JPH07129134A - Driving method for liquid crystal display - Google Patents

Abstract

PURPOSE:To enable high speed switching having accurate bistable characteristics, and reduce an effective value voltage at driving time by changing the timing to add a scanning signal and a data signal, and arranging a dormant pulse period after the data signal is added in a driving method for a liquid crystal display. CONSTITUTION:Scanning signals added with every scanning electrode are composed of two pulses of a first half part and a latter half part, and codes of the first half part and the latter half part are inverse to each other, and the sum of an electric charge quantity stored in a liquid crystal cell by the scanning signal of the first half part and an electric charge quantity stored in the liquid crystal cell by the scanning signal of the latter half part is zero, and data signals added with every signal electrode are composed of two pulses of a first half part and a latter half part, and codes of the first half part and the latter half part are inverse to each other, and the sum of an electric charge quantity stored in the liquid crystal cell by the data signal of the first half part and an electric charge quantity stored in the liquid crystal cell by the data signal of the latter half part is zero, and the first half part of the data signal is impressed within a period of the latter half part of the scanning signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a liquid crystal display device using a liquid crystal electro-optical element used as a liquid crystal display element or a liquid crystal spatial modulation element, and more particularly to a liquid crystal display capable of bistable switching of a nematic liquid crystal. The present invention relates to a method for driving a device.

[0002]

2. Description of the Related Art Up to now, a display method using a liquid crystal includes a DS (dynamic scattering) method and a TN method which converts an electric signal applied to the liquid crystal into optical information.
(Twisted nematic) method, ECB (electrically contro
lled birefringence) system, PC (phase change) system, memory system, GH (guest-host) system, SSF (su)
rfacestabirized felo-electric) method is considered. Among them, the methods currently used as display elements in products such as watches, calculators, word processors, personal computers, and televisions are mainly TN methods using nematic liquid crystal and its improved STN (Super-twisted nematic) method. Is.

However, since its operating principle is a field effect type utilizing the dielectric anisotropy of liquid crystal molecules, the response speed is ms.
Only in the order of ec, the response speed is insufficient when used in combination with the current nematic liquid crystal for applications such as CAD terminals requiring a higher response speed. In addition, since the electro-optical effect is caused by switching between two states, that is, a twisted and homogeneous alignment state of liquid crystal molecules and a state in which the liquid crystal molecules are raised on the substrate surface, the viewing angle with respect to the twist direction of the liquid crystal molecules is Dependencies cannot be avoided in principle.

On the other hand, as a liquid crystal element having a high response speed, Clark (NAClark) and Lagabal (La
gerwall) proposed surface stabilized ferroelectric liquid crystal device (Surface Stabilized Felo-electric Liquid Cl
ystal Display, SSFLCD) (Appl.Phy.Lett., 36, 899
(1980); JP-A-56-107216; US Pat. No. 436692.
No.) The SSFLCD is an element that performs switching on a cone in which liquid crystal molecules can move by utilizing the electrical interaction between the polarities of the spontaneous polarization and the polarity of the electric field that the smectic liquid crystal has. And has the advantage of not being dependent on the viewing angle. On the other hand, since smectic liquid crystals have a layered structure, it is difficult to control the alignment, and it is difficult to recover the alignment once broken due to impact or the like.

In order to solve the above problems, Georges. Duran has proposed two types of bistable liquid crystal display devices using nematic liquid crystals. One is to use a chiral ion as a driving torque (International Publication No. WO 91/11747). Both right-handed and left-handed chiral ions are mixed in a liquid crystal, and a bias is created in the ion distribution by a voltage, and this is the driving torque. It is what In this system, liquid crystal molecules can be switched in parallel to the substrate surface by applying a pulsed electric field as in the SSFLCD. However, since this method uses ions as impurities for driving, an inherently large problem remains in terms of reliability.

The other one uses flexo-polarization as a driving torque. This uses a SiO obliquely evaporated film as an alignment film, and if the film conditions are properly selected, the nematic liquid crystal shows stable alignment in two directions. To use. In this method, flexo-polarization due to orientation distortion is used as a driving torque, so that problems such as impurities do not occur and high reliability is expected. Similar to SSFLCD, this method can switch the liquid crystal molecules in parallel to the substrate surface by applying a pulsed electric field, and the response speed is about 100 μsec. Since the liquid crystal molecules switch in parallel to the substrate surface, the viewing angle dependence. Nor. In addition, since nematic liquid crystal is used, S
Unlike the SFLCD, there is no problem of orientation control, and the operating temperature range can be made sufficiently wide.

Details of the nematic bistable display element are described in Georges. Reported by Duran (1991 SI
D Proceedings PP606〜607, Appl.Phys.Lett.60 (9), 2 Marc
h 1992 pp1085-1086), and its structure is as shown in FIG. In FIG. 9, 11 is a glass substrate, and 15
Is a liquid crystal layer, 12 is a transparent electrode, 14 is a SiO alignment film, 16
Is a spacer. The conditions for forming the SiO alignment film 14 are such that the vapor deposition angle is 74 ° from the substrate radiation, the film thickness is 30Å, and the diameter of the spacer 16 is about 1 to 3 μm.

Under these conditions, the alignment direction of the liquid crystal molecules is as shown in FIG. 10, and the alignment in the direction C perpendicular to the SiO vapor deposition direction and parallel to the substrate surface is stable. But,
Since the anchoring energy of the interface is weak, when a twisting power is applied by adding a chiral material to the liquid crystal, it tilts by θ ° from the substrate surface, and the direction projected on the substrate surface is α ° from the deposition direction of SiO. , And −α °
Orientations in tilted directions A and B appear. Here, the directions A, B, and C represent the long axes of liquid crystal molecules exhibiting bistability.

FIG. 11 schematically shows the relationship between the vapor deposition direction of the alignment film and the alignment direction of the liquid crystal molecules. 25 here
And 25 'indicate the upper and lower interfaces. The figure also shows SiO deposition directions 24 and 24 'and directions 21 to 23 and 21' to 23 'where liquid crystal molecule alignment can be stabilized. The alignment treatment direction of the upper and lower substrates is 45 ° from the anti-parallel directions of the SiO vapor deposition directions 24 and 24 'of the upper and lower substrates.
It is configured to have a twisted direction. As the liquid crystal material, a liquid crystal alone to which a chiral material is added so as to be twisted by 22.5 ° between the upper and lower substrates is used. In addition,
The twist direction of the liquid crystal is Si between the upper and lower substrates shown in FIG.
The direction is opposite to the twist of the O vapor deposition directions 24 and 24 '.

When the liquid crystal material is injected under such conditions, the orientation that can exist stably is limited by the effect of the chiral material, and the two combinations 21-23 'and 23-22' of the liquid crystal molecules are stable. Becomes

FIG. 12 is a diagram schematically showing the orientation of the liquid crystal in the cross section of the liquid crystal cell. Here, (a) is FIG.
1 shows a 21-23 'orientation in FIG.
(B) shows the state of 23-22 'orientation. A liquid crystal material in which Δε, which represents the difference between the component of the liquid crystal dielectric constant parallel to the substrate and the component perpendicular to the substrate, is Δε> 0 and the molecular shape is wedge-shaped (according to Duran's report, 5CB manufactured by Merck is used). When used, flexo polarization occurs due to the orientation strain of the spray. Arrows 26 and 26 'in the figure indicate the direction of flexopolarization, and in FIGS. 12A and 12B, the vertical components of flexopolarization point in opposite directions. Therefore, by applying a pulsed electric field to invert the vertical component of the Fukuleso polarization, it is possible to perform bistable switching between the two states of FIGS. 12 (a) and 12 (b).

FIG. 13 shows a waveform diagram of a drive signal in the liquid crystal device proposed by Duran. This is an example of a composite waveform applied to one pixel in the case of multiplex driving, in which a scanning signal and a data signal are sequentially applied.

First, the liquid crystal molecules can be separated from the alignment film interface by applying the period scanning signal shown by e in FIG. 13, and then the liquid crystal molecules are stabilized by applying the period data signal shown by f. The direction to do is determined. Also, the finally stable direction of the liquid crystal molecules is determined only by the polarity finally applied to the data signal, regardless of the polarity of the scanning signal. However, the data signal has a voltage value smaller than that of the scanning signal.

For example, when the data signal waveform of the polarity of g in FIG. 13A is applied, the stable direction of the liquid crystal molecules becomes the state of orientation as shown in FIG. 12A, and the data signal of the polarity of h. When a waveform is applied, the alignment state shown in FIG.

[0015]

However, based on the above theory, when the liquid crystal cell is actually driven in a multiplex manner by using the driving waveforms shown in FIG. 13, both the scanning signal and the data signal are biased in charge. In order to eliminate the above, a cancel pulse (a pulse that causes the sum of the charge amounts to be 0, which is opposite to the polarity of the pulse applied first) is applied, but even if the data signal is applied after the scan signal is applied, The stable direction of the liquid crystal molecules may not correspond to the last polarity applied to the data signal due to the effect of the polarity finally applied to the scanning signal and the effect of the pulse in the first half of the data signal.

Therefore, black and white display of bistable switching may not be performed properly. This is a fatal defect as a driving method of the bistable display element, and the driving method is not sufficiently satisfactory. Further, in the driving method proposed by Duran as shown in FIG. 13, when 5CB manufactured by Merck is used, when a drivable voltage value and pulse width are applied, the effective value exceeds the liquid crystal threshold value. However, there is a problem in that the liquid crystal molecules rise when not selected, a sufficient contrast cannot be obtained, and the display quality deteriorates. Furthermore, if a pause pulse period is not provided after applying the data signal, the data signal pulse is applied after the scan signal pulse, so that the pixel rewriting time is too short and a liquid crystal material having a slow optical response speed such as 5CB is used. When used, there were cases where accurate switching was not performed.

Further, when the liquid crystal cell is actually driven by using the drive waveform as shown in FIG. 13, the time t in FIG.
That is, there is a problem that the fluctuation of the liquid crystal molecules causes flickering of the picture element to deteriorate the contrast, and a problem that unnecessary voltage is applied and power consumption increases.

Therefore, the present invention has been made in consideration of the above circumstances, and by shifting the timing of applying the scanning signal and the data signal, and providing a pause pulse period after applying the data signal. An object of the present invention is to provide a driving method of a liquid crystal display device capable of performing high-speed switching with accurate bistability and lowering an effective value voltage during driving.

[0019]

The present invention provides a method for driving a liquid crystal display device having the following structure. That is, a pair of substrates arranged to face each other substantially in parallel, a plurality of scan electrodes and a plurality of signal electrodes formed in a matrix on the pair of substrates, and formed on the scan electrodes and the signal electrodes. A liquid crystal cell having alignment means and a liquid crystal interposed in a space sandwiched by the alignment means, and at least one polarizing plate disposed outside the liquid crystal cell. A method for driving a liquid crystal display device having bistability, which switches between two possible alignment states of liquid crystal by selectively applying a scanning signal and a data signal to the signal electrode and maintains the alignment state even when the electric field is cut off. In the above, the scanning signal sequentially scanned and applied to each of the scanning electrodes is composed of two pulses of the first half and the second half, and the scanning signal of the first half and the scanning signal of the second half. The sign of the signal is opposite, and the sum of the amount of charge stored in the liquid crystal cell by the scanning signal of the first half and the amount of charge stored in the liquid crystal cell by the scanning signal of the second half is zero, and each signal electrode The data signal sequentially scanned and added to is composed of two pulses of the first half and the second half, and the signs of the data signal of the first half and the data signal of the second half are opposite,
And the sum of the amount of charge stored in the liquid crystal cell by the data signal of the first half and the amount of charge stored in the liquid crystal cell by the data signal of the second half is zero, and the data within the period of the second half of the scanning signal. A method for driving a liquid crystal display device, wherein the first half of a signal is applied.

The scanning signal sequentially scanned and applied to each of the scanning electrodes is composed of two pulses of the first half and the second half, and the signs of the scanning signal of the first half and the scanning signal of the second half are opposite. And the sum of the amount of charge stored in the liquid crystal cell by the scan signal of the first half and the amount of charge stored in the liquid crystal cell by the scan signal of the second half is zero, and is sequentially scanned for each signal electrode and added. The data signal is composed of two pulses of the first half and the second half, the data signals of the first half and the data signal of the second half have opposite signs, and are stored in the liquid crystal cell by the data signal of the first half. A data signal having a waveform in which the sum of the amount of charge and the amount of charge stored in the liquid crystal cell according to the data signal of the latter half is zero and sequentially added to each of the signal electrodes. Data having a polarity different from that of the scanning signal of the latter half portion, the first half portion of the data signal is selectively applied during the latter half portion of the scanning signal, and the data is sequentially scanned and added for each signal electrode. The present invention provides a method for driving a liquid crystal display device, wherein a data signal is not applied when the signal has the same polarity as the sign of the scanning signal in the latter half portion.

Further, the present invention provides a method of driving a liquid crystal display device, wherein a pause pulse period is provided after adding the data signal in a composite waveform of the scanning signal and the data signal.

It is desirable that the alignment means is composed of an electrode protection film and an alignment film. Further, after the electrode protection film is formed on the scan electrodes and the signal electrodes, the alignment film is formed on the alignment film. It is desirable to perform oblique vapor deposition on top of. Further, it is preferable to use SiO ₂ for the electrode protection film, for example, OCD (OCD P-
59310) is preferably used, but any material may be used as long as it is an electrode protective film, and the material is not limited to this.

The alignment film is made of SiO, MgO, M.
gF₂, Au, CeO₂, CeF₃Al₂O₃, GaAs,
Ge, Si, LiNbO₃, BaTiO₃, Bi₂O
₃F₂, CdSe, CdS, In₂O₃, PbO, Pb
₂S₃, TiO, WO₃, ZnO, ZnS, ZnSe, A
1N, B_FourC, BN, Bi₂Te₃, CdTe, CrS
i₂, Cu ₂S, Fe₂O₃, Fe₃O_Four, HfO₂, In₂O
₃, LiTaO₃, MO-Si₂, NbN, Nb₂O₃, P
bS, PbTiO₃, SiC, Si₃N_Four, SnO₂, Ta
S₂, TiN, TiC, T₂O₃At least one of
It is preferable to use the above inorganic material. Also, for display elements
A nematic liquid crystal is used as the liquid crystal used.

[0024]

According to the first aspect of the present invention, the scanning signal sequentially scanned and applied for each scanning electrode and the data signal sequentially scanned and applied for each signal electrode are respectively composed of two pulses in the first half and the second half. The sign of the first half and the latter half is opposite, and the sum of the amount of charge stored by the signal of the first half and the amount of charge stored by the signal of the second half is zero, and the scanning signal Since the first half of the data signal is applied within the latter half of the period, a high-speed switching operation with accurate bistability can be performed. In addition, since the pause pulse period is provided after adding the data signal, the effective value voltage during driving can be lowered and the driving corresponding to the optical response speed of the liquid crystal material can be provided, and the operation with accurate bistable can be performed. .

Further, according to the second aspect of the present invention, the scanning signal applied by being sequentially scanned for each scanning electrode and the data signal applied by being sequentially scanned by each signal electrode are two pulses in the first half and the second half, respectively. And the signs of the first half and the second half are opposite, and the sum of the amount of charge stored in the liquid crystal cell by the signal of the first half and the amount of charge stored by the signal of the second half is zero. In the case of a waveform, when the data signal sequentially scanned and applied to each of the signal electrodes has a polarity different from that of the scanning signal of the latter half portion, the first half portion of the data signal is applied within the latter half period of the scanning signal. However, if the data signal sequentially scanned and applied to each of the signal electrodes has the same polarity as the sign of the scanning signal of the latter half portion, the data signal is not applied, so that the driving signal is applied. Pixel flickering is reduced decreases the number of waveforms can improve the contrast. Moreover, since the number of rectangular waveforms to be driven is reduced, the power consumption can be reduced.
Further, since the drive waveforms for switching from the bright state to the dark state or from the dark state to the bright state can be controlled independently, it becomes easy to find the optimum drive waveform in each of the bright state and the dark state.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the drawings. The present invention is not limited to this. FIG. 1 shows a sectional view of the structure of a liquid crystal cell in one embodiment of the present invention. Here, 1a and 1b are glass substrates, 2a and 2b are transparent electrodes serving as scanning electrodes or signal electrodes, 3a and 3b are electrode protective films, 4a and 4b.
Is an alignment film, 5 is a liquid crystal layer, and 6a and 6b are spacers.

First, the procedure for forming the bistable nematic liquid crystal cell as shown in FIG. 1 will be described. 1. 1000Å on each of the glass substrates 1a and 1b
The scanning electrodes and the signal electrodes are formed by arranging the electrode patterns in a stripe shape so that the plurality of transparent electrodes (2a, 2b) having a thickness of 2 are parallel to each other. The thickness of the transparent electrode is 30
It is set in the range of 0 to 5000Å, preferably 1000 to 3000Å (1000Å in this embodiment).

2. Next, the electrode protection films 3a and 3b are formed with a film thickness of 1000 Å on the substrate on which the transparent electrode is formed. The thickness of the electrode protective film is 100 to 5000Å, preferably 50.
Set in the range of 0 to 2000Å.

It is preferable to use SiO ₂ or OCD (OCDP-59310) manufactured by Tokyo Ohka Co., Ltd. for the electrode protection films 3a and 3b. The electrode protective film is formed by sputtering when SiO ₂ is used, and is formed by coating the substrate with a spinner and baking when OCD is used (1000 Å in this embodiment).

3. When SiO is used as the alignment film on the substrate formed as described in 2 above, SiO (4a, 4b)
Is obliquely evaporated. At this time, the deposition angle is 7 from the substrate radiation.
It is set in the range of 0 ° to 80 °, preferably 73 ° to 75 ° (74 ° in this embodiment). The film thickness of the alignment film is set in the range of 20 to 200Å, preferably 50 to 100Å (50Å in this embodiment).

4. The SiO vapor deposition directions of the upper and lower substrates are set such that the directions projected on the substrates are shifted by 45 ° from the parallel directions.

Silica beads having a diameter of 1.5 μm are dispersed as spacers 6a and 6b between the upper and lower substrates which have undergone the steps of 5.1 to 4 and are bonded by an epoxy resin sealing member. The diameter of the silica beads is set in the range of 1 to 3 μm, preferably 1.2 to 1.8 μm (about 1.2 to 1.5 μm in this example).

Nematic liquid crystal is injected into the panel substrate formed through the steps of 6.1 to 5 by a vacuum injection method. After the injection, the injection port is sealed with an acrylic UV curable resin. The angle of the projection vector of the panel substrate thus created is 135 °.

Next, a first embodiment of the driving method of the present invention will be described. FIG. 2 is a view of the liquid crystal display device as seen from above, showing a 3 × 3 pixel pattern. This is a liquid crystal cell formed by using the ZLI-3244 manufactured by Merck Co., Ltd. according to the above procedure so that it can be driven in multiplex.

Here, in contrast to the liquid crystal display device of FIG.
It is assumed that the scanning signals 1 to 3 shown in FIG. 3A and the data signals 1 to 3 shown in FIG. In FIG. 3, the vertical axis represents applied voltage (v) and the horizontal axis represents time (μsec). The scan signal 1 is applied to the scan line 1 in FIG. 2, the scan signal 2 is applied to the scan line 2, and the scan signal 3 is applied to the scan line 3. Similarly, the data signal 1 is applied to the data signal line 1 in FIG. 2, the data signal 2 is applied to the data signal line 2, and the data signal 3 is applied to the data signal line 3.

In addition, (c) and (d) of FIG.
When the scanning signal and the data signal of (a) and (b) are combined,
This is a signal waveform obtained by synthesizing rewriting pulses that are actually applied to pixels, and the synthesized signal is applied to each pixel. FIG. 4 (c) is a composite signal waveform that puts the pixel in a bright state, and FIG. 4 (d) is a composite signal waveform that puts the pixel in a dark state. In FIGS. 3 and 4, ZLI-324 manufactured by Merck & Co., Inc.
Numerical values that can be driven when 4 is used, V ₁ = 30v, W ₁ =
It is assumed that 500 μsec, V ₂ = 6 v, W ₂ = 50 μsec are used.

By applying this combined signal,
The liquid crystal molecules existing at the positions of the pixels shaded by the symbol behave exactly so as to exactly match the polarity of the pulse in the latter half of the data signal.

FIG. 7 shows a second embodiment of the driving method of the present invention. This is because the scanning signal and the data signal as shown in FIG. 7 are applied to one pixel of the liquid crystal display device manufactured by using the Merck 5CB according to the above procedure, and the pause pulse period is provided after the data signal is added. It is a thing. In the figure, numerical values that can be driven when using Merck 5CB,
V ₁ = 20v, W ₁ = 500 μsec, V ₂ = 14v, W ₂
= 50 μsec, W ₃ = 28 msec. Here, the pause pulse period is represented by W ₃ .

As described above, first, the composite waveform pulse of the scanning signal and the data signal represented by "C" is applied, and then "D".
When the operation of applying the pulse represented by the above formula 999 times was input as one cycle, the liquid crystal display device maintained white display even after repeating 1000 cycles or more.

Considering the case of driving with a 1 / n duty by _inputting a pause pulse W ₃ , the effective value voltage V _eff1 of the driving waveform in FIG. 7 is V _eff1 = 2 {V ₁ W ₁ + (n- 1) V ₂ W ₂ } / (2nW ₁ + nW ₂ + nW ₃ ), and at a 1/1000 duty, V _eff1 ≈
It becomes 0.048v. Here, n = 1000.

Therefore, the liquid crystal material 5 used here is used.
Since the threshold voltage of CB is about 0.5v, even if the effective value voltage increases during driving, the liquid crystal molecules do not rise in the non-selected pixels, and the deterioration of display quality can be prevented. .

Next, a third embodiment of the driving method of the present invention will be described. In the above-described first embodiment, since the phases of the second half of the scanning signal and the first half of the data signal are matched, the magnitude of the excitation pulse changes, which may cause uneven brightness and darkness. When the length of the signal waveform (W ₂ ) and the value of the voltage (V ₂ ) are changed in order to eliminate this display unevenness, as shown in (c) and (d) of FIG. The size of the excitation pulse changes. Therefore, there is a problem that it is difficult to find the optimum drive waveform in each of the bright state and the dark state. The third embodiment described below solves this problem.

FIG. 2 is a view of the liquid crystal display device as seen from above, showing a 3 × 3 pixel pattern. This is formed so that the liquid crystal cell produced by the above procedure can be driven in multiplex. Here, FIG.
Scanning signal 1 shown in FIG. 15A for the liquid crystal display device of FIG.
˜3 and the data signals 1 to 3 shown in FIG. 15B are input. In FIG. 15, the vertical axis represents the applied voltage (v)
The horizontal axis represents time (μsec).

The scanning signal 1 is the scanning line 1 in FIG. 2, the scanning signal 2 is the scanning line 2 in FIG. 2, and the scanning signal 3 is the scanning line 3 in FIG.
Is applied to each. In addition, (c) and (d) of FIG.
Is a composite waveform of the rewriting pulse that is actually applied to the pixel when the scanning signal and the data signal of FIGS. 15A and 15B are composited, and the composite signal is applied to each pixel.

14 and 15, Z manufactured by Merck & Co., Inc.
Numerical value that can be driven when LI-3244 is used, V ₁ =
30 v, W ₁ = 500 μsec, V ₂ = 6 v, W ₂ = 50
μsec is used. As a result, by applying the rewriting combined signal of FIG. 14C, one pixel in the bright state of FIG. 2 can be brought into the dark state.
By applying the rewriting composite signal of FIG.
One pixel in the dark state can be set to the bright state.

When driven as above, the contrast was 20 when used as a transmissive display and 6 when used as a reflective display. Further, when the voltage value V ₂ of the data signal of FIG. 14D is increased, there is no influence on the switching by the rewriting pulse of (c), and the display quality can be optimized only by the rewriting pulse of (d). It was peeled off.

Next, FIGS. 5 and 6 show a first comparative example in the case where a composite signal is applied by the method proposed by Duran in the related art. Here, as the liquid crystal comparative device, the device prepared in the first embodiment is used, and the matrix-shaped pixels are displayed as in the case of FIG.

FIG. 5A shows scanning signals 1 to 3, and FIG. 5B shows data signals 1 to 3. In addition, (c) and (d) of FIG. 6 are combined waveforms of the rewriting pulse actually applied to the pixel when the scanning signal and the data signal of (a) and (b) of FIG. 5 are combined, This composite signal is applied to each pixel.

5 and 6, as in the third embodiment, V ₁ = 30v, W ₁ = 500 μsec, V ₂ = 6v,
W ₂ = 50 μsec is used. This allows
By applying the rewriting composite signal in FIG. 6C, one pixel in the bright state in FIG. 2 can be set in the dark state,
By applying the combined signal shown in FIG. 6D, one pixel in the dark state shown in FIG. 2 can be brought into the bright state.

As a result of driving with the above waveform, when used as a transmissive display, the contrast is 12,
When used as a reflective display, the contrast is 3
The contrast was about 40% worse than that of the cell of Example 3. Further, in order to measure the difference in power consumption, the same pixel was alternately driven at 0.5 second intervals for black and white display for one hour in the above drive pattern and the drive pattern used in the third embodiment. Power consumption in the example drive pattern: Power consumption in the above drive pattern ≈ 1:
The driving pattern of the third embodiment is about 1.13.
Power consumption can be reduced by about 1%.

Further, when the voltage value V ₂ of the data signal is increased in (d) of FIG. 6, the influence on the switching by both rewriting pulses of (c) and (d) is seen, and both bright and dark are observed. There was a decrease in display quality due to the occurrence of domains.

Next, FIG. 8 shows a second comparative example in the case where the pause pulse period is not provided in the composite waveform diagram 7 shown in the second embodiment. Here, V ₁ = 30v, W ₁ = 500 μsec,
V ₂ = 6v and W ₂ = 50 μsec. As shown in the figure, when the operation of applying the pulse shown in "B" 999 times after inputting the pulse shown in "A" is input as one cycle, when white cycle is repeated for about 10 cycles, It gradually became dark and became unstable. Here, in the waveform of FIG. 8, when the effective value V _{ef f2} in the case of driving with 1 / n duty is _calculated , V _eff2 = 2 (V ₁ W ₁ + nV ₂ W ₂ } / (2nW ₁ + nW ₂ ) When driving at 1/1000 duty, V
_eff2 ≈0.6v.

However, the operation became unstable because the threshold voltage of 5CB was about 0.5v. This is because the liquid crystal molecules rise during non-selection as the effective value increases during driving, failing to provide sufficient contrast, and lowering the display quality. Further, since 5CB has a slow optical response speed, in FIG. 8, there is no pause pulse period after the data signal is applied, and the data signal pulse is applied following the scan signal pulse, so that the pixel rewriting time is short and accurate. It is also due to not switching.

As described above in the three examples and the two comparative examples, by shifting the application timings of the two signals so that the first half of the data signal is applied within the latter half of the scanning signal, High-speed switching operation with accurate bistability is possible.

Further, by providing the pause pulse period after applying the data signal, the effective value voltage at the time of driving can be lowered, the deterioration of display quality can be prevented, and the optical response speed by the liquid crystal material can be reduced. Corresponding drive can be provided and accurate bistable operation is possible.
It is also possible to increase the driving speed by limiting the number of lines of signals applied to the data signal lines and driving by using the partial rewriting method.

Further, when the data signal sequentially scanned and applied to each signal electrode has a polarity different from that of the latter half of the scanning signal, the first half of the data signal is applied within the latter half period of the scanning signal to obtain the signal. When the data signal sequentially scanned and applied for each electrode has the same polarity as the sign of the scanning signal in the second half,
Since the data signal is not applied, the number of rectangular waveforms to be driven is reduced and unnecessary voltage is not applied, so that power consumption can be saved. In addition, flicker of picture elements is reduced, and high-speed switching operation with accurate bistability can be performed. Further, since the drive waveforms for switching light → dark and dark → bright can be controlled independently, it becomes easy to find the optimum drive waveforms in each of the bright state and the dark state.

[0057]

According to the present invention, in the driving method of the liquid crystal display device, the scanning signal and the data signal are applied so that the first half of the data signal is applied within the second half of the scanning signal. , High speed switching with accurate bistability. Further, since the pause pulse period is provided after adding the data signal, the effective value voltage at the time of driving can be lowered, and the driving can be performed corresponding to the optical response speed of the liquid crystal material.

Further, according to the invention of claim 2, when the data signal sequentially scanned and applied for each signal electrode has the same polarity as the sign of the latter half of the scanning signal, the data signal applied subsequently to the scanning signal is Since the voltage is not applied, the number of rectangular waveforms to be driven is reduced and unnecessary voltage is not applied, so that power consumption can be saved. In addition, flicker of picture elements is reduced, and high-speed switching operation with accurate bistability can be performed. Further, since the drive waveform of the bistable switching can be controlled independently, it becomes easy to find the optimum drive waveform in each of the bright state and the dark state.

[Brief description of drawings]

FIG. 1 is a sectional view of a liquid crystal display device of the present invention.

FIG. 2 is a schematic view showing a matrix shape of the liquid crystal display device of the present invention.

FIG. 3 is a waveform diagram of drive signals according to the first embodiment of the present invention.

FIG. 4 is a composite waveform diagram of drive signals according to the first embodiment of the present invention.

FIG. 5 is a waveform diagram of drive signals of a first comparative example of the present invention.

FIG. 6 is a composite waveform diagram of drive signals of a first comparative example of the present invention.

FIG. 7 is a waveform diagram of drive signals according to the second embodiment of the present invention.

FIG. 8 is a waveform diagram of drive signals of a second comparative example of the present invention.

FIG. 9 is a cross-sectional view of a liquid crystal display device in a conventional example.

FIG. 10 is an explanatory diagram showing the stability of alignment of liquid crystal molecules.

FIG. 11 is a schematic diagram showing the relationship between the vapor deposition direction of an alignment film and the alignment direction of liquid crystal molecules in a conventional example.

FIG. 12 is a schematic view showing alignment of liquid crystals in a cross section of a liquid crystal cell in a conventional example.

FIG. 13 is a waveform diagram of a drive signal applied to a liquid crystal display element in a conventional example.

FIG. 14 is a waveform diagram of a rewriting pulse of a drive signal according to the third embodiment of the present invention.

FIG. 15 is a waveform diagram of a drive signal according to the third embodiment of the present invention.

[Explanation of symbols]

 1a, 1b Glass substrate 2a, 2b Transparent electrode 3a, 3b Electrode protective film 4a, 4b Alignment film 5 Liquid crystal layer 6a, 6b Spacer

Claims (7)

[Claims] 1. A pair of substrates arranged substantially parallel to each other, a plurality of scan electrodes and a plurality of signal electrodes formed in a matrix on the pair of substrates, and a pair of scan electrodes and a plurality of signal electrodes. A liquid crystal cell having an aligning means formed in, a liquid crystal interposed in a space sandwiched by the aligning means, and at least one polarizing plate disposed outside the liquid crystal cell, By selectively applying a scanning signal and a data signal to the scanning electrode and the signal electrode, respectively, two alignment states that the liquid crystal can take are switched, and the liquid crystal display device has a bistable state in which the alignment state is maintained even when the electric field is cut off. In the driving method, the scan signal sequentially scanned and applied to each of the scan electrodes is composed of two pulses of a first half and a second half, and the scan signal of the first half and the second half The sign of the scan signal is opposite, and the sum of the charge amount stored in the liquid crystal cell by the scan signal of the first half and the charge amount stored in the liquid crystal cell by the scan signal of the second half is zero, and the signal A data signal sequentially scanned and applied to each electrode is composed of two pulses of a first half and a second half, and the signs of the data signal of the first half and the data signal of the second half are opposite and the data signal of the first half is The sum of the amount of charge stored in the liquid crystal cell by the data signal and the amount of charge stored in the liquid crystal cell by the data signal of the latter half is zero, and the first half of the data signal is within the period of the latter half of the scanning signal. A method for driving a liquid crystal display device characterized by being applied. 2. A pair of substrates arranged to face each other substantially in parallel, a plurality of scan electrodes and a plurality of signal electrodes formed in a matrix on the pair of substrates, and above the scan electrodes and the signal electrodes. A liquid crystal cell having an aligning means formed in, a liquid crystal interposed in a space sandwiched by the aligning means, and at least one polarizing plate disposed outside the liquid crystal cell, By selectively applying a scanning signal and a data signal to the scanning electrode and the signal electrode, respectively, two alignment states that the liquid crystal can take are switched, and the liquid crystal display device has a bistable state that maintains the alignment state even when the electric field is cut off. In the driving method, the scan signal sequentially scanned and applied to each of the scan electrodes is composed of two pulses of a first half and a second half, and the scan signal of the first half and the second half The sign of the scanning signal is opposite, and the sum of the charge amount stored in the liquid crystal cell by the scanning signal of the first half and the charge amount stored in the liquid crystal cell by the scanning signal of the second half is zero, and the signal A data signal sequentially scanned and applied to each electrode is composed of two pulses of a first half and a second half, and the signs of the data signal of the first half and the data signal of the second half are opposite and the data signal of the first half is The sum of the amount of charge stored in the liquid crystal cell by the data signal and the amount of charge stored in the liquid crystal cell by the data signal of the latter half is zero, and the data signal sequentially scanned and added for each signal electrode is If the sign of the scanning signal of the latter half is different from that of the scanning signal of the latter half, the former half of the data signal is selectively applied within the latter half of the scanning signal, and the signal electrodes are sequentially scanned. A method of driving a liquid crystal display device, wherein the data signal is not applied when the added data signal has the same polarity as the sign of the scanning signal of the latter half portion. 3. The method of driving a liquid crystal display device according to claim 1, wherein a pause pulse period is provided after the data signal is added to a composite waveform of the scan signal and the data signal. 4. The alignment means comprises an electrode protective film and an alignment film, the electrode protective film is formed on the scanning electrodes and the signal electrodes, and then the alignment film is formed on the electrode protective film. The method for driving a liquid crystal display device according to claim 1, wherein the liquid crystal display device is obliquely vapor-deposited. 5. The driving of a liquid crystal display device according to claim 4, wherein the electrode protection film is made of a metal oxide for vacuum deposition or a compound material for vacuum deposition, and the alignment film is made of a vacuum deposition material capable of oblique deposition. Method. 6. The method of driving a liquid crystal display device according to claim 1, wherein the liquid crystal is a nematic liquid crystal. 7. The liquid crystal according to claim 1, wherein two possible alignment states of the liquid crystal are formed so that a molecular long axis of the liquid crystal is substantially parallel to the substrate. Driving method of display device.