WO2017153747A1

WO2017153747A1 - Barrier coated substrates

Info

Publication number: WO2017153747A1
Application number: PCT/GB2017/050617
Authority: WO
Inventors: Ian Burnett; Chris Walker
Original assignee: Flexible Barrier Films Limited
Priority date: 2016-03-08
Filing date: 2017-03-08
Publication date: 2017-09-14
Also published as: GB201603950D0; GB2550999B; GB2550999A; GB201703724D0

Abstract

A method for forming a composite barrier layer on a substrate to protect against moisture and gas permeation, the method comprising forming onsaid substrate a composite barrier layer comprising: (i) a polymeric sublayer formed by atmospheric pressure plasma enhanced chemical vapour deposition; and (ii) an inorganic sublayer formed by atmospheric pressure spatial atomic layer deposition. Also described area substrate having such a composite barrier layer formed thereon together with an OLED opto-electronic device comprising such a substrate.

Description

BARRIER COATED SUBSTRATES

FIELD OF THE INVENTION

The present invention relates generally to the coating of substrates, in particular to the production of substrates which are resistant to atmospheric degradation, as we11 as to coated articles obtained thereby.

More particularly, the present invention relates to the

preparation of a substrate having a composite barrier layer protecting against moisture and gas permeation formed thereon which is suitable for use as a substrate in an opto-electronic device, in particular an organic light emitting display (OLED) device or a organic photo voltaic (OPV) device.

BACKGROUND OF THE INVENTION

Organic light emitting display (OLED) devices typically comprise a substrate upon which is deposited an electroluminescent emissive layer of organic material situated between electrodes, the electroluminescent organic material emitting light when an electric current is passed between the conductive elements.

Organic materials commonly used in OLED devices include non- polymeric small molecule organic materials (such as

organometallic chelates and fluorescent and phosphorescent dyes) and polymeric light emitting organic materials (such as

conjugated conductive polymers such as polyfluorenes and poly(p- phenylene vinylenes) . Substrates typically comprise glass or quartz although flexible plastics substrates such as

polyethylene terephthalate (PET) are finding increasing favour due to their lighter weight and improved flexibility.

Due to their high efficiency, vibrancy colour and low power consumption compared to liquid crystal plays (LCDs ) , electroluminescent display devices such as OLEDs are becoming increasingly important and are found in a variety of commercial applications including displays for mobile telephones and television screens, calculators and medical instrumentation.

The growth of interest in wearable technology has led to an increasing emphasis on the development of flexible OLED devices The development of flexible OLED devices in a cost-effective manner suitable for large scale manufacture has, however, prove to be less than straightforward; commonly used substrates such as glass and quartz provide smooth, flat surfaces of desired optical clarity which are resistant to gas and moisture

permeation but such substrates exhibit undesirable mechanical properties such as poor flexibility and resistance to damage, rendering them unsuitable as substrates for flexible devices .

Plastic substrates, although lighter and more flexible than glass substrates and more resistant to damage, offer little resistance to atmospheric factors such as moisture and

oxidation. Exposure to water and atmospheric gases adversely affects the effectiveness of the components of the OLED device, such as the electrodes, as well as degrading the light-emitting polymer, rendering the lifetime of an OLED structure deposited on a plastic substrates significantly shorter than that on a glass substrates .

Various approaches to the problem of protecting OLED substrates from atmospheric degradation have been investigated and reported upon in the literature .

One approach, involving the formation of barrier layers on plastic or glass substrates by the technique of atomic layer deposition (ALD) under vacuum conditions, is described in EP 1629543B. Suitable barrier materials which are disclosed include oxides and nitrides of Groups IVB, VB, VIB, IIA and IV of the Periodic Table and combinations thereof, such as Si0₂, A1₂0₃ and Si₃N₄.

Although this technique provides thin coatings of barrier materials, which is an important consideration in the case of flexible devices utilising plastics substrates as this helps maintain the flexibility of the plastic substrate and its optical transparency, a disadvantage is that grain boundaries present in the coating are a route for permeation of both water vapour and oxygen.

Furthermore, dust particles are overcoated with this layer and so pinholes develop in the barrier layer which cause failure when the OLED is fabricated. The ALD method can also generate particles during pump down to low pressure and also from chemical interactions with the chamber, which particles can become incorporated into the coating causing pinhole defects . Vacuum conditions are necessary to ensure clean conditions for film growth and to minimise contamination that can result in film porosity and barrier breakdown.

The coating of surfaces to form oil or water repellent surfaces using monomeric unsaturated organic compounds, such as

unsaturated halocarbons, by polymerisation on the surface using a plasma deposition process is described in EP 0988412B.

Electrical or electronic devices which have been treated to protect them from liquid damage by applying a polymeric coating under pulsed plasma conditions are described in GB 2434369B.

Methods involving the formation of multiple barrier layers have also been proposed. These, however, tend to involve complex, expensive processing steps which are not readily scaled up to large scale manufacture.

One such method, described in US 6198217B , involves covering an electroluminescent unit with a protective barrier layer comprising an organic barrier layer and an inorganic barrier layer. In this method, the organic layer is applied by spin coating, casting or vacuum deposition and the inorganic barrier layer by a vapour phase technique such as vacuum deposition or sputtering. Suitable organic barrier layers disclosed include photocurable monomers or oligomers and thermoplastic resins; typical inorganic barrier layer materials include oxides, nitrides and metals.

OLED devices provided with a composite barrier layer comprising an alternating series of one or more polymeric planarizing sublayers and one or more high density sublayers (such as metal oxides, metal nitrides, metal carbides and metal oxynitrides) with at least one of the polymeric planarizing sublayers having microparticles incorporated therein are described in US

7012363B. It is disclosed that the polymeric layer with microparticles incorporated may be applied to the substrate using any conventional polymer coating method such as spin coating, sputter deposition, flash evaporation, chemical vapour deposition or polymerisation or curing of a monmomer layer. Sub layers of high density materials are suitably applied using techniques including thermal evaporation, sputtering, plasma- enhanced chemical vapour deposition (PECVD) and electron beam techniques .

Barrier stacks for encapsulating OLEDS comprising at least one polymer layer and at least one barrier layer are described in I 1524709A. Preferably, the polymer layer is an acrylate- containing polymer and the barrier layer a material selected from metal oxides, metal nitrides, metal carbides, metal oxynitrides and combinations thereof. The preparation of the barrier stacks by vacuum deposition methods is preferred and although it is mentioned that the polymer layers in the stack can also be deposited using atmospheric processes such as spin coating and/or spraying, these are very thick layers which degrade optical transparency. Encapsulating layers for OLED devices comprising one or more component layers deposited by atomic layer deposition under vacuum are described in US 2006/0250084A. Encapsulating layers comprising component layers of an organic material and an inorganic material are disclosed. The inorganic material is preferably deposited by atomic layer deposition but the organic materials may be deposited by other conventional coating techniques .

There remains, however, a continuing need for a method for preparing coated substrates suitable for use in OLED devices, particularly flexible substrates, which not only provides a highly effective , ultra-thin and high optical transparency barrier against permeation of moisture and gas but which is cost-effective and can be readily scaled up for commercial manufacture. Cost of manufacture represents a significant barrier for consumer items and methods for preparing coated substrates which reduce the costs involved are of particular commercial interest.

SUMMARY OF THE INVENTION

The present invention is concerned with the preparation of composite barrier layer coated substrates, in particular flexible substrates for use in OLED devices, for providing protection from moisture and gas permeation.

According to a first aspect, the present invention provides a method for forming a composite barrier layer on a substrate to protect against moisture and gas permeation, the method comprising forming on said substrate a composite barrier layer comprising :

(i)a polymeric sublayer formed by atmospheric pressure plasma enhanced chemical vapour deposition; and (ii) an inorganic sublayer formed by atmospheric pressure spatial atomic layer deposition.

In another aspect, the invention provides a substrate having a composite barrier layer formed thereon according to the first aspect of the invention.

In further aspects, the invention also provides an optoelectronic device comprising a substrate prepared according to the first aspect of the invention as well as a method for preparing such an opto-electronic device.

By means of the present invention, very thin composite barrier layers may be prepared which retain flexibility and high optical transmittance and transparency. Such barrier layers may suitably be applied to both sides of an OLED display without adversely affecting its transmittance properties and also, for example, on the front, viewing side of displays where the optical

transmittance determines the brightness and contrast of the display .

Forming the composite barrier layer under atmospheric conditions is advantageous as it obviates the need for expensive vacuum pump and measurement/control equipment. Also, as a consequence, the chambers within which the process is carried out do not need to constructed from materials, such as stainless steel, which can withstand a vacuum, as there is no pressure difference between the process chamber and the outside environment. This enables very significant costs reduction in the processing equipment to around 10% of the vacuum based equivalent, but also cycle times are much shorter as there are no delays waiting for chambers to pump out or vent to atmosphere at the end of the process . BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows schematically a roll to roll apparatus for preparing a composite barrier layer coated substrate according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention describes composite barrier layers formed on a substrate and useful for preventing permeation of moisture and atmospheric gases. As the barrier layer formed is very thin, it does not adversely impact the optical transmission of the substrate .

As used herein, a layer may be a planar sheet or coating formed on at least part of one or more surfaces of a substrate, but it may also be bent or folded to either partially or completely encapsulate the substrate . substrate for use according to any aspect of the invention may rigid or flexible.

In one embodiment, the substrate may be any substrate

conventionally used in opto-electronic devices, as described, for example , by MacDonald et al , Journal of the SID 15/12, 1075-1083 (2007) .

It will be appreciated that depending on the intended use, the substrate may be opaque or transparent .

Suitable rigid substrates include glass, silicon and metals such as aluminium, nickel and indium.

Suitable flexible substrates include polymers such as

polyesters, polyether sulphones and polyimides . Polymers are particularly preferred for use as substrates for flexible OLED devices. In one embodiment of the invention, the substrate comprises a flexible polyester polymer material, preferably poly ( ethylene terephthalate ) (PET) or poly ( ethylene naphthalate (PEN), which materials are commercially available.

The polymeric material of the composite barrier according to the invention may be formed by polymerisation of any monomer capable of undergoing plasma polymerisation to form a polymeric coating layer with moisture or gas permeation protecting properties .

Suitable monomers known in the art include unsaturated organic compounds optionally containing halogen atoms and preferably containing at least one double bond as described in EP 0988412B. The unsaturated moiety may optionally be substituted, directly or via a group such as an ester or sulphonamide, with an alkyl chain which may be optionally substituted by one or more halogen atoms .

In one embodiment, the plasma used to form the polymeric sublayer according to the invention comprises as monomer unsaturated haloalkyl containing compound.

In one particular embodiment, the monomer comprises an acrylate compound of formula

CH₂=CR¹C (0)0 (CH₂) _nR² where n is an integer from 1 to 10, R¹ is hydrogen or Ci_₆alkyl and R² is an alkyl or haloalkyl group.

Particular examples of monomers for use according to the invention include IH, IH, 2H, 2H-heptadecafluorodecyl acrylate, IH, IH, 2H, 2H-perfluorododecyl acrylate .

Other monomers known in the art to undergo plasma polymerisation to produce hydrophobic polymeric coatings are described in GB2477022A and include saturated organic compounds having an optionally substituted alkyl chain of at least 5 carbon atoms which may be interposed with a heteroatom, optionally

substituted alkynes, polyether substituted alkenes and

macrocycles containing at least one heteroatom. These monomers may suitably be used in the present invention to form the polymeric material of the barrier layer.

In another embodiment, a mixture of monomers may be used according to the invention to form a copolymer. Suitable copolymers include copolymers of the monomers described above with diethylene glycol dimethyl ether (DEGDME)

Plasma enhanced chemical vapour deposition is a well-known technique for depositing polymeric coatings on a variety of surfaces, as described in EP 0988412B, mentioned above.

It will be appreciated that the precise conditions under which the plasma polymerisation process is conducted will depend on factors such as the choice of polymer and substrate to be treated, the choice of conditions being routinely determinable by the average skilled person in the art based on the known methods .

The method of plasma enhanced chemical vapour deposition involves generating plasma from the organic compounds which are subjected to an electrical field. In the presence of a

substrate, radicals and molecules of the organic compound polymerise on the substrate.

Formation of the polymeric coating may be obtained using either pulsed or continuous wave plasma deposition. Suitable plasma fo: use according to the invention may be generated by

radiofrequency, microwave or direct current. Atmospheric pressure conditions are preferred as these afford reduced costs in terms of chamber hardware and avoid the need for vacuum apparatus as well as affording reduced cycle times due to elimination of the pumpdown and vent cycles .

Gaseous plasma may suitably be generated in a plasma generating chamber. Any plasma generating chamber conventional in the art may be used such as the plasma chamber described in EP 1729894B. The chamber may be sealed for batch processing or may be adapted to allow the substrate to pass through the chamber in a

continuous process.

Typically, the substrate to be coated and monomer in gaseous state are placed in the plasma chamber, a glow discharge is ignited in the chamber and a suitable voltage is applied. In a particular embodiment, the monomer in gaseous form flows through the chamber and the plasma is ignited as the substrate is passed through the system in a roll to roll system.

In one embodiment of the invention, the monomer in gaseous form is combined with a carrier gas, particularly an inert carrier gas such as nitrogen, helium or argon. Conveniently, in a preliminary step the monomer is heated to a temperature of up to 100°C, suitably a temperature in the range 30-40°C

The relative amounts of monomer vapour to carrier gas will depend on such factors as the specific monomer used and the size of the plasma chamber, as would be well understood by the average skilled person in the art.

Typically, for use according to the present invention, the monomer is delivered at a rate of from 100 to 700mg/minute, for example a rate of from 100-150 mg/minute. The carrier gas, for example nitrogen, is conveniently supplied at a constant rate of from 50-250 standard cubic centimetre per minute (seem) , typically 100 seem. It will be appreciated that the ratio of monomer gas to carrier gas will be selected to achieve the desired flow rate. The glow discharge is generally ignited by applying a voltage, typically using electrodes. In a particular embodiment

according to the present invention, an excitation frequency in the low frequency range, typically 100kHz or less, for example 50 kHz, may be employed. Plasma generated in the frequency range of 1-lOOkHz cause an appropriate fragmentation of the monomer to form a polymer which has very high permeation resistance to water vapour and oxygen and 50kHz gives a peak density of the fragment in the plasma when operated in continuous wave mode

In one embodiment, the plasma is generated with a voltage as a continuous field at an average power of less than 1 w/m² of substrate area.

Typically, the polymer layer has a thickness of between 5 and 20 nm, preferably up to 10 nm although it will be appreciated that a thicker polymer layer may be appropriate to accommodate rough substrate surfaces. A layer of thickness in the order of 50-200 nm may be appropriate, for example, where the back side (non- viewable side) of an OLED device is being encapsulated and the surface has topography associated with the circuits. The front side, or both sides on a both sides viewable display need thinner (of the order of 5-20 nm thickness) polymer layers to retain high optical transparency.

In a particular embodiment according to the invention,

polymerisation is effected at atmospheric pressure and the growth rate can be highly controlled to produce reliable and repeatable very thin layers, suitably up to 10 nm thick, particularly from 1 to 5 nm thick.

The inorganic sublayer of the composite barrier layer according to the invention suitably comprises any inorganic material which exhibits low moisture and gas permability. In one embodiment, the inorganic material is preferably transparent. Conveniently, the inorganic material comprises a metal oxide, a metal nitride, or a metal oxynitride and combinations thereof.

Suitably, the metal oxide is an oxide of silicon, aluminium, titanium, magnesium, tantalum, indium, tin and combinations thereof. Suitable metal nitrides for use according to the invention include aluminium nitride and silicon nitride or combinations thereof. A metal carbide is suitably silicon carbide. A metal oxynitride is suitably silicon oxynitride.

In one embodiment, the inorganic sublayer of the composite barrier layer according to the invention comprises a metal oxide and combinations thereof. In one particular embodiment, the inorganic sublayer comprises aluminium oxide, A1₂0₃.

Atomic layer deposition (ALD) is a technique for depositing thin (approximately 0.1 nm) films on surfaces which affords improved control over the thickness of the deposited film and the uniformity of the coating and can be carried out at lower temperatures compared to other known chemical vapour deposition (CVD) film deposition techniques. Methods and apparatus for atomic layer deposition of thin film materials onto a substrate are well-known in the art and are described, for example, in Suntola, Thin Solid Films, vol 216, p84-49 (1992)

ALD technology involves the formation of a film atomic layer by atomic layer. In conventional ALD (also known as temporal ALD), a substrate is functionalised by exposure to a surface- conditioning precursor and then exposed to a first reactive film precursor in a vacuum chamber, forming a precursor monolayer on the substrate. Typically, excess precursor is then purged by evacuation and then a second precursor, which reacts with the absorbed precursor to form a monolayer of the desired material, is introduced into the chamber. Reaction by-products and excess precursor are then purged. By repeating this deposition cycle a number of times, a layer of desired thickness can be formed on the substrate one molecular layer at a time.

In contrast to chemical vapour deposition, the single atomic layer deposition steps of ALD avoids the formation of columnar structures in the deposited layer through which moisture and gas can easily permate. ALD therefore provides very thin films with low moisture and gas permeability.

Although conventional ALD has found widespread use in thin film deposition, it suffers from the disadvantages that it is a slow technique and that it involves operation under vacuum, meaning that it cannot readily be scaled up for commercial use.

An improved ALD process, known as Spatial Atmospheric Atomic Layer Deposition (SAALD) , which is faster than conventional ALD and avoids the need for a vacuum has been developed in recent years (see Munoz-Rojas et al, Materials Horizons, 2014, 1, 314) and is described in EP 1999295B and EP 1999296B.

In the SSALD method, the precursors are separated in space rather than in time as in conventional ALD. The different precursors are separated by inert gas regions and coating layers are formed by exposing the substrate alternatively to one precursor region than another across the inert gas regions; a first precursor monolayer is formed on the surface, then unreacted precursor is purged in the inert gas region, the second precursor then reacts the monolayer formed in the first precursor region forming a layer of the desired material, after which the sample returns to the first precursor region, passing over the inert gas region where excess precursor and any unwanted by-products are purged.

Suitable surface-conditioning and reactive precursors which may be used in a SAALD method are as described herein for

conventional ALD. Operating temperatures and thicknesses of the inorganic layers formed using a SAALD method are also as described above for conventional ALD. Any suitable inert gas conventional in the art such as nitrogen may be used as the purging gas .

According to the present invention, the inorganic sublayer is formed by a SAALD method.

Suitable precursors which may be employed in an ALD process to prepare an inorganic sublayer of the present invention are well known in the art, as discussed for example by Groner et al, Chem. Mater, vol 16, p 639-645 (2004). The surface upon which the inorganic sublayer is to be deposited is prepared to react with the first reactive molecular precursor using a surface- conditioning precursor, typically one which introduces hydrogen containing ligands such as OH which are reactive with the first reactive precursor. The first reactive precursor is conveniently a metal precursor molecule comprising a metal element bound to a ligand. The second precursor may suitably be any reactant which reacts with the first absorbed precursor to form the desired inorganic material .

In one embodiment according to the invention, where the desired inorganic sublayer comprises aluminium oxide (A1₂0₃) _, the surface- conditioning precursor is water, the first reactive precursor is conveniently trimethyl aluminium (A1₂(CH₃)₃) and the second precursor is water.

Typically, the substrate temperature during deposition of the inorganic sublayer is in the range of room temperature to 100°C. In one preferred embodiment, the substrate is maintained at room temperature during deposition of the inorganic sublayer.

Maintaining the substrate at room temperature during processing is desirable as this means that the method of the invention is compatible with the poly (ethylene terephthalate) (PET) or poly ( ethylene naphthalate (PEN) substrates often preferred by commercial electronics manufaturers .

The inorganic sublayer formed according to the present invention suitably has a thickness of from 0.1 to 20 nm, conveniently from 0.1 to 2 nm, preferably up to 1 nm. A1₂0₃ grows at around 0.1 nm per cycle of the process .

In one particular embodiment when the inorganic sublayer is formed by a SAALD method, the reactive precursors employed are trimethyl aluminium (A1₂(CH₃)₃) and water.

The SAALD process takes place in an inert atmosphere, at atmospheric pressure, with extraction to a safe exhaust and takes place in a few seconds per scan. An advantage of using this method is that it is compatible with the roll to roll or sheet fed high speed continuous processes used in the large scale production of plastic flexible displays and OLEDs .

It will be appreciated that in the composite barrier layer formed by the method of the present invention, the sublayer directly adjacent to the surface of the substrate may be either the polymeric sublayer or the inorganic sublayer.

In one embodiment of the invention, the polymeric sublayer is formed on the substrate and the inorganic sublayer is formed on the polymeric layer. The present inventors have found that this configuration is particularly advantageous as the polymeric layer covers any defects or dust particles on the substrate caused during its manufacture to form a smooth surface upon which the inorganic sublayer may be deposited. The provision of defect free barrier coated substrates is, of course, of

particular importance where the substrate is intended for use in OLED lighting applications where the surface area of the device can be significantly large. In one embodiment, the composite barrier layer according to the invention comprises a single polymeric sublayer and a single inorganic sublayer.

It will be appreciated, however, that the composite barrier layer may comprise multiple alternating polymeric and inorganic sublayers .

Preferably, the polymeric and inorganic sublayers will have a transparency of greater than 97% across the visible range.

The relative proportions of the polymeric sublayer and inorganic sublayer in the composite barrier layer prepared according to the present invention will depend on such factors as the nature of the substrate material, the thickness of the substrate, the adhesion properties of the substrate and the desired optical transmittance of the barrier coated product. Typically, the barrier layer will be less than 1% of the thickness of the thickness of the substrate.lt will, however, be a matter of routine modification for a person skilled in the art to alter the proportions of the composite barrier layer components whilst maintaining the desired protection from moisture and gas permeation .

In one embodiment, the composite barrier layer formed according to the invention has a thickness of up to 20 nm, particularly between 10 and 20 nm. Such thin layers are particularly

desirable as they retain flexibility and optical transparency.

The performance of the composite barrier layer in protecting against moisture and gas permeation may be determined using standard water vapour transmission rate (WVTR) and oxygen permeation tests conventional in the art, such as described in Review of Scientific Instruments, 83, 075118 (2012) and

Proceedings of the IEEE, 93(8), 1478-1482 (2005) For an OLED device, it is widely agreed that the water vapour permeation rate necessary to provide an adequate lifetime is at least l(T⁶g/m²/day

Figure 1 shows schematically a roll to roll apparatus for preparing a composite barrier layer on a substrate according to the present invention.

In the apparatus shown in Figure 1, a continuous substrate runs between a feed roller (4) and a receiving roller (5), passing through separate plasma polymer deposition (2) and SAALD metal oxide deposition (3) regions, each of which regions are enclosed in an atmospheric chamber (6) for cleanliness and safety.

Ionising air knives (1) for the purposes of cleaning and removing dust particles generated are positioned at the entry to the plasma deposition chamber, between the plasma deposition and SAALD metal oxide deposition chamber and at the exit from the SAALD metal oxide deposition chamber. Nitrogen is used as a carrier gas in the plasma deposition chamber and as a purging gas in the SAALD metal oxide deposition chamber.

The integration of ionizing air knives between the process zones and at the entrance and exit to the process significantly reduces the problem of pinholes produced by dust particles such that large areas of defect free barrier film on flexible substrates may be produced.

It will be appreciated that the arrangement of deposition regions ( 2 ) and ( 3 ) shown in Figure 1 could be reversed, that is the SAALD deposition step could be carried out before the plasma polymer deposition step. Similarly, although two separate atmospheric mini-environments (6) are shown in the figure, both deposition regions ((2) and (3)) could be housed in the same mini-environment. Depending on the apparatus configuration, the air ionising knives after stage (2) and stage (3) may not be required . Sheet fed alternatives of the scheme shown in Figure 1 are also possible by replacing the roll to roll apparatus with a system of moving sheets of substrate through the different process zones . In each case ionized air knives prevent the formation of particle defects arising from particles from the plastic film substrate and the chamber environment

Composite barrier layer substrates prepared according to the invention may be used in the manufacture of opto-electronic devices by methods conventional in the art

As used herein, an opto-electronic device refers preferably to an electroluminescent device, particularly organic light emitting display (OLED) device.

Conventional methods for preparing an OLED device may be employed. Suitably, the composite barrier layer coated substrate according to the invention is coated, on the barrier layer side, with a transparent conducting cathode. The cathode, which may typically be indium tin oxide, is suitably deposited on the substrate by sputtering (physical vapour deposition) techniques under vacuum. After the cathode deposition step, the substrate is placed in a dry atmosphere glovebox environment where hole injector and light emitting polymer layers are deposited, typically by thermal evaporation and then the final (anode) conducting layer is deposited by sputtering. Finally, the back of the display is encapsulated for example by sealing a preformed metal can including moisture getters to the display substrate, or by depositing a composite barrier layer as described above directly on to the anode layer.

Throughout the description and claims of this specification the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", mean "including but not limited to", and do not exclude other components or steps. As used herein, the singular encompasses the plural unless the context otherwise requires . In particular where the indefinite article is used, the specification is to be understood as contemplating plurality, as well as singularity, unless the context requires otherwise.

Preferred features of each aspect of the invention may be described in connection with any of the other aspects.

The invention may be further illustrated by way the following non-limiting examples

EXAMPLES

Substrate films of polyethylene terephthalate (PET) and

poly ( ethylene naphthalate (PEN) (available from Dupont Teijin as Teonix Q65FA and Melinex ST506) were cut into rectangles of approx 80mm x 100mm and processed according to the method of the invention to give plastic films with composite barriers made of a perfluorodecyl acrylate polymer derived from the monomer 1H, 1H, 2H, 2H-perfluorododecyl acrylate (available from Apollo Scientific Ltd) and aluminium oxide (A1₂0₃) , with the polymer layer adjacent to the substrate surface and the aluminium oxide layer deposited on the polymer layer.

The formation of the polymer layer on the plastic substrate was performed at atmospheric pressure and in an inert gas

environment which also allows safe evacuation of the monomer and any post reaction products when the plasma is enclosed in a plastic box mini environment. The monomer was passed into the plasma zone by heating it to 30-40°C to maintain a temperature gradient upwards for the monomer container to the plasma zone, and passing nitrogen over the surface of the monomer to carry the vapour into the plasma zone. The flow of nitrogen carrier gas was lOOsccm and the quantity of monomer used was 0.15 g per minute, with the process being run for 2 minutes. The plasma was created using a generator with continuous wave frequency of 50kHz and a power density at less than 1 watt per m² of film area .

The polymer coated substrate was then exposed to an inert gas environment again to ensure that it does not adsorb any water vapour between layers. In a production roll to roll

configuration, this inert gas zone is used to keep the two process steps of the composite layer from interfering with one another .

The metal oxide layer was formed by the method of Spatial

Atmospheric Atomic Layer Deposition (SAALD) using an apparatus as described in EP 1999295B and EP 1999296B mentioned above in which sequential gas slots are arranged in parallel to one another and separated to avoid cross contamination by the

Bernoulli effect such that the gas injection head appears to float without contact over the surface onto which the layers are growing. This precisely controls the ride height of the head over the film and ensures good run to run performance.

A 3 slot SAALD head was used giving 2 atomic layers of the oxide per scan. The precursor used was tri methyl aluminium and the surface conditioning precursor to prepare the surface for growth of A1₂0₃ was water vapour.

The composite barrier layer coated substrates were subsequently fabricated into OLED displays using standard OLED process technology and the backside of the display was encapsulated using a metal can with getters according to the current industry standard .

Lifetimes of the most sensitive red OLED material were

demonstrated by cycling the display on and off in a dry room environment. Even after 20,000 hours, the OLED display was still working without any black spots being observed, indicating that the OLED display materials had not failed due to moisture or oxygen ingress .

Claims

1. A method for forming a composite barrier layer on a substrate to protect against moisture and gas permeation, the method comprising forming on said substrate a composite barrier layer comprising :

(i) a polymeric sublayer formed by atmospheric pressure plasma enhanced chemical vapour deposition; and

(ii) an inorganic sublayer formed by atmospheric pressure spatial atomic layer deposition.

2. A method according to claim 1, wherein the composite barrier layer formed on the substrate has a thickness of up to 20 nm.

3. A method according to claim 1 or claim 2, wherein the polymeric sublayer has a thickness of up to 10 nm.

4. A method according to any one of claims 1 to 3, wherein the inorganic sublayer has a thickness of up to 1 nm.

5. A method according to any one of the preceding claims, wherein the polymeric layer is formed on the substrate and the inorganic sublayer is formed on the polymeric layer.

6. A method according to any one of the preceding claims, wherein multiple alternating polymeric and inorganic sublayers are formed on the substrate .

7. A method according to any one of the preceding claims, wherein the polymeric sublayer is formed by atmospheric pressure plasma deposition using pulsed plasma.

8. A method according to any one of the preceding claims, wherein the polymeric sublayer is formed by polymerisation of a monomer which is an unsaturated haloalkyl containing compound.

9. A method according to claim 5, wherein the monomer comprises an acrylate compound of formula CH₂=CR¹C (0)0 (CH₂) _nR²

where n is an integer from 1 to 10, R¹ is hydrogen or Ci_₆alkyl and R² is an alkyl or haloalkyl group .

10. A method according to claim 9, wherein the monomer comprise 1H, 1H, 2H, 2H-heptadecafluorodecyl acrylate or 1H,1H,2H,2H- perfluorododecyl acrylate.

11. A method according to any preceding claim, wherein the inorganic sublayer comprises a metal oxide, a metal nitride or metal oxynitride and combinations thereof.

12. A method according to claim 11, wherein the inorganic sublayer comprises aluminium oxide, A1₂0₃

13. A method according to any one of the preceding claims, wherein the substrate comprises a flexible polyester polymer material .

14. A method according to claim 12 wherein the substrate comprises poly ( ethylene terephthalate) (PET) or poly ( ethylene naphthalate (PEN) .

15. A substrate having formed thereon a composite barrier layer prepared by a method according to any one of claims 1 to 1 .

16. An opto-electronic device comprising a substrate according to claim 15.

16. Use of a substrate having a composite barrier layer formed thereon according to claim 15 to prepare an opto-electronic device .