Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2002-05-31
2004-06-22
Ben, Loha (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C345S107000, C430S035000, C204S450000, C204S606000
Reexamination Certificate
active
06753999
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electrophoretic displays, especially encapsulated electrophoretic displays, and to systems for addressing such displays.
BACKGROUND OF THE INVENTION
There are a number of interesting display media which provide good optical appearance, the ability to be easily constructed in large areas or on flexible substrates at low cost. Such display media include microencapsulated electrophoretic displays, rotating bichromal ball displays, suspended particle displays, and composites of liquid crystals with polymers, including polymer dispersed liquid crystals, polymer stabilized liquid crystals, and liquid crystal gels.
One drawback of such displays is that they are difficult to practically and economically address. One common means of addressing is known as direct drive addressing, in which each pixel is controlled by its own external drive circuit. This scheme is both expensive and impractical for displays containing a large number of pixels and for displays containing pixels that are tightly packed.
Another means of addressing is active matrix drive addressing, in which an electrically non-linear element is deposited on the display substrate. Examples of such electronically non-linear elements include transistors, diodes, and varistors. While this type of addressing is well-known and widely practiced, it is expensive to produce and difficult to achieve on plastic substrates.
A third means of addressing uses multiplexing, in which the conductive portions of the substrate are patterned so that rows of pixels on the substrate are electrically connected and columns of pixels on the substrate are also electrically connected. Typically, voltages are sequentially placed on the row electrodes, with the pixel data for each row being placed on the column electrode. This type of addressing is used for a variety of display media. Its use is limited, however, to displays in which the optical response as a function of applied voltage is non-linear and in which there is a significant voltage threshold to turn on the pixels. Display media which do not show a pronounced voltage threshold show poor contrast when driven with multiplex addressing drive schemes.
This invention provides electrophoretic displays, especially encapsulated electrophoretic displays, and systems for addressing display media of such displays. Systems of the invention allow for the addressing of display media that have poor threshold behavior without the high costs associated with using direct drive and active matrix drive addressing schemes. This is accomplished by using a multiplex addressing drive scheme in conjunction with a light system that generates a pattern of light.
There are numerous applications that can benefit from such a new addressing means. For instance, with the advent of information storing members (such as RAM and magnetic strips) in wallet-size card, it has become desirable to create ‘smart cards’ capable of displaying on the card the updated information contained in the card. Typical cards such as credit cards have a magnetic strip on the rear surface, and a subset of the information contained on the magnetic strip, such as the cardholder name and card number, is embossed physically onto the front surface of the card. This usually suffices for this purpose, since the information on the strip is static. For transaction type cards, such as debit cards, however, there is a need for a means to display the information, which is stored on the card, as it is constantly changing. For example, phone cards and access cards may have certain value units which are purchased from some central or distributed authority. These value units (such as tokens, in the case of a subway, or phone minutes) may be actually stored locally on the card and interrogated offline, or the card may carry simply an identification number which is verified at each transaction and correlated with a central balance. The balance remaining on the card, however, is usually not indicated to the user. Prior art solutions to this problem involve systems such as that employed in the Washington D.C. subway, where a computer daisywheel printer prints the current balance on the card paper surface directly below the prior balance. There are several problems with this solution. First, the user can no longer simply swipe the card through a reader, but must insert it into a large machine in which the printer is housed. Second, cards made with this paper surface are not very durable, the information is not erased but basically crossed out; as a result, the card may be used only so many times before the balance space is filled up. Accordingly, such cards can benefit from the inclusion of a dynamic medium for updating the information contained thereon. Other examples of portable devices that can benefit from a novel system of updating the display on a card include access cards, smart cards, payment cards, price tags, and lottery tickets.
SUMMARY OF THE INVENTION
The present invention provides electrophoretic displays, especially encapsulated electrophoretic displays, and systems for addressing such displays. Displays of the invention include a photoconductive layer and an electrophoretic layer. Such displays may be rigid or flexible. Displays of the invention may also include a light image generated from a light source, a photoconductive layer, and an electrophoretic layer.
In one embodiment of the invention, a portable display card and system of updating the image on the card of the invention includes a light system that generates a light pattern, a card that includes a photoconductive layer and an electrophoretic layer. The photoconductive layer is adjacent the electrophoretic layer and the pattern of light reduces impedance in the photoconductive layer. The reduced impedance permits an applied electric field to address the electrophoretic layer. In some embodiments, the display cards also have one or more optical barrier layers.
The display cards have a front side and a rear side. When the rear side of the card is exposed to a pattern of light from the light source, light strikes the photoconductive layer and the photoconductive layer impedance decreases. The decreased impedance enables electrodes to apply a voltage, which addresses the electrophoretic layer, forming an updated image on the display card. In some embodiments, an electrode on the rear side of the card is clear. Light from the light source travels through the clear electrode to strike the photoconductive layer.
In another embodiment, the invention relates to an electrophoretic display including a light system, a photoconductive layer placed adjacent the organic, light-emitting layer, and an electrophoretic layer adjacent the photoconductive layer. Light from the organic, light-emitting layer strikes the photoconductive layer at a first point on a first side of the photoconductive layer, which faces the organic, light-emitting layer. A voltage is then generated at a second point on a second side of the photoconductive layer. This second point corresponds to the first point and faces the electrophoretic layer. The voltage at the second point addresses the electrophoretic layer at a predetermined point on the electrophoretic layer.
When the display is not illuminated, the impedance of the photoconductive layer is much greater than the impedance of the electrophoretic layer. The photoconductive layer therefore drops the majority of the applied voltage. When the photoconductive display is illuminated, the impedance of the photoconductive layer decreases, and the majority of the applied voltage then drops across the electrophoretic layer, forming an image. Specifically, the photoconductive layer is biased at a voltage on the “rear” side, which faces the light source. The portions of the photoconductive layer that are exposed to light effectively transfer the voltage to the “front” side of the photoconductive layer, which faces the electrophoretic layer.
The present invention provides a display integrated into a smart card which is capable of being e
Duthaler Gregg M.
Morrison Ian
Paolini Jr. Richard J.
Zehner Robert W.
Ben Loha
E Ink Corporation
Testa Hurwitz & Thibeault LLP
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