Method for roll-to-roll deposition of optically transparent...

Details Method for roll-to-roll deposition of optically transparent... Method for roll-to-roll deposition of optically transparent...

2002-06-14

2004-11-02

Boykin, Terressa (Department: 1711)

Coating processes

Coating by vapor, gas, or smoke

C349S086000, C428S411100, C528S176000, C528S193000, C528S196000, C528S272000

Reexamination Certificate

active

06811815

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to methods for roll-to-roll deposition of optically transparent and high conductivity metallic films for use in plastic display electrodes and other analogous devices, and to composite films made using those methods.
2. General Background and State of the Art
A liquid crystal display (LCD) is a type of flat panel display used in various electronic devices. Generally, LCDs comprise two sheets of polarizing material with a liquid crystal solution therebetween. Each sheet of polarizing material typically comprises a substrate of glass or transparent plastic; a liquid crystal (LC) is used as optical switches. The substrates are usually manufactured with transparent electrodes, typically made of indium tin oxide (ITO) or another conductive metallic layer, in which electrical “driving” signals are coupled. The driving signals induce an electric field which can cause a phase change or state change in the LC material, the LC exhibiting different light-reflecting characteristics according to its phase and/or state.
Liquid crystals can be nematic, smectic, or cholesteric depending upon the arrangement of the molecules. A twisted nematic cell is made up of two bounding plates (usually glass slides or plastic plates), each with a transparent conductive coating (such as ITO or another conductor) that acts as an electrode, spacers to control the cell gap, two cross polarizers (the polarizer and the analyzer), and nematic liquid crystal material. Twisted nematic displays rotate the direction of the liquid crystal by 90°. Super-twisted nematic displays employ up to a 270° rotation. This extra rotation gives the crystal a much deeper voltage-brightest response, also widens the angle at which the display can be viewed before losing much contrast. Cholesteric liquid crystal (CLC) displays are normally reflective (meaning no backlight is needed) and can function without the use of polarizing films or a color filter. “Cholesteric” means the type of liquid crystal having finer pitch than that of twisted nematic and super-twisted nematic. Sometimes it is called “chiral nematic” because cholesteric liquid crystal is normally obtained by adding chiral agents to host nematic liquid crystals. Cholesteric liquid crystals may be used to provide bistable and multistable displays that, due to their non-volatile “memory” characteristic, do not require a continuous driving circuit to maintain a display image, thereby significantly reducing power consumption. Feroelectric liquid crystals (FLCs) use liquid crystal substances that have chiral molecules in a smectic C type of arrangement because the spiral nature of these molecules allows the microsecond switching response time that makes FLCs particularly suited to advance displays. Surface-stabilized feroelectric liquid crystals (SSFLCs) apply controlled pressure through the use of a glass plate, suppressing the spiral of the molecules to make the switching even more rapid.
Some known LCD devices include chemically-edged transparent, conductive layers overlying a glass substrate. See, e.g., U.S. Pat. No. 5,667,853 to Fukuyoshi et al., incorporated herein by reference. Unfortunately, chemical etching processes are often difficult to control, especially for plastic films. Such processes are also not well-suited for production of the films in a continuous, roll-to-roll manner, on plastic substrates.
There are alternative display technologies to LCDs that can be used, for example, in flat panel displays. A notable example is organic or polymer light-emitting devices (OLEDs) or (PLEDs), which are comprised of several layers in which one of the layers is comprised of an organic material that can be made to electroluminesce by applying a voltage across the device. An OLED device is typically a laminate formed in a substrate such as glass or a plastic polymer. A light-emitting layer of a luminescent organic solid, as well as adjacent semiconductor layers, are sandwiched between an anode and a cathode. The semiconductor layers can be whole-injecting and electron-injecting layers. PLEDs can be considered a subspecies of OLEDs in which the luminescent organic material is a polymer. The light-emitting layers may be selected from any of a multitude of light-emitting organic solids, e.g., polymers that are suitably fluorescent or chemiluminescent organic compounds. Such compounds and polymers include metal ion salts of 8-hydroxyquinolate, trivalent metal quinolate complexes, trivalent metal bridged quinolate complexes, Schiff-based divalent metal complexes, tin (IV) metal complexes, metal acetylacetonate complexes, metal bidenate ligand complexes incorporating organic ligands, such as 2-picolylketones, 2-quinaldylketones, or 2-(o-phenoxy) pyridine ketones, bisphosphonates, divalent metal maleonitriledithiolate complexes, molecular charge transfer complexes, rare earth mixed chelates, (5-hydroxy) quinoxaline metal complexes, aluminum tris-quinolates, and polymers such as poly(p-phenylenevinylene), poly(dialkoxyphenylenevinylene), poly(thiophene), poly(fluorene), poly(phenylene), poly(phenylacetylene), poly(aniline), poly(3-alkylthiophene), poly(3-octylthiophene), and poly(N-vinylcarbazole). When a potential difference is applied across the cathode and anode, electrons from the electron-injecting layer and holes from the hole-injecting layer are injected into the light-emitting layer; they recombine, emitting light. OLEDs and PLEDs are described in the following United States patents, all of which are incorporated herein by this reference: U.S. Pat. No. 5,707,745 to Forrest et al., U.S. Pat. No. 5,721,160 to Forrest et al., U.S. Pat. No. 5,757,026 to Forrest et al., U.S. Pat. No. 5,834,893 to Bulovic et al., U.S. Pat. No. 5,861,219 to Thompson et al., U.S. Pat. No. 5,904,916 to Tang et al., U.S. Pat. No. 5,986,401 to Thompson et al., U.S. Pat. No. 5,998,803 to Forrest et al., U.S. Pat. No. 6,013,538 to Burrows et al., U.S. Pat. No. 6,046,543 to Bulovic et al., U.S. Pat. No. 6,048,573 to Tang et al., U.S. Pat. No. 6,048,630 to Burrows et al., U.S. Pat. No. 6,066,357 to Tang et al., U.S. Pat. No. 6,125,226 to Forrest et al., U.S. Pat. No. 6,137,223 to Hung et al., U.S. Pat. No. 6,242,115 to Thompson et al., and U.S. Pat. No. 6,274,980 to Burrows et al.
In a typical matrix-address light-emitting display device, numerous light-emitting devices are formed on a single substrate and arranged in groups in a regular grid pattern. Activation may be by rows and columns, or in an active matrix with individual cathode and anode paths. OLEDs are often manufactured by first depositing a transparent electrode on the substrate, and patterning the same into electrode portions. The organic layer(s) is then deposited over the transparent electrode. A metallic electrode can be formed over the electrode layers. For example, in U.S. Pat. No. 5,703,436 to Forrest et al., incorporated herein by reference, transparent indium tin oxide (ITO) is used as the whole-injecting electrode, and a Mg—Ag—ITO electrode layer is used for electron injection.
Previous methods of manufacturing such films have not succeeded in manufacturing such films by a continuous process on flexible substrates, yielding films with desirable properties such as high transmittance, low electrical resistance, and stability to temperature and humidity.
For example, PCT Publication No. WO 99/36261, by Choi et al. (Polaroid Corp.) published on Jul. 22, 1999, and incorporated by this reference, describes the deposition of ITO/Au/Ag/Au/ITO multilayered films on polymer (Arton substrate). In this multilayered structure, the Ag layer has a thickness of 10-15 nm and the two ITO layers have a thickness of 35-50 nm. As compared with ITO/Ag/ITO multilayered films, an Au/Ag/Au sandwiched layer works as a conductive layer in the multilayered structure and exhibits an enhanced corrosion resistance as the 1-1.5 nm Au layers prevent the water or oxygen from entering the Au/Ag interfacial area. It was reported that the ITO/Au/Ag/Au/ITO films have a sheet resi

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