Optical: systems and elements – Optical modulator – Light wave directional modulation
Reexamination Certificate
2002-06-11
2003-11-11
Ben, Loha (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave directional modulation
C359S267000, C359S271000, C359S275000, C359S237000, C349S014000, C349S033000, C313S483000, C313S525000, C250S2140VT
Reexamination Certificate
active
06646780
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display medium including a switching layer. More specifically, the present invention relates to a light-reflective or light-transmissive display medium including a switching layer whose light absorption spectrum in the visible light range changes due to voltage application. The present invention also relates to a display element and a display device utilizing such a display medium.
2. Description of the Related Art
Recently, in the field of display technique, thin displays are actively developed, and much attention is focused on liquid crystal displays, plasma displays and organic EL displays. Particularly, liquid crystal displays have been rapidly developed and are widely used for example in a mobile phone or an electronic notebook which require displaying with low power consumption, and in a television, a PC or a car navigation system which require high-resolution color display.
FIG. 7
is a sectional view illustrating an example of light-transmissive liquid crystal display. The liquid crystal display
70
shown in
FIG. 7
includes a pair of panels
71
,
72
, spacers
73
for defining a desired gap between the two panels
71
,
72
, a liquid crystal material
74
filled in the gap, and a sealing member
75
for enclosing the liquid crystal material
74
between the panels
71
and
72
. The liquid crystal display
70
further includes a driving circuit and a backlight, which are not illustrated.
The panel
71
includes a glass substrate
71
a,
transparent electrodes
71
b
and TFTs (not shown) arranged on an inner surface of the glass substrate
71
a,
an alignment layer
71
c
formed on the inner surface of the glass substrate
71
a
to cover the transparent electrodes
71
b
and the TFTs, and a polarizer
71
d
formed on the outer surface of the glass substrate
71
a.
The panel
72
includes a glass substrate
72
a,
transparent electrodes
72
b
arranged on the inner surface of the glass substrate
72
a,
an alignment layer
72
c
formed on the glass substrate
72
a
for covering the transparent electrodes
72
b,
and a polarizer
72
d
formed on the outer surface of the glass substrate
72
a.
Generally, the polarizer
72
d
is arranged so that its axis extends parallel to or forms a right angle with respect to the axis of the polarizer
71
d.
The driving circuit is connected to the transparent electrodes
71
b,
71
b.
The backlight is arranged so that light travels from the side of the panel
71
toward the panel
72
.
The liquid crystal display
70
having such a structure displays an image by applying a voltage to selected elements or dots defined between the transparent electrodes
71
b
and the transparent electrodes
72
b.
Specifically, the application of a voltage to the selected portions or dots between the transparent electrodes
71
b,
72
b
generates an electric field between the electrodes, which changes the alignment of the liquid crystal material
74
at the dots. The change in the alignment of the liquid crystal material
74
and the polarizing effect by the paired polarizers
71
d,
72
d
cause a change in the transmittance of light emitted from the backlight, thereby displaying an image. For displaying of a color image, color filters may be disposed between the glass substrate
72
a
and the transparent electrodes
72
b
of the panel
72
to apply a color to transmitting light.
However, since the liquid crystal display
70
is a display device which utilizes polarizing effect, its viewing angle is relatively narrow, which limits the usage. Further, due to the presence of the polarizers
71
d,
72
d
in the light path, the loss of light emitted from the light source is relatively high. Moreover, the utilization of liquid crystal, which is not a solid matter, poses problems that the display is vulnerable to mechanical shock and the display need be used under a restricted ambient temperature condition for proper operation. Further, since each element constituting the liquid crystal display
70
does not have a memory function, a switching element or capacitor element such as a TFT having a relatively complicated structure need be separately provided for each element. A reflective liquid crystal display may also suffer these technical disadvantages.
Moreover, the manufacturing of the liquid crystal panel
70
is rather difficult due to the peculiar structure of the liquid crystal panel
70
. Specifically, to properly load the liquid crystal material
74
between the paired panels
71
,
72
, spacers
73
and a sealing member
75
need be interposed between the panels
71
and
72
. Further, alignment layers
71
c,
72
c
for determining the alignment of the liquid crystal material
74
and polarizers
71
d,
72
d
need be disposed for completing the panels
71
,
72
.
DISCLOSURE OF THE INVENTION
It is, therefore, an object of the present invention to eliminate or lessen the problems of the prior art and to provide a display medium which has a simple structure to serve as a thin display and includes elements each having a memory function.
Another object of the present invention is to provide a display element having a memory function.
Still another object of the present invention is to provide a display device having a memory function.
According to a first aspect of the present invention, there is provided a sheet-like display medium comprising a switching layer containing a switching layer containing a switching material having a light absorption spectrum which changes in a visible light range when a voltage no less than a threshold value is applied while also maintaining the changed light absorption spectrum even after the voltage application is interrupted, and an electrode layer laminated on the switching layer.
With this structure, when a voltage is applied to selected portions of the display medium, the light absorption spectrum (i.e. color) of the switching layer changes at the portions to which the voltage is applied. The light absorption spectrum thus changed is maintained even after the voltage application is interrupted. Therefore, once images or characters are displayed on the display medium by the voltage application to the selected portions, they can be maintained.
For the switching material, use may be made of an organic metal complex having a light absorption spectrum which changes in the visible light range when a voltage no less than the threshold value is applied while also maintaining the changed light absorption spectrum even after the voltage application is interrupted. Preferably, the organic metal complex may be a metal complex of 7,7,8,8-tetracyanoquinonedimethane (hereinafter abbreviated as “TCNQ”) or of a derivative of TCNQ (e.g. Ag-TCNQ and CU-TCNQ).
A metal complex of TCNQ or of a derivative of TCNQ changes its light absorption spectrum when a voltage is applied, and there is a threshold value of the voltage which need be reached for causing such a change. Therefore, the light absorption spectrum changes when a voltage no less than the threshold value is applied. Once the light absorption spectrum is changed, it is maintained even after the voltage application is interrupted. Thus, a metal complex of TCNQ or of a derivative of TCNQ has a memory function for keeping the changed light absorption spectrum.
FIG. 1
is a graph showing measurements of light transmittance of Ag-TCNQ in a non-switched state A, i.e. before a voltage is applied and in a switched state B, i.e. after a voltage is applied. As shown in the graph, with respect to the visible light range, Ag-TCNQ in the non-switched state A has a relatively high light transmittance in the wavelength range of about 450-600 nm and has a relatively low light transmittance in other wavelength ranges. On the other hand, with respect to the visible light range, Ag-TCNQ in the switched state B has a relatively high light transmittance in a wavelength range of no less than about 575 nm and has a relatively low light transmittance in the shorter wavelength ranges. The light transmittance measu
Adachi Chihaya
Tanaka Haruo
Ben Loha
Merchant & Gould P.C.
Rohm & Co., Ltd.
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