Patent Application
20070231490
The present invention relates to the field of physical vapor deposition, and more specifically to the co-deposition of metals and non-metallic materials from vapor.
An OLED device includes a substrate, an anode, a hole-transporting layer made of an organic compound, an organic luminescent layer with suitable dopants, an organic electron-transporting layer, and a cathode. OLED devices are attractive because of their low driving voltage, high luminance, wide-angle viewing and capability for full-color flat emission displays. Tang et al. described this multilayer OLED device in their U.S. Pat. No. 4,769,292 and 4,885,211.
Physical vapor deposition in a vacuum environment is the principal way of depositing thin organic material films as used in small molecule OLED devices. Such methods are well known, for example Barr in U.S. Pat. No. 2,447,789 and Tanabe et al. in EP 0 982 411. The organic materials used in the making of OLED devices are often subject to degradation when maintained at or near the desired rate dependant vaporization temperature for extended periods of time. Exposure of sensitive organic materials to higher temperatures can cause changes in the structure of the molecules and associated changes in material properties.
In U.S. Publication. No. 2004/0135749, Boroson et al. described an organic layer doped with a low work-function metal. For example, a layer of tris(8-quinolinolato)aluminum (III) (Alq) having 1.2% lithium by volume has useful properties. Such a layer was vacuum deposited onto a substrate at a coating station that included two heated boat sources, one each for Alq and lithium.
However, the use of separate sources can create a gradient effect in the deposited film where the material in the source closest to an advancing substrate is over represented in the initial film immediately adjacent the substrate because the material in the last source is over represented in the final film surface. This gradient co-deposition is unavoidable in prior art sources where a single material is vaporized from each of multiple sources.
A further limitation of previous sources is that the geometry of the vapor manifold changes as the material charges are consumed. This change requires that the heater temperature change to maintain a constant vaporization rate; however, it is observed that the plume shape of the vapor exiting the orifices changes as a function of the material thickness and distribution in the source.
It is therefore an object of the present invention to allow a single source to uniformly deposit metals and non-metallic materials to form a layer on a substrate.
This object is achieved by a method for mixing and depositing first and second separate vaporized materials onto a substrate surface to form a layer wherein the first material includes a metal and the second material is non-metallic, comprising:
a) providing a mixing manifold disposed so that vaporized materials are deliverable onto the substrate surface;
b) providing first and second heating elements for separately vaporizing the first and second materials, the heating elements being disposed so that the vaporized materials are deliverable into the mixing manifold; and
c) metering at a controlled rate the first and second materials to the first and second heating elements respectively, so that vaporized materials, including the metal, are delivered to the mixing manifold where they are mixed and subsequently deposited onto the substrate surface to form the layer including the metal.
It is an advantage of the present invention that it permits materials having different vaporization rates and degradation temperature thresholds to be co-sublimated in the same source. It is a particular advantage when one of the materials is a metal and another material is organic.
It is a further advantage of the present invention that it permits linear vaporization rate and vapor composition control by controlling the metering rate of the materials.
It is a further advantage of the present invention that it can rapidly stop and reinitiate vaporization and achieve a steady vaporization rate quickly by controlling the metering rate of the materials, minimizing contamination of the deposition chamber walls and conserving the materials when a substrate is not being coated.
It is a further advantage that the present device achieves substantially higher vaporization rates than in prior art devices with substantially reduced material degradation. Further still, no heater temperature change is required as the source material is consumed.
It is a further advantage of the present invention that it can provide a vapor source in any orientation, which is frequently not possible with previous devices.
Turning now to
First material 15 includes a metal, and desirably a reactive or reducing metal with a work function of less than 4.5 eV. Useful metals for this invention include Al, Li, Cs, Mg, Ca, Ba, or Ag. In some embodiments, as shown in
Second material 20 is a compacted or pre-condensed solid, or a powder. Second material 20 is desirably an organic material. Second material 20 can comprise a single component, or can comprise two or more organic components, each one having a different vaporization temperature. Second material 20 is metered at a controlled rate to a second heating element 40. One example of a metering structure for a second material 20 includes a chamber 65 for receiving a second material 20 and a piston 50 , which are controlled through a force-controlled drive mechanism, for raising second material 20 in chamber 65. Second material 20 is vaporized by a second heating element 40, whereupon the vaporized second material is delivered into a mixing manifold 60. The first and second vaporized materials are mixed in a mixing manifold 60 and subsequently deposited onto the surface of a substrate 85 to form a layer, including the metal of a first material 15.
Vaporization apparatus 10 can also include ways for actively cooling at least one of the materials to be below its vaporization temperature in a portion of the apparatus. For example, vaporization apparatus 10 can include, for temperature control, a first region 30 and a second region 35. First region 30 includes a base block 67, which is a heating base block or a cooling base block, or both, and which can include control passages 69 for delivery of heating or cooling fluids. Control passages 69 through base block 67 allow the flow of a temperature control fluid, that is, a fluid adapted to either absorb heat from or deliver heat to the first region 30. The fluid is a gas, a liquid, or a mixed phase. Vaporization apparatus 10 includes a way for pumping fluid through control passages 69. Pumping devices are well-known to those skilled in the art. Second region 35 includes the region bounded by mixing manifold 60 and second heating element 40, which are part of mixing manifold 60. Second material 20 is actively cooled in first region 30 to be kept below its vaporization temperature. Second heating element 40 in second region 35 heats a thin cross-section of second material 20 above its vaporization temperature, whereby the thin cross-section of second material 20 vaporizes. In the case where second material 20 includes two or more organic components, the temperature of second region 35 is chosen to be above the vaporization temperature of each of the components so that each of the second material 20 components simultaneously vaporizes. In this way, there is a steep thermal gradient, which is on the order of 200° C./mm, between first region 30 and second region 35. This gradient protects all but the immediately vaporizing material from the high temperatures, and the bulk of second material 20 is maintained at a temperature at which it has a low rate of degradation. By vaporization temperature, it is meant that the temperature at which the material vaporizes at the rate desired for material deposition on the substrate under the pressure present in mixing manifold 60. The vaporization temperature is determined by various ways. As described by Long et al. in U.S. Publication No. 2005/0186340, the vaporization rate is proportional to the vapor pressure, so for a desired vaporization rate, the required heating temperature corresponding to the desired vaporization rate is determined. Vaporization apparatus 10 can also include one or more shields 70 located adjacent heated mixing manifold 60 for the purpose of reducing the heat radiated to the facing target substrate. Heat shields 70 are thermally connected to base block 67 for the purpose of drawing heat away from the shields. The upper portion of shields 70 is designed to lie below the plane of the apertures for the purpose of minimizing vapor condensation on their relatively cool surfaces.
The current device and method can achieve high vaporization rates, without causing appreciable degradation of organic materials, as has been described by Long et al. in U.S. Publication No. 2005/0186340. However, vaporization apparatus 10 also permits co-vaporization of a metal, wherein the separate vaporized materials (the metal and the organic materials) are mixed in mixing manifold 60 and are deposited together onto the surface of substrate 85 to form a layer. The constant vaporization rate, and constant volume of vaporizing first and second materials 15 and 20 maintained in second region 35 establish and maintain a homogeneous plume with a constant shape. The plume is herein defined as the vapor cloud exiting vaporization apparatus 10. Such layers that include co-evaporated metal and organic material have been found to be useful. For example, Boroson et al., in U.S. Publication No. 2004/0135749, disclose that an electron-transporting layer of tris(8-quinolinolato)aluminum (III) (Alq) with 1.2% co-evaporated lithium metal can provide a lower voltage OLED device with increased lifetime. In this embodiment, first material 15 is lithium metal and second material 20 is Alq. Another use for such layers is as e.g. an n-type doped organic layer in an intermediate connector of a tandem OLED device, as taught by Hatwar et al. in U.S. application Ser. No. 11/217,026.
A pressure develops as vaporization continues and streams of vapor exit mixing manifold 60 through the series of apertures 90. The conductance along the length of the manifold is designed to be roughly two orders of magnitude larger than the sum of the aperture conductances, as described by Grace et al. in U.S. Publication No. 2004/0144321. This conductance ratio promotes effective pressure uniformity within manifold 60 and thereby reducing flow non-uniformities through apertures 90 distributed along the length of the source, despite potential local non-uniformities in vaporization rate.
Because only a small portion of the materials—the portions resident in second region 35—are heated to the rate-dependent vaporization temperature, although the bulk of the materials are kept well below the vaporization temperature, it is possible to interrupt the vaporization by interrupting heating in second heating region 35, e.g. stopping the movements of piston 50 and metering structure 55. This is done when a substrate surface is not being coated to conserve materials and reduce contamination of any associated apparatus, such as the walls of a deposition chamber, which will be described below.
Because second heating element 40 is a fine mesh screen that prevents powder or compacted material from passing freely through it, vaporization apparatus 10 is used in any orientation. For example, vaporization apparatus 10 is oriented 180° from what is shown in
In practice, vaporization apparatus 10 is used as follows. A quantity of first material is provided into delivery structure 45. A quantity of second material 20, which can comprise one or more components, is provided into chamber 65 of vaporization apparatus 10. In first region 30, second material 20 is actively maintained below the vaporization temperature of each of its organic components. First heating element 25 is heated to a temperature above the vaporization temperature of first material 15. Second heating element 40 is heated to a temperature above the vaporization temperature of second material 20 or each of the components thereof. Both first and second materials 15 and 20, respectively, are metered at controlled rates, whereby they vaporize, mix in mixing manifold 60, and deposit onto a substrate surface to form a layer. When second material 20 includes multiple components, each component simultaneously vaporizes.
Turning now to
In practice, an OLED substrate 85 is placed in deposition chamber 80 via load lock 75 and held by translational apparatus 95 or associated apparatus. Vaporization apparatus 10 is operated as described above, and translational apparatus 95 moves OLED substrate 85 perpendicular to the direction of emission of material vapors from vaporization apparatus 10, thus forming a layer of mixed metallic and non-metallic material on the surface of OLED substrate 85.
In the above vaporization apparatus 10, first heating element 25 is shown as a heated screen. However, the first heating element is not limited to this configuration. For example, turning now to
Turning now to
Turning now to
The addition of optional third container 170 to hold additional first material provides several additional advantages. A large quantity of first material 200 is charged in the apparatus, allowing continuous operation of the device for extended periods of time as described by Long et al. in U.S. application Ser. No. 10/945,941, by Long et al. and U.S. patent application Ser. No. 10/945,940. Also, third container 170 is arranged to be refillable without affecting the operation of first container 150, allowing the device to be continuously operated for even longer periods of time. First material 200 is maintained in third container 170 by e.g. screens 210 and 220 , whose mesh size is chosen to prevent the free flow of powdered material, but to allow controlled flow. Screens 210 and 220 can also be the mechanism for providing measured quantities of first material to move from third container 170 to first container 150 via contact by agitating devices (not shown) that is actuated to cause a quantity of powder to pass through the screen. Such devices include those to vibrate the screen, or a movable arm immediately above or below the screen to allow selective agitation of screens 210 and 220. Agitating devices such as piezoelectric structures 240 prevent the buildup of organic material in the feed path to first container 150. Feeding apparatus 145 of
Turning now to
Additionally, base 280 is included. Base 280 is a heat-dissipating structure to prevent much of the heat from heating element 270 from traversing the length of feeding path 160, and thus can actively cool the material to be below its vaporization temperature because heating element 270 heats the material above its vaporization temperature. Ways of heat dissipation for base 280 have been described by Long et al. in U.S. patent application Ser. No.10/784,585). A steep thermal gradient thereby created protects all but the inmmediately vaporizing material from the high temperatures. This is particularly important when the first material is a low-melting metal (e.g. lithium), or the second material is an organic material. The vaporized material rapidly passes through heating element 270 and can enter into the heated manifold 120.
Turning now to
Material 23 is actively cooled in first region 30 to be kept below its vaporization temperature in a portion of the apparatus. Heating element 43 in second region 35 heats a thin cross-section of material 23 above its vaporization temperature, whereby the thin cross-section of material 23 vaporizes. The temperature of second region 35 is chosen to be above the vaporization temperature of each of the components, including the metal, so that each of the material 23 components simultaneously vaporizes. In this way, there is a steep thermal gradient, which is on the order of 500° C./mm as disclosed by Long et al. in U.S. patent application Ser. No. 10/945,940 and U.S. patent application Ser. No. 11/134,654, between first region 30 and second region 35. This gradient protects all but the immediately vaporizing material from the high temperatures, and the bulk of material 23 is maintained at a temperature at which it has a low rate of degradation.
Turning now to
Variations on this basic method are possible. In one example, the method can include a step just before step 350 to actively cool at least one of the materials, e.g. second material 20 in first region 30 to be below its vaporization temperature. In another example, Steps 310, 320, 340, 360, and 390 is used with vaporization apparatus 105 of
Turning now to
Substrate 420 is an organic solid, an inorganic solid, or includes organic and inorganic solids. Substrate 420 is rigid or flexible and is processed as separate individual pieces, such as sheets or wafers, or as a continuous roll. Typical substrate materials include glass, plastic, metal, ceramic, semiconductor, metal. oxide, semiconductor oxide, semiconductor nitride, or combinations thereof. Substrate 420 is a homogeneous mixture of materials, a composite of materials, or multiple layers of materials. Substrate 420 is an OLED substrate, that is a substrate commonly used for preparing OLED devices, e.g. active-matrix low-temperature polysilicon or amorphous-silicon TFT substrate. The substrate 420 can either be lighttransmissive or opaque, depending on the intended direction of light emission. The light transmissive property is desirable for viewing the EL emission through the substrate. Transparent glass or plastic is commonly employed in such cases. For applications where the EL emission is viewed through the top electrode, the transmissive characteristic of the bottom support is immaterial, and therefore is light transmissive, light absorbing or light reflective. Substrates for use in this case include, but are not limited to, glass, plastic, semiconductor materials, ceramics, and circuit board materials, or any others commonly used in the formation of OLED devices, which is either passive-matrix devices or active-matrix devices.
An electrode is formed over substrate 420 and is most commonly configured as an anode 430. When EL emission is viewed through the substrate 420, anode 430 should be transparent or substantially transparent to the emission of interest. Common transparent anode materials useful in this invention are indium-tin oxide and tin oxide, but other metal oxides can work including, but not limited to, aluminum- or indium-doped zinc oxide, magnesium-indium oxide, and nickel-tungsten oxide. In addition to these oxides, metal nitrides such as gallium nitride, metal selenides such as zinc selenide, and metal sulfides such as zinc sulfide, is used as an anode material. For applications where EL emission is viewed through the top electrode, the transmissive characteristics of the anode material are immaterial and any conductive material is used, transparent, opaque or reflective. Example conductors for this application include, but are not limited to, gold, iridium, molybdenum, palladium, and platinum. The preferred anode materials, transmissive or otherwise, have a work function of 4.1 eV or greater. Desired anode materials are deposited by any suitable way such as evaporation, sputtering, chemical vapor deposition, or electrochemical processes. Anode materials are patterned using well known photolithographic processes.
Because not always necessary, it is often useful that a hole-injecting layer 435 be formed over anode 430 in an organic light-emitting display. The hole-injecting material can serve to improve the film formation property of subsequent organic layers and to facilitate injection of holes into the hole-transporting layer. Suitable materials for use in hole-injecting layer 435 include, but are not limited to, porphyrinic compounds as described in U.S. Pat. No. 4,720,432, plasma-deposited fluorocarbon polymers as described in U.S. Pat. No. 6,208,075, and inorganic oxides including vanadium oxide (VOx), molybdenum oxide (MoOx), nickel oxide (NiOx). Alternative hole-injecting materials reportedly useful in organic EL devices are described in EP 0 891 121 A1 and EP 1 029 909 A1.
Because not always necessary, it is often useful that a hole-transporting layer 440 be formed and disposed over anode 430. Desired hole-transporting materials are deposited by any suitable way such as evaporation, sputtering, chemical vapor deposition, electrochemical structure, thermal transfer, or laser thermal transfer from a donor material. Hole-transporting materials useful in hole-transporting layer 440 are well known to include compounds such as an aromatic tertiary amine, where the latter is understood to be a compound containing at least one trivalent nitrogen atom that is bonded only to carbon atoms, at least one of which is a member of an aromatic ring. In one form the aromatic tertiary amine is an arylamine, such as a monoarylamine, diarylamine, triarylamine, or a polymeric arylamine. Exemplary monomeric triarylamines are illustrated by Klupfel et al. in U.S. Pat. No. 3,180,730. Other suitable triarylarnines substituted with one or more vinyl radicals and comprising at least one active hydrogen-containing group are disclosed by Brantley et al. in U.S. Pat. Nos. 3,567,450and 3,658,520.
A more preferred class of aromatic tertiary amines are those which include at least two aromatic tertiary amine moieties as described in U.S. Pat. Nos. 4,720,432and 5,061,569. Such compounds include those represented by structural Formula A.
wherein:
In one embodiment, at least one of Q1 or Q2 contains a polycyclic fused ring structure, e.g., a naphthalene. When G is an aryl group, it is conveniently a phenylene, biphenylene, or naphthalene moiety.
A useful class of triarylamines satisfying structural Formula A and containing two triarylarnine moieties is represented by structural Formula B.
where:
Another class of aromatic tertiary amines is the tetraaryldiamines. Desirable tetraaryldiamines include two diarylamino groups, such as indicated by Formula C, and linked through an arylene group. Useful tetraaryldiamines include those represented by Formula D.
wherein:
In a typical embodiment, at least one of Ar, R7, R8, and R9 is a polycyclic fused ring structure, e.g., a naphthalene.
The various alkyl, alkylene, aryl, and arylene moieties of the foregoing structural Formulae A, B, C, D, can each in turn be substituted. Typical substituents include alkyl groups, alkoxy groups, aryl groups, aryloxy groups, and halogens such as fluoride, chloride, and bromide. The various alkyl and alkylene moieties typically contain from 1 to about 6 carbon atoms. The cycloalkyl moieties can contain from 3 to about 10 carbon atoms, but typically contain five, six, or seven carbon atoms—e.g., cyclopentyl, cyclohexyl, and cycloheptyl ring structures. The aryl and arylene moieties are typically phenyl and phenylene moieties.
The hole-transporting layer in an OLED device is formed of a single or a mixture of aromatic tertiary amine compounds. Specifically, one can employ a triarylamine, such as a triarylamine satisfying the Formula B, in combination with a tetraaryldiamine, such as indicated by Formula D. When a triarylamine is employed in combination with a tetraaryldiamine, the latter is positioned as a layer interposed between the triarylamine and the electron-injecting and transporting layer.
Another class of useful hole-transporting materials includes polycyclic aromatic compounds as described in EP 1 009 041. In addition, polymeric hole-transporting materials is used such as poly(N-vinylcarbazole) (PVK), polythiophenes, polypyrrole, polyaniline, and copolymers such as poly(3,4-ethylenedioxythiophene)/poly(4 -styrenesulfonate) also called PEDOT/PSS.
Light-emitting layer 450 produces light in response to hole-electron recombination. Light-emitting layer 450 is commonly disposed over hole-transporting layer 440. Desired organic light-emitting materials is deposited by any suitable structure such as evaporation, sputtering, chemical vapor deposition, electrochemical structure, or radiation thermal transfer from a donor material.
Useful organic light-emitting materials are well known. As more fully described in U.S. Pat. Nos. 4,769,292 and 5,935,721, the light-emitting layers of the organic EL element comprise a luminescent or fluorescent material where electroluminescence is produced as a result of electron-hole pair recombination in this region. The light-emitting layers is comprised of a single material, but more commonly include a host material doped with a guest compound or dopant where light emission comes primarily from the dopant. The dopant is selected to produce color light having a particular spectrum. The host materials in the light-emitting layers are an electron-transporting material, as defined below, a hole-transporting material, as defined above, or another material that supports hole-electron recombination. The dopant is typically chosen from highly fluorescent dyes, but phosphorescent compounds, e.g., transition metal complexes as described in WO 98/55561, WO 00/18851, WO 06/57676, and WO 00/70655 are also useful. Dopants are typically coated as 0.01to 10% by weight into the host material. The device and method described herein is used to coat multi-component guest/host layers without the need for multiple vaporization sources.
Host and emitting molecules known to be of use include, but are not limited to, those disclosed in U.S. Pat. Nos. 4,768,292; 5,141,671; 5,150,006; 5,151,629; 5,294,870; 5,405,709; 5,484,922; 5,593,788; 5,645,948; 5,683,823; 5,755,999; 5,928,802; 5,935,720; 5,935,721; and 6,020,078.
Metal complexes of 8-hydroxyquinoline and similar derivatives (Formula E) constitute one class of useful host materials capable of supporting electroluminescence, and are particularly suitable for light emission of wavelengths longer than 500 nm, e.g., green, yellow, orange, and red.
wherein:
From the foregoing it is apparent that the metal is a monovalent, divalent, or trivalent metal. The metal can, for example, be an alkali metal, such as lithium, sodium, or potassium; an alkaline earth metal, such as magnesium or calcium; or an earth metal, such as boron or aluminum. Generally any monovalent, divalent, or trivalent metal known to be a useful chelating metal is employed.
Z completes a heterocyclic nucleus containing at least two fused aromatic rings, at least one of which is an azole or azine ring. Additional rings, including both aliphatic and aromatic rings, are fused with the two required rings, if required. To avoid adding molecular bulk without improving on function the number of ring atoms are typically maintained at 18 or less.
The host material in light-emitting layer 450 is an anthracene derivative having hydrocarbon or substituted hydrocarbon substituents at the 9 and 10 positions. For example, derivatives of 9,10-di-(2-naphthyl)anthracene constitute one class of useful host materials capable of supporting electroluminescence, and are particularly suitable for light emission of wavelengths longer than 400 nm, e.g., blue, green, yellow, orange or red.
Benzazole derivatives constitute another class of useful host materials capable of supporting electroluminescence, and are particularly suitable for light emission of wavelengths longer than 400 nm, e.g., blue, green, yellow, orange or red. An example of a useful benzazole is 2, 2′, 2 ″-(1,3,5-phenylene) tris[1-phenyl-1H-benzimidazole].
Desirable fluorescent dopants include perylene or derivatives of perylene, derivatives of anthracene, tetracene, xanthene, rubrene, coumarin, rhodamine, quinacridone, dicyanomethylenepyran compounds, thiopyran compounds, polyrnethine compounds, pyrilium and thiapyrilium compounds, derivatives of distryrylbenzene or distylbiphenyl, bis(azinyl)methane boron complex compounds, and carbostyryl compounds.
Other organic emissive materials is polymeric substances, e.g. polyphenylenevinylene derivatives, dialkoxy-polyphenylenevinylenes, poly-para-phenylene derivatives, and polyfluorene derivatives, as taught by Wolk et al. in commonly assigned U.S. Pat. No. 6,194,119 B1 and references cited therein.
It is useful that OLED device 410 includes an electron-transporting layer 455 disposed over light-emitting layer 450. Desired electron-transporting materials is deposited by any suitable structure such as evaporation, sputtering, chemical vapor deposition, electrochemical structure, thermal transfer, or laser thermal transfer from a donor material, and is deposited by the device and method described herein. In particular, it is envisioned that an electron-transporting layer doped with a metal is formed by the method of this invention. Preferred electron-transporting materials for use in electron-transporting layer 455 are metal chelated oxinoid compounds, including chelates of oxine itself (also commonly referred to as 8-quinolinol or 8-hydrodxyquinoline). Such compounds help to inject and transport electrons and exhibit both high levels of performance and are readily fabricated in the form of thin films. Exemplary of contemplated oxinoid compounds are those satisfying structural Formula E, previously described.
Other electron-transporting materials include various butadiene derivatives as disclosed in U.S. Pat. No. 4,356,429 and various heterocyclic optical brighteners as described in U.S. Pat. No. 4,539,507. Benzazoles satisfying structural Formula G are also useful electron-transporting materials.
Other electron-transporting materials are polymeric substances, e.g. polyphenylenevinylene derivatives, poly-para-phenylene derivatives, polyfluorene derivatives, polythiophenes, polyacetylenes, and other conductive polymeric organic materials such as those listed in Handbook of Conductive Molecules and Polymers, Vols. 1-4, H.S. Nalwa, ed., John Wiley and Sons, Chichester (1997).
An electron-injecting layer 460 can also be present between the cathode and the electron-transporting layer. Examples of electron-injecting materials include alkaline or alkaline earth metals, alkali halide salts, such as LiF mentioned above, or alkaline or alkaline earth metal doped organic layers.
Cathode 490 is formed over the electron-transporting layer 455. When light emission is through the anode 430, the cathode material is comprised of nearly any conductive material. Desirable materials have effective film-forming properties to ensure effective contact with the underlying organic layer, promote electron injection at low voltage, and have effective stability. Useful cathode materials often contain a low work function metal (<3.0 eV) or metal alloy. One preferred cathode material is comprised of a Mg:Ag alloy wherein the percentage of silver is in the range of 1 to 20%, as described in U.S. Pat. No. 4,885,221. Another suitable class of cathode materials includes bilayers comprised of a thin layer of a low work function metal or metal salt capped with a thicker layer of conductive metal. One such cathode is comprised of a thin layer of LiF followed by a thicker layer of A1 as described in U.S. Pat. No. 5,677,572. Other useful cathode materials include, but are not limited to, those disclosed in U.S. Pat. Nos. 5,059,861; 5,059,862; and 6,140,763.
When light emission is viewed through cathode 490, it should be transparent or nearly transparent. For such applications, metals should be thin or one should use transparent conductive oxides, or includes these materials. Optically transparent cathodes have been described in more detail in U.S. Pat. No. 5,776,623. Cathode materials ate deposited by evaporation, sputtering, or chemical vapor deposition. When needed, patterning is achieved through many well known methods including, but not limited to,through-mask deposition, integral shadow masking as described in U.S. Pat. Nos. 5,276,380 and EP 0 732 868, laser ablation, and selective chemical vapor deposition.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications is effected within the spirit and scope of the invention.
Reference is made to commonly assigned U.S. patent application Ser. No. 10/352,558, filed Jan. 28, 2003, entitled “Method Of Designing A Thermal Physical Vapor Deposition System”, by Grace et al.; U.S. patent application Ser. No. 10/784,585, filed Feb. 23, 2004, entitled “Device And Method For Vaporizing Temperature Sensitive Materials”, by Long et al.; U.S. application Ser. No. 11/134,139, filed May 20, 2005, entitled “Delivering Organic Powder To A Vaporization Zone” by Long et al., which is a Continuation-In-Part of U.S. patent application Ser. No. 10/945,941, filed Sep. 21, 2004, entitled “Delivering Organic Powder To A Vaporization Zone”, by Long et al.; U.S. patent application Ser. No. 11/134,654, filed May 20, 2005, entitled “Delivering Organic Powder To A Vaporization Zone” by Long et al., which is a Continuation-In-Part of U.S. patent application Ser. No. 10/945,940, filed Sep. 21, 2004, entitled “Delivering Organic Powder To A Vaporization Zone” by Long et al.; and U.S. patent application Ser. No. 11/217,026, filed Aug. 31, 2005, entitled “Intermediate Connector For A Tandem OLED Device”, by Hatwar et al.; the disclosures of which are incorporated herein by reference.
