Patent Application
20080158449
The present application relates to display devices, and more particularly to liquid crystal display devices.
The instability of plastic substrates makes registering front and rear electrodes difficult in a roll to roll process. Yet, roll to roll processes are seen as more efficient than batch processes. Accordingly, manufacturers developed processes in which a first electrode is non-patterned and a second electrode is patterned. However, such a construction can result in the presence of unwanted electric fields between the traces on the patterned electrode and the non-patterned electrode that cause unintended shuttering. Therefore, what is needed is either a roll-to-roll process that is capable of accurately registering the front and rear substrates, or a display construction that eliminates or sufficiently reduces the electric field between the traces of the patterned electrode and the non-patterned electrode.
For the purpose of facilitating an understanding of the subject matter sought to be protected, there are illustrative embodiments in the accompanying drawing, from an inspection of which, when considered in connection with the following description and claims, the subject matter sought to be protected, its construction and operation, and many of its advantages should be readily understood and appreciated
In one example a method is provided. A first electrode is formed on a first substrate. A second electrode is formed on a second substrate. A layer of optically active material is positioned between the first electrode and the second electrode. A voltage V(e) is applied between the first electrode and the second electrode to produce an electric field. A layer of dielectric material having at least one area defined by a void is provided. The layer of dielectric material is utilized to reduce the electric field across the optically active material other than in the area defined by the void.
In another example, a method of operating a display is provided. The display comprises a first electrode on a first substrate, a second electrode on a second substrate, and a layer of liquid crystal emulsified material between the first substrate and the second substrate. A voltage V(e) is applied between the first electrode and the second electrode to create an electric field that runs through the layer of liquid crystal emulsified material. At least a portion of the electric field is blocked, through utilization of a dielectric material positioned over the first electrode, to create at least one non-visible area in the display.
Referring to
Registering first electrode 101 and second electrode 103 is difficult in a roll-to-roll process. Consequently, manufacturers developed another construction 150 shown in
By “patterned” it is mean that the electrode itself has geometry. In one example, a patterned electrode is formed by coating a substrate made of a first material, such polyethylene terephthalate, with a layer of material, such as Indium Tin Oxide (ITO) (e.g. through sputtering) and applying a photo resist to it. Portions of this layer are then etched away thereby creating a specific geometry. An un-patterned electrode covers the entire substrate onto which it has been coated or sputtered.
By keeping second electrode 153 un-patterned, registration is no longer required because there is no pattern on the second electrode 153 (i.e. there are no two patterns that need registration). An unwanted by-product of this approach, however, is that the patterned electrode's traces 157 will always overlap with the second unpatterned electrode, thereby creating an electric field in an area where it is not desired to have one.
The construction shown in
Referring to
Display device in one example comprises a first substrate 301 and a first electrode 303 formed on the first substrate. A second substrate 305 and a second electrode 307 formed on the second substrate. A layer of optically active material 309 is positioned between the first substrate 301 and the second substrate 303. In one example, the optically active material is liquid crystal material. It should be noted, however, that the optically active material can comprise any material that either transmits, emits or reflects light based on applied voltage. A layer of dielectric material 311 is formed over the first electrode 303. The dielectric material layer 311 includes a void 313.
Referring further to
Dielectric material layer 311 in one example is a clear dielectric material, such as titanium oxide that is formed over first electrode 303. In one example, dielectric layer 311 is formed over first electrode 303 by utilizing it is a dielectric ink and printing it over first electrode 303 with a method, such as screen printing, pad printing, vapor deposition, or with an ink-jet printer. In one example, dielectric layer 311 has a thickness that is less than or equal to the liquid crystal layer 309. For example, the thickness of the dielectric material may be a few microns. Void 313 in dielectric material 311 defines an area of illumination 315 when an electric field is applied to first electrode 303 and second electrode 307 and light is incident on the optically active material layer 309.
Finally, it should be noted that the dielectric layer in between the two display substrates can be modeled as a capacitor in series with a capacitor that represents the optically active material. To reduce the electric field (or voltage) across the optically active material, the capacitance of the dielectric layer needs to be much smaller than the capacitance of the optically active material. The voltage drop (V1) across a capacitor (C1) in series with a capacitor (C2) is given by the equation V2=C1/(C1+C2). The smaller capacitor sees the larger voltage drop. To make the capacitance of the dielectric layer smaller than the capacitance of the optically active, the designer will need to consider the ratios of the two materials permittivity as well as the ratios of the thicknesses of the two materials. The lower the permittivity and the thicker the dielectric layer, the lower will be the capacitance. However, a thicker dielectric layer could potentially introduce optical problems. Accordingly, the thickness of the material must be balanced against the optical properties that are desired.
Referring to
Referring further to
While particular embodiments have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made without departing from the principles set forth herein. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation.
