JP2001350161A - Liquid crystal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the damage of monostability and the increase of a driving voltage of a chiral smectic liquid crystal. SOLUTION: If a retardation quantity obtained when either one polar voltage is applied to the chiral smectic liquid crystal is defined as RV and a retardation quantity obtained when no voltage is applied is defined as R0, the ratio of them (that is, the rate Rrate=RV/R0) in a panel are not made uniform on the entire surface of the panel but made different for every region. The problem is generated, that if the ratio Rrate is great on the entire surface of the panel, the driving voltage of the chiral smectic liquid crystal is obliged to be increased though its monostability is non damaged and on the contrary, if the ratio Rrate is small on the entire surface of the panel, the monostability of the chiral smectic liquid crystal is damaged. Thus the damage of the monostability and the increase of the driving voltage of the chiral smectic liquid crystal can be prevented.

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 used for a flat panel display, a projection display and the like.

[0002]

2. Description of the Related Art Conventionally, a TFT (Thin Film T)
As a typical liquid crystal mode of a nematic liquid crystal display element which has been widely used as an active element such as a radiator, for example, M.S.
hadt) and W. Helfrich
Rich Applied Physics Letters (A)
Applied Physics Letters)
The twisted nematic mode shown in Vol. 8, No. 4 (published on Feb. 15, 1971), pp. 127-128 is widely used.

On the other hand, recently, a liquid crystal display using an in-plane mode or a vertical alignment mode using a lateral electric field has been announced, and the viewing angle characteristic which has been a defect of the conventional liquid crystal display has been improved. I have.

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 millimeters. It is slower than a second, and 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 type ferroelectric liquid crystal" and "threshold-less antiferroelectric liquid crystal" have been proposed. It is reported that high-speed response of sub-second can be realized.

[0006] On the other hand, the present inventors have disclosed Japanese Patent Application No. 10-177.
No. 145 (hereinafter referred to as a prior application) has invented and proposed a liquid crystal element. In the present invention, for example, the isotropic liquid phase (Iso) -cholesteric phase (Ch) -chiral smectic C phase (SmC *) or the isotropic liquid phase (Iso) -chiral smectic C from the high temperature side
Attention is paid to a phase transition 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 a pair of substrates at the time of Ch-SmC * phase transition or at the time of Iso-SmC * phase transition, and the layer direction is made uniform in one direction. As a result, high-speed response and gradation control are possible, and a high-brightness liquid crystal element with excellent moving image quality can be realized with high mass productivity.

[0007] Ferroelectric liquid crystals and antiferroelectric liquid crystals that perform inversion switching by such spontaneous polarization are liquid crystals exhibiting a chiral smectic liquid crystal phase. In other words, a liquid crystal display device using a chiral smectic liquid crystal is expected to be realized in the sense that the problem concerning the response speed of the conventional nematic liquid crystal can be solved.

[0008]

(1) Incidentally, the magnitude of the applied voltage (that is, the voltage to be applied to switch the liquid crystal molecules to a predetermined tilt angle) differs depending on the thickness of the liquid crystal layer. However, when the thickness of the liquid crystal layer is small, the applied voltage must be increased, and there is a problem associated with that. Hereinafter, this point will be described.

That is, as described above, a smectic liquid crystal having a high-speed response performance and a gradation display capability is expected for a next-generation display and the like. For example, in the device described in Japanese Patent Application No. 177145 or Japanese Patent Application No. 10-177146, when the thickness d of the liquid crystal layer is reduced to make the device a reflective liquid crystal device, the thickness d of the liquid crystal layer is reduced. It has been observed that the voltage value required for switching to a predetermined tilt angle greatly increases in accordance with the following. Such an increase in the voltage value (drive voltage) not only leads to an increase in power consumption of the liquid crystal element, but also causes an increase in the cost of peripheral circuits, and it is necessary to avoid the increase in the voltage value. .

(2) Next, the reason why the applied voltage must be increased when the thickness of the liquid crystal layer is small as described above will be described.

A monostable ferroelectric liquid crystal having a gradation display capability as described in Japanese Patent Application No. 10-177145 is premised on TFT driving, and has an alignment state corresponding to an applied voltage value. To form In this TFT drive, if a direct current is applied to the liquid crystal layer, it causes a burn-in phenomenon due to the uneven distribution of impurity ions. Therefore, an AC drive is generally used. In these modes having spontaneous polarization, an applied AC voltage is applied. The orientation state changes according to the polarity of.

In general, the inversion of bulk molecules is performed faster than the molecules near the interface, and the origin of the monostable mode is substantially the same as the average molecular axis direction when no electric field is applied and the uniaxial orientation processing axis. Considering that it is a state, even if a voltage is applied, the vicinity of the interface maintains the alignment state in a state where no voltage is applied, and it is considered that liquid crystal molecules always undergo a twisted state in molecular inversion in a transient state .

In other words, the above-mentioned monostable ferroelectric liquid crystal has the following characteristics: (1) a portion where a molecule is inverted on a cone in accordance with the intensity of the applied voltage (a portion distant from the substrate) Therefore, hereinafter, referred to as “reversal portion”; * Even when a voltage is applied, the orientation state in which no voltage is applied is maintained, and the portion hardly contributes to the reversal of molecules (portion located near the interface) , And hereinafter referred to as “non-inverted portion”).

It is considered that the thickness of the non-inversion portion strongly depends not on the thickness of the liquid crystal layer itself but on the regulating force of the interface. That is, it is considered that the non-reversal portion becomes thicker when the regulating force of the interface becomes stronger, and conversely, the thickness of the non-reversal portion becomes thinner when the regulating force of the interface becomes weaker.

As described above, the decrease in the thickness d of the liquid crystal layer indicates that the ratio between the inversion portion and the non-inversion portion changes, that is, the ratio occupied by the inversion portion decreases. As a result, it is considered that the voltage value required to switch the liquid crystal molecules to a predetermined tilt angle is increased.

(3) In order to prevent the increase in the applied voltage as described above, it is conceivable to reduce the ratio of the non-inverted portion. However, as described above, this monostable mode is developed by making the average molecular axis direction when no electric field is applied substantially coincide with the uniaxial orientation processing axis, and the non-inverted portion Decreasing the proportion will, in the first place, lead to a loss of monostability itself.

(4) As another method, in order to prevent the increase in the applied voltage as described above, it is conceivable to increase the value of the spontaneous polarization of the liquid crystal itself.

However, increasing the value of the spontaneous polarization leads to an increase in the amount of voltage drop due to inversion of the spontaneous polarization in the active matrix driving, which results in a decrease in the voltage value applied to the liquid crystal. Absent.

The present invention has been made in view of the above-mentioned problems, and a subject thereof is disclosed in Japanese Patent Application No. Hei 10-17714.
Provided are a liquid crystal element having a reduced driving voltage in a liquid crystal mode such as the element described in No. 5, an element having a suppressed increase in driving voltage when a narrow gap cell is formed, and a liquid crystal device using the element. It is to be.

[0020]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and comprises a chiral smectic 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. A pair of substrates on which at least one facing surface has been subjected to a uniaxial alignment treatment for aligning the liquid crystal, a polarizing plate arranged along at least one of the substrates, and at least one of the pair of electrodes An active element connected to each of the electrodes and arranged for each pixel, and a drive circuit for performing active matrix driving, comprising a liquid crystal element performing analog gray scale display, wherein the chiral smectic liquid crystal, when no voltage is applied, 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 is at an angle corresponding to the magnitude of the applied voltage. The liquid crystal tilts to one side from the mono-stabilized position, and when a voltage having a second polarity opposite to the first polarity is applied, the average molecular axis of the liquid crystal is shifted from the mono-stabilized position to a second position. A liquid crystal that tilts in a direction opposite to that when a voltage of one polarity is applied, and a retardation amount R _V obtained when a voltage of either polarity is applied, and a retardation amount R ₀ when no voltage is applied. And the ratio R _rate =
R _V / R _{0 comprises a} plurality of different regions.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS.
An embodiment of the present invention will be described.

The liquid crystal element according to the present invention is provided with a chiral smectic liquid crystal 1 as shown, for example, by reference numerals P ₁ and P ₂ in FIGS. 1 and 2 so that the liquid crystal 1 is sandwiched and opposed to each other. A pair of substrates 2a and 2b are arranged.
In addition, a uniaxial alignment process for aligning the liquid crystal 1 is performed on at least one of the pair of substrates 2a and 2b on the opposing surface (the surface on the side in contact with the liquid crystal 1).

Each of the liquid crystal elements P ₁ and P ₂ has a pair of electrodes 3 a and 3 b for applying a voltage to the liquid crystal 1, and a polarizing plate is arranged along at least one of the substrates 2 a and 2 b. (Not shown).

Incidentally, the pair of electrodes 3a and 3b described above
One of the electrodes is disposed in each pixel (see reference numeral 3b in FIG. 3), but an active element 4 connected to the electrode 3b is disposed in each pixel.

Further, the liquid crystal elements P ₁ and P ₂ are provided with a driving circuit (reference numeral 5 in FIG. 3) for performing active matrix driving.
6) for analog gradation display.

The liquid crystal elements P ₁ and P _{2 according} to the present invention have a non-inverted portion (that is, a portion near the interface of the liquid crystal 1,
Even if a voltage is applied, the alignment state in a state where no voltage is applied is maintained and a portion that hardly contributes to the inversion of molecules) is formed of a plurality of regions having different thicknesses. , And is configured to suppress an increase in applied voltage in a thin region of a non-inversion portion.

By the way, such a configuration (that is, having a thick region and a thin region of the non-inverted portion)
Can be evaluated by the amount of retardation. In other words, when externally observing a plurality of regions having different thicknesses of the non-inverted portions, the difference between these regions can be observed by measuring the amount of transient retardation when a voltage is applied. Hereinafter, this point will be described.

The amount of retardation is represented by the product of the refractive index anisotropy Δn and the thickness d of the liquid crystal layer, and the value of the refractive index anisotropy Δn referred to here is the average as viewed from the direction perpendicular to the substrate. Value when the molecules are aligned in one direction (and when the molecules are aligned in the horizontal plane with the substrate), and the molecular position is twisted in the layer Is a small observed value because it is observed as its average value. As a result, a plurality of regions having different thicknesses of the non-inverted portions can be determined by measuring the amount of transient retardation when applying a voltage. That is, the liquid crystal element according to the present invention has the thick region and the thin region of the non-inversion portion as described above, in other words, it has a plurality of regions having different amounts of retardation. .

That is, according to the present invention, either polarity
Retardation amount R obtained when a voltage of
_VAnd the amount of retardation R when no voltage is applied₀(S
That is, the value Δn of the refractive index anisotropy when no voltage is applied and the liquid crystal layer
Product of thickness d) and ratio R_rate= R _V/ R₀Are different
Characterized by the following region: That is, according to the present invention.
Liquid crystal device, * can be obtained when a voltage of either polarity is applied
The amount of retardation is R_V* The amount of retardation when no voltage is applied (i.e.,
That is, the value of the refractive index anisotropy Δn when no voltage is applied and the thickness of the liquid crystal layer
d) is R₀, And their ratio R_rate= R_V/ R₀Is displayed
What is uniform over the entire surface (the entire image display surface of the liquid crystal element)
Instead, they are different for each region (ie, the liquid crystal element
Is the ratio R_rateAre made up of different areas
).

In this case, the plurality of regions having different ratios R _rate is a region including a pixel (the plurality of regions are formed so as to correspond to each of the pixels. ) And a region that does not include a pixel (a region between adjacent pixels, hereinafter referred to as an “inter-pixel region”). In other words, the ratio R _rate = R _V / R ₀ may be different between the intra-pixel region and the inter-pixel region.
_It is preferable that the _rate is larger than the ratio R _rate in the inter-pixel region.

The value of the retardation amount R ₀ is
When the liquid crystal element is of a transmissive type, the thickness is preferably 240 nm or more. When the liquid crystal element is of a reflective type, the thickness is preferably 120 nm or more.

Next, a method of measuring the amount of transient retardation will be described.

The orientation of liquid crystal molecules when a voltage is applied to the liquid crystal element is divided into a liquid crystal layer near the interface that does not contribute to the polarization rotation of the incident polarized light and a bulk layer having a thickness d _sw that contributes to the polarization rotation.

The purpose of this measurement is to determine the transient switching angle and the amount of retardation in this bulk layer in real time. The authors thought that measurement could be performed by using a phase compensator to obtain these values. That is, a phase compensator having the same value as the amount of retardation of the bulk layer is prepared, and the layers are laminated while adjusting the angle so that the optical axis direction is orthogonal to the liquid crystal molecule orientation direction of the bulk layer. That is, when they are completely orthogonal to each other, it is considered that the retardation of the bulk layer is compensated and the amount of retardation becomes zero, so that no polarization rotation occurs and the transmitted light intensity in the voltage applied state, that is, the darkest state. Therefore, the switching angle of the bulk layer can be estimated by measuring the angle at which the phase compensator is provided at this time. Further, by performing this measurement using an oscilloscope and determining the angle at which the state becomes the darkest at any time,
Transient switching angles can be determined in real time.

Further, as the above-mentioned phase compensator, an ECB mode cell of a nematic liquid crystal can be used instead.
As a result, the amount of retardation can be changed only by changing the voltage applied to the nematic liquid crystal cell. Therefore, while performing the above-described operation of adjusting the stacking angle and appropriately adjusting the voltage applied to the nematic liquid crystal cell, the darkest state is obtained. By finding the condition for taking, both the retardation amount and the switching angle can be obtained at the same time.
The relationship between the voltage applied to the nematic liquid crystal and the amount of retardation can be measured with a Senarmon or Berek compensator. Also for this measurement, by performing this measurement using an oscilloscope and finding the condition that makes it the darkest state at any time,
The transitional switching angle and the amount of retardation can be simultaneously determined in real time.

Next, a method for producing a plurality of regions having different R _rates as described above will be described.

The method for producing a plurality of regions having different R _rates is not particularly limited, but for example, a mask rubbing method is used as one manual throw. That is, after forming an alignment film on the entire surface of the cell, the entire surface of the alignment film is rubbed. After that, a photoresist is applied to the surface of the alignment film, exposed and developed to expose only the alignment film in a specific region, and further rubbed on the entire surface. Thereafter, by removing the resist film (photoresist), it is possible to separately form a region rubbed once and a region rubbed twice in the panel surface.

Other methods include a UV ashing method in which an alignment film is formed on the entire surface of a cell, and only a predetermined portion of the alignment film is decomposed and peeled off by UV irradiation, and then rubbing is performed. Rubbing after laying the alignment film in a desired shape to impart rubbing properties.

On the other hand, R_rateHave different shapes
Although it is not particularly limited, as described above,
R that suppresses increase in drive voltage_ratePixels a large area of
R that is laid in the inner region and contributes to the addition of monostability_rateSmall
It is good to lay a small area in the area between pixels. That is,
Ratio R in elementary region_rateIs R in the inter-pixel region.
_rateIt is better to make it larger. In this case, R
_rateThe shape of the small area of
To form a stripe_rateLarge area shape
Should be formed in an island shape so as to correspond to the pixel area.
No. Also, the size of those areas is, for example, good
It may be adjusted so as to impart qualitative properties._{ra te}Small
Area is formed not in the whole area between pixels but in a part of it.
Is also good.

By the way, the cell thickness may be determined to be different from the cell thickness designed so that the product of the value of the refractive index anisotropy (Δn) of the liquid crystal material and the cell thickness becomes an optimum retardation value. desirable. In particular, in the element of the present invention, the effective Δ
Since the value of n is smaller, the product of the value of the refractive index anisotropy (Δn) of the liquid crystal material and the cell thickness is set to be larger than the cell thickness designed to be the optimum retardation value. It is desirable to determine the cell thickness.

The optimum retardation value mentioned here is a value in which Δnd / λ becomes １ ／ under crossed Nicols when used as a transmissive liquid crystal element, but this value is a value dependent on the wavelength. Therefore, it is necessary to determine the wavelength to be optimized in advance.

From our experience, it is known that, when used as a color display element, 400 nm to 480 nm is suitable as the center wavelength to be optimized from the viewpoint of the color temperature during white display. Therefore, the optimum retardation value is 200 nm to 240 nm. From the above, in the above display element and liquid crystal element, the product of the value of the refractive index anisotropy (Δn) of the liquid crystal material and the cell thickness is 200 nm to 240 nm.
It is desirable to determine the cell thickness so as to be larger than the range of nm.

According to the present invention, 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 is used as an element designed based on the above-described cell thickness design policy. Is provided.

The first of the liquid crystal elements applicable to the present invention is Japanese Patent Application Nos. 10-177145 and 10-177.
146, wherein the phase transition series of the liquid crystal material is isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase (SmC
*) Or an isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC *), in which a positive or negative DC voltage is applied between a pair of substrates during the transition to the SmC * phase. Thus, the alignment direction is aligned only in one of the two layer directions, that is, the deviation direction between the average uniaxial alignment processing axis and the normal direction of the smectic layer is constant. The orientation state of the SmC * phase, which is stabilized inward and whose memory property is lost, is obtained.

The chiral smectic liquid crystal used in the present invention has a phase transition series from the high temperature side, from an isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase (SmC *) or isotropic. Liquid phase (IS
O. ) -Chiral smectic C phase (SmC *) is preferred.

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

[0047]

Embedded image

[0048]

Embedded image

The second liquid crystal element applicable to the present invention includes a chiral smectic liquid crystal 1, and a pair of substrates 2a and 2b are arranged so as to sandwich the liquid crystal 1 and face each other. ing. In addition, a uniaxial alignment process for aligning the liquid crystal 1 is performed on at least one of the pair of substrates 2a and 2b on the opposing surface (the surface on the side in contact with the liquid crystal 1).

The liquid crystal device has a pair of electrodes 3 a and 3 b for applying a voltage to the liquid crystal 1.

The chiral smectic liquid crystal 1
Is a chiral smectic C liquid crystal, and the smectic layer of the liquid crystal has a chevron structure.

The tilt angle δ of the smectic layer having the chevron structure with respect to the substrate normal is at least equal to or greater than the tilt angle 前 記 of the chiral smectic C liquid crystal at the operating temperature (that is, substantially equal to the tilt angle Θ). Or larger angle).

According to this liquid crystal element, when no electric field is applied, the chiral smectic liquid crystal 1 has an average molecular axis of the molecules of the liquid crystal substantially coincident with the average uniaxial alignment processing axis, and the liquid crystal molecules between the crossed Nicol polarizers. It has an orientation state having only one darkest optical axis when sandwiched, and when an electric field is applied, the apparent tilt angle and transmitted light intensity of the chiral smectic liquid crystal continuously change according to the intensity change of the applied electric field. Will change.

In addition to the liquid crystal mode described above, any ferroelectric liquid crystal element in which the orientation vector of liquid crystal molecules is oriented in one direction when no voltage is applied can be applied. For example, JP-A-4-212
16 or a polymer-stabilized ferroelectric liquid crystal.

In the above element, when the retardation amount when no voltage is applied and the retardation amount when voltage is applied are compared,
Since the amount of retardation at the time of applying a voltage is smaller, when a liquid crystal element that displays black when no voltage is applied is used,
In order to obtain a desired amount of transmitted light, a design is made so that the product of the value Δn of the refractive index anisotropy of the liquid crystal material and the cell thickness d is larger than the desired amount of retardation.

In the present invention, the helical pitch in the bulk state of the chiral smectic liquid crystal 1 is preferably longer than twice the cell thickness.

Further, as the chiral smectic liquid crystal 1, an isotropic liquid phase (ISO.)-Cholesteric phase (C
h) -Smectic A phase (SmA) -a chiral smectic C phase (SmC *) having a phase transition series, and in a manufacturing process thereof, the liquid crystal 1 is cooled to a cholesteric phase (Ch) or a smectic A phase (SmA). ) And chiral smectic C phase (SmC *)
An electric field application treatment is preferably applied to the liquid crystal. Furthermore, the liquid crystal 1
The liquid crystal may be subjected to a pressure treatment at a temperature at which the temperature is lowered to show a smectic A phase (SmA) or a chiral smectic C phase (SmC *). Furthermore, as a chiral smectic liquid crystal 1, an isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase (S
In the manufacturing process, an electric field is applied to the liquid crystal 1 at a temperature at which the temperature of the liquid crystal 1 is lowered to show a cholesteric phase (Ch) or a chiral smectic C phase (SmC *). May be applied.

By the way, the inclination angle δ of the smectic layer of the chiral smectic liquid crystal 1 is smaller than the magnitude calculated from the temperature change of the layer spacing in the bulk state of the chiral smectic C liquid crystal at least at the use temperature. Should also be large.

Further, the layer inclination angle δ of the chevron structure in the device changed by the electric field application processing and / or the pressure processing.
But it may be greater than the layer inclination angle [delta] ₀ of the initial chevron structure which is formed by cooling from a high temperature side that indicates the isotropic liquid phase.

In this case, the helical pitch in the bulk state of the chiral smectic C liquid crystal is preferably longer than twice the cell thickness.

[0061] Furthermore, among the plurality of regions, and the retardation amount R _V obtained upon applying either polarity of the voltage, the retardation amount R when no voltage is applied
₀ (that is, the product of the refractive index anisotropy value Δn when no voltage is applied and the thickness d of the liquid crystal layer) in a smaller region of the _rate R _rate = R _V / R ₀ , the ratio is set to 0. It is good to be 90 or less.

Hereinafter, a specific configuration of the liquid crystal element according to the present invention will be described.

In the liquid crystal elements P ₁ and P ₂ , a pair of glass
Substrates 2a, 2 made of highly transparent material such as plastic
The cell has a structure in which a liquid crystal 1, preferably a liquid crystal exhibiting a chiral smectic phase, is sandwiched between b, and a cell is sandwiched between a pair of polarizing plates (not shown) whose polarization axes are orthogonal to each other.

The substrates 2a and 2b are provided with electrodes 3a and 3b made of a material such as In ₂ O ₃ or ITO for applying a voltage to the liquid crystal 1, respectively. Transparent electrodes 3b are arranged in a matrix and each transparent electrode is provided with a TFT or MIM (Metal-Ins).
It is preferable to connect an active element 4 such as an U.S.A.-Ultor-Metal) and provide an opposing electrode 3a on one surface of the other substrate or a predetermined pattern to form an active matrix structure.

[0065] electrodes 3a, On 3b, _SiO 2 having a function such as to prevent these short optionally, Ti
Green insulating films 7a and 7b made of a material such as O ₂ and Ta ₂ O ₅ are provided, respectively.

Further, on the insulating films 7a and 7b, alignment control films 8a and 8b which are in contact with the liquid crystal 1 and function to control the alignment state are provided. Such alignment control films 8a,
8b is subjected to a uniaxial orientation 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 8a and 8b may have different pretilt angles of the molecules of the liquid crystal 1 (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 (uniaxial orientation treatment and the like). Is adjusted.

When the orientation control films 8a and 8b are both uniaxially oriented films, the uniaxial orientation direction (especially the rubbing direction) of each film is parallel or antiparallel depending on the liquid crystal material used. Alternatively, it can be set to cross in the range of 45 ° or less.

The substrates 2a and 2b face each other with the spacer 9 interposed therebetween. Such spacers 9 are used for the substrates 2a and 2b.
To determine the distance between them (cell gap), and silica beads or the like are used. Regarding the cell gap determined here, the optimum range and the upper limit value are different depending on the difference of the liquid crystal material, but the uniform uniaxial orientation, and the average molecular axis of the liquid crystal molecule when no voltage is applied is almost in the average direction of the alignment processing axis. In order to develop an orientation state that is substantially the same as the axis,
It is preferable to set the range of 0.3 to 10 μm. Further, as described above, it is preferable that the value of the cell thickness is appropriately adjusted and set so as to have a desired retardation amount.

In addition to the spacers 9, 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 2a and 2b and to improve the impact resistance of the liquid crystal exhibiting a chiral smectic phase. (Not shown).

In the liquid crystal elements P ₁ and P _{2 having the} above structure, when a liquid crystal exhibiting a chiral smectic phase is used as the liquid crystal 1, 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 are performed. By appropriately setting the materials and processing conditions of the films 8a and 8b, when no voltage is applied, the liquid crystal exhibits an alignment state (first state) in which the average molecular axis (liquid crystal molecules) is monostable. When a voltage of the first polarity is applied, the average molecular axis of the liquid crystal tilts to one side from the mono-stabilized position at an angle corresponding to the magnitude of the applied voltage, and is opposite to the first polarity. When a voltage of the second polarity is applied, the average molecular axis of the liquid crystal is tilted from the monostable position to a side opposite to that applied when the voltage of the first polarity is applied. I do. At this time, the maximum tilt angle due to the application of the voltage of the first polarity (that is, the largest one of the tilt angles based on the mono-stabilized position in the first state) β1 is equal to the voltage of the second polarity. May be larger than the maximum tilt angle β2 (β1> β2). Also, β1 ≧ 5 × β2
You may make it become. Further, β1 = β2 may be satisfied.

As the liquid crystal material exhibiting a chiral smectic phase, biphenyl which exhibits the above-mentioned properties (properties relating to the physical property value cone angle の, the layer spacing d of the smectic layer, and the inclination angle δ inherent to the liquid crystal material) is used. A composition obtained by appropriately selecting and adjusting a hydrocarbon-based liquid crystal material, a naphthalene-based liquid crystal material, and 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, at least one of R, G, and B color filters may be provided on one of the substrates 2a, 2b to form a color liquid crystal device.

The liquid crystal element is connected to both substrates 2a and 2a.
b, a transmission type liquid crystal element in which a pair of polarizing plates is provided, that is, both of the substrates 2a and 2b are translucent substrates, and modulate incident light (for example, light from an external light source) from one substrate side, and Or a reflective liquid crystal element in which a polarizing plate is provided on at least one substrate, that is, the substrate 2a,
The incident light and the reflected light are modulated by providing a reflective plate on one side of 2b or using a reflective material as one substrate itself or a member provided on the substrate, and the light is directed to the same side as the incident side. The present invention can be applied to any of the emission type elements.

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-mentioned 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 having 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.

With reference to FIGS. 2 to 5, an example in which such an active matrix substrate is used in the liquid crystal device of the present invention will be described.

FIG. 3 schematically shows the element with a driving means, focusing on the structure of one substrate (active matrix substrate).

In the configuration shown in FIG. 3, in a panel section corresponding to a liquid crystal element, a scanning signal driver 6 serving as driving means is provided.
Drawing on the horizontal direction as the gate lines G _1, G 2 _..., the drawings on the vertical direction of the source lines S ₁ corresponding to the information signal line which is connected to the information signal driver 5 is a drive means corresponding to the scan lines connected to, S 2 _... is provided with orthogonally with each other while being insulated from each other, a thin film transistor (TFT) 4, and the pixel electrode 3b corresponding to the active elements corresponding to the pixels of the intersections are provided (FIG. So for simplicity 5
Only the area of x5 pixels is shown). It should be noted that an MIM element can be used as the active element in addition to the TFT. The gate lines _{G 1,} G 2 _... is connected to the gate electrode of the TFT 4 (not shown), the source lines _{S 1,} S 2 _... is connected to the source electrode of the TFT 4 (not shown), the pixel electrode 3b is TF
It is connected to a drain electrode (not shown) of T4. In this configuration, the gate lines G ₁ , G ₂ ... Are, for example, line-sequentially scanned and selected by the scanning signal driver 6 and a gate voltage is supplied. Are supplied to the source lines S ₁ , S _2, ...
4 is applied to each pixel electrode.

FIG. 2 shows an example of a sectional structure of each pixel portion (for one pit) in the panel configuration shown in FIG. In the structure shown in the figure, a liquid crystal layer 1 having spontaneous polarization is sandwiched between an active matrix substrate 2b having a TFT 4 and a pixel electrode 3b and a counter substrate 2a having a common electrode 3a, thereby forming a liquid crystal capacitor Clc. (See FIG. 4).

In the active matrix substrate 2b, an example in which an amorphous Si TFT is used as the TFT 4 is shown. The TFT 4 is a substrate 2b made of glass or the like.
Formed thereon, via an insulating film (gate Zemmidorimaku) 7b which is formed on the gate lines G _1, G 2 _... gate electrode 11 which is SeMMitsuru in made of a material such as silicon nitride (SiNx) shown in FIG. 3 a-
An Si layer 12 is provided, and on the a-Si layer 12,
Source electrode 1 is interposed via n + a-Si layers 13 and 14, respectively.
5. The drain electrode 16 is provided apart from each other. The source electrodes 15 correspond to the source lines S ₁ , S ₂ .
And the drain electrode 16 is connected to the pixel electrode 3b made of a transparent conductive film such as an ITO film. In addition, TFT4
The channel protective film 17 covers the a-Si layer 12 in FIG. The TFT 4 is turned on by applying a gate pulse to the gate electrode 11 during a period in which the corresponding gate line is selected for scanning.

Further, in the active matrix substrate 2b, the insulating film 7b (continuously formed with the insulating film on the gate electrode 11) is formed by the pixel electrode 3b and the storage capacitor electrode 20 provided on the glass substrate side of the electrode. A storage capacitor Cs is provided in parallel with the liquid crystal layer 1 by a structure sandwiching the film (see FIG. 4). When the area of the storage capacitor electrode 20 is large, the aperture ratio is reduced, and thus the storage capacitor electrode 20 is formed of a transparent conductive film such as an ITO film.

The TFT 4 on the active matrix substrate 2b
On the pixel electrode 3b, there is provided an alignment film 8b 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, a common electrode 3a and an alignment film 8a for controlling the alignment state of the liquid crystal are laminated on the glass substrate 2a with the same thickness as the entire surface.

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 1.

In the panel structure 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, 1F 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 1 is divided into two fields when exhibiting the optical characteristics shown in FIG. 6 will be described. It should be noted that an element that can obtain the same transmitted light intensity with both positive and negative polarities can be similarly described, and thus the description thereof is omitted.

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 G ₁ , G _2, ... 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 11. Vg is added and T
FT4 is turned on. In a non-selection period Toff corresponding to a period in which another gate line is selected, the gate electrode 1
No voltage is applied to 1 and TFT 4 is in a high resistance state (OFF state)
Thus, a predetermined same gate line is selected for each Toff, and a gate voltage Vg is applied to the gate electrode 11.

FIG. 5B shows the voltage Vs applied to the information signal line (source line) of the pixel. As shown in FIG. 5A, the gate electrode 1 is turned on during the selection period Ton in each field.
1 is applied with a predetermined source voltage (information signal voltage) V from source lines S ₁ , S _2, ... Which are information lines connected to the pixel in synchronization with the gate voltage.
S (reference potential is the potential Vc of the common electrode 3a) is applied.

Here, in the first field (1F) constituting one frame, an optical state to be obtained in the pixel based on information written in the pixel, for example, a voltage-transmittance characteristic corresponding to the liquid crystal used. Or, a source voltage (information signal voltage) having a positive polarity of level Vx according to display information (transmittance)
(The reference potential is the potential Vc of the common electrode 3a). At this time, since the TFT 4 is in the ON state, the voltage Vx applied to the source electrode 15
Is applied to the pixel electrode (3b) through the liquid crystal capacitor Clc.
And the storage capacitor Cs is charged, and the potential of the pixel electrode becomes the information signal voltage Vx. Subsequently, during the non-selection period Toff of the gate line to which the pixel belongs, the TFT 4 has a high resistance (off state). Therefore, during this non-selection period, the selection period T is not applied to the liquid crystal cell (liquid crystal capacitance Clc) and the storage capacitance Cs.
The state in which the charge charged by ON is accumulated is maintained, and the voltage Vx is held. Then, the liquid crystal layer 1 in the pixel
During the period of the first field 1F, the voltage Vx is applied, and in the liquid crystal portion of the pixel, an optical state (transmitted light amount) corresponding to the voltage value is obtained.

Next, in the selection period Ton of the second field (2F), the source voltage (-Vx) having a polarity similar to that of the first field 1F and having substantially the same voltage value Vx.
Is applied to the source electrode 15. At this time, the TFT 4 is in the ON state, the voltage -Vx is applied to the pixel electrode 3b, and the liquid crystal capacitance Clc and the storage capacitance Cs are charged.
The potential of the pixel electrode becomes the information signal voltage -Vx. continue,
During the non-selection period Toff, the TFT 4 has a high resistance (off state). During this non-selection period, the liquid crystal cell (the liquid crystal capacitance Clc) and the storage capacitor Cs store the charge accumulated during the selection period Ton. And the voltage -Vx is maintained. Then, the second liquid crystal layer 1
Voltage -Vx is applied throughout the field 2F of
In the pixel, the optical state (the amount of emitted light) according to this voltage value
Is obtained.

FIG. 5C shows the voltage value Vpix actually held in the liquid crystal capacitance and the storage capacitor of the pixel and applied to the liquid crystal layer 1 as described above, and FIG. FIG. 1 schematically shows the actual optical response (optical response in the case of a transmission type liquid crystal element). As shown in (c), the applied voltages through the two fields 1F and 2F are at the same level (absolute value) Vx whose polarity is just inverted. on the other hand,
As shown in (d), in the first field 1F, a gradation display state (light emission amount) corresponding to Vx is obtained based on, for example, the characteristics shown in FIG. 6, and in the second field 2F, the gradation display state corresponding to -Vx is obtained. Although a tone display state can be obtained, for example, according to the characteristic as shown in FIG. 6, only a slight change in the transmitted light amount is actually obtained, and the transmitted light amount is smaller than Tx and T is close to 0 level.
y.

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%.
% Or less, and the high-speed response characteristics of moving images 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 1 in the first and second fields, the voltage actually applied to the liquid crystal layer 1 is converted into an alternating current, thereby preventing the liquid crystal from being deteriorated.

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. For this reason, the information signal voltage Vs increases the amount of transmitted light by a predetermined level in accordance with the image information (gradation information) to be actually obtained by the pixel in the frame in accordance with the characteristics shown in FIG. It is also preferable to select and apply an obtainable voltage value to display a gradation state with a higher level of transmitted light than the desired gradation state in the first field 1F.

Next, effects of the present embodiment will be described.

According to the present embodiment, gradation display can be performed without deteriorating the monostability of the chiral smectic liquid crystal, and an increase in applied voltage can be suppressed.

[0098]

The present invention will be described below in more detail with reference to examples.

The present inventor produced various liquid crystal panels as shown in the table below by using different cells, alignment film materials and liquid crystal compositions, and confirmed the effects of the present invention.

[0100]

[Table 1]

Hereinafter, for each liquid crystal panel, (1) Adjustment of photosensitive polyimide resin composition (1-1) Adjustment of photosensitive polyimide resin composition PI-A (1-2) Adjustment of photosensitive polyimide resin composition PI- Adjustment of B (2) Cell manufacturing method (2-1) Cell A-1 and A-2 manufacturing method, (2-2) Cell B-1 and B-2 manufacturing method (2-3) Cell C -1, Method for preparing C-2 (3) Method for adjusting liquid crystal composition (3-1) Method for adjusting liquid crystal composition LC-1 (3-2) Method for adjusting liquid crystal composition LC-2 (4) Liquid crystal (5) Observation results of liquid crystal panels 1A-1, 1B-1, and 1C-1 (5-1) Alignment state and driving state of liquid crystal (5-2) Measurement of retardation amount (6) Liquid crystal panel 2A -1,2A-2,2C-1,2C
Observation results for -2 (6-1) Orientation state of liquid crystal (6-2) Optical response (6-3) Square wave response (6-4) Measurement of retardation will be described in detail.

(1) Adjustment of photosensitive polyimide resin composition (1-1) Adjustment of photosensitive polyimide resin composition PI-A A stirrer, a nitrogen inlet tube, a discharge tube equipped with a calcium chloride tube, and a thermometer were attached. A 300 ml four-neck flask was replaced with nitrogen gas in advance. In this flask, N 2 of a polyamic acid having the following repeating unit was placed under a nitrogen stream.
-Methyl-2-pyrrolidone solution (solids concentration 13.5
%) Of 100 g (0.04 mol) and 18.5 g of freshly distilled diethylaminoethyl methacrylate.
(0.1 mol) and stirred at room temperature for 1 hour to obtain a solution (A) in which a salt of polyamic acid and diethylaminoethyl methacrylate was formed.

[0103]

Embedded image

In order to confirm the salt formation, the stretching vibration absorption band of the carbonyl group C ＝ O contained in the polyamic acid was measured with an infrared spectrophotometer (model 270-30 manufactured by Hitachi, Ltd.). However, the absorption band based on C ＝ O contained in a free carboxyl group in polyamic acid is 1700 c
m ^-1 , whereas C was obtained by adding diethylaminoethyl methacrylate to the polyamic acid and stirring.
The absorption band of ＯO shifted to 1600 to 1650 cm ⁻¹ , indicating that a salt was formed.

Then, 58.26 g of special grade N, N-dimethylacetamide was added to 47.4 g of the solution (A) and mixed in an ultrasonic wave to obtain a solution (B).

On the other hand, under a nitrogen stream, 5.2 g of a photopolymerization initiator Irgacure 651 (manufactured by Ciba Geigy) and 2.6 g of a sensitizer Dytocure PAA (manufactured by Daito Kagaku Kogyo Co., Ltd.)
Was dissolved in 15.6 g of special grade N, N-dimethylacetamide to prepare a solution (C).

To 105.66 g of the solution (B) obtained above, 2.34 g of the solution (C) was added and mixed in an ultrasonic wave, followed by pressure filtration using a filter having a pore size of 5 μm.
Photosensitive polyimide resin composition (PI-A) having a solid content of 12.6% (polyamic acid solid content of 5.0%)
Was prepared.

(1-2) Photosensitive polyimide resin composition PI
Adjustment of -B A 300 ml four-necked flask equipped with a stirrer, a nitrogen inlet tube, and a discharge tube thermometer equipped with a calcium chloride tube was replaced with nitrogen gas in advance. In a flask, an N-methyl-2-pyrrolidone solution of a polyamic acid having the following repeating unit (solid content concentration: 13.5%) 100 was placed under a nitrogen stream.
g (0.04 mol) and 18.5 g (0.1 mol) of freshly distilled diethylaminoethyl methacrylate.
l) was added, and the mixture was stirred at room temperature for 1 hour to obtain a solution (A) in which a salt of polyamic acid and diethylaminoethyl methacrylate was formed.

[0109]

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In order to confirm the salt formation, the stretching vibration absorption band of the carbonyl group C ＝ O contained in the polyamic acid was measured with an infrared spectrophotometer (model 270-30 manufactured by Hitachi, Ltd.). However, the absorption band based on C = O contained in a free carboxyl group in polyamic acid is 1700 m
^-1 while C = O after searching by adding diethylaminoethyl methacrylate to polyamic acid.
Has been shifted to 1600 to 1650 cm ⁻¹ , indicating that a salt was formed.

Then, 58.38 g of special grade N, N-dimethylacetamide was added to 47.4 g of the solution (A) and mixed in an ultrasonic wave to obtain a solution (B).

On the other hand, a solution (C) was prepared by dissolving 2.96 g of a photopolymerization initiator Irgacure 369 (manufactured by Ciba Geigy) in 19.24 g of special grade N, N-dimethylacetamide under a nitrogen stream.

To 105.78 g of the solution (B) obtained above, 2.22 g of the solution (C) was added, mixed in an ultrasonic wave, and then filtered under pressure using a filter having a pore size of 5 μm.
Photosensitive polyimide resin composition (PI-B) having a solid content of 12.1% (polyamic acid solid content of 5.0%)
Was prepared.

(2) Manufacturing Method of Cell (2-1) Manufacturing Method of Cells A-1 and A-2 The matrix cells (simple matrix type cells) A-1 and A-2 used in the examples are as follows. It was produced as follows.

As a transparent electrode, an ITO film (about 70 n thick)
A pair of 1.1 mm-thick glass substrates on which m) was formed were prepared.

The photosensitive polyimide resin composition (PI-A) prepared above was applied to this glass substrate by spin coating, and then pre-dried at 100 ° C. for 5 minutes.

Next, a stripe-shaped mask pattern having a mask width of 16 μm and an interval of 4 μm was arranged on the polyimide film. Subsequently, UV light (light energy at a wavelength of 254 nm was 1.44 J / cm
² ) was irradiated and exposed. Next, development was performed for 15 seconds using a developing solution of dimethylformamide / ethanol = 5/5, followed by washing in ethanol and drying the substrate. Thereafter, the substrate is heated and baked at 200 ° C. for 1 hour, and a region (width 4 μm) and a region (width 16 μm) where the stripe-shaped polyimide film exists on the substrate at 50 ° are present.
Was obtained.

Subsequently, the polyimide 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) was adhered to a roll having a diameter of 10 cm, a pushing amount of 0.3 m, and a feed speed of 10 cm /
sec, the number of rotations was 1000 rpm, and the number of times of feeding was 4 times.
The direction of the rubbing treatment was set in a direction perpendicular to the stripe direction of the polyimide film.

Subsequently, as a spacer on one of the substrates,
Silica beads having an average particle size of 1.4 μm were scattered, and the other substrate was bonded so that the polyimide films of the upper and lower substrates coincided with each other, thereby producing a cell A-1.

On one substrate, AlSiCu was used as a reflective electrode.
Cell A-2 was produced in the same manner as described above, except that a 1.1-mm-thick glass substrate having a film (thickness: 120 nm) formed thereon was used and 0.7 μm silica beads were used as spacers.

The pretilt angle of the cell measured by a crystal rotation method was 2.00.

(2-2) Manufacturing method of cells B-1 and B-2 A pair of glass substrates having a thickness of 1.1 mm on which an ITO film (about 70 nm thick) was formed as a transparent electrode was prepared.

The photosensitive polyimide resin composition (PI-B) prepared above was applied to this glass substrate by spin coating, and then pre-dried at 100 ° C. for 5 minutes.

Next, an island-shaped mask pattern (mask area: 16 μm square, grid portion: 4) was formed on the polyimide film.
μm width). Then, UV light from high pressure mercury lamp
Light (light energy at a wavelength of 254 nm is 1.44
J / cm ² ). Next, development was performed for 15 seconds using a developing solution of dimethylformamide / ethanol = 5/5, followed by washing in ethanol and drying the substrate. Thereafter, the substrate is heated and baked at 200 ° C. for 1 hour.
Corner) was obtained.

Subsequently, the polyimide 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: using a rubbing roll in which nylon (NF-77 / manufactured by Teijin) was attached to a roll having a diameter of 10 cm, a pushing amount of 0.3 mm, and a feeding speed of 10 cm.
/ Sec, the number of rotations was 1000 rpm, and the number of times of feeding was 4 times. The direction of the rubbing treatment was set to a direction parallel to one side of the lattice of the polyimide film.

Subsequently, as a spacer on one of the substrates,
Silica beads having an average particle diameter of 1.4 μm were sprayed, and the other substrate was overlapped so that the polyimide films were aligned on the upper and lower substrates, thereby producing a cell B-1.

Also, AlS was used as a reflective electrode on one of the substrates.
Cell B-2 was prepared in the same manner as described above, except that a 1.1 mm thick glass substrate on which an iCu film (120 nm in thickness) was formed and 0.7 μm silica beads were used as spacers.
Was prepared.

The pretilt angle of the cell measured by a crystal rotation method was 2.00.

(2-3) Manufacturing Method of Cells C-1 and C-2 A pair of glass substrates having a thickness of 1.1 mm on which an ITO film (about 70 nm thick) was formed as a transparent electrode was prepared.

On this glass substrate, a polyimide (precursor) having the following repeating unit was applied by spin coating, followed by pre-drying at 80 ° C. for 5 minutes.
The resultant was baked at 00 ° C. for 1 hour to obtain a polyimide film having a thickness of 50 °.

[0131]

Embedded image

Subsequently, the polyimide on the substrate was subjected to a rubbing treatment as a uniaxial orientation treatment by the same method and under the same conditions as in the case of the cell A.

Subsequently, silica beads having an average particle diameter of 1.4 μm were sprayed as spacers on one of the substrates, and the other substrate was overlaid to produce a cell C-1.

Further, AlS was used as a reflective electrode on one of the substrates.
Cell C-2 was prepared in the same manner as described above, except that a 1.1 mm thick glass substrate on which an iCu film (120 nm thick) was formed and 0.7 μm silica beads were used as spacers.
Was prepared.

The pretilt angle of the cell measured by a crystal rotation method was 2.00.

(3) Method for Adjusting Liquid Crystal Composition (3-1) Method for Adjusting Liquid Crystal Composition LC-1
1 was adjusted.

[0137]

Embedded image

The parameters of the liquid crystal composition are shown below.

(3-2) Method of Adjusting Liquid Crystal Composition LC-2 The following liquid crystal compound was mixed to adjust the liquid crystal composition LC-2. The numerical values described together with the mixing formula are weight ratios at the time of mixing.

[0140]

Embedded image

The parameters of the liquid crystal composition are shown below.

(4) Production of liquid crystal panel Cells A-1, B-1, and C-1 produced by the above process
Was injected at a temperature of an isotropic phase, and the liquid crystal was gradually cooled to a temperature showing a chiral smectic liquid crystal phase, thereby producing liquid crystal panels 1A-1, 1B-1, and 1C-1.

On the other hand, the cell A-
1, A-2, C-1, and C-2, a liquid crystal composition LC-2 was injected at an isotropic phase temperature, and the liquid crystal was cooled to a temperature at which a chiral smectic liquid crystal phase was exhibited. SmC
* Before and after the phase transition, a cooling process was performed by applying an offset voltage (DC) voltage of -5 V to produce liquid crystal panels 2A-1, 2A-2, 2C-1, and 2C-2.

(5) Liquid crystal panels 1A-1, 1B-1, 1
Observation Results for C-1 Each of the liquid crystal panels 1A-1 produced as described above,
Regarding 1B-1 and 1C-1, the alignment state of the liquid crystal, driving, and retardation were observed. Hereinafter, the results will be described.

(5-1) Alignment State and Driving State of Liquid Crystal The initial alignment state of the liquid crystal of the liquid crystal panels 1A-1, 1B-1, and 1C-1 was observed with a polarizing microscope. Each was a bistable state in which two domains were mixed.

Liquid crystal panels 1A-1, 1B-1, 1C-1
At room temperature (30 ° C.) ± 50 V, 10 Hz
After applying the rectangular wave and applying the electric field, the alignment state was observed under a polarizing microscope. From the bistable state in which the two domains observed before the electric field application were mixed,
It was observed that the orientation changed to a uniform alignment state having the darkest axis in the rubbing direction.

Liquid crystal panels 1A-1 and 1A after electric field application processing
B-1 and 1C-1 were arranged in a polarizing microscope equipped with a photomultiplier so that the polarization axis was aligned in the rubbing direction to provide a dark field, and the voltage values were 0 to ± 15 V and 0.1 Hz.
Observing the optical response (transmittance) when applying a rectangular wave of the above, it performs domainless switching, and draws a voltage-transmittance curve VT of a V-shaped curve with no hysteresis centering on 0V. I understood. The saturation voltage of the voltage transmittance characteristics of this cell was about 8.0 V on both the positive side and the negative side for 1A-1 and 1B-1. On the other hand, 1C-
As for No. 1, both the positive side and the negative side were about 10.0 V. When the application of the electric field to these liquid crystal panels is stopped, the darkest axis returns to the same uniform state as the rubbing direction, and it can be seen that the most stable position of the molecules in this liquid crystal panel is in the same direction as the rubbing direction.

Since these liquid crystal panels exhibit a continuous optical response to an applied voltage, analog gray scale display can be performed by amplitude modulation by TFT active matrix driving.

(5-2) Measurement of the amount of retardation The retardation of these liquid crystal panels was measured. Measurements were taken without voltage, 30 Hz, ± 10
V square wave alternating current was measured for two of the values during application.
As a measurement method, a value when no voltage was applied was measured using a Bellec compensator, and a value during voltage application was measured according to the method of measuring the average retardation amount during driving described in this specification. At the time of the measurement, the spot of the microscope was squeezed to 1A-1, 1B-1.
As for, the retardation of a place where the polyimide film was not laid was measured. Similarly, for 1C-1, the retardation was measured after narrowing the spot. As a result, the ratio of the retardation value when no voltage is applied to the retardation value when voltage is applied is 1A-1, 1B-
1 was 0.96, while 1C-1 was 0.85. It is considered that the region where the polyimide film is not laid has a larger retardation ratio, and molecules near the interface are also switching. Also, as a result, it seems that 1A-1 and 1B-1 had lower saturation voltages.

(6) Liquid crystal panels 2A-1, 2A-2, 2
Observation results for C-1 and C-2 Each of the liquid crystal panels 2A-1 and 2A-1
With respect to 2A-2, 2C-1 and 2C-2, the alignment state, optical response, rectangular wave response and retardation of the liquid crystal were observed. Hereinafter, the results will be described.

(6-1) Orientation state of liquid crystal The + orientation state of the liquid crystal of the liquid crystal panels 2A-1, 2A-2, 2C-1, and 2C-2 was also observed by a polarizing microscope. In each case, the darkest axis was slightly deviated from the rubbing direction when no voltage was applied, and an almost uniform alignment state in which the layer normal direction was only one direction in the entire cell was observed.

(6-2) Optical Response In order to measure the electro-optical response of the liquid crystal panel, the cells of the liquid crystal panels 2A-1, 2A-2, 2C-1, and 2C-2 were subjected to photomultiplier under crossed Nicols. The polarizing axis was arranged so that the polarization axis was in a dark field with no voltage applied.

± 30 V, 0.2 H at 30 ° C.
Observing the optical response when the z-triangular wave was applied, the amount of transmitted light (transmittance) gradually increased in response to the magnitude of the applied voltage when the voltage of the positive polarity was applied. On the other hand, the state of the optical response at the time of application of the voltage of the negative polarity indicates that although the transmitted light amount changes with respect to the voltage level, the maximum light amount is
When compared with the maximum transmittance when a positive voltage is applied, 1/1
It was about 0.

The saturation voltage of these cells when a positive voltage was applied was measured. The cells 2A-1 and 2C-1 having a liquid crystal layer thickness (cell gap) of 1.4 μm were approximately 4 V and 5 V, respectively. there were. On the other hand, the saturation voltage of 2A-2 was about 5 V for 2A-2 and 2C-2 having a liquid crystal layer thickness (cell gap) of 0.7 μm, whereas the reflected light amount was increased for 2C-2 even when 10 V was applied. Continued to rise gradually and was not saturated even when 10 V was applied.

(6-3) Rectangular Wave Response The liquid crystal panels 2A-1, 2A-2, 2C-1, and 2C-2 were set at 60 Hz (±
The optical level was measured while changing the voltage by applying a rectangular wave voltage of 10 V).

As a result, it was confirmed that the optical response sufficiently responded to the voltage of the positive polarity, and the optical response did not depend on the previous state, and a stable halftone state was obtained. In addition, an optical response of about 1/10 of the case of applying a positive voltage having the same voltage absolute value to a negative voltage is confirmed, and the average value of the optical response to positive and negative voltages does not depend on the previous state. It was confirmed that a stable halftone was obtained.

(6-4) Measurement of retardation The retardation of the liquid crystal panels 2A-1, 2A-2, 2C-1, and 2C-2 was measured.

The measurement was performed with no voltage applied, at 60 Hz,
A ± 10 V square wave alternating current was measured for two values during application. For the measurement method, the value when no voltage was applied was measured using a Berek compensator, and the value during the voltage application was measured according to the method for measuring the average retardation amount during driving described in this specification.
At the time of measurement, the spot of the microscope was squeezed 2A-1,
For 2A-2, the retardation of a place where no polyimide film was laid was measured. Also, 2C-1, 2C
With respect to -2, the spot was similarly narrowed down, and the retardation was measured. As a result, the ratio of the retardation value when no voltage was applied to the retardation value when voltage was applied was 0.96 for 2A-1, whereas 2C-
1 was 0.86. In addition, for 2A-2 in which the liquid crystal layer thickness (cell gap) is 0.7 μm, 0.1 is used.
94 and 2C-2 were 0.82. 2A-1, 2A- in which a polyimide film is laid in a stripe shape
In the case of No. 2, the change amount of the retardation ratio is smaller than the change of the cell gap. On the other hand, in the case of 2C-1 and 2C-2 in which a polyimide film is laid on the entire surface, the retardation ratio is also significantly reduced when the cell gap is reduced.

In the region where the polyimide film is not laid, molecules near the interface are switched even when the cell gap is small. As a result, when the cell gap becomes smaller in 2A-1 and 2A-2, It seems that the rise of the saturation voltage was also small.

[0160]

As described above, according to the present invention,
The gradation display can be performed without deteriorating the monostability of the chiral smectic liquid crystal, and an increase in applied voltage can be suppressed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of the structure of a liquid crystal element according to the present invention.

FIG. 2 is a sectional view showing another example of the structure of the liquid crystal element according to the present invention.

FIG. 3 is a plan view showing another example of the structure of the liquid crystal element according to the present invention.

FIG. 4 is an equivalent circuit diagram showing a structure of a liquid crystal element according to the present invention.

FIG. 5 is a timing chart illustrating an example of a method for driving a liquid crystal element.

FIG. 6 is a diagram showing an example of transmittance-voltage characteristics of a liquid crystal.

[Explanation of symbols]

1 chiral smectic liquid crystal 2a, 2b substrate 3a, 3b electrode 4 TFT (active element) _P 1, _{P 2} crystal panel (liquid crystal device)

Continued on the front page F term (reference) 2H088 EA02 EA12 GA03 GA04 GA17 HA01 HA06 HA08 HA18 JA17 KA07 KA14 MA10 MA13 2H090 KA14 KA15 LA04 LA09 MA06 MA10 MA11 2H093 NA11 NA31 ND09 NF17

Claims (19)

[Claims] 1. A chiral smectic liquid crystal, a pair of electrodes for applying a voltage to the liquid crystal, and a uniaxial alignment treatment for sandwiching the liquid crystal and facing at least one of the opposing surfaces to align the liquid crystal. A pair of substrates, a polarizing plate disposed along at least one of the substrates, an active element connected to at least one of the pair of electrodes and disposed for each pixel, and an active matrix drive. And a drive circuit for performing the analog gray scale display, wherein the chiral smectic liquid crystal, when no voltage is applied,
The liquid crystal shows the 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 is monostable at an angle corresponding to the magnitude of the applied voltage. Tilted to one side from the position, 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 changed to a voltage of the first polarity from the mono-stabilized position. Is a liquid crystal that tilts in a direction opposite to that when voltage is applied, and a ratio R between a retardation amount R _V obtained when a voltage of either polarity is applied and a retardation amount R ₀ when no voltage is applied. A liquid crystal element comprising a plurality of regions having different _rate = R _V / R ₀ . 2. The liquid crystal device according to claim 1, wherein the plurality of regions are a region including a pixel and a region not including a pixel. 3. The ratio R in a region including the pixel
The liquid crystal device according to claim 2, wherein a _rate is larger than a ratio R _{rate in a} region not including the pixel. 4. When a maximum tilt angle when a voltage of the first polarity is applied is β1 and a maximum tilt angle when a voltage of the second polarity is applied is β2, β1> β2. The liquid crystal device according to claim 1, wherein: 5. When the maximum tilt angle when a voltage of the first polarity is applied is β1, and when the maximum tilt angle when a voltage of the second polarity is applied is β2, β1 ≧ 5 × β2 The method according to any one of claims 1 to 4, wherein
A liquid crystal element according to the item. 6. The phase transition series of the chiral smectic liquid crystal is such that the isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase (S
mC *) or an isotropic liquid phase (ISO.)-chiral smectic C phase (SmC *). The liquid crystal device according to claim 1, wherein: 7. The liquid crystal device according to claim 6, wherein a helical pitch of the chiral smectic liquid crystal in a bulk state is longer than twice a cell thickness. 8. When a maximum tilt angle when a voltage of the first polarity is applied is β1 and a maximum tilt angle when a voltage of the second polarity is applied is β2, β1 = β2. The liquid crystal device according to claim 1, wherein: 9. The liquid crystal display device according to claim 1, wherein the chiral smectic liquid crystal is a chiral smectic C liquid crystal, and a smectic layer of the liquid crystal has a chevron structure. Liquid crystal element. 10. The tilt angle of the smectic layer having the chevron structure with respect to the substrate normal is substantially equal to or larger than the tilt angle of the chiral smectic C liquid crystal at least at a use temperature. 10. The liquid crystal element according to 9. 11. The chiral smectic C liquid crystal,
Isotropic liquid phase (ISO.)-Cholesteric phase (Ch)
A liquid crystal having a phase transition series of -smectic A phase (SmA) -chiral smectic C phase (SmC *);
Cholesteric phase (Ch) or smectic A phase (Sm
The liquid crystal device according to claim 10, wherein the electric field application treatment is performed at a temperature that indicates A) or a chiral smectic C phase (SmC *). 12. The chiral smectic C liquid crystal,
Isotropic liquid phase (ISO.)-Cholesteric phase (Ch)
A liquid crystal having a phase transition series of -smectic A phase (SmA) -chiral smectic C phase (SmC *);
Smectic A phase (SmA) and chiral smectic C
The liquid crystal device according to claim 10, wherein the pressure treatment is performed at a temperature indicating a phase (SmC *). 13. The chiral smectic C liquid crystal,
Isotropic liquid phase (ISO.)-Cholesteric phase (Ch)
-A liquid crystal having a phase transition series of a chiral smectic C phase (SmC *), wherein an electric field application treatment is performed at a temperature that indicates a cholesteric phase (Ch) or a chiral smectic C phase (SmC *). The liquid crystal device according to claim 10, wherein 14. The tilt angle of a smectic layer of the chiral smectic C liquid crystal is larger than a size calculated from a temperature change of a layer interval in a bulk state of the chiral smectic C liquid crystal at least at a use temperature. The liquid crystal device according to claim 9, wherein: 15. A layer inclination angle of an initial chevron structure formed by cooling from a high temperature side showing an isotropic liquid phase, wherein a layer inclination angle of a chevron structure in an element changed by an electric field application treatment and / or a pressure treatment is changed. The liquid crystal element according to claim 9, wherein the liquid crystal element is larger than a corner. 16. The liquid crystal device according to claim 9, wherein a helical pitch of the chiral smectic C liquid crystal in a bulk state is longer than twice a cell thickness. 17. The device according to claim 1, wherein the ratio R _rate is 0.90 or less in a region where the ratio R _rate is smaller among the plurality of regions. The liquid crystal element according to the above. 18. The liquid crystal device according to claim 1, wherein a value of the retardation amount R ₀ is 240 nm or more in a case of a transmission type. 19. The liquid crystal device according to claim 1, wherein the value of the retardation amount _R0 is 120 nm or more in the case of a reflection type.