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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical address type display device
which may be used as a display in the field of AV equipment such as a TV
or a video game or OA equipment such as a personal computer or a
wordprocessor.
2. Description of the Related Art
In recent years, a matrix type liquid crystal display device (LCD) has been
requested to make its capacitance larger and larger. That is, with
increase of resolution of a display device, the number of pixels has been
requested to increase from 400.times.600 to 1000.times.1000 or more. The
size of the display screen has been also requested to increase from 10 to
20 inches or more. In an active-matrix driving type LCD, in particular, a
thin film transistor (TFT) driving type LCD, however, there may be brought
about a problem that the increase of scan lines leads to the increase of
wire resistance and a delay of a signal waveform may be caused by the wire
resistance and the floating capacitance or a problem that a voltage ratio
of selected pixels to non-selected pixels cannot be obtained if the number
of scan lines is larger than a threshold value in the simple-matrix
driving type LCD. To solve these problems, there has been proposed a
liquid crystal display device with a high resolution which is capable of
easily increasing pixel driving current through the effect of a light
switching function. (Toyo Rayon, Ltd.: Japanese Patent Lying Open No.
Hei1-173016, Casio Calculator, Ltd.: Japanese Patent Lying Open No.
Hei1-224727, Matushita Electronic Industry, Ltd.: Japanese Patent Lying
Open No, Hei2-89029, Seiko-Epson, Ltd.: Japanese Patent Lying Open No.
Hei2-134617, Sharp, Ltd.,: Japanese Patent Lying Open No. Hei3-263647,
etc.)
Later, the description will be oriented to a method for driving an
active-matrix driving type liquid crystal display device which is one kind
of an optical address type liquid crystal display device (optical scan
type liquid crystal display device) as referring to the drawings.
FIGS. 24 and 25 show an optical address type active-matrix driving type
liquid crystal display device as disclosed in the Japanese Patent
Application No. Hei5-100246 filed by the applicant of the present
application.
In this display device, a basic substrate 21 composing a display panel
includes a plurality of light waveguides Y.sub.1, Y.sub.2, . . . , Y.sub.n
arranged vertically on a glass substrate 21a. A clad layer 23 is formed on
the glass substrate 21a in a manner to cover these light waveguides
Y.sub.1, Y.sub.2, . . . , Y.sub.n. Signal wires X.sub.1, X.sub.2, . . . ,
X.sub.m are arranged horizontally in a manner to be crossed with the light
waveguides Y.sub.1, Y.sub.2, . . . , Y.sub.n. A pixel electrode is formed
in a manner to be substantially buried in each of the areas defined by the
light waveguides Y.sub.1, Y.sub.2, . . . , Y.sub.n and the signal wires
X.sub.1, X.sub.2, . . . , X.sub.m. Light switching elements 26, 26, . . .
each made of a photoconductive film are provided vertically between an
extended portion of the pixel electrode 25 and the signal wires X.sub.1,
X.sub.2, . . . , X.sub.m. Inside of the glass substrate 21a, a light
cut-off layer 28a is provided in a manner to correspond to each of the
light switching elements 26, 26, . . . . This light cut-off layer 28a
serves to prevent light (outer light) from the outer surface of the glass
substrate 21a from being incident to the light switching element 26.
On the opposed surface of the opposed substrate 22, there is formed an
opposed electrode 29 made of a transparent conductive film. On the opposed
surface of the opposed electrode 29, a light cut-off layer 29b is provided
at the location corresponding to the light switching element 26 and serves
to prevent light (outer light) from the outer surface of the opposed
substrate 22 from being incident to the light switching element 26. On the
inside of each of the glass substrates 21a and 22a, an orientation film
27a or 27b is formed and is subject to an orientating treatment. The
substrates 21 and 22 formed as described above are pasted with each other
through a seal 32 and a display medium 33 laid therebetween.
In such an optical display type display device, when a ray of light is
applied from a luminous element array 30 to each light switching element
26 through a micro lens array 31, light waveguides Y.sub.1, Y.sub.2, . . .
, Y.sub.n, the light switching element 26 lowers its impedance so as to
allow a signal voltage to be applied to the light switching element 26,
thereby electrically connecting the signal wires X.sub.1, X.sub.2, . . . ,
X.sub.m with the pixel electrode 25. When no light is applied to the light
switching element 26, the light switching element 28 enhances its
impedance. This results in electrically insulating the signal wires
X.sub.1, X.sub.2, . . . X.sub.m from the pixel electrode 25. That is, this
optical address type display device is arranged to use a scan signal as a
light signal and is driven by using the change of impedance of the light
switching element 26.
FIGS. 26 and 27 show a positional relation among the light switching
element 26, one light waveguide (for example, Y.sub.n), one signal wire
(for example, X.sub.m) and a pixel electrode 25, on which the detailed
explanation about it will be expanded.
This display apparatus uses a method for picking up light from light
scattering portions 24, 24 . . . by forming flaws which are located on the
part of the light waveguide Y.sub.1, Y.sub.2, . . . , Y.sub.n
corresponding to the light switching elements 26 for supplying a ray of
light from the light waveguide Y.sub.1, Y.sub.2, . . . Y.sub.n to light
switching elements 26, . . . effectively.
The part of the ray of light propagating through the light waveguides
Y.sub.1, Y.sub.2, . . . Y.sub.n are scattered at these light scattering
portions and are emitted to the light switching elements 26 as a signal
light.
In order to implement a high-density representation in the optical address
type display device, it is necessary to provide a lot of light scattering
portions 24 in one light waveguide. For example, in a high-definition TV
(HDTV), 1000 or more signal wires X.sub.1, X.sub.2, . . . X.sub.m are
required. 1000 to 5000 light switching elements 26 and light scattering
portions 24 are required for one of the light waveguides Y.sub.1, Y.sub.2,
. . . , Y.sub.n. However, the increase of the light switching elements 26
and the light scattering portions 24 in number brings about the following
problem indicated below.
FIG. 28 shows a relation between quantity of light coming out of an end of
the light waveguide and the number of the light scattering portions 24 on
the light waveguide in the case that the light scattering portions 24
provided in all the light waveguides are the same with each other in size
and form and a ray of light applies from the other end of the light
waveguide. As will be understood from this figure, the quantity of light
passed through the light waveguide and picked up out of the end of the
light waveguide is attenuated exponentially as the light scattering
portions are increased in number. The attenuation not proportional to the
number but exponentially indicates that the quantity of picked light is
different at each location. That is, the quantity of light picked up at
each location is made smaller as the location goes further along the light
waveguide from the light-incident side. In this prior art, since the light
scattering portions 24 are the same in size, the signal light is
attenuated while it is propagating through the light waveguide. As the
light scattering portion 24 goes further from the light-incident side, the
quantity of light picked up at the portion 24 is progressively made
smaller. FIG. 29 shows a V groove of each light pick-up portion 24 and a
light-applied state at the light pick-up portion 24 in the prior art.
In order to obtain even display performance on the screen of the display
device, it is necessary to give even performance to all the light
switching elements 26. For this purpose, the same quantity of light is
required to be picked up at each light scattering portion 24. Hence, it is
necessary to improve exponential attenuation of the quantity of picked-up
light along the light waveguide.
As described above, such a display device as impairing a light waveguide
for forming a V groove as means for picking up light or such a display
device as making the surface of the light waveguide coarse as disclosed in
the Japanese Patent Lying Open No. Hei 1-224727 is required to
mechanically or chemically work the light waveguide. However, the
mechanical work may often impair a glass substrate. To prevent the impair,
a high-level working technique is required. As stated above, in the case
of forming a lot of light scattering portions, the working accuracy may be
insufficient. As the chemical work, a wet etching technique with a
hydrogen fluoride etchant is used. In this case, the etching technique has
difficulty in controlling the form and the size of the light pick-up
portion. This results in making the reproducibility worse. To provide the
light pick-up portion, a method for impairing the light waveguide or
making the surface coarse may be provided. This method makes it impossible
to apply 100% of the scattered light obtained from the light pick-up
portion to the switching element, thereby making the light utilization
efficiency worse.
FIG. 16 is a plan view showing a structure of an optical address type
active-matrix driving type LCD. FIG. 17 is a section cut on the A--A line
of FIG. 16. In the plan view shown in FIG. 16, a glass substrate 105b, a
light cut-off layer 110, an orientation film 109b, a transparent electrode
106, a seal 107, and a liquid crystal layer 108 are not shown though they
are shown on the section shown in FIG. 17.
As shown in FIGS. 16 and 17, on one glass substrate 105a, a plurality of
linear luminous sources Y.sub.1, Y.sub.2, . . . , Y.sub.n-1, Y.sub.n are
ranged in the Y direction. On these linear luminous sources, a plurality
of linear electrodes X.sub.1, X.sub.2, . . . , X.sub.m-1, X.sub.m are
ranged in the X direction and in a manner to be crossed with the linear
luminous sources, respectively.
Each of the linear luminous sources Y.sub.1, Y.sub.2, . . . , Y.sub.n-1,
Y.sub.n, for example, the linear luminous source Y.sub.2, is composed of a
luminous portion 101 formed of an LD or an LED array element and a linear
waveguide 102 for transmitting a ray of light from the luminous portion
101, and a light pick-up portion 116 formed on the linear light waveguide
102. By operating the luminous portion 101, the light is propagated
through the linear light waveguide 102 and is applied to the upper part of
the substrate through the effect of the light pick-up portion 116.
At each of the crosspoints between the linear luminous sources Y.sub.1,
Y.sub.2, . . . , Y.sub.n-1, Y and the linear electrodes X.sub.1, X.sub.2,
. . . , X.sub.m-1, X.sub.m, that is, on the light pick-up portion 116 of
each of the linear luminous sources Y.sub.1, Y.sub.2, . . . , Y.sub.n-1,
Y.sub.n, there is provided a light switching element 103 made of a
photoconductive layer. The linear electrodes X.sub.1, X.sub.2, . . . ,
X.sub.m-1, X.sub.m are formed on the same side as the pixel electrode for
driving a display medium, that is, liquid crystal. The light switching
elements 103 are provided between the linear electrodes X.sub.1, X.sub.2,
. . . , X.sub.m-1, X.sub.m and the linear luminous sources Y.sub.1,
Y.sub.2, . . . , Y.sub.n-1, Y.sub.n, respectively.
On the other glass substrate 105b, a transparent electrode 106 is formed.
The liquid crystal layer 108 is sealed between the substrate and the
sealing member 107.
When a ray of light is applied to the light switching element 103, that is,
the linear luminous source Y.sub.2 is made operative, the light switching
element 103 lowers its impedance so that a signal from the linear
electrode X.sub.1 may be applied to the pixel electrode 104 for changing
an orientating state of liquid crystal.
By operating the linear luminous sources Y.sub.1, Y.sub.2, . . . ,
Y.sub.n-1, Y.sub.n sequentially from Y.sub.1 to Y.sub.n for optical scan,
an electric signal may be correspondingly applied to the linear electrodes
X.sub.1, X.sub.2, . . . , X.sub.m-1, X.sub.m. While the linear luminous
sources Y.sub.1, Y.sub.2, . . . , Y.sub.n-1, Y.sub.n are made luminous,
the light switching element on the linear luminous source is switched on.
Hence, the electric signals from the linear electrodes X.sub.1, X.sub.2, .
. . , X.sub.m-1, X.sub.m may be applied to the pixel electrodes 104,
respectively. That is, in place of an electric gate signal of a TFT film,
the light signals from the linear luminous sources Y.sub.1, Y.sub.2, . . .
, Y.sub.n-1, Y.sub.n serve to scan the light switching element 103.
In the optical scan type liquid crystal display element, a technique for
forming a light waveguide and a method for picking up light are important
to controlling light for switching the liquid crystal. As the technique
for forming a light waveguide, there has been proposed a method for
melting an optical fiber on the glass substrate for forming a highly
reliable and low-loss light waveguide (Sharp, Ltd.: Japanese Patent
Application No. Hei4-4739)
As a method for picking up light, there have been proposed a method for
picking up light scattered by a flaw on the light waveguide (Casio
Calculator, Ltd.: Japanese Lying Open No. Hei1-224727, etc.).
However, a method for scattering light with a flaw has difficulty in
controlling quantity of picked light when working the element. This is a
disadvantage.
SUMMARY OF THE INVENTION
A first object of the present invention is to improve a method for picking
up light from a light waveguide to a light switching element and keep the
quantity of picked light equal at all the pick-up location for realizing
an even display characteristic over all the display.
A second object of the present invention is to provide a display device
which may be arranged to pick up light from a light waveguide without
through the effect of mechanical work or chemical work, efficiently guide
the light to the light switching element, keep the quantity of picked-up
light equal at each location of picking up light, and realize an even
display characteristic on the overall surface of the display.
A third object of the present invention is to provide a large-capacitance
and high-resolution optical scan type liquid crystal display element.
The first object of the invention can be achieved by a display device
comprising an insulated basic substrate, a plurality of light waveguides
ranged on the basic substrate in parallel, a plurality of signal wires
arranged in parallel and in a manner to be crossed with the light
waveguides, respectively, a plurality of photoconductive layers
three-dimensionally laid between the light waveguides and the signal wires
at respective crosspoints between the light waveguides and the signal
wires and for performing a switching operation in response to light sent
from the light waveguides, a plurality of pixel electrodes provided in a
manner to contact with the photoconductive layers and the light
waveguides, an insulated opposed substrate located as opposed to the basic
substrate with a display medium laid between the substrates and having an
opposed electrode on the surface opposed to the basic substrate, light
pick-up grooves provided at the corresponding locations to the
photoconductive layers on the light waveguides and for guiding light
transmitted through the light waveguides to the photoconductive layers,
and the size of each of the grooves being increased progressively along a
transmission path of each of the light waveguide.
The light pick-up groove may be V-formed.
Some light pick-up grooves arranged along and adjacent to the light
waveguide are assumed as one combination and the sizes of the light
pick-up grooves are respective in the combinations of the grooves.
The changing range of the light pick-up grooves is preferably 2 or more and
0.1 n or less for n light pick-up grooves provided on one light waveguide.
The second object of the invention can be achieved by a display device
comprising an insulated basic substrate, a plurality of light waveguides
ranged on the basic substrate and in parallel to each other, a plurality
of signal wires arranged in parallel and in a manner to be crossed with
the light waveguides, respectively, a plurality of photoconductive layers
three-dimensionally laid between the light waveguides and the signal wires
and directly connected with each light guiding portion of the light
waveguides at respective crosspoints between the light waveguides and the
signal electrodes and for performing a switching operation in response to
a light signal from the light guiding portion, a plurality of pixel
electrodes provided to be connected with the photoconductive layers,
respectively, an insulated opposed substrate located in opposition to the
basic substrate with a display medium therebetween and having an opposed
electrode on the surface opposed to the basic substrate, and the relation
among an index of refraction n.sub.1 of the light guiding portion, an
index of refraction n.sub.2 of the photoconductive layer, and an angle of
incidence .theta. of light given from the light guiding portion to the
photoconductive layer meeting the following expression of
n.sub.1 sin .theta.<n.sub.2 ( 1)
Preferably, an area on the interface between the light guiding portion and
the photoconductive layer is increased along a transmission path of the
light waveguide.
A middle layer is provided on the interface between the light guiding
portion and the photoconductive layer and the relation among an index of
refraction n.sub.1 of the light waveguide, an index of refraction n.sub.2
of the photoconductive layer, an index of refraction n.sub.3 of the middle
layer, and an angle of incidence .theta..sub.1 of light given from the
light guiding portion to the middle layer meets the following expression
(2) of
n.sub.1 sin .theta..sub.1 <n.sub.2 and n.sub.1 sin .theta..sub.1 <n.sub.3 (
2)
Preferably, an area of the interface between the light guiding portion and
the middle layer is increased progressively along a transmission path of
the light guiding portion.
Preferably, the middle layer is made of a transparent conductive material.
Preferably, the display medium is made of liquid crystal.
The third object of the invention can be achieved by a light pick-up
portion having a high index of refraction formed in the clad layer formed
on the top of the light waveguide through the effect of an ion exchange
method. The light pick-up portion is located on the part of the light
waveguide corresponding to the light switching portion.
The method for exchanging ions, that is, as one of the methods for
patterning a portion having a high index of refraction on the glass
substrate with accuracy, is a method for forming a portion with a high
index of refraction by replacing sodium ion (Na+) of soda glass with a
monovalent metal ion. Such a monovalent metal ion is silver ion (Ag+) or
thallium ion (Tl+). The change volume (.DELTA..sub.n) of an index of
refraction is .DELTA..sub.n =2 to 8.times.10-2 in Ag+ and .DELTA..sub.n
.gtoreq.0.1 in Tl+ (NISHIHARA Gai: "Optical Integrated Circuit" edited by
Ohm edition).
In the optical address type display device according to the first aspect of
the invention, each form of the plural light pick-up grooves provided on
the light waveguide is made larger along the transmission path so that the
transmitted light may be strongly scattered. This compensates for
attenuation of the quantity of picked-up light along the transmission
path, thereby being able to keep the quantity of picked-up light at any
light pick-up location on the light waveguide. This results in realizing
an even light application on the light switching element at each location.
In the optical address type display device according to the second aspect
of the invention, since the index of refraction defines the light
waveguide and the photoconductive layer made of a material meeting the
above-mentioned expression, the ray of light may be efficiently guided
from the light waveguide to the photoconductive layer.
In the optical address type display device according to the third aspect of
the invention, when a ray of light is applied from a linear luminous
source, the photoconductive layer lowers its impedance so as to enter an
on state. As a result, a signal from the linear electrode is applied to
the pixels of the liquid crystal layer through this photoconductive layer.
As means for applying a ray of light from the linear luminous portion to
the photoconductive layer, a light propagating characteristic is
guaranteed on the light waveguide formed on the substrate and the ray of
light from the luminous source is allowed to be induced to the light
switching portion with high accuracy and high efficiency.
According to the optical address type display device according to the first
aspect of the invention, the quantity of the picked light can be kept even
at any place where the light pick-up portion is formed on the light
waveguide. Hence, each photoconductive layer serves to uniformly perform a
switching operation at any place. This results in offering an even display
characteristic over the screen. The form of this light pick-up portion
makes the working easier. Further, the size of this light pick-up portion
may be changed at each of the light pick-up portions for easier working.
If the total number n of the light pick-up portions is divided into 2 or
more and 0.1 n or less blocks and the size of the light pick-up portions
may be changed at each block, both of the characteristics, that is,
workability and light picking evenness may be satisfied.
According to the optical address type display device according to the
second aspect of the invention, a light signal can be guided from the
light waveguide to the photoconductive layer without mechanically working
the light waveguide. Further, the contact area between the light waveguide
and the photoconductive layer is made larger along the transmission path.
The quantity of picked light is kept even at any place where the light
pick-up portion is formed on the light waveguide. Hence, each
photoconductive layer can evenly do a switching operation at any place.
This results in offering a display device having an even display
characteristic over the screen.
Also, a light signal can be guided from the light waveguide to the
photoconductive layer side through the middle layer without mechanically
working the light waveguide. In this case, provision of the middle layer
makes it possible to more smoothly define the material for the light
waveguide and the photoconductive layer. The contact area among the light
waveguide, the middle layer and the photoconductive layer is made larger
along the transmission path so that the quantity of the picked light is
kept constant at any place where the light pick-up portion is formed on
the light waveguide. Hence, each photoconductive layer can do an even
switching operation at any place and thus the resulting display device
enables to have an even display characteristic over the screen.
According to the optical address type display device according to the third
aspect of the invention, the present invention is capable of patterning
the light pick-up portion with high accuracy and suppressing the degrade
resulting from the heating or cooling of the subsequent process. Hence,
the light propagating characteristic of the light waveguide is guaranteed
so that the light may be incident to the light switching portion with high
accuracy and high efficiency. This results in making it possible to
provide a high-capacitance and high-resolution liquid crystal display
element.
Further objects and advantages of the present invention will be apparent
from the following description of the preffered embodiments of the
invention as illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view showing an optical address type active-matrix liquid
crystal display device according to the embodiment 1 of the present
invention.
FIG. 2 is a view showing an element structure cut on the G-G' section.
FIG. 3 is a sectional view showing a form of a light pick-up portion on a
light waveguide included in the embodiment 1 of the present invention.
FIG. 4 is a sectional view showing an optical address type active-matrix
liquid crystal display device according to the embodiment 2 of the present
invention;
FIGS. 5a and 5b are views showing a light waveguide included in the display
device according to the embodiment 3 of the present invention.
FIG. 6 is a view, showing a light pick-up intensity at each light pick-up
portion.
FIG. 7 is a perspective view showing a positional relation among a signal
wire, a light switching element and a pixel electrode in the embodiment 4
of the present invention.
FIG. 8 is a sectional view cut on the B-B' line of FIG. 7 and FIGS. 8(a),
8(b) show a large window form of a clad layer and FIGS. 8(c), 8(d) show a
small window form of the clad layer.
FIG. 9 is a view showing a relation between an index of refraction n.sub.2
and an attenuating factor k against a ray of light with each wavelength,
about hydrogenated amorphous silicon (a-Si:H).
FIG. 10 is a perspective view showing a positional relation among a signal
wire, a light switching element and a pixel electrode in the embodiment 5
of the present invention.
FIG. 11 is a sectional view cut on the A-A' of FIG. 9 and FIGS. 11(a),
11(b) show a large window form of the clad layer and FIGS. 11(c), 11(d)
show a small window form of the clad layer.
FIG. 12 is a perspective view showing a positional relation among a signal
wire, a light switching element and a pixel electrode in the embodiment 5
of the present invention.
FIG. 13 is a sectional view cut on the line C-C' of FIG. 12 and FIGS.
13(a), 13(b) show a large window form of the clad layer and FIGS. 13(c),
13(d) show a small window form of the clad layer.
FIG. 14 is a view showing a light path formed when a ray of light passes
through three layers having respective indexes of refraction.
FIG. 15 is a plan view showing an optical address type simple-matrix liquid
crystal display device according to the embodiment 6 of the present
invention.
FIG. 16 is a plan view showing an optical scan type active-matrix driving
liquid crystal display device according to the present invention.
FIG. 17 is a section cut on the A--A line of FIG. 16.
FIG. 18 is a principle view showing a structure of a light waveguide and a
method for picking up light shown in FIG. 17.
FIG. 19 is a view showing a manufacturing process for a method for picking
up light in an optical scan type LCD according to the present invention.
FIG. 20 is a view showing a process for an ion exchanging method which is
one kind of a method for picking up light in the optical scan type LCD
according to the present invention.
FIG. 21 is a view showing another manufacturing process for a light
waveguide included in the optical scan type LCD according to the present
invention.
FIG. 22 is a view showing another manufacturing process for a light
waveguide included in the optical scan type LCD according to the present
invention.
FIG. 23 is a view showing another manufacturing process for a light
waveguide included in the optical scan type LCD according to the present
invention.
FIG. 24 is a view showing a conventional optical address type active-matrix
liquid crystal display device filed by the applicant of the present
application.
FIG. 25 is a view showing an element structure cut on the H-H' line of FIG.
24.
FIG. 26 is a perspective view showing a positional relation among a signal
wire, a light switching element and a pixel electrode included in a
conventional optical address type active-matrix liquid crystal display
device filed by the applicant of the present application.
FIG. 27 is a view showing an element structure cut on the D-D' line of FIG.
24.
FIG. 28 is a view showing a relation between the quantity of light guided
out of one end of the light waveguide when light is incident to the other
end of the light waveguide and the number of light scattering portions on
the light waveguide.
FIG. 29 is a sectional view showing a form of a light pick-up portion on
the light waveguide according to the prior art.
FIG. 30 is a model view showing a light waveguide in the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Later, embodiments of the present invention will be described.
EMBODIMENT 1
FIGS. 1 and 2 show an arrangement of an optical address type active-matrix
driving liquid crystal display device according to the present invention.
A basic substrate 1 composing a liquid crystal panel is arranged to have a
glass substrate la as a base and a plurality of light waveguides Y.sub.1,
Y.sub.2, . . . , Y.sub.n arranged on the glass substrate 1a in the Y
direction. The light waveguides Y.sub.1, Y.sub.2, . . . , Y.sub.n are
formed by diffusing thallium ion (Tl+) on the glass substrate 1a with heat
and electric field and patterning the film. Each of the light waveguide
Y.sub.1, Y.sub.2, . . . , Y.sub.n has one end connected to a luminous
portion made of a luminous element array 10 and a micro lens array 11
common to these light waveguides. In this embodiment, to form a
large-screen and a high-definition display device, a high-output LD (laser
diode) array is used as the luminous element array 10. If such a high
output is not required, an LED (Light-emitting Diode) array may be used.
To cover these light waveguides Y.sub.1, Y.sub.2, . . . , Y.sub.n, a clad
layer 3 made of an SiO2 thin film is formed on the surface of the glass
substrate 1a. A plurality of signal wires X.sub.1, X.sub.2, . . . ,
X.sub.m are located on the clad layer 3 in the X direction and in a manner
to be crossed with the light waveguides Y.sub.1, Y.sub.2, . . . , Y.sub.n.
These signal wires X.sub.1, X.sub.2, . . . , X.sub.m are made of Ti as a
main material and are formed by the sputtering technique. As a material of
the signal wires X.sub.1, X.sub.2, . . . , X.sub.m, in addition to Ti, any
material may be used only if it meets the conditions about conductive
performance and manufacturing process such as Ta, Cr, Al or Mo.
On each of the sections formed by crossing the adjacent light waveguides
Y.sub.1, Y.sub.2, . . . , Y.sub.n with the signal wires X.sub.1, X.sub.2,
. . . , X.sub.m respectively, a pixel electrode 5 made of a transparent
conductive ITO film is provided on the clad layer 3. Part of the pixel
electrode 5 is extended over each of the crossed portions between the
light waveguides Y.sub.1, Y.sub.2, . . . , Y.sub.n and the signal wires
X.sub.1, X.sub.2, . . . , X.sub.m. A light switching element 6 made of a
photoconductive layer is provided between the extended part of the pixel
electrode 5 and each of the signal wires X.sub.1, X.sub.2, . . . , X.sub.m
at the location. The light switching element 6 is made of a
photoconductive a-Si:H film. This a-Si:H film is formed to have a
thickness of about 1 .mu.m by means of a plasma CVD technique by using
silane gas (SiH.sub.4) and Hydrogen (H.sub.2). Inside of the glass
substrate 1a, a light cut-off layer 8a is provided at the corresponding
location to each light switching element 6. This light cut-off layer 8a
serves to prevent light (outer light) from the outer surface of the glass
substrate 1a from being incident to the light switching element 6.
In the opposed substrate 2, an opposed electrode 9 made of a transparent
conductive ITO film is formed on the overall surface of the glass
substrate 2a served as a basic material of the substrate 2. The light
cut-off layer 8b is provided at the corresponding location to the light
switching element 6 on this opposed electrode 9 and serves to prevent
light (outer light) from the outer surface of the glass substrate 2a of
the opposed substrate 2 from being incident to the light switching element
6.
On each inside surface of the glass substrates 1a and 2a, an orientation
film 7a or 7b made of polyimide is coated by a spin-coating technique. The
orientation film 7a or 7b is subject to the rubbing treatment. As the
orientation film 7a or 7b, it is possible to use an organic film such as a
polyamide film, various LB films, an SiO film or an oblique evaporated
film of SiO.sub.2. Both of the substrates 1 and 2 formed as above are
pasted with a seal 12 and a liquid crystal material 13 laid therebetween.
The display device formed as above operates as follows. A light signal may
be guided from the luminous element array 10 to the light waveguides
Y.sub.1, Y.sub.2, . . . , Y.sub.n through a micro lens array 11.
On the light waveguides Y.sub.1, Y.sub.2, . . . , Y.sub.n, a light pick-up
portion (light scattering portion) 4 is formed at each of the light
switching elements 6. This light pick-up portion 4 is formed of a V groove
on each of the light waveguides Y.sub.1, Y.sub.2, . . . , Y.sub.n by means
of a blade, for example. A light signal propagated through the light
waveguides Y.sub.1, Y.sub.2, . . . , Y.sub.n is scattered at the light
pick-up portion 4 and then is applied to the light switching element
formed at that location.
The light switching element 6 changes its impedance according to a
bright/dark state of the applied light so as to control flow of current to
the signal wires X.sub.1, X.sub.2, . . . , X.sub.m and the pixel electrode
5 connected to the light switching element 6 for driving the liquid
crystal 13. That is, in the light-applied state, the light switching
element 6 lowers its impedance through the photoconductive effect so that
the signal wires X.sub.1, X.sub.2, . . . , X.sub.m may be electrically
conducted with the pixel electrode 5. This results in applying a data
signal to the liquid crystal 13 between the pixel electrode 5 and the
opposed electrode 9.
In the dark state, the light switching element 6 raises its impedance so
that the signal wires X.sub.1, X.sub.2, . . . , X.sub.m may be
electrically insulated from the pixel electrode 5. In this state, no data
signal is applied to the liquid crystal 13 between the pixel electrode 5
and the opposed electrode 9. Hence, the voltage applied to the liquid
crystal 13 when light is applied is maintained.
In this embodiment, at the location where the quantity of picked-up light
is small on each of the light waveguides Y.sub.1, Y.sub.2, . . . ,
Y.sub.n, the V groove is made larger so that the area of the light
scattering portion may be enlarged for compensating for the attenuated
amount of the picked-up light. That is, as shown in FIG. 3, the V groove
at the location near the light-incident side is shallow and small. The V
groove is made gradually deeper and larger as it goes further from the
light-incident side. With this design of the V groove, the quantity of
light is kept equal in respective ligh | | |
