Function-oriented Knowledge Base \ Electronic paper \ Improve image quality of paper-like display
Dielectric droplets reduce response time of flat panel display
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Introduction Conventional liquid crystal displays exhibit
a substantial response time. It is necessary to reduce the
response time of a flat panel display.
Description To reduce the response time of a flat panel
display, using dielectric droplets movable in a gradient electric
field is proposed. A flat panel display incorporates a plurality
of micro-pump light valves (MLV) to form pixels. Each MLV
consists of a dielectric droplet sandwiched between two transparent
substrates. Coordinate electrodes are provided on the external
surfaces of the substrates and non-wetted areas are formed
on their internal surfaces. A holding electrode creates a
potential energy well to maintain the droplet outside the
viewing area. A switching electrode creates a switching potential
well that accelerates the droplet from the region of the holding
electrode to the viewing area. The non-wetted areas create
potential holding barriers adjacent to the viewing area of
the pixel in order to confine the dielectric droplet when
the voltages are off. The basic principle of the MLV is that
of electrodynamics. This states that a dielectric body tends
to be attracted to a region of a strong electric field, provided
that the dielectric constant of this body is greater than
that of the surrounding area. Sequential voltage switching
on the electrodes changes the depth of the potential wells
within the regions of the holding and switching electrodes.
A sequential change in the depth of the potential wells creates
an electric field gradient between the electrodes. The electric
field gradient causes the droplet to accelerate and move from
the region of the holding electrode to the viewing area. The
obtainable rates may be high, so the time needed for the droplet
to move to the viewing area that corresponds to a pixel response
is reduced. The pixel response time is thus reduced as well.
Therefore, a dielectric droplet reduces the response time
of a flat panel display.
Additional information The forces acting upon the droplet are quadratic
in nature to provide a nonlinear response. The response is
quadratic, so the reaction of the droplet is independent of
the sign of the electric field. For this reason, alternating
voltage is preferably applied. The response time of a pixel
having a size of 30x30x100 microns with a droplet having a
diameter of 30 microns is approximately 10 milliseconds. When
the dielectric droplet is within the region of the holding
electrode, the ambient light can pass through the viewing
area. The non-wetted areas enhance the contrast ratio while
reducing flickering. It will also be noticed that, unlike
liquid crystal displays, the proposed display requires no
polarizers or "transparent" electrode surfaces,
thus providing an inherent increase in brightness. It is essential
that passive addressing of larger displays without active
driver components at each pixel is possible due to the nonlinear
character of the response. The dielectric droplet possesses
a relatively large dielectric constant (greater than 10) and
a relatively small viscosity (less than 10 cP). The droplet
may be methanol or glycol. Polyethylene may be effective to
form the non-wetted surfaces.
