WO2014013425A1

WO2014013425A1 - Outcoupling device fabrication method

Info

Publication number: WO2014013425A1
Application number: PCT/IB2013/055831
Authority: WO
Inventors: Georg Friedrich Gaertner; Hans Peter Loebl; Gerardus Henricus Rietjens
Original assignee: Koninklijke Philips N.V.; Philips Deutschland Gmbh
Priority date: 2012-07-16
Filing date: 2013-07-16
Publication date: 2014-01-23

Abstract

The invention relates to an outcoupling device fabrication method for fabricating an outcoupling device for coupling light out of a light generating unit like an organic light emitting diode. A first material (8) is deposited onto a substrate (9) by using a vapor deposition technique for forming a structured surface on the substrate (9), whereupon a second material (7) is deposited onto the structured surface by using the vapor deposition technique for smoothing the structured surface, wherein the first material (8) and the second material (7) have different refractive indices. The resulting layers have in combination a relatively large density such that the likelihood of water penetration is rather low, thereby reducing the likelihood that the light generating unit is adversely affected by water such that the outcoupling of the light out of the light generating unit can be provided, without significantly reducing the operability of the light generating unit.

Description

Outcoupling Device Fabrication Method

FIELD OF THE INVENTION

The invention relates to an outcoupling device fabrication method and an outcoupling device fabrication apparatus for fabricating an outcoupling device for coupling light out of a light generating unit. The invention relates further to a light source fabrication method and a light source fabrication apparatus for fabricating a light source. The invention relates also to the outcoupling device and the light source. BACKGROUND OF THE INVENTION

WO 2010/077521 A2 discloses a multi-functional optical film for enhancing light extraction from a self-emissive light source. The multifunctional optical film comprises a flexible substrate and a structured layer of extraction elements having a first refractive index. A substantial portion of the extraction elements is in optical communication with a light emitting region of the self-emissive light source when the optical film is located against the self-emissive light source, wherein the extraction elements comprise first nanoparticles of a first size and second nanoparticles of a second size different from the first size. The multifunctional optical film further comprises a backfill layer comprising a material having a second refractive index different from the first refractive index, wherein the backfill layer forms a planarizing layer over the extraction elements. The nanoparticles can be distributed on the substrate by using a dip coating process, wherein the backfill layer is coated onto the dip coated nanoparticles. This process leads to porous layers such that water can penetrate through these layers to the light emitting region of the self-emissive light source. Since a light emitting region of a self-emissive light source is generally adversely affectable by water, the operability of the self-emissive light source can be significantly reduced.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an outcoupling device fabrication method and an outcoupling device fabrication apparatus for fabricating an outcoupling device for coupling light out of a light generating unit, which allow for coupling light out of the light generating unit, without significantly reducing the operability of the light generating unit. It is a further object of the present invention to provide a corresponding light source fabrication method and light source fabrication apparatus for fabricating a light source. It is also an object of the present invention to provide a corresponding outcoupling device and light source.

In a first aspect of the present invention an outcoupling device fabrication method for fabricating an outcoupling device for coupling light out of a light generating unit is presented, wherein the outcoupling device fabrication method comprises:

providing a substrate,

depositing a first material onto the substrate by using a vapor deposition technique for forming a structured surface on the substrate,

depositing a second material onto the structured surface by using the vapor deposition technique for smoothing the structured surface, wherein the first material and the second material have different refractive indices.

Since the first material is deposited on the substrate by using a vapor deposition technique for forming the structured surface on the substrate and since the second material is deposited onto the structured surface by using also the vapor deposition technique for smoothing the structured surface, layers are produced, which in combination are less porous, in particular, which in combination are not porous at all or which only comprise internal pores, thereby reducing the likelihood that water penetrates these layers. This in turn reduces the likelihood that the light generating unit is adversely affected by water such that the outcoupling of the light out of the light generating unit can be provided, without significantly reducing the operability of the light generating unit.

Moreover, since the same deposition technique is used for depositing the first material and the second material, the same setup can be used for both depositing steps, i.e. it is not necessary to move the substrate with the first material to another setup for depositing the second material, thereby reducing the time needed for the fabrication process. Moreover, roughening steps like sandblasting or grinding are preferentially not needed for providing the structured surface, thereby avoiding mechanical stresses which may generally be caused by these roughening steps, and no additional cleaning or drying steps are preferentially needed between the two steps of depositing the first material and the second material.

It should be noted that, although the same deposition technique is preferentially used for depositing the first material and the second material, the parameters of this deposition technique are of course different for depositing the first material and the second material. For instance, different starting materials, temperatures, pressures et cetera can be used with the deposition technique. The outcoupling device is adapted to couple the light generated by the light generating unit out of the light generating unit into the substrate and into air. In a preferred embodiment the light generating unit is an organic light emitting diode (OLED), in particular, a white light emitting OLED. Correspondingly, the outcoupling device is preferentially adapted to couple light out of an OLED. The OLED is preferentially adapted to be arranged on the second material of the outcoupling device for coupling light out of the OLED.

The refractive index difference between the first material and the second material is preferentially equal to or larger than 0.3. The refractive index of the first material is preferentially smaller than the refractive index of the second material. Moreover, the light generating unit preferentially comprises a cathode layer, an anode layer and intermediate layers between the cathode layer and the anode layer for forming an OLED, wherein the refractive index of the second material matches the average refractive index of a) the intermediate layers or b) the intermediate layers and the anode layer, thereby improving the coupling of the light generated by the OLED into the second material and, thus, the outcoupling efficiency, i.e. the efficiency of extracting the light into air. Furthermore, the refractive index of the first material preferentially matches the refractive index of the substrate. Preferentially, a first refractive index matches a second refractive index, if their absolute difference is smaller than 0.1.

The vapor deposition technique can be a chemical vapor deposition (CVD) technique or a physical vapor deposition (PVD) technique. The PVD technique can be, for instance, a sputter deposition technique.

The substrate is preferentially a glass substrate, in particular, a float glass substrate. The second material preferentially smoothes the structured surface by filling up grooves defined by the structured surface.

The second material can form an optically homogenous region above the first material, wherein this optically homogenous region may have a thickness in the outcoupling direction being larger than a coherence length of the light. For instance, if the light generating unit is an OLED, the OLED can generate light having a coherence length in the range of, for example, 3 to 10 μιη such that the thickness of the optically homogenous region in the outcoupling direction may be larger than 10 μιη.

In an embodiment, the refractive index of the second material is equal to or larger than 1.7. It is further preferred that the refractive index of the second material is equal to or larger than 1.8. In an embodiment, the refractive index of the second material is within the range of 1.7 to 2.1. For example, the refractive index of the second material can be 1.85 + 0.05. It has been found that, if the refractive index of the second material is within this range, the outcoupling efficiency can be further increased.

In an embodiment, the anode layer and optionally also the cathode layer are transparent for outcoupling light through the anode layer and optionally the cathode layer. The anode layer is, for example, an indium tin oxide (ITO) layer and the cathode layer can be a metal layer. The intermediate layers include preferentially the organic layers of the OLED.

It is preferred that the vapor deposition technique is CVD, wherein the first material is deposited at a CVD larger than one. The CVD number, which can also be abbreviated N(CVD), is a well known parameter characterizing the CVD process, in particular, whether the CVD is diffusion controlled or kinetically controlled. The CVD number will be described in more detail further below. By using CVD at a CVD number larger than one the first material is effectively inhomogeneously deposited on the surface of the substrate such that the surface becomes structured. It is further preferred that the second material is deposited at a CVD number smaller than one. This allows for an improved filling up of grooves defined by the structures formed by the first material on the surface of the substrate. The first material and the second material can therefore be deposited in the same CVD reactor, i.e. by using the same CVD setup, wherein only the source gases may be switched and the deposition conditions may be changed, especially the deposition

temperature for changing the CVD number.

The vapor deposition technique can use a first gas phase for depositing the first material and a second gas phase for depositing the second material, wherein for switching from depositing the first material to depositing the second material the vapor deposition technique may change transitionally from the first gas phase to the second gas phase for providing a continuous refractive index transition at the border between the first material and the second material. The continuous refractive index transition can suppress Fresnel reflection losses, thereby further improving the outcoupling efficiency.

In a preferred embodiment the first material comprises at least one of Si0₂, SiO_xN_y, A1₂0₃ and a fluoride. The fluoride is, for instance, MgF₂. The second material comprises preferentially at least one of SiO_xN_y, Ge0₂, Ga₂0₃, Hf0₂, Ta₂0₅, Si₃N₄, SiN_y, AION, YAG, Sc₂0₃ and Al₂0₃.

For depositing and forming Si0₂ via a gas phase reaction CVD is preferentially used with silicon containing gas and oxygen containing gas as feed gases, i.e. as gaseous starting compounds. For depositing and forming SiO_xN_y (in short SiON), additionally nitrogen containing gas is preferentially used. For instance, the SiO_xN_y material can be deposited by CVD by using SiH₄, NH₃ and 0₂ or N₂0 as gaseous starting

compounds, diluted in N₂, as described in the article "Rapid Thermal Chemical Vapour Deposition of SiO_xN_y Films" by F. Lebland et al., Applied Surface Science, volume 54, pages 125 to 129 (1992), which is herewith incorporated by reference. By admixture of N₂0 the refractive index of the deposited second material can be continuously varied between 1.46 and 2.2 by adjusting the relative amounts, i.e. the gas flows, of N₂0 and NH₃ in a one step process.

Another possible reaction pathway for depositing SiO_xN_y as the second material is using SiCl₄ with 0₂ and N₂ as gaseous starting compounds for forming SiO_xN_y. Due to the high stability of SiCl₄ for temperatures below 600°C a plasma activated CVD process is preferentially performed like a microwave plasma activated CVD process.

The first material Si0₂ can be deposited by CVD by using, for example, SiH₄ and 0₂ as gaseous starting compounds at a CVD number larger than one, i.e. the CVD is performed at a temperature which ensures that the CVD number is larger than one. The second material can then be deposited by admixing, for instance, N₂0 or NH₃, if SiO_xN_y should be deposited as the second material, at a CVD number smaller than one, i.e. the CVD can be performed at a reduced temperature which ensures that the CVD number is smaller than one.

In a preferred embodiment, after the second material has been deposited on the structured surface, the surface is further smoothed by an additional smoothing step. For instance, an additional thermal and/or polishing treatment or another smoothing treatment can be performed for further smoothing the surface formed by the second material. This can further improve the efficiency of coupling the light out of the light generating unit through the outcoupling device.

In a further aspect of the present invention a light source fabrication method for fabricating a light source is presented, wherein the light source fabrication method comprises:

fabricating an outcoupling device as defined in claim 1,

providing a light generating unit for generating light on the second material of the outcoupling device such that light generated by the light generating unit is outcoupleable by the outcoupling device, i.e. such that the light generated by the light generating unit is extractable into air.

In particular, an anode layer, which is preferentially an ITO layer, several organic layers and a cathode layer are provided on the second material by using known procedures for producing an OLED on the second material. The resulting light source comprises the light generating unit like, for example, an OLED and an outcouphng device for coupling light out of the OLED, wherein the outcouphng device comprises the substrate with the first and second materials.

In a further aspect of the present invention an outcouphng device for coupling light out of a light generating unit is presented, wherein the outcouphng device is producible by an outcouphng device fabrication method as defined in claim 1 and wherein the outcouphng device comprises:

a substrate,

- a first material deposited onto the substrate by using a vapor deposition technique, the first material forming a structured surface on the substrate,

a second material deposited onto the structured surface by using the vapor deposition technique, the second material forming a smoothed surface, wherein the first material and the second material have different refractive indices.

In a further aspect of the present invention a light source being producible by a light source fabrication method as defined in claim 11 is presented, wherein the light source comprises:

an outcouphng device as defined in claim 12,

a light generating unit for generating light, wherein the light generating unit is arranged on the second material of the outcouphng device such that light generated by the light generating unit is outcoupleable by the outcouphng device.

In a further aspect of the present invention an outcouphng device fabrication apparatus for fabricating an outcouphng device for coupling light out of a light generating unit is presented, wherein the outcouphng device fabrication apparatus comprises a deposition device for

depositing a first material onto a substrate by using a vapor deposition technique for forming a structured surface on the substrate,

In a further aspect of the present invention a light source fabrication apparatus for fabricating a light source is presented, wherein the light source fabrication apparatus comprises:

an outcouphng device fabrication apparatus as defined in claim 14, a light generating unit providing unit for providing a light generating unit for generating light on the second material of the outcoupling device such that light generated by the light generating unit is outcoupleable by the outcoupling device.

It shall be understood that the outcoupling device fabrication method of claim 1, the light source fabrication method of claim 11, the outcoupling device of claim 12, the light source of claim 13, the outcoupling device fabrication apparatus of claim 14, and the light source fabrication apparatus of claim 15 have similar and/or identical preferred embodiments, in particular, as defined in the dependent claims.

It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims with the respective independent claim.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Fig. 1 shows schematically and exemplarily an embodiment of a light source comprising a light generating unit and an outcoupling device,

Fig. 2 shows schematically and exemplarily layers of the outcoupling device in more detail,

Fig. 3 shows a flowchart exemplarily illustrating an embodiment of a light source fabrication method for fabricating a light source,

Fig. 4 illustrates schematically a CVD number of a CVD process, and Fig. 5 shows schematically and exemplarily an embodiment of a light source fabrication apparatus for fabricating a light source.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows schematically and exemplarily a light source 1 comprising an outcoupling device 3 and a light generating unit 2, wherein the light generating unit 2 is adapted to generate light and wherein the outcoupling device 3 is adapted to couple the generated light out of the light generating unit 2 into air.

The light generating unit 2 is an OLED comprising a cathode layer 4, an anode layer 6 and intermediate layers 5 between the cathode layer 4 and the anode layer 6. In this embodiment, the cathode layer 4 is a non-transparent metal layer which comprises, for example, copper or silver, and the anode layer 6 is an ITO layer. The intermediate layers 5 can be, for example, two or more layers and include known organic layers which are configured such that light is generated by the intermediate layers 5, if a voltage is applied to the cathode layer 4 and the anode layer 6 via a voltage source 10 schematically shown in Fig. 1. The light generated within the intermediate layers 5 can leave the light generating unit 2 through the anode layer 6 in an outcoupling direction 20. The light source 1 shown in Fig. 1 emits the generated light therefore in the bottom direction. In another embodiment, in addition the cathode layer 4 can be transparent such that the generated light can leave the OLED 2 also through the cathode layer 4. The OLED 2 can therefore be a bottom emitter as shown in Fig. 1, or a bottom and top emitter.

The outcoupling device 3 comprises a substrate 9, a first material 8 and a second material 7. The first material 8 forms a structured surface on the substrate 9, wherein the structured surface is smoothed by the second material 7. The substrate 9 is preferentially a glass substrate, in particular, a float glass substrate. The second material 7 smoothes the structured surface by filling up grooves defined by the first material 8 on the substrate 9.

The part of the second material 7 immediately above the first material 8 comprises curved growth lines, which are caused by depositing the second material on the structured surface formed by the first material 8 on the substrate 9. These growth lines lead to an optically inhomogeneous part of the second material 7 above the first material 8. With increasing distance to the first material 8 in the height direction the curved growth lines disappear and the second material 7 becomes optically homogeneous, thereby forming an optically homogenous layer. This is schematically and exemplarily shown in more detail in Fig. 2, which shows an outcoupling device 2 with growth lines 21. The optically homogenous layer may have a thickness in the outcoupling direction 20 being larger than a coherence length of the generated light. Light generated by an OLED has generally a coherence length between 3 μιη and 7 μιη. The thickness of the optically homogeneous layer formed by the second material 7 is therefore preferentially at least 5 μιη, further preferred about 10 μιη or larger.

The refractive index of the optically homogeneous layer formed by the second material 7 is preferentially similar to an average of the refractive indices of the intermediate layers 5, i.e. the refractive index of the optically homogenous layer formed by the second material 7 preferentially matches with the average of the refractive indices of the intermediate layers 5 of the light generating unit 2. In this embodiment, the intermediate layers 5 have an average refractive index of about 1.8. The refractive index of the optically homogeneous layer formed by the second material 7 is therefore also preferentially about 1.8. In other embodiments, the refractive index of the optically homogeneous layer can have another value, wherein generally the refractive index will be equal to or larger than 1.7.

The second material is preferentially an inorganic material being transparent to the light generated by the OLED 2. In particular, the second material 7 does not absorb the light generated by the OLED 2. Preferentially, the second material comprises at least one of SiOxNy (1.75 ... 1.85), Ge0₂ (1.7), Ga₂0₃ (1.77), Hf0₂ (1.79), Ta₂0₅ (2.08), Si₃N₄ (2.05) and SiN_y (1.9). The numbers in brackets exemplary indicate preferred refractive indices of the respective material. The refractive indices can of course be slightly different depending on the wavelengths of the light provided by light generating unit and optionally also to some extent depending on preparation conditions of the respective material.

The first material 8 and the substrate 9 have a refractive index being smaller than the refractive index of the second material 7. The first material preferentially comprises at least one of Si0₂ (1.46), SiO_xN_y (1.53), A1₂0₃ (1.63), and a fluoride, for instance, MgF₂ (1.37).

In the following an embodiment of a light source fabrication method will exemplarily be described with reference to a flowchart shown in Fig. 3.

In step 101, a substrate 9 is provided. In particular, a planar float glass plate is provided as the substrate. In step 102, the first material 8 is deposited on a planar surface of the substrate 9 by using a CVD process, in order to form a structured surface on the substrate 9. In this embodiment, the CVD process for depositing the first material 8 is performed at a CVD number larger than one. By performing the CVD process at a CVD number larger than one the first material 8 is effectively inhomogeneously deposited on the originally planar surface of the substrate 9 such that the surface becomes structured. For instance, if the first material is Si0₂, it can be deposited on the substrate 9 by using SiH₄ and 0₂ as gaseous starting compounds at a CVD number larger than one. In order to ensure that the CVD process is performed at a CVD number larger than one, the temperature can be chosen accordingly. The CVD number will in the following be described with reference to Fig. 4.

Fig. 4 shows schematically and exemplarily a CVD deposition rate r logarithmically versus the inverse temperature 1/T. The line 30 indicates the dependence of the logarithm of the CVD deposition rate depending on the inverse temperature. Below the point 31 this dependence is substantially linear, wherein this linear dependence corresponds to a CVD number smaller than one. Above the point 31 the dependence is not linear anymore, wherein this region above the point 31 corresponds to a CVD number being larger than one. At the point 31 the CVD number is one. If the CVD number is larger than one, the deposition is diffusion controlled and the deposited first material forms a more columnar structure as shown, for instance, in Fig. 2. If the CVD number is smaller than one, the deposition is kinetically controlled and more homogeneous. Thus, this kinetically controlled region is preferentially used for filling up grooves formed by the first material, as will be described further below with reference to step 103.

The definition of the CVD number is well known and, for example in the isothermal case, given by the product of the mass transport coefficient k_D with the thickness of the boundary layer in the gas phase δ , divided by the diffusion coefficient D_T in accordance with following equation:

N(CVD) = k_D / D_T wherein N(CVD) denotes the CVD number. For more details regarding this well known equation reference is made to, for instance, the thesis "Mass transport and morphology in CVD processes" by C. v. d. Brekel, University of Nijmegen (1978), which is herewith incorporated by reference.

In step 103, the second material 7 is deposited onto the structured surface by using CVD, wherein the second material 7 has a refractive index being larger than the refractive index of the first material 8. The second material 7 is deposited at a CVD number being smaller than one. If the CVD number is smaller than one, the deposition rate and the temperature are in relatively low region, wherein the CVD process is surface controlled or kinetically controlled. Under these conditions grooves of the structured surface can be effectively filled up by the second material 7. The CVD conditions can even be adjusted to fill relatively deep holes, wherein in the corresponding regime the CVD process can also be regarded as being a chemical vapor infiltration (CVI) process. Corresponding CVD parameters are disclosed, for example, in the above mentioned thesis "Mass transport and morphology in CVD processes" by C. v. d. Brekel, pages 33, 42 and 43, Figs. 6 and 7, University of Nijmegen (1978), which is also herewith incorporated by reference. For further details regarding the CVD process, in particular, regarding the CVD number reference is made to the article "Interface Morphology in Chemical Vapour Deposition on Profiled

Substrates" by C. van den Brekel et al., Journal of Crystal Growth, volume 43, pages 488 to 496 (1978), which is herewith incorporated by reference. If the second material is SiO_xN_y, preferentially silicon containing gas, oxygen containing gas and nitrogen containing gas are used as feed gases, i.e. as gaseous starting compounds. For instance, the SiO_xN_y material can be deposited by CVD by using SiH₄, NH₃ and 0₂ or N₂0 as gaseous starting compounds, diluted in N₂, as described in the above mentioned article by F. Lebland et al. By admixture of N₂0 the refractive index of the deposited second material can be continuously varied between 1.46 and 2.2 by adjusting the relative amounts, i.e. the gas flows, of N₂0 and NH₃ in a one step process. Another possible reaction pathway for depositing SiO_xN_y as the second material is using SiCl₄ with 0₂ and N₂ as gaseous starting compounds for forming SiO_xN_y. Due to the high stability of SiCl₄ for temperatures below 600 °C a plasma activated CVD process is preferentially performed like a microwave plasma activated CVD process.

For depositing Si-based layers a feed gas is preferentially used, which comprises a Si containing gaseous species. It is also possible that the Si containing species are not completely gaseous, wherein in this case an inert carrier gas can be used, which carries the Si containing species, which escape under high vapor pressure conditions.

After the second material 7, which is preferentially solid SiON, has been deposited on the first material 8, remaining gaseous reaction products can be exhausted or scavenged.

Depending on the average refractive index of the intermediate layers 5 of the OLED 2, also another second material can be used. For instance, instead of a SiO_xN_y layer the second material can be formed by a SiN_y layer, which may comprise a refractive index of, for instance, 1.9 depending on the deposition conditions.

Moreover, other transparent materials, in particular, other transparent oxides, especially if having a refractive index of 1.7 or higher, can be used instead of SiO_xN_y as the second material. For instance, the second material can comprise at least one of the following transparent oxide, nitride or carbide compounds Ge0₂ (1.7), Ga₂0₃ (1.77), Hf0₂ (1.79 - 1.9),

Ta₂0₅ (2.08), Si₃N₄ (2.05), AION (1.79), YAG (1.82), Sc₂0₃ (2.0), eventually also A1₂0₃

(1.66), if the average OLED index should be so low. For depositing these second materials sufficiently volatile starting compounds are used being preferentially halides of the respective compound, wherein, for instance, for Ge0₂ preferentially GeCl₄, for Ga₂0₃ preferentially

GaCl₃, for Hf0₂ preferentially HfCl₄, for Ta₂Os preferentially TaF₅ or TaCl₅, and for Si₃N₄ preferentially SiF₄ or SiCl₄ are used.

The second material 7 forms preferentially a CVD interlayer having a high refractive index, i.e. a refractive index being larger than the refractive index of the first material and matching the average refractive index of the intermediate layers 5 of the OLED 2, which is, in this embodiment, about 1.8. In contrast, the first material is preferentially a low index material with a refractive index in the range of float glass, i.e. in the range of 1.53. The first material 8 can be, besides Si0₂ (1.46), SiO_xN_y adjusted to a refractive index of, for instance, 1.53, A1₂0₃ (1.63) or a fluoride such as MgF₂ (1.37) or LaF₃ (1.60). The first material can also be a suitable mixture of these compounds for providing a desired refractive index of the first material like a Si0₂/Al₂0₃ mixture.

The first material 7 and the second material 8 can be deposited in the same CVD reactor, i.e. the same setup can be used, wherein only the source gases are switched and the deposition conditions are changed, especially the deposition temperature is changed for modifying the CVD number. In particular, a first gas phase can be used for depositing the first material 8 and a second gas phase can be used for depositing the second material 7, wherein for switching from depositing the first material 8 to depositing the second material 7 the CVD process can be transitionally changed from the first gas phase to the second gas phase and from a CVD number being larger than one to a CVD number being smaller than one for providing a continuous refractive index transition at the border between the first material 8 and the second material 7. The continuous refractive index transition can suppress Fresnel reflection losses, thereby further improving the outcoupling efficiency.

In step 104, which is an optional step, the surface formed by the second material 7 can be further smoothed by an additional smoothing step. For instance, an additional thermal and/or polishing treatment or another smoothing treatment can be performed for further smoothing the surface formed by the second material 7.

In step 105, a light generating unit 2 for generating light is provided on the second material 7 for producing the light source 1. In particular, the anode layer 6, which is preferentially an ITO layer, several organic layers 5 and the cathode layer 4 are provided on the second material by using known procedures for producing an OLED on the second material 7. The resulting light source 1 comprises the OLED 2 and the outcoupling device 3 for coupling light out of the OLED, wherein the outcoupling device 3 comprises the substrate 9 with the structures formed by the first material 8 and the smoothing second material 7.

In step 106, the cathode 4 and the anode 6 can be electrically connected to the voltage source 10 for applying voltage to the light generating unit 2 for allowing the light generating unit 2 to generate light to be outcoupled into air by the outcoupling device 3.

Steps 101 to 104 can be regarded as being steps of an outcoupling device fabrication method for fabricating the outcoupling device. Fig. 5 shows schematically and exemplarily an embodiment of a light source fabrication apparatus 14 for fabricating a light source. The light source fabrication apparatus 14 comprises an outcoupling device fabrication apparatus 13 and a light generating unit providing unit 15. The outcoupling device fabrication apparatus 13 preferentially comprises a deposition device 11 for depositing the first material and the second material onto the substrate 9 in accordance with above steps 101 to 103. In particular, the deposition device 11 is preferentially a CVD deposition device being adapted to deposit the first material 8 onto the substrate 9 at a CVD number being larger than one and to deposit the second material 7 onto the structured surface formed by the first material 8 by using the CVD technique at a CVD number being smaller than one. The deposition device 11 is controlled by a control unit 12. The control unit 12 also controls the light generating unit providing unit 15 to provide the light generating unit 2 on the second material 7 of the outcoupling device 3 such that light generated by the light generating unit 2 is outcouplable by the outcoupling device 3. In particular, different layers of an OLED are deposited on the second material 7 of the outcoupling device 3. The deposition device 11 can comprise extended plasma sources, a gas distribution system and means for moving the substrate, in order to deposit the first material and the second material on large flat glass substrates, i.e. on flat glass substrates having lateral extension in the range of, for instance, 15 cm to 100 cm.

The preparation of medium to large area, i.e. small molecule, OLEDs, especially of the layer structure consisting of organic materials, is usually carried out by thermal evaporation in vacuum on a light transmitting substrate like float glass. A typical OLED structure consists of a thin transparent anode, a hole transport layer, a light emission zone, an electron transport layer and a cathode layer. Unfortunately typically about 50 percent of the light generated remains in the OLED layer stack because of guided modes, about 25 percent remain in the substrate having a relatively low refractive index and only 20 to 25 percent are coupled into air and can be used for lighting applications. This portion of light emitted into air can be increased by a number of measures by about 50 percent to about 36 percent, which is still very low for an efficient use of the OLED.

For monochrome and for white OLED devices the light output into air can be significantly increased by using a substrate having a high refractive index below the OLED. This is based on the fact that by matching the refractive index of this substrate with the average refractive index of the OLED layers of about 1.8 the amount of light in this substrate can be increased by about 50 percent and hence also the amount of light emitted into air by using a suitable light outcoupling structure such as, for instance, a micro lens array or pyramid array. However, the main disadvantage of this approach is that the high refractive index glass substrates used are much more expensive than normal glass substrates having a refractive index of about 1.5 and moreover are much more brittle and have a high chance of breaking during processing. This problem can be overcome, if a normal glass substrate with an optically thick high index layer below the OLED and an additional outcoupling structure near the interface is used, wherein a scattering of the light can be provided at the interface layer between the relatively high refractive index and the relatively low refractive index.

In the embodiment described above with reference to Figs. 1 to 5, firstly a rough layer with relatively low refractive index is prepared on a glass substrate also having a relatively low refractive index per CVD at conditions of a CVD number being larger than one and then it is continued with a smoothing CVD layer having a relatively high refractive index. The advantage is that it can be done in the same CVD reactor, in particular, only by switching the source gases and changing the deposition conditions, especially the deposition temperature. After obtaining the filling up of grooves and the smoothing by the smoothing CVD layer, a major part of the CVD layer with the relatively high refractive index extends preferentially to the anode layer being preferentially an ITO layer below the OLED layer structure. Thus, much more light can be coupled via the smooth surface into the base layer, i.e. the layer formed by the second material, having the relatively high refractive index.

The CVD layer formed by the first material at a CVD number larger than one can show a columnar growth structure as shown, for instance, in Fig. 2 with intermediate layer boundaries, which may be caused by a change of the gas flow, for instance, via a periodic movement of the plasma or the substrate. Fig. 2 shows a schematic cross section of the outcoupling device manufactured completely by CVD. Here the columnar structures at conditions of a CVD number larger than one consist of "low n" Si0₂ and they are coated by SiON at conditions of a CVD number smaller than one, wherein grooves are filled up. The columns may have a height of 1 to 3 μιη and a lateral distance of 1 to 3 μιη. The average thickness of the planarizing SiON layer may vary from 3 to 20 μιη and may be at least three times the typical structural dimension of the rough base, i.e. preferentially at least three times the thickness of the non-uniform layer formed by the first material. The upper surface of the SiON layer may be uneven as schematically indicated in Fig. 2 or it may be planar.

Although in the embodiments described above with reference to Figs. 1 to 5 the used deposition technique is a CVD technique, in other embodiments the outcoupling device can also be fabricated by using PVD, especially a sputtering technique. In particular, the first material can be deposited for forming the scattering layer by reactive high rate pulsed DC sputtering at high gas pressure, in particular, in the range of 10^" mbar. Under these process conditions it is possible to realize layers of, for instance, Si0₂, SiO_xN_y, et cetera, which scatter the light. Subsequently the second material can be deposited for forming a thick dense high index layer onto the scattering layer by altering the process conditions, for instance, sputtering in the 10^" mbar range. Subsequently a transparent conducting oxide can be deposited as anode layer so that the whole substrate manufacturing process can be made in an in-line sputter tool. On the substrate with the anode layer organic intermediate layers and the cathode layer can be provided with known techniques for fabricating an OLED.

As a further variant instead of the CVD preparation of a rough intermediate layer of, for instance, Si0₂ on the glass substrate, wherein the rough

intermediate layer has a relatively low refractive index, it can be started on the flat substrate with depositing particles from an oversaturated CVD reaction, i.e. N(CVD) » 1, on the flat substrate as the first material. These particles could be either Si0₂ particles with a relatively low refractive index or particles with a refractive index being larger than the refractive index of a following smoothing layer, which has preferentially a refractive index matching the average refractive index of the intermediate layers of an OLED and which will be deposited on the particles by CVD as the second material. The particles are, for instance, Ti0₂ (2.37), Nb₂0₅ (2.38), BaTi0₃ (2,45), Zr0₂ (2.2) or the like with a refractive index being equal to or larger than, for instance, 2.2 or 2.3. These particles are preferentially submicron sized. They could also be deposited from an intermixing gas stream carrying such particles. The particles could be created via laser ablation of a solid target, which may have a refractive index being larger than the

refractive index of the smoothing layer, or a gas stream loaded with suitable particles prepared by a different method could be used. These processes could also be conducted subsequently.

Although in the above described embodiments the light generating unit is an OLED, the light generating unit can also be another kind of light generating means. For instance, the light generating unit can also be an inorganic light emitting diode, or the light generating unit can be another light generating unit comprising a region with a relatively high refractive index, which is, for example, larger than 1.7, wherein in this high refractive index region light is generated, which is outcoupled by the outcoupling device, i.e which is extracted and, thus, emitted into air by the outcoupling device with high efficiency.

Although in the embodiment described above with reference to Fig. 1 the outcoupling device is optically connected with the light generating unit, in other embodiments the outcoupling device can also be a separate device, which may already comprise an anode layer, in particular, an ITO layer, on the second material, wherein this separate outcoupling device can be provided to an OLED producer, which provides the OLED layers on the outcoupling device for producing a light source comprising the OLED and the outcoupling device.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

A single unit or device may fulfill the functions of several items recited in the claims. 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.

Method steps for fabricating the outcoupling device, in particular, for fabricating the OLED with the outcoupling device, performed by one or several units or devices can be performed by any other number of units or devices.

Any reference signs in the claims should not be construed as limiting the scope.

The invention relates to an outcoupling device fabrication method for fabricating an outcoupling device for coupling light out of a light generating unit like an organic light emitting diode. A first material is deposited onto a substrate by using a vapor deposition technique for forming a structured surface on the substrate, whereupon a second material is deposited onto the structured surface by using the vapor deposition technique for smoothing the structured surface, wherein the first material and the second material have different refractive indices. The resulting layers have, in combination, a relatively large density such that the likelihood of water penetration is rather low, thereby reducing the likelihood that the light generating unit is adversely affected by water such that the outcoupling of the light out of the light generating unit can be provided, without significantly reducing the operability of the light generating unit.

Claims

CLAIMS:

1. An outcoupling device fabrication method for fabricating an outcoupling device for coupling light out of a light generating unit, the outcoupling device fabrication method comprising:

providing a substrate (9),

depositing a first material (8) onto the substrate (9) by using a vapor deposition technique for forming a structured surface on the substrate (9),

- depositing a second material (7) onto the structured surface by using the vapor deposition technique for smoothing the structured surface, wherein the first material (8) and the second material (7) have different refractive indices.

2. The fabrication method as defined in claim 1, wherein the refractive index of the first material (8) is smaller than the refractive index of the second material (7).

3. The fabrication method as defined in claim 1, wherein the light generating unit (2) comprises a cathode layer (4), an anode layer (6) and intermediate layers (5) between the cathode layer (4) and the anode layer (6), wherein the refractive index of the second material (7) matches the average refractive index of the intermediate layers (5) or of the intermediate layers (5) and the anode layer (6).

4. The fabrication method as defined in claim 1, wherein the refractive index of the first material (8) matches the refractive index of the substrate (9).

5. The fabrication method as defined in claim 1, wherein the vapor deposition technique is chemical vapor deposition, wherein the first material (8) is deposited at a chemical vapor deposition number larger than one.

6. The fabrication method as defined in claim 1, wherein the vapor deposition technique is chemical vapor deposition, wherein the second material (7) is deposited at a chemical vapor deposition number smaller than one.

7. The fabrication method as defined in claim 1, wherein the vapor deposition technique uses a first gas phase for depositing the first material (8) and a second gas phase for depositing the second material (7), wherein for switching from depositing the first material (8) to depositing the second material (7) the vapor deposition changes transitionally from the first gas phase to the second gas phase for providing a continuous refractive index transition at the border between the first material (8) and the second material (7).

8. The fabrication method as defined in claim 1, wherein the first material (8) comprises at least one of Si0₂, SiO_xN_y, A1₂0₃, a fluoride.

9. The fabrication method as defined in claim 1, wherein the second material (7) comprises at least one of SiO_xN_y, Ge0₂, Ga₂0₃, Hf0₂, Ta₂0₅, Si₃N₄, SiN_y, AION, YAG, Sc₂0₃, A1₂0₃.

10. The fabrication method as defined in claim 1, wherein the vapor deposition technique is a physical vapor deposition technique.

11. A light source fabrication method for fabricating a light source, the light source fabrication method comprising:

fabricating an outcoupling device (3) as defined in claim 1,

providing a light generating unit (2) for generating light on the second material (7) of the outcoupling device (3) such that light generated by the light generating unit (2) is outcoupleable by the outcoupling device (3).

12. An outcoupling device for coupling light out of a light generating unit, the outcoupling device (3) being producible by an outcoupling device fabrication method as defined in claim 1, the outcoupling device (3) comprising:

a substrate (9),

a first material (8) deposited onto the substrate (9) by using a vapor deposition technique, the first material (8) forming a structured surface on the substrate (9), a second material (7) deposited onto the structured surface by using the vapor deposition technique, the second material (7) forming a smoothed surface, wherein the first material (8) and the second material (7) have different refractive indices.

13. A light source being producible by a light source fabrication method as defined in claim 11, the light source (1) comprising:

an outcouphng device (3) as defined in claim 12, a light generating unit (2) for generating light, wherein the light generating unit (2) is arranged on the second material (7) of the outcouphng device (3) such that light generated by the light generating unit (2) is outcoupleable by the outcouphng device (3).

14. An outcouphng device fabrication apparatus for fabricating an outcouphng device for coupling light out of a light generating unit, the outcouphng device fabrication apparatus (13) comprising a deposition device (11) for

depositing a first material (8) onto a substrate (9) by using a vapor deposition technique for forming a structured surface on the substrate (9),

depositing a second material (7) onto the structured surface by using the vapor deposition technique for smoothing the structured surface, wherein the first material (8) and the second material (7) have different refractive indices.

15. A light source fabrication apparatus for fabricating a light source, the light source fabrication apparatus (14) comprising:

an outcouphng device fabrication apparatus (13) as defined in claim

14,

a light generating unit providing unit (15) for providing a light generating unit (2) for generating light on the second material (7) of the outcouphng device (3) such that light generated by the light generating unit (2) is outcoupleable by the outcouphng device (3).