Patent Publication Number: US-2017358775-A1

Title: Highly Spreading Polyethylene Glycol Di(meth)acrylate-Based Organic Thin Film Ink Compositions

Description:
FIELD 
     The present teachings relate to various embodiments of an ink composition, and a polymeric thin film formed on a substrate, such as, but not limited by, an OLED device substrate. Various embodiments of the ink composition can be printed using an industrial inkjet printing system that can be housed in a gas enclosure, which gas enclosure defines an interior that has a controlled environment maintained as an inert and substantially low-particle process environment. 
     OVERVIEW 
     Interest in the potential of organic light-emitting diode (OLED) display technology has been driven by OLED display technology attributes that include demonstration of display panels that have highly saturated colors, are high-contrast, ultrathin, fast-responding, and energy efficient. Additionally, a variety of substrate materials, including flexible polymeric materials, can be used in the fabrication of OLED display technology. Though the demonstration of displays for small screen applications, primarily for cell phones, has served to emphasize the potential of the technology, challenges remain in scaling high volume manufacturing across a range of substrate formats in high yield. 
     With respect to scaling of formats, a Gen 5.5 substrate has dimensions of about 130 cm×150 cm and can yield about eight 26″ flat panel displays. In comparison, larger format substrates can include using Gen 7.5 and Gen 8.5 mother glass substrate sizes. A Gen 7.5 mother glass has dimensions of about 195 cm×225 cm, and can be cut into eight 42″ or six 47″ flat panel displays per substrate. The mother glass used in Gen 8.5 is approximately 220 cm×250 cm, and can be cut to six 55″ or eight 46″ flat panel displays per substrate. One indication of the challenges that remain in scaling of OLED display manufacturing to larger formats is that the high-volume manufacture of OLED displays in high yield on substrates larger than Gen 5.5 substrates has proven to be substantially challenging. 
     In principle, an OLED device may be manufactured by the printing of various organic thin films, as well as other materials, on a substrate using an OLED printing system. In addition to the printing of various layers of an OLED stack into a plurality of discrete pixel locations, patterned area printing using an industrial inkjet system can be done. For example, during fabrication of an OLED device, inkjet printing of various encapsulation layers can be done. 
     SUMMARY OF THE DISCLOSURE 
     Ink compositions having spreading properties that render then suitable for printed OLED applications are provided. Also provided are processes for forming polymeric thin film layers on OLED device substrates using the ink compositions. 
     Some embodiments of the ink compositions comprise: 30-50 wt. % of a polyethylene glycol dimethacrylate monomer, a polyethylene glycol diacrylate monomer, or a combination thereof, wherein the polyethylene glycol dimethacrylate monomer and the polyethylene glycol diacrylate monomer have number average molecular weights in the range from about 230 g/mole to about 430 g/mole; 4-10 wt. % of a multifunctional acrylate crosslinking agent, a multifunctional methacrylate crosslinking agent, or a combination thereof; and 40-60 wt. % of a spreading modifier comprising an alkoxylated aliphatic diacrylate monomer, an alkoxylated aliphatic dimethacrylate monomer, or a combination thereof, and having a viscosity in the range from about 14 cps to about 18 cps at 22° C. and a surface tension in the range from about 35 dynes/cm to about 39 dynes/cm at 22° C. 
     In some such embodiments, the spreading modifier has a viscosity in the range from about 14 cps to about 16 cps at 22° C. and a surface tension in the range from about 35 dynes/cm to about 38 dynes/cm at 22° C. 
     In some such embodiments, the ink compositions are characterized in that a drop of the ink composition inkjet printed onto a silicon substrate at a temperature of 23° C. has a spreading rate of at least 0.5 μm/sec, including at least 0.65 μm/sec, as measured by the increase in the drop diameter in the period between 40 seconds post-printing and 180 seconds post-printing. 
     In some such embodiments, the multifunctional acrylate crosslinking agent, multifunctional methacrylate crosslinking agent, or a combination thereof comprises pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, or a combination thereof. 
     In some such embodiments, the ink compositions further comprise 0.1 wt. % to 10 wt. % of crosslinking photoinitiator. The photoinitiator may be 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. Such initiators are available from BASF and sold under the tradenames Irgacure® TPO and Irgacure® TPO-L. Other suitable initiators include alpha ketone initiators, including alpha aminoketones and alpha hydroxyketones. Such initiators are available from BASF and sold under the tradenames Irgacure® 907 and Irgacure® 184. The crosslinking photoinitiator may be present, for example, in an amount in the range from about 3 wt. % to about 6 wt. % of the ink composition. This includes embodiments in which the crosslinking photoinitiator is present in an amount in the range from about 3.75 wt. % to about 4.25 wt. % of the ink composition. 
     In some such embodiments, the ink composition comprises 40-50 wt. % of the polyethylene glycol dimethacrylate monomer, wherein the polyethylene glycol dimethacrylate monomer has a number average molecular weight of about 330 g/mole, and 40-50 wt. % of the spreading modifier. 
     Other embodiments of the ink compositions comprise: 50-75 wt. % of a polyethylene glycol dimethacrylate monomer, a polyethylene glycol diacrylate monomer, or a combination thereof, wherein the polyethylene glycol dimethacrylate monomer and the polyethylene glycol diacrylate monomer have number average molecular weights in the range from about 230 g/mole to about 430 g/mole; 4-10 wt. % of a multifunctional acrylate crosslinking agent, a multifunctional methacrylate crosslinking agent, or a combination thereof; and 15-40 wt. % of a spreading modifier comprising an alkoxylated aliphatic diacrylate monomer, an alkoxylated aliphatic dimethacrylate monomer, or a combination thereof, and having a viscosity in the range from about 14 cps to about 18 cps at 22° C. and a surface tension in the range from about 35 dynes/cm to about 39 dynes/cm at 22° C. 
     In some such embodiments, the spreading modifier has a viscosity in the range from about 14 cps to about 16 cps at 22° C. and a surface tension in the range from about 35 dynes/cm to about 38 dynes/cm at 22° C. 
     In some such embodiments, the ink compositions are characterized in that a drop of the ink composition inkjet printed onto a silicon substrate at a temperature of 23° C. has a spreading rate of at least 0.1 μm/sec, as measured by the increase in the drop diameter in the period between 40 seconds post-printing and 180 seconds post-printing. This includes embodiments of the ink compositions characterized in that a drop of the ink composition inkjet printed onto a silicon substrate at a temperature of 23° C. has a spreading rate of at least 0.14 μm/sec, a spreading rate of at least 0.30 μm/sec, or a spreading rate of at least 0.40 μm/sec, as measured by the increase in the drop diameter in the period between 40 seconds post-printing and 180 seconds post-printing. 
     In some such embodiments, the multifunctional acrylate crosslinking agent, multifunctional methacrylate crosslinking agent, or a combination thereof comprises pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, or a combination thereof. 
     In some such embodiments, the ink compositions further comprise 0.1 wt. % to 10 wt. % of crosslinking photoinitiator. The photoinitiator may be 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. Such initiators are available from BASF and sold under the tradenames Irgacure® TPO and Irgacure® TPO-L. Other suitable initiators include alpha ketone initiators, including alpha aminoketones and alpha hydroxyketones. Such initiators are available from BASF and sold under the tradenames Irgacure® 907 and Irgacure® 184. The crosslinking photoinitiator may be present, for example, in an amount in the range from about 3 wt. % to about 6 wt. % of the ink composition. This includes embodiments in which the crosslinking photoinitiator is present in an amount in the range from about 3.75 wt. % to about 4.25 wt. % of the ink composition. 
     In some such embodiments, the compositions comprise 55-70 wt. % of the polyethylene glycol dimethacrylate monomer, wherein the polyethylene glycol dimethacrylate monomer has a number average molecular weight of about 330 g/mole, and 20-35 wt. % of the spreading modifier. 
     Some embodiments of the processes of forming a polymeric thin film layer on a substrate, comprise: providing an inert processing environment; providing an OLED device substrate having an inorganic thin film formed thereupon; providing an ink composition of a type described herein; printing a layer of the ink composition over a defined area of the substrate including the inorganic thin film, and curing the layer of printed ink, wherein an organic polymeric thin film is formed over the inorganic thin film. 
     In some such processes, the cured layer of printed ink has a thickness of no greater than 2 μm, including thicknesses of no greater than 1 μm. 
     In some such processes, printing the layer of the ink composition over a defined area of the substrate comprises inkjet printing a plurality of drops of the ink composition onto the substrate, whereby the ink drops spread on the substrate and coalesce to form the layer of the ink composition. 
     In some such processes, the multifunctional acrylate crosslinking agent, multifunctional methacrylate crosslinking agent, or a combination thereof comprises pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, or a combination thereof. 
     Some such processes further comprise, before the step of providing an OLED device substrate: providing an industrial printing system housed within the interior of a gas enclosure, wherein the industrial printing system comprises: a printhead assembly comprising at least one printhead; a substrate support system for supporting the substrate; a motion system for the precise positioning of the substrate relative to the printhead assembly; and a UV curing module, wherein printing the layer of the ink composition over a defined area of the substrate comprises printing the layer of the ink composition over a defined area of the substrate using the printhead assembly. The inert process environment may be provided using, for example, an inert gas selected from nitrogen, any of the noble gases, and combinations thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the features and advantages of the present disclosure will be obtained by reference to the accompanying drawings, which are intended to illustrate, not limit, the present teachings. 
         FIG. 1  is a schematic section view of an optoelectronic device, illustrating various aspects of a fabrication. 
         FIG. 2  is a film profile for a polymeric thin film inkjet printed on a silicon substrate. 
         FIG. 3  is a graph showing the diameters of drops of ink compositions 40 seconds after being printed onto a silicon substrate as a function of the spreading modifier concentration of the ink compositions. 
         FIG. 4A  is graph showing the diameters of drops of ink compositions 40 seconds after being printed onto a silicon substrate as a function of the spreading modifier concentration of the ink compositions.  FIG. 4B  is graph showing the diameters of drops of ink compositions 60 seconds after being printed onto a silicon substrate as a function of the spreading modifier concentration of the ink compositions.  FIG. 4C  is graph showing the diameters of drops of ink compositions 90 seconds after being printed onto a silicon substrate as a function of the spreading modifier concentration of the ink compositions.  FIG. 4D  is graph showing the diameters of drops of ink compositions 120 seconds after being printed onto a silicon substrate as a function of the spreading modifier concentration of the ink compositions.  FIG. 4E  is graph showing the diameters of drops of ink compositions 150 seconds after being printed onto a silicon substrate as a function of the spreading modifier concentration of the ink compositions.  FIG. 4F  is graph showing the diameters of drops of ink compositions 180 seconds after being printed onto a silicon substrate as a function of the spreading modifier concentration of the ink compositions.  FIG. 4G  is graph showing the diameters of drops of ink compositions 300 seconds after being printed onto a silicon substrate as a function of the spreading modifier concentration of the ink compositions.  FIG. 4H  is graph showing the diameters of drops of ink compositions 600 seconds after being printed onto a silicon substrate as a function of the spreading modifier concentration of the ink compositions.  FIG. 4I  is graph showing the diameters of drops of ink compositions 900 seconds after being printed onto a silicon substrate as a function of the spreading modifier concentration of the ink compositions. 
         FIG. 5A  is an image of inkjet printed drops of Comparative Ink Composition 2 from Table 14 180 seconds post-printing on a silicon substrate.  FIG. 5B  is an image of inkjet printed drops of Ink Composition 9 from Table 14 180 seconds post-printing on a silicon substrate.  FIG. 5C  is an image of inkjet printed drops of Ink Composition 11 from Table 14 180 seconds post-printing on a silicon substrate.  FIG. 5D  is a line drawing of  FIG. 5A .  FIG. 5E  is a line drawing of  FIG. 5B .  FIG. 5F  is a line drawing of  FIG. 5C . 
         FIG. 6A  is graph showing the degree of curing as a function of ultraviolet dosage for a inkjet printed thin film of Comparative Ink Composition 2 and Ink Composition 11 from Table 14 over a dosage range from 0 mJ/cm 2  to 500 mJ/cm 2 .  FIG. 6B  is graph showing the degree of curing as a function of ultraviolet dosage for a inkjet printed thin film of Comparative Ink Composition 2 and Ink Composition 11 from Table 14 over a dosage range from 0 mJ/cm 2  to 3000 mJ/cm 2 . 
         FIG. 7A  is an image of the film edges for a cured 8 μm thick film inkjet printed from Ink Composition 9 from Table 14.  FIG. 7B  is an image of the film edges for a cured 8 μm thick film inkjet printed from Ink Composition 11 from Table 14.  FIG. 7C  is a line drawing of  FIG. 7A .  FIG. 7D  is a line drawing of  FIG. 13B . 
         FIG. 8  is a flow diagram depicting a process for forming a polymeric thin film on a substrate, according to various embodiments of compositions, systems and methods of the present teachings. 
         FIG. 9  is a front perspective view of view of a printing system tool in accordance with various embodiments of the present teachings. 
         FIG. 10  is a schematic depiction of a UV curing module that can be used in manufacturing a light emitting device. 
         FIG. 11  depicts an expanded iso perspective view of a printing system in accordance with various embodiments of the present teachings. 
         FIG. 12  is an iso perspective view of a printing system in accordance with various embodiments of the present teachings. 
         FIG. 13  is a schematic view of various embodiments of gas enclosure assembly and related system components the present teachings. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     The present teachings relate to various embodiments of an ink composition, which once printed and cured forms a polymeric thin film on a substrate, such as, but not limited by, an OLED device substrate. Various embodiments of the ink composition can be printed using an industrial inkjet printing system that can be housed in a gas enclosure, which gas enclosure defines an interior that has a controlled environment maintained as an inert and substantially low-particle process environment. Patterned printing of an organic thin film on a substrate, for example, but not limited by, an OLED device substrate, in such a controlled environment can ensure a high-volume, high yield process for a variety of OLED devices. 
     It is contemplated that a wide variety of ink formulations can be printed within the inert, substantially low-particle environment of various embodiments of a gas enclosure system of the present teachings. During the manufacture of an OLED display, an OLED pixel can be formed to include an OLED film stack, which can emit light of a specific peak wavelength when a voltage is applied. An OLED film stack structure between an anode and a cathode can include a hole injection layer (HIL), a hole transport layer (HTL), an emissive layer (EL), an electron transport layer (ETL) and an electron injection layer (EIL). In some embodiments of an OLED film stack structure, an electron transport layer (ETL) can be combined with an electron injection layer (EIL) to form an ETL/EIL layer. According to the present teachings, various ink formulations for an EL for various color pixel EL films of an OLED film stack can be printed using inkjet printing. Additionally, for example, but not limited by, the HIL, HTL, EML, and ETL/EIL layers can have ink formulations that can be printed using inkjet printing. 
     As will be discussed in more detail subsequently herein, it is further contemplated that an organic encapsulation layer can be printed on an OLED panel using inkjet printing. An encapsulation ink can comprise a polymer or polymer component, for example, but not limited by, various polyethylene glycol monomer materials, an acrylate, such as a mono- or multidentate acrylate, a methacrylate, such as a mono- or multidentate methacrylate, or other material, as well as copolymers and mixtures thereof, which can be cured using thermal processing (e.g. bake), UV exposure, and combinations thereof. As used herein polymer and copolymer can include any form of a polymer component that can be formulated into an ink and cured on a substrate to form an organic encapsulation layer. Such polymeric components can include polymers and copolymers, as well as precursors thereof, for example, but not limited by, monomers, oligomers, and resins. According to the present teachings, inkjet printing can provide several advantages. First, a range of vacuum processing operations can be eliminated because such inkjet-based fabrication can be performed at atmospheric pressure. Additionally, during an inkjet printing process, an organic encapsulation layer can be localized to cover portions of an OLED substrate over and proximal to an active region, to effectively encapsulate an active region, including lateral edges of the active region. The targeted patterning using inkjet printing results in eliminating material waste, as well as eliminating additional processing typically required to achieve patterning of an organic layer. 
     Organic Thin Film Ink Compositions and Methods 
     Various embodiments of an organic thin layer ink composition of the present teachings can be printed on, for example, but not limited by, an optoelectronic device, such as a wide number of OLED devices, to form an organic encapsulation layer. According to various embodiments of compositions and methods, once cured, the resulting polymeric thin film can provide a fluid barrier, as well as providing planarization of a previously fabricated inorganic encapsulation layer, and additionally providing flexibility desired from an organic encapsulation layer. The fluid barriers can prevent or reduce the permeation of, for example, water and/or oxygen into the OLED devices. 
     As depicted in the schematic section view of  FIG. 1 , for optoelectronic device  50 , a substrate  52  can be provided. Various embodiments of a substrate can include one or more of a thin silica-based glass, as well as any of a number of flexible polymeric materials. For example, substrate  52  can be transparent, such as for use in a bottom-emitting optoelectronic device configuration. One or more layers associated with an OLED stack, such as various organic or other material can be deposited, inkjet printed, or otherwise formed upon the substrate to provide an active region  54 , such as to provide electroluminescent region. Note that active region  54  in  FIG. 1  is illustrated schematically as a single block, but can in detail further include a region having complex topology or structure with multiple discrete devices and film layers. In an example,  50  can include an OLED device, such as comprising an emissive layer, or other layers, coupled to an anode electrode and a cathode electrode. The phrase “active” need not imply any requirement of amplification of electrical energy or transistor activity, and can refer generally to a region wherein optoelectrical activity (e.g., light emission) can occur. Accordingly, active region  54  can be included as a portion of an active matrix OLED or a passive matrix OLED device. 
     Respective layers included in an OLED device, such as in the active region  54 , can be on the order of tens or hundreds of nanometers (nm) thick, or less. Additional organic layers that are not active in the optoelectronic action of the OLED device can be included, and such layers can be on the order of microns thick, or less. An anode electrode or a cathode electrode can be coupled to or can include electrode portion  56  that is laterally offset along the substrate  52  from the active region  54 . As will be discussed in more detail herein, the active region  54  of the device  50  can include materials that degrade in the presence of prolonged exposure to various reactive species gaseous species, such as, but not limited by, water, oxygen, as well as various solvent vapors from device processing. Such degradation can impact stability and reliability. 
     As depicted in  FIG. 1 , an inorganic layer  60 A can be provided for device  50 , such as deposited or otherwise formed on active region  54 . For example, the inorganic layer can be blanket coated (e.g., deposited) over an entirety, or substantially an entirety of a surface of the substrate  52 , including active region  54 . Examples of inorganic materials useful for fabricating inorganic layer  60 A can include various oxides, such as one or more of Al 2 O 3 , TiO 2 , HfO 2 , SiO X N Y  or one or more other materials. Organic layer  62 A can be printed, using for example, inkjet printing. For example, as previous generally discussed herein organic layer  62 A can be printed using an organic thin layer ink that can include various polymer materials that are curable using one or more of a thermal (e.g., bake) or ultraviolet exposure technique, and once cured can form a polymeric thin film, such as organic layer  62 A. Organic layer  62 A can serve as one or more of a planarization layer to planarize and mechanically protect the active region  54 , or as a portion of an encapsulation stack that collectively serves to suppress or inhibit moisture or gas permeation into the active region  54 .  FIG. 1  illustrates generally a multi-layer configuration of encapsulation material layers having inorganic layer  60 A such as including an oxide, and the organic layer  62 A, such as including a polymer that can be used to inhibit or suppress exposure of the active region  54  to reactive gases, such as, but not limited by, moisture or atmospheric gases. As depicted in  FIG. 1 , the multi-layer configuration can be repeated to include second inorganic layer  60 B and second organic layer  62 B. Various additional embodiments of encapsulation layers can be created to provide the mechanical and sealing properties desired for an optoelectronic device. For example, the order of the fabrication of the layers could be reversed, so that an organic encapsulation layer is first fabricated, followed by the fabrication of an inorganic layer. Additionally, more or less numbers of layers can be provided. For example, a structure having inorganic layers  60 A and  60 B as shown, and a single organic encapsulation layer  62 A can be fabricated. 
     Various embodiments of the present ink compositions can be inkjet printed into thin films that are continuous and have well-defined edges, yet have thicknesses of no greater than about 3 μm on such substrates as glass, silicon, and/or silicon nitride. This includes embodiments of the ink compositions that can be printed into continuous thin films having well-defined edges and thicknesses of no greater than about 2 μm, and further includes embodiments of the ink compositions that can be printed into continuous thin films having well-defined edges and thicknesses of no greater than about 1 μm. This is significant because, while highly spreading inks may be good candidates for thin film formation, their highly spreading nature typically results in an uncontrolled, non-uniform spread that provides thin films printed therefrom with poor edge definition. At least partially for this reasons, wetting agents that are used to increase the spreading of an ink composition are generally present in limited amounts as minor components or additives in an ink composition. The present ink compositions overcome this challenge by using alkoxylated aliphatic di(meth)acrylate monomers as controlled spreading modifiers in polyethylene glycol di(meth)acrylate-based ink compositions. When the spreading modifiers are present at high concentrations in the ink compositions, drops of the ink compositions inkjet printed onto a substrate are able to spread and merge into a continuous ultrathin film. Notably, the drop spreading occurs in a controlled fashion so that the edges of the printed ultrathin films are well-defined. As a result, the ink compositions are suited for use in printing organic layers for OLED applications, including organic planarization layers that serve to planarize and mechanically protect an active region or that provide a portion of an encapsulation stack that collectively serves to suppress or inhibit moisture or gas permeation into an active region. 
     The organic thin layer ink compositions comprise one or more polyethylene glycol di(meth)acrylate monomers, a multifunctional crosslinking agent, and a spreading modifier comprising one or more alkoxylated aliphatic di(meth)acrylate monomers. As used herein, the phrase “(meth)acrylate monomer” indicates that the recited monomer may be an acrylate or a methacrylate. Some embodiments of the ink compositions further include crosslinking photoinitiators. 
     Without wishing or intending to be bound to any particular theory of any inventions disclosed herein, it is believed that the polyethylene glycol di(meth)acrylate monomers have a tendency to act as pinning agents that limit the spreading ability of ink compositions on a variety of substrate materials found in OLED devices, including glass substrates, silicon substrates, and silicon nitride substrates, and that the spreading modifiers comprising alkoxylated aliphatic di(meth)acrylate monomers, if present at sufficiently high concentrations, are able to reduce this pinning effect without causing uncontrolled ink drop spreading. This is the case even though the spreading modifiers are present at high concentrations significantly higher than the concentrations of wetting agents typically used in acrylate-based inkjet inks for OLED applications. This is consistent with the observation, discussed in greater detail below, that at relatively low concentrations, (e.g., between about 2 wt. % and about 10 wt. %) increasing the spreading modifier concentration makes little difference in the spreading behavior of the ink compositions, but beyond the threshold concentrations of about 15 wt. %, 30 wt. %, and most dramatically 40 wt. % there are marked up-ticks in the spreadability of the ink compositions. 
     Some embodiments of the ink compositions comprise about 30 wt. % to about 50 wt. % polyethylene glycol di(meth)acrylate monomer. This includes ink compositions that comprise about 40 wt. % to about 50 wt. % polyethylene glycol di(meth)acrylate monomer, and further includes ink compositions that comprise about 45 wt. % to about 50 wt. % polyethylene glycol di(meth)acrylate monomer. These embodiments of the ink compositions comprise about 40 wt. % to about 60 wt. % of the spreading modifier. This includes ink compositions that comprise about 40 wt. % to about 50 wt. % of the spreading modifier and further includes ink compositions that comprise about 40 wt. % to about 45 wt. % of the spreading modifier. The ink compositions can also be characterized by their weight ratios. Thus, some embodiments of the ink compositions have a polyethylene glycol di(meth)acrylate monomer to spreading modifier weight ratio in the range from about 1:2 to 5:4. This includes ink compositions that have a polyethylene glycol di(meth)acrylate monomer to spreading modifier weight ratio in the range from about 4:5 to 5:4, and also includes ink compositions that that have a polyethylene glycol di(meth)acrylate monomer to spreading modifier weight ratio in the range from about 1:1 to 5:4. 
     It has been found that within the above recited weight percent ranges and weight ratios, drops of the ink compositions inkjet printed on inorganic substrates commonly employed in OLEDs, including OLED barrier layers, have an unexpectedly high drop spreading rate. The drop spreading rate can be measured as the increase in the diameter of an inkjet printed drop in the early stages of drop spreading. For example, the drop spreading rate can be measured as the increase in the diameter of a drop in the time period from 40 seconds after it is printed onto a substrate (40 seconds post-printing) to 180 seconds after it is printed onto the substrate (180 seconds post-printing) at a printing temperature of 23° C. By way of illustration, some embodiments of the ink compositions have a spreading rate, as measured by the increase in their drop diameter between 40 seconds and 180 seconds post-inkjet printing on a silicon substrate at 23° C., of at least 0.5 μm/s. This includes embodiments of the ink compositions that have a spreading rate, as measured by the increase in their drop diameter between 40 seconds and 180 seconds post-inkjet printing on a silicon substrate at 23° C., of at least 0.65 μm/s, further includes embodiments of the ink compositions that have a spreading rate, as measured by the increase in their drop diameter between 40 seconds and 180 seconds post-inkjet printing on a silicon substrate at 23° C., of at least 0.7 μm/s, and still further includes embodiments of the ink compositions that have a spreading rate, as measured by the increase in their drop diameter between 40 seconds and 180 seconds post-inkjet printing on a silicon substrate at 23° C., of at least 0.8 μm/s. These high spreading rates make it possible for the printed drops to spread and merge into continuous ultrathin films that have an average thickness of no greater than about 1 μm (although, the ink compositions can also be used to print thicker films). Yet, because the spreading is controlled, the films retain well defined edges and uniform thicknesses. 
     Other embodiments of the ink compositions provide spreading rates that are still unusually fast, but somewhat lower. These ink compositions are suited for applications where an ultrathin film is not required or desired. For example, these lower spreading ink compositions can provide continuous inkjet printed films on a silicon substrate, wherein the films have thicknesses in the range from about 2 μm to about 4 μm and well defined edges. This includes ink compositions that provide continuous inkjet printed films on a silicon substrate, wherein the films have thicknesses in the range from about 2 μm to about 3 μm and well defined edges. These ink compositions comprise about 50 wt. % to about 75 wt. % of the polyethylene glycol di(meth)acrylate monomer. This includes ink compositions that comprise about 55 wt. % to about 70 wt. % polyethylene glycol di(meth)acrylate monomer, and further includes ink compositions that comprise about 55 wt. % to about 60 wt. % polyethylene glycol di(meth)acrylate monomer. The ink compositions comprise about 15 wt. % to about 40 wt. % of the spreading modifier. This includes ink compositions that comprise about 20 wt. % to about 35 wt. % of the spreading modifier and further includes ink compositions that comprise about 30 wt. % to about 35 wt. % of the spreading modifier. The ink compositions can also be characterized by their weight ratios. Thus, some embodiments of the ink compositions have a polyethylene glycol di(meth)acrylate monomer to spreading modifier weight ratio in the range from about 5:4 to about 5:1. This includes ink compositions that have a polyethylene glycol di(meth)acrylate monomer to spreading modifier weight ratio in the range from about 11:7 to about 7:2, and also includes ink compositions that that have a polyethylene glycol di(meth)acrylate monomer to spreading modifier weight ratio in the range from about 11:7 to about 2:1. 
     By way of illustration, some embodiments of these somewhat less rapidly spreading ink compositions have a spreading rate, as measured by the increase in their drop diameter between 40 seconds and 180 seconds post-inkjet printing on a silicon substrate at 23° C., of at least 0.1 μm/s. This includes embodiments of the ink compositions that have a spreading rate, as measured by the increase in their drop diameter between 40 seconds and 180 seconds post-inkjet printing on a silicon substrate at 23° C., of at least 0.14 μm/s, further includes embodiments of the ink compositions that have a spreading rate, as measured by the increase in their drop diameter between 40 seconds and 180 seconds post-inkjet printing on a silicon substrate at 23° C., of at least 0.2 μm/s, and still further includes embodiments of the ink compositions that have a spreading rate, as measured by the increase in their drop diameter between 40 seconds and 180 seconds post-inkjet printing on a silicon substrate at 23° C., of at least 0.3 μm/s. These high spreading rates make it possible for the printed drops to spread and merge into continuous ultrathin films that have an average thickness of no greater than about 3 μm (although, the ink compositions can also be used to print thicker films). Yet, because the spreading is controlled, the films retain well defined edges and uniform coverage and thicknesses. 
     According to the present teachings, various compositions of an organic thin layer ink composition can include a polyethylene glycol dimethacrylate and/or a polyethylene glycol diacrylate having a number average molecular weight in the range from about 230 gm/mole to about 440 gm/mole as the polyethylene glycol di(meth)acrylate monomer. For example, the organic thin layer ink can include polyethylene glycol 200 dimethacrylate and/or polyethylene glycol 200 diacrylate, having a number average molecular weight of about 330 gm/mole and having the generalized structure as shown below: 
     
       
         
         
             
             
         
       
     
     where n is on average 4 and R is independently selected from H and methyl groups. 
     The spreading modifier, which is used to tune the spreading characteristics of various embodiments of the organic thin layer ink compositions, comprises an alkoxylated aliphatic diacrylate, an alkoxylated aliphatic dimethacrylate, or a combination thereof. The formula for an alkoxylated aliphatic diacrylate can be represented as follows: 
     
       
         
         
             
             
         
       
     
     where n can be between 3 to 12. The formula for an alkoxylated aliphatic dimethacrylate can be represented as follows: 
     
       
         
         
             
             
         
       
     
     where n can be between 3 to 12. The alkoxylated aliphatic diacrylate spreading modifiers desirably have a viscosity in the range from about 10 cps to about 20 cps at 22° C., including about 14 cps to about 18 cps at 22° C., and a surface tension in the range from about 35 dynes/cm to 39 dynes/cm at 22° C. This includes embodiments of the spreading modifiers having viscosities in the range from about 14 cps to about 16 cps at 22° C. and a surface tension in the range from about 35 dynes/cm to 38 dynes/cm at 22° C. Methods for measuring viscosities and surface tensions are well known and include the use of commercially available rheometers (e.g., a DV-I Prime Brookfield rheometer) and tensiometers (e.g., a SITA bubble pressure tensiometer). 
     Various alkoxylated aliphatic diacrylate materials are commercially available. For example, alkoxylated aliphatic di(meth)acrylate materials can be provided by Sartomer Corporation. Candidate Sartomer products include Sartomer product number SR-238B, which is 1,6 hexanediol diacrylate with a surface tension of about 35 dynes/cm at 22° C., as well as Sartomer product number SR-9209A, which is described as a proprietary alkoxylated aliphatic diacrylate and has a surface tension of about 35 dynes/cm at 22° C. and a viscosity of about 15 cps at 22° C. For various embodiments of the organic thin layer ink compositions, the aliphatic portion of an alkoxylated aliphatic di(meth)acrylate component can be between 3 to 12 repeating methylene units. For various embodiments of the organic thin layer ink compositions, the aliphatic portion of an alkoxylated aliphatic di(meth)acrylate component can be between 4 to 6 repeating methylene units. 
     The use of the (meth)acrylate based spreading modifiers may be advantageous because they are generally compatible with the polyethylene glycol di(meth)acrylate monomers and the (meth)acrylate based multifunctional crosslinking agents of the ink compositions. As such, their use will not cause the precipitation of the other acrylate or methacrylate based components from solution. In addition, the acrylate and methacrylate based spreading modifiers can participate in the crosslinking of the polyethylene glycol di(meth)acrylate. That is, the spreading modifier(s) can be incorporated into the polymer through similar chemistry, so as not to remain as contaminants after UV curing. 
     The multifunctional (meth)acrylate crosslinking agents desirably have at least three reactive (meth)acrylate groups. Thus, the multifunctional (meth)acrylate crosslinking agents can be, for example, tri(meth)acrylates, tetra(meth)acrylates and/or higher functionality (meth)acrylates. Pentaerythritol tetraacrylate or pentaerythritol tetramethacrylate, di(trimethylolpropane) tetraacrylate and di(trimethylolpropane) tetramethacrylate are examples of multifunctional (meth)acrylates that can be used as a primary cross-linking agent. The term ‘primary’ is used here to indicate that other components of the ink compositions may also participate in crosslinking, although that is not their main functional purpose. For various embodiments of an organic thin layer ink composition, multifunctional (meth)acrylate crosslinking agents can comprise between about 4 to about 10 wt. % of an ink composition. A generalized structure for pentaerythritol tetraacrylate or pentaerythritol tetramethacrylate is shown below. 
     
       
         
         
             
             
         
       
     
     where R is independently selected from H and methyl groups. 
     A generalized structure for di(trimethylolpropane) tetraacrylate or di(trimethylolpropane) tetramethacrylate is shown below. 
     
       
         
         
             
             
         
       
     
     where R′ is independently selected from H and methyl groups. 
     Regarding initiation of the polymerization process, various embodiments of the organic thin layer ink compositions of the present teachings can utilize numerous types of photoinitiators for initiating the polymerization process. In various embodiments the photoinitiators are present in amounts in the range from about 0.1 wt. % to about 10 wt. %, for example, from about 0.1 wt. % to about 8 wt. %. This includes embodiments in which the photoinitiators are present in amounts in the range from about 1 wt. % to about 6 wt. %, further includes embodiments in which the photoinitiators are present in amounts in the range from about 3 wt. % to about 6 wt. %, and still further includes embodiments in which the photoinitiators are present in amounts in the range from about 3.75 wt. % to about 4.25 wt. %. However, amounts outside of these ranges can also be used. The photoinitiator may be a Type I or a Type II photoinitiator. Type I photoinitiators undergo radiation-induced cleavage to generate two free radicals, one of which is reactive and initiates polymerization. Type II photoinitiators undergo a radiation-induced conversion into an excited triplet state. The molecules in the excited triplet state then react with molecules in the ground state to produce polymerization initiating radicals. 
     The specific photoinitiators used for a given ink composition are desirably selected such that they are activated at wavelengths that are not damaging to the OLED materials. For this reason, various embodiments of the ink compositions include photoinitiators that have a primary absorbance with a peak in the range from about 368 nm to about 420 nm. The light source used to activate the photoinitiators and induce the curing of the ink compositions is desirably selected such that the absorbance range of the photoinitiator matches or overlaps with the output of the light source, whereby absorption of the light creates free radicals that initiate polymerization. Suitable light sources may include mercury arc lamps and UV light emitting diodes. 
     An acylphosphine oxide photoinitiator can be used, though it is to be understood that a wide variety of photoinitiators can be used. For example, but not limited by, photoinitiators from the α-hydroxyketone, phenylglyoxylate, and α-aminoketone classes of photoinitiators can also be considered. For initiating a free-radical based polymerization, various classes of photoinitiators can have an absorption profile of between about 200 nm to about 400 nm. For various embodiments of the ink compositions and methods of printing disclosed herein, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) and 2,4,6-trimethylbenzoyl-diphenyl phosphinate have desirable properties. For various embodiments of the ink compositions and printing methods of the present teaching, an acylphosphine oxide photoinitiator can be about 0.1-5 wt. % of a formulation. Examples of acylphosphine photoinitiators include Irgacure® TPO (also previously available under the tradename Lucirin® TPO) initiators for UV curing sold under the tradenames Irgacure® TPO, a type I hemolytic initiator which; with absorption @ 380 nm; Irgacure® TPO-L, a type I photoinitiator that absorbs at 380 nm; and Irgacure® 819 with absorption at 370 nm. By way of illustration, a light source emitting at a nominal wavelength in the range from 350 nm to 395 nm at a radiant energy density of up to 1.5 J/cm 2  could be used to cure an ink composition comprising a TPO photoinitiator. Using the appropriate energy sources, high levels of curing can be achieved. For example, some embodiments of the cured films have a degree of curing of 90% or greater, as measured by Fourier Transform Infrared (FTIR) spectroscopy. 
     The appropriate amount of photoinitiator to include in a given ink composition will depend on the nature of the selected photoinitiator, crosslinking agent and spreading modifier. However, the amount of photoinitiator is desirably selected to minimize the volume change that takes place from the time the ink composition is printed to the time the ink composition is cured into a solid film. An accurate test for measuring the volume change of ink compositions that takes place during the curing and that allows for the precise determination of the appropriate amount of photoinitiator to be included in a given ink composition in order to minimize that volume change can be carried out as follows. A known volume of an ink composition is carefully dispensed into the bottom of a container with a known volume marking (for example, a volumetric flask). The ink composition in the container is then exposed to a radiation source that induces crosslinking and cures the ink composition into a solid film. A volume of deionized (DI) water corresponding to the volume indicated by the volume marking on the container is then dispensed into the container with the cured film. The portion of the DI water above the volume marking is then extracted from the container and weighed to determine the volume of the cured film. By way of illustration, the test can be carried out in a laboratory as follows. Place a 5 mL glass volumetric flask into a glove box, along with a UV-curable ink composition, and a hand-held ultraviolet (UV) lamp. Using an Eppendorf pipette and an appropriate tip, carefully dispense 500 μL of the ink composition into the volumetric flask without touching the tip to the side walls, such that all of the ink composition is dispensed into the bottom of flask. Place the volumetric flask over the UV lamp and turn on the lamp to an appropriate wavelength setting (e.g., 365 nm) for a time sufficient to fully cure the ink composition (e.g., about 180 seconds). Note: the operator should be wearing UV protective glasses. After the ink composition has cured into a solid film, turn off the lamp and place a stopper on flask. Take the stoppered flask with the cured film out of the glove box. Place the flask on a weighing balance, without the glass stopper, and measure its tare weight. Using a Pasteur pipette, carefully dispense (avoiding the side walls) precisely 5 grams of DI water into the volumetric flask. Then remove the flask from the balance, place an empty dry vial on the balance and measure its tare weight. Using a fresh dry Pasteur pipette carefully extract the portion of DI water from volumetric flask that is above the 5 mL mark. At the endpoint of the extraction, the low point of the meniscus of the water must be aligned with the 5 mL mark, as determined by visual inspection. Transfer the full amount of the extracted DI water into the empty vial and measure its weight (w1). The percent volume change (e.g., volume reduction) resulting from the curing of the dispensed ink composition can be calculated using the following equation: 
       Volume change %=100−(( w 1 grams/0.5 grams)×100).
 
     Generally, for ink compositions useful for inkjet printing applications, the surface tension, viscosity and wetting properties of the ink compositions should be tailored to allow the compositions to be dispensed through an inkjet printing nozzle without drying onto or clogging the nozzle at the temperature used for printing (e.g., room temperature; ˜22° C.). Once formulated, various embodiments of the organic thin layer ink compositions can have a viscosity of between about 10 cps and about 25 cps (including, for example, between about 17 cps and about 21 cps) at 22° C. and a surface tension of between about 32 dynes/cm and about 45 dynes/cm (including, for example, between about 38 dynes/cm and about 41 dynes/cm) at 22° C. As jetting temperatures can be between about 22° C. to about 40° C., over such a temperature range, various embodiments of organic thin layer ink formulations can have a viscosity of between about 7-25 cps (including, for example, between about 9 cps and about 19 cps) and a surface tension of between about 30 dynes/cm and about 45 dynes/cm in the temperature range of the printhead. 
     Given that the initiation of polymerization can be induced by light, inks can be prepared to prevent exposure to light. With respect to preparation of organic thin layer ink compositions of the present teachings, in order to ensure the stability of various compositions, the compositions can be prepared in a dark or very dimly lit room or in a facility in which the lighting is controlled to exclude wavelengths that would induce polymerization. Such wavelengths generally include those below about 500 nm. For example, for the preparation of an embodiment of an organic thin film ink formulation, in a fashion that protects the direct exposure to light, the lid of a clean amber vial (for example, Falcons, VWR trace clean) can be removed and then can be placed on a balance; and tared. First, a desired amount of a photoinitiator can be weighed into the vial. Then, after the addition of the spreading modifier component, the polyethylene di(meth)acrylate can be weighed into the vial. Next, the crosslinking agent can be weighed into the vial. (The preceding description lays out one protocol for sequentially incorporating the various components into an ink composition. Other protocols can be used.) Regarding mixing to provide uniform concentration of components, a Teflon® coated magnetic stir bar can be inserted into the vial and the cap of vial secured. The solution can then be stirred, for example, for 30 minutes at temperatures in the range from room temperature to 50° C. and 600-1000 rpm. Thereafter, the ink composition can be filtered, for example, through a 0.1 μm or 0.45 μm PTFE syringe filter or vacuum or pressure filter, followed by sonication for 30 minutes at ambient temperature. The ink composition is then ready for use and should be stored away from light, for example, in a compressed dry air glove box. Various embodiments of an organic thin film ink preparation as described can have a viscosity of between about 17 cps and about 19 cps at 22° C. and a surface tension of between about 37 dynes/cm and about 41 dynes/cm at 22° C. 
     Once the ink compositions are prepared, they can be dehydrated by mixing in the presence of molecular sieve beads for a period of a day or more and then stored under a dry, inert atmosphere, such as a compressed dry air atmosphere. The ink composition should be stored in amber light or in the dark in order to avoid or minimize premature polymerization. For example, the ink composition can be stored in an amber vial. Drying and storage in a dry, inert atmosphere can keep the water content of the ink compositions below about 400 ppm (including, for example, below about 200 ppm), which is desirable for ink jet printing, until the compositions are ready for use. In order to reduce the water content of the ink compositions, a dehydration process can be carried out, wherein molecular sieve beads (e.g., 3 Angstrom; 10% w/w) are added to the composition and the composition is placed on a roller to provide gentle agitation for a period of time (e.g., 5 days), after which the ink composition can be filtered and transferred into a dry atmosphere, such as a compressed dry air atmosphere, and aliquoted into amber vials, followed by capping the vials, to provide a dry air headspace in the vials. The same procedure can be used to produce the same results with a compressed dry air headspace. The ink compositions, particularly those stored under a dry air atmosphere at room temperature (22° C.), can be stable for long periods of time, as determined by the lack of precipitation or separation under visual inspection and the stabilities in their room temperature viscosities and surface tensions. 
     The ink compositions can be printed using a printing system, such as that described in U.S. Pat. No. 8,714,719, which is incorporated herein in its entirety. The films can be cured in an inert nitrogen environment using UV radiation. The cured films display high transparency, as well as uniform thickness. By way of illustration, some embodiments of cured films can have a film thickness variation of 5% or lower. Film thickness uniformity can be measured using a profilometer tool, such as a Veeco Dektak Profilometer tool. To carry out a thickness measurement, a scratch can be made on the film using, for example, a sharp needle on a substrate. Then the substrate can be placed on the tool to measure the height of the scratch well, which represents the thickness of the film printed on the substrate. Some embodiments of the cured films made with the present ink compositions can have a transmission of 90% or greater at wavelengths of 550 nm and above. This includes cured films having a transmission of 99% or greater, and 99.5% or greater, at wavelengths of 550 nm and above. 
     The ink compositions are designed to be applied by inkjet printing and are, therefore, characterized by jettability, wherein a jettable ink composition displays constant, or substantially constant, drop velocities, drop volumes and drop trajectories over time when jetted continuously through the nozzle of a printhead. In addition, the ink compositions are desirably characterized by good latency properties, where latency refers to the time that nozzles can be left uncovered and idle before there is a significant reduction in performance, for instance a reduction in drop velocity or volume and/or a change in trajectory that will noticeably affect the image quality. 
     Example Ink Compositions 
     Tables 1-13 show the formulations for various ink compositions comprising polyethylene glycol di(meth)acrylates and alkoxylated aliphatic di(meth)acrylate monomers. The formulations of Tables 1-5 are provided for purposes of comparison. The formulations of Tables 6-13 represent ink compositions characterized by high spreading rates, wherein the formulations of Tables 11-13 represent the highest spreading ink compositions that are well suited for printing continuous ultrathin inkjet printed films. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Comparative Ink Composition 1 
               
            
           
           
               
               
               
               
            
               
                   
                 Component 
                 Wt. % 
                 Wt. (g) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 SR9209A 
                 2.0 
                 0.200 
               
               
                   
                 PEG-200D 
                 87 
                 8.70 
               
               
                   
                 PET 
                 7.0 
                 0.700 
               
               
                   
                 BASF-TPO 
                 4.0 
                 0.400 
               
               
                   
                 Total 
                 100 
                 10.0 
               
               
                   
                   
               
            
           
         
       
     
     Comparative Ink Composition 1 had a viscosity of 18.2 cps and a surface tension of 39.6 dynes/cm at a temperature in the range from 23° C. to 25° C. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Comparative Ink Composition 2 
               
            
           
           
               
               
               
               
            
               
                   
                 Component 
                 Wt. % 
                 Wt. (g) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 SR9209A 
                 4.0 
                 4.00 
               
               
                   
                 PEG-200D 
                 85 
                 85.0 
               
               
                   
                 PET 
                 7.0 
                 7.00 
               
               
                   
                 BASF-TPO 
                 4.0 
                 4.00 
               
               
                   
                 Total 
                 100 
                 100 
               
               
                   
                   
               
            
           
         
       
     
     Comparative Ink Composition 2 had a viscosity of 18.8 cps and a surface tension of 40.1 dynes/cm at a temperature in the range from 23° C. to 25° C. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Comparative Ink Composition 3 
               
            
           
           
               
               
               
               
            
               
                   
                 Component 
                 Wt. % 
                 Wt. (g) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 SR9209A 
                 6.0 
                 0.600 
               
               
                   
                 PEG-200D 
                 83 
                 8.30 
               
               
                   
                 PET 
                 7.0 
                 0.700 
               
               
                   
                 BASF-TPO 
                 4.0 
                 0.400 
               
               
                   
                 Total 
                 100 
                 10.0 
               
               
                   
                   
               
            
           
         
       
     
     Comparative Ink Composition 3 had a viscosity of 19 cps and a surface tension of 40.4 dynes/cm at a temperature in the range from 23° C. to 25° C. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Comparative Ink Composition 4 
               
            
           
           
               
               
               
               
            
               
                   
                 Component 
                 Wt. % 
                 Wt. (g) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 SR9209A 
                 8.0 
                 0.800 
               
               
                   
                 PEG-200D 
                 81 
                 8.10 
               
               
                   
                 PET 
                 7.0 
                 0.700 
               
               
                   
                 BASF-TPO 
                 4.0 
                 0.400 
               
               
                   
                 Total 
                 100 
                 10.0 
               
               
                   
                   
               
            
           
         
       
     
     Comparative Ink Composition 4 had a viscosity of 18.9 cps and a surface tension of 39.7 dynes/cm at a temperature in the range from 23° C. to 25° C. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Comparative Ink Composition 5 
               
            
           
           
               
               
               
               
            
               
                   
                 Component 
                 Wt. % 
                 Wt. (g) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 SR9209A 
                 10 
                 1.00 
               
               
                   
                 PEG-200D 
                 79 
                 7.90 
               
               
                   
                 PET 
                 7.0 
                 0.700 
               
               
                   
                 BASF-TPO 
                 4.0 
                 0.400 
               
               
                   
                 Total 
                 100 
                 10.0 
               
               
                   
               
            
           
         
       
     
     Comparative Ink Composition 5 had a viscosity of 19.3 cps and a surface tension of 39.7 dynes/cm at a temperature in the range from 23° C. to 25° C. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Ink Composition 6 
               
            
           
           
               
               
               
               
            
               
                   
                 Component 
                 Wt. % 
                 Wt. (g) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 SR9209A 
                 15 
                 1.50 
               
               
                   
                 PEG-200D 
                 74 
                 7.40 
               
               
                   
                 PET 
                 7.0 
                 0.700 
               
               
                   
                 BASF-TPO 
                 4.0 
                 0.400 
               
               
                   
                 Total 
                 100 
                 10.0 
               
               
                   
               
            
           
         
       
     
     Ink Composition 6 had a viscosity of 19.3 cps and a surface tension of 39.7 dynes/cm at a temperature in the range from 23° C. to 25° C. 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Ink Composition 7 
               
            
           
           
               
               
               
               
            
               
                   
                 Component 
                 Wt. % 
                 Wt. (g) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 SR9209A 
                 20 
                 2.00 
               
               
                   
                 PEG-200D 
                 69 
                 6.90 
               
               
                   
                 PET 
                 7.0 
                 0.700 
               
               
                   
                 BASF-TPO 
                 4.0 
                 0.400 
               
               
                   
                 Total 
                 100 
                 10.0 
               
               
                   
               
            
           
         
       
     
     Ink Composition 7 had a viscosity of 19.3 cps and a surface tension of 39.6 dynes/cm at a temperature in the range from 23° C. to 25° C. 
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Ink Composition 8 
               
            
           
           
               
               
               
               
            
               
                   
                 Component 
                 Wt. % 
                 Wt. (g) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 SR9209A 
                 25 
                 2.50 
               
               
                   
                 PEG-200D 
                 64 
                 6.40 
               
               
                   
                 PET 
                 7.0 
                 0.700 
               
               
                   
                 BASF-TPO 
                 4.0 
                 0.400 
               
               
                   
                 Total 
                 100 
                 10.0 
               
               
                   
               
            
           
         
       
     
     Ink Composition 8 had a viscosity of 19.4 cps and a surface tension of 39.5 dynes/cm at a temperature in the range from 23° C. to 25° C. 
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 Ink Composition 9 
               
            
           
           
               
               
               
               
            
               
                   
                 Component 
                 Wt. % 
                 Wt. (g) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 SR9209A 
                 30 
                 3.00 
               
               
                   
                 PEG-200D 
                 59 
                 5.90 
               
               
                   
                 PET 
                 7.0 
                 0.700 
               
               
                   
                 BASF-TPO 
                 4.0 
                 0.400 
               
               
                   
                 Total 
                 100 
                 10.0 
               
               
                   
               
            
           
         
       
     
     Ink Composition 9 had a viscosity of 19.2 cps and a surface tension of 39.5 dynes/cm at a temperature in the range from 23° C. to 25° C. 
     
       
         
           
               
             
               
                 TABLE 10 
               
             
            
               
                   
               
               
                 Ink Composition 10 
               
            
           
           
               
               
               
               
            
               
                   
                 Component 
                 Wt. % 
                 Wt. (g) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 SR9209A 
                 35 
                 3.50 
               
               
                   
                 PEG-200D 
                 54 
                 5.40 
               
               
                   
                 PET 
                 7.0 
                 0.700 
               
               
                   
                 BASF-TPO 
                 4.0 
                 0.400 
               
               
                   
                 Total 
                 100 
                 10.0 
               
               
                   
               
            
           
         
       
     
     Ink Composition 10 had a viscosity of 19.2 cps and a surface tension of 38.8 dynes/cm at a temperature in the range from 23° C. to 25° C. 
     
       
         
           
               
             
               
                 TABLE 11 
               
             
            
               
                   
               
               
                 Ink Composition 11 
               
            
           
           
               
               
               
               
            
               
                   
                 Component 
                 Wt. % 
                 Wt. (g) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 SR9209A 
                 40 
                 4.00 
               
               
                   
                 PEG-200D 
                 49 
                 4.90 
               
               
                   
                 PET 
                 7.0 
                 0.700 
               
               
                   
                 BASF-TPO 
                 4.0 
                 0.400 
               
               
                   
                 Total 
                 100 
                 10.0 
               
               
                   
               
            
           
         
       
     
     Ink Composition 11 had a viscosity of 19.3 cps and a surface tension of 39.1 dynes/cm at a temperature in the range from 23° C. to 25° C. 
     
       
         
           
               
             
               
                 TABLE 12 
               
             
            
               
                   
               
               
                 Ink Composition 12 
               
            
           
           
               
               
               
               
            
               
                   
                 Component 
                 Wt. % 
                 Wt. (g) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 SR9209A 
                 45 
                 4.50 
               
               
                   
                 PEG-200D 
                 44 
                 4.40 
               
               
                   
                 PET 
                 7.0 
                 0.700 
               
               
                   
                 BASF-TPO 
                 4.0 
                 0.400 
               
               
                   
                 Total 
                 100 
                 10.0 
               
               
                   
               
            
           
         
       
     
     Ink Composition 12 had a viscosity of 19.3 cps and a surface tension of 38.7 dynes/cm at a temperature in the range from 23° C. to 25° C. 
     
       
         
           
               
             
               
                 TABLE 13 
               
             
            
               
                   
               
               
                 Ink Composition 13 
               
            
           
           
               
               
               
               
            
               
                   
                 Component 
                 Wt. % 
                 Wt. (g) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 SR9209A 
                 50 
                 5.00 
               
               
                   
                 PEG-200D 
                 39 
                 3.90 
               
               
                   
                 PET 
                 7.0 
                 0.700 
               
               
                   
                 BASF-TPO 
                 4.0 
                 0.400 
               
               
                   
                 Total 
                 100 
                 10.0 
               
               
                   
               
            
           
         
       
     
     Ink Composition 13 had a viscosity of 18.7 cps and a surface tension of 38.7 dynes/cm at a temperature in the range from 23° C. to 25° C. 
     The spreading rate for drops of each ink composition was measured by inkjet printing a drop of ink onto the surface of a silicon wafer at a temperature of approximately 23° C. For each test, 10 grams of each ink composition was prepared and 2 grams injected into the print cartridge of a Dimatix DMP 2831 printer. Drops of the ink compositions were then printed onto the surface of a silicon substrate at a firing velocity of approximately 6 m/s. The silicon substrate was a 1″ Si wafer that had undergone cleaning using an Ultra T cleaning system, followed by baking at 225° C. and exposure to ultraviolet ozone (UVO) for 15 minutes. The Ultra T cleaning is a precision cleaning technology available from the Ultra T Equipment Company, Inc., Fremont, Ca. The Ultra T cleaning system removed all types of particulates from the Si wafer using a high-pressure de-ionized water spray. 
     Beginning at 40 seconds post-printing, pictures were taken of the ink drops as they spread on the silicon at regular time intervals and the diameters of the printed drops were measured from the pictures. Multiple tests were conducted for each ink composition. The results are presented in Table 14. The drop diameter for each of the ink compositions at 40 seconds post-printing is shown in  FIG. 3 . 
     
       
         
           
               
             
               
                 TABLE 14 
               
             
            
               
                   
               
               
                 Ink Composition Spreading Behavior 
               
            
           
           
               
               
               
            
               
                   
                 Drop Diameter at time T (μm) 
                 Spreading 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Formulation 
                 40 s 
                 60 s 
                 90 s 
                 120 s 
                 150 s 
                 180 s 
                 300 s 
                 Rate* (μm/s) 
               
               
                   
               
               
                 Comparative 1 
                 121.7 
                 123.4 
                 126.3 
                 128.5 
                 130.2 
                 130.5 
                 133.6 
                 0.0629 
               
               
                 Comparative 2 
                 122.0 
                 124.8 
                 128.0 
                 128.8 
                 130.2 
                 130.8 
                 131.6 
                 0.0629 
               
               
                 Comparative 3 
                 122.9 
                 128.8 
                 132.5 
                 132.8 
                 134.2 
                 135.6 
                 137.9 
                 0.0907 
               
               
                 Comparative 4 
                 125.4 
                 129.4 
                 131.9 
                 135.3 
                 135.6 
                 136.7 
                 138.1 
                 0.0807 
               
               
                 Comparative 5 
                 126.3 
                 129.4 
                 133.0 
                 135.3 
                 137.3 
                 137.6 
                 139.8 
                 0.0807 
               
               
                 6 
                 138.7 
                 143.8 
                 148.9 
                 151.7 
                 155.1 
                 158.2 
                 164.5 
                 0.1393 
               
               
                 7 
                 141.5 
                 146.1 
                 150.3 
                 154.6 
                 158.2 
                 161.1 
                 169.8 
                 0.1400 
               
               
                 8 
                 147.2 
                 152.9 
                 156.5 
                 160.5 
                 164.2 
                 167.6 
                 175.8 
                 0.1457 
               
               
                 9 
                 171.0 
                 178.9 
                 187.7 
                 197.6 
                 205.0 
                 213.7 
                 238.6 
                 0.3050 
               
               
                 10 
                 178.3 
                 188.2 
                 204.7 
                 218.8 
                 232.4 
                 246.3 
                 288.2 
                 0.4857 
               
               
                 11 
                 260.2 
                 291.3 
                 328.4 
                 350.7 
                 365.2 
                 375.6 
                 408.5 
                 0.8243 
               
               
                 12 
                 282.2 
                 313.4 
                 336.3 
                 353.6 
                 364.3 
                 376.5 
                 409.3 
                 0.6736 
               
               
                 13 
                 320.4 
                 342.2 
                 360.9 
                 375.4 
                 383.9 
                 394.3 
                 434.8 
                 0.5279 
               
               
                   
               
               
                 *Measured as the change in the diameter of an inkjet printed drop beginning 40 seconds after being printed onto a silicon substrate surface and ending 180 seconds after being printed onto the silicon substrate surface. 
               
            
           
         
       
     
     As illustrated in  FIG. 3 , increasing the amount of the spreading modifier in the Comparative Ink Compositions had little effect on their spreading properties. In fact, doubling the amount of the spreading modifier from 2 wt. % (Comparative Ink Composition 1) to 4 wt. % (Comparative Ink Composition 2) had no significant impact on the size of the printed drops at 40 seconds post-printing. Moreover, increasing the amount of the spreading modifier by a factor of five from 2 wt. % (Comparative Ink Composition 1) to 10 wt. % (Comparative Ink Composition 5) resulted in a drop diameter increase of less than 4%. Thus, the trend in drop spreading for the Comparative Ink Compositions is one of sharply diminishing returns with increasing spreading modifier concentration (i.e., decreasing polyethylene glycol di(meth)acrylate monomer to spreading modifier weight ratio). The corresponding drop spreading rates for the Comparative Ink Compositions were also very modest and changed only slightly with increasing spreading modifier content, ranging from about 0.06 μm/s for ink compositions comprising 2 wt. % of the spreading modify to about 0.08 μm/s for ink compositions comprising five times as much spreading modifier. 
     Beyond a spreading modifier concentration of 10 wt. % (i.e., at a polyethylene glycol di(meth)acrylate monomer to spreading modifier weight ratio of about 8:1 or higher), however, increasing the spreading modifier content of the inks composition resulted in multiple, stepped increases in the drop spreading rates of the ink compositions. Thus, in striking contrast to the Comparative Ink Compositions, the most highly spreading ink compositions in Table 14 (Compositions 11-13), which has a polyethylene glycol di(meth)acrylate monomer to spreading modifier weight ratio of about 1.5:1 or lower, undergo a dramatic increase in their drop sizes and spreading rates with an increase in spreading modifier concentration. For example, by increasing the concentration of the spreading modifier four fold, from 10 wt. % (Comparative Example 5) to 40 wt. % (Composition 11), the drop size at 40 seconds more than doubled and the spreading rate increased by more than an order of magnitude. As shown in  FIG. 3 , the effect of spreading modifier concentration is even more pronounced at higher concentrations. 
     The effect of spreading modifier concentration on drop size is shown in the graphs of  FIG. 4A  through  FIG. 4I  for different post-printing time intervals from 40 seconds to 900 seconds. As shown in these graphs, the effect of spreading modifier concentration on drop diameter became more dramatic as time passes, up to at least 900 seconds. The graphs of  FIG. 3  and  FIGS. 4A-4I  further reveal that less pronounced, but still significantly stepped-up spreading rate can also be achieved at spreading modifier concentrations in the range from about 15 wt. % to about 35 wt. % (polyethylene glycol di(meth)acrylate monomer to spreading modifier weight ratios in the range from about 5:1 to about 1.5:1) and, more particularly, in the range from about 30 wt. % to about 35 wt. % (polyethylene glycol di(meth)acrylate monomer to spreading modifier weight ratios in the range from about 2:1 to about 1.5:1). The effect of spreading modifier content on drop spread is shown visually in  FIGS. 5A, 5B, and 5C , which are photographs of inkjet printed drops of Comparative Ink Composition 2, Ink Composition 9, and Ink Composition 11, respectively, 180 seconds post-printing. (The images in  FIGS. 5D, 5E, and 5F  render the images  FIGS. 5A, 5B, and 5C , respectively, as line drawings.) As illustrated in these figures, the ink compositions of  FIGS. 5A and 5C  formed dots which become increasingly thin as they spread and eventually merge into a continuous thin film. 
     Notably, the thin films printed from Ink Compositions 6-13 are continuous and have good edge acuity despite their high spreading modifier concentrations, demonstrating that the alkoxylated aliphatic di(meth)acrylate monomers are able to provide controlled spreading when used in combination with polyethylene glycol di(meth)acrylates. 
     In order to test the ability of the ink compositions to print continuous thin films, films of Comparative Ink Composition 2, Ink Composition 9, Ink Composition 10, and Ink Composition 11 having target thicknesses in the range from 1 μm to 8 μm were printed onto a silicon substrate and a bare glass (Corning Eagle) substrate and cured. The films were printed using the Dimatix DMP 2831 printer over an area of one cm 2  and cured under an ultraviolet (UV; 395 nm) LED. The degree of film curing as a function of UV dosage for thin films of Comparative Ink Composition 2 and Ink Composition 11 are shown in  FIGS. 6A and 6B . Both ink compositions had curing rates suitable for use in printed OLED applications. 
     After curing, the continuity of the films was observed visually and their thicknesses measured via profilometry. The results are presented in Table 15. The glass was cleaned using the Ultra T cleaning system described above. 
     
       
         
           
               
             
               
                 TABLE 15 
               
             
            
               
                   
               
               
                 Thin Film Continuity 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 Continuous 
                 Continuous 
               
               
                   
                 Film Thickness 
                 on Silicon 
                 on Glass 
               
               
                 Formulation 
                 (μm) 
                 Substrate? 
                 Substrate? 
               
               
                   
               
               
                 Comparative 2 
                 2 
                 No 
                 No 
               
               
                 Comparative 2 
                 4, 6, and 8 
                 Yes 
                 Yes 
               
               
                 9 
                 1 
                 No 
                 Yes 
               
               
                 9 
                 2, 3, and 4 
                 Yes 
                 Yes 
               
               
                 10 
                 1 
                 No 
                 Yes 
               
               
                 10 
                 2, 3, 4, 6, and 8 
                 Yes 
                 Yes 
               
               
                 11 
                 1, 2, 3, 4, 6, and 8 
                 Yes 
                 Yes 
               
               
                   
               
            
           
         
       
     
     As shown in the table above, Ink Composition 11 was able to provide a continuous inkjet printed film having a thickness of under 1 μm on the silicon and glass substrates and Ink Compositions 9 and 11 were able to provide continuous inkjet printed films having thicknesses as low as 2 μm on the silicon and as low as 1 μm on the glass. A 40 wt. % spreading modifier ink composition was also able to print a continuous thin film having a thickness of 1 μm on a silicon nitride substrate. 
     The film thicknesses cited herein refer to the average thickness of the cured films measured from edge-to-edge. By way of illustration, the film profile for a thin film having an average thickness of less than 1 μm is shown in  FIG. 2 . The film edge thickness data for films having average thicknesses in the range from about 1 μm to about 4 μm printed using Ink Composition 11 are shown in Tables 16-19. The data include measurements for three films printed onto a glass substrate and one film printed onto a silicon substrate. Notably, in addition to providing ultrathin continuous cured films, the data reveal that the ink compositions are able to provide good film thickness uniformity. 
     
       
         
           
               
             
               
                 TABLE 16 
               
             
            
               
                   
               
               
                 Film 1 Uniformity, Ink Composition 11 on Bare Glass 
               
            
           
           
               
               
               
            
               
                   
                 Target Film Thickness 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 1 μm 
                 2 μm 
                 3 μm 
                 4 μm 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Edge 1 Thickness 
                 0.834 
                 1.88 
                 2.90 
                 3.87 
               
               
                   
                 Edge 2 Thickness 
                 0.748 
                 1.82 
                 3.15 
                 4.04 
               
               
                   
                 Edge 3 Thickness 
                 0.676 
                 1.91 
                 2.68 
                 3.91 
               
               
                   
                 Edge 4 Thickness 
                 0.682 
                 1.88 
                 2.87 
                 3.47 
               
               
                   
                 Average of Four 
                 0.735 
                 1.87 
                 2.90 
                 3.82 
               
               
                   
                 Edges 
                   
                   
                   
                   
               
               
                   
                 Δ(Max − Min) 
                 0.158 
                 0.089 
                 0.478 
                 0.562 
               
               
                   
                 Uniformity** 
                 10.8% 
                 2.38% 
                 8.23% 
                 7.35% 
               
               
                   
               
               
                 **+/− Uniformity = (Max − Min)/(2*Average) 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 17 
               
             
            
               
                   
               
               
                 Film 2 Uniformity, Ink Composition 11 on Bare Glass 
               
            
           
           
               
               
               
            
               
                   
                 Target Film Thickness 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 2 μm 
                 4 μm 
                 6 μm 
                 8 μm 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Edge 1 Thickness 
                 2.41 
                 4.41 
                 7.05 
                 9.39 
               
               
                   
                 Edge 2 Thickness 
                 2.04 
                 4.07 
                 7.25 
                 9.06 
               
               
                   
                 Edge 3 Thickness 
                 2.12 
                 4.24 
                 6.89 
                 9.34 
               
               
                   
                 Edge 4 Thickness 
                 2.14 
                 4.50 
                 6.26 
                 9.50 
               
               
                   
                 Average of Four 
                 2.18 
                 4.30 
                 6.86 
                 9.32 
               
               
                   
                 Edges 
                   
                   
                   
                   
               
               
                   
                 Δ(Max − Min) 
                 0.372 
                 0.428 
                 0.987 
                 0.442 
               
               
                   
                 Uniformity** 
                 8.54% 
                 4.97% 
                 7.20% 
                 2.37% 
               
               
                   
               
               
                 **+/− Uniformity = (Max − Min)/(2*Average) 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 18 
               
             
            
               
                   
               
               
                 Film 3 Uniformity, Ink Composition 11 on Bare Glass 
               
            
           
           
               
               
               
            
               
                   
                 Target Film Thickness 
                 1 μm 
               
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Edge 1 Thickness 
                 0.891 
               
               
                   
                 Edge 2 Thickness 
                 0.889 
               
               
                   
                 Edge 3 Thickness 
                 0.825 
               
               
                   
                 Edge 4 Thickness 
                 0.888 
               
               
                   
                 Average of Four Edges 
                 0.873 
               
               
                   
                 Δ(Max − Min) 
                 0.065 
               
               
                   
                 Uniformity** 
                 3.75% 
               
               
                   
               
               
                 **+/− Uniformity = (Max − Min)/(2*Average) 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 19 
               
             
            
               
                   
               
               
                 Film 1 Uniformity, Ink Composition 11 on Silicon 
               
            
           
           
               
               
               
            
               
                   
                 Target Film Thickness 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 1 μm 
                 2 μm 
                 3 μm 
                 4 μm 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Edge 1 Thickness 
                 0.871 
                 2.28 
                 3.50 
                 4.62 
               
               
                   
                 Edge 2 Thickness 
                 0.859 
                 2.31 
                 3.44 
                 4.64 
               
               
                   
                 Edge 3 Thickness 
                 0.923 
                 2.24 
                 3.49 
                 4.67 
               
               
                   
                 Edge 4 Thickness 
                 0.938 
                 2.28 
                 3.47 
                 4.79 
               
               
                   
                 Average of Four 
                 0.896 
                 2.28 
                 3.48 
                 4.68 
               
               
                   
                 Edges 
                   
                   
                   
                   
               
               
                   
                 Δ(Max − Min) 
                 0.080 
                 0.066 
                 0.053 
                 0.158 
               
               
                   
                 Uniformity** 
                 4.43% 
                 1.45% 
                 0.76% 
                 1.69% 
               
               
                   
               
               
                 **+/− Uniformity = (Max − Min)/(2*Average) 
               
            
           
         
       
     
     The continuous thin films had substantially linear, well defined edges around their perimeters, rather than the irregularly shaped edges that are characteristic of uncontrolled spreading. Examples of well defined edges are shown in  FIGS. 7A and 7B , which are images of the film edges for cured 8 μm thick films inkjet printed from Ink Compositions 9 and 11, respectively.  FIGS. 7C and 7D  are line drawing representations of the images of  FIGS. 7A and 7B , respectively. 
     Systems and Methods for Organic Thin Film Formation on a Substrate 
     As previously discussed herein, manufacture of various OLED devices on a variety of substrates can be done in an inert, substantially particle-free environment to ensure high-yield manufacturing. 
     For clearer perspective regarding substrate sizes that can be used in manufacturing of various OLED devises, generations of mother glass substrate sizes have been undergoing evolution for flat panel displays fabricated by other-than OLED printing since about the early 1990&#39;s. The first generation of mother glass substrates, designated as Gen 1, is approximately 30 cm×40 cm, and therefore could produce a 15″ panel. Around the mid-1990&#39;s, the existing technology for producing flat panel displays had evolved to a mother glass substrate size of Gen 3.5, which has dimensions of about 60 cm×72 cm. In comparison, a Gen 5.5 substrate has dimensions of about 130 cm×150 cm. 
     As generations have advanced, mother glass sizes for Gen 7.5 and Gen 8.5 are in production for other-than OLED printing fabrication processes. A Gen 7.5 mother glass has dimensions of about 195 cm×225 cm, and can be cut into eight 42″ or six 47″ flat panels per substrate. The mother glass used in Gen 8.5 is approximately 220×250 cm, and can be cut to six 55″ or eight 46″ flat panels per substrate. The promise of OLED flat panel display for qualities such as truer color, higher contrast, thinness, flexibility, transparency, and energy efficiency have been realized, at the same time that OLED manufacturing is practically limited to G 3.5 and smaller. Currently, OLED printing is believed to be the optimal manufacturing technology to break this limitation and enable OLED panel manufacturing for not only mother glass sizes of Gen 3.5 and smaller, but at the largest mother glass sizes, such as Gen 5.5, Gen 7.5, and Gen 8.5. One of the features of OLED panel display technology includes that a variety of substrate materials can be used, for example, but not limited by, a variety of glass substrate materials, as well as a variety of polymeric substrate materials. In that regard, sizes recited from the terminology arising from the use of glass-based substrates can be applied to substrates of any material suitable for use in OLED printing. 
     Table 20 below relates generation substrate designation to sizes as often can be found in various sources relating to generation substrates for various OLED devices. Table 9 below summarizes aspect ratios and areas for some known generation-sized substrates as currently available in various sources relating to generation-sized substrates. It should be understood that variation of aspect ratio and hence size may be seen from manufacturer to manufacturer. Additionally, It should be the information provided in Table 9 can be subject to change, given the evolution of the industry. In that regard, updated conversion factors for a specific generation-sized substrate, as well as area in square meters can be obtained any of a variety of generation-sized substrates. 
     
       
         
           
               
             
               
                 TABLE 20 
               
             
            
               
                   
               
               
                 Correlation between area and substrate size 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Generation ID 
                 X (mm) 
                 Y (mm) 
                 Area (m 2 ) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Gen 3.0 
                 550 
                 650 
                 0.36 
               
               
                   
                 Gen 3.5 
                 610 
                 720 
                 0.44 
               
               
                   
                 Gen 3.5 
                 620 
                 750 
                 0.47 
               
               
                   
                 Gen 4 
                 680 
                 880 
                 0.60 
               
               
                   
                 Gen 4 
                 730 
                 920 
                 0.67 
               
               
                   
                 Gen 5 
                 1100 
                 1250 
                 1.38 
               
               
                   
                 Gen 5 
                 1100 
                 1300 
                 1.43 
               
               
                   
                 Gen 5.5 
                 1300 
                 1500 
                 1.95 
               
               
                   
                 Gen 6 
                 1500 
                 1850 
                 2.78 
               
               
                   
                 Gen 7.5 
                 1950 
                 2250 
                 4.39 
               
               
                   
                 Gen 8 
                 2160 
                 2400 
                 5.18 
               
               
                   
                 Gen 8 
                 2160 
                 2460 
                 5.31 
               
               
                   
                 Gen 8.5 
                 2200 
                 2500 
                 5.50 
               
               
                   
                 Gen 9 
                 2400 
                 2800 
                 6.72 
               
               
                   
                 Gen 10 
                 2850 
                 3050 
                 8.69 
               
               
                   
               
            
           
         
       
     
     Manufacturing tools that in principle can allow for the printing of a variety of substrate sizes that includes large-format substrate sizes, can require substantially large facilities for housing such OLED manufacturing tools. Accordingly, maintaining an entire large facility under an inert atmosphere presents engineering challenges, such as continual purification of a large volume of an inert gas. Various embodiments of a gas enclosure system can have a circulation and filtration system internal a gas enclosure assembly in conjunction with a gas purification system external a gas enclosure that together can provide continuous circulation of a substantially low-particulate inert gas having substantially low levels of reactive species throughout a gas enclosure system. According to the present teachings, an inert gas may be any gas that does not adversely alter a product being fabricated under a defined set of conditions. Some commonly used non-limiting examples of an inert gas for the processing of various embodiments of an OLED device can include nitrogen, any of the noble gases, and any combination thereof. Systems and methods of the present teachings can provide a large facility that is essentially hermetically sealed to prevent contamination of various reactive atmospheric gases, such as water vapor and oxygen, as well as organic solvent vapors generated from various printing processes. According to the present teachings, an OLED printing facility would maintain levels for each species of various reactive species, including various reactive atmospheric gases, such as water vapor and oxygen, as well as organic solvent vapors at 100 ppm or lower, for example, at 10 ppm or lower, at 1.0 ppm or lower, or at 0.1 ppm or lower. 
     The need for printing an OLED panel in a facility in which the levels of each of a reactive species should be maintained at targeted low levels can be illustrated in reviewing the information summarized in Table 21. The data summarized on Table 21 resulted from the testing of each of a test coupon comprising organic thin film compositions for each of red, green, and blue, fabricated in a large-pixel, spin-coated device format. Such test coupons are substantially easier to fabricate and test for the purpose of rapid evaluation of various formulations and processes. Though test coupon testing should not be confused with lifetime testing of a printed panel, it can be indicative of the impact of various formulations and processes on lifetime. The results shown in the table below represent variation in the process step in the fabrication of test coupons in which only the spin-coating environment varied for test coupons fabricated in a nitrogen environment where reactive species were less than 1 ppm compared to test coupons similarly fabricated but in air instead of a nitrogen environment. 
     It is evident through the inspection of the data in Table 21, shown below, for test coupons fabricated under different processing environments, particularly in the case of red and blue, that printing in an environment that effectively reduces exposure of organic thin film compositions to reactive species may have a substantial impact on the stability of various ELs, and hence on lifetime. The lifetime specification is of particular significance for OLED panel technology, as this correlates directly to display product longevity; a product specification for all panel technologies, which has been challenging for OLED panel technology to meet. In order to provide panels meeting requisite lifetime specifications, levels of each of a reactive species, such as water vapor, oxygen, as well as organic solvent vapors, can be maintained at 100 ppm or lower, for example, at 10 ppm or lower, at 1.0 ppm or lower, or at 0.1 ppm or lower with various embodiments of a gas enclosure system of the present teachings. 
     
       
         
           
               
             
               
                 TABLE 21 
               
             
            
               
                   
               
               
                 Impact of inert gas processing on lifetime for OLED panels 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 V 
                   
                   
                   
                   
                   
               
               
                   
                 Process 
                 @ 10 
                 Cd/A 
                 CIE (x, y) 
                 T95 
                 T80 
                 T50 
               
            
           
           
               
               
               
               
            
               
                 Color 
                 Environment 
                 mA/cm 2   
                 @ 1000 Cd/m 2   
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Red 
                 Nitrogen 
                 6 
                 9 
                 (0.61, 0.38) 
                 200 
                 1750 
                 10400 
               
               
                   
                 Air 
                 6 
                 8 
                 (0.60, 0.39) 
                 30 
                 700 
                 5600 
               
               
                 Green 
                 Nitrogen 
                 7 
                 66 
                 (0.32, 0.63) 
                 250 
                 3700 
                 32000 
               
               
                   
                 Air 
                 7 
                 61 
                 (0.32, 0.62) 
                 250 
                 2450 
                 19700 
               
               
                 Blue 
                 Nitrogen 
                 4 
                 5 
                 (0.14, 0.10) 
                 150 
                 750 
                 3200 
               
               
                   
                 Air 
                 4 
                 5 
                 (0.14, 0.10) 
                 15 
                 250 
                 1800 
               
               
                   
               
            
           
         
       
     
     In addition to providing an inert environment, maintaining a substantially low-particle environment for OLED printing is of particular importance, as even very small particles can lead to a visible defect on an OLED panel. Particle control in a gas enclosure system can present significant challenges not presented for processes that can be done, for example, in atmospheric conditions under open air, high flow laminar flow filtration hoods. 
     For example, of a manufacturing facility can require a substantial length of various service bundles that can be operatively connected from various systems and assemblies to provide optical, electrical, mechanical, and fluidic connections required to operate, for example, but not limited by, a printing system. Such service bundles used in the operation of a printing system and located proximal to a substrate positioned for printing can be an ongoing source of particulate matter. Additionally, components used in a printing system, such as fans or linear motion systems that use friction bearing, can be particle generating components. Various embodiments of a gas circulation and filtration system of the present teachings can be used in conjunction with particle control components to contain and exhaust particulate matter. Additionally, by using a variety of intrinsically low-particle generating pneumatically operated components, such as, but not limited by, substrate floatation tables, air bearings, and pneumatically operated robots, and the like, a low particle environment for various embodiments of a gas enclosure system can be maintained. Regarding maintaining a substantially low-particle environment, various embodiments of a gas circulation and filtration system can be designed to provide a low particle inert gas environment for airborne particulates meeting the standards of International Standards Organization Standard (ISO) 14644-1:1999, “Cleanrooms and associated controlled environments—Part 1: Classification of air cleanliness,” as specified by Class 1 through Class 5 
     As depicted in  FIG. 8 , process  100  for printing an organic thin film ink on a substrate and then curing the ink can include step  110  of transferring a substrate from a manufacturing tool in which, for example, an inorganic encapsulation layer was fabricated on an OLED substrate device using a vapor deposition process. As will be discussed in more detail subsequently herein, a substrate can be transferred from an inorganic encapsulation fabrication tool to a printing module of a printing tool There can be many advantages of inkjet printing for a variety of processes that can utilize pattered area printing. First, a range of vacuum processing operations can be eliminated because such inkjet-based fabrication can be performed at atmospheric pressure. Additionally, during an inkjet printing process, an organic encapsulation layer can be localized to cover portions of an OLED substrate over and proximal to an active region, to effectively encapsulate an active region, including lateral edges of the active region. The targeted patterning using inkjet printing results in eliminating material waste, as well as eliminating additional processing typically required to achieve patterning of an organic layer, which can result in enhanced particle contamination. For example, masking is a well-known technique used for patterned film deposition, however, masking techniques can create substantial particle contamination. 
     In step  120 , using various embodiments of organic thin layer inks according to the present teachings, a printing tool can be used to print an organic thin film layer over a target print area. In the art of processing, total average cycle time or TACT can be an expression of a unit of time for a particular process cycle. For various embodiments of systems and methods of the present teachings, for a step of printing an organic thin film ink, TACT can be between about 30 seconds to about 120 seconds. Subsequently, as indicated by step  130 , the substrate can be transferred from a printing module of a printing tool to a curing module. With respect to a step of curing, as indicated by step  140 , according to various embodiments of systems and methods of the present teachings, before curing is initiated, a step of allowing the printed organic thin film ink to reach a film layer of uniform thickness can be done. In various embodiments, such a leveling step can be considered a separate step. In various embodiments of systems and methods, leveling can be done in a dedicated chamber, for example, in a holding chamber, and then a substrate can be transferred to a curing chamber. For various embodiments of the present teachings, as will be discussed in more detail herein, a step of leveling can be done in the same chamber as the step of curing. According to various embodiments of systems and methods of the present teachings, TACT for a step of leveling can be between about 170 seconds to about 210 seconds, while TACT for a curing step according to some embodiments can be between about 15 seconds to 60 seconds, while for other embodiments can be between about 25 seconds to about 35 seconds. After curing step  140 , a substrate can be transferred from a UV curing module to another processing chamber, such as an output loadlock chamber, as indicated by process step  150  of process  100 . 
     In order to accomplish process  100  of  FIG. 8 , various embodiments of manufacturing tools of the present teachings that can provide inert, substantially particle-free environments can be used, for example, as shown in  FIG. 9 .  FIG. 9  depicts a perspective view of OLED printing tool  4000  according to various embodiments of the present teachings, which can include first module  4400 , printing module  4500 , and second module  4600 . Various modules, such as first module  4400  can have first transfer chamber  4410 , which can have a gate, such as gate  4412 , for each side of first transfer chamber  4410  to accommodate various chambers having a specified function. As depicted in  FIG. 9  first transfer chamber  4410  can have a load lock gate (not shown) for integration of first load lock chamber  4450  with first transfer chamber  4410 , as well as a buffer gate (not shown) for integration of first buffer chamber  4460  with first transfer chamber  4410 . Gate  4412  of first transfer chamber  4410  can be used for a chamber or unit that can be movable, such as, but not limited by, a load lock chamber. Observation windows, such as observation windows  4402  and  4404  of first transfer chamber  4410 , as well as observation window  4406  of first buffer chamber  4460 , can be provided for an end user to, for example, monitor a process. Printing module  4500  can include gas enclosure  4510 , which can have first panel assembly  4520 , printing system enclosure assembly  4540 , and second panel assembly  4560 . Gas enclosure  4510  can house various embodiments of a printing system. 
     Various embodiments of a gas enclosure can be contoured around a printing system base, upon which a substrate support apparatus can be mounted. Further, a gas enclosure can be contoured around a bridge structure used for the X-axis movement of a carriage assembly. As a non-limiting example, various embodiments of a contoured gas enclosure according to the present teachings can have a gas enclosure volume of between about 6 m 3  to about 95 m 3  for housing various embodiments of a printing system capable of printing substrate sizes from Gen 3.5 to Gen 10. By way a further non-limiting example, various embodiments of a contoured gas enclosure according to the present teachings can have a gas enclosure volume of between about 15 m 3  to about 30 m 3  for housing various embodiments of a printing system capable of printing, for example, Gen 5.5 to Gen 8.5 substrate sizes. Such embodiments of a contoured gas enclosure can be between about 30% to about 70% savings in volume in comparison to a non-contoured enclosure having non-contoured dimensions for width, length and height. 
     Second module  4600  of  FIG. 9  can include second transfer chamber  4610 , which can have a gate, such as gate  4612 , for each side of second transfer chamber  4610  to accommodate various chambers having a specified function. As depicted in  FIG. 9  second transfer chamber  4610  can have a load lock gate (not shown) for integration of second load lock chamber  4650  with second transfer chamber  4610 , as well as a gate (not shown) for integration of second chamber  4660  with second transfer chamber  4610 . Gate  4612  of second transfer chamber  4610  can be used for a chamber or unit that can be movable, such as, but not limited by, a load lock chamber. Observation windows, such as observation windows  4602  and  4604  of second transfer chamber  4610 , can be provided for an end user to, for example, monitor a process. According to various embodiments of systems and methods of the present teachings, chamber  4660  of  FIG. 9  can be a UV curing module. For example, chamber  4660  of  FIG. 9  can be a UV curing module as depicted in  FIG. 10 . 
     First load lock chamber  4450  and second load lock chamber  4650  can be affixably associated with first transfer chamber  4410  and second transfer chamber  4610 , respectively or can be movable, such as on wheels or on a track assembly, so that they can be readily positioned for use proximal a chamber. According to the present teachings, a load lock chamber can be mounted to a support structure and can have at least two gates. For example first load lock chamber  4450  can be supported by first support structure  4454  and can have first gate  4452 , as well as a second gate (not shown) that can allow fluid communication with first transfer module  4410 . Similarly, second load lock chamber  4650  can be supported by second support structure  4654  and can have second gate  4652 , as well as a first gate (not shown) that can allow fluid communication with second transfer module  4610 . 
       FIG. 10  illustrates generally an example an ultraviolet (UV curing) module that can be used in manufacturing a light emitting device. The treatment system can be included as a portion of other systems or techniques described herein. For example, as indicated in  FIG. 10 , UV curing module  4660  could be chamber  4660  of OLED printing tool  4000  of  FIG. 9 . The system can include various regions, such as for use as a curing chamber, or for use as a combination curing and holding chamber. For various embodiments of a curing chamber, a source of ultraviolet emission can be used such as to treat one or more layers deposited on a substrate being fabricated. For example, ultraviolet emission can be used to polymerize or otherwise treat an organic layer deposited on the substrate, such as for use in one or more processes related to manufacturing a flat panel display assembly, such as including an OLED display assembly. 
     According to the present teachings, a UV curing module can include one or more enclosed UV curing chambers such as first UV curing chamber  4661 A, second UV curing chamber  4661 B, and “Nth” UV curing chamber  4661 N. For example, three regions can be included and in another example, other numbers of regions can be included. The regions can be oriented in a “stacked” configuration along a vertical axis of the system, such as shown illustratively in  FIG. 10 . Other configurations can be used, such as a radial configuration of chambers extending outward from a central chamber. For example, transfer chamber  4610  of  FIG. 5  can be second transfer chamber  4610  of  FIG. 9 . 
     In an illustrative example, such as after deposition of an organic layer on a substrate, a leveling operation can be performed. As was previously discussed herein, a duration of a leveling operation can generally be greater than a duration of an ultraviolet treatment operation. Accordingly, in one approach, respective holding regions or “buffer cells” can be used, such as in a stacked configuration with each region configured to house a substrate. In this approach, the leveling operation can proceed without restricting access or otherwise tying up a separate ultraviolet treatment region. However, multiple ultraviolet sources can be used, such including user lower-cost sources. In this manner, a throughput impact of idling an ultraviolet source need not preclude use of the same UV curing chamber (e.g.,  4661 A through  4661 N) for both a holding operation (e.g., buffering or leveling), as well as for an ultraviolet treatment operation, because multiple regions can be configured to provide ultraviolet treatment. Such an approach can also provide redundancy of the ultraviolet sources such that processing can continue even if a particular ultraviolet source fails or is undergoing maintenance. 
     For example, first radiation source  4662 A (e.g., an ultraviolet-emitting LED array) can provide ultraviolet emission, depicted as multiple arrows in  FIG. 10 . A UV apparatus can include a UV single source, a liner array, or a two dimensional array of UV source. The type of source selected can have a specified range of wavelengths to a first substrate  2050 A. As depicted in  FIG. 10 , a first set of radiation sources  4662 A are depicted. Though the term “UV” is used, it is to be understood that the source has a wavelength of light associated with an energy required to initiate a polymerization reaction. In that regard, as free-radical initiation can occur via thermal decomposition as well as photolysis, a source of radiation can include any source effective in initiating a polymerization reaction through a variety of mechanism. The electromagnetic radiation emission can be coupled to an interior of the enclosed region of first UV chamber  4661 A such as through a window  4663  (e.g., a quartz window or an assembly such as including a normalization filter, or other filters or coatings). According to various embodiments of the present teachings, the environment within UV curing chamber  4661 A can be inert and can be isolated from a housing containing the first set of radiation sources  4662 A. According to various systems and methods, in the second enclosed region of UV chamber  466 B, for example, the second substrate  2050 B can be held for a specified duration, such as for leveling or to await availability of other processes. During the specified holding duration, a second set of radiation sources  4662 B can be disabled. 
     Regarding support of substrates, such as  2050 A and  2050 B of  FIG. 10 , the present inventors have recognized, among other things, that for some operations or material systems, such as in relation to leveling a deposited organic layer, visible defects can be induced in the display regions of a substrate when the substrate is supported in a non-uniform manner. For example, pins, support frames, retracted lift-pins, or vacuum apertures in contact with a substrate can induce visible defects in a finished device. 
     Without being bound by theory, it is believed that such defects primarily result from localized variations in thermal conductivity that can create local gradients in the temperature of a substrate during, for example, a leveling operation. In an example, a specified temperature uniformity can be maintained in a local region of the substrate, for example, such that deviation in temperature adjacent to or within the local region is limited. For example, a significant temperature variation across the substrate can be tolerated but such variation can have a limited gradient such that the temperature does not vary significantly over a small distance along the substrate. In this manner, abrupt changes in visible characteristics of the finished display can be avoided and such gradual changes are less likely to be noticed or even detectable. 
     In one approach, regions outside the emitting or display region of the substrate can be used to support a substrate outside of active device areas of a substrate. However, because large portions of a substrate can include emitting regions or portions of the actual display region, it can be impractical to support the substrate only at the periphery of such regions because such support induces unacceptable mechanical forces or stresses elsewhere across a substrate, which may either distort or fracture a substrate. Additionally, the present inventors have also recognized that a correlation can exist between particle generation and a number of instances or locations of contact between other apparatuses and a substrate. 
     Accordingly, the present inventors have recognized that a substrate, such as substrates  2050 A and  2050 B of  FIG. 10  can be supported by a chuck, for example chuck  4664  of first UV chamber  4661 A, such as during an ultraviolet treatment operation, such as at least in part using a pressurized gas “P” to provide a gas cushion. According to various examples, the substrate  4000 A can be supported exclusively by a controlled arrangement of the pressurized gas, “P such as to float the substrate  2050 A. In another example, substrate  2050 A can be mechanically supported in part, such as at a periphery, by one or more pins (e.g., a pin  4666 ) or a support frame, and a weight of substrate  2050 A can be supported in a central region of substrate  2050 A by the pressurized gas, “P.” In another approach, substrate  2050 A can be supported by a pressurized gas “P” impinging on a first surface of substrate  2050 A, and an opposing force can be provided such as by a mechanical stop  4668  contacting an opposing face of substrate  2050 A. Though first UV chamber  4661 A is used for the purpose of illustration, it is to be understood that these teachings apply to all UV chambers shown in  FIG. 10 . Though pressure is shown for the teachings of  FIG. 10 , as will be discussed in more detail in reference to the floatation table of  FIG. 11 , a chuck using pressure and vacuum can also be utilized. In such an example where the substrate  2050 A is supported exclusively by the gas cushion, a combination of positive gas pressure and vacuum can be applied through the arrangement of ports. Such a zone having both pressure and vacuum control can effectively provide a fluidic spring between floatation chuck  4664  and substrate  2050 A. 
     Transfer module  4610  of  FIG. 10  can be a transfer module as described for second transfer module  4610  of  FIG. 9 . Regarding the floatation of a substrate, elevating handler  4612 , which can be housed in transfer module  4610 , can also utilized substrate floatation during a transfer process. Elevating handler  4612  can include a table  4614  (or a corresponding end effector) including pressurized gas “P” to support a substrate at least in part using the pressurized gas. A conveyor, or other apparatus can be used to transport a substrate from, for example, a printing module, such as printing module  4550  of  FIG. 9  through gate  4616 . Such conveyance means can also include such a pressurized gas arrangement, such that a substrate can be conveyed along a path as indicated by the horizontal arrow shown directing substrate  2050 N to UV curing chamber  4661 N. 
     In the illustrative example of  FIG. 10 , an enclosed transfer module  4610  can house the elevating handler  4612  and table  4614 . An inert environment having specified gas purity and specified particulate levels can be established within the enclosed transfer module  4610  as discussed extensively in relation to other examples herein. For example, one or more fan filter units (FFUs) such as a fan filter unit  5202  can be coupled to transfer module  4610 . Duct  5201  can provide a return flow of inert gas to be recirculated using FFU  5202 . A gas purification system  3130  can be coupled to the enclosed transfer module  4610 . While a vertical flow orientation is illustrated in  FIG. 10 , other configurations can be used, such as a lateral flow configuration. Each of the regions  4661 A through  4661 N can either share one or more gas purification loops or can each be served by a respective gas purification loop. Similarly, one or more FFUs can be located to provide a laminar airflow parallel to a surface of substrate in each of the regions  4661 A through  4661 N. A temperature within the enclosed transfer module  4610  or within other portions of the system can be controlled as described extensively in other examples herein, such as using a temperature controller  3140 . As will be described in more detail in the teachings regarding  FIG. 13  herein, the temperature controller  3140  can be coupled, for example through a heat exchanger, to the FFU  5202  or one or more FFUs elsewhere. 
     The regions  4661 A through  4661 N can each include a valve or gate, such as to isolate the inert environment of each enclose region  4661 A through  4661 N from the transfer module  4610  or from each other. Accordingly, such as during maintenance, a particular region can have its inert environment isolated from the rest of the enclosed regions using a valve or gate. 
     An OLED inkjet printing system, such as OLED printing system  2000  of  FIG. 11 , can be housed in include gas enclosure  4510  of printing module  4500  of  FIG. 9 . Various embodiments of a printing system of  FIG. 11 , can be comprised of several devices and apparatuses, which allow the reliable placement of ink drops onto specific locations on a substrate. Printing requires relative motion between the printhead assembly and the substrate. This can be accomplished with a motion system, typically a gantry or split axis XYZ system. Either the printhead assembly can move over a stationary substrate (gantry style), or both the printhead and substrate can move, in the case of a split axis configuration. In another embodiment, a printhead assembly can be substantially stationary; for example, in the X and Y axes, and the substrate can move in the X and Y axes relative to the printheads, with Z axis motion provided either by a substrate support apparatus or by a Z-axis motion system associated with a printhead assembly. As the printheads move relative to the substrate, drops of ink are ejected at the correct time to be deposited in the desired location on a substrate. A substrate can be inserted and removed from the printer using a substrate loading and unloading system. Depending on the printer configuration, this can be accomplished with a mechanical conveyor, a substrate floatation table with a conveyance assembly, or a substrate transfer robot with end effector. For various embodiments of systems and methods of the present teachings, an Y-axis motion system can be based on an air-bearing gripper system. 
     An OLED inkjet printing system, such as OLED printing system  2000  of  FIG. 11 , can be comprised of several devices and apparatuses, which allow the reliable placement of ink drops onto specific locations on a substrate. These devices and apparatuses can include, but are not limited to, a printhead assembly, ink delivery system, a motion system for providing relative motion between a printhead assembly and a substrate, substrate support apparatus, substrate loading and unloading system, and printhead management system. 
     A printhead assembly can include at least one inkjet head, with at least one orifice capable of ejecting drops of ink at a controlled rate, velocity, and size. The inkjet head is fed by an ink supply system which provides ink to the inkjet head. As shown in an expanded view of  FIG. 11 , OLED inkjet printing system  2000  can have a substrate, such as substrate  2050 , which can be supported by a substrate support apparatus, such as a chuck, for example, but not limited by, a vacuum chuck, a substrate floatation chuck having pressure ports, and a substrate floatation chuck having vacuum and pressure ports. In various embodiments of systems and methods of the present teachings, a substrate support apparatus can be a substrate floatation table. As will be discussed in more detail subsequently herein, substrate floatation table  2200  of  FIG. 11  can be used for supporting substrate  2050 , and in conjunction with a Y-axis motion system, can be part of a substrate conveyance system providing for the frictionless conveyance of substrate  2050 . A Y-axis motion system of the present teachings can include first Y-axis track  2351  and second Y-axis track  2352 , which can include a gripper system (not shown) for holding a substrate. Y-axis motion can be provided by either a linear air bearing or linear mechanical system. Substrate floatation table  2200  of OLED inkjet printing system  2000  shown in  FIG. 11  can define the travel of substrate  2050  through gas enclosure assembly  1000  of  FIG. 1A  during a printing process. 
       FIG. 11  illustrates generally an example of substrate floatation table  2200  for a printing system  2000  that can include a floating conveyance of a substrate, which can have a porous medium to provide floatation. In the example of  FIG. 11 , a handler or other conveyance can be used to position a substrate  2050  in first region  2201  of a substrate floatation table  2200 , such as located on a conveyor. The conveyer can position the substrate  2050  at a specified location within the printing system such as using either mechanical contact (e.g., using an array of pins, a tray, or a support frame configuration), or using gas cushion to controllably float the substrate  2050  (e.g., an “air bearing” table configuration). A printing region  2202  of the substrate floatation table  2200  can be used to controllably deposit one or more layers on the substrate  2050  during fabrication. The printing region  2202  can also be coupled to an second region  2203  of the substrate floatation table  2200 . The conveyer can extend along the first region  2201 , the printing region  2202 , and the second region  2203  of the substrate floatation table  2200 , and the substrate  2050  can be repositioned as desired for various deposition tasks, or during a single deposition operation. The controlled environments nearby the first region  2201 , the printing region  2202 , and the second region  2203  can be commonly-shared. According to various embodiments of printing system  2000  of  FIG. 11 , first region  2201  can be an input region, and second region  2203  can be an output region. For various embodiments of printing system  2000  of  FIG. 11 , first region  2201  can be both an input and an output region. Further, function referred to in association with regions  2201 ,  2202 , and  2203 , such as input, printing, and output for illustration only. Such regions can be used for other processing steps, such as conveyance of a substrate, or support of a substrate such as during one or more of holding, drying, or thermal treatment of the substrate in one or more other modules. 
     The printing system  2000  of  FIG. 11  can include one or more printhead devices  2505 , each printhead device having one or more printheads; e.g. nozzle printing, thermal jet or ink-jet type. The one or more printhead devices  2505  can be coupled to or otherwise traversing an overhead carriage, such as first X-axis carriage assembly  2301 . For various embodiments of printing system  2000  of the present teachings, one or more printheads of one or more printhead devices  2505  can be configured to deposit one or more patterned organic layers on the substrate  2050  in a “face up” configuration of the substrate  2050 . Such layers can include one or more of an electron injection or transport layer, a hole injection or transport layer, a blocking layer, or an emission layer, for example. Such materials can provide one or more electrically functional layers. 
     According to the floatation schemes shown in  FIG. 11 , in an example where the substrate  2050  is supported exclusively by the gas cushion, a combination of positive gas pressure and vacuum can be applied through the arrangement of ports or using a distributed porous medium. Such a zone having both pressure and vacuum control can effectively provide a fluidic spring between the conveyor and a substrate. A combination of positive pressure and vacuum control can provide a fluidic spring with bidirectional stiffness. The gap that exists between the substrate (e.g., substrate  2050 ) and a surface can be referred to as the “fly height,” and such a height can be controlled or otherwise established by controlling the positive pressure and vacuum port states. In this manner, the substrate Z-axis height can be carefully controlled in, for example, the printing region  2202 . In some embodiments, mechanical retaining techniques, such as pins or a frame, can be used to restrict lateral translation of the substrate while the substrate is supported by the gas cushion. Such retaining techniques can include using spring loaded structures, such as to reduce the instantaneous forces incident the sides of the substrate while the substrate is being retained; this can be beneficial as a high force impact between a laterally translating substrate and a retaining means can cause substrate chipping or even catastrophic breakage. 
     Elsewhere, as illustrated generally in  FIG. 11 , such as where the fly height need not be controlled precisely, pressure-only floatation zones can be provided, such as along the conveyor in the first or second regions  2201  or  2203 , or elsewhere. A “transition” floatation zone can be provided such as where a ratio of pressure to vacuum nozzles increases or decreases gradually. In an illustrative example, there can be an essentially uniform height between a pressure-vacuum zone, a transition zone, and a pressure only zone, so that within tolerances, the three zones can lie essentially in one plane. A fly height of a substrate over pressure-only zones elsewhere can be greater than the fly height of a substrate over a pressure-vacuum zone, such as in order to allow enough height so that a substrate will not collide with a floatation table in the pressure-only zones. In an illustrative example, an OLED panel substrate can have a fly height of between about 150 micrometers (μ) to about 300μ, above pressure-only zones, and then between about 30μ, to about 50μ, above a pressure-vacuum zone. In an illustrative example, one or more portions of the substrate floatation table  2200  or other fabrication apparatus can include an “air bearing” assembly provided by NewWay® Air Bearings (Aston, Pa., United States of America). 
     A porous medium can be used to establish a distributed pressurized gas cushion for floating conveyance or support of the substrate  2050  during one or more of printing, buffering, drying, or thermal treatment. For example, a porous medium “plate” such as coupled to or included as a portion of a conveyor can provide a “distributed” pressure to support the substrate  2050  in a manner similar to the use of individual gas ports. The use of a distributed pressurized gas cushion without using large gas port apertures can in some instances further improve uniformity and reduce or minimize the formation of mura or other visible defects, such as in those instances where the use of relatively large gas ports to create a gas cushion leads to non-uniformity, in spite of the use of a gas cushion. 
     A porous medium can be obtained such as from Nano TEM Co., Ltd. (Niigata, Japan), such as having physical dimensions specified to occupy an entirety of the substrate  2050 , or specified regions of the substrate such as display regions or regions outside display regions. Such a porous medium can include a pore size specified to provide a desired pressurized gas flow over a specified area, while reducing or eliminating mura or other visible defect formation. 
     Printing requires relative motion between the printhead assembly and the substrate. This can be accomplished with a motion system, typically a gantry or split axis XYZ system. Either the printhead assembly can move over a stationary substrate (gantry style), or both the printhead and substrate can move, in the case of a split axis configuration. In another embodiment, a printhead assembly can be substantially stationary; for example, in the X and Y axes, and the substrate can move in the X and Y axes relative to the printheads, with Z axis motion provided either by a substrate support apparatus or by a Z-axis motion system associated with a printhead assembly. As the printheads move relative to the substrate, drops of ink are ejected at the correct time to be deposited in the desired location on a substrate. A substrate can be inserted and removed from the printer using a substrate loading and unloading system. Depending on the printer configuration, this can be accomplished with a mechanical conveyor, a substrate floatation table with a conveyance assembly, or a substrate transfer robot with end effector. 
     With respect to  FIG. 11 , printing system base  2100 , can include first riser  2120  and second riser  2122 , upon which bridge  2130  is mounted. For various embodiments of OLED printing system  2000 , bridge  2130  can support first X-axis carriage assembly  2301  and second X-axis carriage assembly  2302 , which can control the movement of first printhead assembly  2501  and second printhead assembly  2502 , respectively across bridge  2130 . For various embodiments of printing system  2000 , first X-axis carriage assembly  2301  and second X-axis carriage assembly  2302  can utilize a linear air bearing motion system, which are intrinsically low-particle generating. According to various embodiments of a printing system of the present teachings, an X-axis carriage can have a Z-axis moving plate mounted thereupon. In  FIG. 11 , first X-axis carriage assembly  2301  is depicted with first Z-axis moving plate  2310 , while second X-axis carriage assembly  2302  is depicted with second Z-axis moving plate  2312 . Though  FIG. 11  depicts two carriage assemblies and two printhead assemblies, for various embodiments of OLED inkjet printing system  2000 , there can be a single carriage assembly and a single printhead assembly. For example, either of first printhead assembly  2501  and second printhead assembly  2502  can be mounted on an X,Z-axis carriage assembly, while a camera system for inspecting features of substrate  2050  can be mounted on a second X,Z-axis carriage assembly. 
     In  FIG. 11 , each printhead assembly, such as first printhead assembly  2501  and second printhead assembly  2502  of  FIG. 11 , can have a plurality of printheads mounted in at least one printhead device, as depicted in partial view for first printhead assembly  2501 , which depicts a plurality of printhead devices  2505 . A printhead device can include, for example, but not limited by, fluidic and electronic connections to at least one printhead; each printhead having a plurality of nozzles or orifices capable of ejecting ink at a controlled rate, velocity and size. For various embodiments of printing system  2000 , a printhead assembly can include between about 1 to about 60 printhead devices, where each printhead device can have between about 1 to about 30 printheads in each printhead device. A printhead, for example, an industrial inkjet head, can have between about 16 to about 2048 nozzles, which can expel a drop volume of between about 0.1 pL to about 200 pL. 
     According to various embodiments of a gas enclosure system of the present teachings, given the sheer number of printhead devices and printheads, first printhead management system  2701  and second printhead management system  2702  can be housed in an auxiliary enclosure, which can be isolated from a printing system enclosure during a printing process for performing various measurement and maintenance tasks with little or no interruption to the printing process. As can be seen in  FIG. 11 , first printhead assembly  2501  can be seen positioned relative to first printhead management system  2701  for ready performance of various measurement and maintenance procedures that can be performed by first printhead management system apparatuses  2707 ,  2709  and  2711 . Apparatuses  2707 ,  2709 , and  2011  can be any of a variety of subsystems or modules for performing various printhead management functions. For example apparatuses  2707 ,  2709 , and  2011  can be any of a drop measurement module, a printhead replacement module, a purge basin module, and a blotter module. 
     For OLED printing system  2000  of  FIG. 11 , various embodiments of a printing system can include substrate floatation table  2200 , supported by substrate floatation table base  2220 . Substrate floatation table base  2220  can be mounted on printing system base  2100 . Substrate floatation table  2200  of OLED printing system can support substrate  2050 , as well as defining the travel over which substrate  2050  can be moved through gas enclosure assembly  1000  during the printing of an OLED substrate. A Y-axis motion system of the present teachings can include first Y-axis track  2351  and second Y-axis track  2352 , which can include a gripper system (not shown) for holding a substrate. Y-axis motion can be provided by either a linear air bearing or linear mechanical system. In that regard, in conjunction with a motion system; as depicted in  FIG. 11 , a Y-axis motion system, substrate floatation table  2200  can provide frictionless conveyance of substrate  2050  through a printing system. 
     In reference to  FIG. 12 , printing system  2001  can have all of the elements previously described for printing system  2000  of  FIG. 11 . For example, but not limited by, printing system  2001  of  FIG. 12  can have service bundle housing exhaust system  2400  for containing and exhausting particles generated from a service bundle. Service bundle housing exhaust system  2400  of printing system  2001  can include service bundle housing  2410 , which can house a service bundle. According to the present teachings, a service bundle can be operatively connected to a printing system to provide various optical, electrical, mechanical and fluidic connections required to operate various devices and apparatuses in a gas enclosure system, for example, but not limited by, various devices and apparatuses associated with a printing system. Printing system  2001  of  FIG. 12  can have substrate support apparatus  2250  for supporting substrate  2050 , which can be positioned with precision in the Y-axis direction using Y-axis positioning system  2355 . Both substrate support apparatus  2250  and Y-axis positioning system  2355  are supported by printing system base  2101 . Substrate support apparatus  2250  can be mounted on Y-axis motion assembly  2355  and can be moved on rail system  2360  using, for example, but not limited by, a linear bearing system; either utilizing mechanical bearings or air bearings. For various embodiments of gas enclosure systems, an air bearing motion system helps facilitation frictionless conveyance in the Y-axis direction for a substrate placed on substrate support apparatus  2250 . Y-axis motion system  2355  can also optionally use dual rail motion, once again, provided by a linear air bearing motion system or a linear mechanical bearing motion system. 
     Regarding motion systems supporting various carriage assemblies of the present teachings, such as printing system  2000  of  FIG. 11  and printing system  2001  of  FIG. 12  can have a first X-axis carriage that can be used for mounting a printhead assembly and a second carriage assembly that can be used to mount a variety of various assemblies, such as a camera assembly. For example, in  FIG. 12 , orienting system  2001  can have assembly  2300 A that is depicted having printhead assembly  2500  mounted thereupon and second X-axis carriage assembly  2300 B that is depicted having camera assembly  2550  mounted thereupon. Substrate  2050 , which is on substrate support apparatus  2250 , can be located in various positions proximal to bridge  2130 , for example, during a printing process. Substrate support apparatus  2250  can be mounted on printing system base  2101 . In  FIG. 12 , printing system  2001  can have first X-axis carriage assembly  2300 A and second X-axis carriage assembly  2300 B mounted on bridge  2130 . First X-axis carriage assembly  2300 A can also include first Z-axis moving plate  2310 A for the Z-axis positioning of printhead assembly  2500 , while second X-axis carriage assembly  2300 B can have second Z-axis moving plate  2310 B for the Z-axis positioning of camera assembly  2550 . In that regard, various embodiments of carriage assemblies  2300 A and  2300 B can provide precision X,Z positioning with respect to a substrate positioned on substrate support  2250  for printhead assembly  2500  and camera assembly  2550 , respectively. For various embodiments of printing system  2001 , first X-axis carriage assembly  2300 A and second X-axis carriage assembly  2300 B can utilize a linear air bearing motion system, which is intrinsically low-particle generating. 
     A camera assembly  2550  can include camera  2552 , camera mount assembly  2554  and lens assembly  2556 . Camera assembly  2550  can be mounted to motion system  2300 B on Z-axis moving plate  2310 B, via camera mount assembly  2556 . Camera  2552  can be any image sensor device that converts an optical image into an electronic signal, such as by way of non-limiting example, a charge-coupled device (CCD), a complementary metal-oxide-semiconductor (CMOS) device or N-type metal-oxide-semiconductor (NMOS) device. Various image sensor devices can be configured as an array of sensors for an area scan camera, or a single row of sensors, for a line scan camera. Camera assembly  2550  can be connected to image processing system that can include, for example, a computer for storing, processing, and providing results. As previously discussed herein for printing system  2001  of  FIG. 12 , Z-axis moving plate  2310 B can controllably adjust the Z-axis position of camera assembly  2550  relative to substrate  2050 . During various processes, such as for example, printing and data collection, substrate  2050  can be controllably positioned relative to the camera assembly  2550  using the X-axis motion system  2300 B and Y-axis motion system  2355 . 
     Various camera assemblies can utilize cameras having different capabilities. In various embodiments, camera assembly  2550  of  FIG. 12  can be a high-speed, high-resolution camera. In various embodiments of systems and methods of the present teachings, a line scan camera having about 8192 pixels, with a working height of about 190 mm, and capable of scanning at about 34 kHz can be used. In various embodiments of systems and methods of the present teachings, more than one camera can be mounted on an X-axis carriage assembly for various embodiments of a printing system substrate camera assembly, where each camera can have different specifications regarding field of view and resolution. For example, one camera can be a line scan camera for in situ particle inspection, while a second camera can be for regular navigation of a substrate in a gas enclosure system. Such a camera useful for regular navigation can be an area scan camera having a field of view in the range of about 5.4 mm×4 mm with a magnification of about 0.9× to about 10.6 mm×8 mm with a magnification of about 0.45×. In still other embodiments, one camera can be a line scan camera for in situ particle inspection, while a second camera can be for precise navigation of a substrate in a gas enclosure system, for example, for substrate alignment. Such a camera can be useful for precise navigation can be an area scan camera having a field of view of about 0.7 mm×0.5 mm with a magnification of about 7.2×. Various embodiments of a printing system according to the present teachings may have one or more cameras mounted to an X-axis carriage assembly for the purpose of, for example, inspecting various thin film layers that can be printed on an optoelectronic device, as previously described for  FIG. 1 . 
       FIG. 13  is a schematic diagram showing a gas enclosure system  500 . Various embodiments of a gas enclosure system  500  according to the present teachings can comprise, for example gas enclosure  4510  of  FIG. 9  for various modules and chambers as described for  FIG. 10 . For illustrative purposes,  FIG. 13  will refer to gas enclosure  4510  of  FIG. 9  for housing a printing system, though it is to be understood that these teachings apply to a broad number of enclosures, modules and chambers of the present teachings. 
     Gas purification loop  3130  can be in fluid communication gas enclosure  4510 , and at least one thermal regulation system  3140 . Additionally, various embodiments of gas enclosure system  500  can have pressurized inert gas recirculation system  3000 , which can supply inert gas for operating various devices, such as a substrate floatation table for an OLED printing system. Various embodiments of a pressurized inert gas recirculation system  3000  can utilize a compressor, a blower and combinations of the two as sources for various embodiments of pressurized inert gas recirculation system  3000 , as will be discussed in more detail subsequently herein. Additionally, gas enclosure system  500  can have a circulation and filtration system internal to gas enclosure system  500  (not shown). 
     As depicted in  FIG. 13 , for various embodiments of a gas enclosure assembly according to the present teachings, the design of a filtration system can separate the inert gas circulated through gas purification loop  3130  from the inert gas that is continuously filtered and circulated internally for various embodiments of a gas enclosure assembly. Gas purification loop  3130  includes outlet line  3131  from gas enclosure  4510  of  FIG. 9 , to a solvent removal component  3132  and then to gas purification system  3134 . Inert gas purified of solvent and other reactive gas species, such as oxygen and water vapor, are then returned to gas enclosure  4510  through inlet line  3133 . Gas purification loop  3130  may also include appropriate conduits and connections, and sensors, for example, oxygen, water vapor and solvent vapor sensors. A gas circulating unit, such as a fan, blower or motor and the like, can be separately provided or integrated, for example, in gas purification system  3134 , to circulate gas through gas purification loop  3130 . According to various embodiments of a gas enclosure assembly, though solvent removal system  3132  and gas purification system  3134  are shown as separate units in the schematic shown in  FIG. 13 , solvent removal system  3132  and gas purification system  3134  can be housed together as a single purification unit. 
     Gas purification loop  3130  of  FIG. 13  can have solvent removal system  3132  placed upstream of gas purification system  3134 , so that inert gas circulated from gas enclosure  4510  of  FIG. 9  passes through solvent removal system  3132  via outlet line  3131 . According to various embodiments, solvent removal system  3132  may be a solvent trapping system based on adsorbing solvent vapor from an inert gas passing through solvent removal system  3132  of  FIG. 13 . A bed or beds of a sorbent, for example, but not limited by, such as activated charcoal, molecular sieves, and the like, may effectively remove a wide variety of organic solvent vapors. For various embodiments of a gas enclosure system cold trap technology may be employed to remove solvent vapors in solvent removal system  3132 . As previously discussed herein, for various embodiments of a gas enclosure system according to the present teachings, sensors, such as oxygen, water vapor and solvent vapor sensors, may be used to monitor the effective removal of such species from inert gas continuously circulating through a gas enclosure system, such as gas enclosure system  500  of  FIG. 13 . Various embodiments of a solvent removal system can indicate when sorbent, such as activated carbon, molecular sieves, and the like, has reached capacity, so that the bed or beds of sorbent can be regenerated or replaced. Regeneration of a molecular sieve can involve heating the molecular sieve, contacting the molecular sieve with a forming gas, a combination thereof, and the like. Molecular sieves configured to trap various species, including oxygen, water vapor, and solvents, can be regenerated by heating and exposure to a forming gas that comprises hydrogen, for example, a forming gas comprising about 96% nitrogen and 4% hydrogen, with said percentages being by volume or by weight. Physical regeneration of activated charcoal can be done using a similar procedure of heating under an inert environment. 
     Any suitable gas purification system can be used for gas purification system  3134  of gas purification loop  3130  of  FIG. 13 . Gas purification systems available, for example, from MBRAUN Inc., of Statham, N.H., or Innovative Technology of Amesbury, Mass., may be useful for integration into various embodiments of a gas enclosure assembly according to the present teachings. Gas purification system  3134  can be used to purify one or more inert gases in gas enclosure system  500 , for example, to purify the entire gas atmosphere within a gas enclosure assembly. As previously discussed herein, in order to circulate gas through gas purification loop  3130 , gas purification system  3134  can have a gas circulating unit, such as a fan, blower or motor, and the like. In that regard, a gas purification system can be selected depending on the volume of the enclosure, which can define a volumetric flow rate for moving an inert gas through a gas purification system. For various embodiments of gas enclosure system having a gas enclosure assembly with a volume of up to about 4 m 3 ; a gas purification system that can move about 84 m 3 /h can be used. For various embodiments of gas enclosure system having a gas enclosure assembly with a volume of up to about 10 m 3 ; a gas purification system that can move about 155 m 3 /h can be used. For various embodiments of a gas enclosure assembly having a volume of between about 52-114 m 3 , more than one gas purification system may be used. 
     Any suitable gas filters or purifying devices can be included in the gas purification system  3134  of the present teachings. In some embodiments, a gas purification system can comprise two parallel purifying devices, such that one of the devices can be taken off line for maintenance and the other device can be used to continue system operation without interruption. In some embodiments, for example, the gas purification system can comprise one or more molecular sieves. In some embodiments, the gas purification system can comprise at least a first molecular sieve, and a second molecular sieve, such that, when one of the molecular sieves becomes saturated with impurities, or otherwise is deemed not to be operating efficiently enough, the system can switch to the other molecular sieve while regenerating the saturated or non-efficient molecular sieve. A control unit can be provided for determining the operational efficiency of each molecular sieve, for switching between operation of different molecular sieves, for regenerating one or more molecular sieves, or for a combination thereof. As previously discussed herein, molecular sieves may be regenerated and reused. 
     Thermal regulation system  3140  of  FIG. 13  can include at least one chiller  3142 , which can have fluid outlet line  3141  for circulating a coolant into a gas enclosure assembly, and fluid inlet line  3143  for returning the coolant to the chiller. An at least one fluid chiller  3142  can be provided for cooling the gas atmosphere within gas enclosure system  500 . For various embodiments of a gas enclosure system of the present teachings, fluid chiller  3142  delivers cooled fluid to heat exchangers within the enclosure, where inert gas is passed over a filtration system internal the enclosure. At least one fluid chiller can also be provided with gas enclosure system  500  to cool heat evolving from an apparatus enclosed within gas enclosure system  500 . For example, but not limited by, at least one fluid chiller can also be provided for gas enclosure system  500  to cool heat evolving from an OLED printing system. Thermal regulation system  3140  can comprise heat-exchange or Peltier devices and can have various cooling capacities. For example, for various embodiments of a gas enclosure system, a chiller can provide a cooling capacity of from between about 2 kW to about 20 kW. Various embodiments of a gas enclosure system can have a plurality of fluid chillers that can chill one or more fluids. In some embodiments, the fluid chillers can utilize a number of fluids as coolant, for example, but not limited by, water, anti-freeze, a refrigerant, and a combination thereof as a heat exchange fluid. Appropriate leak-free, locking connections can be used in connecting the associated conduits and system components. 
     The present teachings are intended to be illustrative, and not restrictive. The Abstract is provided to comply with 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.