JP2001209076A - Liquid crystal device and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal device with a uniform alignment state without alignment defects. SOLUTION: The liquid crystal device consists of a chiral smectic liquid crystal, a pair of electrodes, a pair of substrates having been subjected to uniaxial alignment treatment, and a polarizing plate disposed on at least one substrate. The phase transition series of the chiral smectic liquid crystal shows, from the high temperature side, an isotropic liquid crystal phase (Iso.), a cholesteric phase (Ch), and a chiral smectic C phase (SmC*). The uniaxial alignment treatment applied on both substrates is in an antiparallel direction. The liquid crystal molecules on at least one substrate just below the phase transition of the isotropic liquid phase (Iso.) to the cholesteric phase (Ch) show >=10 deg. pretilt angle. An AC voltage is applied to the device at least in the temperature range where the liquid crystal shows the cholesteric phase (Ch).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, a TFT (Thin Film T)
Typical 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 or a vertical alignment (Vertical Alignment) mode using a lateral electric field has been announced, and a field of view which has been a disadvantage of the conventional liquid crystal display 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 in Japanese Patent Application No. 10-1771.
Device described in No. 45 (hereinafter referred to as "prior application 1")
Has been invented and proposed. In the present invention, for example, the isotropic liquid phase (Iso.)-Cholesteric phase (C
h) -chiral smectic C phase or isotropic liquid phase (I
so. )-Focusing on a phase-series material showing a chiral smectic C phase, monostabilization is performed at a position inside the edge of the virtual cone. And, for example, Ch-S
During mC ^* phase transition, or isotropic phase to apply a positive or negative DC voltage between a pair of substrates upon-SmC ^* phase transition, to equalize the layer in one direction, such as by, thereby high-speed response In addition, a high-brightness liquid crystal element which can control gradation and has excellent moving image quality can be realized with high mass productivity. The element of the prior application can reduce the spontaneous polarization value as compared with the various smectic liquid crystal modes described above.
This is an element having good matching with active elements such as.

Further, the present inventors have disclosed in Japanese Patent Application No. 11-2407.
Device described in No. 30 (hereinafter referred to as "prior application 2")
In the above, the element of the prior application 1 is subjected to an anti-parallel (anti-parallel) uniaxial orientation treatment, and the pretilt angle of at least one of the substrates is set to 10 degrees or more, so that a continuous gradation change, so-called “domainless switching” is performed. Has been invented and proposed to be stably feasible. By realizing this domainless switching, high-quality image quality can be realized not only when the liquid crystal element in this mode is applied to not only a direct-view display element but also a projection display or head-mounted display using an enlarged projection system. ing.

As described above, the chiral smectic liquid crystal, particularly the liquid crystal elements of the prior application 1 and the prior application 2, are 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 the used liquid crystal display element is expected.

[0007]

As described above, the smectic liquid crystal elements of the prior application 1 and the prior application 2 having a gradation display capability in a next-generation display or the like such as a high-speed response performance are expected. However, when the orientation control of a high pretilt angle is performed as in the device of the prior application 2, the isotropic phase (Is
o. ) To a cholesteric phase (Ch), string-like disclinations 11 as shown in FIG. 6 were often observed.

The string-shaped disclination generated in the Ch phase may gradually decrease as the temperature decreases in the Ch phase, but the chiral smectic C
It often remains after the temperature has dropped to the (SmC ^* ) phase. In such a case, this disclination not only causes a decrease in the contrast ratio when used as a display element, but in the case of a Ch-SmC ^* phase transition liquid crystal, the disclination line is tightly applied to cause a smectic phase. In some cases, the orientation may be shifted to a vertical orientation (a state in which the smectic layer is arranged substantially parallel to the substrate). When such a vertical alignment region is generated, switching between light and dark becomes impossible, so that the function as a display element is lost.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to suppress the occurrence of string-shaped disclination that appears in the cholesteric phase in the liquid crystal mode of the prior application 2, and to align the liquid crystal. An object of the present invention is to provide a liquid crystal element capable of realizing a uniform alignment state without defects and a method for manufacturing the same.

[0010]

The above object of the present invention is attained by the following invention. That is, the first invention of the present invention provides a chiral smectic liquid crystal, a pair of electrodes for applying a voltage to the liquid crystal, and a uniaxial alignment treatment for sandwiching and opposing the liquid crystal and aligning the liquid crystal. A liquid crystal device comprising a pair of substrates and a polarizing plate on at least one of the substrates, wherein a phase transition series of the chiral smectic liquid crystal isotropic liquid phase (Iso.)-Cholesteric phase (Ch) from a high temperature side. ) -Chiral smectic C (SmC
^* ) Phase, the uniaxial orientation treatment applied to both substrates is antiparallel, and the isotropic liquid phase (Is
o. A) a liquid crystal characterized in that the pretilt angle of the liquid crystal molecule immediately below the cholesteric phase (Ch) phase transition is 10 degrees or more, and an AC voltage is applied at least in a temperature range showing the cholesteric phase (Ch). Element.

A second invention of the present invention provides a chiral smectic liquid crystal, comprising a pair of electrodes for applying a voltage to the liquid crystal, and a uniaxial alignment for sandwiching the liquid crystal and facing the liquid crystal and for aligning the liquid crystal. A method for producing a liquid crystal element, comprising: injecting a cell having a pair of treated substrates and a polarizing plate on at least one of the substrates, wherein a phase transition series of the chiral smectic liquid crystal is isotropic from a high temperature side. Liquid phase (Is
o. ) -Cholesteric phase (Ch) -Chiral smectic C (SmC ^* ) phase, wherein the uniaxial orientation treatment applied to both substrates is antiparallel, and the isotropic liquid phase (Iso.) Of at least one of the substrates. A step of injecting a chiral smectic liquid crystal into a cell when the pretilt angle of the liquid crystal molecule immediately below the cholesteric phase (Ch) phase transition is 10 degrees or more, and applying an AC voltage to the chiral smectic liquid crystal in a temperature range showing at least the cholesteric phase (Ch). A method for manufacturing a liquid crystal element, comprising a step of applying.

In the present invention, the AC voltage is applied.
Temperature range is isotropic liquid of the chiral smectic liquid crystal
Body phase (Iso.)-Cholesteric phase (Ch) transition temperature
To T _NIAnd at least (T_NI-10) ℃ or more
Preferably it is in the temperature range.

As described in the above-mentioned problem, in the case where an alignment state with a high pretilt angle is to be realized, string-shaped disclination often occurs, resulting in a decrease in contrast,
In addition, it caused vertical alignment.

On the other hand, in the present invention, an AC voltage is applied in the cholesteric phase to the element of the prior application 2 in which at least one of the substrates is combined so that the pretilt angle is 10 degrees or more and antiparallel. As a result, a liquid crystal element without disclination can be realized.

At this time, the frequency of the AC voltage is set at 0.1 as a condition that a sufficient voltage can be applied to the liquid crystal layer. lHz-100kHz
z, preferably about 10 Hz to 1 kHz, and with respect to the applied voltage value, from 0.5 to 10 V, preferably from 0.5 to 10 V, in order to sufficiently suppress the occurrence of disclination and prevent damage to the element due to application of a high voltage. It is desirable to apply in a voltage range of 3 to 7V.

The pretilt angle in the present invention is
It is a pretilt angle of a liquid crystal molecule just below an isotropic phase-Ch phase transition temperature. This is because the value of the pretilt angle when the liquid crystal molecules are aligned for the first time in the temperature decreasing process is most important. If it is difficult to measure the temperature at the above-mentioned temperature and if it is confirmed that the pretilt angle has no or very little temperature dependence, the measurement may be performed at any other temperature.

The pretilt angle is determined by a crystal rotation method (“Jpn. J. Appl. Phys.”,
Vo. 119 (1980) No. 10. Short N
ots 2013). The cell for measurement is manufactured by bonding two substrates so that the inclination of the liquid crystal at the interface between the upper and lower substrates is parallel and in the same direction (rubbing axes are parallel and opposite directions: anti-parallel). The measurement procedure is as follows. While rotating the liquid crystal cell perpendicular to the upper and lower substrates and including the alignment processing axis (rubbing axis), a helium-neon laser beam having a polarization plane forming an angle of 45 ° with the rotation axis is perpendicular to the rotation axis. Irradiation is performed from different directions, and the transmitted light intensity is measured by a photodiode through a polarizing plate having a transmission axis parallel to the incident polarization plane on the opposite side. Then, the re-pretilt angle α can be obtained by performing a simulation of fitting a theoretical curve, the following equations (1) and (2) to the spectrum of the transmitted light intensity generated by the interference.

[0018]

(Equation 1)

In this manner, at least one of the substrates
A disclination generation model when a substrate having a high pretilt angle of 0 ° or more is used and antiparallel rubbing conditions are used is considered as follows from the results of detailed microscope observation.

In the cell subjected to the uniaxial orientation treatment, the vicinity of the interface undergoes a phase transition from the isotropic phase to the Ch phase prior to the bulk.
Here, in the case of a high pretilt angle, the regulating force in the uniaxial orientation processing direction is not so large.
May be twisted. Such a twisted orientation state is often observed when it is formed by using foreign matter mixed in spacer beads or cells as nuclei. When such a twisted orientation is formed near one interface and the molecules are oriented neatly in the uniaxial orientation processing direction near the other interface, the molecular orientation direction of the interface when the bulk layer undergoes a phase transition to the cholesteric phase due to the temperature drop Determines the orientation direction of the bulk molecules. That is, the orientation of the bulk molecules 13 is as shown in FIG. 8, and the point A in the figure becomes discontinuous, resulting in disclination. FIG. 8
Represents a view in which the liquid crystal layer is divided from the upper substrate 14a to the lower substrate 14b and viewed from the upper surface of the substrate.

Since such discontinuity causes a vertical alignment when the phase transition to the chiral smectic phase occurs, it is expected that the rising angle of the molecule in the discontinuous line is steeper than in the surrounding alignment state. In any case, such disclination poses a serious problem in a material system in which a phase transition from a cholesteric phase directly to a chiral smectic phase occurs.

The present inventors have found that the application of an AC voltage is effective. That is, by applying an AC voltage in the cholesteric phase, the disclination once formed can be erased. This effect is higher as the voltage is applied on the higher temperature side even in the cholesteric phase, and it is effective to apply the voltage within 10 ° C. from the phase transition temperature (T _NI ) from the isotropic phase to the cholesteric phase. It is also possible to suppress the occurrence itself of disclination by applying a continuous AC voltage until you have transferred completely cholesteric phase from directly above T _NI while cooled from isotropic phase. It is expected that this may be the result of the liquid crystal molecules, which have deviated from the uniaxial alignment processing direction due to the disturbance of the molecules due to the application of the alternating current, being rearranged in the direction in which the liquid crystal molecules should be regulated.

By the above operation, at least (T _NI −
10) A temperature of not less than ° C, preferably T _NI +5 to T _NI -5 ° C
By applying an AC voltage at the above temperature, it is possible to realize an element having uniform orientation without disclination.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method of manufacturing a liquid crystal device according to the present invention, defects can be suppressed by taking the above-mentioned alignment treatment conditions.

Particularly, as a preferred embodiment of the liquid crystal element applied to the above-mentioned manufacturing method, a liquid crystal, a pair of electrodes for applying a voltage to the liquid crystal, and a pair of electrodes which sandwich the liquid crystal and face each other and have at least one facing surface Equipped with a pair of substrates that have been subjected to uniaxial alignment processing to align liquid crystals, and a polarizing plate on at least one substrate, images are displayed in a plurality of frames per second, and the alignment state of the liquid crystal in each frame Is provided, which changes over time.

Further, according to the present invention, there is provided a liquid crystal element 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 liquid crystal element manufactured by the above-described manufacturing method. You.

The liquid crystal element applicable to the present invention is disclosed in
A device described in JP-A-10-177145;
The phase transition series of the liquid crystal material is an isotropic liquid phase (Iso.).
-Cholesteric phase (Ch) -Chiral smectic C
(SmC^*) Phase, SmC^*Phase transition
By applying either positive or negative DC voltage between the substrates,
Align in only one of the two layer directions, ie average
The misalignment direction between the uniaxial orientation axis and the normal direction of the smectic layer
The liquid crystal molecule is assumed to be constant and no voltage is applied.
Stabilizes inside the cone edge and loses its memory
SmC ^*A phase orientation state is obtained. Also at this time
Orientation with pretilt angle of 10 degrees or more in cholesteric phase
It is desirable to perform an orientation treatment to form a state.
No.

The chiral smectic liquid crystal used in the present invention has a phase transition series of, from the high temperature side, an isotropic liquid phase (Iso.)-Cholesteric phase (Ch) -chiral smectic C (SmC ^* ) phase. Is preferred. Hereinafter, specific examples of preferable compounds constituting the liquid crystal composition used in the present invention are shown in formulas (1) to (4).

[0029]

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

[0031]

Embedded image

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

[0033]

Embedded image

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

[0035]

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

Hereinafter, a specific embodiment of the liquid crystal element of the present invention will be described with reference to FIG. In the liquid crystal element 80 shown in the figure, cells having a liquid crystal 85, preferably a liquid crystal exhibiting a chiral smectic phase, sandwiched between a pair of substrates 8la and 8lb made of a highly transparent material such as glass and plastic have mutually orthogonal polarization axes. It has a structure sandwiched between a pair of polarizing plates 87a and 87b.

The substrates 8la and 8lb 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. The transparent electrodes in the form of dots are arranged in a matrix, and a TFT or MIM (Me
A switching element such as a tal-insulator-metal) is connected, and a counter electrode of a predetermined pattern is provided on one surface of the other substrate or an active matrix structure is formed.

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 films 84a and 84b which are in contact with the liquid crystal 85 and function to control the alignment state are provided. At least one of the alignment control films 84a and 84b is subjected to a uniaxial alignment treatment. As such a film, for example, a film obtained by applying a rubbing treatment to the surface of a film obtained by applying a solution of an organic material such as polyimide, polyimide amide, polyamide, or polyvinyl alcohol, or an oxide such as SiO or a nitride obliquely to the substrate is used. An oblique deposition film of an inorganic material deposited at a predetermined angle from the direction can be used.

The orientation control films 84a and 84b may have different pretilt angles of the molecules of the liquid crystal 85 (the film surfaces near the interface between the liquid crystal molecules and the orientation control film) depending on the selection of the materials and the conditions of the treatment (such as uniaxial orientation treatment). Is adjusted.

When the alignment control films 84a and 84b are both uniaxially oriented films, the uniaxial orientation direction (especially the rubbing direction) of each film is anti-parallel or It can be set to cross in an anti-parallel range of 45 ° or less.

The substrates 8la and 8lb are provided with spacers 86.
Are opposed to each other. The spacer 86 determines the distance (cell gap) between the substrates 8la and 8lb, 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 treatment axis when no voltage is applied, it is preferably set in the range of 0.3 to 10 μm.

In addition to the spacers 86, adhesive particles made of a resin material such as an epoxy resin or the like are dispersed in order to improve the adhesiveness between the substrates 1la and 1lb 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 configuration, for example, the alignment control films 84a and 84b are performed. 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.

The liquid crystal material 85 exhibiting a chiral smectic phase includes a hydrocarbon liquid crystal material having a biphenyl skeleton, a phenylcyclohexane ester skeleton, a phenylpyrimidine skeleton, etc., a naphthalene liquid crystal material, and a polyfluorine liquid crystal material. The composition prepared by appropriately selecting is used.

In the liquid crystal device, the substrates 8la and 8lb
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 8la and 8l
b, a transmission type liquid crystal element in which a pair of polarizing plates are provided on both substrates, that is, both substrates 8la and 8lb 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 8la and 8lb, or one of the substrates 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-mentioned 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 obtained. 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 element 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 a panel section 90 corresponding to a liquid crystal element, horizontal gate lines G1, G2,... In the drawing corresponding to scanning lines connected to a scanning signal driver 91 as 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 scan signal driver 91 controls the gate line G
, G2,... are, for example, line-sequentially selected for scanning, and a gate voltage is supplied. 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 (for one bit) in the panel configuration shown in FIG. In the structure shown in FIG.
Active matrix substrate 20 having common electrodes and common electrode 32
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, a 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. In the following, an example in which the liquid crystal layer 49 is divided into two fields in which the transmitted light intensity is sufficient when a voltage of one polarity is applied and the transmitted 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 lower than the gate-on period, the liquid crystal cell (liquid crystal capacitor C _1c ) 31 and the storage capacitor (C
_s ) The charging is completed in 32, and switching is started in the non-selection period in which the gate is turned off. In such a case, the charges charged by the reversal of the spontaneous polarization cancel each other, and 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), and 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 where the charge charged during the selection period Ton is accumulated is maintained, and the voltage -Vx is held. And
The voltage -Vx is applied to the liquid crystal layer 49 in the pixel throughout the second field 2F, 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 lower than the gate-on period, the liquid crystal cell (liquid crystal capacitor C _1c ) 31 and the storage capacitor (C
_s ) The charging is completed in 32, and switching is started in the non-selection period in which the gate is turned off. In such a case, the charged electric charge is canceled by the reversal of the spontaneous polarization, and the voltage applied to the liquid crystal layer takes a value of -Vx '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 and applied to the liquid crystal layer 49 as described above, 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 above-described active matrix driving, 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 use a method of performing full-color display by utilizing color mixing by time division by applying the above-mentioned driving method and combining RGB light sources.

[0069]

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.

[0071]

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) δ (30 ° C.): 21.6 ° SmC ^* Spiral pitch in phase (30 ° C.): 20 μm or more

(Preparation of Liquid Crystal Cell) 700
A pair of glass substrates having a thickness of 1.1 mm on which the ITO film was formed was prepared. A commercially available TFT is placed on the transparent electrode of the substrate.
Orientation film JALS2022 (polyimide, manufactured by Nippon Synthetic Rubber Co., Ltd.) is applied by a spin coat method.
After pre-drying at 5 ° C. for 5 minutes, it was baked at 200 ° C. for 1 hour to obtain a polyimide film having a thickness of 60 °.

Subsequently, the polyimide film on the substrate was subjected to a rubbing treatment with a nylon cloth as a uniaxial orientation treatment. The conditions of the rubbing treatment were as follows: a rubbing roll in which nylon (NF-77, manufactured by Teijin Limited) was adhered to a roll having a diameter of 10 mm, a pushing amount of 0.3 mm, and a feeding speed of 1
0 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 sprayed 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. A cell with a cell gap (empty cell A of a single pixel) was obtained.

(Preparation of Cell for Evaluation of Pretilt Angle) A substrate prepared under the same conditions as the above-mentioned empty cell was prepared, and an average particle diameter of 9 was prepared.
μm silica beads were scattered, and the rubbing directions of the substrates were opposed to each other so as to be antiparallel (anti-parallel) to obtain cells with a uniform cell gap (empty cells of a single pixel).

The liquid crystal composition LC-1 was injected into the empty cell, the temperature was raised to 85 ° C. (Ch phase), and the pretilt angle was measured by the crystal rotation method described above. As a result, the Bretilt angle was 20 degrees.

The liquid crystal composition LC-1 was injected into the empty cell A of a single pixel prepared by the above process at a temperature of the Ch phase by capillary injection and cooled to room temperature. Thereafter, a reorientation treatment was performed in which the temperature was once raised to an isotropic phase, and the liquid crystal was again cooled to a temperature showing a chiral smectic liquid crystal phase via a cholesteric phase. At the time of this cooling, before and after the Ch-SmC ^* phase transition, a cooling process was performed by applying an offset voltage (DC) of -2 V to produce a liquid crystal element sample. In this reorientation process, the process performed on the cell from the isotropic phase to the cholesteric phase was changed to
To D, and the alignment state was confirmed. Table 1 below shows the processing method for each sample.

[0079]

[Table 1]

Element sample A produced by the above process
About ~ D, the orientation state was confirmed at room temperature using a polarizing microscope with a 10-fold objective lens. The results are shown in Table 2 below.

[0081]

[Table 2]

From these results, it is found that applying an AC voltage in the cholesteric phase is effective in suppressing string-like disclination, and in particular, applying a voltage in a temperature range of (T _NI −10) ° C. or higher. Was shown to be effective.

[0083]

As described in detail above, according to the present invention,
In a liquid crystal device using a liquid crystal exhibiting a chiral smectic phase using a high pretilt angle alignment film, it is possible to suppress the occurrence of string-shaped disclination that appears in the cholesteric phase and realize a uniform alignment state without alignment defects. A liquid crystal element can be provided.

[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 an explanatory view showing a string-shaped disclination generated in a conventional liquid crystal element.

FIG. 7 is an explanatory diagram showing a twisted orientation of the liquid crystal that causes the disclination of FIG. 6;

FIG. 8 is an explanatory diagram showing the orientation of the liquid crystal that causes the disclination of FIG. 6;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Disclination 12 Liquid crystal 13 Bulk molecule 14a Upper substrate 14b Lower substrate 15a Interface molecule near upper substrate 15b Interface molecule near lower substrate 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 80 liquid crystal element 8 la 8lb substrate 82a, 82b electrode 83a, 83b insulating film 84a, 84b alignment control film 85 liquid crystal 86 spacer 87a, 87b polarizing plate 90 panel unit 91 scanning signal driver 92 information signal driver 94 thin film transistor (TFT) 95 pixel electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hirohide Munakata 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Ryuichiro Isobe 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inside (72) Inventor Takeshi Kadoba 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term (reference) 2H088 EA12 GA03 GA04 HA03 HA04 HA08 HA18 JA19 KA14 KA20 LA07 MA18

Claims (4)

[Claims] 1. A chiral smectic liquid crystal, a pair of electrodes for applying a voltage to the liquid crystal, and a pair of substrates which face each other while sandwiching the liquid crystal and have been subjected to a uniaxial alignment treatment for aligning the liquid crystal. A liquid crystal device comprising a polarizing plate on at least one of the substrates, wherein the phase transition series of the chiral smectic liquid crystal is an isotropic liquid phase (Is
o. ) -Cholesteric phase (Ch) -Chiral smectic C (SmC ^* ) phase, wherein the uniaxial orientation treatment applied to both substrates is antiparallel, and the isotropic liquid phase (Iso.) Of at least one of the substrates. A liquid crystal element, wherein a pretilt angle of liquid crystal molecules immediately below a cholesteric phase (Ch) phase transition is 10 degrees or more, and an AC voltage is applied at least in a temperature range showing the cholesteric phase (Ch). 2. A temperature range in which the AC voltage is applied,
The chiral smectic liquid crystal isotropic liquid phase (Is
o. 2. The liquid crystal device according to claim 1, wherein the temperature range is at least (T _NI -10) ° C. or more, _assuming that the transition temperature of ())-cholesteric phase (Ch) is T _NI . 3. A pair of electrodes for applying a voltage to the chiral smectic liquid crystal and a pair of substrates which are opposed to each other with the liquid crystal interposed therebetween and which have been subjected to a uniaxial alignment treatment for aligning the liquid crystal. A method of manufacturing a liquid crystal element by injecting a liquid crystal element into a cell having a polarizing plate on at least one substrate, wherein a phase transition series of the chiral smectic liquid crystal isotropic liquid phase (Iso.)-Cholesteric from a high temperature side. Phase (Ch) -chiral smectic C (SmC ^* ) phase, wherein the uniaxial orientation treatment applied to both substrates is anti-parallel,
Injecting the chiral smectic liquid crystal into the cell when the pretilt angle of the liquid crystal molecules immediately below the isotropic liquid phase (Iso.)-Cholesteric phase (Ch) phase transition of at least one of the substrates is 10 degrees or more; Applying a AC voltage at least in a temperature range showing a cholesteric phase (Ch). 4. The temperature range in which the AC voltage is applied is
Isotropic liquid phase of the chiral smectic liquid crystal (Is
o. ) -Cholesteric phase (Ch) transition temperature is T _NIage
At least (T_NI-10) In the temperature range above ℃
4. The method for manufacturing a liquid crystal device according to claim 3, wherein
Law.