JPS61249024A - Liquid crystal optical element - Google Patents

Abstract

PURPOSE:To obtain a good display characteristic which is not affected by temp. fluctuations by detecting the temp. of a display part in which a ferroelectric smectic liquid crystal is sealed and changing the voltage of an AC electric field to be impressed according to a temp. change. CONSTITUTION:The temp. of the liquid crystal display part 601 in which the chiral smectic liquid crystal having a ferroelectric characteristic is sealed is detected by a temp. sensor 615 and the signal thereof is inputted to a phase converter 602. The voltage of the electric field to be impressed is changed by controlling the phase according to the temp. change. With, for example, a phase converter 602, the AC voltage is increased at 1% ratio with temp. decrease by 1 deg.C with 30 deg.C as a reference. Then the stable bistable orientation condition is maintained even if the temp. fluctuates between 10-30 deg.C. The good display characteristic which is not affected by the temp. fluctuation is thus obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a liquid crystal optical element applied to a liquid crystal display element, a liquid crystal-optical shutter array, etc., and more particularly relates to a liquid crystal optical element with improved display and driving characteristics. .

[Description of prior art]

Of ark and La gerwa 11 are optical display elements that utilize the refractive index anisotropy of ferroelectric liquid crystal molecules to control transmitted light in combination with polarizing elements.
It has been proposed (q# Kaisho 56-1072
16, U.S. Patent No. 4367924, etc.)
. This ferroelectric liquid crystal generally exhibits
Chiral smectic O phase (SmO*) or H phase (
SmH*), and under specific layer thickness conditions of this liquid crystal layer, a first optically stable state (first stable orientation) and a second optically stable state ( has the property of taking one of the second stable orientations (second stable orientation) and maintaining that state when no electric field is applied, that is, has bistability;
Furthermore, it responds quickly to changes in electric field, and is expected to be widely used as a display element for high-speed and memory stores.

ε On the other hand, by applying a high-frequency alternating current electric field to a ferroelectric smectic liquid crystal with negative dielectric anisotropy (Δmelt 0),
It is conceivable to provide the ferroelectric liquid crystal with a bistable alignment state consisting of a first stable alignment and a second stable alignment. This method has the advantage that it is not necessary to set the liquid crystal layer to a specific layer thickness.

[Problem that the invention seeks to solve]

However, according to experiments conducted by the present inventors, the bistable alignment state of the ferroelectric smectic liquid crystal imparted in the presence of the above-mentioned high-frequency alternating current electric field has the problem of disappearing due to temperature fluctuations. There was found.

Therefore, an object of the present invention is to solve the aforementioned problems, that is, to provide a liquid crystal device using a ferroelectric smectic liquid crystal in a bistable alignment state that is independent of temperature fluctuations under a high frequency AC electric field. be.

[Means and effects for solving the problems] The present invention provides a liquid crystal cell in which a1 a ferroelectric smectic liquid crystal having negative dielectric constant anisotropy is arranged between a pair of substrates, and 1 b1 a liquid crystal cell in which a ferroelectric smectic liquid crystal having negative dielectric constant anisotropy is disposed between a pair of substrates; c. means for applying an alternating current electric field that imparts a bistable orientation consisting of a first stable orientation and a second stable orientation; c. means for changing the voltage value of the alternating current electric field in accordance with temperature fluctuations; means for selectively applying a first electric field to orient the 1i1 conductive liquid crystal to a first stable orientation and a second electric field to orient it to a second stable orientation, according to input information; The present invention is characterized by a liquid crystal element having means for detecting an optical difference between a light beam passing through a ferroelectric smectic liquid crystal oriented in the first stable orientation and a light ray passing through a ferroelectric smectic liquid crystal oriented in a second stable orientation.

〔Example〕

Hereinafter, the present invention will be described in further detail with reference to the drawings as necessary.

A particularly suitable liquid crystal material for use in the present invention is a chiral smectic liquid crystal having ferroelectricity. Specifically, chiral smectic C phase (Sm
C*), chiral smectic C phase (SmG*), chiral smectic F phase (8mF*), chiral smectic ■ phase (SmI*), or force-cutting smectic H phase (SmH*). I can do it.

For more information on ferroelectric liquid crystals, see, for example, Le Journal
URNAL DE PHYSIQUELETTRE
'') 36 (L-69) 1975 ``Ferroelectric Liquid Crystal'' (Ferroelectr
ic Liquid GrystalsJ; 1 Agelide Physics Letters 1 (“Applie
d Physics Letters”) 36(1
1; 1980 “Submicro Second Bistiple Electro-Optic Switching in Liquid Crystals J” (“submicro.

5econd B15table Blectroop
ticSwitching in Liquid 0
crystalsJ); “Solid State Physics” 16 (141
), 1981 "Liquid Crystal", etc., and among those disclosed in these publications, ferroelectric liquid crystals having negative dielectric constant anisotropy can be used in the present invention.

In particular, as a preferable ferroelectric liquid crystal, one that exhibits a cholesteric phase at a higher temperature side can be used, such as a phenyl ester liquid crystal that exhibits a phase transition temperature listed in the Examples below.

When constructing an element using a stiff material, the element can be supported by a copper block with an embedded heater, etc., as necessary, in order to maintain the temperature state such that the liquid crystal compound forms the desired phase. .

FIG. 1 schematically depicts an example of a cell for explaining the operation of a ferroelectric liquid crystal. Hereinafter, as the desired phase, S
This will be explained using mO* as an example.

11a and llb are Inz OH65n02 or I
A substrate (glass plate) coated with a transparent electrode made of a film such as TO (Indium-Tin Oxide)
In between, a liquid crystal of S m O* phase with a liquid crystal molecular layer 12 oriented perpendicular to the glass surface is sealed. A thick line 13 extends through liquid crystal molecules, and these liquid crystal molecules 13 form a continuous spiral structure in the plane direction of the substrate. The central axis 15 of this helical structure and the liquid crystal molecule 1
The angle formed with the axial direction of 3 is expressed as a tilt angle. This liquid crystal molecule 13 has a dipole moment 14 in a direction perpendicular to the molecule. A voltage Ea higher than a certain threshold is applied from terminals 16a and 16b between the electrodes on substrates 11a and llb.
When the voltage is applied, the helical structure of the liquid crystal molecules 13 is unraveled, and the liquid crystal molecules 13 can change their alignment direction uniformly in the direction of the liquid crystal molecules 13a so that all the dipole moments 14 are oriented in the direction of the electric field. Conversely, when a voltage Eb is applied, the helical structure of the liquid crystal molecules 13 is similarly unraveled, but the liquid crystal molecules 13 are arranged so that all the dipole moments 14 are directed in the opposite direction of the electric field.
can uniformly change the alignment direction in the direction of the liquid crystal molecules 13b. Furthermore, when the voltage Ea or Eb is applied to the alignment state, the liquid crystal molecules return to the original helical structure alignment state when the voltage Ea or Eb is released. The liquid crystal molecules 13 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and short axis direction. Therefore, for example, if crossed Nicol polarizers are placed above and below the glass surface, the polarity of voltage application can be changed. It is easily understood that the optical properties of the liquid crystal optical element change depending on the amount of the liquid crystal.

FIGS. 2(A) and 2(B) show an embodiment of the liquid crystal element of the present invention. FIG. 2(A) is a plan view of the liquid crystal element of the present invention, and FIG. 2(B) is the A-AllT? [Fig.

In the cell structure 100 shown in FIG. 2, a pair of substrates 101a and 101b made of glass or plastic plates are held at a predetermined distance by a spacer 104, and are bonded together with an adhesive 106 to seal the pair of substrates. Furthermore, on the substrate 101a, there is an electrode group (for example, a matrix) consisting of a plurality of transparent electrodes 102.
The scanning voltage application electrode g) of the square electrode structure is formed in a predetermined pattern such as a strip pattern. On the substrate 101b, an electrode group (for example,
Group of electrodes for applying signal voltage in matrix electric fA pathology)
has been formed.

Such transparency'i! Substrate 101 provided with c-pole 102b
Examples of b include silicon oxide, silicon dioxide, aluminum oxide, zirconia, and magnesium fluoride.

Cerium oxide, cerium fluoride, silicon nitride.

Inorganic insulating materials such as silico/carbide, boron substitutes, polyvinyl alcohol, polyimide, polyamideimide,
Polyesterimide, polyvaraxylylene, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyamide polystyrene, cellulose resin,
Melamine resin.

An alignment control film 105 formed of an organic insulating material such as area resin or acrylic resin can be provided.

This orientation control film 105 is obtained by forming a film of an inorganic insulating material or an organic insulating material as described above, and then rubbing the surface in one direction with velvet, cloth, or paper.

In another preferred embodiment of the present invention, the alignment control film 105 can be obtained by forming a film of an inorganic insulating material such as StO or 8i on the substrate 101b by oblique vapor deposition.

It is preferable that the above-mentioned orientation control film 1O5 also functions as an insulating film at the same time, and for this purpose, the orientation control film 10
The film thickness of No. 5 is generally 1001 to 1μ, preferably 5001μ.
It can be set in the range of ~5oooX. This insulating film also has the advantage of being able to prevent the generation of current caused by impurities contained in small amounts in the liquid crystal (103), and therefore does not deteriorate the liquid crystal compound even if the operation is repeated. do not have.

Further, in the liquid crystal confectionery of the present invention, a film similar to the above-mentioned alignment control film 105 can be provided on the other substrate 101a.

The liquid crystal layer 103 in the cell structure 100 shown in FIG.
For example, the liquid crystal layer 103 can be made of SmO*.
Although the thickness is not particularly limited, it is generally 3 μm to 15 μm.
degree is preferred.

Such a cell structure 100 includes substrates 101a and 101.
On both sides of b are polarizers 107 and 1 in a crossed nicol state.
08 are arranged respectively, and these polarizers 107 and 108
Accordingly, optical modulation when a voltage is applied between the electrodes 102a and 102b can be detected.

Now, by applying a high frequency alternating current electric field to the liquid crystal cell l described above in parallel to the liquid crystal molecular layer 12, the electric field Ea or gb
When ζ is applied, the crystals are oriented in some n orientation state in the oriented direction. The alignment state under application of a high frequency AC electric field is referred to as a first stable alignment state and a second stable alignment state. Such a phenomenon occurs because the liquid crystal material has a negative electric constant. The frequency of this alternating electric field must be set to a sufficiently high value of 4!4K, to which the liquid crystal cannot respond at a predetermined voltage value.

The AC voltage has a frequency of 400 Hz or more and 100 KHz or less, and the waveform can be a triangular wave, a sine wave, a rectangular wave, etc., and depending on the thickness of the liquid crystal layer, Vpp (Peak - t
H,peak) is preferably about 20v to 100v.

According to the experiments of the present inventors, the bistability under the condition where an alternating current electric field of a constant voltage value is applied as described above tends to disappear when the temperature decreases to a certain extent; It was found that bistability could be maintained as is by setting the voltage value high. The amount of change in frequency in this case varies depending on the liquid crystal material used, the cell thickness, and various other conditions, but generally, when the temperature fluctuates by 10°C, about 1°C to 20°C is suitable.

An example of a driving method used in the liquid crystal optical device of the present invention is shown below.

Figure 3 (A) shows a displayable matrix electrode structure, in which 31 is used as a scanning pole and 32 is used as an information signal electrode. Figure 3 (B) (a) and (b) are the signals applied to the scanning electrodes, tIc3 (a) represents the scan selection signal, and Figure 3 (B) (b) represents the scan non-selection signal. I'm watching. FIGS. 3(C) and 3(d) show information signals applied to the information signal electrodes, which are selectively applied to the information signal electrodes depending on write input information, respectively. Figure 3 (0) is
) represents the voltage waveform when applied to the pixel using the electrical signal shown in FIG. Figure 3(C) (a) and (b) are the voltage waveforms applied to the pixels on the scanning line to which the scan selection signal was applied, and Figure 3(0), (C) and (d) are: Each corresponds to a pixel to which a scan selection signal is not applied. The voltage applied to these pixels is set below a threshold value. Therefore, by selectively applying the write signals shown in FIGS. 3B, 3C, and 3D in synchronization with the scan selection signal, it is possible to perform sequential writing for each scan line. After writing to the above pixel, the voltage applied to the pixel is set below the threshold as shown in Figure 3 ((J), (C) and (d)), so the writing state on the scanning line is It will be stored in memory for one frame or one field.

FIG. 4(A) shows a time-series signal when such a signal is applied to perform the display shown in FIG. 3(A).

In FIG. 4(A), the high frequency alternating current component added by superimposing it on the information signal is omitted for the sake of simplicity. FIG. 4(B) shows an embodiment in which an auxiliary signal corresponding to the information signal is applied at a phase of Δt to prevent crosstalk.

Furthermore, as another embodiment, it is also possible to apply a high frequency AC component to the scanning electrode side. Furthermore, by applying phase matching to both the scanning electrode side and the signal electrode side, it is also possible to reduce the required breakdown voltage of the terminal driver ICs on the scanning electrode side and the signal electrode side.

FIG. 5 shows yet another embodiment.

In this embodiment, the AC signal is provided as a scanning non-selection signal. The scan selection signal provides the same waveform as that shown in FIG. 3(B)(a). High frequency when selected.

By turning it off, the liquid crystal molecules move easily, making switching easier, and by avoiding the weight of the selection signal (a: low frequency component) and non-selection signal (b: high frequency component), the scanning side This has the advantage of reducing the required breakdown voltage of the dry air 0.

FIG. 6 is a block diagram showing an example of a driving circuit for displaying an MXN dot liquid crystal display panel 601Efi using the liquid crystal element of the present invention. In the figure, 602 is an AC generating circuit (its output X is input to the data signal side superimposing circuit 6071), 603 is an information input, 604 is its clock input, 605 is a scanning line timing input, and 606
is its clock input.

The AC superimposition circuit 607 on the data signal input side has the following equation, where e is the symbol for adding voltage and % I'#I"t X is the voltage value. It has the function of I)l' -I, 'Lightning■
11-8! II■y S, "-8,1゛■y SM -sm+'(E)y (M: running fd) has the wiring function. On the data signal side, information manpower 6
The signal of 03 is sequentially sent to the shift register 609 and the clock 60.
4 and the latch 6101 controlled by the counter 611 are input to the aforementioned AC superimposition circuit 607 and the 1241 circuit 612,
Signals are sent to N data lines. On the scanning signal side, the scanning line timing input 605 and clock input 606 are input to a shift register 613, and the signals are sequentially input to the above-mentioned A, 0 superimposition circuit 608 and 1241 circuit 614. A scanning signal is input.

Further, a temperature sensor 615 detects the temperature near the liquid crystal display section 601 and inputs the signal to the phase converter 602. Therefore, by controlling the phase of the AC signal superimposed on the data line side and the scanning line side based on this temperature, the voltage of the AC signal that is effectively applied is changed. This allows bistability to be maintained even if temperature fluctuations occur.

Hereinafter, the present invention will be explained by giving specific examples.

A liquid crystal element shown in FIG. 3 was used. At this time, a glass substrate was used as the substrate, a transparent 1000-line stripe electrode was used as the electrode, and a polyamide film formed with a surface rubbing treatment was used on the glass substrate on which the electric device was formed.

The distance between these two glass substrates was maintained by a 10 μm spacer made of polyamide. Further, the peripheries of these two glass substrates were sealed with Evokin resin to create a cell.

A mixed ferroelectric liquid crystal having a negative attraction WL4 anisotropy as shown below was injected into this cell under an isokyoshi phase.

mixed lcd 1 part by weight This mixed liquid crystal causes the phase transition shown below.

(SmA; indicates a smectic phase, an Oh5 cholesteric phase, an IsoS, etc. phase) The phase transition point at this time is a value measured by a DSO (differential scanning calorimeter).

Next, after sealing the injection port, the temperature was increased from the Tokichi phase to 0.5°C/h.
It was slowly cooled down to 8 mO* at a rate of . When this liquid crystal element was observed under a microscope under crossed Nicols, the formation of monodomains was confirmed over a wide area, and a pitch of S mo* was observed.

The drive circuit shown in FIG. 6 was incorporated into the liquid crystal element thus prepared to perform display. At this time, a high frequency alternating current [C field of 10 KHz and 60 Vpp was used (1). Therefore, the switching pulse had the waveform shown in Fig. 3 (B) (however, the waveform shown in Fig. 3 (B) was obtained). also showed a high frequency AC waveform). Specifically, tl +tl (tl
-tl )=2 msec%V m 21.5 volts were used. The phase converter was controlled to increase the AC voltage at a rate of 1 ts for a temperature drop of 1°C with 30°C as a reference.

As a result, it was found that a good display state could be obtained even if the temperature varied between 10°C and 30°C.

In other words, this shows that a sufficient bistable state is maintained even if the temperature changes between 10°C and 30°C. In contrast, the phase converter used above When the experiment was repeated in exactly the same way except for omitting the use of
Sufficient display characteristics were not obtained on the low temperature side with respect to temperature fluctuations from 0°C to 30°C. This indicates that no bistable alignment state is formed at low temperatures.

Example 2 A liquid crystal element was produced in exactly the same manner as in Example 1 except that the spacer was replaced. In this liquid crystal element, monodomain formation was observed in a wide area, and unlike Example 1, S m O
The helical pitch of * was not observed (the helical structure was unraveled), but no bistable state was observed when no electric field was applied (however, at an AC voltage of 842 Vpp
When this liquid crystal element was incorporated into a drive circuit and displayed in the same manner as in Example 1, it was found that the stable bistable alignment state was maintained against temperature fluctuations as in Example 1. understood.

〔effect〕

According to the present invention, a stable bistable alignment state can be maintained even when external temperature fluctuations occur, and as a result, there is an advantage that good display characteristics that are independent of temperature fluctuations can be obtained.

[Brief explanation of drawings]

FIG. 1 is a perspective view schematically showing a ferroelectric liquid crystal element of the present invention. FIG. 2(A) is a plan view of the liquid crystal element of the present invention, and FIG. 2(B) is a sectional view taken along the line AN. FIG. 3(A) is a plan view showing how the matrix electrode structure is changed in the present invention, and FIG. 3(B) is an explanatory diagram showing how the waveforms of signals applied to the scanning lines and data lines are changed. 0) is an explanatory diagram showing a voltage signal waveform applied to a ferroelectric liquid crystal. FIG. 4(A) is an explanatory diagram showing the signals used in FIG. 3 in time series, and FIG. 4(B) is an explanatory diagram showing another time series signal. FIG. 5 is an explanatory diagram showing signal waveforms applied to the scanning line and the data line. FIG. 6 is a block diagram showing one example of a drive circuit used in the liquid crystal element of the present invention. Figure 7 (8) Figure 3 (B) (b) ((1) Country (b) (d) To the fourth LI- (2) (△) hv-, +++ (01 (C) Song

Claims (4)

[Claims] (1) In a liquid crystal optical element, a. a liquid crystal cell in which a ferroelectric smectic liquid crystal having negative dielectric constant anisotropy is arranged between a pair of substrates; b. a first stable orientation and a first stable alignment for the ferroelectric liquid crystal; means for applying an alternating current electric field that imparts a bistable orientation consisting of a second stable orientation; c. means for changing the voltage value of the alternating electric field in accordance with temperature fluctuation; and d. the ferroelectric liquid crystal. means for selectively applying a first electric field for aligning the first stable orientation and a second electric field for aligning the second stable orientation according to input information; e. A liquid crystal optical element comprising means for detecting an optical difference between a light beam passing through an oriented ferroelectric smectic liquid crystal and a light beam passing through a ferroelectric smectic liquid crystal aligned in a second stable orientation. (2) A patent claim in which the means for detecting the optical difference is a polarizer, and the polarization axis of the polarizer is parallel or substantially parallel to the direction of the first stable orientation or the second stable orientation. The liquid crystal optical element according to item 1. (3) The means for detecting the optical difference is a pair of crossed Nicol polarizers, and the polarization axis of one of the pair of polarizers is in the first stable orientation or in the second stable orientation. The liquid crystal optical element according to claim 1, which is parallel or substantially parallel to the direction of stable alignment. (4) The liquid crystal optical element according to claim 1, wherein the ferroelectric smectic liquid crystal is a chiral smectic C phase, H phase, I phase, G phase, or F phase.