JP2000275614A - Liquid crystal element and liquid crystal device provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid crystal element which is improved in its monostabilizing, i.e., its image persistence, under no applied voltage and a liquid crystal device equipped with it. SOLUTION: A liquid crystal 21, held between a pair of substrates 41, 42 placed opposite to each other and moreover having at least two stabilized states under no electric field, is composed so as to differentiate threshold characteristics of the two stabilized states. Also electric signals of which the polarities are switched reversedly and alternately are applied to the liquid crystal 21 e.g. via a pixel electrode 43 which applies voltage to the liquid crystal 21 and an active element 44 connected with the pixel electrode 43 and at the same time the one state out of the two stabilized states, in which the liquid crystal 21 is more stabilized is set to be the black display or the initial state.

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, a printer, and the like, and a liquid crystal device having the same, and more particularly to a device using a liquid crystal having at least two stable states under no electric field. About.

[0002]

2. Description of the Related Art Conventionally, a CRT has been most widely used as a display, and this CRT has been widely used as a video output for televisions and VTRs, or as a monitor for personal computers. However, due to the characteristics of this CRT, flicker or scanning stripes due to insufficient resolution lowers the visibility of a still image, or the phosphor deteriorates due to burn-in.

In addition, recently, it has been found that electromagnetic waves generated by a CRT adversely affect a human body, and there is a concern that the health of a VDT worker may be impaired. Furthermore, since the CRT is required to have a large volume behind the screen due to its structure, the convenience of information equipment is significantly impaired, and the space saving of offices and homes is impeded.

There is a liquid crystal element which solves such a drawback of the CRT. As an example of this liquid crystal element, for example, Applied Physics Letters by M. Schadt and W. Helfrich
A liquid crystal using a twisted nematic liquid crystal disclosed in Vol. 18, No. 4 (published on Feb. 15, 1971), pp. 127 to 128 is known.

Further, in recent years, liquid crystal elements called TFTs using this type of liquid crystal have been developed and commercialized. Here, this type of liquid crystal element is one in which a transistor is formed for each pixel, there is no problem of crosstalk, and a 10-12 inch class display is preferable due to rapid progress of production technology in recent years. It is being made with productivity. However, there are still problems in productivity, liquid crystal response speed, and viewing angle with respect to a frame frequency of 60 Hz or more, which is a point that a larger size or a moving image can be reproduced without any problem.

On the other hand, as a liquid crystal element using spontaneous polarization as a switching torque, for example, a chiral smectic liquid crystal element is disclosed in Clark and Lagerwall.
(JP-A-56-107216, U.S. Pat. No. 4,367,924).

Here, as the liquid crystal, a ferroelectric liquid crystal composed of a chiral smectic C phase or a chiral smectic H phase is generally used. Since the ferroelectric liquid crystal performs inversion switching by spontaneous polarization, Since it has a very fast response speed and excellent viewing angle characteristics, it is considered to be suitable as a high-speed, high-definition, large-area simple matrix display element or light valve.

Recently, chiral smectic antiferroelectric liquid crystal devices have also been proposed by Chandani, Takezoe et al. (Japanese Journal of Applied Physics).
ics) 27, 1988, L729). In addition, recently, among the antiferroelectric liquid crystal materials, a V-shaped response characteristic having a thresholdless value, a small hysteresis, and advantageous characteristics for gradation display has been discovered (for example, Japanese Journal of Applied Physics (Japanese Journal)
of Applied Physics) Vol. 36, 3586, 1997
page).

A V-shaped switching liquid crystal having a spontaneous polarization as a switching torque includes a monostable surface-stabilized F
LC (eg Journal of Applied Physics 6
1, 1987, p. 2400), deformed helix FLC (for example, Ferroelectrics 85, 1988).
173), Twisted smectic FLC (for example, Applied Physics Letter 60, 1992, 280).
Page), thresholdless antiferroelectric LC, polymer liquid crystal stabilized FLC
(For example, SID'96 digest 1996/699
Page).

An active matrix liquid crystal element using these liquid crystals has been actively developed to realize a high-speed display sufficient for expressing moving images (for example, Japanese Patent Application Laid-Open No. 9-50049).

[0011]

However, in such a conventional liquid crystal element (active element) using a chiral smectic liquid crystal having ferroelectricity, afterimages due to hysteresis, deterioration of alignment over time, and burn-in are caused. There is still a problem in terms of iso-reliability, and improvement in this aspect is strongly demanded.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and in particular, to provide a liquid crystal element having improved monostability in a state where no voltage is applied, that is, image sticking, and a liquid crystal device having the same. It is intended for.

[0013]

The present invention comprises a pair of substrates facing each other, and a liquid crystal sandwiched between the substrates and having at least two stable states in the absence of an electric field. The threshold characteristics of the two stable states are different from each other, and the more stable state of the liquid crystal among the two stable states is set to a black display or an initial state.

Further, the present invention is characterized in that alignment films having different alignment configurations are formed on the pair of substrates so that threshold characteristics of the two stable states of the liquid crystal are different.

Further, in the invention, it is preferable that the substrate has a pixel electrode for applying a voltage to the liquid crystal, and an active element connected to the pixel electrode.

Further, the present invention is characterized in that an electric signal having an inverted polarity is alternately applied to the liquid crystal via the pixel electrode and the active element.

Further, the present invention is characterized in that a transistor is used as the active element.

Further, the present invention is characterized in that the liquid crystal is a ferroelectric liquid crystal having bistability.

Further, in the present invention, the liquid crystal is a chiral smectic liquid crystal, wherein the chiral smectic liquid crystal is a fluorine-containing liquid crystal compound having a smectic phase or a potential smectic phase, and (a) at least one chiral or achiral liquid crystal compound. A fluorochemical terminal moiety having two methylene groups and optionally having at least one ether oxygen in the chain; (b) a chiral or achiral saturated hydrocarbon terminal moiety;
(C) using a chiral smectic liquid crystal composition containing a compound consisting of a central core portion connecting the terminal portions thereof.

Further, according to the present invention, the spontaneous polarization of the liquid crystal is 10
nC / cm ² or less.

According to the present invention, there is provided a liquid crystal device having a liquid crystal element, wherein the liquid crystal element is as described in any one of the first to eighth aspects.

Further, the present invention is characterized in that, when the operation of the liquid crystal element is completed, a shutdown method for switching the liquid crystal element to a more stable state and a pause method for suspending the liquid crystal element in a more stable state are adopted. .

Further, the present invention is characterized in that a light source is arranged behind the liquid crystal element.

Further, as in the present invention, the liquid crystal sandwiched between a pair of substrates facing each other and having at least two stable states in the absence of an electric field is configured so that the threshold characteristics of the two stable states are different. Then, for example, an electric signal whose polarity is inverted alternately is applied to the liquid crystal via a pixel electrode for applying a voltage to the liquid crystal and an active element connected to the pixel electrode, and the liquid crystal is more out of two stable states. A stable state is defined as a black display or an initial state.

[0025]

Embodiments of the present invention will be described below.

FIG. 1 is a cross-sectional view showing the structure of a liquid crystal device according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a liquid crystal layer composed of a liquid crystal (composition), and a chiral smectic liquid crystal is used as the liquid crystal. In this case, usually, the thickness of the liquid crystal layer 1 is preferably 5 μm or less in order to realize the stability of the ferroelectric phase. Also, 2a and 2b are substrates, glass,
Plastic or the like is used. 3a and 3b are transparent electrodes such as ITO, 5 is a sealing material, 8a and 8b are polarizing plates, and 9 is a light source.

Reference numerals 4a and 4b denote orientation control films, and at least one of the orientation control films is a uniaxial orientation control film. Incidentally, as a method of forming the uniaxial orientation control film, for example, by solution coating or evaporation or sputtering on the substrate,
Inorganic substances such as silicon monoxide, silicon dioxide, aluminum oxide, zirconia, magnesium fluoride, cerium oxide, cerium fluoride, silicon nitride, silicon carbide, boron nitride, polyvinyl alcohol, polyimide, polyimide amide, polyester, polyamide, After forming a film using an organic material such as polyesterimide, polyparaxylene, polycarbonate, polyvinyl acetal, polyvinyl chloride, polystyrene, polysiloxane, cellulose resin, melamine resin, urea resin, and acrylic resin, the surface is velvet, cloth or paper. It is obtained by rubbing with a fibrous material such as

Further, an oblique vapor deposition method in which an oxide or a nitride such as SiO is vapor-deposited from an oblique direction of the substrate may be used. Further, it is also possible to provide a short prevention layer in addition to the above.

In particular, it is preferable to use a polyimide rubbing film as a uniaxial orientation control film in order to obtain better uniaxial orientation. Here, the polyimide is usually obtained by coating and baking in the form of a polyamic acid. In addition, polyamic acid is excellent in productivity because it is easily soluble in a solvent. Further, recently, a polyimide soluble in a solvent has also been produced, and from the viewpoint of such technological advances, polyimide is preferably used because it can obtain better uniaxial orientation and has high productivity.

As a more preferable specific example, a polyimide alignment film having a repeating unit represented by the following general formula (I) is provided in order to improve the uniaxial orientation.

[0031]

Embedded image In the formula, A: a tetravalent group having an aromatic ring, an aromatic polycyclic ring, a heterocyclic ring, or a condensed polycyclic structure; B: an aliphatic group containing an alicyclic group; or-(Ph) _a- (O) _c − (CH ₂ ) _x − (D) _e − (CH ₂ ) _y −
(O) _d- (Ph) _b- (Ph is a phenyl group) a = b: 0 or 1 c = d: 0 when a = b = 0, 0 or 1 when a = b = 1 x, y: each independently an integer of 1 or more, provided that x + y + e is 2 or more and 10 or less. is there.

On the other hand, the two substrates 2a and 2b face each other via a spacer (not shown). The spacer determines the distance (cell gap) between the substrates, and silica beads or the like are used. . Here, the optimum range and upper limit of the cell gap determined by the spacer are different depending on the liquid crystal material, but the uniform uniaxial alignment and the average molecular axis of the liquid crystal molecules when no electric field is applied are almost aligned with the alignment processing axis. Is preferably set in the range of 0.3 to 10 μm in order to express an alignment state substantially the same as the axis in the average direction of the above.

At least one of the alignment control films (polyimide films) 4a and 4b formed on both substrates is usually rubbed to provide uniaxial alignment. It is preferable that the thickness is thin in order to suppress the adverse effect due to the anti-electric field, and specifically, it is preferably 200 ° or less. For the same reason, it is preferable that the spontaneous polarization of the liquid crystal material is also small, specifically, it is preferably 10 nC / cm ² or less.

In the present invention, as will be described later, a liquid crystal having at least two stable states in the absence of an electric field is used, and the threshold characteristic of each stable state is set so that one of the two stable states becomes unstable. It is configured differently. Here, such a state in which the threshold characteristics are different is realized, for example, when the alignment control film is different between the upper and lower cells, or in a case where seizure occurs in any state in a ferroelectric liquid crystal. it can. More typically, this can be realized well by using a film having a large difference in charging characteristics between the upper and lower alignment control films.

As an example of such an orientation control film different between the upper and lower cells, there is a combination of the above-described uniaxial orientation control film and a film having no (or no) uniaxial orientation. Further examples of a film not provided with uniaxial orientation include:
Examples of the material used for the uniaxial orientation control film include those that have not been subjected to the uniaxial orientation control treatment, various polymer materials, and films that have conductivity in the sense of suppressing the influence of a counter electric field.

The film having conductivity may be a film in which conductive fine particles are dispersed in a binder material, and is preferably used in that a charge characteristic can be differentiated from polyimide which is preferably used as a uniaxial alignment control film. .

The asymmetry can be changed by changing the coating solvent. There is also a method of using a monostable state using a driving method, and it is also possible to create a state in which excessively one-sided stable dust is seized by performing processing with a DC voltage for a certain period of time.

On the other hand, the liquid crystal used in the present invention includes:
A chiral smectic liquid crystal such as a ferroelectric liquid crystal and an antiferroelectric liquid crystal is used. More preferably, a surface stabilized ferroelectric liquid crystal having bistability is used. Since these liquid crystals use spontaneous polarization as switching torque, a high-speed liquid crystal element can be realized. The switching speed depends on the drive voltage, but is 1 ms or less, or 5
It is also possible to set it to 00 μs or less, or 100 μs or less.

By the way, in order to exhibit bistability,
The activation energy of the transition between two states needs to be large and can be realized in various ways. The following is an example of easily obtaining bistability. Here, a chiral smectic liquid crystal having a large tilt angle is preferably used. Typically, it is preferably 15 ° or more.

A bi-stable liquid crystal having two states of a uniform having no twist state is also preferably used.
In this case, in order to suppress the twisted state, it is preferable that the presence of ions in the liquid crystal is as small as possible. As a further example,
A chiral smectic liquid crystal whose spontaneous polarization is not too large also has a tendency that the threshold voltage between two states becomes large, and is preferably used. Typically, spontaneous polarization is 10n
C / cm ² or less is preferable. Also, a small spontaneous polarization is preferable in terms of suppressing the hysteresis.

The liquid crystal composition used therefor is, specifically, a fluorine-containing liquid crystal compound having a smectic phase or a potential smectic phase, and (a) having at least one chiral or achiral methylene group, (B) a chiral or achiral saturated hydrocarbon terminal moiety, which may have at least one ether oxygen in the chain;
(C) A chiral smectic liquid crystal composition containing a compound consisting of a central core connecting the terminal portions is preferred.

More preferably, it is a fluorine-containing liquid crystal compound having a smectic phase or a potential smectic phase, wherein (a) at least one chiral or achiral methylene group and at least one ether oxygen in the chain. And (b) a chiral or achiral saturated hydrocarbon terminal portion, and (c) a chiral smectic liquid crystal composition comprising only a compound group consisting of a central core portion connecting the terminal portions.

Further, the liquid crystal composition can be refined to obtain a structure having a small ion content, a good uniform orientation, a bookshelf capable of avoiding zigzag defects and a structure having a small layer tilt angle. It is preferably used because it can be output. In addition, the liquid crystal composition is composed of one or more of the above compounds, and a liquid crystal composition containing essentially no other compound is preferable, but contamination such as a trace amount of impurities is not impaired within a range that does not deteriorate the characteristics. Inclusion is acceptable.

Specific examples of the fluorine-containing compound are described in JP-A-6-329592 (particularly compounds described in Tables 1 to 15) and JP-A-7-316555 (particularly compounds described in Tables 1-1 to 18). Compounds having a perfluoro terminal portion are described in JP-A-63-27451 (particularly the compounds described in Table 1), JP-A-2-142755 (particularly the compounds described in Table 1), and WO 96/3325 (particularly Ta).
(Compound described in ble.). Further, with respect to the compound in which the side chain terminal is substituted with the above-mentioned substituent, JP-A-7-118178 [especially (I-1) to (I-180)]
Described in JP-A-6-256231 [especially (I)
Compounds described in -1) to (I-223)].

By the way, the liquid crystal element of the present invention is a liquid crystal device.
Among the two stable states, a more stable state is used as a black display or an initial state. In particular, when any driving method is used, a more stable state is used as a black display or an initial state.

For example, a driving method in which the entire screen is collectively reset to an initial state and data is written line-sequentially,
In a driving method in which a write signal and a reset signal are alternately written line-sequentially, the reset direction may be a more stable state of at least two stable states of the chiral smectic liquid crystal or a black display state. To apply a drive signal to the device and to design the position of the polarizing plate.
In practice, it is preferable to use a more stable state as an initial state and black display.

As a result, when no voltage is applied to the liquid crystal, the chiral smectic liquid crystal is held in a more stable direction in the black state.

In general, a chiral smectic liquid crystal having spontaneous polarization undergoes mono-stabilization, ie, burn-in, in its alignment state in the absence of a voltage, but at least two of the chiral smectic liquid crystals in the absence of a voltage as in the present invention. By putting it in one of the more stable states,
This normally appearing monostabilization can be significantly improved. And, by remarkably improving the mono-stabilization, the image sticking due to spontaneous polarization can be improved.

The inventor has reported that the chiral smectic liquid crystal having spontaneous polarization forms an electric field in the liquid crystal cell, that is, between the upper and lower substrates, due to the spontaneous polarization. An electric field opposite to the electric field due to the spontaneous polarization is formed, and it is considered that the monostabilization is remarkably improved by the electric field canceling mechanism in the static state.

In addition, based on such a concept, when the liquid crystal element is stopped, the element is similarly shut down so that the liquid crystal is placed in a more stable direction out of at least two stable states. Even if the operation is stopped by the above, the mono-stabilization can be remarkably improved.

On the other hand, as a driving method, a method of once resetting to a more stable state and then writing a desired gradation state can be used. Here, this driving method has an effect of suppressing the previous state history and increasing the reproducibility of the gradation expression ability, as compared with resetting to a more unstable state.

In order to use this driving method, it is preferable that the threshold value between the two states has a difference of 100 mV or more.
More preferably 200 mV or more, more preferably 3 mV
00 mV or more.

Further, the liquid crystal element of the present invention is characterized in that it has at least two stable states in the absence of an electric field, and this modulation state is performed in a state where a plurality of domains coexist or in a state where only one domain exists. Since it can be stored in memory, it has the effect of enabling application development such as partial pixel rewriting in which one part is in a memory state and the other part is in a driving state, a still image mode used as a full memory state, and a low power consumption mode. I have.

Incidentally, since the liquid crystal element of the present invention is an active element, a state in which no voltage is applied to the liquid crystal often appears. Therefore, in the case of such an active element, the effect of the present invention is very remarkably exhibited.

FIG. 2 shows an example of such an active element, in which the configuration shown in FIG. 1 is used as one pixel. In the figure, reference numerals 41 and 42 denote a pair of transparent substrates (for example, glass substrates).
1 and 42, the lower substrate 41 has a transparent pixel electrode 43
And active elements 44 connected to the pixel electrodes 43 are formed in a matrix.

Incidentally, as the active element 44,
It is composed of a thin film transistor called a TFT using a semiconductor such as an amorphous silicon base, a polysilicon type, a μ crystal base, and single crystal silicon. The active element 44 includes a gate electrode (not shown) formed on the substrate 41, a gate insulating film (not shown) covering the gate electrode, a semiconductor layer (not shown) formed on the gate insulating film, and a semiconductor layer (not shown). And a source electrode and a drain electrode (not shown) formed thereon.

On the other hand, as shown in FIG. 3, a gate line (scan line) 4 is provided between the rows of the pixel electrodes 43 on the lower substrate 41.
5, and information signal lines 46 are arranged between the columns of the pixel electrodes 43, respectively. The gate electrode of each TFT 44 is connected to the corresponding gate line 45, and the drain electrode is connected to the corresponding information signal line 46.

Further, each gate line 45 has an end 45a.
Are connected to a row driver 31 for applying a gate signal to scan a gate line 45, and each information signal line 46 applies a signal corresponding to display data to the information signal line 46 via an end 46a. 32.

The gate line 45 is covered with the gate insulating film of the TFT 44 except for the end 45a, and the information signal line 46 is formed on the gate insulating film. The pixel electrode 43 is formed on the gate insulating film, and is connected at one end to the source electrode of the TFT 44.

On the other hand, on the upper substrate 42 of FIG. 2, a transparent electrode 47 facing each pixel electrode 43 of the lower substrate 41 is formed. Here, the counter electrode 47 is formed of one electrode having an area covering the entire display area, and a reference voltage is applied. Then, the transmittance changes in accordance with the information signal voltage applied to the pixel electrode 43, and gradation expression can be performed. In addition, a capacitor serving as an auxiliary capacitance is often arranged for each pixel.

In the figure, 18 and 19 are alignment control films, 20 is a sealing member, 21 is a liquid crystal, and 22 is a spacer. Reference numerals 23 and 24 denote polarizing plates arranged in crossed Nicols.

In the active element described above, when the gate is turned on, charges are injected into the liquid crystal cell which is a pixel, the gate is turned off in a short time, and information is written to the pixel on the next scanning line. Here, since the liquid crystal 21 has spontaneous polarization, it becomes a voltage drop factor when the gate is turned off with the reversal of the spontaneous polarization except when the switching is completed within the gate-on time. Therefore, the spontaneous polarization is preferably not too large, specifically, 10 nC
/ Cm ² or less. This is preferable in order to suppress the alignment deterioration due to the incorporation of polar impurities and the like.

In the present invention, it is preferable that a voltage signal whose polarity is alternately inverted is input from the information signal line 46 when focusing on one pixel. In the present invention, when such polarity inversion driving is performed, the method described below is preferably used.

First, a voltage signal having a code for switching from the initial state to a direction that is not a stable direction is given, and the liquid crystal 21 is switched to be converted into a light modulation signal. This can, of course, be expressed in gradation.

Next, signals having different polarities are given to the liquid crystal 21.
Is switched in a stable direction. Here, the state in which the switching is performed in the stable direction is a black state or an extremely black state when one of the optical axes of the orthogonal polarizing plates 23 and 24 is used as a black display or an initial black element using the stable state optical axis. It will represent a state close to. In this case, when this element is viewed as a display element, it becomes a non-hold type display, and since the liquid crystal element of the present invention performs high-speed switching, it is very preferable in that the image quality of moving image display is excellent.

The time ratio between the period in which the switching is performed in the stable direction and the period in which the switching is performed in the non-stable direction is not particularly limited, but is intended to suppress the image sticking by minimizing the bias of the DC component. It is preferably in the range of 1: 9 to 9: 1, more preferably in the range of 3: 7 to 7: 3.

Further, with respect to the information signal voltage value to be switched in the stable direction, it is also preferable to minimize the bias of the DC component in total in accordance with the time ratio. Typically, a method in which the time ratio is set to 1: 1 and a signal having a different polarity gives a signal whose absolute value is equivalent to that of the immediately preceding or succeeding light modulation signal is preferable.

Such a matrix element is used in a transmission type liquid crystal device or a reflection type liquid crystal device. In addition,
In the case of a transmissive liquid crystal device, a light source is usually used, and in the case of a reflective liquid crystal device, a reflective layer is formed in an element.
Further, the present invention is applied to both a direct view type and a projection type. It can also be used as a light valve for a printer or the like.

FIG. 4 is a block diagram of a liquid crystal display device which is an example of a liquid crystal device having such a liquid crystal element. This liquid crystal display device uses a liquid crystal element in a display panel portion.

In the figure, 101 is a liquid crystal display device, 102 is a graphic controller, 103 is a display panel, 104 is a scanning line driving circuit, 105 is an information line driving circuit, 106 is a decoder, 107 is a scanning signal generation circuit,
108 is a shift register, 109 is a line memory, 11
0 is an information signal generation circuit, 111 is a drive control circuit, 112
Is a GCPU (Central Processing Unit), 113 is a host CP
U and 114 are VRAMs (memory for storing image information). Note that a light source is disposed on the back surface of the display panel 103 (see FIG. 1).

Here, the graphic controller 102
Is the host C with the GCPU 112 and VRAM 114 at the core.
The graphic controller 10 manages and communicates image information between the PU 113 and the liquid crystal display device 101.
The image information from 2 is transferred as display information to the information line drive circuit 105 via the drive control circuit 111 in accordance with the transfer clock, and as scan line address information to the scan line drive circuit 104.

Thereafter, in the information line drive circuit 105, based on the transferred display information, FIG.
Are transferred to the display panel 103 via the information signal generating circuit 110.

In the liquid crystal display device having such a configuration, the liquid crystal element has excellent switching characteristics as described above, so that excellent driving characteristics and reliability are exhibited, and high-definition, high-speed, large-area display is performed. Images can be obtained.

Next, an example of this embodiment will be described. Note that the present embodiment (the present invention) is not limited to these examples.

[0075]

Example 1 In this example, the following compounds were mixed at A / B / C / D = 15/55/25/5 (% by weight) to prepare a liquid crystal composition α.

[0076]

Embedded image The phase transition temperature of this liquid crystal composition α was 87 ° C. for Tiso,
The AC transition temperature was 52 ° C. The tilt angle is 26
°, spontaneous polarization: 6.0 nC / cm ² (all 30 ° C.)
Met.

Next, a cell was manufactured by the following method.

First, a 1.1 mm thick glass substrate (2
), An ITO film having a thickness of about 70 mm was formed as a transparent electrode. Next, a 0.7 wt% solution of a polyimide precursor having a repeating unit shown below in a polyamic acid solution of 0.7 wt% is applied to a pair of substrates on which such an ITO film is formed at 500 rpm for 5 seconds for the first time and at 1500 rpm for the second time. For 30 seconds.

[0079]

Embedded image Next, after pre-drying at 80 ° C. for 5 minutes, baking was performed at 220 ° C. for 1 hour, and thereafter, a rubbing treatment with a nylon cloth was performed on the alignment films on both substrates as a uniaxial alignment treatment. . The film thickness at this time was 60 °.

Next, a ladder-type polysiloxane base material and antimony-doped SnOx oxide ultrafine particles (particle diameter: about 100 °) are dispersed on one of the substrates at a solid content concentration of 10 watts.
t% ethanol / methanol / isopropanol = 4
4/43/13 (wt%) solution at 1500 rpm, 10
The coating was performed by spin coating under the condition of seconds. After this, a pre-drying operation was performed at 80 ° C. for 5 minutes.
The substrate was heated and dried for another hour to prepare another substrate.

Next, an IPA solution in which silica beads having an average particle size of 2.4 μm were dispersed at 0.01% by weight was spin-coated on the surface of the substrate which was not polyimide at 1500 rpm for 10 seconds, and the dispersion density was 100 / mm. ^{About 2} bead spacers were sprayed. Thereafter, a thermosetting liquid adhesive was applied on the substrate by a printing method.

Then, the two substrates thus obtained were bonded to face each other, and heated and cured in an oven at 150 ° C. for 90 minutes to obtain a cell.

Next, activated alumina fine particles 1 were added to the above liquid crystal.
The liquid crystal was injected into the cell prepared as described above, and then a triangular wave of 5 Hz and ± 7 V was applied, and a voltage-transmittance curve was measured by an optical response measurement method described later. . As a result, a hysteresis curve of a typical bistable ferroelectric liquid crystal was obtained. The difference in threshold voltage at the time of 50% inversion at this time was 180 mV.

Next, as shown in FIG. 5, the cell (area 0.9 cm ² ) S and the silicon single crystal transistor T
(On-resistance: 50Ω) and a 2 nF ceramic capacitor C were used to form an active element.

Then, a gate signal having a selection period of 30 μs was given to this active element, and the waveform shown in FIG. 6 was given from the information signal line. In FIG. 6,
Switching to a white or gray state is performed by a positive voltage, and resetting to an initial (black) state is performed by a negative voltage signal. One frame is 16ms, 8
ms is displayed, and 8 ms is not displayed.

(Optical Response) Next, the electro-optical response of the manufactured sample was measured. The measurement was performed using a polarizing microscope equipped with a photomultiplier tube, and the change in transmittance was measured under crossed Nicols. At this time, the cell was set in a state where no electric field was applied so that the more stable alignment direction was darkest.

The transmittance for each frame when the transmittance for white 1 is 100% is shown below. White 2 99% White 3 99% White 4 100% Gray 1 35% Gray 2 39% Gray 3 39% Gray 4 41% Black 1 <1% Black 2 <1% Black 3 <1% Black 4 <1% After applying only the white waveform in FIG. 6 to this cell for 300 hours, the same measurement was carried out. White 2 98% White 3 99% White 4 100% Gray 1 34% Gray 2 39% Gray 340 % Gray 4 40% Black 1 <1% Black 2 <1% Black 3 <1% Black 4 <1% The result was almost unchanged.

<Embodiment 2> In this embodiment, the cell used in Embodiment 1 was set in a more stable orientation direction, left for 200 hours, and then transmitted using the waveform of FIG. When the light amount was measured, white 2 97% white 3 99% white 4 99% gray 1 34% gray 2 39% gray 3 40% gray 4 39% black 1 <1% black 2 <1% black 3 <1% black 4 <1% was obtained, and there was almost no change.

<Embodiment 3> In this embodiment, A / B / D = 37/55/8 (% by weight) of the liquid crystal used in Embodiment 1 (the spontaneous polarization of this liquid crystal at 30.degree. 6 nC / c
m ² . ), The same measurement as in Example 1 was performed. White 2 98% White 3 100% White 4 100% Gray 1 45% Gray 2 50% Gray 3 49% Gray 4 51% Black 1 <1% Black 2 <1% Black 3 <1% Black 4 <1%

After a signal having only a white waveform was continuously applied for 200 hours in the same manner as in Example 1, the amount of transmitted light was measured using the waveform of FIG. 6, and in this case, there was almost no change. Further, after resetting to the black state, leaving the apparatus in that state for 300 hours, and similarly measuring the amount of transmitted light using the waveform of FIG. 6, there was almost no change in this case.

<Embodiment 4> In this embodiment, the cell used in Embodiment 1 is applied up to the position before the reset signal of gray 3 of the driving waveform in FIG. Was no electric field. In this state, halftone could be expressed by the domain gradation. Since then, this state has been maintained over time. When a similar experiment was performed using the cell used in Example 3, similar good results were obtained.
The memory state of domain gradation was able to be expressed. From the above, it has been found that the partial moving image display and the partial still image display are available, and that the entire still image display or the low power consumption mode is possible.

<Embodiment 5> In this embodiment, a cell was prepared in which the thickness of the polyimide film of Embodiment 1 was set to 100 °.
The liquid crystal of Example 1 was injected. At this time, the difference between the threshold voltages was 200 mV. When this was performed in the same experiment as in Example 1, there was almost no change in the threshold characteristic due to driving.

Next, a comparative example will be described.

[0094]

COMPARATIVE EXAMPLE In this comparative example, the direction in which the cell used in Example 1 is less stable is set to an initial state: a black state, the cell used in Example 1 is used, and the amount of transmitted light is determined using the driving waveform of FIG. When measured, white 2 100% white 3 100% white 4 100% gray 144% gray 249% gray 3 48% gray 4 51% black 13% black 24% black 34% black 45% became.

After resetting this to the black state and allowing it to stand for 300 hours, the amount of transmitted light was measured using the driving waveform of FIG. 6, and it was found that white 2 95% white 3 93% white 4 90% gray 136% gray 236% Gray 3 39% Gray 4 42% Black 1 2% Black 2 2% Black 33% Black 4 2% Monostabilization proceeded clearly in the orientation direction left unattended, and image sticking occurred.

[0096]

As described above, according to the present invention, a liquid crystal having at least two stable states in the absence of an electric field is formed.
The threshold characteristics of the two stable states are configured to be different from each other, and the more stable state of the liquid crystal in the two stable states is set to a black display or an initial state. Can be improved.
Further, by improving the mono-stabilization in the state where no voltage is applied in this way, a high-performance, high-speed response, high-quality liquid crystal element having a memory property and a liquid crystal device having the same can be provided.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view showing a configuration of an active element using the configuration shown in FIG. 1 as one pixel.

FIG. 3 is a top view of one substrate of the active element.

FIG. 4 is a block diagram of a liquid crystal device including the liquid crystal element.

FIG. 5 is a circuit diagram of an active element manufactured in Example 1 of the present embodiment.

FIG. 6 is a diagram showing a waveform applied to the active element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal layer 2a, 2b Substrate 3a, 3b Transparent electrode 9 Light source 21 Liquid crystal 41, 42 Transparent substrate 44 Active element 101 Liquid crystal display device 103 Display panel

Continued on the front page (72) Inventor Yukio Hanyu 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Minato Yagyu 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Tsuneki Nukanobu 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term (reference) 2H093 NA11 NA16 NC21 NC34 ND12 NE04 NE06 NF17 NF19 NF20 NG02 NG12 NH02 5G435 AA00 BB12 CC09 EE26 EE30 EE33 FF00 FF01 FF05 GG21 GG23 HH12

Claims (11)

[Claims] A pair of substrates facing each other, and at least two substrates sandwiched between the substrates in an electric field-free state.
And a liquid crystal having two stable states, wherein the liquid crystal is configured such that threshold characteristics of the two stable states are different, and the liquid crystal is more stable among the two stable states in a black display or an initial state. A liquid crystal element characterized by the following. 2. The liquid crystal device according to claim 1, wherein alignment films having different alignment configurations are formed on the pair of substrates so that threshold characteristics of the two stable states of the liquid crystal are different. 3. The liquid crystal device according to claim 1, wherein the substrate has a pixel electrode for applying a voltage to the liquid crystal, and an active element connected to the pixel electrode. 4. The liquid crystal device according to claim 1, wherein an electric signal having an inverted polarity is alternately applied to the liquid crystal through the pixel electrode and the active device. 5. The liquid crystal device according to claim 3, wherein a transistor is used as the active device. 6. The liquid crystal device according to claim 1, wherein the liquid crystal is a ferroelectric liquid crystal having bistability. 7. The liquid crystal is a chiral smectic liquid crystal, wherein the chiral smectic liquid crystal is a fluorine-containing liquid crystal compound having a smectic phase or a potential smectic phase, wherein (a) at least one chiral or achiral methylene group And at least one fluorochemical terminal moiety optionally having an ether oxygen in the chain; (b) a chiral or achiral saturated hydrocarbon terminal moiety; and (c) a central core connecting the terminal moieties. The liquid crystal device according to claim 1, wherein a chiral smectic liquid crystal composition containing a compound comprising: 8. The liquid crystal has a spontaneous polarization of 10 nC / cm ^2.
2. The liquid crystal device according to claim 1, wherein: 9. A liquid crystal device having a liquid crystal element, wherein the liquid crystal element is one according to claim 1. Description: 10. When ending the operation of the liquid crystal element,
10. The liquid crystal device according to claim 9, wherein a shutdown method for shutting down the liquid crystal element for switching to a more stable state and a halt method for halt in a more stable state are adopted. 11. The liquid crystal device according to claim 9, wherein a light source is arranged behind the liquid crystal element.