Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2000-05-12
2003-11-25
Lam, Cathy (Department: 1773)
Stock material or miscellaneous articles
Composite
Of metal
C428S001510, C428S333000, C428S434000, C428S418000, C428S469000, C428S697000, C428S699000, C428S702000
Reexamination Certificate
active
06652981
ABSTRACT:
TECHNICAL FIELD
This invention relates to a wet etching process for patterning transparent electrodes for use in a display device.
BACKGROUND
U.S. patent application Ser. No. 09/009,391, now U.S. Pat. No. 6,379,509, incorporated herein by reference, describes a process for forming a plurality of substantially transparent electrodes on a substrate. This process comprises forming on the substrate, in order, a bottom high index layer, a metallic conductive layer, and a top high index layer having a conductivity of at least about 400 &OHgr;/square. The top high index layer, the conductive layer and, optionally, the bottom high index layer, are patterned by laser ablation to form a plurality of discrete electrodes in the metallic conductive layer. The laser beam is scanned in a raster pattern over the substrate and modulated under the control of digital signals from a raster image processor. After the laser ablation procedure is completed, the electrode assembly is contaminated with surface residue and re-deposited debris. The surface of the assembly is then washed with an aqueous solution containing a surfactant and optionally gently abraded to remove the residue and debris.
SUMMARY
Ablative patterning of the top high index layer, the conductive layer, and, optionally, the bottom high index layer, of the electrode assembly is highly accurate and effective. However, such a process may not be appropriate for all materials and constructions. The high-resolution image file used in a laser ablation apparatus may not be required for all patterning operations. In addition, it may not be feasible to incorporate laser ablation equipment into an existing production facility.
In one aspect, the invention is a process for forming an electrode, the process including forming on a substrate, in order, a bottom high index layer, a conductive layer, and a top high index layer with a conductivity of at least about 400 &OHgr;/square; and chemically etching the bottom high index layer, the top high index layer and the conductive layer to form an electrode in the conductive layer.
In another aspect, the invention is a substantially transparent electrode assembly including a substrate having deposited thereon, in order, a bottom high index layer, a metallic conductive layer, and a top high index layer with a conductivity of at least about 400 &OHgr;/square. The conductive layer includes a plurality of discrete electrodes formed by chemically etching the bottom high index layer, the top high index layer and the conductive layer.
In yet another aspect, the invention is a display device including a substantially transparent electrode assembly. The electrode assembly includes a substrate having deposited thereon, in order, a bottom high index layer, a metallic conductive layer, and a top high index layer with a conductivity of at least about 400 &OHgr;/square. The conductive layer includes a plurality of discrete electrodes formed by chemically etching the bottom high index layer, the top high index layer and the conductive layer.
In another aspect, the invention is an electronic device including this substantially transparent electrode assembly.
The details of one or more embodiments of the invention are set forth in the description below. Other features, objects, and advantages of the invention will be apparent from the description and the claims.
DETAILED DESCRIPTION
The substrate used in the process of the invention may be made from any material with sufficient mechanical integrity and a sufficiently smooth surface to permit the formation of electrodes thereon. The substrate, like the other layers of the electrode assembly, is preferably sufficiently transparent to allow its use in a liquid crystal display. Glass substrates may be used, but it is generally preferred that the substrate be made of a synthetic resin. Preferred resins for this purpose include, for example, polyether sulfones, poly(alkyl)acrylates, cellulose diacetate, polycarbonate, polyesters, high glass transition temperature (Tg) polycarbonate copolymers available from Lonza AG, Basel, Switzerland under the trade designation “POKALON HT,” and poly(bis(cyclopentadiene) condensate)s, such as the material sold by Lonza AG, Basel, Switzerland under the trade designation “TRANSPHAN.” This material is a film made of a polymer sold by Japan Synthetic Rubber Co. Ltd., Tokyo, Japan under the trade designation “ARTON,” which is stated by the manufacturer to be of the formula:
(in which X is a polar group).
The substrate may be coated on one or both surfaces to provide a barrier against gas and moisture, and/or to improve the hardness and scratch resistance of the substrate, and/or to improve the adhesion of the high index layer to the substrate. For example, a hard polymer may be coated on one surface or both surfaces of the substrate. Such a hard coating will typically have a thickness of from about 1 to about 15 &mgr;m, preferably from about 2 to about 4 &mgr;m. The coating may be polymerized by free radical polymerization (initiated either thermally or by ultra-violet radiation) of an appropriate polymeric material. An especially preferred hard coating is the acrylic coating sold under the trade designation “TERRAPIN” by Tekra Corporation, New Berlin, Wis.
A thin (typically 10-40 nm, preferably about 30 nm) layer of silica (SiO
x
) may be applied on one or both surfaces of the substrate to act as a gas and moisture barrier for the eventual liquid crystal display assembly, and to act as an adhesion promoter to improve the adhesion of the bottom high index layer. The term “silica” is used herein means a material of the formula SiO
x
where x is not necessarily equal to two. These silica layers may be deposited by chemical vapor deposition or sputtering of silicon in an oxygen atmosphere, so that the material deposited does not precisely conform to the stoichiometric formula SiO
2
of pure silica. When both a hard coating and a silica layer are applied to the substrate, the layers may be applied in any order. In a preferred embodiment, a first silica layer is applied on a surface of the substrate, followed by, in order, a hard coating and a second silica layer.
In the present process, the following layers are deposited on the substrate, in order: a bottom high index layer, a metallic conductive layer and a top high index layer. A wide variety of techniques may be used to deposit these layers, for example, e-beam and thermal evaporation, but the layers are preferably deposited by sputtering or by chemical vapor deposition. A dc sputtering process is especially preferred, although RF, magnetron and reactive sputtering and low-pressure, plasma-enhanced and laser-enhanced chemical vapor deposition may also be used. When the preferred plastic substrates are used, each of the three layers should be deposited on the substrate at a temperature not greater than about 170° C. to prevent damage to the plastic substrate. The temperature limit of course varies with the exact substrate material used. For example, for a TRANSPHAN substrate, the deposition temperature should not be greater than about 160 to about 165° C.
The bottom high index layer adjacent the substrate may be electrically insulating or conductive. Insulating materials are generally preferred, so if any portion of the bottom high index layer remains between adjacent electrodes after the patterning step, the remaining portion will not cause an electrical short between the electrodes. Such an electrical short is of course undesirable, since it in effect turns the two adjacent electrodes into a single electrode and adversely affects the quality of a liquid crystal display or touch screen in which the electrode assembly is used. However, a conductive high index layer may be used if the patterning conditions ensure that no portion of the bottom high index layer will remain after patterning.
Whether insulating or conductive, the bottom high index layer is typically formed from a metal oxide. Oxides that may be used for the bottom high index layer are indium oxide (In
2
O
3
), titanium dioxide (TiO
Lennhoff Nancy S.
Ram Jyothsna
Buckingham Stephen W.
Lam Cathy
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