Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Plasma excitation
Reexamination Certificate
1999-12-28
2001-10-30
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Plasma excitation
C349S024000, C349S084000, C345S037000
Reexamination Certificate
active
06310665
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical addressing device used for a display apparatus which utilizes an electrooptic material, and a display apparatus using such an optical addressing device. More specifically, the present invention relates to an optical addressing device suitably used for a liquid crystal display apparatus, and a liquid crystal display apparatus using such an optical addressing device.
Liquid crystal display apparatuses are classified based on the driving method thereof into types of an electrical addressing method, a thermal addressing method, and an optical addressing method. Among these types, presently, a passive matrix (PM) type and an active matrix (AM) type of the electrical addressing method are most frequently used as direct-view display apparatuses.
In recent years, needs for a larger size and a higher precision of a display apparatus has increased. Conventional types of liquid crystal display apparatuses however have not satisfactorily responded to these needs. In reality, the largest size of 20 inches diagonally is the limit for products commercially available. Even for trial manufacture, the size is only about 30 inches diagonally. In particular, the PM type has a problem that the contrast is lowered due to crosstalk as the number of pixels increases. The AM type also has a problem that it is difficult to form a number of switching elements (especially, thin film transistors (TFTs)) without occurrence of defects.
A plasma addressed liquid crystal (PALC) display apparatus was developed in 1990 by T. Buzak and his colleagues of Tektronix Inc., U.S. as an AM type liquid crystal display apparatus which does not use semiconductor switching elements such as TFTs (see U.S. Pat. No. 4,896,149 and the corresponding Japanese Laid-Open Publication No. 1-217396, for example). The sectional structure of such a PALC apparatus is diagrammatically shown in FIG.
1
.
A PALC display apparatus
100
has a layered structure consisting of a liquid crystal cell and a plasma cell. A liquid crystal layer
103
is sandwiched by a substrate
101
and a dielectric separator
104
and driven by a potential difference between signal electrodes (column electrodes)
102
and the dielectric separator
104
. The plasma cell has a plurality of plasma discharge channels
105
formed by dividing a space between a substrate
109
and the dielectric separator
104
with a plurality of rib walls
106
. Each plasma discharge channel
105
encloses ionizable gas therein so as to allow plasma to be generated by applying a discharge pulse voltage between a cathode
107
and an anode
108
. The plurality of plasma discharge channels
105
extend in the direction perpendicular to the length of the signal electrodes (column electrodes)
102
, and the cathodes
107
and the anodes
108
serve as scanning electrodes (row electrodes)
110
, thus to effect line-sequential scanning.
In the PALC display apparatus described above, the size can be increased comparatively easily compared with a TFT-incorporated liquid crystal display apparatus. However, the PALC display apparatus has problems as follows. The dielectric separator
104
of the PALC display apparatus
100
is made of a glass thin plate, which is not only expensive but also difficult in handling. In fact, handling of such a glass thin plate becomes more difficult as the size of the display apparatus is larger, increasing the probability of fracture during fabrication of the display apparatus.
The surface of the glass thin plate on the plasma cell side serves as a pseudo-electrode during the driving of the PALC display apparatus. The thickness of the glass thin plate is about 50 to 100 microns, which is larger by ten times or more than that of a general nematic liquid crystal layer, i.e., 3 to 6 microns. In order to drive the PALC display apparatus, therefore, it is required to apply a voltage higher by ten times or more than a voltage with which the liquid crystal layer can be effectively driven. This causes problems such as increasing the burden on a drive circuit and increasing power consumption accompanied by heat generation.
Moreover, since the glass thin plate is fragile in strength, it is very difficult to form an electrode thereon. This is the reason why the electrodes for plasma discharge are formed in parallel with the plane of the substrate as shown in FIG.
1
. This construction is not desirable since it reduces the aperture ratio of the display apparatus and thus lowers display quality.
SUMMARY OF THE INVENTION
An object of the present invention is providing an optical addressing device which can be fabricated at low cost and high yield and is suitable for realization of size increase and high precision, and a liquid crystal display apparatus using such an optical addressing device.
The liquid crystal display apparatus of the present invention includes: a first substrate; a second substrate; a liquid crystal layer sandwiched by the first substrate and the second substrate; a first electrode layer formed on a surface of the first substrate facing the liquid crystal layer; a second electrode layer formed on a surface of the second substrate facing the liquid crystal layer; a third electrode layer electrically connected with the second electrode layer via a photoconductive layer; and a plurality of stripe-shaped light sources disposed outside the second substrate for irradiating at least a portion of the photoconductive layer with light, wherein the electrical conductivity of the photoconductive layer is changed by switching the plurality of light sources to switch electrical connection between the second electrode layer and the third electrode layer and thereby to realize optical addressing of the liquid crystal layer.
In one embodiment., the first electrode layer comprises a single first electrode, the second electrode layer, the photoconductive layer, and the third electrode layer are formed on the surface of the second substrate facing the liquid crystal layer in this order, the second electrode layer comprises a plurality of pixel electrodes arranged in a matrix, the third electrode layer comprises a plurality of signal electrodes extending in parallel with one another in a first direction, and the plurality of light sources are stripe-shaped light sources extending in parallel with one another in a second direction which is different from the first direction.
In another embodiment, the photoconductive layer comprises at least one dot-shaped photoconductive film arranged for each of the plurality of pixel electrodes.
In still another embodiment, the liquid crystal display apparatus further includes a storage capacitor electrically connected with each of the pixel electrodes.
In still another embodiment, the first electrode comprises a transparent conductive layer, the first electrode further comprising a metal electrode electrically connected with the transparent conductive layer.
In still another embodiment, the photoconductive layer includes a substance of which electrical conductivity changes in response to ultraviolet to allow for display in a transmission mode or a reflection mode.
In still another embodiment, the photoconductive layer includes a substance of which electrical conductivity changes in response to visible light to allow for display in a transmission mode or a reflection mode.
In still another embodiment, the photoconductive layer comprises a single photoconductive film.
In still another embodiment, the photoconductive layer comprises a plurality of stripe-shaped photoconductive films extending in parallel with the plurality of stripe-shaped signal electrodes.
In still another embodiment, the plurality of light sources comprise plasma light-emitting channels enclosing ionizable gas therein.
In still another embodiment, the plurality of light sources further include a phosphor which changes ultraviolet emitted from the plasma light-emitting channels to visible light.
In still another embodiment, the first electrode layer comprises a plurality of stripe-shaped first electrod
Chowdhury Tarifur R.
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Sikes William L.
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