x 10^~4 Ωcm is typically considered as being "conducting". The resistance of isolating regions (measured between two conductive zones that are separated by the isolating regions) should typically be about 1 MΩ or higher.

Possible approaches to generate a structure of conductive regions comprise the selective deposition of conductive material, or the removal of excessive conductive material from an initially homogeneous layer (e.g. by ablation or etching). When further processing of the structure is desired, the aforementioned approaches may lead to problems due to sharp edges of conductive material and/or due to debris remaining after the removal of conductive material. The method of the invention avoids such problems because it leaves the shape of the initial layer intact and only changes its electrical properties as desired.

The invention further relates to an Organic Light Emitting Diode (OLED) device which comprises as an electrode at least one structured layer made from an initial layer of an electrically conductive material that has locally been rendered electrically insulating. With other words, said electrode of the OLED device has been produced by a method of the kind described above.

As usual, the OLED device comprises by definition a second electrode and an organic electroluminescent layer that is disposed between the two electrodes. The structured first electrode has the advantage that it has the intact shape of the initial layer and can therefore readily serve as a base for the deposition of other OLED components (electroluminescent layer, second electrode).

In the following, various preferred embodiments of the invention will be described that relate to both the method and the OLED device described above.

Thus the surface of the structured layer my preferably be smooth despite the fact that the layer may have an intricate internal structure of conductive and insulating zones. As already mentioned, the smooth surface of the layer provides a favorable mechanical platform for further components. Moreover, it avoids the generation of high electrical field strengths that could occur at sharp edges of conductive material.

The conductive material of the initial layer and the final structured layer may preferably be transparent in a given range of the electromagnetic spectrum, for example the range of visible light. This makes the structured layer suited for optical applications, for example as a transparent electrode layer in an OLED device.

A transparent conductive material may particularly be constituted by transparent conductive oxides (TCO) or other transparent conductive materials like carbon nano tubes, grapheme, PEDOT:PSS (Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)), conductive coatings etc. Moreover, typical examples of conductive materials comprise indium tin oxide (ITO), doped SnO, doped ZnO, WO3,

There are several possibilities to render a conductive material locally insulating, wherein the applicability of these approaches depends on the particular conductive material that constitutes the initial layer. According to a first basic approach, the conductive material of the initial layer is rendered electrically insulating by a local modification of its chemical composition and/or by a local modification of its crystalline structure. Modification of the chemical composition comprises by definition a (local) change in the relative concentrations of the chemical elements and/or a (local) change of chemical bindings between atoms that constitute the material. Modifications of the chemical composition may for example be achieved by internally rearranging bindings between available atoms, or by adding atoms to or removing atoms from the initial layer. Modifications of the crystalline structure affect the spatial arrangement of atoms, which may take place with or without changing the chemical composition.

A particular modification of the chemical composition of the initial layer is the addition, removal, and/or the change of oxygen bindings. Due to various effects, oxygen is a crucial component that determines the electrical properties of a material. Moreover, oxygen can readily be added to a material.

According to a preferred embodiment, the conductive material is rendered electrically insulating by a local diffusion process which moves atoms or molecules into or out of a region of the conductive material. Such a diffusion process may particularly comprise the addition of an external dopant to the conductive material of the initial layer. The dopant will affect the local chemical composition of the material, which usually also changes the local crystalline structure.

According to another optional approach, the conductive material may be rendered electrically insulating by irradiating and/or by heating it locally.

Electromagnetic radiation and heating supply energy with which the local characteristics of the conductive material can be changed, for example by modifying its chemical composition and/or crystalline structure. Irradiation has the advantage that it can readily be controlled and allows a precise spatial application of the desired changes. The absorption of electromagnetic radiation may directly change the chemical composition (e.g. by breaking bindings or by triggering diffusion processes) or crystalline structure; in many cases, electromagnetic radiation will however first lead to a local heating which then effects the desired chemical and/or crystalline changes.

The mentioned local irradiation and/or heating may preferably be achieved with laser light which allows to apply high intensities to spatially well defined areas.

During local irradiation and/or heating, the initial layer may at least partially be brought into contact with specific materials, for example by covering it with a removable coating or paste or by exposing it to a specific atmosphere. Thus a possible exchange of material with the surroundings can be controlled.

The aforementioned specific atmosphere may for example comprise a protective gas (e.g. oxygen, nitrogen, inert gases as Ar) that does not react with or diffuse into the initial layer. In this way the stoichiometry of the initial layer can be protected. In another embodiment, the specific atmosphere may comprise a dopant, for example oxygen or oxygen compounds. In this case it is intended that new material (the dopant) is introduced into the irradiated or heated zone of the initial layer.

According to still another approach for rendering the conductive material electrically insulating, the conductive material is locally contacted with a plasma. A plasma is a material in a gaseous state in which the atoms are (at least partially) ionized and which comprises free electrons. A plasma is therefore highly reactive and will hence readily enter the conductive material of the initial layer when it comes into contact with it.

It was already mentioned that the initial layer typically has the form of a sheet with a height that is comparatively small with respect to its width and length. According to a preferred embodiment of the invention, the structuring of the layer may (at least particularly) occur with respect to its height. Hence the conductive material of the initial layer may be rendered electrically insulating in a region that does not extend through the complete thickness of the initial layer. As a result, there will remain conductive material below, above, or around said insulating region which supports the current distribution and hence leads to more homogenous devices, while current flow in a direction transverse to the layer is (locally) inhibited.

According to another embodiment of the invention, the region which is rendered electrically insulating encircles completely a region of conductive material, wherein the encirclement is determined with respect to a given plane, e.g. a surface of the structured layer. In combination with the aforementioned embodiment, OLED devices can be designed in this way that comprise light emitting regions which are completely encircled by non-light emitting regions, wherein these encircled regions are supplied with current through conductive material bridging the insulating ring.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. These

embodiments will be described by way of example with the help of the accompanying drawings in which:

Fig. 1-3 schematically illustrate consecutive steps of the fabrication of an

OLED device with a method according to the present invention;

Fig. 4 shows an alternative OLED device with an insulating region that does not reach through the complete layer thickness;

Fig. 5 shows a bottom view of the OLED device of Figure 4.

Like reference numbers in the Figures refer to identical or similar components. It should be noted that the drawings are not to scale. DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will in the following be described with respect to the production of an OLED device. The method is however not restricted to this application but also useful in other scenarios in which layers with a structured conductivity are applied.

During the fabrication of Organic Light Emitting Diode (OLED) substrates, the transparent electrode material - usually that of the anode - often has to be structured to create several separate anode areas. For a cheap fabrication of OLED substrates, it is therefore desirable to have a simple structuring process of the anode material.

The aforementioned structuring may be realized with conventional lithography, or by using a laser to ablate transparent conductive oxide (TCO) material. For OLED substrates, different thickness regimes of the device impose however particular constraints to such processes that are difficult to comply with. Moreover, ablating TCO material creates sharp edges that lead to an increase of the electrical field strength in this area. This may in turn result in locally increased stress for the organic electroluminescent material and a tendency to short the product. Moreover, sharp edges are conventionally covered by some insulating materials, which provide elements that may diffuse into the light emitting material, preventing it from creating light. Besides generation of sharp edges and the accompanying drawbacks, the ablation also creates particle debris. Reducing such debris requires dedicated exhaust systems and subsequent cleaning processes. Nevertheless, it will be impossible to suppress debris completely. Even particles smaller than the thickness of the OLED, however, are known to be potential weaknesses of the devices. This holds especially for the small molecule OLEDs because of the vacuum deposition process and associated shadowing effects.

In view of this situation, it is proposed here to render the conductive material (e.g. a TCO) locally electrically isolating. In this way it is no longer necessary to ablate the material, and no debris will be produced and no sharp edges will be created. Thus, the known drawbacks of laser ablation will be avoided. In the accompanying Figures, this general concept is illustrated for an exemplary production of an OLED device.

Figure 1 shows a first step of the fabrication procedure, in which a homogeneous initial layer 2' of a conductive material is provided on a transparent substrate 1, for example on a glass plate. The conductive material of the initial layer 2' may be a TCO like indium tin oxide (ITO). A typical thickness of the layer 2' ranges between a few 10 nm and a few μm. Typical values for ITO are 80-250 nm but will vary for different materials due to different specific resistivities and absorption properties.

Figure 2 illustrates the step of locally rendering the initial layer 2' electrically insulating. For the purpose of illustration, two different processes are shown in the same picture, though in practice only one kind of process will usually be applied for a single workpiece.

On the left hand side of Figure 2, the initial layer is irradiated from above with laser light 10a. By proper focusing, the light is restricted to a desired region 3 a. The laser light 10a locally heats up the TCO material and induces a change of the material properties. Continuously operating CW-lasers in the non total absorbing wavelength regime for the different materials seem to be especially appropriate for this approach.

The changes that are induced by the laser light 10a in the TCO material may comprise a modification of crystalline structures, stoichiometry, or both depending on the TCO material and the appropriate mechanism for electrical conductivity.

In ITO the electrical conductivity results from a given crystal structure, a doping of the semi-conducting material Snθ2 with Zn atoms, and the subsequent creation of oxygen vacancies. Since the conductive crystalline structure is already stable and starting to form at about 150 ⁰C, a local heating is not a reasonable approach to modify the crystalline structure. However, "doping" the ITO with oxygen creates defects and reduces the density of vacancies which terminates (at least reduces) the electrical conductivity.

The corresponding procedure is shown on the right hand side of Figure 2, where laser light 10b locally heats a region 3b of the initial layer. In the space above the initial layer, a gaseous atmosphere with a dopant D is provided, for example with oxygen O2. Heating of the region 3b will then allow this dopant D to diffuse into the ITO material, where it can change the chemical composition and render the region 3b electrically insulating.

Besides the termination of electrical conductivity, the described approaches often have no other effects. In particular, the optical properties of ITO remain unchanged, resulting in even more freedom in the product design of OLED devices. Hence it may be of advantage that it is possible to create separated individual anode areas not being visible in the off-state and also hardly being visible in the on-state of the OLED device. Nevertheless, the invention is not limited to applications that need invisible modifications of the electrical properties, but can also be applied for materials in which a change of conductivity is accompanied by a change of optical properties.

As a result of the processes shown in Figure 2, the initial layer 2' is transformed into a structured layer 2 that is composed of electrically conductive regions 2a (consisting of the unchanged original conductive material, e.g. ITO) and electrically insulating regions 3 a, 3b. The shape of the layer 2 is however the same as that of the initial layer 2', i.e. there is particularly a smooth surface S onto which other components can be built, and there is no debris of a material removal that might affect further processing.

While the example shows a structuring in x- and y-direction, also a structuring in z-direction (height of initial layer 2') would be possible, too (cf. Figs.4, 5).

Figure 3 shows schematically the final OLED device 100 that is achieved after an organic electroluminescent layer 3 and a second (transparent or non-transparent) electrode layer 4 have been deposited on the structured electrode layer 2. When an appropriate voltage is applied between the electrode layers 2 and 4, light is generated in the electroluminescent layer 3 in the zones above the conductive regions 2a, which can leave the OLED device 100 through the transparent structured anode layer 2 and the transparent substrate 1.

A variety of modifications of the above procedures are possible. Thus various doped Znθ2:x materials are for example also potential TCO materials that can be used as OLED anode. In this case the situation is a little bit different due to the different mechanisms of conductivity, and hence also the transformation process has to be different. In Znθ₂:Al, (AZO) the aluminum is simply used as a dopant and thus getting it oxidized helps to prevent conductivity. Such an oxidation may be feasible by just changing the oxygen bonds within the material, i.e. no externally fed diffusion is needed. For example: loss of conductivity for AZO is known to happen when tempering in oxygen at higher temperatures. As an example, ZnO: Al exhibits a sheet resistance of 27 Ohm per square at room temperature without any temperature treatment. Tempering the AZO layer at 500⁰C, the sheet resistance increase to 7912 Ohm square after 2h treatment and O.lMOhm square after 4h treatment, which is 4 orders of magnitude larger compared to the initial sheet resistance. A similar trend is achieved with Ti layers tempered in oxygen atmosheres. For other TCO materials the situation might be different and require different approaches for organic transparent and conductive materials and for example carbon nano tube layers it may even be different to that (for the latter the laser has to distort the tubes for example).

For the doping procedures described above, diffusion processes can be used. To realize this only locally on a substrate, different processes may be applied. One approach may comprise to locally heat the substrate being located within a gas that basically consists of the doping material - or the dopant is applied as a paste or thin film. As shown in Figure 2 for the case of ITO, a local laser induced heating within an oxygen rich atmosphere will be appropriate to help the oxygen diffuse into the ITO.

Realization of local diffusion processes might, however, also be realized using plasma printing. Plasma printing is a special setup of an atmospheric plasma process (for example an atmospheric pressure chemical vapor deposition, APCVD) that is laterally only locally applied using the TCO as one electrode. Here an oxygen plasma can be ignited/realized in a defined local region which then results in a diffusion of oxygen (or other reactive gas components) into the ITO. This process can also be used to induce other reactions with the film material (reduction for example) and can even be used to deposit coatings (potentially insulating films also).

An advantage of the laser induced approaches is the small size of feasible structures. However, all the presented approaches lead to a passivation without debris creation and sharp edges.

Figure 4 and 5 illustrate an OLED device 200 according to another embodiment of the invention. Basically, the layered composition of the OLED device 200 is similar to that of the previous embodiment, i.e. the device comprises a sequence of a transparent substrate 1 , a structured layer 2 serving as an electrode, an organic electroluminescent layer 3, and a second electrode layer 4. A difference is, however, that the insulating region 3 a in the structured layer 2 does not extend in z-direction through the complete thickness of the structured layer 2. In the shown embodiment, the insulating region 3a is particularly located at the surface of the structured layer 2 that contacts the organic electroluminescent layer 3.

As a result of the described design, a bridge 2c of conductive material remains below the insulating region 3 a, which electrically connects the outer

(completely) conductive region 2a with an inner (completely) conductive region 2b. Nevertheless, charge transport in z-direction is inhibited by the insulating region 3 a, preventing the generation of light in zones of the electroluminescent layer 3a above the insulating region 3 a.

Figure 5 shows a bottom view onto the transparent layer 1 of the OLED device 200 of Figure 4. As the insulating region 3a shall form a closed circle, a ring D always remains dark, while the residual regions Ll, L2 can emit light. Such a design is possible because voltage supply to the completely encircled inner region L2 is provided by the conductive bridges 2c below the dark ring D.

In summary, the above examples illustrate a method for the fabrication of transparent and conductive substrates with locally structured electrical properties while maintaining a smooth surface (interface) preventing locally inhomogeneous electrically field strengths and particle generation from the production process. Further optional features of the method comprise:

Using a locally created diffusion process to dope the original homogeneously coated TCO material.

Using a laser to enhance/create the diffusion process.

Using a protective/dopant providing gas atmosphere.

Using a plasma printing process.

Using a protective/dopant/CVD providing/enhancing gas.

Moreover, the invention relates to a substrate for stacked OLEDs fabricated with the described procedures, said substrate having failure prevention structures in case of shorts of OLED devices.

Finally it is pointed out that in the present application the term

"comprising" does not exclude other elements or steps, that "a" or "an" does not exclude a plurality, and that a single processor or other unit may fulfill the functions of several means. The invention resides in each and every novel characteristic feature and each and every combination of characteristic features. Moreover, reference signs in the claims shall not be construed as limiting their scope.

Claims

CLAIMS:

1. A method for the production of a structured layer (2) having at least one electrically conductive region (2a, 2b, 2c), particularly of a structured OLED electrode (2), comprising the following steps:

- producing an initial layer (2') of an electrically conductive material; - rendering the conductive material of the initial layer (2') electrically insulating outside the intended conductive region (2a, 2b, 2c).

2. An OLED device (100, 200), comprising as an electrode at least one structured layer (2) made from an initial layer (2') of an electrically conductive material that has locally (3 a, 3b) been rendered electrically insulating.

3. The method according to claim 1 or the OLED device (100, 200) according to claim 2,

characterized in that the structured layer (2) has a smooth surface (S).

4. The method according to claim 1 or the OLED device (100, 200) according to claim 2,

characterized in that the conductive material is transparent.

5. The method according to claim 1 or the OLED device (100, 200) according to claim 2,

characterized in that the conductive material is selected from the group consisting of a transparent conductive oxide, indium tin oxide (ITO), organic hole injection layers like PEDOT:PSS, carbon nano tubes, grapheme, doped SnO, doped ZnO, WO₃, MoO₃, and ZnO₂: Al.

6. The method according to claim 1 or the OLED device (100, 200) according to claim 2,

characterized in that the conductive material is rendered electrically insulating by a local modification of its chemical composition and/or of its crystalline structure.

7. The method or the OLED device (100, 200) according to claim 6, characterized in that the chemical composition is changed by adding, removing, and/or changing oxygen bindings.

8. The method according to claim 1 or the OLED device (100, 200) according to claim 2,

characterized in that the conductive material is rendered electrically insulating by a local diffusion process.

9. The method according to claim 1 or the OLED device (100, 200) according to claim 2,

characterized in that the conductive material is rendered electrically insulating by locally irradiating and/or heating it.

10. The method or the OLED device (100, 200) according to claim 9, characterized in that the irradiation and/or heating is achieved with laser light (10a, 10b).

11. The method according to claim 1 or the OLED device (100, 200) according to claim 2,

characterized in that the conductive material is rendered electrically insulating by contacting the initial layer (2') at least partially with a specific material, particularly a specific atmosphere.

12. The method or the OLED device (100, 200) according to claim 11, characterized in that the specific atmosphere comprises a protective gas and/or a dopant, particularly oxygen or oxygen compounds.

13. The method according to claim 1 or the OLED device (100, 200) according to claim 2,

characterized in that the conductive material is rendered electrically insulating by contacting it locally with a plasma.

14. The method according to claim 1 or the OLED device (200) according to claim 2,

characterized in that the conductive material is rendered electrically insulating in a region (3a) that does not extend through the complete thickness of the initial layer (2').

15. The method according to claim 1 or the OLED device (200) according to claim 2,

characterized in that the region (3 a) which is rendered electrically insulating completely encircles a region (2b) of conductive material.