A liquid crystal electro-optical device comprising a pair of substrates at least one of them is light-transmitting, electrodes being provided on said substrates, and an electro-optical modulating layer being supported by said pair of substrates, provided that said electro-optical modulating layer comprises an anti-ferroelectric liquid crystal material or a smectic liquid crystal material which exhibits anti-ferroelectricity, and a transparent material.

BACKGROUND OF THE INVENTION 
1. Industrial Field of Application 
The present invention relates to a polymer dispersed liquid crystal 
electro-optical device comprising a liquid crystal/resin composite 
composed of a high molecular resin having dispersed therein a liquid 
crystal material. More particularly, it relates to a liquid crystal 
electro-optical device having a high scattering efficiency. 
2. Prior Art 
Conventional liquid crystal electro-optical devices include the well known 
and practically used devices operating in a TN (twisted nematic) or an STN 
(super twisted nematic) mode. These liquid crystal electro-optical devices 
are based on nematic liquid crystal and the like. Furthermore, devices 
using ferroelectric liquid crystals have recently come to our knowledge. 
Those known liquid crystal electro-optical devices basically comprise a 
first and a second substrate each having established thereon an electrode 
and a lead, and a liquid crystal composition being incorporated 
therebetween. By taking this assembly, the state of the liquid crystal 
molecules can be varied by applying an electric field to the liquid 
crystal composition, because the liquid crystal material itself has an 
anisotropy in dielectric constant, or, in the case of a ferroelectric 
liquid crystal, it exhibits spontaneous polarization. The electro-optical 
effect which results therefrom is made use of in the aforementioned liquid 
crystal electro-optical devices. 
In a liquid crystal electro-optical device operating in a TN or STN mode, 
an alignment treatment, i.e., rubbing, is applied to align the liquid 
crystal molecules along the rubbing direction at each of the planes in 
contact with the two substrates by which the liquid crystal layer is 
sandwiched. Rubbing is applied to the upper and the lower planes as such 
that their directions may be displaced by 90.degree. or by an angle 
between 200.degree. and 290.degree. from each other. Accordingly, the 
intermediate liquid crystal molecules in the liquid crystal layer, i.e., 
those between the upper and the lower molecules positioned at an angle of 
from 90.degree. to 290.degree. adjacent to the substrates arrange 
themselves into a spiral to achieve a configuration of lowest energy. In 
the case of an STN type liquid crystal device, a chiral substance is 
optionally added to the liquid crystal material if necessary. 
The aforementioned devices, however, require polarizer sheets to be 
incorporated. Moreover, the liquid crystal molecules need to be regularly 
arranged ill the liquid crystal electro-optical device to achieve a 
predetermined alignment. The alignment treatment as referred herein 
comprises rubbing an alignment film (ordinarily an organic film) with a 
cotton or a velvet cloth along one direction. If not for this treatment, 
the liquid crystal molecules are unable to attain a predetermined 
alignment, and hence, no electro-optical effect can be expected therefrom. 
Accordingly, conventional liquid crystal electro-optical devices above 
unexceptionably comprise a pair of substrates which make a container to 
hold therein a liquid crystal material. Then, the optical effect which 
results from the oriented liquid crystal having charged into the container 
can be utilized. 
There is also known another type of liquid crystal, a polymer dispersed 
liquid crystal (referred to sometimes hereinafter as PDLC), which can be 
used without incorporating any polarizer sheets and applying an alignment 
treatment and the like. In FIG. 7 is shown schematically a PDLC. A PDLC 
electro-optical device comprises a solid polymer 4 having dispersed 
therein a granular or sponge-like liquid crystal material 3 between a pair 
of light-transmitting substrates 1 to give a light-control layer. A liquid 
crystal device of this type can be fabricated by dispersing microcapsules 
of a liquid crystal material in a polymer, and then forming a thin film 
thereof on a substrate or a film. The liquid crystal material can be 
encapsulated using, for example, gum arabic, poly(vinyl alcohol), and 
gelatin. 
In the case of liquid crystal molecules being encapsulated in poly(vinyl 
alcohol), for example, if they show a positive dielectric anisotropy in 
the thin film, an electric field may be applied in such a manner that 
their major axes may be arranged in parallel with the electric field. 
Accordingly, a transparent state can be realized if the refractive index 
of the encapsulated liquid crystal is equal to that of the polymer. When 
no electric field is applied, the liquid crystal microcapsules take a 
random orientation and the incident light is scattered because the 
refractive index of the liquid crystal greatly differs from that of the 
polymer. Thus, an opaque or a milky white state is realized. In FIG. 8 is 
shown the change of transmittance in relation with the applied voltage in 
the liquid crystal electro-optical device above. The transmittance changes 
with increasing and decreasing voltage as indicated with arrows in the 
figure. If the liquid crystal microcapsules have a negative dielectric 
anisotropy and if the average refractive index of the liquid crystal is 
equal to that of poly(vinyl alcohol), a transparent state can be realized 
by applying no electric field. 
The term "average refractive index" as referred herein is defined as 
follows. When no electric field is applied to a liquid crystal material on 
a non-treated substrate, the refractive indices thereof are found to be 
distributed as shown in FIG. 10. In the figure, n.sub.o and n.sub.e 
represent the refractive index for an ordinary light and an extraordinary 
light, respectively. The "average refractive index" is then defined as the 
index n.sub.ave at the maximum distribution intensity in the curve as 
shown in FIG. 10. 
In the presence of an electric field, on the other hand, a milky white or 
an opaque state results, because the liquid crystal molecules are arranged 
as such that the major axes thereof make a right angle with respect to the 
direction of the electric field to thereby develop a difference in 
refractive index. A similar result is obtained if the liquid crystal 
molecules themselves exhibit spontaneous polarization along a direction 
vertical to the major axes of the liquid crystal molecules. In such a 
case, the transmittance changes with increasing or decreasing voltage as 
shown in FIG. 9. In this manner, a PDLC electro-optical device provides 
various types of information by making the best of the difference between 
the transparent and the opaque state. 
Polymer dispersed liquid crystals include not only those of the 
encapsulated type, but also those comprising liquid crystal materials 
being dispersed in an epoxy resin, or those utilizing phase separation 
between a liquid crystal and a resin which results by irradiating a light 
for curing a photocurable resin being mixed with a liquid crystal, or 
those obtained by impregnating a three-dimension polymer network with a 
liquid crystal. All those enumerated above are referred to as "polymer 
dispersed liquid crystals" in the present invention. 
Because the electro-optical devices using PDLCs are free of polarizer 
sheets, they yield a far higher light transmittance as compared with any 
of the conventional electro-optical devices operating on TN mode, STN 
mode, etc. More specifically, because the light transmittance per 
polarizer sheet is as low as about 50%, the light transmittance of an 
active matrix display using a combination of polarizer sheets as a result 
falls to a mere 1%. In an STN type device, the transmittance results as 
low as 20%. Accordingly, an additional backlighting is requisite to 
compensate for the optical loss to lighten those dark displays. In the 
case of a PDLC electro-optical device, by contrast, 50% or more of light 
is transmitted. This is clearly an advantage of a device using no 
polarizer sheets. 
Because a PDLC takes two states, i.e., a transparent state and an opaque 
state, and transmits more light when used in a liquid crystal 
electro-optical device, the R & D efforts are more paid for developing 
devices of a light transmitting type. More specifically, particular notice 
is taken to a light-transmitting liquid crystal electro-optical device of 
a projection type. 
A projection type liquid crystal electro-optical device comprises placing 
the liquid crystal electro-optical device panel on a light path of a light 
beam being generated from a light source, and then projecting the light 
against a flat panel through a slit being provided at a predetermined 
angle. If the liquid crystal molecules in the liquid crystal panel have a 
positive dielectric anisotropy, they take a random orientation to realize 
an opaque (milky white) state in the low electric field region; i.e., at 
any voltage below a threshold voltage at which the liquid crystal 
molecules do not respond to the applied voltage. The light incident to a 
panel at such a state is scattered to widen the light path. The light 
having scattered then proceeds to the slit, but most of them are cut off 
to yield a dark state on the flat panel. 
On the other hand, when the liquid crystal molecules respond to the applied 
electric field and when they are thereby arranged in parallel with the 
direction of the electric field, a light incident thereto passes straight 
forward to yield a bright state at a high contrast on the flat panel. When 
the liquid crystal molecules have a negative dielectric anisotropy, or 
when they have spontaneous polarization along a direction vertical to the 
major axes of the molecules, and if the average refractive index of the 
liquid crystal molecules coincide with that of the polymer resin matrix, 
the liquid crystal electro-optical device panel turns transparent when no 
electric field is applied; it reversely turns opaque to yield a dark state 
by scattering the light when an electric field is applied. 
As described in the foregoing, the switching of states of a PDLC occurs, in 
principle, by the scattering of light. That is, in passing through the 
light control layer comprising the resin and the liquid crystal droplets 
which differ from each other in terms of refractive index, the light 
incident on the transparent substrate side greatly changes its course each 
time it comes to the boundary between the resin and the liquid crystal. 
Accordingly, the incident light reaches the substrate on the other side in 
a completely scattered state. To increase the scattering efficiency of the 
light control layer, it is preferred that the liquid crystal droplets are 
more frequently brought into contact with the resin along the thickness 
direction of the light control layer. The more the boundary between a 
resin and a liquid crystal droplet is provided for a light, the more 
scattered the light becomes. Accordingly, the scattering efficiency can be 
increased by providing a thicker control layer. However, a thicker control 
layer adversely increases the spacing between the substrates, that is, the 
distance between the electrodes. A longer distance between the electrodes 
require a larger driving voltage for switching the light control layer. 
This makes it impossible to drive the liquid crystal cell with an ordinary 
IC (integrated circuit), particularly with a TFT (thin film transistor). 
A practically feasible liquid crystal electro-optical device should, in 
general, 
1) be driven at a low voltage; 
2) have rapid response; and 
3) be driven at a speed of 0.1 msec (100 .mu.sec) or less even in a cell 
having a thickness in the range of from 2.5 to 10 .mu.m. 
Most of the conventional PDLC electro-optical devices are based on a 
nematic liquid crystal material, and are yet to satisfy the required quick 
response. No liquid crystal electro-optical device which satisfy all of 
the requirements enumerated above and still capable of providing a rapid 
optical response to dynamic displays without using any polarizer sheets is 
proposed to present. However, a PDLC electro-optical device using a 
ferroelectric liquid crystal material is known as a device which satisfy a 
part of the requirements above. This type of liquid crystal 
electro-optical device, however, because of the ferroelectric nature of 
the liquid crystal, exhibits a piezoelectric effect while it is driven. 
More specifically, the liquid crystal being incorporated between the 
electrodes undergoes shrinking by the electric field being applied for 
driving the liquid crystal, and such a change in volume initiates 
vibration of the substrates as a source of noise. Furthermore, such a 
vibration of the substrates my cause damage to the liquid crystal 
electro-optical device due to the peeling off which occurs on the pair of 
substrates which are adhered to make a cell. 
SUMMARY OF THE INVENTION 
The present invention has been accomplished with an aim to provide a liquid 
crystal electro-optical device free of the aforementioned problems. 
Accordingly, the present invention provides an electro-optical device 
comprising a pair of substrates at least one of which is transparent; an 
electro-optical modulating layer provided between said substrates and 
comprising an antiferroelectric liquid crystal and a transparent material; 
and means for applying an electric field to said antiferroelectric liquid 
crystal. Said means comprises an active matrix circuit. The liquid crystal 
electro-optical device according to the present invention is therefore 
improved in response speed and freed from the problems attributed to 
change in volume of the liquid crystal material.

DETAILED DESCRIPTION OF THE INVENTION 
The liquid crystal droplets to be dispersed in the light control layer 
according to the present invention can be prepared by any of the three 
representative fabrication processes as follows. 
(1) A 4:6 to 8:2 mixture of a liquid crystal material and an ultraviolet 
(UV) curable resin is injected between a pair of substrates, and a UV 
light is irradiated thereto from the surface of the substrate to cure the 
resin. Preferably, on irradiating UV light to the mixture, the sample is 
previously heated to a temperature about 5.degree. to 40.degree. C. higher 
than the transition temperature at which the mixture of the liquid crystal 
and the resin undergoes transition from an isotropic phase to a liquid 
crystal phase. 
(2) A solution having previously prepared by dissolving a liquid crystal 
and a resin in a solvent is applied to the surface of a substrate by a 
spinner process or by casting, and the solvent is gradually evaporated. 
The resin for use in this process include poly(ethylene terephthalate), 
polyfumarates, polycarbazoles, and PMMA [poly(methyl methacrylate)]. 
(3) A liquid crystal is encapsulated with poly(vinyl alcohol) to obtain 
microcapsules of the liquid crystal. 
As shown in FIG. 2(A), spherical liquid crystal droplets 104 can be 
obtained by any of the processes above. In FIG. 7, those spherical 
droplets 3 can also be seen. In FIG. 2(A) and FIG. 7 are shown basic 
liquid crystal cells using a liquid crystal material according to the 
present invention. Needless to say, liquid crystal displays having a known 
active matrix structure can be fabricated making use of the present 
invention as well. In FIGS. 2(B) and 2(C) are shown active matrices using 
a reverse stagger type TFT and a coplanar TFT, respectively. 
The present invention is illustrated in greater detail referring to 
non-limiting examples below. It should be understood, however, that the 
present invention is not to be construed as being limited thereto. 
EXAMPLE 1 
As shown in FIG. 2(A), a polymer dispersed liquid crystal was fabricated 
first by a known process. The present Example refers to a polymer 
dispersed liquid crystal using a UV curable resin. A transparent 
conductive coating, i.e., an ITO (Indium-Tin-Oxide) film 102, was 
deposited on a light-transmitting substrate 101 by a known vapor 
deposition or sputtering process to a thickness of from 500 to 2,000.ANG.. 
The ITO film thus obtained had a sheet resistivity of from 20 to 200 
.OMEGA./cm.sup.2. The film thus obtained was patterned by an ordinary 
photolithographic process. The resulting first and second substrates were 
adhered together under pressure, while maintaining a spacing of from 5 to 
100 .mu.m, preferably from 7 to 30 .mu.m, by incorporating an inorganic 
spacer between the substrates. In this manner, the cell spacing can be 
maintained constant at about the diameter of the spacer. As the liquid 
crystal material, an ester based anti-ferroelectric liquid crystal having 
a refractive index of 1.6 and a .DELTA.n of 0.2 was mixed with a 
photocurable resin having a refractive index of 1.573 and comprising a 
mixed system of an urethane oligomer and an acrylic monomer. 
The aforementioned mixed material was stirred and subjected to ultrasonic 
vibration to obtain a homogeneous mixture. The mixing was effected by 
heating the mixture while applying stirring and ultrasonic vibration to 
obtain a homogeneous mixture as a liquid of an isotropic phase, and the 
resulting mixture was cooled to obtain a liquid crystal phase. This method 
was found very effective for obtaining the desired liquid crystal mixed 
system. 
The resulting liquid crystal mixed system was injected between the first 
and the second substrates above at a temperature higher than the S.sub.A 
-I phase transition temperature of the liquid crystal mixed system, and an 
UV light was irradiated thereto at an intensity of from about 10 to 100 
mW/cm.sup.2 for a duration of from about 30 to 300 seconds to cure the 
resin while allowing the mixed system to undergo phase separation into a 
liquid crystal and a resin. As a result, liquid crystal droplets 104 
surrounded by a resin (transparent material) 105 were formed. 
The liquid crystal device thus obtained scatters light when no electric 
field is applied between the electrodes having established on the upper 
and the lower substrates, because the liquid crystal molecules are 
arranged in a random orientation. When a voltage is applied to the 
electrodes, on the other hand, the liquid crystal molecules align along a 
particular direction according to the direction of the electric field. At 
this state, light can be transmitted by the electro-optical effect which 
is generated by the anisotropy in refractive index of the liquid crystal 
material. A maximum light transmission can be achieved if the refractive 
index of the liquid crystal material along the direction of light 
transmittance is equal to that of the light-transmitting substance on 
applying an electric field. 
The liquid crystal material used in the present Example undergoes a phase 
transition sequence of Iso-SmA-SmC.sub.A.sup.* -Cry. More specifically, it 
undergoes phase transition from Iso to SmA at 92.degree. C., from SmA to 
SmC.sub.A.sup.* at 60.degree. C., and from SmC.sub.A.sup.* to Cry at 
-20.degree. C. It has a positive dielectric anisotropy with a 
birefringence .DELTA.n of about 0.2, and a spontaneous polarization of 12 
nC/cm.sup.2. 
The liquid crystal electro-optical device thus obtained yielded a switching 
rate at 25.degree. C. of 40 .mu.sec, and the corresponding response speed 
was high. It required a relative high threshold voltage of from 5 to 9 
V/.mu.m for driving the liquid crystal. However, because the liquid 
crystal electro-optical device of the present invention has a high light 
scattering efficiency, the device itself can be made thinner by reducing 
the spacing between the substrates and hence the driving voltage can be 
reduced to a level well comparable to a generally employed voltage. 
Because an anti-ferroelectric liquid crystal material is used in the device 
according to the present invention, the shrinkage of the liquid crystal 
material due to volume change thereof on applying an electric field for 
driving the device can be considerably reduced as compared with that of a 
ferroelectric liquid crystal material. Thus, no vibration occurs on the 
substrate of the liquid crystal electro-optical device according to the 
present invention. 
Furthermore, a higher contrast can be achieved with a liquid crystal 
electro-optical device comprising an antiferroelectric smectic liquid 
crystal according to the present invention. This is ascribed to the fact 
that the smectic layer structure, i.e., the structure which the 
anti-ferroelectric liquid crystal material takes in the dispersed 
droplets, can be deformed by the electric field being applied thereto. 
Thus, the refractive index of the liquid crystal material can be greatly 
differed from that of the transparent material comprising a resin. This is 
in clear contrast with the case using a ferroelectric liquid crystal 
material, because the smectic layer structure of the ferroelectric liquid 
crystal material as dispersed droplets cannot be deformed by an external 
electric field. 
EXAMPLE 2 
An active matrix addressed liquid crystal cell using the liquid crystal 
material described in Example 1 was fabricated. Referring to FIG. 2(B), 
the fabrication process is described below. An ITO coating 112 was 
deposited on a first substrate 111 by a known sputtering process to a 
thickness of from 5 to 200 nm. A soda-lime glass substrate was used as the 
first substrate 111. If a TFT is to be formed directly on the first 
substrate, the use of an alkali-free glass substrate is preferred from the 
viewpoint of preventing the TFT from being contaminated by an alkali. 
A black coating was formed in stripes to give black stripes 121 to avoid 
exposure of amorphous silicon of the TFT to external light. Thus was the 
first substrate completed. 
An amorphous silicon TFT 117 having a gate insulator 118 based on silicon 
nitride was established by a known process on a second substrate made of 
an alkali-free glass such as a Corning 7059. A polyimide film 119 which 
serves as an interlayer insulator and also as a smoothing layer was formed 
at a thickness of from 200 to 1000 nm. Then, data connections 110 for an 
active matrix were formed using Cr, and a pixel electrode 113 using ITO 
was established further thereon to complete the second substrate. 
The first and the second substrates thus obtained were adhered together in 
the same manner as in Example 1 by incorporating spacers (not shown in the 
Figure) to maintain a distance between the substrates in a range of from 5 
to 100 .mu.m, preferably, from 7 to 30 .mu.m. Then, the same liquid 
crystal material as that used in Example 1 was injected into the resulting 
cell structure, and UV light at an intensity of from about 10 to 100 
mW/cm.sup.2 was irradiated to the liquid crystal material from the first 
substrate side to cure the resin. Thus was obtained liquid crystal 
droplets 114 being surrounded by the resin 115. At this point, the liquid 
crystal material portion under the black stripes 121 remains uncured, 
because this portion is not necessary for the display. 
The active matrix addressed liquid crystal panel thus obtained comprises a 
circuit structure as shown in FIG. 4(A). In FIG. 4(A) is given a part, 
i.e., a 2.times.2 matrix of the entire structure. The planar view of the 
second substrate of the present Example is given in FIG. 6(A). Referring 
to FIG. 6(A), a pixel electrode 404 and a TFT 403 are provided in a region 
defined by a gate line (scan line) 401 and a data line 402. Then, 
connections for pixel matrix were provided to the liquid crystal panel by 
a known TAB (tape automated bonding) process, and a voltage at a proper 
level was applied to each of the connections to confirm the display of 
images. 
EXAMPLE 3 
An active matrix addressed liquid crystal cell using the liquid crystal 
material described in Example 1 was fabricated. Referring to FIG. 2(C), 
the fabrication process is described below. An ITO coating 132 was 
deposited on a first substrate 131 by a known sputtering process to a 
thickness of from 5 to 200 nm. A soda-lime glass substrate was used as the 
first substrate 131. If a TFT is to be formed directly on the first 
substrate, the use of an alkali-free glass substrate is preferred from the 
viewpoint of preventing the TFT from being contaminated by an alkali. 
Black stripes 141 were also formed in the same manner as in Example 2. 
Thus was the first substrate completed. 
A polycrystalline silicon (polysilicon) TFT 137 having a gate insulator 138 
based on silicon oxide was established by a known process on a second 
substrate made of a heat-resistant alkali-free glass such as a Corning 
1733 and quartz glass. An interlayer insulator 139 was formed on the TFT 
element 137 at a thickness of from 200 to 1000 nm. Then, data connections 
140 for the active matrix were formed using Cr, and a pixel electrode 133 
using ITO was established further thereon to complete the second 
substrate. 
The first and the second substrates thus obtained were adhered together in 
the same manner as in Example 1 by incorporating therebetween spacers (not 
shown in the Figure) to maintain a distance between the substrates in a 
range of from 5 to 100 .mu.m, preferably, from 7 to 30 .mu.m. Then, the 
same liquid crystal material as that used in Example 1 was injected into 
the resulting cell structure, and UV light at an intensity of from about 
10 to 100 mW/cm.sup.2 was irradiated to the liquid crystal material from 
the first substrate side to cure the resin. Thus was obtained liquid 
crystal droplets 134 being surrounded by the resin 135. At this point, the 
liquid crystal material portion under the black stripes 141 remains 
uncured, because this portion is not necessary for the display. 
The active matrix addressed liquid crystal panel thus obtained comprises a 
circuit structure as shown in FIG. 4(A). In FIG. 4(A) is given a part, 
i.e., a 2.times.2 matrix of the entire structure. A driver circuit was 
formed together on the same substrate of the liquid crystal panel of the 
present Example. Accordingly, no external driver circuit was necessary for 
the present liquid crystal panel. Thus, required signals were externally 
input to the liquid crystal panel to confirm the display of images. 
EXAMPLE 4 
An active matrix addressed liquid crystal cell of a CMOS (complementary 
MOS) transfer gate type using the liquid crystal material described in 
Example 1 was fabricated. The circuit structure of the matrix fabricated 
in the present Example is shown in FIG. 4(B). An N-channel TFT (NTFT) and 
a P-channel TFT (PTFT) were established on a single pixel, so that they 
may function in a complementary manner. Thus, the active matrix circuit 
for applying an electric field to the antiferroelectric liquid crystal may 
comprise at least two transistors having different conductivity types from 
each other for each pixel of the electro-optical device in accordance with 
the present invention. Black stripes and an ITO transparent conductive 
film were formed on the first substrate in the same manner as in Examples 
2 and 3. 
The process for fabricating the second substrate is described below making 
special reference to the fabrication of a CMOS TFT (CTFT). The fabrication 
steps are shown schematically by a cross section view in FIG. 3. The 
second substrate may be made from a heat resistant alkali-free glass such 
as Corning 1733 glass and quartz glass, but in this Example, an N/O glass 
(a product of Nippon Electric Glass Co., Ltd.) was used. The N/O glass has 
an excellent heat resistance and a thermal expansion coefficient equal to 
that of quartz, but contains elements unfavorable for a TFT, such as Li, 
at a considerable amount. Thus, a silicon nitride coating 202 was formed 
on the second substrate at a thickness of from 20 to 200 nm to prevent the 
unfavorable alkali elements from influencing the overlying TFT. 
Furthermore, a 100 to 1,000 nm thick silicon oxide coating 203 was 
deposited thereon by sputtering to provide a basecoating for the TFT. 
Then, a substantially intrinsic semiconductor film, which may be either 
amorphous or polycrystalline, an amorphous silicon film 204, for example, 
was formed at a thickness of from 50 to 500 nm on the basecoating obtained 
above. This was followed by the deposition of a silicon oxide film 205 at 
a thickness of from 10 to 100 nm by sputtering, for use as a cap. The 
resulting structure was then annealed at 600.degree. C. for 60 hours in a 
nitrogen atmosphere to effect recrystallization. Thus was obtained a 
structure as shown in FIG. 3(A). 
The resulting structure was then patterned into islands to establish an 
NTFT region 207 and a PTFT region 206. 
Then, a silicon oxide film was deposited as a gate insulator 208 at a 
thickness of from 50 to 150 nm thereon by ECR (electron cyclotron 
resonance) plasma-assisted CVD (chemical vapor deposition) process or by 
sputtering, and a 500 nm thick aluminum coating was deposited further 
thereon by sputtering. The aluminum coating was patterned to establish 
gate electrode portions 209 and 210 for the PTFT and NTFT, respectively. 
The channel was provided at a length of 8 .mu.m and a width of 8 .mu.m. 
The resulting structure is illustrated in FIG. 3(B). 
Then, electric current was applied to the gate electrode portions, i.e., 
gate electrodes with connections 209 and 210, to form aluminum oxide 
coatings 211 and 212 on and to the surroundings (upper and side surfaces) 
of the portions 209 and 210 by an anodic oxidation process. The anodic 
oxidation process was conducted under the same conditions as those 
described in the inventions provided by the present inventors, as are 
disclosed in Japanese patent application Nos. 4-30220 and 4-38637. Thus 
was obtained an anodically oxidized film at a thickness of about 350 nm. 
Phosphorus as an N-type impurity was then introduced into the island-like 
semiconductor portions 206 and 207 by ion implantation, using the gate 
electrode portions 211 and 212 as the masks according to a self-aligned 
process. Further then, the NTFT portion only was covered with, for 
example, a photoresist as a masking material 219 as shown in FIG. 3(C), 
and boron as a P-type impurity was introduced into the portion 206 in a 
self-aligned manner. In this manner were obtained the P-type impurity 
regions 213 and 215, as well as the N-type impurity regions 216 and 218. 
Channel regions 214 and 217 for PTFT and NTFT, respectively, were also 
obtained as a consequence. 
After conducting ion doping, the amorphous regions having resulted by 
impurity injection were activated by subjecting them to laser annealing as 
illustrated in FIG. 3(D). The conditions for the laser annealing are the 
same as those described in the previous inventions of the present authors, 
as disclosed in Japanese patent application Nos. 4-30220 and 4-38837. 
Furthermore, after establishing interlayer insulators 220 and 221, contact 
holes were bore, and a chromium coating was provided thereon by 
sputtering. The chromium coating thus obtained was patterned to establish 
connections 222, 223, and 224 to obtain a structure as shown in FIG. 3(E). 
Finally, a polyimide coating 225 was provided on the second substrate by a 
known spin-coating process to smooth the surface. Then, a contact hole was 
formed thereon to establish a pixel electrode 228 using ITO to complete 
the second substrate. 
The first and the second substrates thus obtained were adhered together in 
the same manner as in Example 1 by incorporating therebetween spacers to 
maintain a distance between the substrates in a range of from 5 to 100 
.mu.m, preferably, from 7 to 30 .mu.m. Then, the same liquid crystal 
material as that used in Example 1 was injected into the resulting cell 
structure, and UV light at an intensity of from about 10 to 100 
mW/cm.sup.2 was irradiated to the liquid crystal material from the first 
substrate side to cure the resin. Thus was obtained liquid crystal 
droplets being surrounded by the resin. 
The active matrix addressed liquid crystal panel thus obtained comprises a 
circuit structure as shown in FIG. 4(B). In FIG. 4(B) is given a part, 
i.e., a 2.times.2 matrix of the entire structure. A driver circuit was 
formed together on the same substrate of the liquid crystal panel of the 
present Example as in the liquid crystal panel obtained in Example 3. 
Accordingly, no external driver circuit was necessary for the present 
liquid crystal panel. Thus, for driving the circuit of the present 
Example, a method as described in the previous invention of the present 
inventors, as disclosed in Japanese patent application No. 3-208848, may 
be employed. The liquid crystal panel thus obtained in the present Example 
was driven according to substantially the same method disclosed in the 
aforementioned Japanese patent application No. 3-208848 to confirm the 
display of images. 
EXAMPLE 5 
An active matrix addressed liquid crystal cell of a CMOS transfer gate type 
using the liquid crystal material described in Example 1 was fabricated. 
The circuit structure of the matrix fabricated in the present Example is 
shown in FIG. 4(C). An N channel TFT (NTFT) and a P channel TFT (PTFT) 
were established on a single pixel, so that they may function in a 
complementary manner. In FIG. 8(B) is shown a plan view for the circuit 
established on the second substrate of the present Example. The circuit 
comprises a region defined by a first and a second scan line 411 and 412, 
respectively, and a data line 413, in which a pixel electrode 418, an NTFT 
414, and a PTFT 415 are established. 
The first and the second substrates were fabricated essentially in the same 
process as described in Example 4, except for the circuit arrangement. The 
first and the second substrates thus obtained were adhered together in the 
same manner as in Example 1. The same liquid crystal material as that used 
in Example 1 was injected into the resulting cell structure, and UV light 
at an intensity of from about 10 to 100 mW/cm.sup.2 was irradiated to the 
liquid crystal material from the first substrate side to cure the resin. 
Thus was obtained liquid crystal droplets being surrounded by the resin. 
For driving the circuit of the present Example, a method as disclosed in 
Japanese patent application Nos. 63-82177 and 63-966361 may be employed. 
The liquid crystal panel thus obtained in the present Example was driven 
according to substantially the same method disclosed in the aforementioned 
Japanese patent application No. 63-82177 to confirm the display of images. 
EXAMPLE 6 
An active matrix addressed liquid crystal cell of a CMOS inverter type 
using the liquid crystal material described in Example 1 was fabricated. 
The circuit structure of the matrix fabricated in the present Example is 
shown in FIG. 4(D). As shown in the figure, it was designed as such that 
an N-channel TFT (NTFT) and a P-channel TFT (PTFT) may be established on a 
single pixel, so that they may function in a complementary manner. In FIG. 
6(C) is shown a plan view for the circuit established on the second 
substrate of the present Example. The circuit comprises a region defined 
by a first and a second scan line 421 and 422, respectively, and a data 
line 423, in which a pixel electrode 426, an NTFT 424, and a PTFT 425 are 
established. 
The first and the second substrates were fabricated essentially in the same 
process as described in Example 4, except for the circuit arrangement. The 
first and the second substrates thus obtained were adhered together in the 
same manner as in Example 1. The same liquid crystal material as that used 
in Example 1 was injected into the resulting cell structure, and UV light 
at an intensity of from about 10 to 100 mW/cm.sup.2 was irradiated to the 
liquid crystal material from the first substrate side to cure the resin. 
Thus was obtained liquid crystal droplets being surrounded by the resin. 
For driving the circuit of the present Example, a method as described in 
the previous invention of the present inventors, as disclosed in Japanese 
patent application No. 3-163871, may be employed. The liquid crystal 
panel, thus obtained in the present Example was driven according to 
substantially the same method disclosed in the aforementioned Japanese 
patent application No. 3-163871 to confirm the display of images. 
EXAMPLE 7 
An active matrix addressed liquid crystal cell of an advanced CMOS inverter 
type using the liquid crystal material described in Example 1 was 
fabricated. The circuit structure of the matrix fabricated in the present 
Example is shown in FIG. 4(E). As shown in the figure, it comprises a CMOS 
inverter in a single pixel and a switching transistor being provided on 
the scan line connected thereto. That is, the circuit according to the 
present Example is different from that of Example 6 in that it economizes 
on scan lines; i.e., the aperture ratio can be increased because one scan 
line is sufficient for the entire single pixel array. 
The first and the second substrates were fabricated essentially in the same 
process as described in Example 4, except for the circuit arrangement. The 
first and the second substrates thus obtained were adhered together in the 
same manner as in Example 1. The same liquid crystal material as that used 
in Example 1 was injected into the resulting cell structure, and UV light 
at an intensity of from about 10 to 100 mW/cm.sup.2 was irradiated to the 
liquid crystal material from the first substrate side to cure the resin. 
Thus was obtained liquid crystal droplets being surrounded by the resin. 
For driving the circuit of the present Example, a method as described in 
the previous invention of the present inventors, as disclosed in Japanese 
patent application No. 3-169308, may be employed. The liquid crystal panel 
thus obtained in the present Example was driven according to substantially 
the same method disclosed in the aforementioned Japanese patent 
application No. 3-189308 to confirm the display of images. 
EXAMPLE 8 
An active matrix addressed liquid crystal cell of an advanced CMOS buffer 
type using the liquid crystal material described in Example 1 was 
fabricated. The circuit structure of the matrix fabricated in the present 
Example is shown in FIG. 4(F). As shown in the figure, it comprises a CMOS 
buffer in a single pixel, and a switching transistor being provided on the 
scan line connected thereto. That is, the circuit according to the present 
Example economizes on scan lines; i.e., the aperture ratio can be 
increased because one scan line is sufficient for the entire single pixel 
array. 
The first and the second substrates were fabricated essentially in the same 
process as described in Example 4, except for the circuit arrangement. The 
first and the second substrates thus obtained were adhered together in the 
same manner as in Example 1. The same liquid crystal material as that used 
in Example 1 was injected into the resulting cell structure, and UV light 
at an intensity of from about 10 to 100 mW/cm.sup.2 was irradiated to the 
liquid crystal material from the first substrate side to cure the resin. 
Thus was obtained liquid crystal droplets being surrounded by the resin. 
For driving the circuit of the present Example, a method as described in 
the previous invention of the present inventors, as disclosed in Japanese 
patent application No. 3-169307, may be employed. The liquid crystal panel 
thus obtained in the present Example was driven according to substantially 
the same method disclosed in the aforementioned Japanese patent 
application No. 3-169307 to confirm the display of images. 
EXAMPLE 9 
As shown in FIG. 7, a polymer dispersed liquid crystal was fabricated first 
by a known process. The present Example refers to a polymer dispersed 
liquid crystal using a UV curable resin. A transparent conductive coating, 
i.e., an ITO film 2, was deposited on a light-transmitting substrate 1 by 
a known vapor deposition or sputtering process to a thickness of from 500 
to 2,000.ANG.. The ITO film thus obtained had a sheet resistivity of from 
20 to 200 .OMEGA./cm.sup.2. The film thus obtained was patterned by an 
ordinary photolithographic process. The resulting first and second 
substrates were adhered together under pressure, while maintaining a 
spacing of from 5 to 100 .mu.m, preferably from 7 to 30 .mu.m, by 
incorporating an inorganic spacer between the substrates. In this manner, 
the cell spacing can be maintained constant at about the diameter of the 
spacer. As the liquid crystal material, an ester based anti-ferroelectric 
liquid crystal having a refractive index of 1.6 and a .DELTA.n of 0.2 was 
mixed with a photocurable resin having a refractive index of 1.62 and 
comprising a mixed system of an urethane oligomer and an acrylic monomer. 
The aforementioned mixed material was stirred and subjected to ultrasonic 
vibration to obtain a homogeneous mixture. The mixing was effected by 
heating the mixture while applying stirring and ultrasonic vibration to 
obtain a homogeneous mixture as a liquid of an isotropic phase, and the 
resulting mixture was cooled to obtain a liquid crystal phase. This method 
was found very effective for obtaining the desired liquid crystal mixed 
system. 
The resulting liquid crystal mixed system was injected between the first 
and the second substrates above at a temperature higher than the S.sub.A 
-I phase transition temperature of the liquid crystal mixed system, and an 
UV light was irradiated thereto at an intensity of from about 10 to 100 
mW/cm.sup.2 for a duration of from about 30 to 300 seconds to cure the 
resin while allowing the mixed system to undergo phase separation into a 
liquid crystal and a resin. As a result, liquid crystal droplets 3 
surrounded by a resin 4 were formed. 
The electro-optical modulating layer of the liquid crystal device as shown 
in FIG. 11 thus obtained transmits a light incident thereon when no 
electric voltage (no electric signal) is applied to the electro-optical 
modulating layer between the electrodes having established on the upper 
and the lower substrates, because the liquid crystal molecules 1 are 
arranged in a random orientation and the average refractive index of the 
liquid crystal is almost equal to that of the resin in the random 
orientation. When a voltage (an electric signal) is applied to the 
electro-optical modulating layer, on the other hand, the liquid crystal 
molecules align themselves in such a manner that the major axes thereof be 
vertical to the direction of the applied electric field owing to the 
spontaneous polarization 2 of the liquid crystal molecules 1. At this 
state, a difference in refractive index is generated between the liquid 
crystal and the polymer resin and the electro-optical modulating layer 
scatters a light incident thereon. 
The liquid crystal material used in the present Example undergoes a phase 
transition sequence of Iso-SmA-SmC*-SmC.sub.A.sup.* -Cry. More 
specifically, it undergoes phase transition from Iso to SmA at 100.degree. 
C., from SmA to SmC.sup.* at 84.degree. C., from SmC.sup.* to 
SmC.sub.A.sup.* at 82.degree. C., and from SmC.sub.A.sup.* to Cry at 
-10.1.degree. C. It has a dielectric anisotropy with a birefringence 
.DELTA.n of about 0.2, and a spontaneous polarization of 80 nC/cm.sup.2. 
The electro-optical characteristics of the liquid crystal electro-optical 
device comprising the antiferroelectric liquid crystal thus obtained are 
listed in Table 1. 
TABLE 1 
______________________________________ 
Transmittance 
Threshold Voltage Response Speed 
______________________________________ 
95% (0 V) 9.5 V/.mu.m 8.0 .mu.sec. 
(when increasing a voltage) 
(0-&gt;80 V) 
56% (80 V) 
5.5 V/.mu.m 306 .mu.sec. 
(when decreasing a voltage) 
(80-&gt;0 V) 
______________________________________ 
The values given in Table 1 are the characteristics at 80.degree. C. As can 
be clearly read from the transmittance, a PDLC using an anti-ferroelectric 
liquid crystal material yields a voltage-transmittance relation as shown 
in FIG. 9. This is in clear contrast to that shown in FIG. 8, which 
corresponds to a voltage-transmittance curve of a conventional PDLC. The 
liquid crystal electro-optical device thus obtained yielded a far higher 
switching rate as compared to that of a device using a conventional 
nematic liquid crystal material, hence yielding a higher response speed. 
It required a relative high threshold voltage for driving the liquid 
crystal as shown in Table 1. However, because the liquid crystal may be 
replaced by another one having a higher birefringence, i.e., a liquid 
crystal having a higher light scattering power, the device itself can be 
made thinner by reducing the spacing between the substrates. Accordingly, 
the driving voltage can be reduced to a level well comparable to a 
generally employed voltage. 
Because an anti-ferroelectric liquid crystal material is used in the device 
according to the present invention, the shrinkage of the liquid crystal 
material due to volume change thereof on applying an electric field for 
driving the device can be considerably reduced as compared with that of a 
ferroelectric liquid crystal material. Thus, no vibration occurs on the 
substrate of the liquid crystal electro-optical device according to the 
present invention. 
Furthermore, a higher contrast can be achieved with a liquid crystal 
electro-optical device according to the present invention. This is 
ascribed to the fact that the smectic layer structure, i.e., the structure 
which the anti-ferroelectric liquid crystal material takes in the 
dispersed droplets, can be deformed by the electric field being applied 
thereto. Thus, the refractive index of the liquid crystal material can be 
greatly differed from that of the transparent substance. This is in clear 
contrast with the case using a ferroelectric liquid crystal material, 
because the smectic layer structure of the ferroelectric liquid crystal 
material as dispersed droplets cannot be deformed by an external electric 
field. 
It should be further added that the liquid crystal material used in the 
present invention shows a hysteresis in the threshold voltage 
characteristics because it is based on an anti-ferroelectric liquid 
crystal material. This is advantageous in realizing an electro-optical 
device having far improved in response time and a memory function, as 
compared with the conventional PDLC devices based on a nematic or a 
ferroelectric liquid crystal. 
In the present specification, the dispersed liquid crystal materials were 
described as droplets, and they were expressed with circles or spherical 
shapes in the drawings. However, the liquid crystal materials are not 
restricted to droplets or those having circular shapes, and the same 
effect as on those above may also be expected on the liquid crystal 
materials present in other shapes and forms. For example, as shown in the 
micrograph of FIG. 1, a three-dimensional network, which is the resin 
observed as a white portion, may be present between the substrates and the 
liquid crystal may be held in the cavities provided therein. 
Furthermore, a dichroic dye and the like may be added to the 
electro-optical modulating layer to fabricate a liquid crystal 
electro-optical device of a guest-host type. 
In addition, the matrix circuits used in Examples 2, 3, 4, 5, and 8 may be 
replaced by those shown in FIGS. 5(A), 5(B), 5(C), and 5(D). 
In FIG. 5(E) is shown the tilt angle of the anti-ferroelectric liquid 
crystal molecules on applying a voltage to the anti-ferroelectric liquid 
crystal material according to the present invention. It can be seen that 
the anti-ferroelectric liquid crystal molecules can be stabilized at a 
larger tilt angle by applying thereto a voltage being stabilized at a 
value higher than the threshold voltage. However, a fluctuation in the 
applied voltage may destabilize the anti-ferroelectric liquid crystal 
molecules. In the circuits illustrated in FIGS. 5(A), 5(B), 5(C), and 
5(D), capacitors are provided to absorb such fluctuations and to thereby 
stabilize the anti-ferroelectric liquid crystal molecules to assure a 
stable display on a liquid crystal electro-optical device. 
As described in detail in the foregoing, the present invention provides a 
PDLC electro-optical device having a high scattering efficiency under no 
applied electric field and favorable light transmitting characteristics 
under an applied electric field. The present invention also provides 
another type of a PDLC electro-optical device having favorable light 
transmitting characteristics under no applied electric field and a high 
scattering efficiency under an applied electric field. 
In the former type of the liquid crystal electro-optical device, a 
switching speed of 40 .mu.sec or even higher is obtained; i.e., a device 
having a quick response of 100 or more times as quick as that of a 
conventional device is obtained even on a cell having an inter electrode 
spacing (thickness of the electro-optical modulating layer) of from 5 to 
10 .mu.m. Furthermore, the use of an anti-ferroelectric liquid crystal as 
the liquid crystal material results in a favorable dielectric property 
with a relative dielectric constant of 10 to 100. This enables realization 
of a higher switching rate even on a device having a low electric field 
intensity, i.e., on such having a thick liquid crystal cell or such under 
a low voltage. This is because, if the electric field were to be 
maintained constant, a higher relative dielectric constant signifies that 
a higher force can be exerted to the liquid crystal molecules for their 
aligning. 
In the latter type of the liquid crystal electro-optical device, a 
switching speed of 400 .mu.sec or even higher is obtained; i.e., a device 
having a quick response of 20 or more times as quick as that of a 
conventional device is obtained even on a cell having an inter electrode 
spacing of from 5 to 10 .mu.m. Furthermore, the use of an 
anti-ferroelectric liquid crystal as the liquid crystal material results 
in a favorable dielectric property with a spontaneous polarization as 
large as 80 nC/cm.sup.2. This enables realization of a higher switching 
rate even on a device to which only an electric field of low intensity can 
be applied, i.e., on such having a thick liquid crystal cell or such under 
a low voltage. This is because, if the electric field were to be 
maintained constant, a higher spontaneous polarization signifies that a 
higher force can be exerted to the liquid crystal molecules for their 
driving. 
The conventional ferroelectric liquid crystal devices comprising polarizer 
sheets comprised cells as thin as from 1.3 to 2.3 .mu.m in thickness. 
However, they were not practically feasible because they were too thin and 
were therefore apt to cause short circuit between the upper and the lower 
substrate electrodes due to contaminations and the like. This problem 
could be overcome by increasing the interelectrode spacing to a length of 
from 2.5 to 10 .mu.m. An electro-optical device having a cell thickness of 
5 .mu.m, for example, was substantially free of short circuit, and a 
switching time of 500 .mu.sec or shorter could be obtained thereon at a 
little expense of reduced electric field intensity. In particular, a 
switching time of 100 .mu.sec or even shorter was obtained on an 
electro-optical device of the former type referred hereinbefore. 
It should be noted, moreover, that conventional PDLC electro-optical 
devices based on nematic liquid crystals had no hysteresis in the 
threshold voltage characteristics and hence no memory function of the 
display. In the liquid crystal electro-optical device according to the 
present invention, the use of an anti-ferroelectric liquid crystal 
material yields a threshold voltage of 9.5 V/.mu.m on applying an electric 
field to effect the transition from a light-transmitting state to a 
scattering state. On cutting off the electric field to effect the 
transition from a light-scattering state to a light-transmitting state, 
the threshold voltage is, however, 5.5 V/.mu.m. This clear hysteresis can 
be taken the best for use as a memory. 
Furthermore, a bright liquid crystal display which suffers less optical 
loss was realized by using no polarizer sheets. That is, a liquid crystal 
panel having a paper-like appearance with a milky white background was 
obtained. In particular, an image of high contrast can be realized by 
combining the liquid crystal material of the present invention with an 
active matrix. Accordingly, a display having an appearance similar to that 
of a printed matter was realized. 
While the invention has been described in detail and with reference to 
specific examples thereof, it will be apparent to one skilled in the art 
that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.