JPH07159789A - Method for orienting liquid crystal - Google Patents

Abstract

PURPOSE:To provide the method with which a liquid crystal can be oriented into such a good oriented state that the disorder of the orientation is hardly generated over the whole liquid crystal layer even when large ruggedness are present on the surface in contact with the liquid crystal of any of a pair of substrates of the liquid crystal element. CONSTITUTION:A ferroelectric liquid crystal in the active matrix liquid crystal element is heated to form the isotropic phase (Iso phase). Thereafter, the liquid crystal is cooled so that its temp. is lowered from the side of the counter- substrate, on the surface in contact with the liquid crystal of which smaller recessed and projecting parts are present, of the pair of substrates of the liquid crystal element to subject the liquid crystal to transition to the chiral smectic liquid crystal phase (SmC* phase).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal alignment method.

[0002]

2. Description of the Related Art Generally, a liquid crystal element is constructed by sandwiching a liquid crystal between a pair of substrates each having an electrode and an alignment film formed thereon. A nematic liquid crystal is used for this type of liquid crystal element. There are a TN type or STN type liquid crystal element, a ferroelectric or antiferroelectric liquid crystal element using a ferroelectric liquid crystal or an antiferroelectric liquid crystal, and the like.

In general, these liquid crystal elements are manufactured by joining the pair of substrates through a frame-shaped sealing material and filling a liquid crystal between the two substrates by a vacuum injection method in a region surrounded by the sealing material. Alternatively, it is manufactured by a manufacturing method in which an appropriate amount of liquid crystal is supplied onto one of the substrates and then the pair of substrates is bonded via a frame-shaped sealing material.

By the way, the above liquid crystal element is required to have a substantially uniform alignment state of the liquid crystal over the entire display area. However, the liquid crystal is not always well aligned only by sandwiching the liquid crystal between the substrates. To obtain a liquid crystal element in which the alignment state of the liquid crystal is uniform, after assembling the liquid crystal element,
It is necessary to arrange the alignment state of the liquid crystal.

The process for adjusting the alignment state of the liquid crystal is generally called a re-alignment process.
The assembled liquid crystal element is placed in a heating tank such as an oven, and the temperature in the tank is raised to heat the liquid crystal in the liquid crystal element to an isotropic phase which is an isotropic liquid. By gradually lowering, the liquid crystal is moved from both substrate sides of the liquid crystal element to a liquid crystal phase (nematic liquid crystal nematic phase, ferroelectric liquid crystal chiral smectic C phase,
In the antiferroelectric liquid crystal, a method of transitioning to a chiral smectic C _A phase) is used.

[0006]

However, in the above-described conventional alignment method, the liquid crystal in the liquid crystal element is heated to an isotropic phase, and then the liquid crystal is dropped on both substrate sides of the liquid crystal element by the temperature drop in the bath. Therefore, if there is a large unevenness on the surface of one of the two substrates of the liquid crystal element that comes into contact with the liquid crystal, the alignment state of the liquid crystal will be disturbed near the uneven portion of this substrate. I have the problem of being lost.

That is, FIG. 19 is a sectional view of a part of a liquid crystal element in which liquid crystal is aligned by a conventional method.
2 shows an active matrix type ferroelectric liquid crystal device.

In order to enable gradation display, this ferroelectric liquid crystal element has, as the ferroelectric liquid crystal, a spiral pitch of molecular alignment shorter than a distance between a pair of substrates and has no memory property of an alignment state. It uses a liquid crystal. The ferroelectric liquid crystal is called DHF liquid crystal.

In this ferroelectric liquid crystal device, the DHF liquid crystal is enclosed between the substrates in a spiral structure.
This DHF liquid crystal has a first alignment state in which liquid crystal molecules are substantially aligned in one direction and a liquid crystal molecule is generally aligned in the other direction according to a voltage applied between electrodes facing each other across a liquid crystal layer. And the average alignment direction of the liquid crystal molecules is aligned to any alignment state intermediate between the first alignment state and the second alignment state due to the distortion of the helical structure of the molecular alignment. .

Although the DHF liquid crystal does not have a memory property of the alignment state, it can have any of the intermediate alignment states described above.
It is said that gray scale display is possible by adopting an active matrix method in which a non-linear element such as the above is used as an active element and holding a voltage that maintains the above-mentioned arbitrary alignment state even during a non-selection period.

The structure of the liquid crystal element shown in FIG. 19 will be described. This liquid crystal element uses a TFT as an active element and is one of a pair of transparent substrates 1 and 2 made of glass or the like, which is located on the lower side in the figure. On the substrate 1, transparent pixel electrodes 3 and TFTs 4 which are active elements are arranged and arranged in the column direction and the row direction. Hereinafter, this substrate 1 is referred to as a TFT substrate.

The TFT 4 has a gate electrode 5 formed on the surface of the substrate 1 and a gate insulating film 6 covering the gate electrode 5.
And an i-type semiconductor film 7 of a-Si formed on the gate insulating film 6 so as to face the gate electrode 5,
The source electrode 9s and the drain electrode 9d are formed on both sides of the i-type semiconductor film 7 with the n-type semiconductor film 8 made of a-Si (amorphous silicon) doped with impurities interposed therebetween. A blocking insulating film 10 protects the channel region of the i-type semiconductor film 7.

The gate insulating film 6 of the TFT 4 is made of SiN
The gate insulating film 6 is a transparent insulating film made of (silicon nitride) or the like, and is formed over substantially the entire surface of the substrate 1. The pixel electrode 3 is formed on the gate insulating film 6, and one end of the pixel electrode 3 is connected to the source electrode 9s of the TFT 4.

On the substrate 1, the TFTs 4 in each row are
A gate line (not shown) for supplying a gate signal to
Data line 1 for supplying data signal to TFT 4 of each column
2 is wired. The gate line is T on the surface of the substrate 1.
The data line 12 is formed integrally with the gate electrode 5 of the FT 4, and the data line 12 is an interlayer insulating film 11 formed so as to cover the TFT 4.
And is connected to the drain electrode 9d of the TFT 4 through a contact hole provided in the interlayer insulating film 11. The TFT 4 and the data line 12 are covered with a protective insulating film 13.

On the other hand, in FIG.
A transparent counter electrode 15 in the form of a single film is formed to face all the pixel electrodes 3 of the TFT substrate 1. Hereinafter, this substrate 2 is referred to as a counter substrate.

On the TFT substrate 1 and the counter substrate 2, horizontal alignment films 14 and 1 made of polyimide or the like are provided.
6 is formed, and the alignment films 14 and 16 are subjected to the alignment treatment by rubbing.

The TFT substrate 1 and the counter substrate 2 are bonded to each other at their peripheral portions via a frame-shaped sealing material (not shown).
The HF liquid crystal 17 is sandwiched.

In the DHF liquid crystal 17, the spiral pitch of the spiral structure has a wavelength in the visible light band (400 nm to 700 n).
m) or less, for example, a ferroelectric liquid crystal composition having a spiral pitch of 300 nm to 400 nm, the spiral pitch of which is the substrate 1,
Since it is smaller than the interval of 2 (about 2 to 3 μm), it is sandwiched between the substrates 1 and 2 with a spiral structure.

The DHF liquid crystal 17 has a layer structure in which the normal direction of the layer having the layer structure of the smectic C phase is regulated by the alignment films 14 and 16 subjected to the alignment treatment of the substrates 1 and 2. When a voltage exceeding a predetermined value is applied between the pixel electrode 3 and the counter electrode 15 that face each other across the liquid crystal layer, the liquid crystal molecules 17a are changed depending on the polarity of the applied voltage. When the liquid crystal molecules 17a are aligned in either one of the first alignment state and the second alignment state in which the liquid crystal molecules 17a are aligned in the other direction, and the voltage is between the above voltage values, the DHF is generated. Since the helical structure of the liquid crystal 17 is distorted according to the voltage, the liquid crystal molecules 17a are aligned in an alignment state in which the average alignment direction is an intermediate direction between the liquid crystal molecule alignments in the first and second alignment states. The average alignment direction of the liquid crystal molecules 17a in this alignment state corresponds to the applied voltage value.

Since this ferroelectric liquid crystal device is of the active matrix type, it is possible to hold the voltage for maintaining the DHF liquid crystal 17 in the intermediate alignment state even during the non-selection period, and It is said that it is possible to display with gradation by changing the transmittance.

However, in the ferroelectric liquid crystal element in which the liquid crystal is aligned by the above-mentioned conventional alignment method, the alignment state of the liquid crystal 17 is disturbed, so that the display is uneven and the contrast is low.

This is because the surface of the alignment film 14 in contact with the liquid crystal of the TFT substrate 1 is projected by the TFT 4, and the length of the main chain of the liquid crystal molecule 17a (long axis of the molecule) is 1 to 2.
While the height is 0 nm, the height of the convex portion is 400 to 60.
Since it is as large as 0 nm, when the liquid crystal 17 heated to the isotropic phase is transferred from both substrates 1 and 2 to the liquid crystal phase (chiral smectic C phase) like the conventional alignment method, the TFT substrate 1 In the vicinity of the rising surface and the corner surface of the convex portion of the alignment film 14 generated by the TFT 4, the liquid crystal 17 is disorderly arranged as shown in FIG.

Then, the disorder of the orientation in the vicinity of the convex portion is
Since it also affects the liquid crystal around it, the liquid crystal 17 in that region
There is a defect in the smectic layer structure, which causes display unevenness and deterioration of contrast.

Here, the disorder of the alignment state of the liquid crystal in the active matrix ferroelectric liquid crystal element using the DHF liquid crystal has been described as an example, but the alignment state of the liquid crystal when the liquid crystal is aligned by the conventional alignment method is described. Disturbance is caused not only in other ferroelectric liquid crystal elements or antiferroelectric liquid crystal elements, TN or STN type liquid crystal elements using nematic liquid crystal, or in liquid crystal elements of other types, not limited to the active matrix type. When there is a large unevenness on the surface of one of the two substrates that is in contact with the liquid crystal, the unevenness is remarkable.

According to the present invention, even if there is a large concave portion or convex portion on the surface of one of the two substrates of the liquid crystal element, which comes into contact with the liquid crystal, the liquid crystal is aligned in a good alignment state with almost no disturbance throughout the liquid crystal layer. The purpose of the present invention is to provide a method for aligning liquid crystals that can be used.

[0026]

In the alignment method of the present invention, the surface of the pair of substrates of the liquid crystal element in contact with the liquid crystal in the isotropic phase has small irregularities, and the temperature is lowered from the substrate side, and the irregularities are small. It is characterized in that the liquid crystal undergoes a phase transition to a liquid crystal phase from the substrate side.

The present invention is applied, for example, to the alignment of liquid crystals of an active matrix liquid crystal element in which a pixel electrode and an active element are provided on one substrate and a counter electrode is provided on the other substrate. The liquid crystal heated to a tropic phase is made to undergo a phase transition from the substrate side provided with the counter electrode to the liquid crystal phase.

The liquid crystal may be a ferroelectric liquid crystal or an antiferroelectric liquid crystal having a chiral smectic C phase or a chiral smectic C _A phase, or a nematic liquid crystal exhibiting a nematic phase at room temperature.

[0029]

As in the alignment method of the present invention, the liquid crystal heated to the isotropic phase is transferred to the liquid crystal phase from the substrate side of the pair of substrates of the liquid crystal element, which has a small unevenness on the surface in contact with the liquid crystal. Then, the liquid crystal is aligned in a uniform alignment state from the substrate side to the other substrate side.

Therefore, even if there is a large unevenness on the surface of the other substrate in contact with the liquid crystal, the disorder of the alignment state of the liquid crystal is
It only occurs near the interface with the uneven surface, and therefore
The liquid crystal can be aligned over the entire liquid crystal layer in a good alignment state with almost no disturbance.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments in which the present invention is applied to the alignment of liquid crystals of an active matrix ferroelectric liquid crystal device will be described below with reference to the drawings. 1 to 5 show a first embodiment of the present invention. FIG. 1 shows both of a liquid crystal element when a ferroelectric liquid crystal is changed from an isotropic phase to a liquid crystal phase (chiral smectic C phase). FIG. 2 is a diagram showing a temperature drop curve of a substrate, FIG. 2 is a molecular alignment model diagram in each phase of the ferroelectric liquid crystal, and FIGS. 3 and 4 are phases of the ferroelectric liquid crystal at each time of t _{1 to} t ₇ in FIG. FIG. 5 is a diagram showing a transition state, and FIG. 5 is a partial cross-sectional view of an active matrix ferroelectric liquid crystal device in a state where alignment is completed. Here, the thickness of the ferroelectric liquid crystal layer between the substrates 1 and 2 is 10 to 25 μm.

In the above ferroelectric liquid crystal device, as the ferroelectric liquid crystal, a DHF liquid crystal having a spiral pitch of the molecular arrangement shorter than the distance between the pair of substrates and having no memory property of the alignment state is used, and the active matrix is used. This method enables gradation display, and since the basic configuration thereof is the same as that shown in FIG. 19, duplicated description will be assigned the same reference numerals in the figure and omitted.

The liquid crystal of the ferroelectric liquid crystal element is aligned as follows. First, the phase transition of the ferroelectric liquid crystal will be described. The ferroelectric liquid crystal (D
The HF liquid crystal) 17 has a chiral smectic C phase (hereinafter referred to as Sm C ^* phase) which is an original liquid crystal phase depending on temperature.
And a smectic A phase (hereinafter referred to as Sm A phase),
It has a physical property of undergoing a phase transition between a chiral nematic phase (hereinafter referred to as N ^* phase) and an isotropic phase which is an isotropic liquid (hereinafter referred to as Iso phase).

In FIG. 2, (a) is the alignment state of the liquid crystal molecules 17a when the ferroelectric liquid crystal is in the Sm C ^* phase, and (b) is the liquid crystal molecule 1 when it is in the Sm A phase.
7a shows the alignment state, 7c shows the alignment state of the liquid crystal molecules 17a when in the N ^* phase, and FIG. 7d shows the alignment state of the liquid crystal molecules 17a when in the Iso phase. When the temperature of the dielectric liquid crystal is raised, as shown by the solid arrow in FIG. 2, the liquid crystal transitions from the SmC ^* phase to the Iso phase through the Sm A phase and the N ^* phase, and then the temperature is lowered. , Fig. 2
As indicated by the broken line arrow, the phase returns from the Iso phase to the original Sm C ^* phase through the N ^* phase and the Sm A phase.

As for the orientation of the ferroelectric liquid crystal 17, as shown in FIGS. 3 and 4, the liquid crystal element A is sandwiched by a pair of upper and lower heating plates 31, 32, and the heating plates 31, 32 are arranged.
Control the temperature of.

The liquid crystal element A has the T shown in FIG.
A manufacturing method in which the FT substrate 1 and the counter substrate 2 are bonded to each other via a frame-shaped sealing material 18 and a region between the two substrates 1 and 2 surrounded by the sealing material 18 is filled with a liquid crystal 17 by a vacuum injection method, Alternatively, it is manufactured by a manufacturing method in which an appropriate amount of liquid crystal is supplied onto one of the substrates and then the pair of substrates 1 and 2 are joined via the frame-shaped sealing material 18.

Although the structure of the heating plates 31 and 32 is not shown, for example, the heating means and the cooling means are provided in a plate body made of a metal plate or the like having excellent thermal conductivity. The temperature can be controlled arbitrarily.

The method of orienting the ferroelectric liquid crystal 17 will be described. This orientation is as follows.
By heating 32 to heat the liquid crystal element A from both substrates 1 and 2, the liquid crystal 17 in the liquid crystal element A is heated to the Iso phase, and after the liquid crystal 17 is sufficiently in the Iso phase, By controlling the temperatures of the heating plates 31 and 32 so that the temperatures of the substrates 1 and 2 of the liquid crystal element A are respectively lowered by the descending curves as shown in FIG. 1, the pair of substrates 1 and 2 of the liquid crystal element A is controlled. Of the alignment films 14 and 15 with which the liquid crystal 17 is in contact
The temperature is gradually decreased from the side of the substrate having small surface irregularities, that is, the side of the counter substrate 2 in which the liquid crystal 17 contacts (alignment film surface) is almost flat, and the liquid crystal 1 is moved from the side of the counter substrate 2.
It is carried out by transferring 7 to the Sm C ^* phase.

As described above, after the ferroelectric liquid crystal 17 in the liquid crystal element A is heated to the Iso phase, the temperature is gradually lowered from the counter substrate 2 side, and is heated to the Iso phase. The liquid crystal 17 is supplied from the side of the counter substrate 2 to the TFT substrate 1
The phase transitions toward the side as follows.

[0040] That is, in (a) is 3, the time t ₁ in FIG. 1, i.e. shows the state of the liquid crystal 17 immediately before the start of the temperature drop of the heating plate 31 and 32, this time, the liquid crystal element The liquid crystal 17 in A is I over the entire liquid crystal layer.
It is a so phase.

Then, when the temperature of the counter substrate 2 is first lowered from this state, the liquid crystal 17 becomes I from the counter substrate 2 side.
The so phase → N ^* phase → Sm A phase → Sm C ^* phase transition.
3B to 3D show the phase transition states of the liquid crystal 17 at the times t _{2 to} t ₄ in FIG.

In this embodiment, as shown in FIG. 1, the temperature of the TFT substrate 1 is higher than the Iso phase → N ^* phase transition temperature until the temperature of the counter substrate 2 reaches the Sm C ^* phase transition temperature. The temperatures of the heating plates 31 and 32 are controlled so as to maintain the temperature. Therefore, the state of the liquid crystal 17 at the time of t ₄ in FIG. 1 is as shown in (d) of FIG. To the Sm C ^* phase, and the liquid crystal on the TFT substrate 1 side remains in the Iso phase, while a liquid crystal that has transitioned to the Sm A phase and a liquid crystal that has transitioned to the N ^* phase exist in layers. It is in a state of being. As described above, when the liquid crystal phase is formed from the flatter counter substrate 2 side, the liquid crystal 17 is aligned without disorder.

Then, when the temperature of the TFT substrate 1 is lowered, the phase transition of the liquid crystal 17 from the counter substrate 2 side further progresses, and finally the liquid crystal 17 in the liquid crystal element A spreads over the entire liquid crystal layer Sm C. ^* Be in phase. (E) to (g) of FIG.
Shows the phase transition state of the liquid crystal 17 at each time from t _{5 to} t ₇ in FIG.

According to the above-mentioned alignment method, the ferroelectric liquid crystal 17 in the liquid crystal element A is heated until it becomes the Iso phase, and then the surface of the pair of substrates 1 and 2 of the liquid crystal element A which is in contact with the liquid crystal 17 is heated. Since the temperature is lowered from the counter substrate 2 side having a small unevenness and the liquid crystal 17 is transferred from the counter substrate 2 side to the Sm C ^* phase which is the liquid crystal phase of the ferroelectric liquid crystal, the liquid crystal 17 is entirely in the liquid crystal layer. It is possible to align in a good alignment state with almost no disturbance over the entire length.

That is, when the liquid crystal 17 heated to the Iso phase as in the above alignment method is transferred from the counter substrate 2 side where the surface in contact with the liquid crystal 17 is a substantially flat surface to the Sm C ^* phase, The liquid crystal 17 is TF from the counter substrate 2 side.
Since it is aligned in a uniform alignment state toward the T substrate 1, the surface of the TFT substrate 1 in contact with the liquid crystal 17 is the TFT 4
Even if the surface has large projections and depressions, the liquid crystal 1
As shown in FIG. 5, the disturbance of the alignment state of No. 7 occurs only very slightly in the vicinity of the interface with the rising surface or the corner surface of the convex portion corresponding to the TFT 4.

Therefore, if the ferroelectric liquid crystal 17 is aligned by this alignment method, the liquid crystal 17 has a good alignment state with almost no disturbance over the entire liquid crystal layer, that is, has a uniform smectic layer structure over the entire liquid crystal layer. Since it can be oriented in a state, it is possible to obtain an active matrix ferroelectric liquid crystal element having no display unevenness and good contrast.

Both of the alignment films 14 and 16 may be rubbed in a predetermined direction, but if the alignment film 14 on the TFT substrate 1 side is rubbed, the TFT 4 is insulated by static electricity generated during the rubbing. Since the liquid crystal phase is formed from the counter substrate 2 side in the above alignment method, the alignment film 14 on the TFT substrate 1 side may not be subjected to rubbing treatment.

The above alignment method can also be applied to a liquid crystal element in which the counter substrate 2 is provided with a color filter for obtaining a colored display and a light shielding film for eliminating leaked light between pixels.

FIG. 6 is a sectional view of a part of the active matrix ferroelectric liquid crystal device in which the color filter and the light-shielding film are provided on the counter substrate 2 in a state where the alignment is completed. Color filters 19 of a plurality of colors (for example, three colors of red, green, and blue) are alternately arranged to face each pixel electrode 3 of the TFT substrate 1, and Cr (chrome) is provided between these color filters 19. A light-shielding film 20 made of a metal film such as the above or a black resist or the like (black resist in the figure) is formed.

In this liquid crystal element, the color filter 19 and the light shielding film 20 are covered with a transparent protective insulating film 21, and the counter electrode 15 is formed on the protective insulating film 21. The structure of the other parts of this liquid crystal element is the same as that shown in FIG.

In this liquid crystal element, since there is a step between the color filter 19 and the light-shielding film 20 depending on the difference in film thickness, the surface of the alignment film 15 in contact with the liquid crystal 17 of the counter substrate 2 has the step. The unevenness on the surface of the alignment film 16 on the counter substrate 2 side is
Since it is much smaller than the unevenness due to the protrusion of the TFT 4 portion on the side, if the substrate ferroelectric liquid crystal 17 is aligned from the counter substrate 2 side by the alignment method described above, the liquid crystal 17 is formed.
Can be oriented in a good alignment state in which there is almost no disturbance over the entire liquid crystal layer (a state in which a uniform smectic layer structure is formed over the entire liquid crystal layer).

In the above embodiment, after the liquid crystal 17 in the liquid crystal element A is heated to the Iso phase, the temperatures of the substrates 1 and 2 of the liquid crystal element A are respectively set to the descending curves as shown in FIG. Although the temperature is lowered, the temperature of both the substrates 1 and 2 may be lowered according to the following falling curve.

That is, FIGS. 7 (a) to 7 (d) respectively show the ferroelectric liquid crystals showing the second to fifth embodiments of the present invention from the Iso phase to the liquid crystal phase (Sm C ^* phase). FIG. 7 is a temperature drop curve diagram of both substrates of the liquid crystal element when the liquid crystal element is lowered, and even if the temperature of both the substrates 1 and 2 of the liquid crystal element A is lowered by such a lowering curve, the ferroelectric property of heating to the Iso phase is obtained. The liquid crystal 17 can be transferred from the counter substrate 2 side to the Sm C ^* phase.

FIG. 8 is a drop curve shown in FIG. 7A, t ₁ when the temperature of both substrates 1 and 2 of the liquid crystal element A is lowered.
Ferroelectric phase transition state of the liquid crystal at each time ~t _7, 9 t when the temperature is lowered the temperature of the substrates 1 and 2 of the liquid crystal element A in drop curve shown in FIG. 7 (b) The phase transition state of the ferroelectric liquid crystal at each time of _{1 to} t ₇ , FIG. 10 shows the temperature drop of both substrates 1 and 2 of the liquid crystal element A by the drop curve shown in FIG. The phase transition state of the ferroelectric liquid crystal at each time from t _{1 to} t ₇ , when the temperature of both substrates 1 and 2 of the liquid crystal element A is lowered by the descent curve shown in FIG. 7D. Of t
Shows a ferroelectric phase transition state of the liquid crystal at each time of ₁ ~t _7.

As described above, Iso phase → N ^* phase → S
S of ferroelectric liquid crystal that undergoes phase transition in the order of m A phase → Sm C ^* phase
Since the orientation state upon transition to the m C ^* phase largely depends on the orientation state on the Sm A phase before transition to the Sm C ^* phase, control of the orientation state on the Sm A phase is particularly important, S
If there is no disorder in the orientation state in the mA phase, the orientation state at the time of transition to the Sm C ^* phase also becomes a good orientation state without any disturbance.

Therefore, after the phase transition of the ferroelectric liquid crystal progresses until the liquid crystal in contact with the TFT substrate 1 becomes the SmA phase, the phase transition from the TFT substrate 1 side to the Sm C ^* phase is also promoted. You may

That is, for example, FIG. 8 (f) and FIG.
After the liquid crystal on the counter substrate 2 side is in the Sm C ^* phase and the liquid crystal on the TFT substrate 1 side is in the Sm A phase as in (f) of 1,
The temperature of the FT substrate 1 may be lowered to the same temperature as that of the counter substrate 2, and the liquid crystal may be transferred to the Sm C ^* phase from this TFT substrate 1 side, and (e) in FIG. After the entire liquid crystal layer becomes the Sm A phase as in e), T
The temperature may be lowered first from the FT substrate 1 side, and the phase transition to the Sm C ^* phase may proceed from the TFT substrate 1 side toward the counter substrate 2 side.

Further, the ferroelectric liquid crystal undergoes phase transition without passing through the N ^* phase, in addition to the transition to the Sm C ^* phase, Sm A phase, N ^* phase and Iso phase depending on the temperature as described above. However, the present invention can also be applied to the alignment of ferroelectric liquid crystals exhibiting such a phase transition.

12A and 12B respectively show
FIG. 9 is a temperature drop curve diagram of both substrates of a liquid crystal element when a ferroelectric liquid crystal showing sixth and seventh embodiments of the present invention is transitioned from an Iso phase to a liquid crystal phase (Sm C ^* phase).

The sixth and seventh embodiments are examples in which the ferroelectric liquid crystal undergoes a phase transition without passing through the N ^* phase, and the ferroelectric liquid crystal is heated until it becomes the Iso phase. After that, if the temperature of both substrates 1 and 2 of the liquid crystal element A is lowered according to the descending curve as shown in FIG. 12A or 12B, the ferroelectric liquid crystal is transferred from the counter substrate 2 side to the Sm C ^* phase. The phase can be changed to. In this case as well, the temperature of the TFT substrate 1 is controlled and lowered so that the substrate temperature does not become lower than the temperature of the liquid crystal in contact with the TFT substrate 1.

FIG. 13 is a drop curve shown in FIG. 12A, showing the ferroelectric liquid crystal at each time of t ₁ to t ₅ when the temperature of both substrates 1 and 2 of the liquid crystal element A is lowered. A phase transition state, FIG. 14 is a drop curve shown in FIG. 12B, and the ferroelectric liquid crystal at each time of t ₁ to t ₅ when the temperature of both substrates 1 and 2 of the liquid crystal element A is lowered. In any of the examples, the ferroelectric liquid crystal 17 heated to the Iso phase is, from the counter substrate 2 side, Iso phase → Sm A phase → Sm C
^* Transition in the order of phases.

Here, an example is given in which the ferroelectric liquid crystal undergoes a phase transition without passing through the N ^* phase, but the ferroelectric liquid crystal undergoes a phase transition without passing through the Sm A phase. If I
Ferroelectric liquid crystal heated to the so phase is the opposite substrate 2
From the side, the transition proceeds in the order of Iso phase → N ^* phase → Sm C ^* phase.

Further, the present invention is not limited to the ferroelectric liquid crystal (DHF liquid crystal) in which the spiral pitch of the molecular arrangement is shorter than the distance between the pair of substrates and does not have the memory property of the alignment state. Can be applied to the alignment of other ferroelectric liquid crystals, such as ferroelectric liquid crystals that have a shorter distance than the distance between a pair of substrates and do not have the memory property of the alignment state, and can also be applied to the alignment of antiferroelectric liquid crystals. .

The liquid crystal phase of the antiferroelectric liquid crystal is the chiral smectic C _A phase (hereinafter referred to as the SmC _A phase), and the antiferroelectric liquid crystal heated to the Iso phase has the following (1 ) made in the Sm C _a ^* phase by phase transition in either order to (2).

(1) Iso phase → Sm A phase → Sm C _A ^* phase (2) Iso phase → Sm A phase → Sm C ^* phase → Sm C _A ^* phase (3) Iso phase → Sm C _A ^* phase ( 4) Iso phase → N ^* phase → Sm C _A ^* phase (5) Iso phase → N ^* phase → Sm C ^* phase → Sm CA _A ^* phase (6) Iso phase → N ^* phase → Sm A phase → Sm C _A ^* phase (7) Iso phase → N ^* phase → Sm A phase → Sm C ^* phase → Sm C _A
^* Phase The liquid crystal between the substrates of the liquid crystal element using the ferroelectric liquid crystal and the liquid crystal element using the antiferroelectric liquid crystal in which the helical pitch of the above molecular arrangement is shorter than the distance between the pair of substrates and does not have the memory property of the alignment state. Since the layer thickness is thicker than the liquid crystal layer thickness of the liquid crystal element using the DHF liquid crystal described above, it is easy to control the temperature of the liquid crystal between the two substrates, and thus to easily control the formation of the liquid crystal layer structure.

Furthermore, the present invention is not limited to a ferroelectric or antiferroelectric liquid crystal element, but a TN using a nematic liquid crystal.
The present invention can also be applied to the alignment of liquid crystals of the STN type or STN type liquid crystal element.

FIG. 15 is a temperature drop curve diagram of both substrates of the liquid crystal element when the liquid crystal showing the eighth embodiment of the present invention is transitioned from the Iso phase to the liquid crystal phase. 2 is an example in which the present invention is applied to the alignment of nematic liquid crystal in a TN type liquid crystal device of the system.

In this embodiment, after heating the nematic liquid crystal until it becomes the Iso phase, the temperature of both substrates 1 and 2 of the liquid crystal element A is lowered by a descending curve as shown in FIG.
According to this embodiment, the nematic liquid crystal can be transferred from the counter substrate 2 side to the nematic phase (hereinafter referred to as N phase).

FIG. 16 shows the descent curve shown in FIG. 15 from t ₁ to t when the temperature of both substrates 1 and 2 of the liquid crystal element A is lowered.
₃ shows the phase transition state of the nematic liquid crystal at each time of ₃ and the nematic liquid crystal heated to the Iso phase 2
2 shifts from the counter substrate 2 side to the N phase, so TF
Even if the surface of the T substrate 1 in contact with the liquid crystal 22 is a surface having large projections and depressions of the TFT 4 portion, the liquid crystal 22 has a good alignment state with almost no disturbance over the entire liquid crystal layer, that is, uniform over the entire liquid crystal layer. It can be oriented in a twist orientation state.

A left-handed or right-handed turning agent (for example, a chiral liquid crystal) is added to the nematic liquid crystal 22, and the nematic liquid crystal 22 rotates counterclockwise or right depending on the turning property of the turning agent. Twisted around. The twist angle is 80 to 120 in the TN liquid crystal mode.
(Preferably 85 to 110 °), and 180 to 300 ° (preferably 220 to 2) in the STN liquid crystal mode.
60 °).

In each of the above-mentioned embodiments, the phase transition of the liquid crystals 17 and 22 from the counter substrate 2 side is advanced in the layer thickness direction of the liquid crystal phase. May be obliquely advanced with respect to the layer thickness direction of the liquid crystal phase.

17 and 18 show a ninth embodiment of the present invention. In this embodiment, the temperature of both substrates 1 and 2 of the liquid crystal element A is lowered according to the drop curve shown in FIG. 1 to lower the temperature of both substrates 1 and 2 of the liquid crystal element A when the ferroelectric liquid crystal is aligned. This is an example in which the temperature is controlled so as to have a low temperature from one end (right end in the figure) to the other end (left end in the figure) of the substrate. FIG. 17 shows each time from t ₁ to t _{4 in} FIG. 18 shows the phase transition state of the ferroelectric liquid crystal 17 in FIG.
4 shows the phase transition state of the ferroelectric liquid crystal 17 at each time from t ₅ to t ₇ .

That is, in this embodiment, the temperatures of both substrates 1 and 2 of the liquid crystal element A are lowered with the above temperature gradients, respectively, to cause the phase transition of the liquid crystal 17 from the counter substrate 2 side. The liquid crystal phase is allowed to proceed obliquely with respect to the layer thickness direction, and in this embodiment as well, the liquid crystal can be aligned in a good alignment state with almost no disturbance throughout the liquid crystal layer.

Further, the present invention can be applied not only to the active matrix system but also to the alignment of the liquid crystal of the liquid crystal device of other system, and in particular, the liquid crystal of one of the substrates of the liquid crystal device is in contact with the liquid crystal device. When the surface has large unevenness, the liquid crystal can be aligned in a much better alignment state than in the conventional alignment method.

[0075]

According to the alignment method of the present invention, the temperature of the liquid crystal is adjusted from the side of the pair of substrates of the liquid crystal element in which the liquid crystal in the isotropic phase state is sandwiched between the pair of substrates, in which the unevenness of the surface in contact with the liquid crystal is small Since the liquid crystal is transferred to the liquid crystal phase from the side of the substrate having the smaller unevenness, there is a large unevenness on the surface of one of the two substrates of the liquid crystal element where the liquid crystal is in contact. Also, the liquid crystal can be aligned in a good alignment state with almost no disturbance over the entire liquid crystal layer.

[Brief description of drawings]

FIG. 1 is a temperature drop curve diagram of both substrates of a liquid crystal element when a ferroelectric liquid crystal is transitioned from an Iso phase to an Sm S ^* phase, showing a first embodiment of the present invention.

FIG. 2 is a model diagram of a molecular alignment in each phase of the ferroelectric liquid crystal.

FIG. 3 is a diagram showing a phase transition state of a ferroelectric liquid crystal at each time of t _{1 to} t ₄ in FIG.

FIG. 4 is a diagram showing a phase transition state of a ferroelectric liquid crystal at each time of t _{5 to} t ₇ in FIG.

FIG. 5 is a partial cross-sectional view of an active matrix ferroelectric liquid crystal device in a state where alignment is completed.

FIG. 6 is a partial cross-sectional view of an active matrix ferroelectric liquid crystal device in which a color filter is provided on a counter substrate in a state where alignment is completed.

FIG. 7 is a temperature drop curve diagram of both substrates of the liquid crystal element when the ferroelectric liquid crystal is transited from the Iso phase to the Sm C ^* phase, showing the second to fifth embodiments of the present invention.

FIG. 8 is a diagram showing a phase transition state of the ferroelectric liquid crystal at each time of t ₁ to t ₇ when the temperature of both substrates of the liquid crystal element is lowered by the drop curve shown in FIG. 7A. .

FIG. 9 is a diagram showing a phase transition state of the ferroelectric liquid crystal at each time of t ₁ to t ₇ when the temperature of both substrates of the liquid crystal element is lowered by the drop curve shown in FIG. 7B. .

FIG. 10 is a diagram showing a phase transition state of the ferroelectric liquid crystal at each time of t ₁ to t ₇ when the temperature of both substrates of the liquid crystal element is lowered by the drop curve shown in FIG. 7C. .

FIG. 11 shows the liquid crystal element A with the descent curve shown in FIG.
FIG. 6 is a diagram showing a phase transition state of the ferroelectric liquid crystal at each time of t ₁ to t ₇ when the temperature of both substrates 1 and 2 is lowered.

FIG. 12 is a temperature drop curve diagram of both substrates of the liquid crystal element when the ferroelectric liquid crystal showing the sixth and seventh embodiments of the present invention is transitioned from the Iso phase to the Sm C ^* phase.

FIG. 13 is a diagram showing a phase transition state of the ferroelectric liquid crystal at each time of t ₁ to t ₅ when the temperature of both substrates of the liquid crystal element is lowered by the drop curve shown in FIG. .

FIG. 14 is a diagram showing the phase transition state of the ferroelectric liquid crystal at each time of t ₁ to t ₅ when the temperature of both substrates of the liquid crystal element is lowered by the drop curve shown in FIG. .

FIG. 15 is a temperature drop curve diagram of both substrates of a liquid crystal element when a nematic liquid crystal showing an eighth embodiment of the present invention is transitioned from Iso phase to N phase.

16 is a diagram showing a phase transition state of the nematic liquid crystal at each time of t ₁ to t ₃ when the temperature of both substrates of the liquid crystal element is lowered by the drop curve shown in FIG.

FIG. 17 shows a ninth embodiment of the present invention, and the ferroelectric liquid crystal at each time of t ₁ to t ₄ when the temperature of both substrates of the liquid crystal element is lowered by the falling curve shown in FIG. Phase transition state diagram of.

FIG. 18 also shows the ninth embodiment of the present invention, and the ferroelectricity at each time of t ₅ to t ₇ when the temperature of both substrates of the liquid crystal element is lowered by the drop curve shown in FIG. Phase transition phase diagram of liquid crystal.

FIG. 19 is a partial cross-sectional view of an active matrix ferroelectric liquid crystal device in which liquid crystal is aligned by a conventional alignment method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... TFT substrate 2 ... Counter substrate 3 ... Pixel electrode 4 ... TFT 15 ... Counter electrodes 14,16 ... Alignment film 17 ... Ferroelectric liquid crystal 19 ... Color filter 20 ... Light-shielding film 21 ... Protective insulating film 22 ... Nematic liquid crystal 31. 32 ... Heating plate

Claims (8)

[Claims] 1. The temperature of the liquid crystal is lowered from the side of the pair of substrates of a liquid crystal element in which the liquid crystal in the isotropic phase state is sandwiched between the pair of substrates, in which the unevenness of the surface in contact with the liquid crystal is small, A method for aligning a liquid crystal, characterized in that the liquid crystal undergoes a phase transition to a liquid crystal phase from the side of a substrate having a small unevenness. 2. A liquid crystal element is an active matrix liquid crystal element in which a pixel electrode and an active element are provided on one substrate and a counter electrode is provided on the other substrate, and the liquid crystal heated to an isotropic phase is used as the counter electrode. The method for aligning liquid crystal according to claim 1, wherein a transition is made to a liquid crystal phase from the side of the substrate provided with the electrodes. 3. The liquid crystal phase is a ferroelectric liquid crystal or an antiferroelectric liquid crystal, and the liquid crystal phase is a chiral smectic C phase or a chiral smectic C _A phase. Liquid crystal alignment method. 4. The liquid crystal alignment method according to claim 3, wherein the liquid crystal heated to an isotropic phase transitions to a chiral smectic C phase or a chiral smectic C _A phase through a chiral nematic phase. . 5. The liquid crystal alignment method according to claim 3, wherein the liquid crystal heated to an isotropic phase transitions to a chiral smectic C phase or a chiral smectic C _A phase through a smectic _A phase. . 6. The liquid crystal heated to an isotropic phase transitions to a chiral smectic C phase or a chiral smectic C _A phase through a chiral nematic phase and a smectic _A phase.
The method for aligning a liquid crystal according to. 7. The liquid crystal is a ferroelectric liquid crystal, and the ferroelectric liquid crystal is a liquid crystal having a helical pitch of molecular alignment shorter than a distance between a pair of substrates and having no memory property of an alignment state. The method for aligning a liquid crystal according to claim 1 or 2. 8. A liquid crystal element is a TN liquid crystal mode or STN
The liquid crystal alignment method according to claim 1 or 2, wherein the liquid crystal mode is a liquid crystal mode, and the liquid crystal phase is a nematic phase.