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Function-oriented Knowledge Base \ Electronic paper \ Improve image quality of paper-like display

Organic-based field effect transistors address pixel without interference from adjacent pixels in microencapsulated displays

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A microencapsulated electrophoretic display is comprised of a layer of microcapsules with a liquid. The liquid contains colored particles having a zeta potential caused by interaction with the liquid. The microcapsule layer is sandwiched between two layers with parallel linear transparent electrodes. The electrodes form an addressing matrix with image elements (pixels) in the gaps between the crossing row and column electrodes. When an addressing voltage is applied to a pair of a row electrode and a column electrode, the electric field between the electrodes drives the colored particles to either of the electrodes. The particles adhere to the microcapsule wall adjoining the electrode and remain there after the voltage cutoff. No energy is thus needed to maintain the image. Such displays exhibit diffusion reflection in natural light and are bistable and optically and electrically efficient. However, the microencapsulated displays do not provide sufficient contrast and resolution. These drawbacks are caused by interference (crosstalk) with an individual pixel from adjacent pixels. An interference-free method for addressing pixels is based upon using the threshold properties of an array of transistor elements in which one transistor is associated with one pixel. The pixel is connected through the transistor to the addressing electrodes. The transistor array can be fabricated through vacuum deposition of silicon on glass. However, this process is complex and expensive for forming large area displays due to problems of creating silicon transistors on plastic or other flexible films. It is necessary to address a display pixel without interference from adjacent pixels in a large area display.
Using organic-based field effect transistors to address display pixels without interference from adjacent pixels is proposed. An organic-based field effect transistor is comprised of an organic semiconductor (for example, polythiophene). The display is comprised of an encapsulated display medium, as well as organic-based field effect transistors. The display medium contains a plurality of particles in the liquid and has an initial surface and a secondary surface. Organic-based field effect transistors for addressing the display pixels are positioned on the secondary surface of the display medium. A row electrode is electrically connected to the gates of all the transistors in its row. Each column electrode is electrically connected to the drains of all the organic-based field effect transistors in its column. An organic-based field effect transistor to which operating voltages are simultaneously applied from a bus of rows, and a bus of columns opens and applies the electric field to the pixel medium. Under the influence of the applied electric field, electrophoretic movement of the particles occurs within the layer of this pixel, changing the optical state of the pixel. At the same time, the adjacent pixels connected to closed transistors (unaffected by the voltage needed to open them) preserve their previous state due to the threshold properties of the transistors. Therefore, organic-based field effect transistors eliminate interference between adjacent pixels.
Additional information
The elimination of interference provides for an increase in the display resolution. The array of the organic-based field effect transistors is printed on a large flexible plastic substrate and joined with a layer of an encapsulated medium into a common display. The size of an organic-based field effect transistor may range from 1 percent to 100 percent of the area of the pixel addressed by the transistor. The display medium may be comprised of rotating or twisting microencapsulated balls. Along with electrophoretic particles, the liquid (or at least one of the pixel electrodes) may have one of the contrasting colors.
US Patent 6518949; Link >>
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