JPH0438329B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gradation display device such as a liquid crystal television using ferroelectric liquid crystal.

[Conventional technology]

In LCD television panels that use the conventional active matrix drive method, thin film transistors (TFTs) are arranged in a matrix for each pixel, and a gate-on pulse is applied to the TFTs to bring the source and drain into conduction. is applied from the source and stored in the capacitor, and the liquid crystal (e.g. twisted nematic - TN liquid crystal) is driven in response to this stored image signal.At the same time, gradation is displayed by modulating the voltage of the video signal. is being carried out.

However, in active matrix drive type television panels using such TN liquid crystals,
Because the TFT used has a complex structure,
In addition to the large number of structural steps and high manufacturing costs, the thin film semiconductors that make up TFTs (e.g. polysilicon, amorphous silicon)
There are problems in that it is difficult to form a film over a wide area.

On the other hand, as something that can be manufactured at low manufacturing cost,
A passive matrix drive type display panel using TN liquid crystal is known, but in this display panel, as the number of scanning lines (N) increases, one screen (1
The time during which an effective electric field is applied to one selected point (duty ratio) decreases at a rate of 1/N while scanning a selected point (frame), which causes crosstalk and does not result in a high-contrast image. In addition, when the duty ratio becomes low, it becomes difficult to control the gradation of each pixel by voltage modulation, making it unsuitable for display panels with high-density wiring, especially LCD television panels. .

In order to solve these fundamental problems of conventional TN liquid crystals, a ferroelectric liquid crystal element having bistability has been proposed, such as in US Pat. No. 4,367,924 by Clark and Lagerwall et al.

[Problem that the invention seeks to solve]

However, the above-mentioned bistable ferroelectric liquid crystal element basically has only two optically stable states, and it is difficult to display gradations using this liquid crystal element. A strange problem arose.

[Actions and means for solving problems]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks, and more specifically, to provide a display device for displaying gradations in a display panel, particularly a liquid crystal television panel, having high density pixels over a wide area. .

The present invention has the following features: a. A matrix electrode composed of scanning lines and data lines intersecting at intervals, an insulating film provided on the scanning lines or data lines, and an insulating film disposed between the scanning lines and the data lines, It has a ferroelectric liquid crystal that produces either one orientation state or the other orientation state depending on the polarity of the voltage, and has a volume resistivity of 1×10 ⁹ Ω・cm or more, and has scanning lines and data lines. a display panel in which pixels are formed at intersections with b) scanning the scanning lines sequentially and applying a scanning selection signal having one polarity pulse and the other polarity pulse to the selected scanning line; during a scan selection period, and in synchronization with the one-polarity pulse during the scan selection period, causing pixels on the selected scan line to have one orientation state or the other orientation state; After applying the voltage, in synchronization with the other polarity pulse during the scan selection period, the one polarity pulse is applied to the pixels on the scan line selected for the scan, and has the opposite polarity to the first voltage. a first means for applying a second voltage that maintains the orientation state during the pulse period; and the other orientation state, and determining the number of selections of one orientation state and the other orientation state in a plurality of field scans according to the gradation data. (The polarities of the voltages applied to the scan lines and data lines in this specification are based on the voltages applied to the scan lines that are not selected for scanning.) More specifically, the driving method used in the present invention is to apply a scanning signal to the scanning line, apply a binary video image signal having a bright signal and a dark signal to the data line in synchronization with the scanning signal, and apply the binary video image signal having a bright signal and a dark signal to the data line. When displaying a video image by setting selected pixels from a matrix pixel group formed by lines and data into either a bright state or a dark state, one screen of the video image is formed. The period is divided into a plurality of fields, and for each field period, a signal is sent to set a pixel selected according to the gradation of one screen of the matrix image group to either a bright state or a dark state. Gradation display can be performed by applying voltage to the data line.

〔Example〕

The present invention will be explained below with reference to the drawings.

The optical modulating substance used in the driving method of the present invention is capable of forming a first optically stable state (for example, a bright state) and a second optically stable state depending on the applied electric field.
A material is used that has an optically stable state (for example, a dark state), that is, has a bistable state with respect to an electric field, and in particular, a liquid crystal having such a property.

As a liquid crystal having bistability that can be used in the driving method of the present invention, a chiral smectic liquid crystal having ferroelectricity is most preferable, and among them, chiral smectic C phase (SmC*) and H phase (SmH* ), I phase (SmI*), F phase (SmF*) and G
SmG* liquid crystal is suitable. This ferroelectric liquid crystal is described in “LE JOURNAL DE PHYSIQVE”.
LETTRE”) 36, 1975 “Fero Electric
"Liquid Crystals" (Ferroelectric)
“Liquid Crystals”); “Applied Physics Letters”
(“Applied Physics Letters”) 36 (11) 1980 “Submicro Second Bistable Electroobtaining Switching in Liquid Crystals”; “Solid State Physics” 16 (141) 1981 “Liquid Crystals” etc. The ferroelectric liquid crystals disclosed in these documents can be used in the present invention.

More specifically, examples of ferroelectric liquid crystal compounds used in the method of the present invention include decyloxybenzylidene-p'-amino-2-methylbutylcinnamate (DOBAMBC), hexyloxybenzylidene-p'-amino- 2-chloropropyl cinnamate (HOBACPC) and 4-o-(2-methyl)
-butylresolcylidene-4'-octylaniline (MBRA8) and the like.

When constructing an element using these materials,
The liquid crystal compound is SmC*, SmH*, SmI*, SmF
In order to maintain the temperature state such that *, SmG *,
If necessary, the element can be supported by a copper block or the like in which a heater is embedded.

FIG. 1 schematically depicts an example of a ferroelectric liquid crystal cell. 11a and 11b are In ₂ O ₃ ,
SnO ₂ and ITO (indium-tein-oxide)
It is a substrate (glass plate) coated with transparent electrodes such as, etc., and SmC* phase liquid crystal with a liquid crystal molecular layer 12 oriented perpendicular to the glass surface is sealed between the substrates (glass plates). A thick line 13 represents a liquid crystal molecule, and this liquid crystal molecule 13 has a dipole moment (P⊥) 14 in a direction perpendicular to the molecule. When a voltage higher than a certain threshold is applied between the electrodes on the substrates 11a and 11b, the helical structure of the liquid crystal molecules 13 is unraveled, and the dipole moment (P⊥) 14
The alignment direction of the liquid crystal molecules 13 can be changed so that they all face in the direction of the electric field. The liquid crystal molecules 13 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and the short axis direction. Therefore, for example, polarizers arranged in a crossed nicol position can be placed above and below the glass surface. For example, it is easily understood that the liquid crystal optical modulation element is a liquid crystal optical modulation element whose optical characteristics change depending on the polarity of applied voltage. At this time, in the present invention, bistability can be imparted by using a liquid crystal having negative dielectric anisotropy as the ferroelectric liquid crystal and applying an alternating current bias. Furthermore, when the thickness of the liquid crystal cell is made sufficiently thin (for example, 1μ), the helical structure of the liquid crystal molecules unwinds (non-helical structure) even when no electric field is applied, as shown in Figure 2, and its dipole The moment P or P' is oriented either upward 24a or downward 24b. When an electric field Ea or Eb of different polarity above a certain threshold is applied to such a cell as shown in FIG. The liquid crystal molecules change accordingly to the first stable state 23a (bright state).
or the second stable state 23b (dark state).

There are two advantages to using such a ferroelectric liquid crystal as an optical modulation element. Firstly, the response speed is extremely fast, and secondly, the alignment of liquid crystal molecules has bistability. To explain the second point with reference to FIG. 2, for example, when an electric field Ea is applied, the liquid crystal molecules are oriented in a first stable state 23a, and even when the electric field is turned off, the liquid crystal molecules remain in the first stable state 23a. When a maintained and opposite electric field Eb is applied,
The liquid crystal molecules are aligned in the second stable state 23b and change their orientation, but they remain in this state even when the electric field is turned off, and each stable state has a memory function. Further, each orientation state is maintained as long as the applied electric field Ea does not exceed a certain threshold value. In order to effectively realize such fast response speed and bistability, it is preferable for the cell to be as thin as possible, and generally from 0.5μ to
20μ, especially 1μ to 5μ is suitable. A liquid crystal-electro-optical device having a matrix electrode structure using this type of ferroelectric liquid crystal has been proposed, for example, by Clark and Ragabal in US Pat. No. 4,367,924.

FIG. 3 is a liquid crystal display drive control circuit diagram of this embodiment.

In the figure, DSP is a liquid crystal display unit, and A ₁₁ , A ₁₂ , . . . , A ₄₄ indicate each pixel. M
1, M2, and M3 are frame memories, each 4×4
= has a memory capacity of 16 bits. Memory M1,
Data is sent to M2 and M3 from the data bus DB, and write/read and address are controlled by the control bus CB.

FC is a field switching signal, DC is its decoder, MPX is a multiplexer that selects one of the outputs of memories M1, M2, and M3, MM is a monostable multivibrator, GT is a gate signal, FG is a clock oscillator, and CK is a clock. signal, AND is an AND gate, F is a row scanning clock signal, CNT is a counter, SR is a serial input parallel input shift register, DR1 to DR4 are column drive circuits, DR5 to DR8
is the row driving circuit.

The operation of the circuit shown in FIG. 3 will be explained below with reference to FIGS. 4 to 6.

FIG. 4 shows the gradation data of each pixel in one frame (a period forming one screen of a video image),
The most significant bit MSB of each gradation data is stored in memory M3.
Then, the middle bit is stored in memory M2, and the least significant bit is stored in memory M2.
The LSBs are respectively input to the memory M1 via the data bus.

When the field switching signal FC is generated at time _t1 , the decoder DC sets the multiplexer MPX to select data from the memory M1. At the same time, FC is input to monostable multivibrator MM, which generates gate signal GT, and gates
Open the AND and output the four clocks of the clock signal CK as the row scanning signal F to the counter CNT.
Counter CNT is clocked by driver DR5 at the first clock.
Turn on. At this time, the data of the first row of the memory M1 is input to the shift register SR, and only the driver DR4 is in the on state. Therefore, only the liquid crystal pixel A ₁₃ is set to the dark level, and the other liquid crystal pixels A ₁₁ , A ₁₂ , and A ₁₄ are set to the bright level. Then, the row scanning signal F is input as a memory row switching signal to the controller shown in the attached figure, and the next second row data from the memory M1 is input to the shift register SR.
6 is turned on, and at the same time, the data of the second digit of M1 is transferred from the shift register SR to drivers DR1 to DR1, respectively.
Input to DR4. At this time, drivers DR2 and DR
3, DR4 is turned on, pixels A ₂₂ , A ₂₃ , and A ₂₄ are set to dark level, and A ₂₁ is set to bright level. The above operation is repeated for the third and fourth rows.

When the fourth row scanning signal F for selecting the fourth row is input to the counter CNT, the counter CNT outputs a memory switching request signal MC to a controller (not shown), and the memory is switched to M2, and the second field is Move. At this time, each liquid crystal pixel set in the bright or dark state in the first field has a memory function, and the ferroelectric liquid crystal with a non-helical structure shown in FIGS. Therefore, the state is maintained.

Similarly, the second field is also a field switching signal.
FC causes multiplexer MPX to select data from memory M2, and gate signal GT causes row scanning signal F to be input to counter CNT and shift register SR. Then, row scanning is performed at the same period as the first field, and each liquid crystal pixel is set to a dark state or a bright state. The same applies to the third field.

In this embodiment, the ratio of the first, second, and third field periods is 1: the same as the weighting of each bit.
It is set to 2:4. Therefore, for example, the gradation data of pixel _A11 is 2 as shown in FIG. 5, but in this case, it is at the dark level only during the second field period,
2/7 of one frame period is in a dark state. Also, pixels
The gradation data of A ₂₄ is 5, but in this case, the first
and the third field period becomes the dark level, and the second field period becomes the dark level.
The field period is maintained at a bright level, and 5/7 of one frame period is in a dark state. Furthermore, the gradation data of pixel _A42 is 7, and at this time, the dark state is maintained during all field periods. In other words, in this embodiment, it is possible to express eight gray levels.

By controlling the display time ratio within a frame, that is, the display duty, in this manner, it becomes possible to express an apparent halftone. When the third field ends and one frame ends, the data in the memories M1 to M3 are rewritten by the control bus CB and data bus DB, and the data of the next frame is stored in the memory.

Although one frame is divided into three fields in this embodiment, it is possible to display halftones by dividing it into two or more fields. Also, although each field period is determined by the amount of scaling with the same weighting as the data bits, it is also possible to make the amount of scaling equal by dividing it equally. However, in this case, it is necessary to decode the gradation data.

FIGS. 7a and 7b are scan lines B ₁ , B ₂ , B ₃ ,
The electrical signals applied to _B4 are shown, with FIG. 7a showing the signal deformation during scanning, and FIG. 7b showing the signal waveform during non-scanning.

Figures 7c and d are data lines D ₁ , D ₂ ,
The video image signals applied to D ₃ and D ₄ are shown, and FIG. 7 c shows a signal waveform for controlling a pixel having a bistable ferroelectric liquid crystal to, for example, a "bright" state, and FIG. ” represents the signal waveform that controls the state.
That is, the threshold voltage for providing the first stable state of a liquid crystal cell having bistability is Vth ₁ (threshold for providing the bright state), and the threshold voltage for providing the second stable state is −Vth ₂ (threshold value for giving a dark state), the scanning signal _shown in _{FIG .} When this alternating voltage is applied as a scanning signal, the first phase of the liquid crystal corresponding to the optical "bright" or "dark" state is
Alternatively, an important effect can be obtained in that a state change between the second stable states can be caused quickly.

On the other hand, the scanning line to which no scanning signal is applied is
As shown in FIG. 7b, it is in a grounded state and the electrical signal is 0.

In the above, each voltage value is set to a desired value that satisfies the following relationship.

V ₂ , (V ₁ −V ₂ )<Vth ₁ <V ₁ +V ₂ and −(V ₁ +V ₂ )<−Vth ₂ <−V ₂ , −(V ₁ −V ₂ ). FIG. 8 shows the voltage waveform applied to the pixel when the voltage is applied to the pixel.

As is clear from FIGS. 8a to 8d, the pixels on the scanning line to which the scanning signal shown in FIG. 7a is applied are on the threshold scanning line at phase _t2 , and the image signal in FIG. 7c is synchronized. At phase t ₂ , a voltage V ₁ +V ₂ exceeding the threshold value Vth ₁ is applied to the pixel to which the voltage is applied (as shown in FIG. 8a). Furthermore, in the pixels that exist on the same scanning line and to which the image signals _{of FIG} .
(V ₁ +V ₂ ) is applied (as shown in FIG. 8b). Therefore, on the scanning line to which the scanning signal is applied, in response to the application of V ₂ or -V ₂ to the data line, the liquid crystal molecules align to the first stable state and form a bright state, or Alternatively, a dark state can be formed by aligning the orientation to a second stable state. In any case, it has nothing to do with the previous history of each pixel.

On the other hand, the voltage waveform applied to the pixels on the scanning line to which the scanning signal shown in FIG. 7b is not applied is V ₂ or -V ₂ as shown in FIGS. 8c and d.
and does not exceed the threshold voltage. Therefore, the liquid crystal molecules in each pixel on this scanning line maintain the information written in the previous step without changing their alignment state. That is, when a scanning signal is applied to a scanning line, the signal for one line is written, and that signal is written during one frame period or one field period until the next scanning signal is applied. state can be maintained.

Therefore, even if the number of scanning lines increases, the actual duty ratio remains unchanged and the contrast does not deteriorate at all. At this time, the values of V ₁ and V ₂ and the value of phase (t ₁ + t ₂ )=T depend on the liquid crystal material used and the thickness of the cell, but are usually 3 volts to 70 volts. A range of 0.1 μsec to 2 msec is used. Here, in the method of the present invention, the electrical signal applied to the scanning line to which the scanning signal is applied is the first
from a stable state (supposed to be "bright" when converted to an optical signal) to a second stable state (supposed to be "dark" state when converted to an optical signal), or vice versa. In order to facilitate this change, an important feature is that the scanning line to which the scanning signal is applied is given an alternating voltage signal, for example from +V ₁ to -V ₁ . Further, the voltages applied to the data lines are set to be different voltages to specify a bright or dark state.

In this driving example, preferably, the values of the voltages V _ON1 and V _ON2 oriented in the first and second stable states at the selected point and the voltage V _OFF applied at the non-selected point are set to the average threshold voltage Vth ₁ It is preferable to set it as far away from Vth ₂ as possible. When considering variations between elements or within an element, it is stable if the values of |V _ON1 | and |V _ON2 | are more than twice the value of |V _OFF |. It was confirmed that this method is advantageous in terms of obtaining sexual characteristics. Further, under such voltage application conditions, a state change between two stable states can be quickly achieved. When realized using the driving method explained in FIG. 8, the voltage applied to the corresponding pixel without information (b ) at phase t ₂ |V ₁ −V ₂ |, similarly to the voltage V _OFF applied to non-selected pixels, is sufficiently spaced from the value of V _ON1 , especially 1/1.2 of V _ON1 . It is preferable to set the following. Therefore, corresponding to the example of FIG. 8, the condition is 1<|V ₁ (t)|/|V ₂ |<10.

More generally speaking, the voltage applied to each pixel and the electrical signal applied to each electrode need not be symmetrical or stepped. In order to express it generally, including this case, the phase t ₁ +
The maximum value of the electrical signal (voltage due to the difference from ground potential) applied to the scanning line within t ₂ is V ₁ (t)max,
The minimum value is V ₁ (t)min, and the electric signal corresponding to the presence of information applied to the selected data line is
When V ₂ is the electrical signal corresponding to no information applied to the unselected data line (both are voltages due to the difference from the ground potential), V ₂ ' is required for stable drive to satisfy the following conditions. preferred for.

1<|V ₁ (t)max|/|V ₂ |<10 1<|V ₁ (t)min|/|V ₂ |<10 1<|V ₁ (t)max|/|V ₂ ′| <10 and 1<|V ₁ (t)min|/|V ₂ '|<10 Based on the embodiment described in FIG. 8, the electrical signal V ₁ applied to the scan line and the electrical signal applied to the data line When the ratio of ±V ₂ is changed, the maximum voltage |V ₁ +V ₂ | applied to the selected point (between the selected data line and the selected or unselected scanning line) and the unselected point (unselected data line) and the selected or unselected scan line), and at the selected point, e.g. phase t ₁ in FIG. _3B -a (or phase t ₂ in FIG. 3B-b) Applied voltage |
FIG. 9 is a graph showing the ratio of V ₂ +V ₁ | (all expressed as absolute values). As can be seen from this graph, the value of the ratio k=|V ₁ /V ₂ | is 1<
K, particularly preferably in the range 1<K<10.

FIGS. 10 and 11 show another example of driving according to the present invention. Figure 10a shows the scanning signal applied to the scanning line, Figure 10b shows the signal applied to the scanning line during non-scanning, and Figures 10c and d.
denotes an information signal (corresponding to a bright signal and a dark signal) for writing pixels on a scanning line to which a scanning signal is applied into a bright state and a dark state, respectively. Therefore, the 11th
Figure a shows the voltage waveform of the pixel on the scanning line to which the write signal of Figure 10 c is applied, and Figure 11 b shows the voltage waveform of the pixel of Figure 10 d among the pixels on this scanning line. It represents the voltage waveform of a pixel to which a signal is applied. Also, Figures 11c and d are pixels in Figure 10c and d, respectively, of the pixels on the scanning line during non-scanning.
This shows the voltage waveform when the signal is applied.

In this driving example, the voltage value V is Vth ₁ < 2V and -
By setting V>-Vth 2 to a desired value that satisfies ₂ >-2V, as mentioned above, one line of information written during scanning of the scanning signal will be retained until the next scanning signal is applied. Retained.

FIGS. 12 and 13 show modified embodiments of the drive example shown in FIGS. 10 and 11 described above. Figures 12a and b show the signal waveforms applied to the scanning line, Figures 12c and d show the signal waveforms applied to the data line, and Figures 13a and b show the pixels on the scanning line to which the scanning signal is applied. 13c and d show the voltage waveforms applied to the pixels on the scanning line when the scanning signal is not scanning.

By adopting the driving examples shown in FIGS. 7, 8, and 10 to 13 to the time chart shown in FIG. 6, a video image having gradation can be formed or displayed. be able to. Furthermore, in the present invention, a bistable liquid crystal element is created by arranging color filters in each pixel, for example, in a stripe shape or a mosaic shape, and when this element is driven by the above-described driving method, gradation changes can be achieved. Can display color images.

Therefore, the method of the present invention is applicable to liquid crystal televisions that display monochrome or color images with gradation;
In particular, it can be applied to LCD pocket color televisions, which are much smaller and lighter than conventional CRT color televisions.

Further, in the method of the present invention, for example, one frame period is set to 1/30 second (sec), and the first field shown in FIG. 6 is set to 1/210 second (sec), and 8 gray scales are displayed. In the case of display panels, as mentioned above, the response speed of ferroelectric liquid crystal can be set to about 0.1 μsec, so the number of scanning lines in the display panel can be reduced to 1.
Since it is possible to wire up to ×10 ⁷ /210 lines (approximately 4750 lines), multi-gradation display with high density pixels is possible, and the number of scanning line lines can be reduced to the number of scanning lines of normal television. If the number of lines is about 100, it becomes possible to display more gradations than the above-mentioned 8 gradations.

Next, let us consider the problems that may actually arise when the above-described driving method for performing gradation display is applied to a display device. In FIG. 14, among the pixels formed at the intersections of the scanning electrodes S ₁ to S ₅ ... and the signal electrodes I ₁ to I ₅ ..., the pixels in the shaded area are in the "bright" state, and the pixels shown in white are in the "bright" state. It corresponds to the "dark" state. Now, if we pay attention to the display on _the signal electrode I ₁ in FIG.
All other pixels B are in the "dark" state. As an example of the driving method in this case,
FIG. 15 shows a time series representation of the scanning signal, the information signal applied to the signal electrode _I1 , and the voltage applied to the pixel A.

For example, when driven as shown in Figure 15,
When the scanning signal _S1 is scanned, a voltage of 3V exceeding the threshold value _Vth2 is applied to the pixel A at time _t2 , so the pixel A is in a stable state in one direction, regardless of the previous history. Transition (switch) to a bright state. After that, while S ₂ to _{S 5} . . . are being scanned, the voltage of -V continues to be applied as shown in _FIG .
However, in reality, when displaying information in which one signal (corresponding to "dark" in this case) continues to be given on one signal electrode, scanning The following data shows that problems can occur when the number of lines is extremely large and high-speed driving is required.

Figure 16 shows the ferroelectric liquid crystal material.
DOBAMBC (162 in Figure 16) and
This is a plot of the application time dependence of the voltage threshold Vth required for switching when HOBACPC (161 in FIG. 16) is used. In both cases, the liquid crystal thickness is 1.6μ, and the temperature is controlled at 70℃. In the case of this experiment, the substrates on both sides in which the liquid crystal was to be sealed were glass plates on which ITO was vapor-deposited, and the voltage was Vth ₁ Vth ₂ (≡Vth).

As is clear from FIG. 16, the threshold value Vth is dependent on the application time, and it is understood that the shorter the application time, the steeper the slope becomes. From this, if the driving method as shown in _FIG . Even if the pixel A is switched to the "bright" state, a voltage of -V continues to be applied after the _S2 scan, so the pixel A is switched to the "dark" state during the completion of one screen scan, resulting in the above-mentioned gradation display. It can be seen that there is a risk that the gradation display will not be good when the drive is performed.

In particular, if the above-mentioned insulating film is formed on the electrode, a voltage drop will occur from the time of pulse application, and a voltage equivalent to this voltage drop will be applied as a reverse polarity voltage at the time of pulse switching. This aspect is made clear in FIG. That is, in the waveform shown by A in FIG. 15, a voltage of 3V is not applied at phase _t2 ,
A voltage drop by α gradually occurs, and at the moment this write signal is cut off, an additional voltage of -α is applied, causing the problem of hastening the above-mentioned reversal phenomenon.

Therefore, the present inventors attempted to study the bistable ferroelectric liquid crystal that constitutes the liquid crystal element, and found that the volume resistivity of the liquid crystal was 1×
10 ⁹ Ω・cm or more, more typically 1×10 ⁹ Ω・cm ~
1×10 ¹³ Ω・cm, preferably 1×10 ¹⁹ Ω・cm ~ 1
×10 ¹³ Ω・cm, particularly preferably 1 × 10 ¹¹ Ω・cm ~
It has been found that by adjusting the resistance to 1×10 ¹³ Ω·cm, the above-mentioned inversion phenomenon can be prevented, and a signal once written can maintain its written state until the next writing.

On the other hand, when the volume resistivity is set to 1×10 ⁹ Ω・cm or less, the voltage drop α becomes approximately 3V/3 when 3V is applied, and the display is reversed in the middle of the screen, as will be made clear in the example below. .

To obtain the aforementioned ferroelectric liquid crystal with a volume resistivity of 1×10 ⁹ Ω・cm or more, for example, an ion-adsorbing substance (Al ₂ O ₃ particles; alumina particles, silica gel, etc.) is applied to the ferroelectric liquid crystal. A method is used in which the mixture is mixed in a proportion of 10 to 30% by weight, stirred vigorously for several hours, and then filtered. Ion-adsorbing substances are
Particulate materials with an average particle size of about 10 to 50 μm are preferred.

The "volume resistivity" described in this specification is measured by applying a rectangular pulse using the two-frequency method using the circuit shown in FIG. 17, and calculating ρ (volume resistivity) from the following formula. be able to.

I=I _C +I _R =4f・C・V+V/R V: Measurement voltage f: Rectangular wave frequency I _C : Current value of capacitive component I _R : Current value of R component C: Capacitance of liquid crystal R: Resistance of liquid crystal (Ω) By changing f, I ₁ = 4f ₁・C・V+V/R I ₂ =4f ₂・C・V+V/R p=RS/d d: Liquid crystal film thickness (cell gap) s: Electrode area In a preferred embodiment of the present invention, at least one of the opposing electrodes constituting the liquid crystal cell may be provided with an insulating film made of an insulating material.

The insulating materials used in this case are not particularly limited, but include silicon nitride, hydrogen-containing silicon nitride, silicon carbide, hydrogen-containing silicon nitride, silicon oxide, boron nitride, Inorganic insulating materials containing hydrogen such as boron nitride, cerium oxide, aluminum oxide, zirconium oxide, titanium oxide and magnesium fluoride, or polyvinyl alcohol, polyimide, polyamideimide, polyesterimide, polyparaxylylene, Organic insulating materials such as polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyvinyl acetate, polyamide, polystyrene, cellulose resin, melanin resin, urea resin, acrylic resin, and photoresist resin are used as the insulating film. The film thickness of these insulating films is 5000〓 or less, preferably 100〓~
5000〓, especially 500〓~3000〓 is suitable.

In addition, in the case of the capacitance formed by these insulating films, the above-mentioned inversion phenomenon can be more effectively prevented by setting the capacitance to 5.5×10 ³ PF/cm ² or more. . Its preferred capacity is 5.5
×10 ³ PF/cm ² to 3.0 × 10 ⁵ PF/cm ² , especially in the range of 9.0 × 10 ³ PF/cm ² to maintain sufficient insulation.
5.5×10 ⁴ PF/cm ² is suitable.

Hereinafter, the present invention will be explained according to detailed examples.

Example 1 A polyimide film (made of polyamic acid resin from a combination of pyromellitic anhydride and 4,4'-diaminodiphenyl ether) having a film thickness of 1000㎓ was applied to each of the opposing matrix electrodes formed of crossed strips of ITO. A 5wt% N-methylpyrrolidone solution was applied, and the polyimide film was formed by heating at a temperature of 250°C through a ring-closing reaction.The surfaces of this polyimide film were rubbed so that they were parallel to each other to create a cell with a cell thickness of 1μ. did.

Next, DOBAMBC adjusted within Canon Inc.
(Desyloxybenzylidene-P'-amino-2-methylbutylcinnamate) 0.3 parts by weight of alumina particles (average particle size 30μ) were mixed in and heated at an isotropic phase temperature for about 2 hours. Mechanical stirring was performed. After this stirring, the mixed liquid is filtered,
I have filtered out DOBAMBC. This DOBAMBC was injected into the above-mentioned cell by a vacuum injection method under an isotropic phase, and the cell was sealed. After that, slow cooling (5℃/hour)
An SmC* liquid crystal cell was created using the following method. Using this liquid crystal cell, the volume resistivity of the liquid crystal was determined by measuring the current value when a voltage of 10V at 32Hz and 10V at 64Hz was applied, and it was found to be 3.7×10 ⁹ Ω・cm
It was hot.

A crossed Nicol polarizer and an analyzer were arranged on both sides of this liquid crystal cell, and this liquid crystal element was incorporated into the circuit shown in FIG. 3, and the circuit operations shown in FIGS. 4 to 6 were carried out. At this time, signals having the waveforms shown in FIGS. 7 and 8 were applied between opposing matrix electrodes. On this occasion,
The scanning signal had an alternating waveform of +8 volts and -8 volts as shown in FIG. 4a, and the write information had +8 volts and -4 volts, respectively.

Moreover, one frame period was set to 30 m·sec.

As a result, the gradation display state of this liquid crystal element was normal even when the above-mentioned gradation display driving was performed.

Example 2 The same procedure as Example 1 was performed, except that HOBACPC (hexyloxybenzylidene-P'-amino-2-chloropropyl cinnamate) prepared within Canon Co., Ltd. was used in place of DOBAMBC used in Example 1. A liquid crystal cell was created in a similar manner.

When the volume resistivity of the liquid crystal in this liquid crystal cell was measured, it was 1.6×10 ¹⁰ Ω·cm. moreover,
When this liquid crystal cell was arranged with a polarizer and an analyzer in the same manner as in Example 1 and then driven for gradation display in the same manner, similarly good gradation display was obtained.

〔effect〕

It is possible to perform gradation display according to the gradation signal.

[Brief explanation of drawings]

1 and 2 are perspective views schematically showing a liquid crystal element used in the driving method of the present invention. FIG. 3 is an explanatory diagram showing the drive control circuit of the present invention. FIGS. 4 and 5 a to 5 d are explanatory diagrams showing an example of pixel gradation data. Figure 6 shows
FIG. 3 is an explanatory diagram showing a time chart when used in the driving method of the present invention. Figures 7a-d, Figures 10a-
d and FIGS. 12 a to d are explanatory diagrams showing signal waveforms during driving, and FIGS. 8 a to d, FIGS. 11 a to d, and FIGS. 13 a to d show voltage waveforms applied to pixels. It is an explanatory diagram. FIG. 9 is an explanatory diagram showing a change in drive stability due to a change in the absolute value k of the ratio of the electric signal V ₁ applied to the scanning line and the electric signal ±V ₂ applied to the data line. FIG. 14 is a plan view of the matrix electrode structure used in the present invention. 1st
FIG. 5 is an explanatory diagram of a time chart showing signals applied to the liquid crystal element of the present invention. FIG. 16 is an explanatory diagram showing the dependence of voltage application time on threshold voltage in a ferroelectric liquid crystal. FIG. 17 is an explanatory diagram showing a circuit used when measuring the volume resistivity of liquid crystal.

Claims (1)

[Scope of Claims] 1 a. A matrix electrode composed of scanning lines and data lines intersecting at intervals, an insulating film provided on the scanning lines or data lines, and disposed between the scanning lines and the data lines. It has a ferroelectric liquid crystal that produces either one orientation state or the other orientation state depending on the polarity of the applied voltage, and has a volume resistivity of 1×10 ⁹ Ω・cm or more, and has a scanning line. a display panel in which pixels are formed at the intersections of the and the data lines, b sequentially scanning the scanning lines, applying a scanning selection signal having one polarity pulse and the other polarity pulse to the selected scanning line; During the applied scan selection period and in synchronization with the one-polarity pulse during the scan selection period, causing pixels on the selected scan line to have one orientation state or the other orientation state. After applying the first voltage, in synchronization with the other polarity pulse during the scan selection period, the pixel on the selected scan line is applied with a voltage opposite in polarity to the first voltage, a first means for applying a second voltage that maintains the orientation state during the period of the one-polarity pulse; A display having a second means for selecting one of the orientation state and the other orientation state, and determining the number of selections of the one orientation state and the other orientation state in multiple field scans according to the gradation data. Device.