JP3176079B2 - Optical modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical modulation device for performing gradation display, and more particularly to a liquid crystal device for gradation display using a liquid crystal having at least two stable states, for example, a ferroelectric liquid crystal.

[0002]

2. Description of the Related Art In a conventional liquid crystal television panel using an active matrix drive system, thin film transistors (TFTs) are arranged in a matrix for each pixel, and a gate-on pulse is applied to the TFTs to make a conduction state between a source and a drain. At this time, a video image signal is applied from a source and stored in a capacitor. A liquid crystal (for example, a twisted nematic: TN-liquid crystal) is driven in accordance with the stored image signal, and simultaneously modulates a voltage of the video signal. Thus, gradation display is performed.

[0003]

However, an active matrix driving type television panel using such a TN liquid crystal or an STN (super twisted nematic) liquid crystal has a response speed of several hundred milliseconds and will be developed in the future. Expected ED and HD (hig
When used for driving a television that supports hvision, there is a problem in that defects such as residual images remain.

On the other hand, a ferroelectric liquid crystal having bistability has a fast response time of several hundred microseconds, and therefore, attempts have recently been made to use the ferroelectric liquid crystal for gradation driving of a television.

As one example of such a method, there is charge control driving of a ferroelectric liquid crystal. _{Q = f (P s, a} ) between which the ferroelectric liquid crystal domain inversion area (a) injecting charge amount and (q) ... P _s: that there is a spontaneous polarization becomes correlation of the ferroelectric liquid crystal In this method, a gradation display is performed by injecting a charge amount corresponding to an inversion area for each display of the ferroelectric liquid crystal.

The above-mentioned charge control drive is a very effective means for gray scale display using a bistable ferroelectric liquid crystal, but may have some disadvantages at the same time.

One of them is a hysteresis phenomenon in voltage-transmittance characteristics. Hereinafter, the phenomenon will be described.

FIG. 4 is a configuration diagram of a commonly used ferroelectric liquid crystal. In FIG. 4, reference numerals 14 and 14 'denote substrates, 1
3, 13 'are transparent conductive layers, 12, 12' are insulating layers, 1
Reference numerals 0 and 10 'denote alignment layers, and reference numeral 11 denotes a ferroelectric liquid crystal layer.

FIG. 5 is an equivalent circuit when gradation display is performed by active matrix charge control driving using a ferroelectric liquid crystal. In the drawing, T ₁₁ , T ₁₂ , T ₂₁ , T ₂₂ ... Indicate thin film transistors (TFTs) used as switching elements driven by active matrix. LC ₁₁ , LC ₁₂ , L
C ₂₁ , LC ₂₂ ... Are TFTs T ₁₁ , T ₁₂ ,
T ₂₁ , T _22, ... Drain electrodes 4, 4 ′, 4 ″,
4 ′ ″ and a pixel made of a ferroelectric liquid crystal sandwiched by a counter electrode 8. C ₁₁ , C ₁₂ , C ₂₁ , C ₂₂ ... Are connected to the gate lines 1 _a , 1 _a ′,.
4 ″, 4 ″ ″, and a capacitor for accumulating drive signal charges. Now, using the circuit described above, a reset pulse 11 is applied to each pixel at a period of 16.7 ms (60 Hz) with a driving waveform as shown in FIG.
When a write pulse corresponding to each gradation is applied, a transmittance as shown in FIG. 6B is generated. The transmittance indicated at 13 at this time is a transmittance corresponding to approximately 12 write pulses.

Now, the write pulse 1 with such a drive waveform
The plot of the transmittance 13 with respect to 2 is the voltage-transmittance characteristic described above. An example is shown in FIG. As is apparent from the figure, a so-called hysteresis phenomenon in which the transmittance is different between the voltage rising 14 and the voltage falling 15 is observed.

FIG. 8 qualitatively explains the hysteresis phenomenon. (B) of FIG. 8 corresponds to 14 in FIG. That is, it is a direction in which the number of black domains is reduced, and from the viewpoint of driving, it is necessary to write white after reset.
On the other hand, FIG. 8A shows the direction in which the number of black domains is increased, and it is not necessary to write white after reset from the viewpoint of driving. That is, when looking at the write pulse, the former (14) requires a larger voltage than the latter (15).

As described above, when gradation display is performed by the charge control method using the driving method as shown in FIG. 6, a hysteresis phenomenon occurs in the voltage-transmittance characteristic inevitably.

In addition, when the above-described active matrix driving is performed, there is a problem that the response of the liquid crystal is alienated by continuous application of a direct current (DC) component for a long time during driving. This is due to the DC
It is considered that the component induces the uneven distribution of the internal ions of the liquid crystal, which forms an electric field.

FIG. 9 shows a phenomenon that occurs when the driving waveform shown in FIG. 6 is applied. From FIG. 9, it can be clearly seen that the transmittance is gradually reduced by the repeated pulse application. Next, this phenomenon will be described with reference to FIG. In the waveform shown in FIG. 6, the liquid crystal feels like a geometrically positive DC component is excessively applied. FIG. 10 shows how this DC component acts on the liquid crystal.

By the application of the positive DC component, charges are accumulated between the insulating layer portions 10 and 10 'and the liquid crystal portion 11, and the partial pressure of the liquid crystal becomes negative due to the charge accumulated components. "White" writing becomes difficult.

The above-described hysteresis phenomenon and the alienation of driving due to the DC component are a serious problem in gray scale display by the active matrix method because the pixel display voltage cannot be uniquely determined.

[0017]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical modulation element which has solved the above-mentioned disadvantages. Specifically, the alignment film is made to have a low resistance. The hysteresis phenomenon in the voltage-transmittance characteristic is reduced, and there is no instability due to the DC component, and the alignment film has a highly uniform alignment that does not disturb the alignment even when the resistance is reduced. An optical modulation element is provided.

[0018]

According to the present invention, there is provided a step of preparing one substrate, and applying a siloxane liquid containing dispersed ultrafine Sb-doped tin oxide particles having a particle diameter of 100 ° or less to the substrate. Heat treating the applied siloxane liquid layer to form a polysiloxane film containing ultrafine Sb-doped tin oxide particles having a particle size of 100 ° or less, and rubbing the polysiloxane film; A step of disposing the other substrate at an interval with respect to one substrate, and a step of disposing a chiral smectic liquid crystal at the interval.
(excluding b-doped tin oxide particles).

According to the present invention, in an active matrix optical modulation element for performing a gradation display, the resistance of the alignment film is reduced by using a polymer in which an ultrafine conductive material is dispersed for the alignment layer. The hysteresis phenomenon and the instability due to the DC component can be eliminated.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The ferroelectric liquid crystal used for the optical modulation material of the present invention will be described below, and then the embodiments of the present invention will be described.

The optical modulator usable in the present invention includes:
Has a first optically stable state (eg, forming a bright state) and a second optically stable state (eg, forming a dark state) in response to an applied electric field, ie, at least with respect to the electric field. A substance having two stable states, particularly a liquid crystal having such properties, is optimal.

As the liquid crystal having at least two stable states which can be used in the optical modulation element of the present invention, a chiral smectic liquid crystal having ferroelectricity is most preferable, among which chiral smectic C phase (SmC ^* ),
H phase (SmH ^* ), I phase (SmI *), F phase (SmF ^* )
And a liquid crystal of G phase (SmG *) is suitable. This ferroelectric liquid crystal is referred to as "Le Journal de Fisique Lettre" (LEJOURNAL DE PHYS).
IQUE LETTER ") Vol. 36 (L-69) 19
1975 "Ferroelectric Liquid Crystals"("FerroelectricLiquid"
Crystals "):" Applied Physics L.
Vol. 36, No. 11, 1980, "Submicro Second Bistable Electrooptic Switching in Liquid Crystals"("Submicro Second Bis").
table Electro-optic Switch
hing in Liquid Crystal
s "): Solid state physics 16 (141) 1981" Liquid crystal "and the like, and in the present invention, the ferroelectric liquid crystal disclosed therein can be used.

More specifically, as an example of the ferroelectric liquid crystal compound used in the method of the present invention, desyloxybenzylidene-P'-amino-2-methylbutylcinnamate (D
OBAMBC), hexyloxybenzylidene-P'-
Amino-2-chloropropylcinnamate (HOBAC
PC) and 4-0- (2-methyl) -butylresorcylidene-4'-octylaniline (MBRA8).

When a device is formed using these materials, the liquid crystal compounds are SmC ^* , SmH ^* , SmI *, SmF
^The element can be supported by a copper block or the like in which a heater is embedded, if necessary, in order to maintain the temperature at which the temperature becomes ^* , SmG *.

FIG. 11 schematically illustrates an example of a ferroelectric liquid crystal cell. 11 and 11 'are In ₂ O ₃ , Sn
It is a substrate (glass plate) coated with a transparent electrode such as O ₂ or ITO (indium-tein-oxide), and an SmC ^* phase liquid crystal in which the liquid crystal molecular layer 12 is oriented so as to be perpendicular to the glass surface. It is enclosed. Lines 13 shown by bold lines represent liquid crystal molecules.
Is the dipole moment (P
⊥) 14 is provided. When a voltage higher than a certain threshold is applied between the electrodes on the substrates 11 and 11 ′, the helical structure of the liquid crystal molecules 13 is released, and the dipole moment (P⊥) 14 is oriented in the direction of the electric field. You can change direction. The liquid crystal molecules 13 have an elongated shape, exhibit refractive index anisotropy in the major axis direction and the minor axis direction,
Therefore, it is easily understood that, for example, if polarizers arranged in a crossed Nicols positional relationship with each other above and below the glass surface are provided, a liquid crystal optical modulation element whose optical characteristics change depending on the polarity of applied voltage. Further, when the thickness of the liquid crystal cell is sufficiently reduced (for example, 1 μm), the helical structure of the liquid crystal molecules is unwound (non-helical structure) even when no electric field is applied as shown in FIG. P or P 'takes an orientation state of either upward (24) or downward (24'). When an electric field E or E 'having a polarity equal to or more than a certain threshold is applied to such a cell as shown in FIG. 12, an upward direction 24 or a downward direction 24' corresponding to the electric field vector of the dipole moment electric field E or E 'is obtained. In response, the liquid crystal molecules are aligned in one of the first stable state 23 (bright state) and the second stable state 23 '(dark state).

There are two advantages of using such a ferroelectric liquid crystal as the optical modulation element. First, the response speed is extremely fast, and second, the orientation of the liquid crystal molecules has bistability. The second point will be described with reference to FIG. 12, for example. When an electric field E is applied, the liquid crystal molecules change to the first stable state 23.
In this state, the first stable state 23 is maintained even when the electric field is cut off, and when the electric field E 'in the opposite direction is applied, the liquid crystal molecules are oriented to the second stable state 23'. Although the direction of the molecule is changed, it is maintained in this state even after the electric field is cut off, and each has a memory function in a stable state. In order to effectively realize such a high response speed and bistability, it is preferable that the cell is as thin as possible, generally 0.5 μm to 20 μm, particularly 1 μm to 5 μm.
μm is suitable. A liquid crystal-electro-optical device having a matrix electrode structure using this type of ferroelectric liquid crystal is, for example,
It is proposed in U.S. Pat. Nos. 4.367.924 and 4.840.462.

Next, the details of the optical modulation element according to the present invention will be described based on embodiments.

Embodiment 1 FIG. 1 is a schematic view showing an example of an optical modulation device according to the present invention. In FIG. 1, 1 and 1 'are substrates, and 2 and 2' are ITO.
It is a transparent conductive film made of a film. Reference numerals 3 and 3 ′ denote polymer polymerization layers in which an ultrafine conductive material is dispersed, and specifically,
An FLC alignment film 4 obtained by rubbing a polysiloxane film in which SnO ₂ : sb ultrafine particles are dispersed is a ferroelectric liquid crystal layer.

The reference numerals 1 and 1 'are 1.1 mm thick non-alkali glass NA40 made of sea squirt glass, and the 2 and 2' ITO films were formed to a thickness of 700 ° by a reactive RF ion plating method in oxygen gas. Things. The polysiloxane orientation layer is prepared by dispersing siloxane in a solvent as a solid component and adding 2.5 wt% of a mixture of ethylyl silica and SnO ₂ : ultrafine particles, and then forming a solid component of SnO ₂ : s
The b ratio (conducting material ratio) was set to 40%, and this dispersion was spin-coated, and then heat-treated at a temperature of 150 ° C. for 1 hour to form a 500 ° polysiloxane: SnO ₂ film by rubbing.

The gap between the liquid crystals was formed of 1.5 μmφ silica beads, into which ferroelectric liquid crystal was injected.

The orientation state of the obtained FLC was uniform and uniform. The resulting VT curve is shown in FIG. As is clear from FIG. 2, SnO ₂ : S
b is not dispersed at all (FIG. 2)
In comparison with 1), it can be seen that the hysteresis of the VT characteristic is clearly reduced.

FIG. 3 shows the correlation of the all-white writing response time when the black reset leaving time is changed. In FIG. 3, 1 is an FLC of a polysiloxane alignment film in which SnO ₂ : sb is not dispersed at all, and 2 is an FLC of this embodiment. FIG. 3 clearly shows that the FLC of the present invention has eliminated the instability due to the DC component.

Example 2 In a siloxane solution similar to that in Example 1, 2.5% by weight of a solid component having a conductive material ratio of 80% was dispersed.

This dispersion was spin-coated on an ITO substrate in the same manner as in Example 1, baked at 150 ° C. for 1 hour, and rubbed. Next, a cell assembly was performed, and liquid crystal was injected.

Observation of the orientation state of the device by a polarizing microscope revealed that the device had a uniform uniform orientation as in Example 1, and the VT characteristic hysteresis was greatly reduced.

It is to be noted that uniform orientation can be obtained even with a polysiloxane oriented film (conducting material ratio of 40 to 90%) having a conducting material ratio other than those of Examples 1 and 2, and a reduction in hysteresis of VT characteristics can be achieved. Was.

[0037]

As described above, according to the present invention, by using a polysiloxane polymer in which an ultrafine conductive material is dispersed in an alignment film, the resistance of the alignment film can be reduced and the ferroelectric liquid crystal can be obtained. Can suppress the hysteresis phenomenon of the VT characteristic peculiar to the halftone display and the instability due to the DC component. Further, it is possible to obtain a uniform uniform orientation while suppressing the disorder of the orientation generally caused by lowering the resistance of the orientation film.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing one example of an optical modulation element of the present invention.

FIG. 2 shows the VT characteristic of the optical modulation element of the present invention and the conventional F
5 is a graph showing VT characteristics of LC.

FIG. 3 is a graph showing a correlation between a white writing time and a difference in a black leaving time between an optical modulation element of the present invention and a conventional FLC.

FIG. 4 is a schematic view showing an example of a general ferroelectric liquid crystal.

FIG. 5 is an equivalent circuit when performing gray scale display by active matrix charge control driving using a ferroelectric liquid crystal.

FIG. 6 is a graph showing a relationship between a driving waveform and transmittance.

FIG. 7 is a graph showing a relationship between a writing voltage and transmittance.

FIG. 8 is a schematic diagram qualitatively showing a hysteresis phenomenon.

FIG. 9 is a graph showing a phenomenon of alienation of a response of a liquid crystal due to a DC component.

FIG. 10 is a schematic diagram showing a phenomenon of alienation of a response of a liquid crystal due to a DC component.

FIG. 11 is a schematic view showing one example of a ferroelectric liquid crystal cell.

FIG. 12 is a schematic diagram showing one example of a ferroelectric liquid crystal cell.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Tomoko Murakami, Inventor Tomoko Murakami 3-30-2, Shimomaruko, Tokyo Canon Inc. (72) Inventor Akio Maruyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (56) References JP-A-3-92824 (JP, A) JP-A-63-121020 (JP, A) JP-A-2-221923 (JP, A) JP-A-2-167389 (JP, A) A) JP-A-62-70815 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1337 G02F 1/137

Claims (1)

(57) [Claims] 1. A step of preparing one substrate, a step of applying a siloxane solution containing dispersed ultrafine Sb-doped tin oxide particles having a particle size of 100 ° or less on the substrate, The layer is subjected to a heat treatment, which results in a particle size
Forming a polysiloxane film containing ultrafine Sb-doped tin oxide particles of 100 ° or less, rubbing the polysiloxane film, and arranging the other substrate so as to face the one substrate at an interval. And a method for producing a liquid crystal device having a step of arranging chiral smectic liquid crystals at the intervals (excluding ultrafine Sb-doped tin oxide particles having a particle diameter of 100 °).