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Electrophoretic cells with a voltage threshold Disclosure Number: IPCOM000130344D
Publication Date: 2005-Oct-21
Document File: 2 page(s) / 13K

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Electrophoretic cells with a voltage threshold


The creation of a threshold in an electrophoretic system is suggested via coating one or more of the electrodes with an organic photoconductor film. When this photoconductor is homogeneously illuminated by the already present backlight it's non-linear resistance creates a voltage threshold that in turn allows passive matrix addressing. This has been shown to work. Note this is NOT optically addressing of a display as the backlight is homogenously lit.


For passive matrix addressing of an electrophoretic display a threshold must be present.

An electrical threshold has therefore been proposed and been shown to work. While an electrical threshold is a solution it has disadvantages. The first disadvantage is that it requires an extra (gate) electrode in the cells. This may increase the manufacturing cost but more importantly the driving of this electrode requires more drivers. An extra electrode also reduces the aperture of the cell and thus the contrast is reduced. During addressing of such a display the gate lines that are not being addressed have to be held at a repelling voltage. This can also have negative effects due to d.c. build-up.

We suggest a two electrode electrophoretic cell (no electrical gate) where a layer of material with a non-linear resistance is coated on at least one of the electrodes. The electrical resistance of this layer decreases rapidly when the voltage dropped over the layer is increased. This is different from most materials that are ohmic and therefore have a constant R irrespective of the applied voltage (at least until dielectric breakdown). If the layer has a rapid decrease in resistance for voltages of say, above 20 V then any voltage below 20V is dropped over the non-linear layer while that above 20V is dropped over the electrophoretic suspensio...