Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2000-04-06
2001-12-04
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C345S107000, C204S450000
Reexamination Certificate
active
06327072
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to electrophoretic displays and, in particular, to electrophoretic displays using microcells.
BACKGROUND OF THE INVENTION
A variety of electronic display devices operate by the principle of electrophoresis. In such displays, an electrophoretic suspension contains electrophoretically mobile particles. Many electrophoretic displays suffer from several failure modes. In one failure mode, the particles stick or agglomerate together and the desired visual effect is reduced. In another failure mode, the particles migrate across the face of the display (particularly under the influence of gravity). Both of these failure modes result in a nonuniform display.
As such, current electrophoretic display technology produces a display that neither is as bright nor has as much contrast as is desired. Current displays are not capable of achieving uniform brightness or good contrast due to limitations in their construction. Thus, new materials and methods of construction are needed to provide electrophoretic displays with acceptable brightness and contrast.
SUMMARY OF THE INVENTION
The present invention provides electrophoretic displays having a suspending fluid and particles that are contained in microcells of certain geometries. These microcells are disposed on a substrate with walls that define a void. The void can be filled with a suspending medium and particles. Microcells according to the invention provide displays with less particle agglomeration, less unwanted particle migration, better brightness, and/or better contrast than current displays.
Throughout the Specification, the invention is described as a display or an array for ease of description. However, the compositions and processes disclosed herein are equally applicable to “elements”. A display or an array are examples of the broader concept of an element. One or more elements can be ordered into a display, array, or other articles of manufacture. Elements can include any of the features described for a display or an array. As used herein, “cell” and “microcell” are used interchangeably, unless otherwise specified, or otherwise apparent from context. Also, as used herein, “suspending fluid” and “suspending medium” are used interchangeably, unless otherwise specified, or otherwise apparent from context.
Generally, particles move within the microcell under the influence of a voltage. Depending upon the location of the particles and the composition of the suspending fluid, various visual states are available. In one highly generalized example, reflecting particles, located at the front of the cell (towards a viewer) in a colored dye, will reflect light and appear “white.” When the reflecting particles move towards the rear of the cell (opposite the viewer) upon application of an electric, the particles will be obscured by the dyed fluid and will appear “dark” to a viewer.
In one aspect of the invention, an electrophoretic display element includes at least one substrate and at least one cell that is defined by a cell wall and that is disposed on the substrate. The cell has a width that is not greater than about three times a height of the cell wall, preferably from about two to about three time the height of the cell wall.
The electrophoretic display element can have any of the following features. A cell wall can be less than 10 micrometers wide. The substrate can include a control grid electrode structure, and the cell can include two laminated structures. The cell wall can be formed at least in part with a technique such as photolithography, sandblasting, screenprinting, embossing, laser etching or radiation curing. The substrate can be permeable to a suspending fluid and substantially impermeable to electrophoretic particles, such that the suspending fluid and the particles fill a cavity defined by the cell walls. The substrate can be coated with a polymer, and the polymer can be insoluble in a suspending medium contained within a cavity defined by the cell walls. A suspending fluid contained within a cavity defined by the cell walls can be a substantially clear liquid.
In another aspect of the invention, an electrophoretic display element includes a substrate and at least one cell defined by a cell wall and disposed on the substrate. The cell contains a suspending medium and a plurality of electrophoretic particles, and the cell has a shape that minimizes hydrodynamic motion within the suspending medium within the cell. The hydrodynamic motion can be caused by, for example, convective currents within the suspending medium within the cell.
REFERENCES:
patent: 5930026 (1999-07-01), Jacobson et al.
patent: 6067185 (2000-05-01), Albert et al.
patent: 6130773 (2000-10-01), Jacobson et al.
Comiskey Barrett
Morrison Ian
Wilcox Russell J.
E Ink Corporation
Epps Georgia
Testa Hurwitz & Thibeault LLP
Thompson Tim
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