JP2002049060A - Chiral smectic liquid crystal element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chiral smectic liquid crystal element with high contrast. SOLUTION: The chiral smectic liquid crystal element is provided with a chiral smectic liquid crystal, a pair of electrodes applying voltage to the liquid crystal, a pair of substrates holding the liquid crystal in between and placed opposite to each other and a polarizing plate on at least one out of the substrates. Furthermore, alignment controlling layers arranged on the substrates are formed by an oblique vapor deposition method an alignment direction of a liquid crystal long molecular axis in the smectic liquid crystal phase and a vopor deposition direction are almost perpendicularly intersecting and an angle between columns formed in the vapor deposition and the substrates is <=70 deg.. A phase transition sequence of the chiral smectic liquid crystal is an isotropic liquid phase-a cholesteric phase-a chiral smectic C phase or an isotropic liquid phase-a chiral smectic C phase from the higher temperature side. At least one out of the substrates is provided with active elements connected to electrodes corresponding to respective pixels.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chiral smectic liquid crystal device used for a light valve used in a flat panel display, a projection display, a printer and the like.

[0002]

2. Description of the Related Art Conventionally, a TFT (Thin Film T)
Representative liquid crystal modes of a nematic liquid crystal display element widely used as a display element using an active element such as a ransistor are, for example, “M. Schadt” and “W. Helfrich”. Applied Phys
sics Letters "Vol. 18, No. 4 (197
Twisted Nmatic (Twisted N) shown on pages 127 to 128
e) mode is widely used. On the other hand, recently, a liquid crystal display using an in-plane switching (In-Plane Switching) mode using a lateral electric field and a vertical alignment (Vertical Alignment) mode has been announced. The angular characteristics have been improved. As described above, there are several liquid crystal modes for use in a TFT display element using such a nematic liquid crystal. In any of these modes, the response speed of the liquid crystal is several tens of milliseconds or more. Slow, further improvement in response speed is required.

In order to improve the response speed of such a conventional nematic liquid crystal device, recently, several liquid crystal modes using a liquid crystal exhibiting a chiral smectic phase have been proposed. For example, "short-pitch type ferroelectric liquid crystal", "polymer stable ferroelectric liquid crystal", "thresholdless antiferroelectric liquid crystal" and the like have been proposed, but although not yet commercialized, It is also reported that high-speed response of sub-millisecond or less can be realized.

On the other hand, the present inventors have disclosed Japanese Patent Application Laid-Open No. 2000-338.
Patent No. 464 (hereinafter referred to as "prior application 1") has been invented and proposed. In the present invention, for example,
From the high temperature side, isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase (SmC ^* ) or isotropic liquid phase (ISO.)-Chiral smectic C
Attention is paid to a phase-series material showing a phase (SmC ^* ), and monostabilization is performed at a position inside the edge of the virtual cone. Then, for example, a positive or negative DC voltage is applied between the pair of substrates at the time of the Ch-SmC ^* phase transition or at the time of the isotropic phase-SmC ^* phase transition, so that the layer direction is made uniform in one direction. Accordingly, a high-speed response and gradation control can be performed, and a high-brightness liquid crystal element excellent in moving image quality can be realized with high mass productivity. Since the element of the prior application can reduce the spontaneous polarization value as compared with the above-mentioned various smectic liquid crystal modes, it is an element having good matching with an active element such as a TFT.

[0005] Similarly, we have disclosed in JP-A-2000-01007.
No. 6 (hereinafter referred to as “prior application 2”) has been invented and proposed. In the present invention, for example, from the high temperature side, isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase (SmC ^* ) or isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC) ^* ) Focusing on the phase-series material indicated by ⁽ ), monostabilization is performed at the position of the virtual cone edge. And, for example, at the time of Ch-SmC ^* phase transition or isotropic phase -S
either positive or negative DC between a pair of substrates during mC ^* phase transition
By applying a voltage, the layer direction is made uniform in one direction, whereby high-speed response and gradation control are possible.
A high-brightness liquid crystal element with excellent moving image quality can be realized with high mass productivity. The element of the prior application 2 has a small hysteresis, can realize a stable halftone display, and can reduce the spontaneous polarization value as compared with other various smectic liquid crystal modes described above. Is a good element.

As described above, a chiral smectic liquid crystal, in particular, a liquid crystal element using the liquid crystal elements of the prior applications 1 and 2 is used in the sense that the problem relating to the response speed of the TFT liquid crystal display using the nematic liquid crystal can be solved. The realization of liquid crystal display elements is expected.

[0007]

As described above, a smectic liquid crystal element as described in the prior application, which has a gradation display capability in a next-generation display or the like such as a high-speed response performance, is expected. However, when alignment control is performed using rubbing represented by polyimide, there is a serious problem that a streak caused by rubbing becomes a problem and the contrast deteriorates.

The present invention has been made to solve such problems of the prior art, and provides a chiral smectic liquid crystal element which can be easily formed and has a high contrast by using an oblique evaporation method. The purpose is to do so.

[0009]

That is, the present invention provides a chiral smectic liquid crystal, a pair of electrodes for applying a voltage to the liquid crystal, a pair of substrates opposed to each other with the liquid crystal interposed therebetween, and at least one of the substrates. A polarizing plate is provided, and the orientation control layer provided on the substrate is formed by oblique deposition, and the deposition direction is substantially orthogonal to the long-axis alignment direction of the liquid crystal molecules in the smectic liquid crystal phase. A liquid crystal device wherein the angle between the column and the substrate to be formed is 70 ° or less, wherein the phase transition series of the chiral smectic liquid crystal is isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic from a high temperature side. C phase (SmC ^* ) or isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC ^* )
Wherein at least one of the substrates has an active element connected to an electrode corresponding to each pixel, which is a chiral smectic liquid crystal element.

In the liquid crystal device of the present invention, when no voltage is applied, the average molecular axis of the liquid crystal shows a first state in which the average molecular axis is monostable, and when a voltage of the first polarity is applied, the average molecular axis of the liquid crystal becomes The tilt is tilted to one side from the mono-stabilized position at an angle corresponding to the magnitude of the applied voltage, and when a voltage having a second polarity opposite to the first polarity is applied, the average molecular axis of the liquid crystal is A liquid crystal element that tilts from the mono-stabilized position in a direction opposite to a direction in which a voltage of the first polarity is applied, and a liquid crystal element in which a voltage of the first polarity is applied and a liquid crystal in which the voltage of the second polarity is applied. It is preferable that β ₁ > β ₂ where β ₁ and β ₂ are the tilt angles in the maximum tilt state with reference to the mono-stabilized position of the average molecular axis in the first state in the first state.

The tilt in the maximum tilt state based on the mono-stabilized position in the first state of the average molecular axis of the liquid crystal when the voltage of the first polarity is applied and when the voltage of the second polarity is applied. Β ₁ and β ₂ respectively, β ₁ > 5
× β ₂ is preferred.

Further, when no voltage is applied, the average molecular axis of the liquid crystal shows a first state in which the average molecular axis is monostable, and when a voltage of the first polarity is applied, the average molecular axis of the liquid crystal becomes smaller than the magnitude of the applied voltage. When tilted to one side from the mono-stabilized position at an appropriate angle, and when a voltage of a second polarity having a polarity opposite to the first polarity is applied, the average molecular axis of the liquid crystal is mono-stabilized. It is preferable that the liquid crystal element does not substantially change from the position.

The helical pitch of the chiral smectic liquid crystal in a bulk state is preferably a liquid crystal element longer than twice the cell thickness.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The above object of the present invention is solved by the present invention described below.

That is, the first of the present invention is chiral smectic
A liquid crystal, a pair of electrodes for applying a voltage to the liquid crystal,
An alignment control layer is formed by using a pair of substrates opposed to each other while sandwiching a liquid crystal.
Is formed by oblique evaporation and the liquid in the smectic liquid crystal phase is
The deposition direction is almost perpendicular to the uniaxial direction of the crystal molecules
The angle between the column and the substrate formed during evaporation is
70 ° or less, and a polarizing plate on at least one of the substrates.
A liquid crystal device comprising the chiral smectic liquid
The phase transition series of the crystal is isotropic liquid phase (IS
O. ) -Cholesteric phase (Ch) -Chiral smectic
Check C phase (SmC ^*) Or isotropic liquid phase (ISO.)-
Chiral smectic C phase (SmC^*) Wherein said
At least one of the substrates used for the liquid crystal element corresponds to each pixel
Having an active element connected to the
This is a chiral smectic liquid crystal element.

Also, the chiral smectic liquid crystal device
Means that the average molecular axis of the liquid crystal is monostable when no voltage is applied.
Indicates a first state, and when a voltage of the first polarity is applied,
The average molecular axis of the liquid crystal is at an angle corresponding to the magnitude of the applied voltage.
Tilt to one side from the mono-stabilized position,
When a voltage having a second polarity opposite to the polarity of
The average molecular axis of the crystal is the first polarity from the monostabilized position.
Liquid crystal element that tilts to the opposite side when the
There is a voltage of the first polarity and a voltage of the second polarity
Simple average of the average molecular axis of liquid crystal in the first state when applied
Of tilt in the maximum tilt state based on
Angle is β₁, Β_TwoAnd β ₁> Β_TwoLiquid
A crystal element, wherein β₁, Β_TwoIs β₁> 5 × β_Two
Is more preferable. Or β_TwoIs virtually
It is preferably b. Use reflective electrode on one substrate
Alternatively, it can be used as a reflection type liquid crystal element.

When an orientation control layer typified by polyimide is used, usually uniaxial orientation is imparted by a method called rubbing. In this method, the streak orientation caused by rubbing has been a problem.

Therefore, the present inventors have found a method for stably producing a very uniform alignment state in a process by oblique deposition, which is an alignment control method that is uniform from a microscopic viewpoint. For the method of oblique deposition, see "Liquid Crystal Device Handbook" (edited by 142 Committee of the Japan Society for the Promotion of Science) P242
It is described in detail on the page. The liquid crystal composition has a cholesteric (or chiral nematic) phase -SA phase-
There have been reported many examples in which a liquid crystal composition having a chiral smectic C phase (SmC ^* ) or a SA-chiral smectic C phase (SmC ^* ) phase series is imparted with uniaxial orientation by an oblique deposition film. ("Preprints of Liquid Crystal Symposium" 198
7 years 3Z05, 1988 3B1243B125)
The orientation direction of the liquid crystal molecules was parallel to the deposition direction, and the normal direction of the layer and the oblique deposition direction were parallel in the smectic phase.

FIG. 6 is a schematic view showing an example of the oblique evaporation method, FIG. 6 (a) is an oblique evaporation apparatus, and FIG. 6 (b) is an explanatory view of an evaporation angle. In the figure, 61 is a substrate, 62 is a film thickness monitor, 63 is an evaporation source, 64 is a shutter, 65 is an exhaust pump, and θ is a deposition angle. The 64 shutter is formed so as to open during vapor deposition. The deposition angle θ is shown in FIG.
(B) shows the deposition angle in the direction of A.

In the oblique deposition method, as shown in FIG. 6, the column formation angle is controlled by the deposition angle θ. When the layer normal direction and the vapor deposition direction are parallel, a pretilt is given to the liquid crystal molecules. As a problem of the oblique deposition method, it is very difficult to control the column angle, and it is very difficult to control in-plane variation of a large display, variation between lots, and the like. The present inventors have proposed a liquid crystal having a cholesteric (chiral nematic) -chiral smectic C phase (SmC ^* ) phase series, or an isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC ^* ) phase series. It was found that by using the composition, the alignment direction of the long axis of the liquid crystal molecules was almost perpendicular to the oblique deposition direction.

More specifically, when the layer normal direction and the vapor deposition direction are parallel, a pretilt angle depending on the column forming angle is provided. As a problem of the oblique evaporation method in such a case, since a substance such as SiO is radially evaporated from a point-like evaporation source, even if the evaporation angle is strictly controlled, the material to be evaporated is a large panel. In this case, the column angle will be different in the panel plane.
As a result, in-plane non-uniformity of the pretilt angle occurs in a large-sized panel, so that the in-plane non-uniformity of element characteristics has been a problem. Since a similar problem can occur between panels in a multi-paneling process of extracting a plurality of panels from the same substrate, it can be easily predicted that this causes a variation between panels.

On the other hand, the present inventors use the liquid crystal composition having a cholesteric (chiral nematic) -SmC ^* phase series as a phase series, so that the alignment direction of the long axis of the liquid crystal molecules becomes almost perpendicular to the oblique deposition direction. I understood. It is generally known that when such an alignment state is taken, the pretilt angle becomes zero. It has been confirmed by the present inventors that the pretilt angle is also zero in the present invention. That is, by appropriately adjusting the column angle using the Ch-SmC ^* phase series, an element having uniform in-plane characteristics without in-plane unevenness of the pretilt angle can be obtained.

FIG. 7A is a schematic diagram showing the state of liquid crystal molecules when a liquid crystal composition having a smectic A phase series is given uniaxial orientation by an oblique deposition film.

Reference numeral 11 denotes a substrate, 12 denotes a column formed by oblique evaporation, and 13 denotes liquid crystal molecules. As shown, the column 12 is a deposition having a columnar structure deposited from a certain deposition direction 15. The deposition angle in this case is a large angle. The liquid crystal molecules 13 have a long shape, and the long shape is shown on the paper. The liquid crystal molecules 13 form a layer 14 in the direction shown by the dotted line from the slope of the column. The normal direction 16 of the layer is shown in the figure.

On the other hand, FIG. 7 (b) is a schematic view showing the state of liquid crystal molecules when a liquid crystal composition having no smectic A phase is imparted with uniaxial orientation by an oblique deposition film. . The inventor of the present invention imparted uniaxial orientation to the liquid crystal molecules having no such smectic A phase series by an oblique deposition film.

FIG. 7B shows 11, 12, and 13
The same thing as (a) is shown. As shown in FIG. 7B, the liquid crystal molecules having no smectic A phase sequence, that is, liquid crystal molecules different from the liquid crystal molecules constituting the liquid crystal composition having the smectic A phase sequence, are oriented in the direction perpendicular to the paper. It was found by the inventor that the long direction was directed to the object. In other words, it was found that the deposition direction was perpendicular to the liquid crystal molecule long axis direction.

Further, in such a case, in the case of a liquid crystal element in which the angle θc between the column formed at the time of vapor deposition and the substrate is 70 ° or less, preferably 30 ° to 70 °, That is, not only streaks generated when a rubbing treatment was performed on an alignment film such as polyimide were not observed, but also so-called zigzag defects caused by the C1 orientation and the C2 orientation were not observed. And in the case of such a liquid crystal element, a liquid crystal element with high contrast could be provided. The angle θc between the column and the substrate
Indicates the angle formed between a side of the column parallel to the deposition direction of the triangle and the surface of the substrate when the column is formed in a triangular shape by oblique deposition.

In the case of a liquid crystal device having a cholesteric-chiral smectic C phase series in which the alignment is controlled by rubbing a polyimide-based alignment film, it is known that the major axis direction of the molecule is inclined about 0 ° to 10 ° from the rubbing direction. Have been. It was found that even in the case of the oblique deposition method, the substrate was inclined with respect to the deposition direction as in the case of rubbing. The direction of the liquid crystal molecules is slightly shifted from the deposition direction and the vertical direction. In the case of this alignment state, the pretilt angle of the liquid crystal molecules is almost 0 °, and it becomes very easy to control the alignment by controlling the column angle. That is, even if the column angle is slightly deviated, the pretilt angle, which affects the characteristics of the liquid crystal element, remains unchanged at almost 0 °, so that strict control of the column angle becomes unnecessary, resulting in a very wide process margin. become. Furthermore, there was little variation from a micro viewpoint, and very uniform orientation could be achieved.

Particularly, as a preferred embodiment of the display element, a liquid crystal, a pair of electrodes for applying a voltage to the liquid crystal, and a pair of electrodes for sandwiching the liquid crystal and facing the liquid crystal and aligning the liquid crystal on at least one facing surface. A pair of substrates on which oblique deposition is performed, and a polarizing plate on at least one of the substrates, a liquid crystal in which images in a plurality of frames are displayed in one second and the alignment state of the liquid crystal changes with time in each frame. An element is provided.

Further, the present invention provides a liquid crystal device using a chiral smectic liquid crystal in which the liquid crystal exhibits a monostable state when no voltage is applied as described above, as a device manufactured by the above-described device manufacturing method. You.

The liquid crystal element applicable to the present invention is disclosed in JP-A-2000-338564 or JP-A-2000-38464.
01076, wherein the phase transition series of the liquid crystal material is isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase (Sm
C ^* ), or an isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC ^* ), and a positive or negative DC voltage is applied between a pair of substrates during the transition to the SmC ^* phase. In this way, only one of the two layer directions is aligned, that is, the deviation direction between the average uniaxial alignment processing axis and the normal direction of the smectic layer is constant, and the virtual cone edge of the liquid crystal molecule is applied in the state of no voltage application. The orientation state of the SmC ^* phase is stabilized on the upper side or the inner side, and the memory property is lost.

In the chiral smectic liquid crystal used in the present invention, the phase transition series is such that the isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase or isotropic liquid phase (high temperature side). ISO.)-Chiral smectic C phase is preferred.

Specific examples of preferred compounds constituting the liquid crystal composition used in the present invention are shown in (1) to (4) below.

[0034]

Embedded image

R ₁ , R ₂ : straight-chain or branched alkyl group having 1 to 20 carbon atoms which may have a substituent X ₁ , X ₂ : single bond, O, COO, OOC Y ₁ , Y ₂ , Y ₃ , Y ₄ : H or F n: 0 or 1

[0036]

Embedded image

R ₁ , R ₂ : linear or branched alkyl group having 1 to 20 carbon atoms which may have a substituent X ₁ , X ₂ : single bond, O, COO, OOC Y _{1, Y 2, Y 3,} Y 4: H or F

[0038]

Embedded image

R ₁ , R ₂ : linear or branched alkyl group having 1 to 20 carbon atoms which may have a substituent X ₁ , X ₂ : single bond, O, COO, OOC Y _{1, Y 2, Y 3,} Y 4: H or F

[0040]

Embedded image

R ₁ , R ₂ : straight-chain or branched alkyl group having 1 to 20 carbon atoms which may have a substituent X ₁ , X ₂ : single bond, O, COO, OOC Y _{1, Y 2, Y 3,} Y 4: H or F

Hereinafter, a specific embodiment of the liquid crystal device of the present invention will be described with reference to FIG.

In the liquid crystal element 80 shown in FIG. 7, a substrate 81 made of a pair of highly transparent materials such as glass and plastic is used.
The cell has a structure in which a liquid crystal 85, preferably a liquid crystal exhibiting a chiral smectic phase is sandwiched between a and 81b, and is sandwiched between a pair of polarizing plates 87a and 87b whose polarization axes are orthogonal to each other.

The substrates 81a and 81b are provided with electrodes 82a and 82b made of a material such as In ₂ O ₃ or ITO for applying a voltage to the liquid crystal 85, respectively. Dot-shaped transparent electrodes are arranged in a matrix, and a TFT or MIM (Met (Met)
Al-Insulator-Metal) and other switching elements are connected, and an opposing electrode having a predetermined pattern is formed on one surface of the other substrate or the other substrate to form an active matrix structure.

The electrodes 82a, On 82b, SiO ₂ having a function such as to prevent these short as necessary,
An insulating film 83a made of a material such as TiO ₂ , Ta ₂ O ₅ ,
83b are provided respectively.

Further, on the insulating films 83a and 83b, alignment control layers 84a and 84b which are in contact with the liquid crystal 85 and function to control the alignment state are provided. The orientation control layers 84a and 84b are obliquely deposited films, and include SiO, S
iOx, CaF _{2 and the} like are known.

The substrates 81a and 81b are
Are opposed to each other. The spacer 86 determines a distance (cell gap) between the substrates 81a and 81b, and silica beads or the like are used. Regarding the cell gap determined here, the optimum range and the upper limit are different depending on the difference of the liquid crystal material, but the uniform uniaxial orientation,
In order to develop an alignment state in which the average molecular axis of the liquid crystal molecules is substantially the same as the average direction axis of the alignment processing axis when no voltage is applied, it is preferable to set the average molecular axis in the range of 0.3 to 10 μm.

In addition to the spacer 86, adhesive particles made of a resin material such as an epoxy resin are dispersed to improve the adhesiveness between the substrates 81a and 81b and to improve the impact resistance of the liquid crystal exhibiting a chiral smectic phase. (Not shown).

In the liquid crystal element 80 having the above-described structure, when a liquid crystal exhibiting a chiral smectic phase is used as the liquid crystal 85, the composition of the material is adjusted, and further, the processing of the liquid crystal material and the element structure, for example, the alignment control layers 84a and 84b By appropriately setting the material, processing conditions, and the like, when no voltage is applied, the liquid crystal exhibits an alignment state in which the average molecular axis (liquid crystal molecules) of the liquid crystal is monostable. Of the average molecular axis, the tilt angle changes continuously according to the magnitude of the applied voltage, and the voltage of the other polarity (second polarity) is applied. Sometimes, the average molecular axis of the liquid crystal exhibits characteristics such that it tilts at an angle corresponding to the magnitude of the applied voltage. At this time, the characteristic may be such that the maximum tilt angle by applying the voltage of the first polarity is larger than the maximum tilt angle by applying the voltage of the second polarity. Alternatively, the characteristics may be such that the average molecular axis does not tilt regardless of the magnitude of the applied voltage when the voltage of the second polarity is applied.

As the liquid crystal material exhibiting a chiral smectic phase, biphenyl having the above-mentioned properties (properties relating to the physical property value cone angle Θ, the layer spacing d of the smectic layer, and the inclination angle δ inherent to the liquid crystal material) is used. A composition prepared by appropriately selecting a hydrocarbon-based liquid crystal material, a naphthalene-based liquid crystal material, or a polyfluorine-based liquid crystal material having a skeleton, a phenylcyclohexane ester skeleton, a phenylpyrimidine skeleton, or the like is used.

In the liquid crystal device, the substrates 81a and 81b
At least one of R, G, and B color filters may be provided to provide a color liquid crystal element. Further, a method of performing full-color display using time-division color mixture by sequentially switching the R, G, and B light sources as the light source can also be used.

Note that the liquid crystal element is composed of substrates 81a and 81
b, a transmissive liquid crystal element in which a pair of polarizing plates is provided on both substrates, ie, both the substrates 81a and 81b are translucent substrates, and incident light from one substrate side (for example, light from an external light source) Or a reflection type liquid crystal element in which a polarizing plate is provided on at least one substrate, that is, a reflection plate is provided on one of the substrates 81a and 81b, or one substrate is provided. The present invention can be applied to any type of element that modulates incident light and reflected light by using a reflective material as a member provided on itself or a substrate and emits light to the same side as the incident side.

In the present invention, a drive circuit for supplying a gradation signal to the above-described liquid crystal element is provided, and by applying the above-described voltage, a continuous tilt angle from the monostable position of the average molecular axis of the liquid crystal is set. A liquid crystal display element that performs gradation display by utilizing the change and the characteristic that the amount of light emitted from the element changes continuously can be configured. For example, by using an active matrix substrate provided with the above-described TFT or the like as one substrate of a liquid crystal element and performing active matrix driving by amplitude modulation with a driving circuit, analog gray scale display can be performed.

Next, an example in which such an active matrix substrate is used in the liquid crystal device of the present invention will be described with reference to FIGS. FIG. 2 schematically shows the liquid crystal element provided with a driving means, mainly focusing on the configuration of one substrate (active matrix substrate).

In the configuration shown in FIG. 2, in the panel section 90 corresponding to the liquid crystal element, horizontal gate lines G1, G2,... In the drawing corresponding to the scanning lines connected to the scanning signal driver 91 as the driving means. , Corresponding to the information signal lines connected to the information signal driver 92 as the driving means, are provided so as to be orthogonal to each other while being insulated from each other in the vertical direction in the drawing. A thin film transistor (TFT) 94 corresponding to a switching element and a pixel electrode 95 are provided corresponding to the pixel at each intersection (only a 5 × 5 pixel area is shown for simplification). In addition, as a switching element, in addition to TFT, MI
An M element can also be used. Gate lines Gl, G2 ...
Is connected to the gate electrode (not shown) of the TFT 94,
Are connected to a source electrode (not shown) of the TFT 94, and the pixel electrodes 95 are connected to a drain electrode (not shown) of the TFT 94. In such a configuration, the scanning signal driver 91 controls the gate line G
, G2... are line-sequentially selected for scanning and a gate voltage is supplied, and an information signal voltage corresponding to information to be written to each pixel is supplied from the information signal driver 92 in synchronization with the scanning selection of the gate line. Are supplied to the lines S1, S2,... And are applied to each pixel electrode via the TFT 94.

FIG. 3 shows an example of a sectional structure of each pixel portion (1 bit) in the panel configuration as shown in FIG. In the structure shown in FIG.
Active matrix substrate 20 having a common electrode 42
Liquid crystal layer 4 having spontaneous polarization between opposing substrates 40 provided with
9 are sandwiched to form a liquid crystal capacitor (C _1c ) 31.

As for the active matrix substrate 20, an example in which an amorphous Si TFT is used as the TFT 94 is shown. The TFT 94 is formed on a substrate 21 made of glass or the like, and the gate lines G1, G2,.
Silicon nitride (SiN) on the gate electrode 22 connected to
x), an a-Si layer 24 is provided via an insulating film (gate insulating film) 23 made of a material such as
4, a source electrode 27 and a drain electrode 28 are provided separately from each other via n ⁺ a-Si layers 25 and 26, respectively.

The source electrode 27 is connected to the source line S shown in FIG.
, S2,..., and the drain electrode 28 is connected to a pixel electrode 95 made of a transparent conductive film such as an ITO film.
The channel protection film 29 covers the a-Si layer 24 of the TFT 94. The TFT 94 has a gate electrode 2 during a period in which the corresponding gate line is selected for scanning.
A gate pulse is applied to 2 to turn it on.

Further, in the active matrix substrate 20, the insulating film 23 (continuously provided with the insulating film on the gate electrode 22) is formed by the pixel electrode 95 and the storage capacitor electrode 30 provided on the glass substrate side of the electrode. A storage capacitor (C _s ) 32 is provided in parallel with the liquid crystal layer 49 by a structure sandwiching the film. When the area of the storage capacitor electrode is large, the aperture ratio is reduced, and thus the storage capacitor electrode is formed of a transparent conductive film such as an ITO film.

The TFT 9 of the active matrix substrate 20
On the pixel electrode 95 and the pixel electrode 95, there is provided an alignment film 43a which has been subjected to a uniaxial alignment process such as a rubbing process for controlling the alignment state of the liquid crystal.

On the other hand, in the counter substrate 40, the glass substrate 41
A common electrode 42 and an alignment film 43b for controlling the alignment state of the liquid crystal are laminated on the entire surface with the same thickness.
The cell structure is sandwiched between a pair of polarizing plates whose polarization axes are orthogonal to each other (not shown).

In the pixel portion of the panel having the above structure, a liquid crystal having spontaneous polarization, for example, a liquid crystal exhibiting a chiral smectic phase is used as the liquid crystal layer 49.

In the panel configuration shown in FIGS. 2 and 3, polycrystalline S
A substrate provided with an i (p-Si) TFT can be used.

FIG. 4 shows an equivalent circuit of a pixel portion of the panel shown in FIG. The active matrix driving utilizing the characteristics of the liquid crystal device having the above structure will be described with reference to FIGS. In the active matrix driving of the liquid crystal element of the present invention, for example, a period (one frame) for displaying certain information in one pixel is divided into a plurality of fields (for example, IF and 2F shown in FIG. 5).
In the field, an emitted light amount according to predetermined information is obtained on average. Hereinafter, an example in which the liquid crystal layer 49 is divided into two fields in a case where the transmission light intensity is sufficient when a voltage of one polarity is applied and the transmission light intensity is smaller when the polarity is reversed, will be described.

FIG. 5A shows a voltage applied to one gate line serving as a scanning line connected to the pixel when focusing on one pixel. In the liquid crystal element having the above structure, the gate lines G1, G2,... Are selected, for example, line-sequentially for each field, a predetermined gate voltage Vg is applied to one gate line during the selection period Ton, and a voltage is applied to the gate electrode 22. Vg is applied, and the TFT 94 is turned on. In a non-selection period Toff corresponding to a period in which another gate line is selected, no voltage is applied to the gate electrode 22 and the TFT 94 enters a high resistance state (off state), and a predetermined same gate line is selected for each Toff. As a result, a gate voltage Vg is applied to the gate electrode 22.

FIG. 5B shows the voltage Vs applied to the information signal line (source line) of the pixel. As shown in FIG. 5A, in each field, the gate electrode 2 is turned on during the selection period Ton.
When a gate voltage is applied to the pixel 2, a predetermined source voltage (information signal voltage) Vs (reference) is applied to the source electrode 27 from the source lines S 1, S 2,. (The potential is the potential Vc of the common electrode 42)
Is applied.

Here, in the first field (1F) that constitutes one frame, optical information to be obtained by the pixel based on information written in the pixel, for example, voltage-transmittance characteristics according to the liquid crystal used. Source voltage of positive polarity (information signal voltage) of level Vx according to state or display information (transmittance)
(The reference potential is the potential Vc of the common electrode 42). At this time, since the TFT 94 is in the ON state, the voltage Vx applied to the source electrode 27
8, and is applied to the pixel electrode 95 to provide a liquid crystal capacitance (C _1c ).
31 and the storage capacitor 32 (C _s ) are charged, and the potential of the pixel electrode becomes the information signal voltage Vx. Subsequently, in the non-selection period Toff of the gate line to which the pixel belongs, the TFT
Since the resistor 94 has a high resistance (OFF state), during this non-selection period, the liquid crystal cell (liquid crystal capacitor C _1c ) 31 and the storage capacitor (C
_s ) At 32, the state in which the charge charged during the selection period Ton is accumulated is maintained, and the voltage Vx is held. Then, the voltage Vx is applied to the liquid crystal layer 49 in the pixel throughout the period of the first field IF, and an optical state (light transmission amount) corresponding to the voltage value is obtained in the liquid crystal portion of the pixel.
At this time, if the response speed of the liquid crystal is slower than the gate-on period, the charging of the liquid crystal cell (liquid crystal capacitor C _1c ) 31 and the storage capacitor (C _s ) 32 is completed, and switching starts in the non-selection period in which the gate is turned off. . In such a case, the charged charge is offset by the reversal of spontaneous polarization,
The voltage applied to the liquid crystal layer takes a value of Vx ′ smaller than Vx as shown in FIG.

Next, in the selection period Ton of the second field (2F), the source voltage (-Vx) having a polarity opposite to that of the first field IF and having substantially the same voltage value Vx.
Is applied to the source electrode 27. At this time, TFT 94 is ON state, the voltage -Vx is applied to the pixel electrode 95, charged in the liquid crystal capacitance (C _1c) 31 and the storage capacitor 32 (C _s) is performed, the potential of the pixel electrode data signal voltage −Vx. Subsequently, in the non-selection period Toff, the TFT 94
Becomes a high resistance (off state), during this non-selection period, the liquid crystal cell (liquid crystal capacitance C _1c ) 31 and the storage capacitance (C _s ) 32 change the state in which the charges charged during the selection period Ton are accumulated. And the voltage -Vx is maintained. Then, the second field 2 is added to the liquid crystal layer 49 in the pixel.
The voltage -Vx is applied throughout the F period, and the pixel obtains an optical state (light emission amount) corresponding to the voltage value. At this time, similarly, when the response speed of the liquid crystal is slower than the gate-on period, the charging of the liquid crystal cell (liquid crystal capacitor C _1c ) 31 and the storage capacitor (C _s ) 32 is completed, and switching is performed during the non-selection period when the gate is turned off. Be started. In such a case, the charged charge is offset by the reversal of spontaneous polarization,
The voltage applied to the liquid crystal layer takes a value of -Vx 'which is smaller than -Vx as shown in FIG.

FIG. 5C shows the voltage value Vpix actually held in the liquid crystal capacitor and the storage capacitor of the pixel as described above and applied to the liquid crystal layer 49, and FIG. The actual optical response (optical response in the case of a transmissive liquid crystal element) is schematically shown. As shown in FIG.
The applied voltage is the same level (absolute value) Vx ′ whose polarity is inverted from each other through the two fields 1F and 2F. On the other hand, as shown in FIG.
In the second field 2F, a gradation display state corresponding to -Vx 'is obtained, but in practice, only a slight change in the amount of transmitted light is obtained. However, the transmitted light amount is smaller than Tx and becomes Ty close to the 0 level.

In the active matrix driving as described above, when liquid crystal exhibiting a chiral smectic phase is used, gradation display based on good high-speed response can be performed, and at the same time, gradation display of one pixel level can be performed. Since it is divided into a first field for obtaining a high transmitted light amount and a second field for obtaining a low transmitted light amount and is continuously performed, the time aperture ratio is 50%.
As a result, the high-speed moving image response characteristics perceived by human eyes are also improved. Further, in the second field, the transmitted light amount does not become completely zero due to a slight switching operation of the liquid crystal molecules, so that the luminance perceived by human eyes during the entire frame period is secured. Further, since the voltage of the same level is inverted and applied to the liquid crystal layer 49 in the first and second fields, the voltage actually applied to the liquid crystal layer 49 is converted into an alternating current, thereby preventing the liquid crystal from deteriorating.

In the above-described active matrix driving, 2
In one entire frame composed of fields, a transmitted light amount obtained by averaging Tx and Ty is obtained. Therefore, as the information signal voltage Vs, a voltage value capable of obtaining a large amount of transmitted light by a predetermined level is selected according to image information (gradation information) to be actually obtained by the pixel in the frame. It is also preferable to display the gradation state with a higher level of transmitted light than the desired gradation state in the first field IF by applying the voltage.

Although not described in detail here, it is also possible to apply a method of performing full color display by utilizing color mixture by time division by combining the above driving method and RGB light sources.

[0073]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments.

Example 1 (Preparation of liquid crystal composition) A liquid crystal composition LC-1 was prepared by mixing the following liquid crystal compounds. The numerical values described in the structural formula are weight ratios at the time of mixing.

[0075]

Embedded image

The physical properties of the liquid crystal composition LC-1 are shown below. Phase transition temperature (° C.) Iso. (86.3) Ch (61.2) SmC ^* (−
7.2) Cry. Spontaneous polarization (30 ° C.): Ps = 2.9 nC / cm ² Cone angle (30 ° C.): Θ = 23.3 ° (100 Hz, ±)
12.5 V, cell gear gap = 1.4 μm) Inclination angle δ of the smectic layer (30 ° C.): 21.6 °
(Cell gap = 1.4 μm) Spiral pitch in SmC ^* phase (30 ° C): 20 μm or more

Incidentally, DSC measurement (measuring device: Perkin
"DSC Pyrisl" manufactured by Elmer, measurement conditions: After holding at 100 ° C for 1 minute, -3 at 5 ° C / min.
After cooling down to 0 ° C and then keeping at -30 ° C for 5 minutes,
The temperature was raised at a rate of 5 ° C./min to 100 ° C.), and the measurement was performed at a lower temperature. As a result, the liquid crystal device did not exhibit an SmA phase.

[Measurement of spontaneous polarization Ps]
K. Miyasato et al., "Direct Measurement Method of Spontaneous Polarization of Ferroelectric Liquid Crystal by Triangular Wave" (Journal of the Japan Society of Applied Physics, 22, 10, (661) 1983, "Direct Method"
with Triangle Waves for
Measuring Spontaneos Po
laration in Ferroelectric
c Liquid Crystal ", asdescr
ibed by K.I. Miyasato et al.
(Jap. J. appl. Phys. 22. No. 1)
0, L661 (1983))).

[Measurement of cone angle Θ] ± 12.5 to ± 50
V, an AC (alternating current) of 1 to 100 Hz is applied between the upper and lower substrates of the liquid crystal element via electrodes, and the liquid crystal element disposed therebetween is rotated in parallel with the polarizing plate under orthogonal Nicols, and at the same time, the photomultiplier is rotated. The first extinction position (the position where the transmittance is lowest) and the second extinction position are obtained while detecting the optical response with (Hamamatsu Photonics). Then, 1/2 of the angle from the first extinction position to the second extinction position at this time is defined as a cone angle Θ.

[Measurement of Angle of Inclination δ of Smectic Layer] The angle of inclination of the smectic layer is basically determined by a method performed by Clark or Lagerwal (Japan Displ.
ay'86, Sep. 30 to Oct. 2,1986,4
56-458) or the method of Ouchi et al.
P. 27 (5) (1988) 725-728). As a measuring device, a rotating cathode X-ray diffractometer (manufactured by MAC Sysense) was used. In order to reduce the absorption of X-rays to the glass substrate of the liquid crystal cell, a microsheet (80 μm) manufactured by Corning was used for the substrate. Was.

(Production of Liquid Crystal Cell A) An active matrix substrate having an a-Si TFT having the pixel structure described above as one substrate and a silicon nitride film as a gate insulating film, and an RGB substrate as an opposing substrate. 1. having a color filter and a transparent electrode having a thickness of 70 nm;
A pair of 1 mm substrates was prepared. The screen size was 3 inches. This is a vacuum evaporator EBH6 manufactured by Nihon Vacuum Corporation.
Using a mold, SiO was vapor-deposited under vacuum. (Vacuum degree 13
3.32 × 10 ⁻⁶ Pa (10 ⁻⁶ Toor), deposition rate 1
nm / s)

Inclination angle of substrate (deposition angle θ, see FIG. 6)
Prepared five types of 0 °, 20 °, 30 °, 60 °, and 80 ° (SiO film thickness is 60 nm). Subsequently, silica beads having an average particle size of 1.5 μm are sprayed as spacers on one of the substrates, and the substrates are opposed to each other so that the deposition directions of the substrates are antiparallel to each other (anti-parallel). An active matrix panel A) was obtained.

(Production of Liquid Crystal Cell B) An active matrix substrate having an a-Si TFT having the pixel structure described above as one substrate and having a silicon nitride film as a gate insulating film, and an RGB substrate as an opposing substrate 1. having a color filter and a transparent electrode having a thickness of 70 nm;
A pair of 1 mm substrates was prepared. The screen size was 3 inches. On the transparent electrode of the substrate, a commercially available alignment film for TFT SE7992 (manufactured by Nissan Chemical Industries, Ltd.) was applied by spin coating, followed by pre-drying at 80 ° C. for 5 minutes, and then heating at 200 ° C. for 1 hour. Baking, film thickness 50nm
Was obtained.

Subsequently, the polyimide film on the substrate was subjected to a rubbing treatment with a nylon cloth as a uniaxial orientation treatment. The conditions for the rubbing treatment were as follows: a rubbing roll in which nylon (NF-77 / manufactured by Teijin) was bonded to a roll having a diameter of 10 cm;
cm / sec, the number of rotations was 1000 rpm, and the number of times of feeding was 4 times. Subsequently, silica beads having an average particle size of 1.5 μm are scattered as spacers on one of the substrates, and the rubbing directions of the substrates are opposed to each other so as to be antiparallel to each other. (Active matrix panel B) was obtained.

Panels A and B produced by the above process
The liquid crystal composition LC-1 is injected at a temperature of a Ch phase, and the liquid crystal is cooled to a temperature showing a chiral smectic liquid crystal phase.
During this cooling, before and after the Ch-SmC ^* phase transition,
A liquid crystal panel A (oblique deposition panel) and a liquid crystal panel B (polyimide-based alignment film panel) were produced by performing a cooling process by applying an offset voltage (DC) voltage of 2 V.
Contrast and orientation of these liquid crystal panels A and B were observed. Table 1 shows the results.

Note that the liquid crystal panel A and the liquid crystal panel in the smectic liquid crystal phase had a liquid crystal molecule long axis alignment direction and a vapor deposition direction of 2 degrees, and the liquid crystal panel B had a 2 degree direction.

[0087]

[Table 1]

(Note 1) The column angle was determined by taking a photograph of a cross section with an electron microscope and measuring the angle between the substrate and the column. (Note 2) The contrast was obtained from the output value from the photomultimeter.

As shown in Table 1, in the oblique deposition method, more uniaxial orientation was obtained at a column angle of 70 ° or less, and further at a column angle of 30 ° or more. When the column angle was 70 ° or less, and more preferably 30 ° or more, a higher contrast value than that obtained by rubbing was obtained.

[0090]

As described above, according to the present invention, it is possible to obtain a chiral smectic liquid crystal element which is easy to process and has high contrast by using the oblique deposition method.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one embodiment of a liquid crystal element of the present invention.

FIG. 2 is a diagram schematically showing a liquid crystal element of the present invention provided with a driving means, with a focus on the structure of one substrate.

3 is a schematic diagram showing an example of a cross-sectional structure of each pixel portion (for one bit) in the panel configuration shown in FIG.

FIG. 4 is a diagram showing an equivalent circuit of a pixel portion of the panel.

FIG. 5 is a diagram illustrating active matrix driving of a liquid crystal element.

FIG. 6 is a schematic diagram illustrating an example of an oblique deposition method.

FIG. 7 is a schematic view showing columns and liquid crystal molecules obtained by oblique deposition.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Substrate 12 Column 13 Liquid crystal molecule 14 layer 15 Deposition direction 16 Layer normal direction 20 Active matrix substrate 21 Substrate 22 Gate electrode 23 Insulating film (gate insulating film) 24 a-Si layer 25, 26 n ⁺ a-Si layer 27 Source Electrode 28 Drain electrode 29 Channel protective film 30 Storage capacitor electrode 31 Liquid crystal capacitor 32 Common electrode 40 Counter substrate 41 Glass substrate 42 Common electrode 43 a, 43 b Alignment film 49 Liquid crystal layer 61 Substrate 62 Film thickness monitor 63 Evaporation source 64 Shutter 65 Exhaust pump θ Deposition angle 80 Liquid crystal element 8la, 8lb Substrate 82a, 82b Electrode 83a, 83b Insulating film 84a, 84b Alignment control layer 85 Liquid crystal 86 Spacer 87a, 87b Polarizing plate 90 Panel section 91 Scan signal driver 92 Information signal driver 94 Thin film transistor (TF) ) 95 pixel electrode

Continuing on the front page (72) Inventor Yoji Asao 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Ryuichiro Isobe 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Hirohide Munakata 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 2H088 EA12 EA33 FA02 FA29 GA03 GA04 GA17 HA03 HA08 HA12 HA28 JA17 KA12 KA14 MA02 MA13 2H090 HB03X HB03Y HB04Y HBX HB08Y HC01 HD14 KA14 LA02 LA04 LA15 LA16 MA06 MA10 MB02 MB03 4H027 BA06 BD16 BD18 BD20 BE02 DE01 DE03 DE09 DF01 DJ01

Claims (5)

[Claims] 1. A liquid crystal display comprising: a chiral smectic liquid crystal, a pair of electrodes for applying a voltage to the liquid crystal, a pair of substrates sandwiching the liquid crystal, and a polarizing plate on at least one of the substrates. Is formed by oblique deposition, the deposition direction of the liquid crystal molecules in the smectic liquid crystal phase is substantially orthogonal to the deposition direction, and the angle between the column and the substrate formed during deposition is 70 °. Wherein the phase transition series of the chiral smectic liquid crystal is isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase (Sm)
C ^* ) or isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC ^* ), wherein at least one of the substrates has an active element connected to an electrode corresponding to each pixel. Characteristic chiral smectic liquid crystal element. 2. When no voltage is applied, the average molecular axis of the liquid crystal shows a first state in which the average molecular axis is monostable, and when a voltage of the first polarity is applied, the average molecular axis of the liquid crystal becomes smaller than the magnitude of the applied voltage. The tilt is tilted to one side from the mono-stabilized position at an appropriate angle, and the average molecular axis of the liquid crystal is mono-stabilized when a voltage of a second polarity having a polarity opposite to the first polarity is applied. It is a liquid crystal element that tilts from the position to the opposite side when a voltage of the first polarity is applied, and the average molecular axis of the liquid crystal when the voltage of the first polarity is applied and when the voltage of the second polarity is applied. When the tilt angles of the maximum tilt state based on the mono-stabilized position in the first state are β ₁ and β ₂ , respectively, β ₁ >
chiral smectic liquid crystal device according to claim 1, wherein the beta _2. 3. A tilt in a maximum tilt state with reference to a mono-stabilized position in the first state of the average molecular axis of the liquid crystal when a voltage of the first polarity is applied and when a voltage of the second polarity is applied. Where β ₁ and β ₂ respectively, β ₁ > 5 ×
_3. The chiral smectic liquid crystal device according to claim _2, which is β2. 4. When no voltage is applied, the average molecular axis of the liquid crystal shows a first state in which the average molecular axis is monostable, and when a voltage of the first polarity is applied, the average molecular axis of the liquid crystal becomes smaller than the magnitude of the applied voltage. When tilted to one side from the mono-stabilized position at an appropriate angle, and when a voltage of a second polarity having a polarity opposite to the first polarity is applied, the average molecular axis of the liquid crystal is mono-stabilized. 2. The chiral smectic liquid crystal device according to claim 1, wherein the liquid crystal device does not substantially change from the position where it is placed. 5. The helical pitch of the chiral smectic liquid crystal in a bulk state is longer than twice the cell thickness.
5. The chiral smectic liquid crystal device according to any one of items 4 to 4.