CA1331409C - Ferroelectric liquid crystal device - Google Patents
Ferroelectric liquid crystal deviceInfo
- Publication number
- CA1331409C CA1331409C CA000615536A CA615536A CA1331409C CA 1331409 C CA1331409 C CA 1331409C CA 000615536 A CA000615536 A CA 000615536A CA 615536 A CA615536 A CA 615536A CA 1331409 C CA1331409 C CA 1331409C
- Authority
- CA
- Canada
- Prior art keywords
- liquid crystal
- electrodes
- electric field
- voltage
- ferroelectric liquid
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Abstract
ABSTRACT OF THE DISCLOSURE
A liquid crystal apparatus comprising a ferro-electric liquid crystal device matrix having electrodes, including scanning electrodes and signal electrodes spaced from and intersecting with each other, and a ferroelectric liquid crystal disposed between the scanning electrodes and the signal electrodes, a driving circuit for applying a driving voltage selectively to the intersections of the scanning electrodes and the signal electrodes, and a uniform electric field application circuit for applying an alternating electric field to all or a prescribed part of the intersections before the application of said driving voltage; said ferroelectric liquid crystal providing two average molecular directions forming an angle 2.theta.a therebetween in the absence of an electric field after application of an alternating electric field, said angle 2.theta.a being larger than an angle 2.theta. formed between two average molecular directions of the ferroelectric liquid crystal in the absence of an electric field before application of the alternating electric field.
A liquid crystal apparatus comprising a ferro-electric liquid crystal device matrix having electrodes, including scanning electrodes and signal electrodes spaced from and intersecting with each other, and a ferroelectric liquid crystal disposed between the scanning electrodes and the signal electrodes, a driving circuit for applying a driving voltage selectively to the intersections of the scanning electrodes and the signal electrodes, and a uniform electric field application circuit for applying an alternating electric field to all or a prescribed part of the intersections before the application of said driving voltage; said ferroelectric liquid crystal providing two average molecular directions forming an angle 2.theta.a therebetween in the absence of an electric field after application of an alternating electric field, said angle 2.theta.a being larger than an angle 2.theta. formed between two average molecular directions of the ferroelectric liquid crystal in the absence of an electric field before application of the alternating electric field.
Description
1~31~
This application is a division of co-pending Canadian patent application Serial No. 516,944, entitled FE~ROELECTRIC LIQUID CRYSTAL DEVICE, filed August 27, 1986.
The present invention relates to a liquid crystal device for use in a liquid crystal display device, an optical shutter array, etc., and more particularly to a ferroelectric liquid crystal device having improved display and driving characteristics, because of improved initial alignment or orientation of liquid crystal molecules.
Clark and Lagerwall have proposed the use of a liquid crystal device having bistability (Japanese Laid-Open Patent Application No. 107216/1981, U.S. Patent No.
4,367,924, etc.). As the bistable liquid crystal, a ferroelectric liquid crystal having chiral smectic C
(SmC*) phase or H (SmH*) phase is generally used. The ferroelectric liquid crystal has bistability, i.e., has -two stable states comprising a first stable state and a second stable state, with respect to an electric field applied thereto. Accordingly, different from the conventional TN-type liquid crystal in the above-mentioned device, the liquid crystal is oriented to the first stable state in response to one electric field vector and to the `
second stable state in response to the other electric field vector. Further, this type o* liquid crystal very quickly assumes either one of the above-mentioned two stable states in reply to an ~
'.`':" :.
. : ~
~ 3 3 ~
electric field applied thereto and retains the state in the absence of an electric field. By utilizing these properties, essential improvements can be attained with respect to the above-mentioned difficul- ; -~
ties involved in the conventional TN-type liquid crystal device.
In order to provide a uniform orientation or : .. . .
alignment characteristic to a ferroelectric liquid crystal in the above described type of device, there 10 has been known to apply a uniaxial alignment treatment ;~
onto a substrate surface. More specifically, the ~ ;
uniaxial alignment treatment includes a method of rubbing a substrate surface with velvet, cloth or paper in one direction, or a method of obliquely depositing SiO or SiO2 on a substrate surface.
By applying an appropriate uniaxial alignment treatment to a substrate surface, a specific bistable condition has been provided as an initial alignment ~ -characteristic. Under such an initial alignment ~;
condition, however, there have been.observed practical problems such as~poor contrasts and low light-transmittances during an optical modulation test carried out by using polarizers arranged in cross ~
nicols in combination with the device. ~-More specifically, in a ferroelectric liquid crystal device of the type described above, a state wherein molecules of a liquid crystal (hereinafter ~, ''~' sometimes abbreviated as "LC") are twisted from an upper substrate to a lower substrate in an LC molecular layer (twist alignment state) as shown in Figure 21 is readily developed rather than a state wherein 1C ``
molecules are aligned in parallel with each other in an LC molecular layer (parallel alignment state) as shown in Figure 22. Such a twist alignment of LC
molecules leads to various disadvantages for a display device such that the angle formed between the LC
molecular axes in the first orientation state and the~
second orientation state (tilt angle) is apparently ~ ;
decreased to result in a decrease in contrast or light transmittance, and an overshooting occurs in the , response of the LC molecules at the time of switching `
between the orientation states to result in an observ-able fluctuation in light transmittance. For this reason, it is desired that the LC molecules are placed in the parallel alignment state for a display device.
~ :
SUMMARY OF THE INVENTION
The present invention has been accomplished to solve the above mentioned problems and aims at provid-ing a liquid crystal device improved in display characteristics by realizing the parallel alignment state of liquid crystal molecules.
We have observed that the above mentioned twist alignment state can be transformed into the parallel ~ `
: :::
~ 3 ~
alignment state by applying an appropriate alternating voltage (hPreinafter sometimes represented by an AC
voltage for parallel alignment) to a bistable ferroelectric liquid crystal.
According to the present invention, there is provided a liquid crystal apparatus comprising a ferro-electric liquid crystal device matrix having electrodes, including scanning electrodes and signal electrodes spaced from and intersecting with each other, and a ferroelectric liquid crystal disposed between the scanning electrodes and the signal electrodes, a driving circuit for applying a driving voltage selectively to the intersections of the :
scanning electrodes and the signal electrodes, and a uniform electric field application circuit for applying an --alternating electric field to all or a prescribed part of the intersections before the application of said driving : ;
voltage; said ferroelectric liquid crystal providing two :
average molecular directions forming an angle 2ea .~
therebetween in the absence of an electric field after ~`
application of an alternating electric field, said angle 2ea being larger than an angle 2e formed between two average molecular diractions of the ferroelectric liquid crystal in the absence of an electric field before :~ .
application of the alternating electric field.
These and other objects, features and advantages of the present invention will become more apparent upon a ~: cbnsideration of the following description of`the ~ -preferred embodiments of the present invention taken in conjunction with the accompanying drawings. ~:
The following drawings and detailed description of . ": ,.
:
~ ~3~ ~3.3 the invention are directed not only to the liquid crystal apparatus which is the subject of the present invention, but also to the ferroelectric liquid crystal device and liquid crystal apparatus which are claimed in co-pending Canadian patent application Serial No. 516,944, of which the present application is a div:ision.
_LEF DESCRIPTION OF THE DRAWINGS
Figure ~ is a schematic plan view for illustrating an LC cell according to the present invention;
Figures 2 and 3 are a plan view and a sectional view, respectively, of an LC cell;
Figure 4 is a circuit diagram for AC voltage application;
Figures 5 and 6 are respectively a schematic view for illustrating a ferroelectric liquid crystal cell;
Figures 7, 10, 12, 15, 17 and 20 are respectively a circuit diagram of an example of the liquid crystal apparatus according to the present invention;
Figures 8 and ll are circuit diagrams of switches used in the examples shown in Figures 7 and 10, ~-.
respectively;
Figure 9 is a sectional view showing another example : ~
of the LC device according to the present invention; ~ ;
Figures 13 and 18 are respectively a timing chart :~
for illustrating voltage signals used in an -~
' ' ' . ~
` . ' ' '.~'.'.' ~''~' .; ~ ~ ',,.
'',' ~ ' '"
;; ~ " ': ' `
'''~'~`'"";;
1 3 3 ~
example of the present invention;
Figure 14 is an illustration of matrix picture elements in an embodiment of the present invention;
Figures 16 and 19 are circuit diagrams of the 5 final stages of the driver circuits in the apparatus -~
shown in Figures 15 and 17; and Figure 21 and 22 are respectively a schematic view of projection of C directors on a chiral smectic ~i `
molecular layer in a twist alignment state and in a -10 parallel alignment state, respectively. ;~ ;
,- ~
~ DESCRIPTION OF THE PREFERRED EMBODIMENTS
~i ~ .- ; ,-:
i~ ~ Liquid crystal materials most suited for the ~;
present invention are chiral smectic liquid crystals `~ l5 showing ferroelectricity. More specifically, liquid ;~
crystals showing chiral smectic C phase (SmC*), G phase ~ ;
(SmG*), F phase (SmF*), I phase (SmI*) or H phase (SmH*) are available.
Details of ferroelectric liquid crystals are ;~
described in, e.g., "LE JOURNAL DE PHYSIQUE LETTERS"
36 (L-69) 1975, "Ferroelectric Liquid Crystals"i ;
~ , . , ~ . ,.
"Applied Physics Letters" 36 (11) 1980, "Submicro Second Bistable Electrooptlo Switching in Liquid Crystals"; "Kotai Butsuri (Solid State Physics)" 16 ~5 (141~ 1981, "Liquid Crystals", etc. In the present invention, ferroelectric liquid crystals disclosed in these publications may he used.
1331~
Examples o ferroelectric liquid crystal compounds include decyloxybenzylidene-p'-amino-2-methylbutyl cinnamate (DOBAMBC), hexyloxybenzylidene-p'-amino-2-chloropropyl cinnamate (HOBACPC), 4-o- ;
(2-methyl)-butylresorcylidene-4'-octylaniline (~A 8), etc. Especially preferred class of chiral smectic -liquid crystals used in the liquid crystal device according to the present invention are those showing a cholesteric phase at a temperature higher than the ;~; ;
temperature for giving a smectic phase. A specific example of such chiral smectic liquid crystal is a blphenyl ester type liquid crystal compcund showing ~ " . . ":
phase transition temperatures as shown in an example ~ -described hereinafter.
lS When a devlce is~constituted using these materials, the device may be supported with a block of `
copper, etc., in which a heater is embedded in order to ~ ,;,, .~ .":~
realize a temperature condition where the liquid crystal~compounds assume a desired phase.
Referring t,o Figure 5, there is schematically ` ~;
shown an example of a ferroelectric liquid crystal cell for explanation of the operation thereof. An example -` `;`
where an SmC* phase constitutes a desired phase is ~
explained. Reference numerals 51 and 51a denote base ~.
plates (qlass plates~ on which a transparent electrode of, e.g., In2O3, SnO2, ITO (Indium-Tin~Oxide), etc., ,~
` is disposed, respectively. A liquid crys~al of an ,: ~",~
~ 3 ~
SmC*-phase in which liquid crystal molecular layers 52 are aligned perpendicular to surfaces of the glass plates is hermetically disposed therebetween. A full line 53 shows liquid crystal molecules. The liquid -crystal molecules 53 continuously form a helical struc-ture in the direction of extension of the base plates.
The angle formed between the central axis 55 and the axis of a liquid crystal molecule 53 is expressed as . Each liquid crystal molecule 53 has a dipole moment (Pl) 54 in a direction perpendicular to the axis thereof. When a voltage higher than a certain threshold level is applied between electrodes formed on the base plates 51 and 51a, a helical structure of the liquid crystal molecule 53 is unwound or released , ~ ~
~: is to change the alignment direction of respective liquid ` crystal molecules 53 so that the dipole moments (P~
54 are all directed in the direction of the electric field. The liquid crystal molecules 53 have an ;~
elongated shape and show refractive anisotropy between 20 the long axis and the short axis thereof. Accordingly, ` -~
;~ it is easily understood that when, for instance, polarizers arranged in a cross nicol relationship, i.e., with their polarlzing directions crossing each other, are disposed on the upper and the lower surfaces 25 of the glass plates, the liquid crystal cell thus `~
arranged functions as a liquid crystal optical modula~
tion device of which optical characteristics vary ; ~ ` . .:
~, "' -'.'' ~
~33~
g .:
depending upon the polarity of an applied voltage.
The liquid crystal layer in the liquid crystal , ":, ':
device of the present invention may be rendered sufficiently thin in thickness (e.g., less than 10 . ~
As the thickness of the liquid crystal layer is decreased, the helical structure of the liquid crystal molecules is ]oosened even in the absence of an ; ;~ -electric field whereby the dipole moment assumes either of the two states, i.e., P in an upper direction 64 or Pa in a lower direction 64a as shown in Figure 6.
:: : ,~ ,,:
One half of the angle between the molecular axis 63 and ``
the molecular axis 63a is referred to as a tilt angle ^ '~
, which is the same as half the apical angle of the --;cone of the helical structure. When an electric field 15 ~ E or Ea higher than a certain threshold level and different from each other in polarity as shown in Figure 6 is applied to a cell having the above~
mentioned characteristlcs, the dipole moment is dlrected~eLther in the upper direction 64 or in the lower direction 64a depending on the vector of the electric field E or Ea. In correspondence with this, the~llquid crystal molecules are oriented in either of a first stable state 63 and a second stable state 63a 25When the above-mentloned ferroelectric liquid crystal is used as an optical modulation element, it is possible to obtain two advantages as briefly touched ;~
`:" , ` ';'^, '~'~
`: . - . . .::
: .
~ 3 3 ~
on hereinbefore. First is that the response speed is quite fast. Second is that the orientation of the liquid crystal shows bistability. The second advantage will be further explained, e.g., with reference to ", Figure 6. When the electric field E is applied to ~-the liquid crystal molecules, they are oriented in :
the first stable state 63. This state is stably -~
retained even if the electric field is removed. On ~ ~;
the other hand, when the electric field Ea of which ~-~ ~ -direction is opposite to that of the electric field E is applied thereto, the liquid crystal molecules are oriented to the second stable state 63a, whereby the directions of molecules are changed. This state is similarly stably retained even if the electric field is removed. Further, as long as the magnitude ~`
of the electric field E or Ea being applied is not ~;~
above a certain threshold value, the liquid crystal molecules are placed ln the respective orientation states. In order to effectively realize high response speed and bistability, lt is preferable that the thickness of the cell is as thin as possible.
The most serious problem encountered in form~
ing a device using such a-ferroelectric liquid crystal has been, as briefly mentioned hereinbefore, that it ~` ?5 is difficult to form a cell having a highly uniform .
; monodomain wherein liquid crystal layers having an SmC* phase are aligned perpendicular to the base plate ;~
, ~'','.' ' ':
~, ::;
-1 1- ~' ~ , , phasea and the liquid crystal molecules are aligned ;~
almost in parallel with the base plate phases. ~ -There has been heretofore known a method of applying a uniaxial orientation treatment to base plate surfaces when a large area of a liquid crystal ; cell is produced. The uniaxial orientation treatment is effected by rubbing the base plate surfaces with velvet, cloth or paper in a single direction or by the oblique or tilt vapor deposition of Sio or SiO2 10 onto the base plate surfaces. However, such a uni- ~-axlal orientation treatment as by the rubbing or the oblique vapor deposltion has been considered in- ;
appropri~ate for a ferroelectric liquid crystal since such~an orientation treatment per se hinders the ` ---bistability of the liquid crystal, based on which drlving utllizing a memory characteristic is realized.
According t~ our further study, it has been found~possible to provide a specific bistable state `~
as~descrlbed hereinafter by~applying a suitable uni~
This application is a division of co-pending Canadian patent application Serial No. 516,944, entitled FE~ROELECTRIC LIQUID CRYSTAL DEVICE, filed August 27, 1986.
The present invention relates to a liquid crystal device for use in a liquid crystal display device, an optical shutter array, etc., and more particularly to a ferroelectric liquid crystal device having improved display and driving characteristics, because of improved initial alignment or orientation of liquid crystal molecules.
Clark and Lagerwall have proposed the use of a liquid crystal device having bistability (Japanese Laid-Open Patent Application No. 107216/1981, U.S. Patent No.
4,367,924, etc.). As the bistable liquid crystal, a ferroelectric liquid crystal having chiral smectic C
(SmC*) phase or H (SmH*) phase is generally used. The ferroelectric liquid crystal has bistability, i.e., has -two stable states comprising a first stable state and a second stable state, with respect to an electric field applied thereto. Accordingly, different from the conventional TN-type liquid crystal in the above-mentioned device, the liquid crystal is oriented to the first stable state in response to one electric field vector and to the `
second stable state in response to the other electric field vector. Further, this type o* liquid crystal very quickly assumes either one of the above-mentioned two stable states in reply to an ~
'.`':" :.
. : ~
~ 3 3 ~
electric field applied thereto and retains the state in the absence of an electric field. By utilizing these properties, essential improvements can be attained with respect to the above-mentioned difficul- ; -~
ties involved in the conventional TN-type liquid crystal device.
In order to provide a uniform orientation or : .. . .
alignment characteristic to a ferroelectric liquid crystal in the above described type of device, there 10 has been known to apply a uniaxial alignment treatment ;~
onto a substrate surface. More specifically, the ~ ;
uniaxial alignment treatment includes a method of rubbing a substrate surface with velvet, cloth or paper in one direction, or a method of obliquely depositing SiO or SiO2 on a substrate surface.
By applying an appropriate uniaxial alignment treatment to a substrate surface, a specific bistable condition has been provided as an initial alignment ~ -characteristic. Under such an initial alignment ~;
condition, however, there have been.observed practical problems such as~poor contrasts and low light-transmittances during an optical modulation test carried out by using polarizers arranged in cross ~
nicols in combination with the device. ~-More specifically, in a ferroelectric liquid crystal device of the type described above, a state wherein molecules of a liquid crystal (hereinafter ~, ''~' sometimes abbreviated as "LC") are twisted from an upper substrate to a lower substrate in an LC molecular layer (twist alignment state) as shown in Figure 21 is readily developed rather than a state wherein 1C ``
molecules are aligned in parallel with each other in an LC molecular layer (parallel alignment state) as shown in Figure 22. Such a twist alignment of LC
molecules leads to various disadvantages for a display device such that the angle formed between the LC
molecular axes in the first orientation state and the~
second orientation state (tilt angle) is apparently ~ ;
decreased to result in a decrease in contrast or light transmittance, and an overshooting occurs in the , response of the LC molecules at the time of switching `
between the orientation states to result in an observ-able fluctuation in light transmittance. For this reason, it is desired that the LC molecules are placed in the parallel alignment state for a display device.
~ :
SUMMARY OF THE INVENTION
The present invention has been accomplished to solve the above mentioned problems and aims at provid-ing a liquid crystal device improved in display characteristics by realizing the parallel alignment state of liquid crystal molecules.
We have observed that the above mentioned twist alignment state can be transformed into the parallel ~ `
: :::
~ 3 ~
alignment state by applying an appropriate alternating voltage (hPreinafter sometimes represented by an AC
voltage for parallel alignment) to a bistable ferroelectric liquid crystal.
According to the present invention, there is provided a liquid crystal apparatus comprising a ferro-electric liquid crystal device matrix having electrodes, including scanning electrodes and signal electrodes spaced from and intersecting with each other, and a ferroelectric liquid crystal disposed between the scanning electrodes and the signal electrodes, a driving circuit for applying a driving voltage selectively to the intersections of the :
scanning electrodes and the signal electrodes, and a uniform electric field application circuit for applying an --alternating electric field to all or a prescribed part of the intersections before the application of said driving : ;
voltage; said ferroelectric liquid crystal providing two :
average molecular directions forming an angle 2ea .~
therebetween in the absence of an electric field after ~`
application of an alternating electric field, said angle 2ea being larger than an angle 2e formed between two average molecular diractions of the ferroelectric liquid crystal in the absence of an electric field before :~ .
application of the alternating electric field.
These and other objects, features and advantages of the present invention will become more apparent upon a ~: cbnsideration of the following description of`the ~ -preferred embodiments of the present invention taken in conjunction with the accompanying drawings. ~:
The following drawings and detailed description of . ": ,.
:
~ ~3~ ~3.3 the invention are directed not only to the liquid crystal apparatus which is the subject of the present invention, but also to the ferroelectric liquid crystal device and liquid crystal apparatus which are claimed in co-pending Canadian patent application Serial No. 516,944, of which the present application is a div:ision.
_LEF DESCRIPTION OF THE DRAWINGS
Figure ~ is a schematic plan view for illustrating an LC cell according to the present invention;
Figures 2 and 3 are a plan view and a sectional view, respectively, of an LC cell;
Figure 4 is a circuit diagram for AC voltage application;
Figures 5 and 6 are respectively a schematic view for illustrating a ferroelectric liquid crystal cell;
Figures 7, 10, 12, 15, 17 and 20 are respectively a circuit diagram of an example of the liquid crystal apparatus according to the present invention;
Figures 8 and ll are circuit diagrams of switches used in the examples shown in Figures 7 and 10, ~-.
respectively;
Figure 9 is a sectional view showing another example : ~
of the LC device according to the present invention; ~ ;
Figures 13 and 18 are respectively a timing chart :~
for illustrating voltage signals used in an -~
' ' ' . ~
` . ' ' '.~'.'.' ~''~' .; ~ ~ ',,.
'',' ~ ' '"
;; ~ " ': ' `
'''~'~`'"";;
1 3 3 ~
example of the present invention;
Figure 14 is an illustration of matrix picture elements in an embodiment of the present invention;
Figures 16 and 19 are circuit diagrams of the 5 final stages of the driver circuits in the apparatus -~
shown in Figures 15 and 17; and Figure 21 and 22 are respectively a schematic view of projection of C directors on a chiral smectic ~i `
molecular layer in a twist alignment state and in a -10 parallel alignment state, respectively. ;~ ;
,- ~
~ DESCRIPTION OF THE PREFERRED EMBODIMENTS
~i ~ .- ; ,-:
i~ ~ Liquid crystal materials most suited for the ~;
present invention are chiral smectic liquid crystals `~ l5 showing ferroelectricity. More specifically, liquid ;~
crystals showing chiral smectic C phase (SmC*), G phase ~ ;
(SmG*), F phase (SmF*), I phase (SmI*) or H phase (SmH*) are available.
Details of ferroelectric liquid crystals are ;~
described in, e.g., "LE JOURNAL DE PHYSIQUE LETTERS"
36 (L-69) 1975, "Ferroelectric Liquid Crystals"i ;
~ , . , ~ . ,.
"Applied Physics Letters" 36 (11) 1980, "Submicro Second Bistable Electrooptlo Switching in Liquid Crystals"; "Kotai Butsuri (Solid State Physics)" 16 ~5 (141~ 1981, "Liquid Crystals", etc. In the present invention, ferroelectric liquid crystals disclosed in these publications may he used.
1331~
Examples o ferroelectric liquid crystal compounds include decyloxybenzylidene-p'-amino-2-methylbutyl cinnamate (DOBAMBC), hexyloxybenzylidene-p'-amino-2-chloropropyl cinnamate (HOBACPC), 4-o- ;
(2-methyl)-butylresorcylidene-4'-octylaniline (~A 8), etc. Especially preferred class of chiral smectic -liquid crystals used in the liquid crystal device according to the present invention are those showing a cholesteric phase at a temperature higher than the ;~; ;
temperature for giving a smectic phase. A specific example of such chiral smectic liquid crystal is a blphenyl ester type liquid crystal compcund showing ~ " . . ":
phase transition temperatures as shown in an example ~ -described hereinafter.
lS When a devlce is~constituted using these materials, the device may be supported with a block of `
copper, etc., in which a heater is embedded in order to ~ ,;,, .~ .":~
realize a temperature condition where the liquid crystal~compounds assume a desired phase.
Referring t,o Figure 5, there is schematically ` ~;
shown an example of a ferroelectric liquid crystal cell for explanation of the operation thereof. An example -` `;`
where an SmC* phase constitutes a desired phase is ~
explained. Reference numerals 51 and 51a denote base ~.
plates (qlass plates~ on which a transparent electrode of, e.g., In2O3, SnO2, ITO (Indium-Tin~Oxide), etc., ,~
` is disposed, respectively. A liquid crys~al of an ,: ~",~
~ 3 ~
SmC*-phase in which liquid crystal molecular layers 52 are aligned perpendicular to surfaces of the glass plates is hermetically disposed therebetween. A full line 53 shows liquid crystal molecules. The liquid -crystal molecules 53 continuously form a helical struc-ture in the direction of extension of the base plates.
The angle formed between the central axis 55 and the axis of a liquid crystal molecule 53 is expressed as . Each liquid crystal molecule 53 has a dipole moment (Pl) 54 in a direction perpendicular to the axis thereof. When a voltage higher than a certain threshold level is applied between electrodes formed on the base plates 51 and 51a, a helical structure of the liquid crystal molecule 53 is unwound or released , ~ ~
~: is to change the alignment direction of respective liquid ` crystal molecules 53 so that the dipole moments (P~
54 are all directed in the direction of the electric field. The liquid crystal molecules 53 have an ;~
elongated shape and show refractive anisotropy between 20 the long axis and the short axis thereof. Accordingly, ` -~
;~ it is easily understood that when, for instance, polarizers arranged in a cross nicol relationship, i.e., with their polarlzing directions crossing each other, are disposed on the upper and the lower surfaces 25 of the glass plates, the liquid crystal cell thus `~
arranged functions as a liquid crystal optical modula~
tion device of which optical characteristics vary ; ~ ` . .:
~, "' -'.'' ~
~33~
g .:
depending upon the polarity of an applied voltage.
The liquid crystal layer in the liquid crystal , ":, ':
device of the present invention may be rendered sufficiently thin in thickness (e.g., less than 10 . ~
As the thickness of the liquid crystal layer is decreased, the helical structure of the liquid crystal molecules is ]oosened even in the absence of an ; ;~ -electric field whereby the dipole moment assumes either of the two states, i.e., P in an upper direction 64 or Pa in a lower direction 64a as shown in Figure 6.
:: : ,~ ,,:
One half of the angle between the molecular axis 63 and ``
the molecular axis 63a is referred to as a tilt angle ^ '~
, which is the same as half the apical angle of the --;cone of the helical structure. When an electric field 15 ~ E or Ea higher than a certain threshold level and different from each other in polarity as shown in Figure 6 is applied to a cell having the above~
mentioned characteristlcs, the dipole moment is dlrected~eLther in the upper direction 64 or in the lower direction 64a depending on the vector of the electric field E or Ea. In correspondence with this, the~llquid crystal molecules are oriented in either of a first stable state 63 and a second stable state 63a 25When the above-mentloned ferroelectric liquid crystal is used as an optical modulation element, it is possible to obtain two advantages as briefly touched ;~
`:" , ` ';'^, '~'~
`: . - . . .::
: .
~ 3 3 ~
on hereinbefore. First is that the response speed is quite fast. Second is that the orientation of the liquid crystal shows bistability. The second advantage will be further explained, e.g., with reference to ", Figure 6. When the electric field E is applied to ~-the liquid crystal molecules, they are oriented in :
the first stable state 63. This state is stably -~
retained even if the electric field is removed. On ~ ~;
the other hand, when the electric field Ea of which ~-~ ~ -direction is opposite to that of the electric field E is applied thereto, the liquid crystal molecules are oriented to the second stable state 63a, whereby the directions of molecules are changed. This state is similarly stably retained even if the electric field is removed. Further, as long as the magnitude ~`
of the electric field E or Ea being applied is not ~;~
above a certain threshold value, the liquid crystal molecules are placed ln the respective orientation states. In order to effectively realize high response speed and bistability, lt is preferable that the thickness of the cell is as thin as possible.
The most serious problem encountered in form~
ing a device using such a-ferroelectric liquid crystal has been, as briefly mentioned hereinbefore, that it ~` ?5 is difficult to form a cell having a highly uniform .
; monodomain wherein liquid crystal layers having an SmC* phase are aligned perpendicular to the base plate ;~
, ~'','.' ' ':
~, ::;
-1 1- ~' ~ , , phasea and the liquid crystal molecules are aligned ;~
almost in parallel with the base plate phases. ~ -There has been heretofore known a method of applying a uniaxial orientation treatment to base plate surfaces when a large area of a liquid crystal ; cell is produced. The uniaxial orientation treatment is effected by rubbing the base plate surfaces with velvet, cloth or paper in a single direction or by the oblique or tilt vapor deposition of Sio or SiO2 10 onto the base plate surfaces. However, such a uni- ~-axlal orientation treatment as by the rubbing or the oblique vapor deposltion has been considered in- ;
appropri~ate for a ferroelectric liquid crystal since such~an orientation treatment per se hinders the ` ---bistability of the liquid crystal, based on which drlving utllizing a memory characteristic is realized.
According t~ our further study, it has been found~possible to provide a specific bistable state `~
as~descrlbed hereinafter by~applying a suitable uni~
2~0 axlal orientation~treatment to base plate surfaces ^` `
; - and by arranging a polarizer ln the specific axis direction to realize driving effectively utilizing ``
a memory characteristic.~
Figure 1 is a schematic view illustrating `~`
molecular orieutatlon states in a liquld crystal device according to the present invention. Figure 2 is a plan view of an example of a liquid crystal cell used `.'...~.~ ', ' ~ , ~ 3 ~ !
in the present invention and Figure 3 is a sectional view of the cell taken along the line III-III shown , -;
in Fiuure 2.
Referring to Figures 2 and 3, an LC cell 1 comprises a pair of substrates 3a and 3b of glass or a plastic, respectively provided thereon with stripe electrodes 4a and 4b of 1000 A-thick ITO (Indium Tin Oxide) stripe electrode films and further thereon with alignment films 5a and 5b of 10 A - 1 ~m, preferably L0 100 A - 5000 A, in thickness. Between the alignment . . , ~
films are disposed polyimide spacers of 1 ~-dot shape ; so as to retain the liquld crystal layer 2 in a constant thickness over a wide area. The above mentioned two substrates, after having been subjected to a rubbing treatment, are secured to each other to .. ~; : , ~, :. ::
form a cell into which the liquid crystal is then introduced.
Hereinbelow, an example wherein an ester type liquid crystal mixture was used is explained with reference to Figures 1 through 3. The ester-type mixture liquid crystal showed the following phase transition temperatures as determined by microscopic observation~
Iso.(isotropic phase) ~ Ch.(cholesteric phase) 75C~ SmA (smectic A phase) 50C' SmC below 0C
; Cry.(crystal phase) ; ~ '.. '' ', ~' 1 3 ~ 9 -13- ~
When the liquid crystal layer was formed in a :
sufficiently large thickness (about 100 ~), the SmC*
phase assumed a helical structure and the pitch was about 6 u.
In the present invention, in order to realize the parallel alignment state, it is desirable that at ,,:'' least one of the alignment films 5a and 5b comprises ; a polymer film having a polarity term ~YbP) of 20 dyne/cm or below, preferably 10 dyne/cm or below, ~: lO particularly preferably 7 dyne/cm or below.
According to our measurement, various polymer films usable as alignment films showed the following polarity terms~
Film speciesPolarity term,(YbP) -~
~:; 15 polyethylene2.6 dyne/cm ~ polyvinyl alcohol 3.3 dyne/cm ,;~:`
,~ Nylon 12 3.7 dyne~cm Nylon 11 5.0 dyne/cm .. '.. ;,.~;
: Nylon 2001 7.2 dyne/cm Nylon 3001 11.5 dyne/cm .
polyimide* 22.6 dyne/cm ~ ,,2 *The polymide film was formed by a dehydro~
ring closure reaction at 300C of a coating film of a~`'~,:"'`,`
` polyamic acid which was a dehydro-condensation product ,-', 25 Of pyromellitlc dianhydride and 4,4'-diaminodiphenyl,~,'!~"`'.' ether. ;,:, The above mentioned values of polarity terms,~";",::~
: - ' ';''''-'' : .~'.: .~ ' .~. !
-14 1 3 3 ~
are those measured according to a method described in Nippon Settyaku Kyokaishi (Journal of Adhesion Society of Japan) vol. 18, No. 3 (1972), pp. 131-141 under the conditions of a temperature of 20C and a relative humidity of 55 %. The B-series liquids (containing no hydrogen bonding component or dispersion component) were 5 species of methylene iodide, tetrabromoethane, ~ ~
a-bromonaphthalene, tricresyl phosphate, and hexa- ~-chlorobutadiene. The above values are respectively an average of measured values obtained with the five liquids. ~-; Further, the above prepared 100 ~-thick cell ; gave a spontaneous polarization of 10 nC (nano-Coulomb)/cm2 at 25C as measured by the triangular-15 wave application method (K. Miyasato et al., Japanese ~ ;
: , .
~ ~ Journal of Applied Physics 22 (10), p.p. 661-663 ~
~ :
(1983)i "Direct Method with Triangular Waves for Measuring Spontaneouà Polarization on Ferroelectric Liquid Crystal"?. There is a tendency that the 20~ lncrease~in~tilt~angle under the memory atate by the AC applicatlon according to the present invention may be easily accompllshed for a liquid crystal having a relatively large spontaneous polarization. For this reason, a ferroeIectrlc liquid cryatal having a spontaneous polarization at 25C of 5 nC/cm2 or larger, particularly 10 nC/cm2 - 300 nC/cm2, is suited for the present invention. The values, however, can vary ~: "~
':~ : ' .`'~
-15- ~ 3 ~ 9 depending on the kinds of the alignment films.
The preparation procedure of a ferroelectric liquid crystal cell 1 as shown in Figures 2 and 3 is ~ ;
supplemented hereinbelow.
First, a cell structure 1 containing the above mentioned biphenyl ester type liquid crystal is set in such a heating case (not shown) that the whole cell 1 is uniformly heated therein. When, the cell 1 is heated to a temperature (about 95C) where the liquid crystal in the cell assumes an isotropic phase. The temperature of the heating case is decreased whereby the liquid crystal in the cell 1 is subjected to a ` ~ temperature decreasing stage. In the temperature i`;
decreasing stage, the liquid crystal in the isotropic . i,. ... .
l5 phase is transformed at about 90C into a cholesteric , ``
phase having a grandjean texture and, on further ~ ``
cooling, transformed from the cholesteric phase to an ` ~
Sm~ phase which-is a uniaxially anisotropic phase at ~i about 75C. At this~time, the axes of the liquid `` '~
crystal molecules in the SmA phase are aligned in the rubbing direction.
Then, the liquid crystal in the SmA phase is `, transformed into an SmC* phase on further cooling, whereby a monodomain of SmC* phase with a non-spiral -~ 25 structure is formed if the cell~thickness is of the~ ~;
order of, for example, 3 ~m or less. ~ `~
Referring again to Figure 1, the figure is a ", `'`',,'','~' 1 ~ 3 ~
a schematic plan view illustrating the state of orien-tation of liquid crystal molecules as viewed from above the substrate face 15.
In the figure, the two-head arrow 10 indicates -S a direc'ion of a uniaxial orientation treatment, i.e., the direction of rubbing in this embodiment. In the SmA phase, liquid crystal molecules are oriented or aligned in an average molecular axis direction 11 which coincides with the rubbing direction 10. In the SmC*
phase, the average molecular axis direction of the :
liquid crystal molecules is tilted to a direction 12, so that~the rubbing direction 10 and the average molecular axis direction 12 forms an angle ~ to result in a first stable orientation state. When a voltage is applied between a pair of base plates in this stage, the average molecular axis direction of the liquid crystal molecules in the SmC* phase is changed to ~
saturation angle ~ larger than the angle ~, where ~' a third stable orlentation~state is attained. The average molecular~axis~direction at this tlme is denoted by a reference numeral 13. When the voltage ~-;;-` lS then réturned to zero, the liquid crystal molecules are returned to~the former first~molecular axis direction 12. Accordingly, the liquid crystal mole-?5 cules have-a memory characteristic in the state of ~`~
the first molecular axis direction 12. When a vol~age of the opposite polarity is applied in the state of ~ ^
, ,-:
.:
-17- 13314~3 ~ ~
the molecular axis direction 12 and the voltage is sufficiently high, the average molecular axis direc-tion of the liquid crystal molecules is shifted to :
and saturated at a fourth stable orientation state giving an average molecular axis direction 13a. Then, when the voltage is returned to zero, the liquid .'';,:
crystal molecules are returned to and settled at the second stable state giving the average molecular axis ~ ~
direction 12a. As a result, when the polarizing ~.
: l0 direction 14 of one polari~er is set in the same ' .:~
, . . ..
direction as the molecular axis direction 12 forming :-:
the angle ~, an optical contrast between an ON state and an OFF state can be improved in a driving method ~ utilizing an orientation between the first and second .;. .
;~ lS stable orientation states and the memory characteris~
tics. :.
The angle ~ is detected as an average of the :: :
molecular axes in one stable state, and a reason for ~;
~: the angle ~ being smaller than the angle ~ may be attributable to the fact that the liquid crystal ~ molecules are not aligned or oriented in completely :~ parallel with each other in an SmC* layer so that the :
average molecular axis orientation provides the angle . It is considered possible in principle to have : 25 the angle ~ be in concord with the angle ~
It is very effective to increase the value of ~ ; .
for the purpose of transmittance of a liquid crystal .
'' ' ' -18- 1331~
device. More specifically, in a liquid crystal device utilizing the birefringence of a liquid crystal, a transmittance with right angle cross nicols is deter-mined by the following equation: ~;
; 5 I/Io = sln24- sin2(~nd~
wherein Io denotes an incident light intensity, I a transmitted light intensity, ~ a tilt angle, ~n a , ~ , ~ refractive index anisotropy, d the thickness of a !~
: . :.
liquid crystal layerj and ~ the wavelength of an incident light. The above equation holds true with a case wherein one polarlzation axis of the rLght angle cross nicols is arranged to coincide with the average ; molecular axis direction in one stable state and the -transmittance is obtalned when the liquid crystal molecules are~re-oriented to the other stable state, wherein the liquid crystal molecules are aligned in completely parallel with the substrate faces. It has ;~
been also conflrmed, however, that the above equation ~ ;~
;20 also holds true with a~case wherein the molecular axis ~ ;~
` directions providing the angle ~ are nearly parallel with the substrate faces. As a result, the maximum -transmittance~ls~obtaiDed at the tilt angle ~ = 22.5~.
The measurement of the before mentioned ~, ~a ~ ~25 and ~ has been conducted ln the followlng manner.
`~ A pair of polarizers are disposed in right angle cross ~ nlcols to sandwlch a liquld crystal cell, A posltive : ~ ~ . '" :.. ..
-19- 'i"' ' ~
~ 3 3 ~
pulse exceeding the threshold voltage is applied across the cell, and the cross nicol polarizers are rotated - -~
with respect to the cell while retaining their relative :
positions to a position where the darkest state of the ~-cell is reached. Then, a negative polarity pulse exceeding the threshold voltage is applied to the cell, ~
and the cross nicol polarizers are again rotated until :
:" ~ " . .
the darkest state of the cell is again reached. The ;
rotation angles between the positions providing the 1~ two darkest states thus measured for the respective conditions correspond to twice the tilt angle ~, ~a and ~ . Further to say, the tilt angles 0 and 0a are those in the memory state, so that they are measured ;~
after removal of the pulse voltages. On the other hand, the tile angle ~ is measured while the pulse voltages are applied. Specific examples of actual ,-. ., ~ .
measurement are explained hereinbelow.
Example 1 -i~
Two cells havlng a cell thickness _ of 1.1 ~m and 1.8 ~m, respectlvely, were prepared by using a polyimide film having a polarity term (YbP) of 7.5 dyne/cm for both the alignment films Sa and 5b. The tilt angles B were respectively measured at 8.0 and 7.5 which are both below the optimum value. Then, two polarities of pulses respectively of DC 50 volts were applied to the cells (d = 1.1 ~m and d = 1.8 ~m), ;
whereby the tilt angle ~ were respectively measured .: . :
~" , :
-20- ~33~
at 23.1 and 24.0 which are close to the optimum value.
Further, switching between the bistable states was effected by using various magnitudes of voltage 5 pulses in combination with various pulse durations ~;
with respect to the two cells, whereby the following swiching voltages were obtained.
Table 1 ' , '' ' ~ ~
~ 10 Pulse duration (m.sec) 1.5 1.0 0.5 , .'~.
d = 1.1 (~m) 10.1 V10.1 V 10.1 V
_ , ,., d = 1.8 (~m) 14.0 V14.0 V 14.0 V
Further, various AC voltages in the ranges of ;
10 - 150 V and 20 - 100 Hz were applied to the cells, and after the removal of the voltages, the tilt angle a between the bistable states and the pulse duration w ltage characteristics of pulses for switching between~bistable~states were again examined.
When the AC voltages were applied for 10 ; seconds, the following results were obtained. The effective frequency range for increasing the tilt -- `
angle ~ was 30 - 40 Hz and no remarkable difference ~ `
25 in effectiveness was observed in this range. At the ;
frequency of 40 Hz, no remarkable difference in tilt angle Oa was observed in the range of 10 - 50 V, ~`~
,.. i", :: '~. . .'~. ' -21- 1 3 ~ 1 4 (~ 9 whereas in the range of 50 - 60 V, the domains of ~a = 21.0 and ~a = 18.8 began to appear for the all thickness of d = 1.1 ~m and d = 1.8 ~m, respectively.
Further, in the range of 60 - 150 V, the domains developed entirely to provide a very good contrast.
Over 150 V, however, the monodomains were disordered and other defects were also observed. ~`
Switching voltages after the application of the voltage of 60 - 150 V were as shown in the following Table 2 for switching between the bistable states giving the tilt angle ~a.
Table 2 Pulse duration [m.sec) 1.5 1.0 0.5 _ _ .,,~
d = 1.1 ~m) 14.6 V 16.1 V 18.6 V
:
d = 1.8 (~m) 16.9 V 17.4 V 21.1 V ;~
.
As is apparent from the above Table 2 in 20~comparison with Table 1, the parallel alignment state giving the tilt angle ~a required higher switching voltages than in the bistable state before the AC
voltage application. This is considered to be because the title angle ~a approached to ~ , so that it was necessary to apply an energy~for also inverting liquid crystal molecules in the vicinity of the alignment films to invite an inevitable increase in driving ~,',:~.:
~`
-22- ~ 3 3 ~
voltage for switching.
The transmittance given by the tilt angle 0a after the AC voltage application increased to 14 % for the cell thickness of d = 1.1 ~m and 19 % for d = 1.8 5 ~m, which were nearly three times the values before the AC application.
Example 2 ~ The procedure of Example 1 was repeated except -~ that polyvinyl films having a polarity term YbP of~ ;~
; - and by arranging a polarizer ln the specific axis direction to realize driving effectively utilizing ``
a memory characteristic.~
Figure 1 is a schematic view illustrating `~`
molecular orieutatlon states in a liquld crystal device according to the present invention. Figure 2 is a plan view of an example of a liquid crystal cell used `.'...~.~ ', ' ~ , ~ 3 ~ !
in the present invention and Figure 3 is a sectional view of the cell taken along the line III-III shown , -;
in Fiuure 2.
Referring to Figures 2 and 3, an LC cell 1 comprises a pair of substrates 3a and 3b of glass or a plastic, respectively provided thereon with stripe electrodes 4a and 4b of 1000 A-thick ITO (Indium Tin Oxide) stripe electrode films and further thereon with alignment films 5a and 5b of 10 A - 1 ~m, preferably L0 100 A - 5000 A, in thickness. Between the alignment . . , ~
films are disposed polyimide spacers of 1 ~-dot shape ; so as to retain the liquld crystal layer 2 in a constant thickness over a wide area. The above mentioned two substrates, after having been subjected to a rubbing treatment, are secured to each other to .. ~; : , ~, :. ::
form a cell into which the liquid crystal is then introduced.
Hereinbelow, an example wherein an ester type liquid crystal mixture was used is explained with reference to Figures 1 through 3. The ester-type mixture liquid crystal showed the following phase transition temperatures as determined by microscopic observation~
Iso.(isotropic phase) ~ Ch.(cholesteric phase) 75C~ SmA (smectic A phase) 50C' SmC below 0C
; Cry.(crystal phase) ; ~ '.. '' ', ~' 1 3 ~ 9 -13- ~
When the liquid crystal layer was formed in a :
sufficiently large thickness (about 100 ~), the SmC*
phase assumed a helical structure and the pitch was about 6 u.
In the present invention, in order to realize the parallel alignment state, it is desirable that at ,,:'' least one of the alignment films 5a and 5b comprises ; a polymer film having a polarity term ~YbP) of 20 dyne/cm or below, preferably 10 dyne/cm or below, ~: lO particularly preferably 7 dyne/cm or below.
According to our measurement, various polymer films usable as alignment films showed the following polarity terms~
Film speciesPolarity term,(YbP) -~
~:; 15 polyethylene2.6 dyne/cm ~ polyvinyl alcohol 3.3 dyne/cm ,;~:`
,~ Nylon 12 3.7 dyne~cm Nylon 11 5.0 dyne/cm .. '.. ;,.~;
: Nylon 2001 7.2 dyne/cm Nylon 3001 11.5 dyne/cm .
polyimide* 22.6 dyne/cm ~ ,,2 *The polymide film was formed by a dehydro~
ring closure reaction at 300C of a coating film of a~`'~,:"'`,`
` polyamic acid which was a dehydro-condensation product ,-', 25 Of pyromellitlc dianhydride and 4,4'-diaminodiphenyl,~,'!~"`'.' ether. ;,:, The above mentioned values of polarity terms,~";",::~
: - ' ';''''-'' : .~'.: .~ ' .~. !
-14 1 3 3 ~
are those measured according to a method described in Nippon Settyaku Kyokaishi (Journal of Adhesion Society of Japan) vol. 18, No. 3 (1972), pp. 131-141 under the conditions of a temperature of 20C and a relative humidity of 55 %. The B-series liquids (containing no hydrogen bonding component or dispersion component) were 5 species of methylene iodide, tetrabromoethane, ~ ~
a-bromonaphthalene, tricresyl phosphate, and hexa- ~-chlorobutadiene. The above values are respectively an average of measured values obtained with the five liquids. ~-; Further, the above prepared 100 ~-thick cell ; gave a spontaneous polarization of 10 nC (nano-Coulomb)/cm2 at 25C as measured by the triangular-15 wave application method (K. Miyasato et al., Japanese ~ ;
: , .
~ ~ Journal of Applied Physics 22 (10), p.p. 661-663 ~
~ :
(1983)i "Direct Method with Triangular Waves for Measuring Spontaneouà Polarization on Ferroelectric Liquid Crystal"?. There is a tendency that the 20~ lncrease~in~tilt~angle under the memory atate by the AC applicatlon according to the present invention may be easily accompllshed for a liquid crystal having a relatively large spontaneous polarization. For this reason, a ferroeIectrlc liquid cryatal having a spontaneous polarization at 25C of 5 nC/cm2 or larger, particularly 10 nC/cm2 - 300 nC/cm2, is suited for the present invention. The values, however, can vary ~: "~
':~ : ' .`'~
-15- ~ 3 ~ 9 depending on the kinds of the alignment films.
The preparation procedure of a ferroelectric liquid crystal cell 1 as shown in Figures 2 and 3 is ~ ;
supplemented hereinbelow.
First, a cell structure 1 containing the above mentioned biphenyl ester type liquid crystal is set in such a heating case (not shown) that the whole cell 1 is uniformly heated therein. When, the cell 1 is heated to a temperature (about 95C) where the liquid crystal in the cell assumes an isotropic phase. The temperature of the heating case is decreased whereby the liquid crystal in the cell 1 is subjected to a ` ~ temperature decreasing stage. In the temperature i`;
decreasing stage, the liquid crystal in the isotropic . i,. ... .
l5 phase is transformed at about 90C into a cholesteric , ``
phase having a grandjean texture and, on further ~ ``
cooling, transformed from the cholesteric phase to an ` ~
Sm~ phase which-is a uniaxially anisotropic phase at ~i about 75C. At this~time, the axes of the liquid `` '~
crystal molecules in the SmA phase are aligned in the rubbing direction.
Then, the liquid crystal in the SmA phase is `, transformed into an SmC* phase on further cooling, whereby a monodomain of SmC* phase with a non-spiral -~ 25 structure is formed if the cell~thickness is of the~ ~;
order of, for example, 3 ~m or less. ~ `~
Referring again to Figure 1, the figure is a ", `'`',,'','~' 1 ~ 3 ~
a schematic plan view illustrating the state of orien-tation of liquid crystal molecules as viewed from above the substrate face 15.
In the figure, the two-head arrow 10 indicates -S a direc'ion of a uniaxial orientation treatment, i.e., the direction of rubbing in this embodiment. In the SmA phase, liquid crystal molecules are oriented or aligned in an average molecular axis direction 11 which coincides with the rubbing direction 10. In the SmC*
phase, the average molecular axis direction of the :
liquid crystal molecules is tilted to a direction 12, so that~the rubbing direction 10 and the average molecular axis direction 12 forms an angle ~ to result in a first stable orientation state. When a voltage is applied between a pair of base plates in this stage, the average molecular axis direction of the liquid crystal molecules in the SmC* phase is changed to ~
saturation angle ~ larger than the angle ~, where ~' a third stable orlentation~state is attained. The average molecular~axis~direction at this tlme is denoted by a reference numeral 13. When the voltage ~-;;-` lS then réturned to zero, the liquid crystal molecules are returned to~the former first~molecular axis direction 12. Accordingly, the liquid crystal mole-?5 cules have-a memory characteristic in the state of ~`~
the first molecular axis direction 12. When a vol~age of the opposite polarity is applied in the state of ~ ^
, ,-:
.:
-17- 13314~3 ~ ~
the molecular axis direction 12 and the voltage is sufficiently high, the average molecular axis direc-tion of the liquid crystal molecules is shifted to :
and saturated at a fourth stable orientation state giving an average molecular axis direction 13a. Then, when the voltage is returned to zero, the liquid .'';,:
crystal molecules are returned to and settled at the second stable state giving the average molecular axis ~ ~
direction 12a. As a result, when the polarizing ~.
: l0 direction 14 of one polari~er is set in the same ' .:~
, . . ..
direction as the molecular axis direction 12 forming :-:
the angle ~, an optical contrast between an ON state and an OFF state can be improved in a driving method ~ utilizing an orientation between the first and second .;. .
;~ lS stable orientation states and the memory characteris~
tics. :.
The angle ~ is detected as an average of the :: :
molecular axes in one stable state, and a reason for ~;
~: the angle ~ being smaller than the angle ~ may be attributable to the fact that the liquid crystal ~ molecules are not aligned or oriented in completely :~ parallel with each other in an SmC* layer so that the :
average molecular axis orientation provides the angle . It is considered possible in principle to have : 25 the angle ~ be in concord with the angle ~
It is very effective to increase the value of ~ ; .
for the purpose of transmittance of a liquid crystal .
'' ' ' -18- 1331~
device. More specifically, in a liquid crystal device utilizing the birefringence of a liquid crystal, a transmittance with right angle cross nicols is deter-mined by the following equation: ~;
; 5 I/Io = sln24- sin2(~nd~
wherein Io denotes an incident light intensity, I a transmitted light intensity, ~ a tilt angle, ~n a , ~ , ~ refractive index anisotropy, d the thickness of a !~
: . :.
liquid crystal layerj and ~ the wavelength of an incident light. The above equation holds true with a case wherein one polarlzation axis of the rLght angle cross nicols is arranged to coincide with the average ; molecular axis direction in one stable state and the -transmittance is obtalned when the liquid crystal molecules are~re-oriented to the other stable state, wherein the liquid crystal molecules are aligned in completely parallel with the substrate faces. It has ;~
been also conflrmed, however, that the above equation ~ ;~
;20 also holds true with a~case wherein the molecular axis ~ ;~
` directions providing the angle ~ are nearly parallel with the substrate faces. As a result, the maximum -transmittance~ls~obtaiDed at the tilt angle ~ = 22.5~.
The measurement of the before mentioned ~, ~a ~ ~25 and ~ has been conducted ln the followlng manner.
`~ A pair of polarizers are disposed in right angle cross ~ nlcols to sandwlch a liquld crystal cell, A posltive : ~ ~ . '" :.. ..
-19- 'i"' ' ~
~ 3 3 ~
pulse exceeding the threshold voltage is applied across the cell, and the cross nicol polarizers are rotated - -~
with respect to the cell while retaining their relative :
positions to a position where the darkest state of the ~-cell is reached. Then, a negative polarity pulse exceeding the threshold voltage is applied to the cell, ~
and the cross nicol polarizers are again rotated until :
:" ~ " . .
the darkest state of the cell is again reached. The ;
rotation angles between the positions providing the 1~ two darkest states thus measured for the respective conditions correspond to twice the tilt angle ~, ~a and ~ . Further to say, the tilt angles 0 and 0a are those in the memory state, so that they are measured ;~
after removal of the pulse voltages. On the other hand, the tile angle ~ is measured while the pulse voltages are applied. Specific examples of actual ,-. ., ~ .
measurement are explained hereinbelow.
Example 1 -i~
Two cells havlng a cell thickness _ of 1.1 ~m and 1.8 ~m, respectlvely, were prepared by using a polyimide film having a polarity term (YbP) of 7.5 dyne/cm for both the alignment films Sa and 5b. The tilt angles B were respectively measured at 8.0 and 7.5 which are both below the optimum value. Then, two polarities of pulses respectively of DC 50 volts were applied to the cells (d = 1.1 ~m and d = 1.8 ~m), ;
whereby the tilt angle ~ were respectively measured .: . :
~" , :
-20- ~33~
at 23.1 and 24.0 which are close to the optimum value.
Further, switching between the bistable states was effected by using various magnitudes of voltage 5 pulses in combination with various pulse durations ~;
with respect to the two cells, whereby the following swiching voltages were obtained.
Table 1 ' , '' ' ~ ~
~ 10 Pulse duration (m.sec) 1.5 1.0 0.5 , .'~.
d = 1.1 (~m) 10.1 V10.1 V 10.1 V
_ , ,., d = 1.8 (~m) 14.0 V14.0 V 14.0 V
Further, various AC voltages in the ranges of ;
10 - 150 V and 20 - 100 Hz were applied to the cells, and after the removal of the voltages, the tilt angle a between the bistable states and the pulse duration w ltage characteristics of pulses for switching between~bistable~states were again examined.
When the AC voltages were applied for 10 ; seconds, the following results were obtained. The effective frequency range for increasing the tilt -- `
angle ~ was 30 - 40 Hz and no remarkable difference ~ `
25 in effectiveness was observed in this range. At the ;
frequency of 40 Hz, no remarkable difference in tilt angle Oa was observed in the range of 10 - 50 V, ~`~
,.. i", :: '~. . .'~. ' -21- 1 3 ~ 1 4 (~ 9 whereas in the range of 50 - 60 V, the domains of ~a = 21.0 and ~a = 18.8 began to appear for the all thickness of d = 1.1 ~m and d = 1.8 ~m, respectively.
Further, in the range of 60 - 150 V, the domains developed entirely to provide a very good contrast.
Over 150 V, however, the monodomains were disordered and other defects were also observed. ~`
Switching voltages after the application of the voltage of 60 - 150 V were as shown in the following Table 2 for switching between the bistable states giving the tilt angle ~a.
Table 2 Pulse duration [m.sec) 1.5 1.0 0.5 _ _ .,,~
d = 1.1 ~m) 14.6 V 16.1 V 18.6 V
:
d = 1.8 (~m) 16.9 V 17.4 V 21.1 V ;~
.
As is apparent from the above Table 2 in 20~comparison with Table 1, the parallel alignment state giving the tilt angle ~a required higher switching voltages than in the bistable state before the AC
voltage application. This is considered to be because the title angle ~a approached to ~ , so that it was necessary to apply an energy~for also inverting liquid crystal molecules in the vicinity of the alignment films to invite an inevitable increase in driving ~,',:~.:
~`
-22- ~ 3 3 ~
voltage for switching.
The transmittance given by the tilt angle 0a after the AC voltage application increased to 14 % for the cell thickness of d = 1.1 ~m and 19 % for d = 1.8 5 ~m, which were nearly three times the values before the AC application.
Example 2 ~ The procedure of Example 1 was repeated except -~ that polyvinyl films having a polarity term YbP of~ ;~
3.3 dyne/cm were used in place of the polyimide films on the glass substrates and a cell thickness of d = 1.5 ~m was adopted. ~Basically similar results as follows were obtained.
; Effective AC`voltage: 45-70 V, 30-70 Hz AC applicatlon time: 5 - 20 seconds -Tllt angle~
Before AC voltage application B = 7.8 Durlng~DC voltage application ~ = 22.8 Aft~er~AC voltage application Ba = 21.6 ~;
20~ Switching voltages were as shown in the follow-ing Table 3.
Pulse duratlon (m.sec~) ¦ 1.5 ¦ 1.0 ¦ 0-5 ~, ~ :;
Voltage (V~ ~ 16.2 17.0 21.4 ~, -23- ~33~
The transmittance was 6 ~ before the AC voltage ;~
application and 18 ~, i.e., three times, after the application.
Example 3 "
As described hereinbefore, a ferroelectric liquid crystal phase having bistability is generally produced through temperature decrease from another ~ - ;
higher temperature phase. In this example, the cells ~ used in Examples 1 and 2 were cooled while applying ;~ lO thereto an AC electric field of 40 V and 50 Hz, whereby uniform monodomains of parallel alignment states were realized over a wide area.
Example 4 A cell which has been transformed into a ;~
parallel alignment state providing a high contrast due to application of an AC~electric field can return to an original low contrast state after standing for l;
several days. Accordingly, when a ferroelectric liquid crystal cell in a paralleL~alignment state providing ~a~tilt~angle ~a is used for a display device, iù is `, necessary and effective to~apply an AC voltage to the ~;
cell before use thereof or when the contrast is lowered , during use. Figure 4 is~a diagram for illustrating a peripheral circuit for the~above mentioned AC applica~
; 2`5 tion. Referrlng to Figure 4, transparent electrodes 41 and 42 formed on a pair of glass substrates for sandwiching a liquid crystal are disposed mutually at ~`
., :, .
~::; ~ . ., -I
~24- ~331~9 '::
right angles to form picture elements in the form of a matrix. These electrodes 41 and 42 are connected to driver circuits 43 and 44, respectively, for applying ., -, .: :.
voltages thereto. An AC voltage generator 45 is disposed selectively connectable to the electrodes 42. ;;~ -More specifically, the driver circuit 42 and ~
., :., ":
the AC voltage generator 45 are connected to the ,, ~
transparent electrodes through changeover switches 46. When the switches are closed to the driver cir- ~ -~
cuit 44, image display signals are supplied to the ~; electrodes 42, whereas when the switches are closed f~to the AC voltage generator 45, an AC voltage is s~imultaneously applied to all the electrodes 42. In this way, a ferroelectric liquid crystal is retained lS in the alignment state providing the tilt angle Oa in the present invention. `~
On the other hand, the driver circuit 43 `-supplies a constant voltage, e.g., O volt, to all the ~ -electrodes 41.
20 ~Example~5 ~ ;
`~`Figure 7 shows another example of circuit for ~ applying an AC voltage. Reference numerals 71 and 72 ? ` ~respèctively denote transparent electrodes disposed `mutually at right angles to form matrix picture elements and formed a pair of glass substrates sand~
wiching a liquid crystal. Numerals 73 and 74 respec~
tively denote clriver circuits for applying voltages ~, ..
,.: ., ~:::, -.
-25- ~ 3~
.
to the electrodes, and 75 an AC voltage generator.
Switches 76, 77, 78 and 79 are selectively turned ON and OFF as required for AC application.
When the picture elements are driven in a desired manner, the switches 76 and 77 are turned ON and the switches 78 and 79 are turnecl OFF.
~ Ihen an AC electric field is applied for realizing the parallel alignment state, the switches 76 and 77 are turned OFF, and the switches 78 and 79 l0 are turned ON. The switches 76 and 77 are turned OFF ~;
~ .:
in order to protect the driver circuits 73 and 74.
Figure 8 illustrates a circuit example for one electrcde line 71. Generally, the withstand voltage o~ a tran~
sistor is to a value of the order of a driving voltage.
: , ; l5 However, the AC voltage applied through a line 80 is required to be higher than an ordinary driving voltage.
For this reason, so as not apply a load exceed-ing the withstand voltage to transistors 81a and 81b, power supplies to the driver circuits~73 and 74 are `~
dLsconnected by means of one switch 76a among the ~` switched 76, whereby the driver circuits 73 and 74 are protected. ;
Examp~e 6 ; The liquid crystal apparatus used in Example 5 ~ 25 requires a rather complicated switching mechanism. In ;~ this example, in order to decrease the number of switches, a two-layer electrode structure is adopted. ~ :
: ~
133~l~s~ .
A sectional view for this arrangement is shown in Figure 9, in which numerals 90a and 90b denote transparent substrates such as glass plates, 91a and 91b matrix electrodes, and 92a ancl 92b whole area 5 electrodes covering the whole pic1:ure area. The whole ~
area electrodes 92a and 92b are insulated from the ~; , matrix electrodes 91a and 91b by insulating films 93a ~ ;
and 93b. The circuit arrangement of a liquid crystal device having the two-layer electrode structure is shown in Figure 10. The whole area electrodes 92a and 92b are disposed so as to sandwich the matrix ~ ;
electrodes 108 (combination of 91a and 91b). As in Example 5, at the time of driving, an AC application ; power~supply 102 is turned OFF and switches 103 and lS 104 are turned ON. At the time of AC application, the `, switches 103 and 104 are turned OFF and the AC power supply 102 is turned ON. The switches 103 and 104 have a~function of protecting driver circuits 105 and 106 from electrical damage and also a function of ~ ; 20 electrically floating the inner matrix electrodes 108 ;~ to effectively apply an AC field supplied from the whoIe area electrodes 92a and 92b outside the matrix `~
~; electrodes to the inner SmC* liquid crystal layer. "' `
Figure 11 shows a driver circuit for one line used in this example. In order that the electric field applied from the whole area electrodes 92a and `
92b outside the matrix electrodes 108 is effectively ;;~;~
1 3 ~ 9 ! :
applied to the liquid crystal layer, it is necessary to place the matrix electrodes 108 by a switch 104a. ~
According to this example, the drlver circuit ;
corresponding to the number of lines can be turned OFF
from the ground altogether by turning off the switch 104a, so that the swltching mechanism can be simpli-fied.
Example 7 According to a system as shown in Figure 12, ~ ~;
10 driver circuits 121 and 122 can be completely isolated from matrix electrodes 126 by switches 123 and 124, so ~-~
that the matrix electrodes are completely electrically floated at the time of applying a voltage to whole area electrodes. On the other hand, at the time of lS driving, the AC circuit 127 is turned OFF. According i to this circuit arrangement, the driver circuits can be protected from electrical damage when a high voltage AC application is required.
Examples 8 ~
: .
Example 1 was substantially repeated while the polyimide films on the glass substrates were respec~
` ! ... :
~ tively replaced by polyethylene films (Example 8), .,~ . , Nylon 12 films (Example 91, Nylon 11 films (Example 10) -~
; and polyimide films (Example 11), and the cell thick--.
25 nes5 d was set to 1.5 ~m. The tilt angles 0a for the ;~
respective celLs after an AC application of 70 V and ~
` 70 Hz for 20 seconds. The results are summarized in ~ , ; " :
1 3 3 ~
the following table.
Example Alignment film (YbP) Tilt angle ~a 8 polyethylene (2.6 dyne/cm) 20.0 ~: `
9 Nylon 2 (3.7 " ) 18.5 Nylon 11 (5.0 " ) 18.0 11 polyimide (22.6 " ) 8 :;~ Further, according to a p:referred embodiment .
~` of the present invention, there is provided a liquid crystal apparatus comprising: a liquid crystal device ~: lO comprising matrix electrodes including scanning signal lines and information signal lines spaced from and intersecting with each other, and a ferroelectric liquid crystal material disposed between the matrix :.
electrodes; a scanning signal side liquid crystal .
~ 15 driver circuit, and peripheral circuits thereof ;~; including a latch circuit and a shift register cir- -cuit; and an lnformation signal side liquid crystal ~ .
driver circuit and peripheral circuits including a .
latch circuit and a shift register circuit; wherein the llquid c~rystal drlver clrcuits, the latch circuits and the shift register circuits are respectively of the same structure cn the scanning signal side and the information signal side; and an alternating voltage is : simultaneously applied to all the picture elements ~'!`~`~'',`,'~'',,'.
: 25 from at least one of the driver circuits.
In this embcdiment, the` AC voltage for parallel ,~
,, , ., ~, ;, ~ alignment is provided as a combination of signals from .;;~.
~: ' . ,'.: . ' ~: ,, "'~:
,~ . . ,'.` ':
I
-29- 1 331~
the scanning signal side driver circuit and the infor-mation signal side driver circuit having the same wave height and frequency and reverse phases. After the AC voltage application for parallel alignment, display signals corresponding to given image signals are applied. ~ ~ ;
In this embodiment, the output stage transis-tors constituting the scanning signal side driver ~-, ~ ~
circuit and the information signal side driver circuit -10 are those having the same withstand voltage which is ~ ;
equal to or above the waveheight of the AC voltage for parallel alignment. -~
It is required that the AC voltage for parallel alignment is such that liquid crystal molecules can ,. . .
cause switching between bistable states while suffi~
ciently responding thereto. The voltage waveheight ~ -~
thereof strongly depends on the kinds of liquid crystal materiaI and alignment film used and the frequency, and ; may be adjusted to the same order as the waveheight of 2~0 pulse vo?tages for~switching.
; Driver circuits and peripheral circuits thereof -~
for a liquid crystal device in a matrix arrangement are made~symmetrical. In other words, so-called vertical units and horizontal units of these circuits are made , ~:
of the same construction. By this arrangement, one set of these may be used for the scanning signal l1nes !~
and the other may b4 used for the information signal ~ -:
:~ .
~ 3 3 ~
lines hy only changeover switching, so that the verti-cal writing and horizontal writing can be easily switched. Furthermore, by similarly connecting two - ~;
driver circuits to driving power supplies, it is possible to apply an AC voltage for parallel alignment from a driving power supply prior to writing pulses.
This embodiment is explained with reference to the drawings.
Figure 14 shows an electrode arrangement for ,.; :, a matrix display comprising scanning signal lines and information signal lines forming picture elements at ; respecti~e intersections, and an example of display formed at the picture elements.
In Figure 14, S1 - S5 denote scanning signal ~`:
lines and I1 - I5 denota display signal lines. It is assumed that the hatched picture elements correspond ; ~`:
to a "black" writing state and the white picture ~ -. ", ~ : ~
elements correspond to a "white" writing state.
Figure 13, especially at the display signal 20 application period, shows a timing chart for forming , `~
; i.. ;":
a display state shown in Figure 14 according to a line-sequential writing mode wherein the scanning . :,, .-~ .:
signal lines S1 - S5 are line-sequentially scanned - `
and the columns of the information signal line I1 and ~-25 I2 are alternately written in "white" and "black". In ~;
Figure 13, ~T denotes a writing pulse duration, and i~ ;~
it is assumed that a positive electric field is used ;~
; ,. . . ~
1 3 31~ ~ 9 ~; :
for writing "white" and a negative electric field is used for writing "black". It is also assumed that ~ .
writing pulses are those having a pulse durations of ~ :
~T and waveheights of +3Vo exceeding the threshold.
More specifically, Figure 13 corresponds to a ~ :
scheme wherein picture elements on a scanning signal line are first written in "white" and selected picture .
elements on the scanning line are then written in "black" (line clear-line writing), and the information lO signal includes a writing signal and an auxiliary ;
signal subsequent thereto for preventing a crosstalk caused by continuation of the same polarity of signals.
Immediately after energization of the driving circuits, as shown at the AC application period in lS Figure 13, AC voltages for parallel alignment are simaltaneously applied to all the scanning signal lines and the information signal lines with the same voltage heights V', with rectangular waves of the same fre~
quency, but:in antiphases. As a result, a rectangular ~`~
20 AC voltage of a waveheight 2V' is applied across the :~
substrates~
Thé AC voltage for parallel alignment is for transforming liquid crystal molecules from the twist -.~ .
state into the parallel state, and the waveheight and ;~
25 pulse duration thereof may be set to values respec- .". .
tively exceeding those of the writing pulses. In this .
example, a writing pulses of 1 msec and 10V was used, -32- l 3 3 whereas a rectangular AC voltage of 50 Hz and about 20 V (Vpp.) was applied for several seconds to realize `~
the parallel alignment state. ~
The liquid crystal material used herein was a ~ ;
ferroelectric liquid crystal composition comprising, as the major components, p-n-octy]oxybenzoic acid-p'- ; ;
(2-methylbutyloxy)phenyl ester ancl p-n-nonyloxybenzoic acid-p'-(2-methylbutyloxy)phenyl ester. The liquid ;, : .. -crystal cell was prepared by providing an alignment film of polyvinyl alcohol (PVA) on ITO pattern elec-trodes on a pair of glass substrates, followed by :-rubbing, and fixing to provide a cell thickness of about 1.5 ~m. Between the transparent electrodes and ~`
the alignment films, insulatlng films of SiO2 may be -15 inserted.
Figùre 15 shows a circuit arrangement for a ; liquid crystal apparatus according to the present ~ ~-invention. In Figure 15, the same circuit arrangement is used for both the scanning signal side and the . ;
information signal side, wherein reference numeral 156 denotes a Liquid crystal matrix panel, 157 an i information signal side driver circuit, 158 a scanning .,..,, ,, :
signal side driver circuit, 159 and 150 latch circuits, 151 and 152 S/R (shift register) circuits, 153 a driving power supply, 154 a driving voltage control circuit, and 155 an I/F ~lnterface). `
In operation, when a main switch (not shown) ` '`''~`', ~( =~
r~
-33- 1331~
is first turned on, an AC voltage of vs' is applied to all the scanning electrodes and an AC voltage of VI' of antiphases with Vs' is applied to all the information signal electrodes respectively at a pulse -duration of ~T', so that a rectangular AC voltage of VAc Vs' + VI' (peak-to-peak) is applied across the upper and lower substrates as an AC voltage for parallel alignment. After this AC voltage is applied ~ . ~ - . .
for a prescribed period to transform the liquid crystal molecules into a parallel alignment state, display driving signal voltages, i.e., a scanning , .
signal voltage of 3Vo and -2Vo and an information signal voltage of +V0 both having a pulse duration of ~ -T, are set by a driving voltage control circuit 154, -;
and a muItiplex driving is started depending on input ; signals DH.
Further, switching between the horizontal writing and the vertical writing may be easily effected by~changing switches SW 16 - 18 depending on a H/V -;-20 switching signal 160 to exchange the scanning signal ;~
side and the information signal side.
` ~ Figure~16 shows a circuit structure at the i final stage of the driver circuit 157 or 158 shown in Figure 15. Tr1 and Tr2 denote output stage transis-~` ~ 25 tors. Referring to the driving waveform shown in Figure 13, the withstand voltages Vc of the two output stage transistors are equally set to satisfy the ,: ,,:,:
~ " ~
r~
-34_ 1 3 3 ~
following relationship:
( S ~ VI ) ~ V0 Further, by appropriately selecting the liquid crystal material, the ]cind of the alignment film, and -the frequency of the AC voltage for parallel alignment, it is possible in this embodiment to satisfy the : ' ' '~ '.' " ', ,.
: following rela~ionship.
~ ~ ~ Vc > V' - VO. ' ''~.'':';'.. ' Anyway, as the two driver circuits 157 and 158 are equally connected to the driving power supply 153, an AC voltage for parallel alignment having a wave-height and a pulse duratlon equal to or larger than those of the writing pulses as shown in Figure 13 may be applied between V+ and V terminals shown in Figure ~ :~
lS 16 prior to the input of a display signal DH' shown in Figure 16 to accomplish the parallel alignment of the ~ .
liquid crystal.
According to another preferred embodiment of ;~
: the present invention, there is provided a liquid 20 crystal:apparatus comprising: a liquid crystal device ..
~: comprising matrix electrodes including scanning signal lines and information slgnal lines spaced from and intersecting with~each other~ and a liquid crystal .
material disposed between the matrix electrodes, each :
25 intersection of the scanning signal lines and the ~.
information signal lines in combination with the ~ :
:~ liquid crystal material disposed therebetween ~"'~..',' ~
" ~:
_35_ ~33~J~
constituting a picture element, a scanning signal side driver circuit, and an information signal side driver circuit; the liquid crystal apparatus being so con-structed that an alternating voltage is applied to the - -whole picture elements prior to application of display signals according to a multiplex driving scheme.
In this embodiment, the application of display : signals and the application of an AC voltage for parallel alignment are controlled by a common driving power supply circuit. The application of the AC
voltage for parallel alignment may be effected by selecting either of the two methods, one of which ~:
comprises applying the AC voltage from either one of the scanning signal side driver circuit and the infor- ;~
mation signaI side driver circuit and grounding the other side of:signal lines all together during the : AC voltage application period, and the other of which comprises AC voltages of mutually antiphases from the scanning signal~side driver circuit and the information signal~side driver circuit.~
The AC~voltage for parallel alignment may for . `
example be a rectangular waveform of alternating -~
: ~ ~ :: : :; :
polarities, the~voltage waveheight of which may be set to a value higher than the voltage of display ~`: 25 signals required for switching of the liquid crystal ~
;~ in the parallel alignment state. .~
Thus, according to this embodiment, liquid .- .-' ~ ': . . ~.':
1 3 3 1 4 ~ 9 -36- :
crystal driver circuits each connected to the scanning signal side and the information signal side are connected to a common driving po~wer circuit, and the display signal voltages and the AC voltaye for parallel alignment are applied from the driving power supply circuit. More specifically, prior to multiplex driving using display signals, an AC voltage of, e.g., rectan-gular pulses having desired waveheight and pulse duration is applied to preliminarily place the liquid ;~;~
crystal in a parallel alignment state, and then the , ~
liquid crystal driving for display is started.
Figure 17 shows an example of liquid crystal ~ -apparatus for supplying signal voltages as shown in --:
Figure 18.
~; l5In Figure 17, reference numeral 171 denotes ; an interface (I/F), 175 denotes a shift register (S/R~ -~
~, circuit, 176 a latch circuit, 177 an information signal side driver circuit, 178 a scanning signal side driver `~;
circuit, and 179 an LC matrix panel. A driving power 20 supply circuit 170~comprlses a driving power supply ; ~-170a and a driving voltage control circuit 170b.
~; In operation, when a main switch (not shown) `~
is first turned on, AC~voltages for parallel alignment -~
~; havlng waveheights Vs' and VI' and a pulse duration ~T' ~;
~` 25 are applied in mutually antiphases to all the scanning electrodes and the information signal electrodes, respectively, so that a rectangular AC voltage of `~: ''''`,'', `'`, ', ~
_37_ ~ 3 3 ~
VAc (peak-to-peak) = Vs' + VI' is applied across the upper and lower substrates. After this AC voltage is applied for a prescribed period to transform the liquid ~- ~
crystal molecules into a parallel alignment state, ~ ~ ;
dispaly driving signal voltages, i.e., a scanning signal voltage of 3Vo and -2Vo and an information `~
signal voltage of +V0 both having a pulse duration of ~T, are set by a driving voltage control circuit 15~
and a multiplex driving is started. The waveheights Vs', VII and the pulse duration ~T' of the AC voltage or~parallel alignment are larger than the waveheight 3Vol V0 and the pulse~duration ~T, respectively, of the writing pulses.
Figure 19 shows a circuit structure at the final stage of the driver~circult 177 or 178 shown in `
F~igure 17. Tr1~and Tr2 denote output stage transis-tors. The wlthstand voltages of the two transistors ; are~ equally set, so that the withstand voltage Vsc ln the scanning s~ignal~side driver circuit 178 will 20 sat~lsfy~Vsc~> Vs~an~d~ the withstand voltage VIc ln ` `
the lnformatlon slgnal side driver circult will ~ ~: s ; satisfy~;VIc ~> VI',~while referring to Figure 17.
Further, when the AC voltage for parallel allgnment is applied~from;~either one of the scanning ;~
25 ~signal side driver circuit 178 and the information signal~side drlver clrcuit 179, the following condi-t~ions may be set:
Vsc > 1/2VAC' VIC
and the information signal side electrodes are grounded during the period for applying thè AC voltage for parallel alignment, for example, when the AC voltage is supplied from the scanning signal side electrodes.
In this way, an AC voltage for parallel align~
ment which is a littIe lower than the withstand voltages Vsc and VIc of the output stage transistors -~
Tr1 and Tr2 shown ln Figure 19 may be applied between ~: .....
~; 10 V~ and V terminals shown in Figure 17 from the driving power supply circuit 170 prior to the multiplex driving using a display signal DH shown in the figure, thereby to accomplish the parallel alignment of the liquid crystal in advance.
lS In this embodiment, a driving power supply for providing display slgnals~and a power supply for providing an AC voItage for parallel alignment are made common. As shown in Flgure 20, however, separate power supplies may be disposed in combination with an approp-20 ~riate changeover switch 201, so that an AC power supply ;
; 170c is connected when the main switch is turned on, ;~
and the switch 201~is changed over to the driving power ; supply 170a after a prescribed period.
The AC voltage for parallel alignment may be set to a value exceeding the threshold voltage of a . .
. ~.. , ferroelectric liquid crystal used, preferably selected ~` from the range of 1~0 - 500 V, partioularly 20 - 500 V, .
_39_ ~ 331~
in terms of a peak-to-peak voltage, and the frequency thereof may be 0.1 Hz or above, preferably in the range of 20 Hz - 5 KHz. The period for application thereof may be 1 sec to 10 min, preferably 5 sec to 5 min. -The AC voltage may comprise continuous or -intermittent pulses.
More specifically, the pulse duration of the pulse voltage used in the above mentioned pulse voltage ; ~
application treatment may suitably be in the range of ~`
1 ~sec - 10 msec, particularly 10 ~sec - 1 msec.
; Further, the pulse spacing may suitably be in the range of 1 - 100 times~, particularly 2 - 50 times, the pulse ~ -duration.
The alternating voltage for pulse alignment 15 has been explained with rather simple AC voltage -c ;
signals but may comprise positive and negative com-ponents of unsymmetrical forms, i.e., with different waveheights (magnitudes) and pulse durations between `~
the positive and negative components or pulses.
20 ~ Some~descript~lon l5 added to describe the ~ ;
microscoplc lnternal structure of a chiral smectic -~ ~ ferroelectric liquid crystal layer. Figure 21 i5 a schematic view~of a section taken~along a smectic molecular layer extending perpendicularly to the substrates of a liquid ~rystal cell wherein the spiral structure has been released to establlsh a bistability condition in a twist alignment, and illustrates the '\ !`' ;;~`~ '. " .`.'~
_40_ ~ 3:3~
arrangement of C directors (molecular axes) 211 and corresponding spontaneous polarizations 212. The uppermost circles which correspond to the projection of a liquid crystal cone on the smectic molecular layer represent the states in the neighborhood of the upper substrate, while the lowermost circles .-: . , , represent the states in the neighborhood of the lower substrate. Referring to Figure 21, the state at (a) ~-provides an average spontaneous polarization 213a ;-~
directed downward, and the state at (b) provides an ; ;-average spontaneous polarization 213b directed upward.
As a result, by applying different directions of electric field to the liquld crystal layer, switching - between the states (a) and (b) is caused.
Figure 22 is a sahematic sectional view corre~
sponding to Figure 21 of a liquid crystal cell which is in an ideal parallel alignment state where no twisting of C directors 211 across the thickness of the liquid crystal cell is involved. The spontaneous polarization 211~ is upward in the state at (a) and ;;~
downward in the state at (b).
For the purpose of generalization, cases where C directors are somewhat tilted with respect to the substrate faces are shown in the figures. `~
. -~ 25 As described hereinabove, according to the ~
:, present invent:Lon, a high AC electric field is applied ~;
to a ferroelectric liquid crystal cell under bistability ~
- ., ~ : .
. :'`;
~33~
-41- :
condition, whereby the tilt angle under the bistability ~ :
condition after removal of the AC electric field is ~ ~:
enlarged to increase the contrast of the cell. Also by cooling the cell while applying the high AC electric ~ -field to establish a bistability state, a wide tilt :; : ..:
angle state is more uniformly obtained. Furthermore, ;~
by providing a ferroelectric liquid crystal apparatus ~.
; with a high AC electric field-application circuit which , '~
is applicable to the apparatus on use, an apparatus -: 10 which can resume a wide tilt angle state as desired may be obtained, so that a display apparatus or a .
shutter device rich in light transmittance and contrast and also having a high speed responsive characteristic, -: high picture element density and large area can be 15 realized.
" , ~
~ 20 ,~
~ 25 ,.::, ,.: ~ : ,: .:
';;.: . '~
; ,~: . .
, . i ~ , ' ',~
,, ,, :~
~`'''..,,.^.~',. ' ,,.,,,.. ' '
; Effective AC`voltage: 45-70 V, 30-70 Hz AC applicatlon time: 5 - 20 seconds -Tllt angle~
Before AC voltage application B = 7.8 Durlng~DC voltage application ~ = 22.8 Aft~er~AC voltage application Ba = 21.6 ~;
20~ Switching voltages were as shown in the follow-ing Table 3.
Pulse duratlon (m.sec~) ¦ 1.5 ¦ 1.0 ¦ 0-5 ~, ~ :;
Voltage (V~ ~ 16.2 17.0 21.4 ~, -23- ~33~
The transmittance was 6 ~ before the AC voltage ;~
application and 18 ~, i.e., three times, after the application.
Example 3 "
As described hereinbefore, a ferroelectric liquid crystal phase having bistability is generally produced through temperature decrease from another ~ - ;
higher temperature phase. In this example, the cells ~ used in Examples 1 and 2 were cooled while applying ;~ lO thereto an AC electric field of 40 V and 50 Hz, whereby uniform monodomains of parallel alignment states were realized over a wide area.
Example 4 A cell which has been transformed into a ;~
parallel alignment state providing a high contrast due to application of an AC~electric field can return to an original low contrast state after standing for l;
several days. Accordingly, when a ferroelectric liquid crystal cell in a paralleL~alignment state providing ~a~tilt~angle ~a is used for a display device, iù is `, necessary and effective to~apply an AC voltage to the ~;
cell before use thereof or when the contrast is lowered , during use. Figure 4 is~a diagram for illustrating a peripheral circuit for the~above mentioned AC applica~
; 2`5 tion. Referrlng to Figure 4, transparent electrodes 41 and 42 formed on a pair of glass substrates for sandwiching a liquid crystal are disposed mutually at ~`
., :, .
~::; ~ . ., -I
~24- ~331~9 '::
right angles to form picture elements in the form of a matrix. These electrodes 41 and 42 are connected to driver circuits 43 and 44, respectively, for applying ., -, .: :.
voltages thereto. An AC voltage generator 45 is disposed selectively connectable to the electrodes 42. ;;~ -More specifically, the driver circuit 42 and ~
., :., ":
the AC voltage generator 45 are connected to the ,, ~
transparent electrodes through changeover switches 46. When the switches are closed to the driver cir- ~ -~
cuit 44, image display signals are supplied to the ~; electrodes 42, whereas when the switches are closed f~to the AC voltage generator 45, an AC voltage is s~imultaneously applied to all the electrodes 42. In this way, a ferroelectric liquid crystal is retained lS in the alignment state providing the tilt angle Oa in the present invention. `~
On the other hand, the driver circuit 43 `-supplies a constant voltage, e.g., O volt, to all the ~ -electrodes 41.
20 ~Example~5 ~ ;
`~`Figure 7 shows another example of circuit for ~ applying an AC voltage. Reference numerals 71 and 72 ? ` ~respèctively denote transparent electrodes disposed `mutually at right angles to form matrix picture elements and formed a pair of glass substrates sand~
wiching a liquid crystal. Numerals 73 and 74 respec~
tively denote clriver circuits for applying voltages ~, ..
,.: ., ~:::, -.
-25- ~ 3~
.
to the electrodes, and 75 an AC voltage generator.
Switches 76, 77, 78 and 79 are selectively turned ON and OFF as required for AC application.
When the picture elements are driven in a desired manner, the switches 76 and 77 are turned ON and the switches 78 and 79 are turnecl OFF.
~ Ihen an AC electric field is applied for realizing the parallel alignment state, the switches 76 and 77 are turned OFF, and the switches 78 and 79 l0 are turned ON. The switches 76 and 77 are turned OFF ~;
~ .:
in order to protect the driver circuits 73 and 74.
Figure 8 illustrates a circuit example for one electrcde line 71. Generally, the withstand voltage o~ a tran~
sistor is to a value of the order of a driving voltage.
: , ; l5 However, the AC voltage applied through a line 80 is required to be higher than an ordinary driving voltage.
For this reason, so as not apply a load exceed-ing the withstand voltage to transistors 81a and 81b, power supplies to the driver circuits~73 and 74 are `~
dLsconnected by means of one switch 76a among the ~` switched 76, whereby the driver circuits 73 and 74 are protected. ;
Examp~e 6 ; The liquid crystal apparatus used in Example 5 ~ 25 requires a rather complicated switching mechanism. In ;~ this example, in order to decrease the number of switches, a two-layer electrode structure is adopted. ~ :
: ~
133~l~s~ .
A sectional view for this arrangement is shown in Figure 9, in which numerals 90a and 90b denote transparent substrates such as glass plates, 91a and 91b matrix electrodes, and 92a ancl 92b whole area 5 electrodes covering the whole pic1:ure area. The whole ~
area electrodes 92a and 92b are insulated from the ~; , matrix electrodes 91a and 91b by insulating films 93a ~ ;
and 93b. The circuit arrangement of a liquid crystal device having the two-layer electrode structure is shown in Figure 10. The whole area electrodes 92a and 92b are disposed so as to sandwich the matrix ~ ;
electrodes 108 (combination of 91a and 91b). As in Example 5, at the time of driving, an AC application ; power~supply 102 is turned OFF and switches 103 and lS 104 are turned ON. At the time of AC application, the `, switches 103 and 104 are turned OFF and the AC power supply 102 is turned ON. The switches 103 and 104 have a~function of protecting driver circuits 105 and 106 from electrical damage and also a function of ~ ; 20 electrically floating the inner matrix electrodes 108 ;~ to effectively apply an AC field supplied from the whoIe area electrodes 92a and 92b outside the matrix `~
~; electrodes to the inner SmC* liquid crystal layer. "' `
Figure 11 shows a driver circuit for one line used in this example. In order that the electric field applied from the whole area electrodes 92a and `
92b outside the matrix electrodes 108 is effectively ;;~;~
1 3 ~ 9 ! :
applied to the liquid crystal layer, it is necessary to place the matrix electrodes 108 by a switch 104a. ~
According to this example, the drlver circuit ;
corresponding to the number of lines can be turned OFF
from the ground altogether by turning off the switch 104a, so that the swltching mechanism can be simpli-fied.
Example 7 According to a system as shown in Figure 12, ~ ~;
10 driver circuits 121 and 122 can be completely isolated from matrix electrodes 126 by switches 123 and 124, so ~-~
that the matrix electrodes are completely electrically floated at the time of applying a voltage to whole area electrodes. On the other hand, at the time of lS driving, the AC circuit 127 is turned OFF. According i to this circuit arrangement, the driver circuits can be protected from electrical damage when a high voltage AC application is required.
Examples 8 ~
: .
Example 1 was substantially repeated while the polyimide films on the glass substrates were respec~
` ! ... :
~ tively replaced by polyethylene films (Example 8), .,~ . , Nylon 12 films (Example 91, Nylon 11 films (Example 10) -~
; and polyimide films (Example 11), and the cell thick--.
25 nes5 d was set to 1.5 ~m. The tilt angles 0a for the ;~
respective celLs after an AC application of 70 V and ~
` 70 Hz for 20 seconds. The results are summarized in ~ , ; " :
1 3 3 ~
the following table.
Example Alignment film (YbP) Tilt angle ~a 8 polyethylene (2.6 dyne/cm) 20.0 ~: `
9 Nylon 2 (3.7 " ) 18.5 Nylon 11 (5.0 " ) 18.0 11 polyimide (22.6 " ) 8 :;~ Further, according to a p:referred embodiment .
~` of the present invention, there is provided a liquid crystal apparatus comprising: a liquid crystal device ~: lO comprising matrix electrodes including scanning signal lines and information signal lines spaced from and intersecting with each other, and a ferroelectric liquid crystal material disposed between the matrix :.
electrodes; a scanning signal side liquid crystal .
~ 15 driver circuit, and peripheral circuits thereof ;~; including a latch circuit and a shift register cir- -cuit; and an lnformation signal side liquid crystal ~ .
driver circuit and peripheral circuits including a .
latch circuit and a shift register circuit; wherein the llquid c~rystal drlver clrcuits, the latch circuits and the shift register circuits are respectively of the same structure cn the scanning signal side and the information signal side; and an alternating voltage is : simultaneously applied to all the picture elements ~'!`~`~'',`,'~'',,'.
: 25 from at least one of the driver circuits.
In this embcdiment, the` AC voltage for parallel ,~
,, , ., ~, ;, ~ alignment is provided as a combination of signals from .;;~.
~: ' . ,'.: . ' ~: ,, "'~:
,~ . . ,'.` ':
I
-29- 1 331~
the scanning signal side driver circuit and the infor-mation signal side driver circuit having the same wave height and frequency and reverse phases. After the AC voltage application for parallel alignment, display signals corresponding to given image signals are applied. ~ ~ ;
In this embodiment, the output stage transis-tors constituting the scanning signal side driver ~-, ~ ~
circuit and the information signal side driver circuit -10 are those having the same withstand voltage which is ~ ;
equal to or above the waveheight of the AC voltage for parallel alignment. -~
It is required that the AC voltage for parallel alignment is such that liquid crystal molecules can ,. . .
cause switching between bistable states while suffi~
ciently responding thereto. The voltage waveheight ~ -~
thereof strongly depends on the kinds of liquid crystal materiaI and alignment film used and the frequency, and ; may be adjusted to the same order as the waveheight of 2~0 pulse vo?tages for~switching.
; Driver circuits and peripheral circuits thereof -~
for a liquid crystal device in a matrix arrangement are made~symmetrical. In other words, so-called vertical units and horizontal units of these circuits are made , ~:
of the same construction. By this arrangement, one set of these may be used for the scanning signal l1nes !~
and the other may b4 used for the information signal ~ -:
:~ .
~ 3 3 ~
lines hy only changeover switching, so that the verti-cal writing and horizontal writing can be easily switched. Furthermore, by similarly connecting two - ~;
driver circuits to driving power supplies, it is possible to apply an AC voltage for parallel alignment from a driving power supply prior to writing pulses.
This embodiment is explained with reference to the drawings.
Figure 14 shows an electrode arrangement for ,.; :, a matrix display comprising scanning signal lines and information signal lines forming picture elements at ; respecti~e intersections, and an example of display formed at the picture elements.
In Figure 14, S1 - S5 denote scanning signal ~`:
lines and I1 - I5 denota display signal lines. It is assumed that the hatched picture elements correspond ; ~`:
to a "black" writing state and the white picture ~ -. ", ~ : ~
elements correspond to a "white" writing state.
Figure 13, especially at the display signal 20 application period, shows a timing chart for forming , `~
; i.. ;":
a display state shown in Figure 14 according to a line-sequential writing mode wherein the scanning . :,, .-~ .:
signal lines S1 - S5 are line-sequentially scanned - `
and the columns of the information signal line I1 and ~-25 I2 are alternately written in "white" and "black". In ~;
Figure 13, ~T denotes a writing pulse duration, and i~ ;~
it is assumed that a positive electric field is used ;~
; ,. . . ~
1 3 31~ ~ 9 ~; :
for writing "white" and a negative electric field is used for writing "black". It is also assumed that ~ .
writing pulses are those having a pulse durations of ~ :
~T and waveheights of +3Vo exceeding the threshold.
More specifically, Figure 13 corresponds to a ~ :
scheme wherein picture elements on a scanning signal line are first written in "white" and selected picture .
elements on the scanning line are then written in "black" (line clear-line writing), and the information lO signal includes a writing signal and an auxiliary ;
signal subsequent thereto for preventing a crosstalk caused by continuation of the same polarity of signals.
Immediately after energization of the driving circuits, as shown at the AC application period in lS Figure 13, AC voltages for parallel alignment are simaltaneously applied to all the scanning signal lines and the information signal lines with the same voltage heights V', with rectangular waves of the same fre~
quency, but:in antiphases. As a result, a rectangular ~`~
20 AC voltage of a waveheight 2V' is applied across the :~
substrates~
Thé AC voltage for parallel alignment is for transforming liquid crystal molecules from the twist -.~ .
state into the parallel state, and the waveheight and ;~
25 pulse duration thereof may be set to values respec- .". .
tively exceeding those of the writing pulses. In this .
example, a writing pulses of 1 msec and 10V was used, -32- l 3 3 whereas a rectangular AC voltage of 50 Hz and about 20 V (Vpp.) was applied for several seconds to realize `~
the parallel alignment state. ~
The liquid crystal material used herein was a ~ ;
ferroelectric liquid crystal composition comprising, as the major components, p-n-octy]oxybenzoic acid-p'- ; ;
(2-methylbutyloxy)phenyl ester ancl p-n-nonyloxybenzoic acid-p'-(2-methylbutyloxy)phenyl ester. The liquid ;, : .. -crystal cell was prepared by providing an alignment film of polyvinyl alcohol (PVA) on ITO pattern elec-trodes on a pair of glass substrates, followed by :-rubbing, and fixing to provide a cell thickness of about 1.5 ~m. Between the transparent electrodes and ~`
the alignment films, insulatlng films of SiO2 may be -15 inserted.
Figùre 15 shows a circuit arrangement for a ; liquid crystal apparatus according to the present ~ ~-invention. In Figure 15, the same circuit arrangement is used for both the scanning signal side and the . ;
information signal side, wherein reference numeral 156 denotes a Liquid crystal matrix panel, 157 an i information signal side driver circuit, 158 a scanning .,..,, ,, :
signal side driver circuit, 159 and 150 latch circuits, 151 and 152 S/R (shift register) circuits, 153 a driving power supply, 154 a driving voltage control circuit, and 155 an I/F ~lnterface). `
In operation, when a main switch (not shown) ` '`''~`', ~( =~
r~
-33- 1331~
is first turned on, an AC voltage of vs' is applied to all the scanning electrodes and an AC voltage of VI' of antiphases with Vs' is applied to all the information signal electrodes respectively at a pulse -duration of ~T', so that a rectangular AC voltage of VAc Vs' + VI' (peak-to-peak) is applied across the upper and lower substrates as an AC voltage for parallel alignment. After this AC voltage is applied ~ . ~ - . .
for a prescribed period to transform the liquid crystal molecules into a parallel alignment state, display driving signal voltages, i.e., a scanning , .
signal voltage of 3Vo and -2Vo and an information signal voltage of +V0 both having a pulse duration of ~ -T, are set by a driving voltage control circuit 154, -;
and a muItiplex driving is started depending on input ; signals DH.
Further, switching between the horizontal writing and the vertical writing may be easily effected by~changing switches SW 16 - 18 depending on a H/V -;-20 switching signal 160 to exchange the scanning signal ;~
side and the information signal side.
` ~ Figure~16 shows a circuit structure at the i final stage of the driver circuit 157 or 158 shown in Figure 15. Tr1 and Tr2 denote output stage transis-~` ~ 25 tors. Referring to the driving waveform shown in Figure 13, the withstand voltages Vc of the two output stage transistors are equally set to satisfy the ,: ,,:,:
~ " ~
r~
-34_ 1 3 3 ~
following relationship:
( S ~ VI ) ~ V0 Further, by appropriately selecting the liquid crystal material, the ]cind of the alignment film, and -the frequency of the AC voltage for parallel alignment, it is possible in this embodiment to satisfy the : ' ' '~ '.' " ', ,.
: following rela~ionship.
~ ~ ~ Vc > V' - VO. ' ''~.'':';'.. ' Anyway, as the two driver circuits 157 and 158 are equally connected to the driving power supply 153, an AC voltage for parallel alignment having a wave-height and a pulse duratlon equal to or larger than those of the writing pulses as shown in Figure 13 may be applied between V+ and V terminals shown in Figure ~ :~
lS 16 prior to the input of a display signal DH' shown in Figure 16 to accomplish the parallel alignment of the ~ .
liquid crystal.
According to another preferred embodiment of ;~
: the present invention, there is provided a liquid 20 crystal:apparatus comprising: a liquid crystal device ..
~: comprising matrix electrodes including scanning signal lines and information slgnal lines spaced from and intersecting with~each other~ and a liquid crystal .
material disposed between the matrix electrodes, each :
25 intersection of the scanning signal lines and the ~.
information signal lines in combination with the ~ :
:~ liquid crystal material disposed therebetween ~"'~..',' ~
" ~:
_35_ ~33~J~
constituting a picture element, a scanning signal side driver circuit, and an information signal side driver circuit; the liquid crystal apparatus being so con-structed that an alternating voltage is applied to the - -whole picture elements prior to application of display signals according to a multiplex driving scheme.
In this embodiment, the application of display : signals and the application of an AC voltage for parallel alignment are controlled by a common driving power supply circuit. The application of the AC
voltage for parallel alignment may be effected by selecting either of the two methods, one of which ~:
comprises applying the AC voltage from either one of the scanning signal side driver circuit and the infor- ;~
mation signaI side driver circuit and grounding the other side of:signal lines all together during the : AC voltage application period, and the other of which comprises AC voltages of mutually antiphases from the scanning signal~side driver circuit and the information signal~side driver circuit.~
The AC~voltage for parallel alignment may for . `
example be a rectangular waveform of alternating -~
: ~ ~ :: : :; :
polarities, the~voltage waveheight of which may be set to a value higher than the voltage of display ~`: 25 signals required for switching of the liquid crystal ~
;~ in the parallel alignment state. .~
Thus, according to this embodiment, liquid .- .-' ~ ': . . ~.':
1 3 3 1 4 ~ 9 -36- :
crystal driver circuits each connected to the scanning signal side and the information signal side are connected to a common driving po~wer circuit, and the display signal voltages and the AC voltaye for parallel alignment are applied from the driving power supply circuit. More specifically, prior to multiplex driving using display signals, an AC voltage of, e.g., rectan-gular pulses having desired waveheight and pulse duration is applied to preliminarily place the liquid ;~;~
crystal in a parallel alignment state, and then the , ~
liquid crystal driving for display is started.
Figure 17 shows an example of liquid crystal ~ -apparatus for supplying signal voltages as shown in --:
Figure 18.
~; l5In Figure 17, reference numeral 171 denotes ; an interface (I/F), 175 denotes a shift register (S/R~ -~
~, circuit, 176 a latch circuit, 177 an information signal side driver circuit, 178 a scanning signal side driver `~;
circuit, and 179 an LC matrix panel. A driving power 20 supply circuit 170~comprlses a driving power supply ; ~-170a and a driving voltage control circuit 170b.
~; In operation, when a main switch (not shown) `~
is first turned on, AC~voltages for parallel alignment -~
~; havlng waveheights Vs' and VI' and a pulse duration ~T' ~;
~` 25 are applied in mutually antiphases to all the scanning electrodes and the information signal electrodes, respectively, so that a rectangular AC voltage of `~: ''''`,'', `'`, ', ~
_37_ ~ 3 3 ~
VAc (peak-to-peak) = Vs' + VI' is applied across the upper and lower substrates. After this AC voltage is applied for a prescribed period to transform the liquid ~- ~
crystal molecules into a parallel alignment state, ~ ~ ;
dispaly driving signal voltages, i.e., a scanning signal voltage of 3Vo and -2Vo and an information `~
signal voltage of +V0 both having a pulse duration of ~T, are set by a driving voltage control circuit 15~
and a multiplex driving is started. The waveheights Vs', VII and the pulse duration ~T' of the AC voltage or~parallel alignment are larger than the waveheight 3Vol V0 and the pulse~duration ~T, respectively, of the writing pulses.
Figure 19 shows a circuit structure at the final stage of the driver~circult 177 or 178 shown in `
F~igure 17. Tr1~and Tr2 denote output stage transis-tors. The wlthstand voltages of the two transistors ; are~ equally set, so that the withstand voltage Vsc ln the scanning s~ignal~side driver circuit 178 will 20 sat~lsfy~Vsc~> Vs~an~d~ the withstand voltage VIc ln ` `
the lnformatlon slgnal side driver circult will ~ ~: s ; satisfy~;VIc ~> VI',~while referring to Figure 17.
Further, when the AC voltage for parallel allgnment is applied~from;~either one of the scanning ;~
25 ~signal side driver circuit 178 and the information signal~side drlver clrcuit 179, the following condi-t~ions may be set:
Vsc > 1/2VAC' VIC
and the information signal side electrodes are grounded during the period for applying thè AC voltage for parallel alignment, for example, when the AC voltage is supplied from the scanning signal side electrodes.
In this way, an AC voltage for parallel align~
ment which is a littIe lower than the withstand voltages Vsc and VIc of the output stage transistors -~
Tr1 and Tr2 shown ln Figure 19 may be applied between ~: .....
~; 10 V~ and V terminals shown in Figure 17 from the driving power supply circuit 170 prior to the multiplex driving using a display signal DH shown in the figure, thereby to accomplish the parallel alignment of the liquid crystal in advance.
lS In this embodiment, a driving power supply for providing display slgnals~and a power supply for providing an AC voItage for parallel alignment are made common. As shown in Flgure 20, however, separate power supplies may be disposed in combination with an approp-20 ~riate changeover switch 201, so that an AC power supply ;
; 170c is connected when the main switch is turned on, ;~
and the switch 201~is changed over to the driving power ; supply 170a after a prescribed period.
The AC voltage for parallel alignment may be set to a value exceeding the threshold voltage of a . .
. ~.. , ferroelectric liquid crystal used, preferably selected ~` from the range of 1~0 - 500 V, partioularly 20 - 500 V, .
_39_ ~ 331~
in terms of a peak-to-peak voltage, and the frequency thereof may be 0.1 Hz or above, preferably in the range of 20 Hz - 5 KHz. The period for application thereof may be 1 sec to 10 min, preferably 5 sec to 5 min. -The AC voltage may comprise continuous or -intermittent pulses.
More specifically, the pulse duration of the pulse voltage used in the above mentioned pulse voltage ; ~
application treatment may suitably be in the range of ~`
1 ~sec - 10 msec, particularly 10 ~sec - 1 msec.
; Further, the pulse spacing may suitably be in the range of 1 - 100 times~, particularly 2 - 50 times, the pulse ~ -duration.
The alternating voltage for pulse alignment 15 has been explained with rather simple AC voltage -c ;
signals but may comprise positive and negative com-ponents of unsymmetrical forms, i.e., with different waveheights (magnitudes) and pulse durations between `~
the positive and negative components or pulses.
20 ~ Some~descript~lon l5 added to describe the ~ ;
microscoplc lnternal structure of a chiral smectic -~ ~ ferroelectric liquid crystal layer. Figure 21 i5 a schematic view~of a section taken~along a smectic molecular layer extending perpendicularly to the substrates of a liquid ~rystal cell wherein the spiral structure has been released to establlsh a bistability condition in a twist alignment, and illustrates the '\ !`' ;;~`~ '. " .`.'~
_40_ ~ 3:3~
arrangement of C directors (molecular axes) 211 and corresponding spontaneous polarizations 212. The uppermost circles which correspond to the projection of a liquid crystal cone on the smectic molecular layer represent the states in the neighborhood of the upper substrate, while the lowermost circles .-: . , , represent the states in the neighborhood of the lower substrate. Referring to Figure 21, the state at (a) ~-provides an average spontaneous polarization 213a ;-~
directed downward, and the state at (b) provides an ; ;-average spontaneous polarization 213b directed upward.
As a result, by applying different directions of electric field to the liquld crystal layer, switching - between the states (a) and (b) is caused.
Figure 22 is a sahematic sectional view corre~
sponding to Figure 21 of a liquid crystal cell which is in an ideal parallel alignment state where no twisting of C directors 211 across the thickness of the liquid crystal cell is involved. The spontaneous polarization 211~ is upward in the state at (a) and ;;~
downward in the state at (b).
For the purpose of generalization, cases where C directors are somewhat tilted with respect to the substrate faces are shown in the figures. `~
. -~ 25 As described hereinabove, according to the ~
:, present invent:Lon, a high AC electric field is applied ~;
to a ferroelectric liquid crystal cell under bistability ~
- ., ~ : .
. :'`;
~33~
-41- :
condition, whereby the tilt angle under the bistability ~ :
condition after removal of the AC electric field is ~ ~:
enlarged to increase the contrast of the cell. Also by cooling the cell while applying the high AC electric ~ -field to establish a bistability state, a wide tilt :; : ..:
angle state is more uniformly obtained. Furthermore, ;~
by providing a ferroelectric liquid crystal apparatus ~.
; with a high AC electric field-application circuit which , '~
is applicable to the apparatus on use, an apparatus -: 10 which can resume a wide tilt angle state as desired may be obtained, so that a display apparatus or a .
shutter device rich in light transmittance and contrast and also having a high speed responsive characteristic, -: high picture element density and large area can be 15 realized.
" , ~
~ 20 ,~
~ 25 ,.::, ,.: ~ : ,: .:
';;.: . '~
; ,~: . .
, . i ~ , ' ',~
,, ,, :~
~`'''..,,.^.~',. ' ,,.,,,.. ' '
Claims (6)
1. A liquid crystal apparatus comprising:
a ferroelectric liquid crystal device matrix having electrodes, including scanning electrodes and signal electrodes spaced from and intersecting with each other, and a ferroelectric liquid crystal disposed between the scanning electrodes and the signal electrodes, a driving circuit for applying a driving voltage selectively to the intersections of the scanning electrodes and the signal electrodes, and a uniform electric field application circuit for applying an alternating electric field to all or a prescribed part of the intersections before the application of said driving voltage; said ferroelectric liquid crystal providing two average molecular directions forming an angle 2.theta.a therebetween in the absence of an electric field after application of an alternating electric field, said angle 2.theta.a being larger than an angle
a ferroelectric liquid crystal device matrix having electrodes, including scanning electrodes and signal electrodes spaced from and intersecting with each other, and a ferroelectric liquid crystal disposed between the scanning electrodes and the signal electrodes, a driving circuit for applying a driving voltage selectively to the intersections of the scanning electrodes and the signal electrodes, and a uniform electric field application circuit for applying an alternating electric field to all or a prescribed part of the intersections before the application of said driving voltage; said ferroelectric liquid crystal providing two average molecular directions forming an angle 2.theta.a therebetween in the absence of an electric field after application of an alternating electric field, said angle 2.theta.a being larger than an angle
2.theta. formed between two average molecular directions of the ferroelectric liquid crystal in the absence of an electric field before application of the alternating electric field.
2. A liquid crystal apparatus according to claim 1, wherein said driving voltage and said alternating voltage are separately applied to the matrix electrodes.
2. A liquid crystal apparatus according to claim 1, wherein said driving voltage and said alternating voltage are separately applied to the matrix electrodes.
3. A liquid crystal apparatus according to claim 1, wherein said ferroelectric liquid crystal comprising a pair of uniformly extending electrodes each being isolated from the matrix electrodes and extending over the whole intersections, the driving voltage is applied between the matrix electrodes from the driving circuit, and the alternating voltage is applied between the pair of uniformly extending electrodes.
4. A liquid crystal apparatus according to claim 3, wherein said matrix electrodes are floated while the alternating voltage is applied from the uniform electric field application circuit.
5. A liquid crystal apparatus according to claim 4, wherein said ferroelectric liquid crystal is formed in a layer having thickness thin enough to release the spiral structure of the ferroelectric liquid crystal.
6. A liquid crystal apparatus according to claim 5, wherein said ferroelectric liquid crystal is a chiral smectic liquid crystal.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000615536A CA1331409C (en) | 1985-10-03 | 1989-10-23 | Ferroelectric liquid crystal device |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP220755/1985 | 1985-10-03 | ||
| JP22075585A JPS6279427A (en) | 1985-10-03 | 1985-10-03 | Liquid crystal device |
| CA516944 | 1986-08-27 | ||
| CA000615536A CA1331409C (en) | 1985-10-03 | 1989-10-23 | Ferroelectric liquid crystal device |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000615536A Division CA1331409C (en) | 1985-10-03 | 1989-10-23 | Ferroelectric liquid crystal device |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000615536A Division CA1331409C (en) | 1985-10-03 | 1989-10-23 | Ferroelectric liquid crystal device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1331409C true CA1331409C (en) | 1994-08-09 |
Family
ID=25671081
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000615536A Expired - Fee Related CA1331409C (en) | 1985-10-03 | 1989-10-23 | Ferroelectric liquid crystal device |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1331409C (en) |
-
1989
- 1989-10-23 CA CA000615536A patent/CA1331409C/en not_active Expired - Fee Related
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US5013137A (en) | Ferroelectric liquid crystal device having increased tilt angle | |
| US4902107A (en) | Ferroelectric liquid crystal optical device having temperature compensation | |
| US4738515A (en) | Driving method for liquid crystal device | |
| US4712877A (en) | Ferroelectric display panel of varying thickness and driving method therefor | |
| US4941736A (en) | Ferroelectric liquid crystal device and driving method therefor | |
| EP0529701B1 (en) | Display device | |
| EP0177365B1 (en) | Liquid crystal device for time-division driving | |
| US5500749A (en) | Ferroelectric liquid crystal element with an AC holding voltage below the level at which the molecules migrate | |
| US4898456A (en) | Liquid crystal optical device | |
| CA1279918C (en) | Ferroelectric liquid crystal device | |
| EP0542518A2 (en) | Liquid crystal element and driving method thereof | |
| US4770501A (en) | Optical modulation device and method of driving the same | |
| JPS61249024A (en) | Liquid crystal optical element | |
| US4707078A (en) | Ferroelectric liquid crystal devices using field-stabilized states | |
| DE69216548D1 (en) | Liquid crystal device and display device | |
| CA1317386C (en) | Ferroelectric liquid crystal device | |
| CA1317387C (en) | Ferroelectric liquid crystal device | |
| CA1331409C (en) | Ferroelectric liquid crystal device | |
| JPS61249025A (en) | Liquid crystal optical element | |
| US5109291A (en) | Ferroelectric liquid crystal optical modulation device having non-pixel portions controlled to a predetermined orientation state | |
| JPH0422487B2 (en) | ||
| JPH0422489B2 (en) | ||
| Sako et al. | Switching behavior of surface stabilized ferroelectric liquid crystals induced by pulse voltages | |
| US5016989A (en) | Liquid crystal element with improved contrast and brightness | |
| JPH0422488B2 (en) |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |