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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Introduction 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.
Description 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.
