JP2721489B2 - Display device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a storage type display panel, and more particularly to a display device having a ferroelectric liquid crystal display panel. 2. Description of the Related Art The use of bistable liquid crystal devices has been addressed by Clark and Lagerwell.
11) (JP-A-56-10721).
No. 6, US Pat. No. 4,367,924, etc.). As the liquid crystal having bistability, a ferroelectric liquid crystal having a chiral smectic C phase (SmC *) or an H phase (SmH *) is generally used. This liquid crystal is
A bistable state consisting of an optically stable state (first alignment state) and a second optically stable state (second alignment state),
Therefore, unlike the optical modulation element used in the above-mentioned TN type liquid crystal, for example, the liquid crystal is oriented in the first optically stable state with respect to one electric field vector, and the second liquid crystal is aligned with the other electric field vector. The liquid crystal is aligned in an optically stable state. In addition, this type of liquid crystal has a property of rapidly taking one of the above two stable states in response to an applied electric field and maintaining the state when no electric field is applied.
By utilizing such properties, a substantial improvement can be obtained for many of the problems of the TN type device described above. [0003] In a display device using a TN-type element, the TN-type element itself does not have a memorizing property, so that the display content is not stored on a display panel. Although no special display content erasing means was required for holding, in the above-described display panel using a bistable ferroelectric liquid crystal, the display content was stored in the display panel, so the display was particularly performed by backlight illumination. In the case of a transmissive display device for identifying the contents, the stored display contents cannot be identified when the backlight is turned off, but when the backlight is turned on, the previously written display contents appear. Had a security problem. In addition, in the case of a storage type liquid crystal, if it is placed in one alignment state for a long time, the state becomes more stable than the other alignment state, and the bistability may be deteriorated. An object of the present invention is to provide a display device which solves the above-mentioned problem. That is, the present invention provides a display panel having liquid crystal, a plurality of scanning lines and a plurality of information lines disposed between a pair of substrates, and a display panel comprising the same. A driving circuit for driving, and a controller for controlling the driving circuit, wherein when the switch for terminating the display is turned off, the driving circuit erases the display contents. In a display device for supplying a signal to the display panel, the liquid crystal is a chiral smectic liquid crystal in a uniform alignment state, and the signal is simultaneously transmitted to all of the plurality of information lines in order to align the liquid crystal in one alignment state. Is applied to the display device. According to the present invention, by using a chiral smectic liquid crystal in a uniform alignment state, it is possible to display a bright, high-contrast image with no fluctuation in the amount of transmitted light. In addition, the chiral smectic liquid crystal can be stored in the uniform orientation state over the entire screen in order to align the display screen to one orientation state all at once before entering the non-use state for a long time, so when resuming use, Bistability degradation, alignment defects,
It can prevent image sticking, and can display images with the same high brightness and contrast as before, without fluctuation in the amount of transmitted light, and can maintain confidentiality. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 (SmC *) and chiral smectic G phase (SmG
*), A chiral smectic F phase (SmF *), a chiral smectic I phase (SmI *), or a chiral smectic H phase (SmH *). For details of the ferroelectric liquid crystal, refer to “Le Journal de Physique Le Terre” (“LE JOURNA
L DE PHYSIQUE LETTERS ") 19
1975, No. 36 (L-69), "Ferroelectric Liquid Crystals"("Ferroel
electric Liquid Crystals ");
“Applied Physics Letters” (“Appl
ied PhysicsLetters ") 1980
Year, 36 (11), “Submicro Second Second Edition”
Bistable Electroobtic Switching in Liquid Crystals "(Submicr
o Second Bistable Electro
optic Switching in Liquid
Crystals ");" Solid State Physics ", 1981, 1
No. 6 (141), "Liquid crystal" etc.
In the present invention, these disclosed ferroelectric liquid crystals can be used. Specific examples of the ferroelectric liquid crystal compound include desyloxybenzylidene-p'-amino-2-methylbutylcinnamate (DOBAMBC) and hexyloxybenzylidene-p'-amino-2-chloropropylcinnamate (HOBACPC). ), 4-o- (2-methyl)-
Butylresorsilidene-4'-octylaniline (MB
RA8). In particular, as a preferable ferroelectric liquid crystal, a liquid crystal exhibiting a cholesteric phase on a higher temperature side can be used. For example, a biphenyl ester-based liquid crystal exhibiting a phase transition temperature described in the following examples can be used. When an element is formed using these materials, the element should be supported by a copper block or the like in which a heater is embedded, if necessary, in order to maintain the liquid crystal compound in a desired phase. Can be. FIG. 3 schematically illustrates an example of a cell for explaining the operation of the ferroelectric liquid crystal. Hereinafter, a description will be given using SmC * as an example of the desired phase. Reference numerals 31 and 31 'denote substrates (glass plates) covered with a transparent electrode made of a thin film such as In ₂ O ₃ , SnO ₂ or ITO (Indium-Tin Oxide), between which a liquid crystal molecule layer 32 is formed of glass. A liquid crystal of SmC * phase, which is oriented so as to be perpendicular to the plane, is sealed. A thick line 33 represents a liquid crystal molecule.
Numeral 3 continuously forms a spiral structure in the plane direction of the substrate. The angle between the central axis 35 of the helical structure and the axial direction of the liquid crystal molecules 33 is represented as H. This liquid crystal molecule 33
Is the dipole moment (P
⊥) 34. When a voltage equal to or higher than a certain threshold is applied between the electrodes on the substrates 31 and 31 ', the helical structure of the liquid crystal molecules 33 is released, and the liquid crystal molecules 33 are oriented so that all dipole moments (P⊥) 34 are directed in the direction of the electric field. You can change direction. The liquid crystal molecules 33 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 crossed Nicol polarizers are placed above and below the glass surface, a liquid crystal optical element whose optical characteristics change depending on the voltage application polarity will be obtained. The thickness of the liquid crystal cell preferably used in the liquid crystal optical element of the present invention can be made sufficiently small (for example, 10 μm or less). As shown in FIG. 4, as the liquid crystal layer becomes thinner, the helical structure of the liquid crystal element is unwound and becomes non-helical even when no electric field is applied, and the dipole moment P or P ′ of the liquid crystal element increases upward. Or, it takes either the downward direction 44 '. An angle which is 1/2 of the angle formed between the molecular axis of the liquid crystal molecules 43 and 43 'is referred to as a tilt angle H, and this tilt angle H is equal to 1/2 of the apex angle of the cone in a helical structure. When an electric field E or E 'having a different polarity or more than a certain threshold is applied to such a cell by the voltage applying means 41 and 41' as shown in FIG.
The dipole moment changes direction upwards 44 or downwards 44 ′ in response to the electric field vector of the electric field E or E ′, and accordingly, the liquid crystal molecules are in the first stable state 43 or the second stable state 43 ′. Orientation. As described above, there are two advantages of using such ferroelectricity as a liquid crystal optical element. The first is that the response speed is extremely fast, and the second is that the orientation of the liquid crystal molecules has bistability. The second point is
For example, referring to FIG. 4, when the electric field E is applied, the liquid crystal molecules are oriented to the first stable state 43. This state is stable even when the electric field is turned off. Also, the electric field E 'in the opposite direction
When liquid crystal molecules are applied, the liquid crystal molecules are oriented to the second stable state 43 'and change the direction of the molecules, but remain in this state even after the electric field is cut off. In order to effectively realize such a high response speed and bistability, it is preferable that the cell is as thin as possible. However, if bistability is lost, the direction of molecules may not be changed even when an electric field is applied. FIG. 1 is a circuit diagram of a display device according to the present invention. In FIG. 1, 11 is a storage type display panel, particularly a ferroelectric liquid crystal panel, 12 is a scanning line driving circuit, 13 is an information line driving circuit, and 14 is a controller. In the display device shown in FIG. 1, when the operator switches the main switch to the off state in order to end the display state, a display content erasing signal is generated and the signal is output to the controller 14. . At this time, the scanning line driving circuit 12 is controlled by a controller signal from the controller 14.
And the information line drive circuit 13 are enabled.
In this state, the controller 14 generates an erase signal to the scanning line drive circuit 12 and erase data to the information line drive circuit 13. The signal output from the scanning line drive circuit 12 when erasing the display contents can be the same scanning signal as the scanning signal used at the time of writing, and the information lines are simultaneously ferroelectrically synchronized with the output signal. A signal for aligning the crystalline liquid crystal in one stable state (white) can be applied. Thereby, it is possible to prevent occurrence of an afterimage of the final display image due to deterioration of the bistability. FIG. 5 shows signals V output from the scanning line driving circuit 12 and the information line driving circuit 13, respectively.
S _1, and VS ₁ ... and the VI _1, VI ₂ ... represents a. Further, in the present invention, in addition to the output signal described above, for example, 2Vo pulses are simultaneously applied to the scanning line, and synchronized with this, the information line is applied to the information line.
A method of applying a Vo pulse can also be used. Next, after erasing the display contents, an end signal is sent from the scanning line drive circuit 12 to the controller 14, and a power supply voltage cutoff signal is transmitted from the controller 14 to the power supply controller circuit 15, where the power supply voltage is cut off. In the present invention, when the display content is identified by the illumination of the backlight 16 provided behind the display panel 11, the display content erasing signal is transmitted to the controller 14 by the controller 14.
And the controller 14 controls the backlight 1
6 can be turned off. When a display is performed by the above-described display device, for example, video RAM address data is transmitted to the controller 14. At this time, the scanning line drive circuit 12 and the information line drive circuit 13 are enabled by a control signal from the controller 14. The controller 14 decodes the video RAM address data and transmits the scanning line address signal and the display data to the scanning line driving circuit 12 and the information line driving circuit 13, respectively, to perform the display. FIG. 2 is a circuit diagram of another display device of the present invention. FIG. 2 is a reference example. Next, after the erasure of the display contents is completed, an end signal is transmitted from the scanning line driving circuit 12 to the controller 14, and the scanning line driving circuit 12 and the information line driving circuit 13 are controlled to drive for display. The display is performed. In the display device shown in FIG. 2, when the display contents are identified by the illumination of the backlight 16 provided behind the display panel 11, the lighting of the backlight 16 is controlled by the controller receiving the end signal. 14. In the present invention, the voltages for erasing the display contents written on the display panel 11 are output to the information lines and the scanning signals VS ₁ , VS ₁ ... Output to the scanning lines as shown in FIG. Are the voltages of the erase signals VI ₁ , VI ₂ ..., And an AC voltage is preferably used as the voltage at this time. In the present invention, the above-mentioned AC voltage can be used as an AC voltage for forming a uniform alignment state of the ferroelectric liquid crystal element shown in FIG. In the ferroelectric liquid crystal device described above, the liquid crystal molecules are arranged in parallel in the liquid crystal molecule layer (uniform alignment state) as shown in FIG. A state where the liquid crystal molecules are twisted from the upper substrate toward the lower substrate (twist alignment state) is easily realized. When the liquid crystal molecules are twisted in this way, the angle (tilt angle) formed by the liquid crystal molecule axes in the first alignment state and the second alignment state becomes apparently small, and the contrast and the amount of transmitted light are reduced. In addition, various over disadvantages such as fluctuations in the amount of transmitted light due to flicker on the display screen are observed due to the appearance of overshoot in the response of the liquid crystal molecules at the time of switching the alignment state. I have. Therefore, as a display element, it is desired that the liquid crystal molecules are in a uniform alignment state. FIG. 7 shows an arrangement of directors or C directors 71 and corresponding spontaneous polarizations 72 when the helix structure is released and the liquid crystal cell is cut in the plane of the smectic layer of the bistable state. The top circle (corresponding to the projection of the liquid crystal cone onto the smectic layer surface) shows the situation near the upper substrate, and the bottom circle shows the situation near the lower substrate. In FIG. 3A, the direction of the average spontaneous polarization 73b is downward, and the average spontaneous polarization 73a of b is downward. Therefore, switching occurs between a and b by the electric field. FIG. 6 shows an arrangement of C directors in a case where there is no twist structure in the thickness direction of the liquid crystal cell, that is, in an ideal case. For generalization, the figure shows a case where the liquid crystal molecules are slightly tilted with respect to the substrate surface. The directions of the spontaneous polarization are a, upward b, and downward. This figure 6
In the uniform orientation state shown in FIG. 7, an AC voltage, for example, a threshold voltage or more (10 to 500 V) and a frequency of 0.1 Hz or more, preferably 10 Hz to 5 kHz, is applied to the ferroelectric liquid crystal in the twisted state shown in FIG. This can be easily realized. According to the present invention, the uniform alignment state of the ferroelectric liquid crystal element described above can be easily realized by an AC voltage applied to the display panel when erasing display contents. Therefore, in this case, the display content erasing method voltage is preferably an AC voltage having a voltage of 10 V to 500 V and a frequency of 0.1 Hz or more. According to the present invention, at the start of the operation of the display device, the previously written display contents are erased, and furthermore, the display contents which are bistable with respect to the ferroelectric liquid crystal element are displayed. A uniform orientation state can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a control system block diagram of a display device according to an embodiment of the present invention. FIG. 2 is a control system block diagram of a display device according to another embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a liquid crystal cell used in the present invention. FIG. 4 is a schematic diagram for explaining a liquid crystal cell used in the present invention. FIG. 5 is a diagram showing a display content erasing signal used in the present invention. FIG. 6 is a diagram for explaining characteristics of a liquid crystal used in the present invention. FIG. 7 is a diagram for explaining characteristics of a liquid crystal.

Claims (1)

(57) [Claims] A display panel having liquid crystal and a plurality of scanning lines and a plurality of information lines disposed between a pair of substrates; a driving circuit for driving the display panel; and a controller for controlling the driving circuit. A driving circuit for supplying a signal for erasing display contents to the display panel when the switch for ending the display is switched to an off state, wherein the liquid crystal is a chiral liquid in a uniform alignment state. A display device, wherein the display device is a smectic liquid crystal, and the signal is applied to all of the plurality of information lines at once to align the liquid crystal in one alignment state. 2. A signal applied to all of the plurality of information lines at the same time is:
2. The display device according to claim 1, wherein the display device is a unipolar voltage signal having a pulse width longer than a pulse width of a scan selection signal sequentially applied to the plurality of scan lines. 3. The controller transmits a power supply voltage cutoff signal to the power supply controller circuit after the display content is erased, and transmits a signal for turning off a backlight provided behind the display panel to the backlight. The display device according to claim 1, wherein: 4. A signal applied to all of the plurality of information lines at the same time is:
A unipolar voltage signal having a pulse width longer than a pulse width of a scan selection signal sequentially applied to the plurality of scan lines, wherein the controller supplies a power supply voltage cutoff signal after erasing the display content. The display device according to claim 1, wherein a signal transmitted to a controller circuit to turn off a backlight provided behind the display panel is transmitted to the backlight.