JPS61241731A - Smectic liquid crystal device - Google Patents

Abstract

PURPOSE:To perform writing under a bright and dark conditions with a faster scanning speed which can be executed by one-frame scanning, by using alternating signals having a time width which is greater than the longer inverting time for a liquid crystal panel using a smectic liquid crystal compound, as write signals. CONSTITUTION:Since the liquid crystal molecule of a selected picture element receives the action of an electric field of a time of duration T1 which is longer than an inverting time tau1 of a pulse at the time of a voltage -V1 and shorter than another inverting time tau2 when the 1st mode signal is impressed, the picture element sufficiently inverts to a dark condition. When the 2nd mode signal is impressed, the liquid crystal molecule of the selected picture element receives an electric filed of a duration of time T2 which is longer than the inverting time tau1 of another pulse P3 at the time of a voltage -V. Therefore, the picture element once changes to a dark condition. However, since continuously impressed pulses P4 have a time width T2 which is longer then the inverting time tau2 from a dark condition to a bright condition under a voltage V1, the liquid crystal molecule is inverted from the dark condition written by the pulse P3 and writes a bright condition. Therefore, writing of the dark and bright conditions can be executed at a very high speed of hundreds microseconds mus.

Description

TECHNICAL FIELD The present invention relates to a chiral smectic liquid crystal device, and more particularly to a drive circuit for a smectic liquid crystal display panel.

(Prior Art) In recent years, liquid crystal devices using chiral smectic C phase have attracted attention as display devices with high-speed response and memory retention, and optical shutters for cameras and printers.

As a ferroelectric liquid crystal compound having this chiral smectic C phase, for example, 2-methybutyl P-[(P-n
8, L2. L3. They are arranged in a twisted spiral structure for each L4.

By the way, a liquid crystal cell is produced by injecting this liquid crystal compound having a chiral smectic C phase between two substrates B and H having a gap (for example, about 1 m) smaller than the helical period (usually several gm). (Fig. 9A), the liquid crystal molecules lose their helical structure and have a domain whose molecular axis is parallel to substrates B and H, tilted at an angle θ clockwise from the layer normal direction, and one counterclockwise domain. It has a mixed state of domains that are tilted by 0 or 10 degrees around the molecule (see figure), and also has an electric dipole in the direction perpendicular to the molecular axis.

Therefore, if one domain has an electric dipole pointing upwards with respect to the substrates B, H, the other domain will have an electric dipole pointing downwards, so when an electric field is applied between the substrates 8.8, All liquid crystal molecules are aligned at a position tilted either 10 degrees or -θ from the normal direction of the layer,
When an electric field in the opposite direction is applied, the liquid crystal molecules are also reversed and aligned all at once at positions tilted by 10 or 10 degrees.

When polarizing plates are placed on both sides of this cell and an electric field is applied,
The movement of liquid crystal molecules creates bright and dark states, allowing it to function as a display panel or optical shutter (
(Fig. 1θ), the liquid crystal panel constructed in this manner has an extremely fast response speed on the order of microseconds, and has the excellent property of retaining the pattern once displayed even after the electric field is removed.

In particular, this memory retention property is a very acceptable characteristic in terms of saving drive power; It becomes necessary to do
There is a problem in that it takes time to change the display pattern.

(Objective) In view of the above-mentioned problems, an object of the present invention is to provide a novel smectic liquid crystal device with a high scanning speed and capable of writing in a bright state and a dark state in one frame scan.

(Summary of the Invention) That is, the present invention is characterized in that one substrate is uniaxially aligned, the other substrate is randomly aligned horizontally, and the gap in the space is formed by a helical pitch of a ferroelectric chiral smectic liquid crystal compound. A smectic liquid crystal panel is configured as follows: an alternating signal having a time width between the first inversion time and the second inversion time of the liquid crystal compound; and an alternating signal having a time width larger than the longer inversion time of the liquid crystal compound. The point is that the alternating signal is applied selectively.

(Structure) Therefore, details of the present invention will be described below based on illustrated embodiments.

FIG. 1 shows an embodiment of a smectic liquid crystal device used in the present invention, and reference numeral l in the figure indicates one substrate constituting a liquid crystal display panel, and segment electrodes 1a, made of transparent conductive material, A thin film of polyimide is provided by printing or dipping on the surface of an electrically insulating transparent plate 1b such as glass on which 1a, 1a, etc. are formed, and a polyimide thin film is provided on the surface of the electrically insulating transparent plate 1b, which has uniform orientation in all directions along the surface of the substrate 1. 2 is the other substrate constituting the liquid crystal display panel, which is formed by forming a horizontal alignment film layer 1c (FIG. 2A). A polyimide thin film is provided on the surface of the electrically insulating transparent plate 2b on which the common electrodes 2a, 2a, 2a, . . . are formed, and the surface of this thin film is rubbed in one direction to impart orientation in only one direction. These two substrates 1.2 are composed of a random horizontal alignment film layer IC and a random horizontal alignment film layer 2c with a gap smaller than the helical pitch of the liquid crystal compound. The uniaxial alignment film layers 2c 2C are arranged in parallel to face each other, and S-4-0 (
2-Methyl) butyl resol cylidene-4-alkyl n
- A ferroelectric smectic liquid crystal compound 3 made by mixing equal proportions of thictylaniline and P-n-octylphenyl-Po-6-methyloctyloxybenzoate is filled, and the periphery of the substrate is sealed with a sealant. The display panel 6 is formed by forming a cell structure. Note that reference numerals 4.5 in the figure each indicate a polarizing plate disposed on the surface of the substrate.

When voltage is applied to the electrodes of the liquid crystal panel configured in this way and the domain reversal speed is investigated, as shown in Figure 3, when the same level of voltage is applied, the speed at which the domain changes from a bright state to a dark state is r1 and the rate of change from the dark state to the bright state (7:2) are different, and a response time difference Δτ occurs between the two.

The present invention actively utilizes the time difference Δr at the time of switching the display state to execute writing in the bright state and writing in the dark state at the same time.

Next, details of the drive circuit according to the present invention will be explained based on an embodiment.

FIG. 4 shows an embodiment of the present invention, in which reference numeral 7 denotes a common electrode drive circuit 8 connected to the common electrodes 2a, 2a, 2a, . . . of the above-mentioned smectic liquid crystal panel 6. are segment electrodes 1a, la, la...
A segment electrode drive circuit connected to the segment electrode drive circuit is configured to apply an electric field of the first mode or the second mode to the pixel according to the write state during line sequential scanning, and apply an electric field of the third mode to the pixel when not selected. ing.

That is, during pixel selection.

■At a voltage of 1v11, a negative direction pulse P1 with a time width T1 between 1, which is the time required to change from a bright state to a dark state, and 2, which is the time required to change from a dark state to a bright state;
Figure 5 a), a dark state write signal consisting of a positive direction pulse P2 with a voltage of 1vtl and a time width of T1, and a voltage IVt/Nl.
The first mode signal consists of a maintenance signal that alternates between
, ■ A negative direction pulse P3 with a time width T2 of 2 or more in the time required to change from a dark state to a bright state at the same level of voltage Ivtl (see the same figure), and a positive direction pulse with a time width T2 at a voltage 1v11. A bright state write signal consisting of P4, and a second mode signal (d) consisting of a sustain signal, and a third mode signal (d) consisting of an alternating signal with a voltage 1v1/N1 and a time width that does not cause inversion in liquid crystal molecules when not selected. It is configured to selectively output a mode signal (E).

Next, the operation of the device thus constructed will be explained.

When no electric field is applied to the electrodes 1a and 2a, the liquid crystal molecules are enclosed in a narrow gap that is less than the helical pitch, so that one end of the liquid crystal molecules is aligned with the random horizontal alignment film layer Lc.
Under the condition that the liquid crystal molecules are captured by and free in the plane direction, the other ends of the liquid crystal molecules are biased in one direction by the uniaxial alignment film layer 2C. As a result, the substrate l, 2
All the liquid crystal molecules filled in the panel are aligned in one direction to maintain a uniform optical density over the entire panel surface without revealing any pattern, thereby forming a uniform background.

In this state, when the first mode signal is applied, the liquid crystal molecules of the selected pixel are affected by the electric field whose duration T1 is longer than 1 in the inversion time and shorter than 2 in the inversion time at the voltage -vI of the pulse P8. It is inverted to a sufficiently dark state to receive light. When pulse P2 is applied after this reversal,
The time width TI of this pulse P2 switches from a dark state to a bright state.

Since the time is shorter than τ2, the liquid crystal molecules of the selected pixel cannot be inverted to the bright state and maintain the dark state, that is, the state written by the pulse P. A sustain signal applied after this write signal dynamically holds the liquid crystal molecules of the selected pixel in a dark state position.

When the second mode signal is applied, the liquid crystal molecules of the selected pixel are
At the inversion time at voltage -■ of pulse P3! Since it is affected by the electric field with a longer duration T2, it temporarily changes to a dark state. However, the pulse P4 that is subsequently applied is
Since the inversion time from the dark state to the bright state at this voltage vI has a time width T2 longer than 2, the liquid crystal molecules are inverted from the dark state written by the pulse P3 to the bright state. will be written. A sustain signal applied after this write signal dynamically maintains the liquid crystal molecules of the selected pixel in a bright state.

As a result, writing in the dark state and writing in the bright state can be executed at extremely high speeds of several hundreds of seconds.

Needless to say, in the above process, the liquid crystal molecules
Since voltages with the same voltage level and duration are alternately applied,
No residual charge is generated in the pixel.

Hereinafter, in this way, either the first mode signal or the second mode signal is selected in accordance with the state to be written, and the dark state and bright state can be written by scanning one frame.

In this embodiment, after displaying the pattern, an alternating voltage having a peak value of l/N of the driving voltage is applied to maintain the displayed content. Since the liquid crystal molecules are captured by one new alignment axis, the orientation of the liquid crystal molecules is maintained even if the application of the alternating voltage is removed, and the display content can be stored.

Further, in this embodiment, the first mode signal is used for writing in the dark state, and the second mode signal is used for writing in the bright state, but these may be changed as appropriate depending on the operating characteristics of the target liquid crystal panel. Needless to say.

FIG. 6 shows a second embodiment of the present invention, in which gradation display is performed using the change in pixel density with respect to the electric field application time shown in FIG. 7. When selecting a pixel, When the peak voltage is 1■11, the time width Tx is between the time τ1 required for the tip side to change from the bright state to the dark state from V1/2 and the time required for the tip side to change from the dark state to the bright state 2.
A dark state write signal consisting of a negative direction pulse P5 modulated by (A in the same figure) and a positive direction pulse P6 whose tip side is modulated by a time width Tx from 1/2 at a peak voltage Iv+I, and a voltage 1v□ 4th mode signal consisting of a maintenance signal alternating with /Nl (B), ■H-') M, pressure b (I Vt I te, Iv+
/ 21, the pulse P7 in the negative direction is modulated by a time width Ty larger than the time τ2 required for the tip side to change from the dark state to the bright state (c), and the peak voltage is 1V.
1, the positive direction pulse P8 modulated by the time width TV
A bright state write signal consisting of a voltage (v t / Nl
A fifth mode signal (d) consisting of a sustain signal alternating with.

Also, when not selected ■Signal of the third mode mentioned above (E) It is configured to apply .

According to this embodiment, when the fourth mode signal is applied, the liquid crystal molecules of the selected pixel change to the dark state side with a concentration proportional to the voltage -v+ of this pulse P and the time width Tx (seventh mode signal).
figure). When the pulse P6 is applied in such a state, the peak voltage v is required to switch from the dark state to the bright state.
Since the time width Ty of 1 is shorter than 2 in the reversal time, the liquid crystal molecules cannot move to the dark state position, and the pulse P5
The density state written by is retained. A sustain signal applied after this write signal causes the liquid crystal molecules to dynamically maintain the display intensity about the selected position.

When the fifth mode signal is applied, the liquid crystal molecules are exposed to the pulse P7
Since the time width Ty of the inversion time is longer than 2, the state changes once to a dark state. However, the 72nd day pulse that is continuously applied has a time width Ty that is sufficient to move the liquid crystal molecules from the dark state to the bright state side, so the liquid crystal molecules do not respond to the pulse P.
It is moved from the dark state written by 7 to the bright state side, and the brightness proportional to the time width TV is written. As a result, a pattern with gradation can be written in one step at a very high speed of several hundreds of seconds.

Note that in this embodiment, gradation is given to the dark state and bright state, but the same effect can be achieved even if gradation is given only to one of them, for example, when writing in the dark state. That is clear.

In addition to the above-mentioned smectic liquid crystal having ferro-atductive properties, pyrimidine-based liquid crystal compounds represented by the general formula % and 2-methylbutyyl P-[(P-n-decyloxybenzylidene)
A chiral smectic liquid crystal compound such as amine] can be used.

In the above embodiment, a uniaxially oriented film layer and a random horizontally oriented film layer are formed using polyimide on the surface of the substrate, but in addition to polyimide, polyvinyl alcohol can be used as the material for forming the -axis oriented film. In addition to polyimide, materials for forming the random horizontal alignment film on the other substrate include epoxy, polyvinyl alcohol, fluororesin, polyurethane, silane, etc. Phenol.

It was confirmed that organic films such as urea and inorganic films formed by vapor-depositing 5t02, MgF2, etc. can be used.

(Effects) As described above, according to the present invention, an alternating signal having a time width between the first inversion time and the second inversion time of the liquid crystal compound is applied to a liquid crystal panel using a smectic liquid crystal compound, and Since the write signal is an alternating signal with a time width larger than the longer reversal time, writing of the bright state and dark state can be performed within one frame scanning period while taking advantage of memory retention and background uniformity. As a result, chiral smectic liquid crystal display devices such as display devices with high scanning speeds and optical shutters can be realized.

[Brief explanation of the drawing]

FIG. 1 is a perspective cross-sectional view of an apparatus showing one embodiment of the liquid crystal panel used in the present invention, FIG. The figure is an explanatory diagram showing the applied voltage and response speed in the same device as above, FIG. 4 is a block diagram of the device showing one embodiment of the present invention, and FIGS. The waveform diagrams in FIGS. 6(A) to 6(E) show the operation in
Waveform diagrams and FIG. 7 each showing other embodiments of the present invention are as follows:
An explanatory diagram showing the relationship between electric field application time and pixel concentration, Figure 8 is a schematic diagram showing the molecular arrangement of chiral smectic liquid crystal, and Figures 9 (a) and (b) respectively show cell gaps below the helical pitch of liquid crystal molecules. FIG. 10 is an explanatory diagram showing the relationship between domains of smectic liquid crystal and polarized light. 1... Substrate 1a... Electrically insulating transparent plate IC.
... Random horizontal alignment film layer 2 ... Substrate 2a ... Electrically insulating transparent plate 2C.
...-Axis alignment film layer

Claims (1)

[Claims] A substrate with uniaxial orientation on the surface and a substrate with random horizontal orientation on the surface are arranged in parallel with the orientation surfaces facing each other,
A smectic liquid crystal panel in which a ferroelectric chiral smectic liquid crystal compound is sealed in a space formed by two substrates, and a gap in the space is limited to a helical pitch or less of the liquid crystal compound; 1. A smectic liquid crystal device comprising circuit means for selectively outputting an alternating signal having a time width between a second inversion time and a second inversion time, and an alternating signal having a time width larger than the longer inversion time.