JPH05265002A - Liquid crystal optical modulating element - Google Patents

Abstract

PURPOSE:To obtain stable bistability and to eliminate unstability without depending on the spacing structure of oriented films by decreasing hysteresis phenomena, fading phenomena and unstability phenomena and simultaneously preventing the disturbance in liquid crystal orientability, thereby attaining uniform orientation. CONSTITUTION:This element has a ferroelectric liquid crystal 24, counter substrates 23b for clamping this liquid crystal and a voltage impressing means having electrodes 5, 8 for impressing a voltage to the ferroelectric liquid crystal 24. The oriented films 9 formed by diagonal vapor deposition are formed via buffer layers 21a, 21b on these electrode surfaces. The oriented films 9 and the buffer layers 21a, 21b respectively have the spacings and pinholes to enable the charge transfer between the ferroelectric liquid crystal 24 and the electrodes 5, 8. The element has the substrates, a pair of the electrode substrates which face each other and have the electrodes provided on the substrates and the oriented films provided on the electrodes on the respective opposite surfaces and the liquid crystal sealed therebetween. Pinholes for taking conduction between the liquid crystal part and the electrodes are provided by >=1 per one picture element in the oriented film parts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal optical element, and more particularly to a liquid crystal optical element which is capable of performing gray scale display by using a ferroelectric liquid crystal having spontaneous polarization and exhibiting at least two optically stable states. It is a thing.

[0002]

2. Description of the Related Art Ferroelectric liquid crystal (FLC) as a liquid crystal having spontaneous polarization has been noticed for its advantages such as high-speed response and memory property, and has been actively developed for the purpose of display elements, light valves and the like. ing. Optical shutter arrays, high-definition display devices driven by a simple matrix, and high-density recording light valves in combination with photoconductors have been put into practical use as devices utilizing the above advantages.

In the past, this type of element has generally been used for monochrome display by simple matrix drive. However, it is expected to be applied to a moving image display by active matrix driving using a thin film transistor (TFT), and this characteristic is described in U.S.P. S. P. No. 4840462 or Proceed
ing of the SID, vol30 / 2, 19
89 "Ferro-electric Liquid
"Crystal Video Display" and the like. For driving a liquid crystal optical element of this type, as shown in, for example, US Pat. No. 4,840,462, reset and write (write) signals are time-divided into horizontal periods. In addition, for example, in an element that displays a gray scale by the above driving method, an electrode layer 22 is formed on a substrate 23 such as glass as shown in FIG. Layer 20 for orienting the liquid crystal 24
Is provided, and this is rubbed, and the ferroelectric liquid crystal 24 is injected.

Further, regarding the active matrix driving for the purpose of gradation display, further, it is further described in JP-A-2-1892.
It is also disclosed in the official gazette. In this active matrix driving method, a reset signal and a write signal are applied to one pixel with a phase shift, and the charge amount Q and the ferroelectricity injected into the pixel electrode by the write signal are applied. Spontaneous polarization Ps of liquid crystal
Domain gradation (area gradation) by the balance with the amount of charge cancellation ΔS · Ps (ΔS is the inversion area) due to the inversion of
Is to realize.

[0005]

However, the above-mentioned active matrix driving method is a very effective means for gradation display using a bistable ferroelectric liquid crystal, but at the same time, it has some drawbacks. is there.

One of them is a hysteresis phenomenon in the voltage / transmittance characteristic. The phenomenon will be described below.

FIG. 10 is a sectional view showing the structure of a generally used ferroelectric liquid crystal element. In the figure, 15
Reference numerals a and 15b denote electrode substrates facing each other, and the substrate 14 and the transparent electrode layer 1 formed on the facing surface, respectively.
3, the insulating layer 12, and the alignment layer 10. Reference numeral 11 is a ferroelectric liquid crystal layer arranged between the alignment layers 10 of the electrode substrates 15a and 15b. FIG. 11 is an equivalent circuit diagram when gray scale display is performed by active matrix driving using such a ferroelectric liquid crystal element. In the figure, T indicates a large number of thin film transistors (TFTs) used as switching elements for performing active matrix driving. LC is a large number of pixels made of a ferroelectric liquid crystal sandwiched by a drain electrode (pixel electrode) 3 of each thin film transistor T and a counter electrode 4. Reference numeral 2 is a signal wiring for supplying a voltage signal that forms a drive waveform of liquid crystal to each drain electrode 3, and the supply of this signal to each drain electrode 3 is on / off controlled by the thin film transistor T. Reference numeral 4 is a scanning signal wiring for supplying a gate signal for turning on / off the thin film transistor T.

In this structure, each pixel LC has a drive waveform as shown in FIG.
Reset pulse 117 with 6.7 ms (60 Hz)
And a write pulse 119 corresponding to each gradation is applied, the transmittance T changes as shown in FIG. At this time, the transmittance in the curved portion 121 is a transmittance substantially corresponding to the write pulse 119. Further, a write pulse 119 having a drive waveform as shown in FIG.
The voltage / transmittance characteristic described above is obtained by plotting the change in the transmittance T in the curved portion 121 with respect to the change in the pulse height (writing voltage V). An example thereof is shown in FIG. As is clear from this figure, a so-called hysteresis phenomenon in which the transmittance T is different between the characteristic curve 123 at the time of voltage boosting and the characteristic curve 125 at the time of voltage reduction is recognized.

FIG. 14 is a diagram for qualitatively explaining this hysteresis phenomenon. FIG. 14B corresponds to the curve 123 in FIG. That is, the black domain 127
Shows the case of decreasing
It is necessary to write white after reset. On the other hand, FIG.
(A) shows a case where the black domain 127 is increased, and it is not necessary to write white after resetting when viewed from the driving surface. That is, regarding the write pulse, in the case of decreasing the black domain, as compared with the case of increasing it,
It will require a larger voltage. in this way,
When gray scale display is performed by the charge control method using the driving method based on the driving waveform as shown in FIG.
A hysteresis phenomenon occurs in the transmittance characteristic.

Further, when the active matrix drive as described above is performed and a direct current (DC) component is continuously applied to the FLC for a long time, the response of the liquid crystal is obstructed, and the fading phenomenon that the transmittance gradually decreases. Occurs. FIG. 15 is a graph showing how the transmittance T changes with time t when the driving waveform as shown in FIG. 12A is repeatedly applied. According to this, it is clearly understood that when the pulse is repeatedly applied, the fading phenomenon occurs in which the transmittance T gradually decreases with the passage of time t. It is considered that this is because the DC component induces uneven distribution of internal ions in the liquid crystal, which forms an electric field.

FIG. 16 is a diagram for explaining this fading phenomenon. In the case of the waveform shown in FIG.
The geometrically positive DC component is applied excessively to the liquid crystal. FIG. 16 shows how this DC component acts on the liquid crystal. That is, the application of the positive DC component causes the accumulation of electric charge between the insulating layer portion 129 and the liquid crystal 11, and the partial pressure of the liquid crystal due to the electric charge accumulation component is in the negative direction. Become. On the other hand, the present inventors have proposed to cancel the DC component by the auxiliary pulse.

Further, as another cause of the fading phenomenon, the spontaneous polarization P of the liquid crystal when a voltage is applied to the liquid crystal.
It is conceivable that charge accumulation occurs due to s, and as a result, internal ions unevenly distributed with respect to spontaneous polarization form an electric field. On the other hand, the time constant (C) for relaxing the internal electric field induced by the spontaneous polarization in the reset section is set.
It has been proposed that the element structure using the FLC material having R) stably forms a halftone without affecting the next frame by the action of spontaneous polarization. However, when performing FLC domain gradation, electrodes, alignment layers, F
At the same time that charge is transferred between LCs, the domain gradually expands due to the effect of charge transfer at the FLC interface, and the transmittance is not constant for the relaxation time.
There is a problem that a phenomenon called so-called instability occurs, which has an adverse effect particularly when realizing a high gradation.

The above-mentioned hysteresis phenomenon, fading phenomenon, and instability phenomenon are major obstacles when the gradation display is performed by the active matrix method, because the pixel display voltage cannot be uniquely determined.
Therefore, the present inventors provide an alignment film directly on an electrode and use an orthorhombic vapor deposition film having a gap structure in the alignment film, whereby the above hysteresis phenomenon, fading phenomenon, and instability occur in active matrix driving. We are proposing to enable gradation display without phenomena.

According to this proposal, a good orientation is obtained, but since the SiO column of the electrode part reflects the shape of the underground, if the underground has irregularities like a transparent electrode such as ITO,
In some cases, the alignment of the SiO columns is disturbed and the orientation is locally disturbed. Further, such unevenness causes a problem that the bistability of the ferroelectric liquid crystal is lost.

It is an object of the present invention to prevent a liquid crystal alignment disorder in a liquid crystal device in which such a hysteresis phenomenon, a fading phenomenon and an instability phenomenon are reduced, and to obtain a uniform uniform alignment, and a stable bistability. The goal is to get the sex. Another object is to eliminate the instability in the liquid crystal optical element by other means that does not depend on the gap structure of the alignment film.

[0016]

To achieve the above object, in the first invention, a ferroelectric liquid crystal, a counter substrate sandwiching the ferroelectric liquid crystal, and a ferroelectric liquid crystal provided on the counter surface of the counter substrate are provided. In a liquid crystal optical element provided with a voltage applying means having an electrode for applying a voltage to, while forming an oblique vapor deposition alignment film on the electrode surface via a buffer layer,
The alignment film and the buffer layer have a gap and a pinhole, respectively, which allow the charge transfer between the ferroelectric liquid crystal and the electrode.

Here, the voltage applying means is, for example, at least a pixel electrode for applying a voltage to the ferroelectric liquid crystal in pixel units, a signal wiring for supplying a voltage signal to this pixel electrode, and this signal. An active switching element for controlling on / off of the connection between the wiring and the pixel electrode,
Further, the active switching element is provided with a scanning wiring for supplying a signal for on / off controlling the active switching element, and both resetting and writing of the ferroelectric liquid crystal are performed by active matrix driving.

The buffer layer is preferably a thin film containing an inorganic compound such as TiO ₂ --SiO _x or Ta ₂ O ₅ as a main component, and the thickness thereof is 0.005 to 0.2 μm.
Is preferable, and 0.01-0.05 μm is more preferable.

The material of the obliquely vapor-deposited alignment film is preferably an inorganic oxide such as SiO, ZrO ₂ or TiO ₂ as a main component, and the column length thereof is 0.01.
˜0.6 μm, and the column angle is preferably 0 to 60 °.

In the second invention which does not depend on the gap structure of the alignment film, a pair of opposed substrates each having a substrate, an electrode provided on the substrate, and an alignment film provided on the electrode on opposite surfaces, respectively. In the liquid crystal optical element including the electrode substrate and the liquid crystal sealed between the electrode substrates, the alignment film portion is provided with one or more pinholes for establishing conduction between the liquid crystal portion and the electrodes per pixel. .. As the alignment film, an organic film such as polyimide, polypyrrole, or polyvinyl alcohol can be used.

The liquid crystal used in both the first and second inventions exhibits ferroelectricity and forms a first optically stable state, for example, a bright state in response to an applied electric field, and a second optical state. A chiral smectic liquid crystal having a state forming a stable state, for example, a dark state, that is, having at least two stable states with respect to an electric field, is most preferable, and among them, a chiral smectic C phase (SmC).
^* ), H phase (SmH ^* ), I phase (SmI ^* ), F phase (S
Liquid crystals of mF ^* ) or G phase (SmG ^* ) are suitable.
Of course, other liquid crystals having similar properties can also be used.

More specifically, desiloxybenzylidene-P'-amino-2-methylbutyl cinnamate (DO
BAMBC), hexyloxybenzylidene-P'-amino-2-chloropropylcinnamate (HOBACP)
Ferroelectric liquid crystal compounds such as C) and 4-o- (2-methyl) -butylresorcylidene-4'-octylaniline (MBRA8).

When a device is formed using these materials, the liquid crystal compounds are SmC ^* , SmH ^* , SmI ^* , Sm.
If necessary, in order to maintain the temperature state of F ^* or SmG ^* , the element may be supported by a copper block or the like in which a heater is embedded, and thermal control may be performed when the liquid crystal is driven.

[0024]

FIG. 17 is a schematic diagram conceptually illustrating the liquid crystal element according to the present invention. In the figure, 23a and 23b are ITO
Is a substrate (glass plate) coated with transparent electrodes such as
In the meantime, liquid crystal of SmC ^* phase, which is oriented so that the liquid crystal molecular layer 21 is perpendicular to the glass surfaces of the substrates 23a and 23b, is enclosed. Reference numeral 16 represents a liquid crystal molecule, and this liquid crystal molecule 16 has a dipole moment (P
⊥) 17.

In such a structure, the substrates 23a, 2
When a voltage of a certain threshold value or more is applied between the electrodes on 3b, the helical structure of the liquid crystal molecules 16 is unraveled, and the dipole moment 17
The orientation direction of the liquid crystal molecules 16 can be changed so that all are oriented in the electric field direction. The liquid crystal molecule 16 has an elongated shape, and exhibits refractive index anisotropy in the major axis direction and the minor axis direction thereof. Therefore, it is easy to understand that by arranging the polarizers on the outer sides of the counter substrates 23a and 23b so as to have a crossed Nicols positional relationship, a liquid crystal optical modulation element whose optical characteristics change depending on the polarity of voltage application is easily understood. To be done. Further, the thickness of the liquid crystal cell is made sufficiently thin, for example, 1
In the case of μm, as shown in FIG. 18, when an electric field E or E ′ having a polarity different from a certain threshold value is applied, the dipole moment 17 is directed upward (corresponding to the electric field vector of the electric field E or E ′). Solid line 17) or downward (dashed line 1)
7 '), and the liquid crystal molecules are oriented to either the first stable state (solid line 16; bright state) or the second stable state (broken line 16'; dark state) accordingly.

There are two advantages of using an optical modulator having such a ferroelectric liquid crystal. Firstly, the response speed is extremely fast, and secondly, the alignment of the liquid crystal molecules has bistability. The second advantage is shown in FIG.
The liquid crystal molecules are aligned in the first stable state (solid line 16) when the electric field E is applied, but this state is maintained even when the electric field is cut off. Also,
When an electric field E'in the opposite direction is applied, the liquid crystal molecules are oriented in the second stable state (broken line 16 ') and change their orientation. However, even if the electric field is cut off, this state is maintained and the memory function is maintained in each stable state. Have. With such a fast response speed,
In order to effectively realize the bistability, it is preferable that the liquid crystal cell forming the device is as thin as possible, generally 0.5
A thickness of -20 μm, preferably 1-5 μm is suitable.

A liquid crystal / electro-optical device using this type of ferroelectric liquid crystal and having a matrix electrode structure has been proposed, for example, in US Pat. Nos. 4,367,924 and 4,840,462. In the case of such a structure,
When driving is performed by applying a voltage from the outside, if the exchange of charges in the film thickness direction between the liquid crystal and the electrodes is smoothly performed, the uneven distribution of ions due to the DC component of the external voltage and spontaneous polarization can be quickly alleviated. However, conventional alignment film materials generally have high resistance and a large insulating effect.

On the other hand, in the present invention, the alignment film and the buffer layer each have a gap and a pinhole for allowing the charge transfer between the ferroelectric liquid crystal and the electrode, or the conduction between the liquid crystal and the electrode is stopped. Since one or more pinholes are provided in the pixel for improving the influence of the uneven distribution of ions due to the DC component of the external voltage and the spontaneous polarization, a desired halftone can be stably displayed. become.

In addition, the buffer layer reduces the influence of the shape of the underground electrode, and does not disturb the arrangement of the SiO column or the like of the obliquely vapor-deposited alignment film. Therefore, the disorder of the alignment is prevented and the ferroelectricity is improved. The bistability of the liquid crystal is retained.

[0030]

EXAMPLE 1 FIG. 2 is a sectional view showing the basic structure of an optical modulation element according to a first example of the present invention. In the figure, 23a and 23b are substrates, 22a and 22b are transparent electrodes made of an ITO film formed on the substrates 23a and 23b, respectively.
a and 21b are buffer layers formed on the transparent electrodes 22a and 22b, respectively, and 20a and 20b are oblique vapor deposition alignment films made of SiO and formed on the buffer layers 21a and 21b, respectively. Two
5b is constructed. Reference numeral 24 is a ferroelectric liquid crystal disposed between the alignment films 20a and 20b. Transparent electrodes 22a, 22b
Includes a pixel electrode and a counter electrode for the pixel electrode. The alignment films 20a and 20b and the buffer layers 21a and 21b have gaps and pinholes, respectively, which allow charge transfer between the ferroelectric liquid crystal 24 and the electrodes 22a and 22b.

The substrates 23a and 23b are HOYA NA40 non-alkali glass with a double-sided polishing process having a thickness of 1.1 mm, and the ITO films 22a and 22b have a thickness of 700 Å by the reactive ion plating method in O _2. It was formed. The buffer layers 21a and 21b are made of TiO ₂ --Si.
After applying an organic solution containing O ₂ (trade name: MOF) by a spinner and sintering at 300 ° C., 800Å
It is formed with a thickness of.

The oblique vapor deposition alignment films 20a and 20b are produced by using the vapor deposition apparatus shown in FIG. In FIG. 3, 30 is a vacuum chamber, 31 is an oblique vapor deposition alignment film 20.
a substrate on which a and 20b are formed, 32 a chimney crucible as an evaporation source of SiO, 33 a power source of this evaporation source, 34 a slit, 35 a roller for sending the substrate 31, 36 a rotary pump, 37 a mechanical booster pump , 38
Is a cryopump and 39 is a switching valve.

In this vapor deposition apparatus, the SiO particles emitted from the crucible 32 reach the substrate 31 through the slit 34. On the other hand, the roller 35 rotates at an angular velocity ω, which causes the substrate 31 to move at a constant velocity v. Further, as shown in FIG.
Only SiO particles having an angle component of θ with respect to one surface can reach. Table 1 shows vapor deposition conditions in this apparatus.

[0034]

[Table 1] The SiO oblique vapor deposition alignment film 20 thus formed
After applying silica beads of 1.5 μmΦ as a gap agent onto a and 20b by a spinner and drying, a sealing agent is printed and the electrode substrates 25a and 25b are adhered to form a cell, in which a ferroelectric liquid crystal is formed. Is vacuum-injected to form the device.

FIG. 1 is an enlarged sectional view of this optical modulator. Portions corresponding to those in FIG. 2 are indicated by the same numbers. Figure 1
In, 6 is a TFT, 8 is a pixel electrode made of ITO,
5 is a counter electrode, 9 is S for forming an SiO oblique vapor deposition alignment film
iO column. The TFT 6 is connected to the pixel electrode 8 and is switched by the gate signal to write the write signal V
The W or reset signal VR is led to the pixel electrode 8.
The orientation film on the side of the counter electrode 5 is also configured in the same manner as above, and the counter electrode 5 is kept at the ground potential.

FIG. 4 shows a device constructed in this manner as shown in FIG.
3 is a graph showing write voltage / transmittance (VT) characteristics when continuously driven by a constant reset and write signal as in 2 (a). Compared with the VT characteristic 42 of the element having the conventional rubbing alignment film, the VT characteristic 41 of the element of the present example clearly has a reduced hysteresis.

FIG. 5 is a graph showing changes in the all-white writing response time t ₂ with respect to changes in the black reset leaving time t ₁ . In the figure, a curve 51 shows the case of the optical modulation element of the embodiment, and a broken line curve 52 shows the case of the optical modulation element using the conventional rubbing alignment film. According to this, it is clear that the above-mentioned instability is resolved.

FIG. 6 is a graph showing the change in relative transmittance with the passage of time, where 61 is the case of this embodiment and 62 is the case of the conventional example.

FIG. 7 shows that after left for a certain time t "black",
6 is a graph showing a change in transmittance T when "white" halftone writing is performed. In the figure, a curved line 71 indicates the case of the device of this example, and a broken line curved line 72 indicates the conventional case. In comparison with the case of the conventional rubbing alignment film, it can be seen that the fading phenomenon is hardly seen in the case of this example.

The reason why the problem that occurs when the gradation display of the ferroelectric liquid crystal is performed is solved is explained as follows. That is, as schematically shown in FIG. 1, since the SiO column 9 formed by SiO oblique deposition has a gap structure, the buffer layers 21a and 21b are partially exposed, and Since the underground buffer layers 21a and 21b are very thin and there are appropriate pinholes in them,
The electrodes 5 (22a) and 8 (22b) are electrically connected to the liquid crystal layer 24. For this reason, ions (in this case, negative ions) caused by the DC imbalance as shown in FIG. 12 between the write voltage VW and the reset voltage VR applied to the ferroelectric liquid crystal 24 are accumulated on the electrode 8. Also, it is considered that the above-mentioned ions are neutralized by the transfer of electrons at this interface. It is considered that this neutralization phenomenon similarly occurs in the ground electrode 5 facing the pixel electrode 8. Therefore, it is considered that the above-mentioned problem is solved because the coercive electric field generated by the accumulation of ions on the surface of the alignment film as in the above-mentioned conventional example is not formed.

When the alignment state of the optical modulation element of this example was observed with a polarization microscope, it was found to be uniform uniform alignment. Further, when the temperature was raised to the isotropic phase and the re-orientation treatment was performed, a perfect bistable state was exhibited in the temperature range of the SmC ^* phase. When the tilt angle θ _a was measured, θ _a = 1
It is 4 to 14.5 °, and the cone angle Θ of the injected ferroelectric liquid crystal 24 is about Θ to 15 °. Considering that the cone angle Θ of the ferroelectric liquid crystal 24 is almost the same as the tilt angle of the cell. It was found that θ _a was open.

Further, the substrates 23a and 23b were made of thin film glass having a thickness of 80 μm to prepare a similar device, and the layer structure thereof was measured by the X-ray circuit folding method. FIG. 8 is a graph showing the X-ray diffraction pattern. In the figure, since only one diffraction peak is seen, it can be seen that the layer structure of the liquid crystal 24 is an oblique bookshelf structure as shown in FIG.

Example 2 As the buffer layers 21a and 21b, Ta ₂ O ₅ was formed to a thickness of 800 Å by using the electron beam evaporation method, and an oblique vapor deposition alignment film similar to that of Example 1 was formed thereon with a base pressure. Is -10 ^-7
torr. , Deposition rate 5Å / sec, θ in Fig. 3
Was formed at a temperature of 85 °. An element was prepared in the same manner as in Example 1 except for the above, and the orientation state, hysteresis of VT characteristics, instability, and fading phenomenon were measured. As a result, the orientation was a uniform uniform orientation and was bistable. It was also confirmed that hysteresis, instability, and fading phenomenon were significantly reduced.

Example 3 The buffer layers 21a and 21b are the same as in Example 1, and the oblique vapor deposition alignment films 20a and 20b (9) are formed in the same apparatus as in Example 1 using ZrO ₂ instead of SiO. Filmed This film has a base pressure of -10 ^-7 torr. The vapor deposition rate was 5Å / sec and θ in FIG. 3 was 85 °, and the column length of the oblique vapor deposition films 20a and 20b was 400Å.
An element was prepared in the same manner as in Example 1 except for the above, and the orientation state, hysteresis of VT characteristics, instability, and fading phenomenon were measured. As a result, the orientation was uniform and uniform and bistable. It was also confirmed that hysteresis, instability, and fading phenomenon were significantly reduced.

Example 4 The buffer layers 21a and 21b were the same as in Example 1, and the oblique vapor deposition alignment films 20a and 20b were formed in the same apparatus as in Example 1 using TiO ₂ instead of SiO ₂ . This film has a base pressure of -10 ^-7 torr. , Deposition rate is 5Å /
sec, θ in FIG. 3 was 85 °, and the column length of the obliquely evaporated films 20a and 20b was 400Å. An element was prepared in the same manner as in Example 1 except for the above, and the orientation state, hysteresis of VT characteristics, instability, and fading phenomenon were measured. As a result, the orientation was uniform and uniform and bistable. It was also confirmed that hysteresis, instability, and fading phenomenon were significantly reduced.

Example 5 The buffer layers 21a and 21b were formed by forming Ta ₂ O ₅ to a thickness of 800 Å by using electron beam evaporation, and the oblique vapor deposition alignment films 20a and 20b were formed on the buffer layers 21a and 21b instead of ZrO. ₂
With a base pressure of -10 ^-7 torr. , Deposition rate is 5
The film was formed under the condition of Å / sec and θ of 85 ° in FIG. An element was prepared in the same manner as in Example 1 except for the above, and the orientation state, hysteresis of VT characteristics, instability, and fading phenomenon were measured. As a result, the orientation was a uniform uniform orientation and bistable. It was also confirmed that hysteresis, instability, and fading phenomenon were significantly reduced.

Embodiment 6 FIG. 19 shows a sixth embodiment of the present invention. This figure shows a cross section of the electrode interface of one pixel of the liquid crystal element. This device is manufactured as follows. First, the transparent electrode 22 made of ITO or the like is formed on the glass substrate 23 by reactive sputtering or the like for 1000 to 1
After forming a film with a film thickness of about 500Å, spinner coating the polyimide on it, bake at 150 ℃, 500 ~ 1
Form a film of 000Å. Next, a silicon-containing resist, such as SNR (trade name: manufactured by Toyo Soda Co., Ltd.), is applied to the polyimide film by spinner coating and baking treatment to obtain about 3
A film is formed to a thickness of 00 to 500Å. Next, an electron beam is drawn on this resist to form a space pattern having a diameter of 0.1 to 2 μm. At this time, the substrate may be heated to, for example, 100 to 350 ° C. depending on the material. A laser or the like may be used instead of the electron beam.

Next, the polyimide is etched using this resist as a mask. For example, the etching is performed with an RIE device under the conditions of a power of 130 W and a pressure of 1 to 5 Pa using O ₂ gas. After that, the mask is removed by etching. As a result, the alignment film 20 having the pinholes 26 corresponding to the space pattern is formed. This etching is performed by a RIE device using a fluorine-based gas such as CF ₄ + H ₂ . Alternatively, it may be removed by immersing it in hydrofluoric acid.

Next, the two electrode substrates thus formed are subjected to a rubbing treatment on the polyimide surface, and these substrates are placed facing each other with the rubbing surface inside.
A cell having a gap of about 5 μm is formed, and liquid crystal is injected under vacuum.

When the liquid crystal element having pinholes in the pixel formed in this way is to be driven by applying a voltage from the outside, the alignment film 20 in the film thickness direction is arranged between the liquid crystal and the electrodes. Transfer of charges is extremely smooth. As a result, it is possible to quickly alleviate the uneven distribution of ions due to the external voltage DC component and spontaneous polarization. Further, according to this structure, the rubbing treatment for aligning the liquid crystal can be performed as usual, and if the size of the pinhole is about 0.1 to 2 μm, the influence on the alignment state is extremely small.

Further, especially when displaying a gradation at a high frequency such as a television rate, it is also practical to reduce the resistance of both the liquid crystal and the alignment film to reduce the time constant. By lowering the resistance value of
Although the exchange of charges at the alignment film interface is smooth, this also increases the tendency of domain expansion. On the other hand, according to the pinhole structure, while the charge is rapidly relaxed in the film thickness direction, a desired halftone can be stably displayed without affecting the domain spread.

Embodiment 7 FIG. 20 shows a seventh embodiment of the present invention. This figure shows a cross section of the electrode interface of one pixel of the liquid crystal element. This device is manufactured as follows. First, a transparent electrode 22 made of ITO or the like is formed on the glass substrate 23 with a thickness of about 1000 to 1500 Å by reactive sputtering or the like, and a polyimide is spinner-coated on the transparent electrode 22 and then baked at about 150 ° C. for 300 to 5
An insulating film 28 of 00Å is formed. Next, a silicon-containing resist, for example, SNR (trade name: manufactured by Toyo Soda Co., Ltd.) is spinner-coated and baked on the polyimide film to form a film having a thickness of about 300 to 500 Å.

Next, an electron beam is drawn on this resist to form a space pattern having a diameter of 0.1 to 3 μm. At this time, the substrate may be heated to, for example, 100 to 350 ° C. depending on the material. A laser or the like may be used instead of the electron beam. Alternatively, SiO _{2 is formed} on the polyimide.
Is formed into a film with a thickness of 300 to 500 Å by sputtering, and PMMA (polymethylmethacrylate) is patterned on SiO ₂ by an ordinary photolithography process to form a desired space pattern. good.

Next, using the resist thus formed as a mask, the polyimide is etched by O ₂ gas in an RIE apparatus. After that, the mask is removed by etching. As a result, the insulating film 28 having the pinhole 26 is formed. This etching is performed by a RIE device using a fluorine-based gas such as CF ₄ + H ₂ . Alternatively, it may be removed by immersing it in hydrofluoric acid. Then FL
In order to orient C, for example, by the SiO oblique deposition method,
The column 29 is formed. The pinhole pattern is much larger than this column system.

Finally, the two electrode substrates thus formed are faced to each other with the column surface facing inward, and 1 to 5 μm.
The device is completed by forming a cell having a certain gap and vacuum-injecting liquid crystal.

When a liquid crystal element having a pinhole portion in a pixel formed through the above steps is to be driven by applying a voltage from the outside, it is caused by the DC component of the external voltage and spontaneous polarization. The uneven distribution of ions can be quickly alleviated.

[0057]

As described above, according to the present invention, the oblique vapor deposition alignment film is formed through the buffer layer, and the alignment film and the buffer layer enable the charge transfer between the ferroelectric liquid crystal and the electrode. Since each pixel has one or more pinholes for establishing conduction between the liquid crystal part and the electrode in the alignment film portion, it has uniform uniform alignment. And a perfect bistable state orientation is obtained, and the external voltage DC
It is possible to quickly alleviate the uneven distribution of ions due to the spontaneous polarization of the component and the FLC molecule itself, and especially the hysteresis of the voltage / transmittance characteristic peculiar to gray scale display by active matrix driving using a ferroelectric liquid crystal. It is possible to eliminate the phenomenon, instability and fading phenomenon and stably obtain a desired halftone.

Further, since the alignment film portion is provided with one or more pinholes for establishing conduction between the liquid crystal portion and the electrode per pixel, it is caused by the external voltage DC component and the spontaneous polarization of the FLC molecule itself. It is possible to quickly alleviate the uneven distribution of ions, and it is possible to stably obtain a desired halftone without alienating the reaction of the liquid crystal particularly when performing high gradation display.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view of an optical modulator according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the basic configuration of the optical modulation element according to the first embodiment of the present invention.

3 is a configuration diagram of an apparatus for producing an alignment film of the element of FIG.

FIG. 4 is a graph showing a comparison of write voltage / transmittance characteristics between the optical modulation element of FIG. 1 and a conventional element.

FIG. 5 is a graph showing how the all-white writing response time t ₂ changes with respect to the black reset leaving time t ₁ .

FIG. 6 is a graph showing changes in relative transmittance with time, in the case of the first embodiment and the case of the conventional example.

FIG. 7 is a graph showing changes in the transmittance T in the case of performing “white” halftone writing after being left for a certain time t “black”, in the case of the first embodiment and the case of the conventional example.

8 is a graph of an X-ray diffraction pattern of the optical modulator of FIG.

9 is a schematic cross-sectional view showing the layer structure of the optical modulator of FIG.

FIG. 10 is an explanatory diagram of a liquid crystal element according to a conventional example.

FIG. 11 is an equivalent circuit diagram when gray scale display is performed by active matrix driving using a ferroelectric liquid crystal element according to a conventional example.

FIG. 12 is an explanatory diagram showing a drive waveform in a liquid crystal element and a change in transmittance due to the drive waveform.

13 is a graph of a voltage / transmittance characteristic curve in the liquid crystal element of FIG.

FIG. 14 is an explanatory diagram for qualitatively explaining a hysteresis phenomenon.

FIG. 15 is a graph showing changes in transmittance when the drive waveform is continuously applied to the device of FIG.

FIG. 16 is a schematic diagram for explaining a fading phenomenon.

FIG. 17 is a schematic diagram conceptually illustrating a liquid crystal element according to the present invention.

18 is a schematic diagram showing a change in orientation due to an electric field in the device of FIG.

FIG. 19 is a sectional view of an electrode interface of a liquid crystal device according to a sixth embodiment of the present invention.

FIG. 20 is a sectional view of an electrode interface of a liquid crystal device according to a seventh embodiment of the present invention.

FIG. 21 is a cross-sectional view showing a configuration of a liquid crystal element according to another conventional example.

[Explanation of reference numerals] 9: SiO column, 23, 23a, 23b: substrate, 2
2, 22a, 22b: electrodes, 20, 20a, 20b: alignment film, 26: pinhole, 28: insulating film, 24: FLC

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Tomoko Murakami 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (14)

[Claims] 1. A ferroelectric liquid crystal, an opposing substrate sandwiching the ferroelectric liquid crystal, and a voltage applying unit having an electrode for applying a voltage to the ferroelectric liquid crystal, the electrode being provided on an opposing surface of the opposing substrate. In the liquid crystal optical modulation element, an oblique vapor deposition alignment film is formed on the electrode surface via a buffer layer, and the alignment film and the buffer layer enable charge transfer between the ferroelectric liquid crystal and the electrode. A liquid crystal optical modulation element having a gap and a pinhole, respectively. 2. The voltage applying means includes at least a pixel electrode for applying a voltage to the ferroelectric liquid crystal in a pixel unit, a signal wire for supplying a voltage signal to the pixel electrode, the signal wire and the pixel electrode. An active switching element for controlling ON / OFF of a connection between the active switching element and a scan wiring for supplying a signal for controlling the ON / OFF of the active switching element, and resetting and writing of the ferroelectric liquid crystal Both are performed by active matrix driving.
The liquid crystal light modulation element described. 3. The liquid crystal optical modulation element according to claim 1, wherein the buffer layer is a thin film containing an inorganic compound as a main component. 4. The thin film containing the inorganic compound as a main component,
TiO ₂ —SiO _x , and its film thickness is 0.005 to 0.
The liquid crystal optical modulation element according to claim 3, which has a thickness of 2 μm. 5. The liquid crystal optical modulation element according to claim 4, wherein the film thickness is 0.01 to 0.05 μm. 6. The thin film containing the inorganic compound as a main component is T
a ₂ O _5, and the liquid crystal optical modulation element according to claim 3, wherein a film thickness which is a 0.005～0.2Myuemu. 7. The liquid crystal optical modulation element according to claim 6, wherein the film thickness is 0.01 to 0.05 μm. 8. The liquid crystal optical modulation element according to claim 1, wherein the material of the oblique vapor deposition alignment film is an inorganic oxide. 9. The liquid crystal optical modulation element according to claim 8, wherein the main component of the inorganic oxide is SiO. 10. The column length of the oblique deposition film is 0.01.
The liquid crystal optical modulation element according to claim 9, wherein the liquid crystal optical modulation element has a thickness of ˜0.6 μm. 11. The column angle of the oblique deposition film is 0-6.
The liquid crystal optical modulator according to claim 9, wherein the liquid crystal optical modulator is 0 °. 12. The liquid crystal optical modulation element according to claim 8, wherein the material of the inorganic oxide is ZrO ₂ . 13. The liquid crystal optical modulation element according to claim 8, wherein the material of the inorganic oxide is TiO ₂ . 14. A pair of opposing electrode substrates each having a substrate, an electrode provided on the substrate, and an alignment film provided on the electrode on opposing surfaces, and a liquid crystal sealed between them. In the liquid crystal optical modulation element, in the alignment film portion,
1 pinhole for electrical connection between the liquid crystal part and the electrode
A liquid crystal optical modulation element comprising one or more pixels.