WO2005051525A1

WO2005051525A1 - Permeation barrier coating or layer with modulated properties and methods of making the same

Info

Publication number: WO2005051525A1
Application number: PCT/CA2004/002006
Authority: WO
Inventors: Grzegorz Czeremuszkin; Mohamed Latreche; Michael Robert Wertheimer
Original assignee: Polyvalor, Limited Partnership
Priority date: 2003-11-25
Filing date: 2004-11-23
Publication date: 2005-06-09

Abstract

An improved barrier-coating against permeation of gases and vapors, especially useful for use in substrates for organic electronic devices and for encapsulation of those devices, comprising a layer of a material with modulated properties. Modulated properties mean multiple gradual, periodic or oscillating changes of at least one physical, chemical or structural parameter of the material, which are spatially continuous within the coating. The physical properties of the barrier coating material thus exhibit a smooth transition between any two points across the material thickness, and therefore the coating is free from abrupt interfaces. This improved barrier-coating also has better mechanical stability.

Description

PERMEATION BARRIER COATING OR LAYER WITH MODULATED PROPERTIES AND METHODS OF MAKING THE SAME

TECHNICAL FIELD

[0001] This invention relates to an improved barrier layer, as a barrier to permeation of gases and vapors, especially for use in organic electronic devices.

The invention also relates to an organic electronic device incorporating the improved barrier layer. The invention also relates to a method for producing the barrier layer, and to a method of producing an organic electronic device incorporating the barrier layer.

BACKGROUND ART

[0002] Organic electronic devices, especially organic light emitting diodes,

OLEDs, are susceptible to deterioration by even trace amounts of oxygen and water. This invention relates to extending the lifetime of such organic electronic devices (e.g., organic light emitting diode- and/or photovoltaic devices) by protecting them against oxygen and water vapor, using a barrier material comprising an impermeable coating with modulated properties. This invention also relates to methods of producing such coatings for such devices. To date, glass plates have been the supporting substrate of choice, since glass has excellent barrier and transparency properties, and a metal sheet or a second glass plate has been used as the encapsulating means. On the other hand, glass has the drawbacks of brittleness, high-weight, and rigidity. Replacing glass with impermeable plastic substrates according to the invention will resolve those problems, thereby enabling non-breakable, flexible, light and inexpensive display devices.

[0003] Producing and using plastics having barrier-coatings against oxygen and water permeation is known from the prior art, ranging from flexible food packaging to packaging of OLED devices.

[0004] It is known in the flexible packaging art, to coat polymer films or sheets with thin inorganic coatings, for example, metal oxide coatings, to render the polymer films or sheets less permeable to oxygen and water vapor. However, it is very difficult, in manufacturing practice, to produce such coatings without some pinholes or other types of defects, which permit passage of oxygen and water molecules through the otherwise impermeable coatings. Consequently, the levels of permeability achieved using such barrier-providing methods, which are typical for flexible packaging in the food and other industries, will certainly not meet the far more demanding requirements for packaging organic electronics. [0005] OLED devices provide a new generation of active organic displays of high energy efficiency, large viewing angle, excellent color definition and contrast and most important, of potentially low cost. In OLED-based displays, high-quality images can be created by a matrix of many light emitting diodes encapsulated in transparent materials. The diodes are patterned to form a pixel matrix, where a single pixel junction emits light of a given color. All organic displays, developed so far, contain oxygen- and moisture-sensitive components, namely, organic semiconductors and electron- injecting metals. Therefore, it is necessary to use materials with ultra-high barrier properties against permeation of water and oxygen for organic long-life display devices. Device manufacturers estimate that transmission rates, which are several orders of magnitude lower than those characteristic for coatings used in flexible food packaging, are required to provide organic electronic devices with lifetimes of at least 10,000 hrs.

[0006] An additional important requirement from a device manufacturer's standpoint is thermal stability. Certain processes in display production lines require the substrate to be heated above 200°C; this limits the number of suitable plastic materials available, to polymeric films with high Tg (glass transition) values, and it also limits designs of permeation barriers (discussed below) to those which are stable at elevated temperatures. Enhanced thermal stability is a particular characteristic of coatings according to the present invention. Another solution to the thermal stability problem may be depositing the barrier coating onto the plastic substrate after the latter has undergone processes requiring excessive heating. This, however, may not always be feasible; by using the invention, it is not necessary to change the manufacturing process sequence. [0007] The prior art describes single- and multi-layer inorganic coatings, deposited on plastic substrates in order to decrease permeation of gases and vapors. It is also known in the display manufacturing art, to coat polymer films or sheets with thin inorganic coatings or composite inorganic/organic multilayer coatings, to render the polymer films or sheets essentially impermeable to oxygen and water vapor. The latter types of structures consist of several distinct layers of different materials having finite thicknesses, for example, comprising alternating polymeric and inorganic layers, or stack(s) of various ceramic coatings.

[0008] Single- and multilayer coatings have also been cited specifically for the protection of OLED devices. Although it is commonly accepted in the prior art that single-layer coatings provide insufficient protection to OLEDs against permeating gases and vapors, several patents nevertheless describe single-layer coatings of improved impermeability. U. S. Patent 6,406,802 presents an organic electroluminescent color display comprising a substrate with the single-layer barrier containing silicon oxide. The device includes, starting from the substrate, a fluorescence converting layer, an organic layer formed of a thermo setting resin or an ultraviolet curing resin, and a barrier layer. U. S. patent application US 2003/0025448 describes a display encapsulated with a single-layer carbon coating that limits oxygen and water permeation through the backside of the display. [0009] It has also been proposed to improve impermeability of flexible polymeric substrates and of OLED encapsulation means by depositing multilayer coatings. U. S. Patent 6,413,645 shows the OLED device with a multilayer barrier coating composed of several alternating stacks of a metal oxide and acrylate polymer. Such a system, however, does not possess sufficient thermal stability for the plastic substrate for OLEDs. U. S. Patent 6,492,026 describes the same types of coatings using polymer substrates with glass transition temperatures higher than 120°C, thereby improving thermal stability. U. S. Patent 6,146,225 describes a barrier for preventing water or oxygen molecules from reaching the OLED device, produced by depositing an organic coating and subsequently an inorganic coating between the device and the surrounding environment. U. S. Patent 5,757,126 describes a method of passivating organic devices by overcoating the plastic substrate with a multilayer overcoating; the latter consists of alternating layers of a transparent polymer film and of a transparent dielectric material.

[0010] Typical single- and multilayer coatings, including organic/inorganic or inorganic/inorganic layers, are all characterized by the presence of abrupt interfaces between the substrate and the coating, as well as between subsequent coating layers.

[0011] A coating with modulated properties exhibits smooth transitions of a given physical property between any two points across the coating thickness; therefore, the coating is free from abrupt interfaces. Such modulated, or "graded index" layers are known from the optical coating art, where modulated properties include multiple gradual, or oscillating changes of the refractive index within the coating, thus providing particular light-reflection and light-transmission properties. Such optical filters, known as "rugate filters", have precisely- controlled refractive index profiles (Angstrom unit precision) of successive layers across the coating thickness, and they can provide excellent narrow-band filters. U. S. Patent 6,392,801 shows a polarizing beam-splitter including a rugate filter, which contains multiple layers of modulated composition, thereby comprising a surface coating with oscillating higher and lower index across its thickness. The filter is produced from at least two materials having different indices of refraction. For certain applications, the coatings may consist of two layers displaying graded index of refraction, as described in U. S. Patent 6,436,541, which presents conductive antireflective coatings consisting of two or more layers of anti-static film coating deposited on a substrate. In one embodiment, the surface of the film is roughened to provide a graded index of refraction.

[0012] Coatings having non-uniform structure across their thickness, contrary to coatings with non-uniform composition, have also been described in prior art. U. S. Patent 6,432,478 reveals a ceramic heat barrier coating of low thermal conductivity, and a process for depositing of said coating. A ceramic heat barrier coating is deposited on a substrate in such a way that the coating has a columnar growth pattern, which is interrupted and repeated a number of times throughout its thickness by successive renucleations of the ceramic deposit growth. This is achieved by a vapor phase deposition process, wherein a nucleating gas is introduced intermittently during deposition. However, coatings with columnar structure are known to exhibit high permeation to gases and vapors, and they can therefore not be used for enhanced barrier purposes. [0013] An optical filter having a profiled multilayer structure is described in U. S. Patent 6,256,148. It presents a rugate filter coating for reflecting electromagnetic waves, comprising a transparent coating on a substrate; the coating has incrementally varying depths of constant index of refraction. This optical filter therefore differs from the ones with modulated structure, by comprising distinguishable sub-layers of finite thickness and constant refractive index.

[0014] U. S. Patent 6,425,987 describes a technique for depositing multilayer interference thin films, using silicon as the only coating material. The technique involves using only one coating material (pure silicon) to deposit thin films under high vacuum, by using an ion source with a working gas (or gases) to control the varying refractive index of the thin film during growth. This technique can be used to deposit different kinds of optical thin films with different refractive indices or index gradients, and to make different kinds of multilayer interference filters without opening the vacuum chamber during the process.

[0015] Recent trends in organic electronics, namely, the development of polymer-, oligomer-, and dendrimer- based organic light emitting diode devices, caused differentiation between OLED devices (organic light emitting diodes, based on small molecules) and PLED devices (polymeric light emitting diodes, based on macromolecules). However, this distinction is artificial since all polymers, oligomers and dendrimers used to produce light emitting devices are

"organic"; therefore, they all belong to the OLED category, by definition. This is taken for granted in this text.

DISCLOSURE OF THE INVENTION

[0016] This invention seeks to provide a barrier layer functioning as a barrier to permeation of gases and vapors.

[0017] Still further, this invention seeks to provide a composite sheet comprising an organic support film supporting the barrier layer.

[0018] The invention also seeks to provide an organic electronic device incorporating the aforementioned composite as a support substrate and/or barrier covering of the encapsulation envelope of the device. [0019] The invention also seeks to provide a method for producing the barrier layer.

[0020] Still further, the invention seeks to provide a method of producing the composite.

[0021] The invention also seeks to provide a method of producing an organic electronic device incorporating the composite of the invention.

[0022] In accordance with one aspect of the invention, there is provided a barrier layer as a barrier to permeation of gases and vapors, the barrier layer exhibiting a modulated property across its thickness such that the layer is free from abrupt interfacial variation in said property across its thickness.

[0023] In accordance with another aspect of the invention, there is provided a composite sheet for an organic electronic device comprising an organic polymer support film and a barrier layer of the invention, supported on the support film.

[0024] In accordance with still another aspect of the invention, there is provided a method of producing a barrier layer of the invention comprising vapour depositing on a support surface to form a coating layer on said support surface, and changing at least one characteristic of the vapour deposition in a controlled manner effective to produce said modulated property in said coating layer.

[0025] In accordance with a particular embodiment of this latter aspect of the invention, the support surface is defined by an organic polymer support film, and recovering a composite of said film and said coating layer.

[0026] In accordance with still another aspect of the invention, there is provided an organic electronic device in which photovoltaic devices or light emitting diodes are encased in a barrier envelope comprising a substrate supporting said devices or diodes and a barrier covering, said substrate and covering being impermeable to oxygen and water vapor, the improvement wherein at least one of said substrate and covering comprises a composite sheet of the invention.

[0027] In yet another aspect of the invention, there is provided in a method of manufacturing an organic electronic device in which light emitting organic diodes are encased in a barrier envelope comprising a substrate supporting said diodes and a barrier covering, said substrate and covering being impermeable to oxygen and water vapor, the improvement wherein at least one of the substrate and covering comprises a composite sheet of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Fig. 1 illustrates graphically dependence of oxygen transmission rate on coating thickness;

[0029] Fig. 2 illustrates schematically a support substrate of the invention;

[0030] Fig. 3 illustrates schematically a support substrate of the invention in another embodiment;

[0031] Fig. 4 illustrates schematically a support substrate of the invention in yet another embodiment;

[0032] Fig. 5 illustrates schematically an OLED device of the invention;

[0033] Fig. 6 illustrates schematically an OLED device of the invention in another embodiment;

[0034] Fig. 7 illustrates schematically an OLED device of the invention in yet another embodiment;

[0035] Fig. 8 illustrates schematically an OLED device of the invention in still another embodiment; and

[0036] Fig. 9 illustrates schematically an OLED device of the invention in yet another embodiment. DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS [0037] Organic electronic devices, especially OLEDs and organic photovoltaic devices, are susceptible to deterioration by even small traces of oxygen and water. A particular object of this invention is to provide an organic electronic device, having a flexible film substrate and an encapsulation, both of which possess enhanced impermeability to oxygen and water vapor. In such an electronic device, the flexible film substrate and/or the encapsulation comprise an organic polymer film having thereon a barrier coating or layer with modulated properties, in which degradation of barrier characteristics arising from mechanical stresses in the coating during heating, bending or flexing are greatly reduced. The coating contains no abrupt interfaces therein, the absence of abrupt interfaces leading to a dissipation of possible internal stresses. This, in turn, allows one to produce modulated-property coatings of increased thickness, and thereby enhanced impermeability to oxygen and water vapor. [0038] It is also a particular object of this invention to provide an organic electronic device, the outer layer of which is the passivation layer, with an encapsulating barrier coating or layer having modulated properties therein. The coating contains no abrupt interfaces therein, which leads to a dissipation of possible internal stresses. This, in turn, allows one to produce modulated- property coatings of increased thickness, and thereby enhanced impermeability to oxygen and water vapor.

[0039] Another particular object of this invention is to provide a flexible film barrier support substrate for an OLED device.

[0040] Yet another particular object of this invention is to provide a method of producing a single layer barrier coating with graded or modulated properties for application in oxygen- and water-sensitive organic electronic devices, such as OLED, organic photovoltaic devices, and other types of organic electronic devices (e.g., liquid crystal-, electrophoretic displays, etc.). [0041] In accordance with a particular embodiment of the invention, organic electronic components are supported on a transparent substrate impermeable to oxygen and water vapor, wherein the transparent substrate comprises: i) an organic polymer support film, and ii) a single coating layer on the support film and disposed intermediate the support film and the light emitting diodes, the single layer having multiple gradual or oscillating changes of at least one property of the coating material, changes of which are spatially continuous, so that the coating exhibits modulated properties across its thickness. The changing property may include at least one of the following physical, chemical and structural parameters of the coating material: composition, chemical structure, morphology, density, nanoporosity, solubility and diffusivity towards small inorganic and organic molecules, electrical conductivity, real and imaginary parts of the dielectric permitivity, polarizability, free energy, free volume, crystallinity, degree of crosslinking, viscosity, Young modulus, hydrophobicity, hydrophilicity, electron affinity, rigidity, and chemical reactivity toward oxygen and water molecules, including the capability of forming hydrogen bonds and chemical covalent or ionic bonds. Those properties are known to be directly or indirectly related to permeability of the coating material. [0042] In accordance with another particular aspect of the invention, organic light emitting diodes are supported on a transparent substrate which is impermeable to oxygen and water vapor, and they are encapsulated with a flexible barrier having improved impermeability, where the improvement comprises a single coating layer having multiple gradual or oscillating changes of at least one property of the coating material, which are spatially continuous thus exhibiting modulated properties along its thickness. The modulated property can include at least one of the following physical, chemical and structural properties of the coating material: composition, chemical structure, morphology, density, nanoporosity, solubility and diffusivity of inorganic and organic small molecules, electrical conductivity, real and imaginary parts of the dielectric permitivity, polarizability, free energy, free volume, crystallinity, degree of crosslinking, viscosity, Young modulus, hydrophobicity, hydrofilicity, electron affinity, rigidity, and chemical reactivity toward oxygen and water molecules, including the capability of forming hydrogen bonds and chemical covalent or ionic bonds. [0043] In accordance with another aspect of the invention, organic light emitting diodes are supported on a flexible transparent substrate with improved impermeability to oxygen and water vapor according to the invention, and they are encapsulated with a flexible barrier having improved impermeability according to the invention, thus providing a flexible and transparent OLED or photovoltaic device.

[0044] In accordance with yet another particular aspect of the invention, there is provided a method of producing a transparent support substrate and of producing an encapsulating envelope for use in organic electronic devices such as OLED, photovoltaic, liquid crystal and electrophoretic displays, involving: i) exposing a transparent polymer film to a vacuum process, for example, to a low temperature electric discharge plasma, and/or to a vacuum annealing at elevated temperature, and ii) coating the polymer film surface with a coating layer having modulated properties, using the physical vapor deposition (PVD) or the plasma enhanced chemical vapor deposition (PECVD) process, or their combination, where modulated properties of the coating result from continuously and repetitively changing, in a controlled manner, at least one of the characteristics of the deposition process. Such characteristics may include: deposition rate, flux and energy of ion bombardment, bias voltage, UV-, visible- and near infrared light emission from the deposition zone, the plasma's electron energy distribution function, ion temperature, concentration of specific ions, total thickness of the deposited coating, intensity and polarization of light reflected from the coating. Those characteristics can be measured in real time during the deposition, and they thereby allow one to monitor and control the process during its operation. [0045] Preferably, characteristics of the deposition process with modulated coating properties are modified by continuously, repetitively, and controUably changing at least one of the following process parameters: power delivered to the deposition zone, contribution of power delivered from independent power sources to the deposition zone, external electrical bias voltage, local gas flow and pressure in the deposition zone, reactive gas flow rate and composition, inert gas flow rate and composition, supplying additional UV vacuum UV (VUV) or infrared radiation, substrate positioning in the deposition zone, substrate movement, web speed, geometry of applied electromagnetic, magnetic and electric fields, intensity and frequency of electromagnetic, magnetic and electric fields and temperature.

[0046] It is especially important to provide coatings with modulated properties, which are produced by using PECVD, where modulated properties can be obtained by repetitive oscillating changes of power delivered to the deposition zone in the form of direct current (DC), alternating current (AC), radio frequency (RF), microwave (MW) or combinations thereof. Such changes can consist of sequential gradual transitions from high power delivered to the discharge to low power delivered to the discharge and vice versa, where the repetition rate and profile in time of those changes are predetermined. [0047] It is also important to produce coatings with modulated properties using PECVD processes, where modulated properties can be provided by changing the substrate position with respect to at least one of the powered- and grounded electrodes, to the gas feed inputs, or to the pumping outlet, where the gas flow field and the electromagnetic-, magnetic- or electric fields in the plasma display spatial gradients.

[0048] It is also important to produce coatings with modulated properties using PECVD processes, where the modulated properties are obtained by repetitively changing the intensity and/or the geometry of the local and/or overall electromagnetic-, magnetic-, and electric fields in plasma.

[0049] It is also possible to produce coatings with modulated properties by using a PVD process equipped with multiple deposition and/or particle bombardment sources operating simultaneously, whereby modulated properties are obtained by repetitively changing parameters of a deposition process or by moving the substrate with respect to those sources along a predetermined pathway, for example, by continuously and smoothly changing the substrate distance from each source both horizontally and vertically. Such a predetermined pathway is fully contained in the co-deposition zone, so that the continuous PVD process provides the coating with modulated properties.

[0050] The barrier coating or layer in this invention is of any coating material employed for gas and vapor barrier properties, and especially impermeability to oxygen and water vapor. Especially preferred are coating materials that are depositable on a support film by vapor deposition, for example, physical vapor deposition (PVD) or plasma enhanced chemical vapor deposition (PECVD) or a combination thereof.

[0051] In the present invention, the barrier coating or layer may in effect be a single layer, a property of which, including chemical composition, is modulated across the thickness of the coating or layer. This is to be contrasted with prior barriers employing a plurality of discrete coatings or layers, in which abrupt interfacial variations occur at the junctions of the coatings. i) OLED [0052] Organic light emitting diode devices rely on electroluminesce, their general structure is well established and is not the subject of this invention. Such devices employ component layers which are sensitive to oxygen and water molecules and must thus be effectively sealed from ingress of oxygen and water vapor while maintaining transparency to light and different desired physical characteristics.

[0053] In general an OLED comprises a plurality of light emitting diodes mounted on a support substrate. The support substrate must have high transparency to light, and present a barrier to oxygen and water vapor. The diodes placed on the support substrate are covered by a barrier covering, also impermeable to oxygen and water vapor. The support substrate and covering together form a barrier envelope encasing the diodes. ii) Polymer Films [0054] Polymer support films may be employed both for the support substrate and the barrier covering of the OLED device. The support films of the support substrate and barrier covering may be the same or different. [0055] The support film should be transparent and of any suitable organic polymer, including homopolymers, copolymers and terpolymers which can be fabricated as a suitably thin film having the necessary and desirable physical characteristics to form a barrier support substrate or covering for the diodes, physical characteristics of particular importance are strength and flexibility at desired film thicknesses for the OLED device.

[0056] While the polymer films do not need to be and generally will not be impermeable to oxygen and water vapor, polymer films which are of lesser permeability to oxygen and water vapor will generally be preferred to those of higher permeability. [0057] Suitable polymers for the polymer film include, by way of example, polyolefins, for example, polyethylene and polypropylene; cyclopolyolefins, for example, polynorbornenes; polycarbonates; polyesters; polyarylates, polyacrylates, polyethyleneterephthalate; polyethylenenaphthalate; polystyrene; polyamides; polyimides; polyethersulfone, and polyorganosilicones, as well as other transparent polymers and copolymers including other high T_g polymers. The polymer film may include one or more layered polymer components.

[0058] Preferred polymer films are chosen from high T_g polymers, for example, cyclopolyolefins, polyethersulfones, polyarylates, and from polyethyleneterephthalate and polyethylenenaphthalate.

[0059] The polymer films will suitably have a thickness of 5 μm to 1000 μm, preferably 25 μm to 500 μm. iii) Modulated Barrier Layer [0060] The barrier layer provides a barrier to oxygen and water vapor and may be of a single or variable chemical composition when formed as a modulated coating impermeable to oxygen and water vapor. [0061] Suitable coating components may be formed from transparent materials, such as oxides, nitrides, mixed compositions, and salts; for example, SiO_x, SiO_xC_y, Si_xN_y, Si_xN_yC_z, SiO_xN_y, TiO_x, Al_xO_y, SnO_y, indium-tin oxide, magnesium fluoride, magnesium oxyfluoride, calcium fluoride, tantalum oxide, yttrium oxide, zirconium oxide, barium oxide, magnesium oxide, titanium oxide, niobium oxide, hafnium oxide, and mixtures thereof, wherein x is from 1 to 3, y is 0.01 to 5, and z is 0.01 to 5. Particular examples include silica, alumina and titania; other examples include amorphous carbon, borosilicate, sodium and potassium glass. [0062] Preferred coating materials are stoichiometric or non-stoichiometric silicon oxide deposited by plasma, stoichiometric or non-stoichiometric silicon nitride, silicon oxynitride and their mixtures deposited by plasma; and modulated structures including one or both of silicon dioxide, silicon nitride and silicon oxynitride, and polymer coatings, for example, polyacrylates or organic plasma polymers obtained from organosilicones, hydrocarbons or acrylates.

[0063] The barrier coating layer suitably has a thickness of 10 nm to 10 μm, preferably 60 nm to 5 μm and more preferably 100 nm to 2 μm.

[0064] In a particular embodiment, the coating layer may alternate in composition, in a modulated manner, with, for example, inorganic and organic zones.

[0065] The composite sheet comprising the support film and the barrier layer should be transparent to light and suitably will have a transparency greater than 65% and preferably greater than 85%, measured according to ASTM D

1746-97.

[0066] The barrier coating layer which forms the barrier to oxygen and water vapor should suitably display an oxygen transmission rate lower then 1 cm³/(m²day-atm), and preferably lower than 0.01 cm³/(m²day-atm) and more preferably lower than 0.005 cm /(m day-atm) measured according to ASTM F

1927 or D 3958; and a water vapor transmission rate (WVTR) lower than 0.01 g/(m day-atm), preferably lower than 0.005 g/(m day-atm) and more preferably lower than 0.001 g/(m²day-atm) as measured according to ASTM F 1249. iv) Method of producing Composite Sheet [0067] The method of producing the composite sheet essentially involves coating the organic polymer film, as described hereinbefore, with a coating layer, as described hereinbefore. [0068] The barrier coating layer may be applied by various coating techniques, but preferably by physical vapor deposition (PVD), for example, evaporation or sputtering or by chemical vapor deposition (CVD), for example, plasma enhanced chemical vapor deposition (PECVD) or organic vapor phase deposition (OVPD). These methods are capable of producing very thin coatings, which are stable and flexible but of satisfactory hardness, and which exhibit low oxygen and water vapor permeations. PVD and PECVD are carried out under partial vacuum.

[0069] The coating technique is modified, in accordance with the invention and as described herein, so that the formed barrier coating layer exhibits a modulated property across its thickness. v) Applications of Composite Sheet [0070] In one embodiment the composite sheet forms the front, transparent support of an OLED device, the diodes of the device being encapsulated on the other side by a suitable non-transparent barrier covering, also impermeable to oxygen and water vapor, thus providing the OLED device having one-side light emission. A suitable non-transparent barrier covering material may be of a metal can, plate, foil or an evaporated film, as is well known in the OLED art. [0071] In another embodiment the composite sheet forms the front, transparent background of an OLED device, and the barrier covering on the other side is also formed of a transparent support substrate of the invention, thus providing an OLED device that is transparent and emits light on both sides. A composite sheet according to the invention thus encapsulates the diodes both as the front support and as the rear barrier covering, together forming a barrier envelope. [0072] In still another embodiment, the composite sheet of the invention forms the barrier covering and the front support of the OLED device is of another material, for example, glass, as known in the OLED art.

[0073] In still another embodiment, an OLED device is supported on a plastic barrier support and a barrier layer of the invention is deposited on the

OLED device, whereby the OLED device is thin film encapsulated.

[0074] In yet another embodiment, an OLED device is supported on a glass support, and a barrier layer of the invention is deposited on the OLED device.

[0075] The composite sheet according to the invention may be used also in other types of devices, such as liquid crystal displays or in organic photovoltaic devices, which are known in the prior art to require transparent materials impermeable to oxygen and water vapor. vi) Manufacture of OLED [0076] The OLED is suitably formed under vacuum conditions to minimize introduction of contaminants which may chemically or physically damage the OLED or alter its characteristics. Small molecule diode components, sensitive to oxygen and water molecules, are deposited onto the support substrate by vacuum evaporation. One particular type of organic light emitting diode, namely, polymeric light emitting diodes (PLED) may, for example, be deposited onto the composite sheet, for example, from a solution in a suitable organic solvent in an inert atmosphere. The composite sheet is produced as outlined hereinbefore. Thereafter, in a vacuum process a transparent conductive layer, for example, indium-tin oxide, is deposited on the composite sheet. [0077] The transparent conductive layer is patterned to form the lower electrode of the diode, which is the hole-injecting layer. On the hole-injecting layer there is deposited, successively, the hole-transporting layer and the electron-transporting layer, both of which are organic layers, and thereafter the electron- injecting layer which forms the upper electrode, and which may be, for example, of calcium, lithium, magnesium or aluminium, or suitable metal alloys. [0078] The afore-mentioned layers may be deposited by vacuum evaporation, well known in the OLED art.

[0079] Instead of vacuum evaporation, the organic layers and the upper electrode may also be deposited by printing, for example, ink jet printing, stamping or other transfer techniques in an inert atmosphere, as well known in the PLED art. vii) Advantages [0080] Advantages of the invention are related to (i) the mechanical properties of the coatings and to (ii) the permeation mechanism of gases and vapors through these ultra-high permeation barrier-coatings. [0081] Single- and multilayer coatings described in the prior art, possess abrupt interfaces between the substrate and the coating, and between successive component layers. On a microscopic scale, this results in stress accumulation at the interfaces which, beside dust particles, is the main source of coating defects during handling and processing of the substrate. Using defect detection methods described in the literature [1], it can be shown that even small tensile stress applied to barrier-coated plastic films may produce new pinholes or cracks in the coating. This occurs during film stretching, at a much lower level than the moderate tensile stress required to initiate the first cracks in the coating. i) Mechanical Properties [0082] Plastic substrates for OLEDs are typically thicker than 100 μm and the encapsulated flexible OLED devices are typically thicker than 200 μm; therefore, their exposure to excessive tensile deformation during a production process, although possible, is rather unlikely. On the other hand, bending and flexing of these substrate films and of the encapsulated flexible devices occurs frequently during processing, handling, and in final use. This may even be an integral part of the display manufacturing process, for example, during roll-to- roll processing. Bending and flexing of these relatively thick substrates and devices will expose their outer surface to tensile deformation, which may create defects in the coating. Coatings with modulated properties in accordance with the invention, on the other hand, are free from abrupt interfaces and thus also from potential stress-accumulation zones. Therefore, they display a much lower tendency towards creating defects during bending and flexing than do multilayer or single layer coatings with abrupt interfaces. ii) Permeation Mechanism [0083] The typical dependence of gas and vapor transmission rates versus coating thickness is shown schematically in Fig. 1. Below the so-called critical thickness, d_c, the coating displays no barrier effect at all. At d=d_c, permeation drops by several Orders of magnitude and then decreases more slowly with increasing d values. For still greater d, at the so-called inflection point, transmission rates increase due to defect creation in the coating, which becomes too thick, stressed, and excessively fragile. Barrier-coatings with modulated properties provide not only very high barrier improvement factors, BIF, but also extend the inflection point to higher values of the total coating thickness, d. This, in turn, allows one to deposit and to safely use coatings of greater total thickness, which possess very low defect number density, good flexibility and improved stretchability. Barrier coatings with modulated properties are therefore very useful in preventing oxygen and moisture ingress into flexible organic electronic devices. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS WITH REFERENCE TO THE DRAWINGS

[0084] The drawings are further described hereinafter:

[0085] Fig. 1 shows dependence of oxygen transmission rate, OTR in [cm

(STP)/ cm s cm Hg], through the silica-coated PET film (13 μm) on the coating thickness, d, in [nm]; A indicates inflection point.

[0086] Fig. 2 shows a support substrate for organic electronics (100) comprising a flexible film (20) and a barrier coating (10) thereon with modulated properties.

[0087] Fig. 3 shows a support substrate for organic electronics (100) consisting of a composite flexible film (20) comprising film layers (21 and 22), and a barrier coating (10) thereon with modulated properties.

[0088] Fig. 4 shows a support substrate for organic electronics (100) comprising a flexible film (20), a barrier coating thereon with modulated properties (10) and a surface layer (60).

[0089] Fig. 5 shows an OLED device (200) on a flexible film substrate

(20), which comprises a coating with modulated properties (10) enclosed using an encapsulating means (40) which, in turn, also comprises the coating with modulated properties (410). The coating is deposited onto a flexible film (420) and attached to the OLED layer (50) using a resin layer (460). The OLED components include bottom conductive layer (ITO or/and TFT-silicon) (52), hole transporting layer (54), electron transporting layer (56), and top electrode (58).

[0090] Fig. 6 shows an OLED device (200) on a flexible film substrate

(20) comprising the coating with modulated properties (10) enclosed using a thin-film encapsulating means (40).

[0091] Fig. 7 shows an encapsulation (40) and glass (30) based OLED device (200) comprising a coating with modulated properties (410); a) thin film encapsulation, where the coating with modulated properties (410) is deposited onto a passivation layer (440), which, in turn, is in contact with OLED components (50). The latter include bottom conductive layer (ITO or/and TFT- silicon) (52), hole transporting layer (54), electron transporting layer (56), and top electrode (58); b) thin film encapsulation, where the coating with modulated properties (410), which is deposited onto a passivation layer (440) is additionally protected by a polymer layer (420); c) thin film encapsulation consisting of the coating with modulated properties (410).

[0092] Fig. 8 shows an OLED device (200) on a flexible substrate (100) comprising a barrier-coating with modulated properties (10) therein, and enclosed using an encapsulating mean (40) which comprises the coating with modulated properties (410). a) thin film encapsulation, where the barrier-coating with modulated properties (410) is deposited onto a passivation layer (440), which, in turn, is in contact with OLED components (50). The latter include bottom conductive layer (ITO or/and TFT-silicon) (52), hole transporting layer (54), electron transporting layer (56), and top electrode (58); b) thin film encapsulation, where the coating with modulated properties (410), which is deposited onto a passivation layer (440) is additionally protected by a polymer layer (420); c) thin film encapsulation using the coating with modulated properties (410).

[0093] Fig. 9' shows an OLED device (200) on a flexible substrate (100), which comprises the flexible film (20) and the coating with modulated properties (10). The OLED device is enclosed using an encapsulating means (40), which also comprises the coating with modulated properties (410). The coating is deposited onto a flexible film (420) and attached to the OLED layer using an intermediate layer (460). EXAMPLES Example 1

[0094] A coupon of optical grade polyester film (PET) was placed into a

PECVD vacuum chamber, directly onto the powered electrode. The chamber was evacuated and deposition of silica (SiO₂)- like coating was performed in an RF plasma discharge (13.56 MHz, 80 W) using a mixmre of hexamethyldisiloxane (HMDSO)/ O₂/Ar at an approximate molar ratio of 1 :8:3, respectively. During the deposition, oxygen flow was smoothly modulated manually from a high content (1 :8:3) to a low content (1 :0:3), then back again to a high content. After 5 minutes, during which the concentration of oxygen in the chamber was changed twice, HMDSO flow was terminated, thus causing a gradual decrease in the concentration of silicon source gas in the plasma. The sample, across its entire thickness, was then composed of the PET substrate in contact with silica, which gradually changed to plasma-polymerized HMDSO, then gradually changing back to silica, which was finally modified at the surface by the final exposure to oxygen/argon plasma. The sample had a hydrophilic surface, displaying a low water contact angle (<10°). Example 2

[0095] A coupon of optical grade PET film substrate was placed in a

PECVD vacuum chamber, directly onto the powered electrode. The chamber was evacuated and deposition of a silica coating was performed in an RF plasma discharge (13.56 MHz, 80 W) using a mixture of HMDSO/ O₂/Ar at an approximate molar ratio of 1 :8:3, respectively. During the deposition, the oxygen flow was manually modulated from a high content (1 :8:3) to a low content (1 :0:3), and back again to a high content. After 5 minutes, during which the concentration of oxygen in the chamber was changed twice, oxygen flow was stopped, this time causing a gradual decrease in the concentration of oxidizing gas in the plasma. Across its entire thickness, the sample was then composed of the PET substrate in contact with silica, which then gradually changed to plasma- polymerized HMDSO, then gradually changed back to silica, which again gradually changed to plasma-polymerized HMDSO. The sample had a highly hydrophobic surface, displaying a high water contact angle (>70°). Example 3

[0096] A coupon of optical grade PET film substrate was placed in the

PECVD vacuum chamber, directly onto the powered electrode. The chamber was evacuated and deposition of a silica coating was performed in an RF plasma discharge (13.56 MHz, 150 - 10 W) using a mixture of HMDSO/O₂ /He at an approximate molar ratio of 1 :5:3, respectively. During the deposition, the discharge power was gradually decreased from 150 W to 10 W, then gradually increased from 10 W to 150 W. This procedure was repeated three times, so that the coating was deposited during oscillating changes of power fed to the plasma. The intensities of optical emission lines characteristic for SiH^1" and O^* were used to control the process. The sample, across its entire thickness, was then composed of the PET substrate, in contact with highly densified silica, which gradually changed to silica of lower densification degree, which then gradually changed back to high-density silica, etc.

[0097] The samples produced in this experiment, described above, displayed values of oxygen- and water permeation rates, OTR < 0.005 cm /m day and WVTR< 0.005 g/m day, which were lower than the sensitivity limits of the measuring apparatus (so-called MOCON systems), according to standard permeation test procedures: ASTM D3985 and F1927 and ASTM F1249, respectively. Example 4

[0098] A coupon of optical grade, hard-coated polyarylate (substrate film) was placed in the PECVD vacuum chamber, directly onto the powered electrode. The chamber was evacuated and deposition of a silica coating was performed in an RF plasma discharge (13.56 MHz, 350 - 5 W) using a mixture of HMDSO/O /He at an approximate molar ratio of 1:5:3, respectively. During the deposition, the negative DC self-bias voltage was gradually changed from -600 V to -50 V, and then gradually from -50 V to -600 V. This was achieved simply by varying the discharge power. The procedure was repeated three times, so that the coating was deposited during oscillating changes of the self-bias voltage at the substrate, thus it was exposed to controlled, varying ion bombardment of slowly oscillating intensity. The sample, across its entire thickness, was then composed of the PET substrate, the interphase between the substrate and the silica coating, and high- density silica, which gradually changed to silica of lower density, then changing back to high-density silica, etc. The samples produced in this experiment, described above, displayed values of oxygen- and water permeation rates, OTR < 0.005 cm³/m²day and WVTR< 0.005 g/m²day, which were lower than the sensitivity limits of the measuring apparatus (so-called MOCON systems), according to standard permeation test procedures: ASTM D3985 and F1927 and ASTM F1249, respectively.

[0099] The presence of an extended "interphase" region is characteristic to

PECVD coatings deposited on plastic substrates at high values of self-bias voltage. However, the presence of this interphase between the substrate and the coating is also observed for the case of PECVD coatings deposited under constant plasma parameters, and it does not depend on gradual or oscillating changes of the bias voltage, power or gas flow. Example 5

[0100] A coupon of optical grade, hard-coated polyester substrate film was placed in the PECVD vacuum chamber, onto the powered electrode. The chamber was evacuated and deposition of a silica coating was performed in an RF plasma discharge (13.56 MHz, 350 - 5 W) using a mixture of HMDSO/O₂He at an approximate molar ratio of 1 :5:3, respectively. During the deposition, the negative DC self-bias voltage was varied sinusoidally between -600 V and - 50 V. This was achieved by controlling the discharge power, using an external function generator operating at 1 Hz. The process was continued for 3 minutes, so that the coating was deposited during rapid profiled changes of the self-bias voltage at the substrate thus being exposed to ion bombardment of (1Hz) oscillating intensity. The sample, across its entire thickness, was then composed of the PET substrate / the interphase region between the substrate and the silica coating comprising high-density silica, which then gradually changed to silica of lower density, then back again to high-density silica, etc. The plasma process used in this experiment is not equivalent to so-called "pulsed plasma", which consists of sequential ON and OFF phases of discharge plasma. [0101] The samples produced in this experiment, described above, displayed values of oxygen- and water permeation rates, OTR < 0.005 cm /m day and WVTR< 0.005 g/m day), which were lower than the sensitivity limits of the measuring apparatus (so-called MOCON systems), according to standard permeation test procedures: ASTM D3985 and F1927 and ASTM F1249, respectively.

Reference(s)

(1) G. Czeremuszkin et al, Ecole Polytechnique, Canada

43rd Annual Technical Conference Proceedings, SVC, Denver, April 15-20, 2000, p.408.

(2) G. Czeremuszkin et al, Ecole Polytechnique, Canada

42nd Annual Technical Conference Proceedings, SVC, Chicago, April 17-22, 1999, p.176.

(3) A.S. da Silva Sobrinho et al, Ecole Polytechnique, Canada

42nd Annual Technical Conference Proceedings, SVC, Chicago, April 17-22, 1999, p.396.

Claims

CLAIMS:

1. A barrier layer as a barrier to permeation of gases and vapor, the barrier layer exhibiting a modulated property across its thickness such that the layer is free from abrupt interfacial variation in said property across its thickness.

2. A barrier layer according to claim 1, wherein said property has multiple gradual or oscillating changes across said thickness, said changes being spatially continuous.

3. A barrier layer according to claim 1 or 2, wherein said property includes at least one physical, chemical or structural parameter selected from composition, chemical structure, morphology, density, nanoporosity, solubility and diffusivity towards small inorganic and organic molecules, electrical conductivity, real and imaginary parts of the dielectric permitivity, polarizability, free energy, free volume, crystallinity, degree of crosslinking, viscosity, Young modulus, hydrophobicity, hydrophilicity, electron affinity, rigidity, and chemical reactivity toward oxygen and water molecules.

4. A composite sheet for an organic electronic device comprising: i) an organic polymer support film, and ii) a barrier layer according to claim 1, 2 or 3, supported on said support film.

5. A sheet according to claim 4 wherein said film has a thickness of 5 μm to 1000 μm and said barrier layer has a thickness of 10 nm to 10 μm.

6. A sheet according to claim 5 wherein said film has a thickness of 25 μm to 500 μm.

7. A sheet according to claim 5 or 6 wherein said barrier layer has a thickness of 60 nm to 5 μm.

8. A sheet according to claim 5 or 6 wherein said barrier layer has a thickness of 100 nm to 2 μm.

9. A sheet according to any one of claims 4 to 8 wherein said barrier layer is formed from a member selected from the group consisting of SiO_x, SiO_xC_y, Si_xN_y, Si_xN_yC_z, SiO_xN_y, TiO_x, Al_xO_y, SnO_y, indium-tin oxide, magnesium fluoride, magnesium oxyfluoride, calcium fluoride, tantalum oxide, yttrium oxide, zirconium oxide, barium oxide, magnesium oxide, titanium oxide, niobium oxide, hafnium oxide, and mixmres thereof, wherein x is from 1 to 3, y is 0.01 to 5, and z is 0.01 to 5.

10. A sheeting according to any one of claims 4 to 8 wherein said barrier layer is plasma deposited stoichiometric or non-stoichiometric silicon oxide, silicon nitride or silicon oxynitride.

11. A sheet according to any one of claims 4 to 8 wherein said barrier layer is a polyacrylate coating or an organic plasma deposited organic polymer obtained from organisilicones, hydrocarbons or acrylates.

12. A sheet according to any one of claims 4 to 1 1 having a transparency greater than 65% measured according to ASTM D 1746-97; and said barrier layer displays an oxygen transmission rate lower than 1 cm /(m day- atm) measured according to ASTM F 1927 or D 3950; and a water vapor transmission rate (WVTR) lower than 0.01 g/cm day-atm) as measured according to ASTM F 1249.

13. A sheet according to any one of claims 4 to 12 wherein said film is of a high Tg polymer selected from the group consisting of cyclopolyolefins, polyethersulfones, polyarylates, polyethyleneterephthalate and polyethylenenaphthalate.

14. A method of producing a barrier layer as defined in claim 1, 2 or 3, comprising: vapor depositing on a support surface to form a coating layer on said support surface, and changing at least one characteristic of the vapor deposition in a controlled manner effective to produce said modulated property in said coating layer.

15. A method according to claim 14, wherein said support surface is defined by an organic polymer support film, and recovering a composite of said film and said coating layer.

16. In an organic electronic device in which light emitting diodes are encased in a barrier envelope comprising a substrate supporting said diodes and a barrier covering, said substrate and covering being impermeable to oxygen and water vapor, the improvement wherein at least one of said substrate and covering comprises a composite sheet, as defined in any one of claims 4 to 13.

17. In a method of manufacturing an organic electronic device in which light emitting organic diodes are encased in a barrier envelope comprising a substrate supporting said diodes and a barrier covering, said substrate and covering being impermeable to oxygen and water vapor, the improvement wherein at least one of said substrate and covering comprises a composite sheet, as defined in any one of claims 4 to 13.

18. A method of producing a transparent support substrate and of producing an encapsulating envelope for use in organic electronic devices such as OLED, photovoltaic, liquid crystal and electrophoretic displays, involving: i) exposing a transparent polymer film to a vacuum process, and ii) coating the polymer film surface with a coating layer having modulated properties, using a physical vapor deposition (PVD) or a plasma enhanced chemical vapor deposition (PECVD) process, or a combination thereof, where modulated properties of the coating result from continuously and repetitively changing, in a controlled manner, at least one of the characteristics of the deposition process.

19. A method according to claim 18 wherein said vacuum process comprises at least one of a low temperature electric discharge plasma, and a vacuum annealing at elevated temperature.

20. A method according to claim 18 or 19, wherein the characteristics of the deposition process, with resulting modulated coating properties, are modified by continuously, repetitively, and controUably changing at least one of the following process parameters: power delivered to the deposition zone, contribution of power delivered from independent power sources to the deposition zone, external electrical bias voltage, local gas flow and pressure in the deposition zone, reactive gas flow rate and composition, inert gas flow rate and composition, supplying additional UV, vacuum UV (VUV) or infrared radiation, substrate positioning in the deposition zone, substrate movement, web speed, geometry of applied electromagnetic, magnetic and electric fields, intensity and frequency of electromagnetic, magnetic and electric fields and temperature.

21. In an organic electronic device in which a photovoltaic device is encased in a barrier envelope comprising a substrate supporting said photovoltaic device and a barrier covering, said substrate and covering being impermeable to oxygen and water vapor, the improvement wherein at least one of said substrate and covering comprises a composite sheet, as defined in any one of claims 4 to 13.

22. In a method of manufacturing an organic electronic device in which a photovoltaic device is encased in a barrier envelope comprising a substrate supporting said photovoltaic device and a barrier covering, said substrate and covering being impermeable to oxygen and water vapor, the improvement wherein at least one of said substrate and covering comprises a composite sheet, as defined in any one of claims 4 to 13.