JPH05188884A - Method for driving active matrix liquid crystal display device - Google Patents

Abstract

PURPOSE:To accelerate scanning speed and to form one picture in plural fields by charging liquid crystal by electrifying a switching element just for time shorter than the response time of the liquid crystal, and driving liquid crystal polymers by the charged electric field. CONSTITUTION:Liquid crystal having autonomous polarization is used for the liquid crystal, the liquid crystal LC is charged by electrifying switching elements S and P just for time shorter than the response time of the liquid crystal and therefore, the liquid crystal polymers are driven. One field is formed by line sequentially driving the liquid crystal LC of picture element electrodes corresponding to all the scan lines, one picture is formed by continuously combining the plural fields, and the picture of plural gradations is obtained. In this case, the electric field is impressed through the three-terminal or two-terminal switching element S or P to the liquid crystal LC of the respective picture elements arranged in the shape of a matrix. A scan line signal to turn on/off this switching element S is defined as a switching signal, and a data line signal is defined as a signal for liquid crystal drive.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method of an active matrix liquid crystal display device used as a liquid crystal display element or a liquid crystal spatial modulation element.

[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 cont
rolled birefringence) method, PC (phase change)
A system, a memory system, a GH (guest-host) system, a thermo-optical system, etc. are considered.

Among them, the systems currently used as display elements in watches, calculators, word processors, personal computers, televisions, etc. are mainly the TN system using nematic liquid crystal and its improved STN system.

This is a mode in which the dielectric anisotropy and refractive index anisotropy of nematic liquid crystal molecules are used, and the director of the liquid crystal molecules moves with respect to an electric field. But T
When the N-type liquid crystal element is driven in multiplex, the driving margin rapidly narrows as the number of scanning lines increases.
There is a drawback that sufficient contrast cannot be obtained. Therefore, it is difficult to make a large display capacitance element. In addition, Super Twisted Nematic (Supertwi
sted Nematic, STN type or Supertwisted Birefre
ngence Efect, SBE type) and double layer supertwisted nem type
atic DSTN type) display element.

However, these still have drawbacks such as a decrease in contrast and a slow response speed as the number of lines increases. In order to solve the problems such as the decrease in contrast due to the increase in the number of scanning lines and the slow response speed of nematic liquid crystal, switching elements such as thin film transistors (TFT) and MIM (metal-insulator-metal) elements are arranged on the substrate. An active matrix type liquid crystal display device combined with a conventional TN type liquid crystal has been put into practical use,
It is used in applications such as televisions that require a fast response speed. However, its operating principle is a field effect type that utilizes the dielectric anisotropy of liquid crystal molecules, so the problem of a long response time of the order of msec is not sufficiently solved, and in particular,
For applications such as CAD terminals requiring a higher response speed, the combination with the current nematic liquid crystal is insufficient in response speed.

In addition, the TN type and ST used in the present liquid crystal display, including those combined with active elements, are also used.
In the N-type method, the electro-optical effect is caused by a 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. In principle, the viewing angle dependence on can not be avoided.

On the other hand, a display device using a ferroelectric liquid crystal or an antiferroelectric liquid crystal in which molecules themselves have spontaneous polarization is proposed as a liquid crystal display device having a high response speed (ferroelectric property). Liquid crystal display element Ferroelectric Liquid Cr
ystal Display, anti-ferroelectric liquid crystal display element Anti-Ferroele
ctric Liquid Crystal) is available. A ferroelectric liquid crystal display element (hereinafter referred to as FLCD) is an element that uses electrical interaction between the polarities of spontaneous polarization of liquid crystal molecules and the polarity of an external electric field to perform switching on a cone in which liquid crystal molecules can move. Because of this, extremely high-speed switching (response on the order of several μsec) is possible compared to nematic liquid crystals.

In the ferroelectric liquid crystal, a surface-stabilized ferroelectric liquid crystal device (Surface Stab) proposed by Clark and Lagerwall has been proposed.
ilized Feloelectric Liquid Crystal Display, SSF
LCD) (Appl. Phy. Lett., 36,899 (1980); JP-A-56)
-107216 gazette; US Pat. No. 4,366,924), such as a method using bistability or a method using scattering such as a dynamic scattering mode of liquid crystal, and viewing angle dependence utilizing the high-speed response of ferroelectric liquid crystal. Several display modes that do not have a display have been proposed, and they are regarded as promising next-generation liquid crystal displays.

[0009]

An element using such a ferroelectric liquid crystal has an excellent aspect as compared with a conventional TN type liquid crystal display element such as a fast response speed and no visual dependence. On the other hand, there are some problems to be solved which are different from those of the TN type liquid crystal display device.

For example, in the case of an SSF type ferroelectric liquid crystal display: fast response (response time of the order of μsec) wide viewing angle (caused by the viewing angle characteristics of the polarizing plate) bistability (even if the electric field is zero) It retains the previous alignment state), which is an excellent characteristic not found in the three TN type and STN types, but on the other hand It is extremely difficult to get the status. Since the switching of the molecules of the ferroelectric liquid crystal does not have a clear threshold value, the contrast decreases due to the movement of the molecules generated by the electric field (bias electric field) applied to the liquid crystal when the display is not selected. -Due to the property of bistability, gradation display is difficult in principle. Such a problem is an obstacle in realizing and applying the SSF type liquid crystal panel (SSFLCD).

The problems in SSFLCD are all inclusive of the problems in other display modes using ferroelectric liquid crystals and display modes of antiferroelectric liquid crystals. The most important problem among them is the problem caused by the application of bias waveform during driving, that is, the bias electric field (crosstalk electric field) applied during non-selection as shown in FIG. ) Various problems caused by. (FIG. 1 shows an electric field applied to a data line and a scan line and an electric field applied to each picture element of a liquid crystal cell in the case of simple matrix driving, and 1H represents one horizontal scanning period. Exist).

Although it varies slightly depending on each display mode, in any case, the following points lead to deterioration of display characteristics, which is a serious problem.・ Liquid crystal molecules move due to the bias electric field, which causes the memory to break and deteriorates memory performance.・ Contrast deterioration due to light leakage due to movement of molecules and poor light shielding. -Shift of gradation level due to difference in applied bias waveform.

Further, in the display using the ferroelectric liquid crystal or the anti-ferroelectric liquid crystal, the display principle is theoretical in the mode utilizing the bistable state and the display mode utilizing the threshold characteristic with respect to the applied electric field strength of the liquid crystal. It is not possible to display gray scales, or in modes that use the transmittance or scattering intensity corresponding to the applied electric field strength, there is a clear controllable gradation expression as mentioned in the problem caused by the bias electric field. However, it is difficult to realize uniform gradation within the plane as a practical liquid crystal display panel.

According to the present invention, a liquid crystal having spontaneous polarization, that is, a ferroelectric liquid crystal or an antiferroelectric liquid crystal, is combined with a switching element to have high speed, high contrast, wide viewing angle characteristics, and gradation display or high display. An object of the present invention is to provide a driving method of a liquid crystal display device capable of reducing resolution or power consumption.

[0015]

The present invention is an active matrix in which switching elements connected to scan lines and data lines and picture element electrodes for applying an electric field to liquid crystal through the switching elements are arranged in a matrix. In a method of driving a liquid crystal display device, a liquid crystal having spontaneous polarization is used as the liquid crystal, and a switching element is energized for a time shorter than the response time of the liquid crystal to charge the liquid crystal, thereby driving the liquid crystal molecules and simultaneously scanning all scan lines. One field is formed by line-sequentially driving the liquid crystal of the picture element electrode corresponding to, and a plurality of fields are continuously combined to form one screen to obtain a screen with a plurality of gradations. A method for driving an active matrix liquid crystal display device is provided.

The scanning times of the fields forming one screen may be equal to each other, but the scanning times of the fields forming one screen are different from each other, which enables more gradation display.

That is, when one screen is formed by n fields, a screen with a maximum of 2 ⁿ gray scales can be obtained.

It is preferable to set the polarity and magnitude of the electric field so that the electric field applied to the liquid crystal cancels out within the display time of one screen, but the electric field applied to the liquid crystal is displayed within the display time of a plurality of screens. The polarity and magnitude of the electric field may be set so as to cancel each other out.

Further, a high frequency pulse having a period shorter than the response time of the liquid crystal may be applied to the liquid crystal so that the electric field applied to the liquid crystal is canceled.

That is, the liquid crystal display device according to the present invention has the following constitution. -A pair of substrates are arranged so as to face each other. -Pixel electrodes are arranged in a matrix on one substrate. -A switching element is formed on each pixel electrode.

A structure in which an electric field can be applied to the liquid crystal between the picture element electrode and the counter electrode via the switching element. A liquid crystal having spontaneous polarization, that is, a ferroelectric liquid crystal or an antiferroelectric liquid crystal is interposed between the substrates.

A liquid crystal having spontaneous polarization is used in an operation mode having at least an ON / OFF state, and has a stable ON state or OFF state at a positive or negative constant electric field strength or more or a state where the electric field strength is zero. To show. Further, in the above liquid crystal display device, the liquid crystal is driven by the driving method having the following characteristics. One screen is displayed with the following drive configuration.・ One screen is rewritten at regular intervals. -A screen is formed by scanning the switching elements that form the screen one or more times.

The scanning of all switching elements is performed in each scanning unit such as one element or one line. -Each scanning time is constant or changes with the screen rewriting cycle. The pulse applied to the liquid crystal has the following characteristics.

The switching element may be driven with a pulse width shorter than the response time of the liquid crystal. The voltage applied to the liquid crystal in the ON state of the switching element is held for each pixel electrode when the switching element shifts from the ON state to the OFF state. The liquid crystal on / off state is changed for each scan of all switching elements forming one screen, and the liquid crystal on / off state with respect to the time axis is combined and driven. -The average of the electric field strengths applied to the liquid crystal within the time for displaying one screen is not always zero.・ The pulse applied to the liquid crystal of one picture element in each of a plurality of scans for displaying one screen is a pulse for turning on the liquid crystal, a pulse for turning off the liquid crystal, and applied to the cell It is roughly divided into three pulses for canceling the generated electric field. The pulse for turning on / off and the pulse for canceling the electric field applied to the cell are not applied within the same scanning time.

The high-frequency waveform is not superposed during the scanning period for applying the pulse for turning on / off, and the scanning time for applying the pulse for canceling the charge in the on / off state is as follows. High frequency waveforms are superimposed.・ The peak value of the pulse to turn on / off is constant, and the peak value of the pulse to cancel the electric field applied to the cell is within the time for displaying one screen for each picture element. It has a value corresponding to the pattern of the liquid crystal on / off state. The following configuration can be added to the light source of the liquid crystal display element.

When the light intensity changes, the light intensity changing period is synchronized with the period of scanning the switching element of the liquid crystal display element, and the brightness can be changed for each scanning. Alternatively, it can be considered that the light intensity is apparently constant in a state where the period in which the light intensity changes is not synchronized with the period in which the switching element of the liquid crystal display element is scanned. Or
The light intensity is constant.

With the above device structure and driving method, high-resolution display capable of high-speed rewriting or multi-gradation display by combination of ON / OFF of liquid crystal is possible. An equivalent circuit in the case of matrix driving the liquid crystal display device to which the present invention is applied is shown in FIG. 66 (a) and FIG. 66 (b).
In these figures, an electric field is applied to the liquid crystal LC of each picture element arranged in a matrix through a 3-terminal or 2-terminal switching element S or P.

As the switching elements S and P, any element can be used as long as it allows a current to flow in the on state and has a high impedance in the off state. For example, in the ON state as shown in FIG. 2, an electric field applied to the liquid crystal is applied, and in the OFF state, a thin film transistor (T
An element such as FT) or a diode element or an element such as a MIM or a varistor in which a current flows in a circuit at a certain voltage or more as shown in FIG. 3 and becomes high impedance below that can be used.

A case where the present invention is applied to a cell having this structure will be described. Ferroelectric liquid crystal, when switching,
Unlike a nematic liquid crystal, it does not have a clear threshold value, and even if it is a weak electric field, when an electric field is applied, the liquid crystal molecule reacts to the electric field, and the electrical action between the dipole of the liquid crystal molecule and the externally applied electric field is exerted. It has been confirmed that the liquid crystal molecules move on a movable cone to a position where the strong interaction and the helical force of the liquid crystal are in equilibrium, and this is considered to cause a decrease in contrast.

The effect of combining the switching element with the ferroelectric liquid crystal has the following two states of the liquid crystal cell in the non-selected state during driving. (1) The bias electric field is not applied to the liquid crystal. (2) The liquid crystal is in a high impedance state in a circuit. The phenomenon of (1) has the following effects. In the normal simple matrix method, a signal for rewriting another picture element is always applied to the data line even if an arbitrary picture element is in a non-selected state. This electric field, that is, the bias electric field (FIG. 1) causes liquid crystal molecules to move, which causes a phenomenon that leads to deterioration of contrast and deterioration of memory property.

However, the signal for driving the other picture element portion by attaching the switching element is such that the switching element is in the OFF state as shown in FIG. 2 (three-terminal nonlinear element) and FIG. 4 (two-terminal nonlinear element). As long as it is, it is not applied to the liquid crystal. Therefore, since the liquid crystal molecules do not move when not selected, it is possible to prevent the deterioration of the contrast and the deterioration of the memory property due to the bias electric field applied in the simple matrix driving. As a result, the display improves the contrast of the displayed image and the display quality. FIG. 2 schematically shows the characteristics of the TFT element. The electric fields of the scan signal and the data signal applied to the gate and source terminals of the TFT and the electric field applied to the liquid crystal from the drain terminal of the TFT are shown in FIG. It is shown.

FIG. 3 schematically shows the element characteristics of the two-terminal element. FIG. 4 schematically shows signals applied to the data line and the scan line and an electric field applied to the liquid crystal at that time in the case of the two-terminal element. A signal shown as a scan signal in the drawing is applied from the scan line, and a data signal is applied from the data line. Further, due to the phenomenon of (2), when the switching element changes from the on state to the off state, a part of the electric field applied to the liquid crystal is held by the capacitor component of the liquid crystal cell.

Due to the electric field held in the off state of the switching element, the liquid crystal molecules are different from when the electric field strength is zero (the polarization of the liquid crystal molecules, the held external electric field, the force of winding the liquid crystal in a spiral, etc. are balanced. ) Hold in position.

The state in which the liquid crystal molecules are in equilibrium with respect to a certain holding electric field in the OFF state of the switching element is used as one display state, and the other display state is the state in which the direction of the holding electric field is opposite or the holding electric field is changed. If the intensity of zero is used, the liquid crystal is driven by applying an electric field to the liquid crystal to switch the liquid crystal within the on time of the switching element and the time when the switching element turns on once and then turns on again. It only takes the time required for.

This means that the pulse width for operating the switching element is narrowed and the voltage to be applied to the liquid crystal is lowered. However, the electric field required to switch the liquid crystal is such that the spontaneous polarization of the liquid crystal molecules moves inside the liquid crystal cell, causing a current to flow inside the cell, causing the electric field held by the capacitor component of the liquid crystal cell to be discharged. Strictly speaking, an electric field that is a combination of the electric field discharged by the switching of the liquid crystal and the electric field for maintaining the state of the liquid crystal is required to occur.

Further, since the electric field required to switch the molecules of the ferroelectric liquid crystal is small, it is not necessary to charge the electric field to the liquid crystal and the capacitor up to about 90% of the capacity unlike the normal TN type liquid crystal. Therefore, existing TFT and M
A switching element such as IM, for example, a-Si TF which requires a gate width of 15 μsec or more in TN type liquid crystal.
Even the T element can perform the switching operation of the liquid crystal molecules with the gate width of 10 μsec or less, which is sufficiently applicable to the present invention.

Further, the width of the pulse itself for operating the switching element is narrowed: increase in the number of switching elements that can be driven per frame; increase in the number of scans (the number of fields) for one screen display;・ It is effective in realizing reduction of power consumption.

These effects mean an increase in the number of switching elements that can be driven per frame, that is, an increase in display capacity. Increasing the number of scans (the number of fields) for one screen display depends on the drive waveform. Increasing the frame frequency means making the electric field applied to the liquid crystal alternating and enabling gradation display by time division.
This means enhancing the quality of the displayed image.

Furthermore, since the direct current component applied to the liquid crystal is reduced by lowering the voltage of the switching pulse of the liquid crystal itself, even if the liquid crystal is driven by a non-bipolar pulse, the liquid crystal is more effective than the simple matrix drive of the ferroelectric liquid crystal. The impact on it is small. A new display method of the present invention, that is, a DC electric field, is obtained by taking advantage of driving at a low voltage and increasing the number of scans for one-screen display generated by combining a switching element and a liquid crystal having spontaneous polarization as described above. High-contrast and multi-gradation display can be achieved by dynamic driving.

The display principle of this new system will be described below. Note that liquid crystal active matrix driving in the following description is performed by the method shown in FIG. 66A using a three-terminal switching element, and the gate terminal is used to turn the switching element S ON / OFF via the scan line. The scan line signal applied to the switching element is a switching signal and the data line is a switching element S.
The data line signal applied to the liquid crystal through the source terminal / drain terminal is used as the liquid crystal driving signal.

[Black and White Display] The waveforms shown in FIGS. 5 to 9 are drive waveforms for black and white display. In FIG. 5, since the switching element itself is turned off in a state where the electric field applied to the liquid crystal is not zero, a direct current component is always applied to the liquid crystal. In the figure, the shaded region is a region where the electric field is indeterminate because the switching state of the liquid crystal is not defined. The characteristics of this case are that the data line signal is held at the fall of the scan line signal, and that no waveform that cancels the electric field applied to the liquid crystal is applied.

In FIG. 6, the switching element is turned off after the electric field applied to the liquid crystal becomes zero so that the electric field is applied to the liquid crystal only when a pulse is applied. The characteristics of this case are that the data line signal is zero at the time of the fall of the scan line signal, and that no waveform that cancels the electric field applied to the liquid crystal is applied.

In FIG. 7, since the switching element itself is turned off when the electric field applied to the liquid crystal is not zero, a direct current component is always applied to the liquid crystal.
However, since the direction of the electric field is reversed between the first scan and the second scan, the DC component applied to the liquid crystal itself as a whole is within the difference between the first scan time and the second scan time. It is only the electric field component that is applied to. The characteristic of this case is that the data line signal is held at the fall of the scan line signal and that a waveform having a phase opposite to the display waveform is applied so as to cancel the electric field applied to the liquid crystal. Is.

In FIG. 8, the switching element is turned off after the electric field applied to the liquid crystal becomes zero so that the electric field is applied to the liquid crystal only when a pulse is applied. Further, since the directions of the electric fields are reversed between the first scanning and the second scanning, the DC component applied to the liquid crystal itself is canceled out as a whole. The characteristic of this case is that the data line signal is zero at the fall of the scan line signal, and a waveform having a phase opposite to the display waveform is applied so as to cancel the electric field applied to the liquid crystal. That is.

In FIG. 9, since the switching element itself is turned off when the electric field applied to the liquid crystal is not zero, a direct current component is always applied to the liquid crystal.
However, since the direction of the electric field is reversed between the first scan and the second scan, and the electric field is zero in the third and subsequent scans,
The DC components applied to the liquid crystal itself are canceled out as a whole. However, in this case, within the scanning time from the third time onwards,
It is required that the liquid crystal is in a memory state that does not shift from the on state to the off state, from the off state to the on state, in a metastable state, or in a slow relaxation process. The characteristic of this case is that the data line signal is held at the fall of the scan line signal, and a waveform having a phase opposite to the displayed waveform is applied so as to cancel the electric field applied to the liquid crystal, and then the electric field is applied. That is, the switching element is operated so that

The display state of the liquid crystal during the time when the electric field is held at zero is a state for displaying information to be recognized by humans, and the electric field applied immediately before the electric field is zero. In this state, it is required to hold the display state to be recognized at least within the range of human recognition by the state by the memory or the transient state in the relaxation process.

In FIG. 5, FIG. 7, and FIG. 9, the switching of the liquid crystal is completed within one field period, so that the time for turning on the switching element is shorter than that of the other drive waveforms, and the application to the liquid crystal is performed. A small electric field is required.

In the drive waveforms shown in FIGS. 7, 8 and 9, there is scanning for displaying the liquid crystal display state which is the reverse of the original display state. But to the human eye, 1/10
High-speed blinking of sec or less cannot be recognized, and since it has the characteristic that only the time average of changes in brightness due to blinking can be recognized, the scan time of the target display state and the target display The scanning time for maintaining the state (this time is the display time) is longer than the intended display state and the scanning time for displaying the reverse (this time is the reverse display time) If you do
The intended display state is recognized, and the difference in brightness at this time is (difference in brightness by human eyes) = (length of display time) x
It can be roughly considered as (brightness at display time)-(length of non-display time) x (brightness at non-display time).

As a display method, there are the following three methods for making a difference in brightness between the display time and the non-display time. A. As shown in FIG. 10, the display time is set longer than the non-display time. Make one scan time during display longer than one scan time during non-display B. The number of display scans is greater than the number of non-display scans. C. As shown in FIG. 11, the light intensity of the liquid crystal light source is changed in synchronization with the scanning. The light intensity during the display time is made stronger than the light intensity during the non-display time. D. As shown in FIG. 12, a high-frequency component that the liquid crystal molecules cannot completely switch is superimposed on the electric field applied to the liquid crystal during the non-display time. That is, the liquid crystal molecules are held in the state of almost the display time.

The characteristic of the case of FIG. 10 is that the data line signal is held at the fall of the scan line signal, and that the display waveform is applied so as to cancel the electric field applied to the liquid crystal. The non-display time is shorter than the display time.

FIG. 11 shows data line signals and scan line signals when matrix driving is performed as in FIG.
It shows changes in the light quantity of illumination of the liquid crystal cell at that time. In this figure, regarding the pulse applied to the liquid crystal itself, the signal itself applied to each of the data line and the scan line is no different from that in FIG. In this case, in addition to the characteristic of the timing of applying the electric field in FIG. 10, the light amount of the light source is larger than the other time from the end of scanning of all the scan lines within the display time to the non-display time. It has become.

The characteristics of FIG. 12 are that the data line signal is held at the fall of the scan line signal and that the display waveform is applied so as to cancel the electric field applied to the liquid crystal. That is, a high frequency component is superimposed on the liquid crystal during the display time. In order to apply such a high frequency superposed waveform to the liquid crystal, when the switching element is a TFT, a waveform such that a high frequency is superposed in the non-display time is applied to the counter electrode of the TFT. Good. Further, in the two-terminal element, the waveforms may be synthesized so that the high frequency is superimposed on the signal of the data line during the non-display time. In this case, the amplitude V _hf of the high frequency components applied is, V ₀ is the prerequisites in <V _D -V _hf against V ₀ which two-terminal element.

A. B. In the method described in (1), the difference in the length of the display time and the non-display time leads to the average brightness that the human eye perceives. C. In the method shown in, the difference between the light intensity during the display time of the light source and the light intensity during the non-display time is recognized as the brightness. Therefore, the relationship between the light intensity change of the light source element and the scanning time of each switching element is closely related to the display characteristics. The light source used in this method is shown in FIG.
Although it is ideal to show the light intensity characteristics as shown in, the light source actually used in the liquid crystal is an incandescent bulb whose light intensity changes depending on the applied effective value, a fluorescent lamp, or electroluminescence (EL). There is a device like a lamp that emits light in response to a pulse and then the light intensity decays, but since the scanning time is a few msec, the light source that can be used is a pulse like a fluorescent lamp or EL. Those that respond to this are suitable for this application.

In the case of the fluorescent tube, the light intensity changes as shown in FIG. 14 with respect to the applied pulse for lighting. In a normal liquid crystal display, the fluorescent tube is turned on by a high-frequency pulse in order to eliminate flicker, but in the present invention, a pulse for turning on the fluorescent tube is applied during display time as shown in FIG. However, a method of changing the light intensity is conceivable in which the pulse for lighting the fluorescent tube is not generated during the non-display time. Also, in order to change the brightness stepwise, it is possible to change the brightness within the display time and the brightness during the non-display time by varying the number of pulses for lighting during the scanning time. There is no problem in practical use. In the case of using electroluminescence (EL), the light intensity changes as shown in FIG. 16 with respect to the applied pulse for lighting. Also in this case, as shown in FIG. 15, the fluorescent tube can be driven in the same way.

D. In the method shown in (1), in the case of a display mode (for example, SSFLC) in which the positive / negative of the pulse turns on / off the display, in the case of a liquid crystal material with a negative Δε, the stabilization effect due to superposition of high frequency components is Occurs, and it becomes difficult for switching to occur, and as a result, the ferroelectric liquid crystal molecules do not switch completely, so
The change in transmitted light intensity in the off state is reduced. Also, Δε
In the case of a positive liquid crystal material, the high frequency component causes a perturbation around a stable position on the cone where the liquid crystal molecule can move, so light leakage or scattering always occurs due to the movement of the liquid crystal molecule due to the high frequency component. This is because the amount of light leakage or scattering is smaller than the change in transmitted light intensity in the on / off state in the state where high frequency components are not superimposed. As described above, the cause differs depending on whether the Δε of the liquid crystal material is positive or negative, but since the change in transmitted light intensity during the non-display time is smaller than the change in transmitted light intensity during the display time, it is possible to reduce the contrast when viewed as a display. It is possible to prevent it. In order to display with more contrast as an actual device,
The most effective way is to combine the above three methods.

[Gradation Display] In the present method, one screen is displayed by scanning a large number of times. Therefore, gradation display is performed by time division, that is, each pixel is displayed by each scanning. It is possible to display the gradation by turning on / off and by an on / off pattern in a plurality of fields forming one screen. However, in the present driving method, since the liquid crystal is driven more directly, it is necessary to drive the liquid crystal with a waveform different from that used in the simple matrix shown in FIG. For example, the waveforms shown in FIGS. 17 and 18 are examples.

In the waveform shown in this figure, it is not clear whether the signal for driving the ferroelectric liquid crystal at the edge from the ON state to the OFF state of the switching signal is 0V or not, but the state shown by the liquid crystal is In this case, even when the switching element is in the off state, the display state indicated by the liquid crystal is already determined by the signal for driving the liquid crystal applied when the switching element is in the on state, and therefore, distinction is omitted .. FIG. 17 and FIG.
It is an example of a pattern of an applied pulse when displaying 6 gradations. In this figure, the application timing of the switching signal (gate pulse) is shown at equal intervals. In this case, the gradation 1 and the gradation 2 are observed with the same brightness, but by changing the application timing of the switching signal, 16 gradations can be obtained by utilizing the time difference between the switching signals. The feature of this figure is that the direct current component applied to the liquid crystal is not canceled within one screen, and the scanning time constituting one screen is constant. In the case of this method, when the display cycle of one screen is shortened, it is difficult to make the application timing of the switching signal sufficiently different, and the pattern of 16 gradations may only be able to identify substantially 5 gradations.

Further, by limiting the display state of the liquid crystal to two values of ON / OFF, the display state of the liquid crystal is the ON state or the OFF state even if an electric field having a certain electric field strength or more is applied. By utilizing this, it becomes possible to drive so as to cancel the DC component applied to the liquid crystal when driving the liquid crystal. For example, the method shown in FIGS. 19 and 20 is used.

19 and 20 show examples of the timing of the applied pulse when displaying 16 gradations according to the present method. The feature of this figure is that there is only one scanning time for applying a pulse for canceling the electric field applied to the liquid crystal within one screen, and the electric field applied to the liquid crystal within the cycle for displaying one screen is That is, they are offset and the scanning time that constitutes one screen is constant. Also in the case of this method, FIG. 17 and FIG.
If the display cycle of one screen is shortened in the same way as
In some cases, only 5 gradations can be identified in the gradation pattern.

When performing multi-gradation display, the DC components applied to the cells within the display time are significantly deviated, and in order to cancel them completely, a pulse that is much larger than the pulse applied during the display time is required. May become. In such a case, when a large pulse is applied to the liquid crystal cell, there are many problems in device characteristics such as the orientation being remarkably changed. To prevent such problems,

Instead of applying one large pulse in one non-display time, the pulse is applied in several non-display times within the screen forming time as shown in FIGS. 21 and 22. 21 and 22 are examples of the timing of applied pulses when displaying 16 gradations according to the present method. The feature of this figure is that there is a scanning time for applying a pulse for canceling the electric field applied to the liquid crystal within one screen, and that pulse exists several times within one screen, and That is, the electric fields applied to the liquid crystal are canceled in the cycle of displaying one screen.

There is a method of applying a pulse during the non-display time so as not to completely cancel the pulses applied for the display shown in FIGS. 23 and 24 and FIGS. 25 and 26. 23 and 24 are examples of the timing of the applied pulse when displaying 16 gradations according to the present method. The feature of this figure is that there is only one scanning time for applying a pulse for canceling a part of the electric field applied to the liquid crystal within one screen.

FIG. 25 and FIG. 26 show an example of the timing of the applied pulse when displaying 16 gradations in a state where the electric fields applied to the liquid crystal are not completely cancelled, as in FIGS. 23 and 24. 23 and 24, the pulse for canceling a part of the electric field applied to the liquid crystal has the same level as the on / off signal of the liquid crystal, and is positive in accordance with the display pattern. Alternatively, it means that a negative electric field is applied. As described above, in the present driving method by the element structure in which the ferroelectric liquid crystal of the present invention and the switching element are combined,
Although it has been shown that a new gradation display, which has not been seen before, can be realized, the following two points are the keys to gradation display by this driving method.

How to prevent deterioration of contrast due to non-display pulse applied to liquid crystal? Can be recognized between high-speed blinking patterns as gradations? However, these two problems extend the idea shown in black and white display. You can think about it. That is, the first problem is further alleviated by making the change in the light amount due to ON / OFF of the non-display liquid crystal smaller than the change in the light amount for one scale of gradation during display time.

The second problem is that by changing the weight (the length of the scanning time or the light intensity of the light source) for each of a plurality of scans, the ON / OFF combination is turned on each time. / Can be differentiated off. By differentiating the ON / OFF for each scanning time, for example, the 4 BIT signal necessary for displaying 16 gradations is set to each B
It becomes possible to use IT as ON / OFF of the picture element in each scanning.

In the case of displaying more gradations by this method, the maximum number of gradations that can be displayed is determined by how many scans one screen is displayed. That is, the number of scans for displaying one screen (including the number of scans for canceling the electric field) is m; the maximum number of ^{gray scales} that can be displayed is 2 ^mn , where n is the number of scans for canceling the applied electric field. Become.

When the light intensity of the light source during the time for displaying one screen and the sum of the time are equal, the difference is recognized as a pattern when viewed with the eyes, but the difference in brightness cannot be clearly recognized (the brightness cannot be recognized). However, the number of gray scales that can be actually used may decrease because a phenomenon such as (recognizing an averaged image) occurs. In particular, gradation of the same brightness is generated due to light leakage due to pulses during the non-display time and light loss due to scattering / absorption.

Example 1 [Production of Liquid Crystal Cell] A ferroelectric liquid crystal cell having no switching element (FIG. 27) was produced by the following procedure.

1. On each of the glass substrates 1a and 1b, a plurality of transparent electrodes (2a and 2b) having a thickness of 1000 Å are formed by arranging the electrode patterns in stripes so as to be parallel to each other. The thickness of the transparent electrode can be set in the range of 300 to 5000Å, preferably 1000 to 3000Å.

On the substrate of 2.1, the electrode protective films 3a and 3b are formed.
Is formed with a film thickness of 1000Å. The thickness of the electrode protection film is 300 ~
It can be set to 5000Å, preferably in the range of 500 to 2000Å. SiO ₂ or OCD (OCD P-59310) manufactured by Tokyo Ohka Co., Ltd. was used for the electrode protection film. In the case of SiO ₂ , the electrode protective film was formed by sputtering, and in the case of OCD, the electrode protective film was formed by coating the substrate with a spinner and then firing.

Alignment films 4a and 4b are formed on the substrate of 3.2 400
Form with a film thickness of Å. The alignment film material was formed by applying PSI-XA-2001 (polyimide) manufactured by Chisso Petrochemical Co., Ltd. or RN715 manufactured by Nissan Chemical Co., Ltd. using a spin coater and baking. The thickness of the alignment film can be set in the range of 200 to 1000Å.

The substrate prepared in 4.3 is subjected to a uniaxial orientation treatment by a rubbing method using a rayon cloth. The rubbing direction at this time is such that the rubbing directions are the same when the substrates 9 and 10 are bonded so that the electrode patterns are orthogonal to each other.

Silica beads having a diameter of 3.0 μm are dispersed as spacers 6 between the upper and lower substrates which have undergone the steps of 5.1 to 4 and are bonded by a sealing member 7 made of epoxy resin.

The above-mentioned ferroelectric liquid crystal composition 5 according to the present invention was injected into the panel manufactured through the steps of 6.1 to 5 by a vacuum injection method. After the injection, the injection port was sealed with an acrylic UV curable resin.

[Driving of Liquid Crystal Cell] In order to confirm the driving characteristics of the liquid crystal cell manufactured as described above, a principle experiment was conducted by a sample hold circuit based on the operating principle of the switching element. That is, the switching element is turned on by the sampling state of the sample hold circuit,
The operation state was confirmed by using the OFF state of the switching element and the hold state of the sample hold circuit (hereinafter abbreviated as "hold state").

In this sample hold circuit, the liquid crystal cell is used as a hold capacitor. The sample hold circuit used is a circuit as shown in FIG. FIG. 28 is a circuit diagram of a switching element-liquid crystal cell composite element using a sample and hold circuit that is almost equivalent to an element in which a switching element and a liquid crystal cell are combined. In this circuit, LF398 manufactured by National Semiconductor is used for the sample hold circuit.

Hereinafter, the sampling source signal of the sample-hold circuit is called a "liquid crystal driving signal", the sampling signal is called a "switching signal", and the pulse width of the sampling signal is called a "gate pulse width".

As the ferroelectric liquid crystal cell, the SSF type ferroelectric liquid crystal cell prepared above is used and placed so that the change in transmitted light intensity when a pulse is applied between the polarizing plates in the crossed Nicols is maximized. The change in transmitted light intensity of the cell with respect to the electric field was measured by a phototransistor. Liquid crystal cell switching is a square wave (500Hz) to which the liquid crystal responds.
Normalization is performed by setting the maximum and minimum values of the transmitted light intensity at 1 and 0, respectively. As the light source of the measurement system, a direct current driven incandescent bulb that does not fluctuate in light intensity at high frequencies was used.

Driving Experiment (1) Using BDH-858 (manufactured by BDH) as a liquid crystal material, the voltage applied to the liquid crystal when the liquid crystal drive signal and the switching signal are applied at the timings shown in FIG. The change in transmitted light intensity when the pulse to apply is applied ・ The change in the transmitted light intensity when the pulse to turn off is applied are plotted in FIGS. 30 and 31 (the peak value of the liquid crystal drive signal is ± 5 v ). FIG. 29 schematically shows changes in the electric field applied to the liquid crystal when a switching signal and a liquid crystal drive signal are applied to the circuit of FIG.

FIG. 30 shows the timing of pulses applied to the circuit shown in FIG. 28, the current flowing through the liquid crystal cell, and the optical response when the liquid crystal changes from the OFF state to the ON state.

FIG. 31 shows the timing of the pulses applied to the circuit shown in FIG. 28, the current flowing through the liquid crystal cell, and the optical response when the liquid crystal changes from the ON state to the OFF state. Also, the peak value of the liquid crystal drive signal is ± 5
FIG. 32 is a plot of the average transmitted light intensities of ON and OFF of the display state of the liquid crystal in the hold state when V is V and the pulse width of the switching signal is changed from 0.1 μsec to 1000 μsec. In FIG. 32, the liquid crystal material is BDH-85.
30 shows a change in the light transmittance of the cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG.

When ZLI-3654 (manufactured by Merck) or CS-1024 (manufactured by Chisso) is used as the liquid crystal material, the width of the switching signal in this experimental circuit is 0.1 μsec to 1000 μsec.
FIG. 33 and FIG. 34 are plots of the average transmitted light intensities of ON and OFF of the display state of the liquid crystal in the hold state when the values are changed up to. In Figure 33, the liquid crystal material is ZL.
30 shows changes in light transmittance of the cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 29 in the case of I-3654.

FIG. 34 shows changes in the light transmittance of the cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 29 when the liquid crystal material is CS-1024.

From the above experiment, the following items were confirmed. When switching liquid crystal molecules with spontaneous polarization,
When the picture element is not selected in the circuit, the electric field applied until immediately before is retained by opening the picture element. Because of this effect, it is possible to switch by applying a pulse that is significantly shorter than the pulse width required to switch the material alone by the conventional simple matrix method for the time to apply the electric field to the liquid crystal. Shows. However, the time required for one full scan at this time must be longer than the response time of the liquid crystal.

[Comparative Example] The change in transmitted light intensity of the cell when only the liquid crystal drive signal of FIG. 35 was applied to the ferroelectric liquid crystal was measured. FIG. 36 shows the electric field applied to the liquid crystal when the pulse width of the gate signal is changed and only the liquid crystal drive signal is applied to the liquid crystal cell, and the change in the transmitted light amount of the liquid crystal cell at that time. That is, FIG. 36 shows a change in light transmittance of the cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG.

[Comparative Example] The pulse applied to the liquid crystal prior to the sample hold signal of the sample hold circuit is 0.
The change in transmitted light intensity when applied at the timing shown in FIG. That is, FIG. 37 schematically shows changes in the electric field applied to the liquid crystal when a switching signal and a liquid crystal drive signal are applied to the circuit of FIG. FIG. 38 is a plot of the transmitted light intensity of the liquid crystal when the pulse width of the gate signal at that time is changed.
Is. That is, FIG. 38 shows changes in the light transmittance of the cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG.

[Comparative Example] The timing shown in FIG. 39 in which the pulse applied to the sample hold circuit is changed to a bipolar pulse and the pulse applied to the liquid crystal before the sample hold signal of the sample hold circuit becomes 0v. The change in the transmitted light intensity when the voltage was applied was measured. FIG. 39 shows
FIG. 29 is a schematic diagram showing changes in the electric field applied to the liquid crystal when a switching signal and a liquid crystal drive signal are applied to the circuit of FIG. 28. FIG. 40 is a plot of the transmitted light intensity of the liquid crystal when the pulse width of the gate signal at that time is changed. That is, FIG. 40 shows a change in light transmittance of the liquid crystal cell with respect to a switching signal when an electric field is applied at the timing shown in FIG. 39. In each of the above comparative examples, it is shown that at least a pulse having a width corresponding to the memory pulse width is required to switch the liquid crystal because the electric field is not held.

Driving Experiment (2) The change of the transmitted light intensity was similarly examined by changing the timing of the pulse applied to the sample hold circuit to the waveform shown in the figure. When BDH-858 (manufactured by BDH) is used as the liquid crystal material, the pulse width of the sampling signal can be changed from 0.1 μsec.
FIG. 41 shows a change in transmitted light intensity of the liquid crystal cell with respect to a pulse applied at the timing of FIG. 41 when the voltage of the liquid crystal drive signal is ± 10 after changing to 1000 μsec. Figure 4
FIG. 1 schematically shows changes in the electric field applied to the liquid crystal when a switching signal and a liquid crystal drive signal are applied to the circuit of FIG.

Differences caused by applying a pulse at the timing shown in the figure when the transmitted light change amount in a rectangular wave (500 Hz) at which the liquid crystal can respond to the pulse width of the sampling signal for each liquid crystal material is set to 1. Intensity of transmitted light in four hold states, that is, (1) Hold state immediately after applying a pulse to turn on (2) Hold state sampled at 0V after on state (3) Pulse to turn off Hold state immediately after application of (4) Hold state sampled at 0 V after the off state is plotted in FIG. That is, FIG.
Is the light transmittance in the state where the applied electric field of the cell with respect to the switching signal when the electric field is applied to the liquid crystal cell at the timing shown in FIG. 39, and is set high again when the applied electric field becomes zero. The initial state of the light transmittance in the impedance state shows a change from the ON state and the OFF state. The following items were confirmed from the results of FIG. 42.

In this case, the optical response is caused by the first liquid crystal driving signal, and when the switching element is operated next, the electric field applied to the liquid crystal is discharged, so that the direct current component applied to the liquid crystal is reduced. It becomes possible to drive. By combining the TFT and the SSFLCD, the scanning time for displaying one screen can be made shorter than that of the simple matrix type SSFLCD. Since the memory property of the liquid crystal itself is used for the alignment state of the liquid crystal used for display, the applied electric field can be small.

[Comparative Example] The change of the transmitted light intensity was similarly examined by changing the timing of the pulse applied to the sample hold circuit to the waveform shown in FIG. FIG. 44 is a plot of the transmitted light intensity of the liquid crystal when the pulse width of the gate signal is changed when the display time = non-display time. That is, FIG. 43 shows the circuit of FIG. 28 at the pulse timing such that the display time and the non-display time are equal.
It is a diagram schematically showing changes in the electric field applied to the liquid crystal when a switching signal and a liquid crystal drive signal are applied,
FIG. 44 shows changes in the light transmittance of the cell with respect to the switching signal when the liquid crystal cell electric field is applied at the timing shown in FIG. In FIG. 44, since the display time and the non-display time are equal to each other, an optical response occurs, but the brightness as one screen is averaged so that the transmitted light intensity is almost 50% and the clear display is obtained. It means that the on / off of is not obtained.

Driving Experiment (3) The change of the transmitted light intensity was similarly examined by changing the timing of the pulse applied to the sample hold circuit to the waveform shown in FIG. FIG. 46 is a plot of the transmitted light intensity of the liquid crystal when the pulse width of the gate signal at that time is changed.
Is. That is, FIG. 45 shows a case where the display time and the non-display time are equal and the switching signal and the liquid crystal drive signal are applied to the circuit of FIG. 28 at the timing of the waveform and the pulse in which the high frequency is superimposed on the non-display time. 46 schematically shows changes in the electric field applied to the liquid crystal of FIG.
47 shows changes in the light transmittance of a cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 45 and 46 show FIGS. 43 and 44.
Similarly, the display time and the non-display time are equal,
Since the high frequency is superposed during the non-display time, when the movement of the molecules of the liquid crystal is the liquid crystal (Δε> 0) used in this embodiment, the molecules themselves try to move, but The frequency is high and the molecules cannot follow the electric field to switch completely. Therefore, the optical change during the non-display time is sufficiently smaller than the change in the display time. That is, although an effective electric field for canceling the DC component is applied, the liquid crystal molecules do not move following this and an optical change hardly occurs.

In this case, the high frequency wave superposed on the liquid crystal should be at least shorter than the time required for the optical change of the liquid crystal to be 50% (preferably shorter than the time required for the optical change of 10%). Desired. In the case of the liquid crystal material used in this example, the response time of the liquid crystal is 80 μsec.
Therefore, the pulse width of the high frequency is required to be at least 50 μsec or less. In the embodiment, the superimposed high frequency pulse width is 3 μsec (frequency 167 KHz, Vpp = ±
5V).

Driving Experiment (4) The change of the transmitted light intensity was similarly examined by changing the timing of the pulse applied to the sample hold circuit to the waveform shown in FIG. FIG. 48 is a plot of the transmitted light intensity of the liquid crystal when the pulse width of the gate signal is changed at that time.
Is. That is, FIG. 47 shows the electric field applied to the liquid crystal when the switching signal and the liquid crystal drive signal are applied to the circuit of FIG. 28 at the pulse timing such that the length of the non-display time becomes shorter than the display time. FIG. 48 schematically shows the change, and FIG. 48 shows the change in the light transmittance of the cell with respect to the switching signal when the liquid crystal cell electric field is applied at the timing shown in FIG. 47. FIG. 48 shows an optical change when the display time and the non-display time have different lengths. When the length of non-display time relative to the display time is display time: non-display time = 10 msec: 5 msec, the optical change is from 33% (1/3) to 66%
It occurs in the range of (2/3).

Driving Experiment (5) The change of the transmitted light intensity was similarly examined by changing the timing of the pulse applied to the sample hold circuit to the waveform shown in FIG. FIG. 50 is a plot of the transmitted light intensity of the liquid crystal when the pulse width of the gate signal at that time is changed.
Is. That is, in FIG. 49, the timing of the switching signal and the liquid crystal drive signal applied to the circuit of FIG. 28 for displaying four gradations without canceling the electric field applied to the liquid crystal (the scanning time is different). Driving method) for each gradation, and FIG. 50 shows a change in light transmittance of each gradation cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. It is shown. In addition, in FIG. 49, the first scanning time: the second scanning time = 5 msec: 10 msec. Further, in FIG. 50, since the liquid crystal driving method does not have the non-display time for canceling the electric field, it is not necessary to reduce the light intensity in the bright state and the dark state, and the optical change is gradation 0. Is 1%, gradation 1 is 33%, gradation 2 is 67%, and gradation 3 is 100%. In addition, four gradations with different transmitted light intensities are obtained by two scans forming one screen.

Driving Experiment (6) The change of the transmitted light intensity was similarly examined by changing the timing of the pulse applied to the sample hold circuit to the waveform shown in FIG. FIG. 52 is a plot of the transmitted light intensity of the liquid crystal when the pulse width of the switching signal at that time is changed. FIG. 51 shows a drive waveform provided with a non-display time for canceling the applied electric field. Here, the display time on the front side of the non-display time is 4 msec, the display time on the rear side of the non-display time is 8 msec, and the non-display time is 2 msec. The waveforms shown in the examples cannot completely cancel out the electric field applied to the liquid crystal cell.

FIG. 52 shows changes in transmitted light intensity due to driving with the waveform shown in FIG. 51. The transmittance in the operating state of each gradation is 15% at gradation 0 and 43 at gradation 1. %, Gradation 2 is 57%, and gradation 3 is 86%. Since the non-display time for canceling the electric field applied to the liquid crystal is provided, light intensity loss occurs in both the bright state and the dark state, so that the optical dynamic range is narrowed. In addition, four gradations (2 ^3-1 gradations) having different transmitted light intensities are obtained by scanning three times (3 fields) that form one screen.

Driving Experiment (7) The characteristics were examined with a structure in which the light intensity of the light source was synchronized with the signal for driving the liquid crystal cell. A fluorescent lamp was used as the light source. The timing of the pulse applied to the sample hold circuit and the change in the light intensity of the light source in this case is as shown in FIG. 53. The change in the transmitted light intensity at this time was examined. FIG. 54 is a plot of the transmitted light intensity of the liquid crystal when the pulse width of the switching signal at that time is changed. That is, FIG. 53 shows a switching signal applied to the circuit of FIG. 28 for displaying four gradations by changing the intensity of the illumination light of the liquid crystal in synchronization with the pulse applied to the liquid crystal panel.
FIG. 54 schematically shows changes in the liquid crystal drive signal and the liquid crystal light source. FIG. 54 shows the light transmittance of each gradation cell with respect to the switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. It shows the changes.

The characteristic of this experiment is that the brightness of the backlight is changed in synchronization with the drive signal of the liquid crystal. The driving frequency of the backlight during the display time before the non-display time was set to 25 Hz. The backlight for the display time on the rear side of the non-display time does not apply the driving pulse of the backlight for 2 msec at the beginning of the display time on the rear side, and the drive frequency of the backlight for 2 msec or more from the beginning of the display time on the rear side. Is 5
It is set to 0 Hz, and the application of the driving pulse of the backlight is stopped during the non-display time.

In FIG. 54, the liquid crystal switching itself is the same as that in FIG. 52, but the brightness of the screen changes due to the change in the driving frequency of the light source, so that the difference in the transmitted light intensity between the gradations can be made large. ing. In this case, gradation 0 is 50
%, Gradation 1 is 35%, gradation 2 is 65%, gradation 3 is 90%
% (100% of the transmitted light intensity is based on the brightness when the backlight drive frequency is 25 KHz).

Example 2 [Fabrication of TFT Matrix Cell] FIGS. 55 and 56 are sectional views of a ferroelectric liquid crystal cell using an amorphous silicon TFT, and FIG. 57 is a perspective view of a TFT substrate. Shows the panel structure of the present invention. This liquid crystal cell was produced as follows.

1. A Ta film was formed on the glass or plastic substrate 31 by sputtering and patterned into a predetermined shape to form a gate wiring 32 and a gate electrode 35. An insulating film 33 is formed on the substrate of 2.1 by plasma CVD.
(SiNx), semiconductor film 40 (a-Si), n + layer 41
(Phosphorus-doped a-Si) is formed to form the semiconductor film 4
0 (a-Si), n + layer 41 (phosphorus-doped a-S
i) was patterned. An ITO film was formed on the substrate of 3.2 by sputtering and patterned to form a pixel electrode 37. A Ti film is formed on the substrate of 4.3 by sputtering and patterned to form a source electrode 36 and a drain electrode 38.
Formed. An insulating layer 42 (SiO ₂ ) having a thickness of 500 Å was formed on the substrate of 5.4. The light shielding layer 44 was formed on the substrate of 6.5.

7. A counter electrode 45 made of an ITO film was formed on another substrate by sputtering. An insulating layer 42 (SiO ₂ ) having a thickness of 500 Å was formed on the substrate of 8.7. Insulation layer thickness is 300 ~ 5000Å, preferably
It can be set in the range of 500 to 2000Å. An alignment layer 43 (PSI-XA-2001 (manufactured by Chisso Petrochemical Co., Ltd.) or RN715 (manufactured by Nissan Chemical Co., Ltd.)) is formed on the substrates of 9.6 and 8 to a thickness of 400 Å using a spin coater (46, 4).
7). Alignment layer thickness is 100-5000Å, preferably 500-
It can be set in the range of 2000Å. The substrates 46 and 47 prepared in 10.9 are uniaxially oriented by rubbing using a rayon cloth. The rubbing direction at this time is such that the rubbing directions are the same when the substrates 46 and 47 are bonded together. 3.0 μm in diameter between the upper and lower substrates after 11.1-10 steps
Disperse the silica beads of and paste them together with a sealing member made of epoxy resin. 12. The ferroelectric liquid crystal composition of the present invention was injected into the panel prepared through the above steps by a vacuum injection method. After the injection, the injection port was sealed with an acrylic UV curable resin.

Driving Experiment (1) FIG. 58 shows the timing of the pulses applied to the gate, source and common terminals of the cell in which the above TFT is formed.
The change in the transmitted light intensity was examined in the same manner by changing to the waveform shown in.
That is, FIG. 58 shows the timing of the signals applied to the gate, source and common electrodes of the TFT panel and the electric field applied to the liquid crystal when a high frequency is superimposed during the non-display time.

FIG. 59 is a plot of the transmitted light intensity of the liquid crystal when the pulse width of the gate signal is changed at that time.
Is. That is, FIG. 59 shows changes in the light transmittance of the cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG.

A feature of this experiment is that a high frequency is applied to the liquid crystal from the common terminal during the non-display time. Here, the high frequency superimposed from the common terminal during the non-display time is
Vpp = ± 5V at a frequency of 250KHz, display time,
The non-display time was 4 msec. Although FIG. 59 does not operate with a gate signal of 1 μsec or less obtained by performing the equivalent circuit up to then, switching is performed with a gate signal width shorter than the optical response of the liquid crystal material, and high frequency is applied. It is shown that the overlapping method can obtain the difference in optical equivalent light intensity even in an actual TFT panel. The transmitted light intensity here is about 22% in the off state and about 79% in the on state.

Driving Experiment (2) Further, the timing of the pulse applied to the gate, source and common terminals of this cell was changed to the waveform shown in FIG. FIG. 61 is a plot of the transmitted light intensity of the liquid crystal when the pulse width of the gate signal is changed at that time. That is, FIG.
Is an address TFT whose non-display time is longer than display time.
FIG. 61 shows timings of signals applied to the gate, source and common electrodes of the panel and electric field applied to the liquid crystal. FIG. 61 shows switching signals when the electric field is applied to the liquid crystal cell at the timing shown in FIG. It shows changes in light transmittance of the cell.

A feature of this experiment is that the display time length and the non-display time length are different, and the display time length and the non-display time length used in the examples are 9 msec and 3 ms, respectively.
ec. FIG. 61 shows that although the gate signal of 1 μsec or less obtained by the equivalent circuit up to now does not operate, switching is performed with a gate signal width shorter than the optical response of the liquid crystal material and the display time. It is shown that the difference in optical equivalent light intensity can be obtained even in an actual TFT panel by the time difference between the non-display time and. The transmitted light intensity here has a value of about 25% in the off state and about 75% in the on state.

Driving Experiment (3) The change of the transmitted light intensity was similarly examined by changing the timing of the pulse applied to each of the gate, source and common terminals of this cell to the waveform shown in FIG. FIG. 63 is a plot of the transmitted light intensity of the liquid crystal when the pulse width of the gate signal is changed at that time. That is, FIG. 62 shows the timing of the switching signal and the liquid crystal driving signal applied to the gate, source, and common electrodes of the TFT panel for displaying four gradations without canceling the electric field applied to the liquid crystal (each scanning time). FIG. 63 schematically shows different driving methods) for each gradation, and FIG. 63 shows the light transmittance of each gradation cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. It shows the change of.

The feature of this experiment is that the electric field applied to the liquid crystal has a waveform that is not canceled at all. The lengths of the first half display time and the second half display time used here are 4 msec and 8 msec, respectively. The feature of FIG. 63 is that
Although it does not operate with a gate signal of 1 μsec or less obtained by the equivalent circuit up to that point, switching is performed with a gate signal width shorter than the optical response of the liquid crystal material, and four gradations are obtained. It is a thing. Further, the optical change is 0% for gradation 0, 33% for gradation 1 and 6 for gradation 2.
7% and gradation 3 becomes 100%. In addition, four gradations with different transmitted light intensities are obtained by two scans forming one screen. However, in a situation where the same image is displayed for a long time, a large DC component is applied to a specific part, so this driving method is not preferable.

Driving Experiment (4) The change of the transmitted light intensity was similarly examined by changing the timing of the pulse applied to the gate, source and common terminals of this cell to the waveform shown in FIG. That is, FIG.
The gate and source of the TFT panel for displaying four gradations with a combination of waveforms that cancel the electric field applied to the liquid crystal,
The timings of the switching signals applied to the common electrode and the liquid crystal driving signals (driving methods such that the scanning times are different) are schematically shown for each gradation.

FIG. 65 is a plot of the transmitted light intensity of the liquid crystal when the pulse width of the gate signal at that time is changed.
Is. That is, FIG. 65 shows a change in the light transmittance of the cell of each gradation with respect to the switching signal when the electric field is applied to the liquid crystal cell at the timing shown in FIG.

This experiment is characterized in that a non-display time for applying a pulse for canceling the electric field applied to the liquid crystal is provided, and the display time on the front side, the display time on the rear side, and the non-display time are set. The length was 4 msec, 8 msec, and 2 msec, respectively. As shown in FIG. 65, the characteristic of this experiment is that the gate signal width is shorter than the optical response of the liquid crystal material, although it does not operate with the gate signal of 1 μsec or less obtained by the equivalent circuit up to that point. That is, switching is performed with 4 gradations. The optical changes are as follows: gradation 0 is 14%, gradation 1 is 43%, and gradation 2 is 57%.
%, Gradation 3 is 86%. In addition, four gradations (2 ^3-1 gradations) having different transmitted light intensities are obtained by scanning three times forming one screen. However, when the waveform shown in FIG. 64 is applied in the pulse setting of this embodiment, the electric fields are not completely canceled out.

From the experimental results in the above Examples 1 and 2, the following matters were mainly clarified. By turning off the switching element while applying an electric field to the liquid crystal, the screen can be scanned with a gate signal that is shorter than the time required for the liquid crystal molecules to optically switch.・ In order to reduce the brightness change of the display due to the brightness change of the non-display time within the cycle of displaying the electric field applied to the liquid crystal on one screen, the non-display time is shortened with respect to the display time. It is effective to change the light intensity of the light source in synchronization with the scanning of the panel. -By setting the difference in the transmitted light intensity of the liquid crystal in each of the m times of scanning to display one screen, the maximum number of gradations 2 ^m that can be output in the number of scans to display one screen can be displayed. It is possible.

[0115]

The effect of the invention is to use a liquid crystal having spontaneous polarization.
The switching element is energized for a time shorter than the response time of the liquid crystal to charge the liquid crystal, and the liquid crystal molecules are driven by the charged electric field, whereby the scanning speed is increased and one screen is formed by combining a plurality of fields. Therefore, it is possible to obtain a screen with a plurality of gradations by combining the fields.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an electric field applied to a data line and a scan line and an electric field applied to each picture element of a liquid crystal cell when a simple matrix drive is performed.

FIG. 2 is a waveform diagram showing characteristics of an active matrix liquid crystal display device having TFT elements.

FIG. 3 is a device characteristic diagram of a two-terminal device.

FIG. 4 is a waveform diagram showing characteristics of an active matrix liquid crystal display device having a two-terminal element.

FIG. 5 is a diagram showing an electric field applied to a data line and a scan line in the case of matrix driving according to the present invention;
It is a wave form diagram which showed the electric field applied to the liquid crystal at that time.

FIG. 6 is a waveform diagram showing a comparative example of a data line signal and a scan line signal in the case of matrix driving, and a data line applied to the liquid crystal at that time.

FIG. 7 is a waveform diagram showing a data line signal and a scan line signal in the case of matrix driving and an electric field applied to the liquid crystal at that time in the present invention.

FIG. 8 is a waveform diagram showing a comparative example of a data line signal and a scan line signal in the case of matrix driving, and an electric field applied to the liquid crystal at that time.

FIG. 9 is a waveform diagram showing a data line signal, a scan line signal in the case of matrix driving and an electric field applied to the liquid crystal at that time in the present invention.

FIG. 10 is a waveform diagram showing a data line signal, a scan line signal in the case of matrix driving and an electric field applied to the liquid crystal at that time in the present invention.

FIG. 11 is a waveform diagram showing a data line signal and a scan line signal in the case of matrix driving in the present invention, and changes in the light amount of illumination of the liquid crystal cell at that time.

FIG. 12 is a waveform diagram showing a data line signal, a scan line signal in the case of matrix driving and an electric field applied to the liquid crystal at that time in the present invention.

FIG. 13 is a waveform diagram showing an ideal light amount change method of the light source when synchronizing the light amount change of the light source with the scanning of the switching element.

FIG. 14 is a waveform diagram showing a change in light intensity of the fluorescent tube when the fluorescent tube is caused to emit light by a pulse.

FIG. 15 is a waveform diagram showing an example of how to change the light amount of the light source with respect to the timing of the pulse applied to the switching element of the liquid crystal panel when the fluorescent tube is used as the illumination light of the liquid crystal.

FIG. 16 is a waveform diagram showing a drive signal of an EL element when the EL element emits light and a change in light intensity at that time.

FIG. 17 is a waveform diagram showing the timing of applied pulses when displaying 16 gradations in a form in which the electric fields applied to the liquid crystal are not completely canceled in the present invention.

FIG. 18 is a waveform chart showing the timing of applied pulses when displaying 16 gray scales, in addition to FIG. 17 in the present invention.

FIG. 19 is a waveform diagram showing the timing of the applied pulse when displaying 16 gradations in the present invention.

20 is a waveform chart showing the timing of applied pulses in the case of displaying 16 gradations, together with FIG. 19 in the present invention.

FIG. 21 is a waveform diagram showing the timing of applied pulses when displaying 16 gradations in the present invention.

22 is a waveform chart showing the timing of the applied pulse when displaying 16 gradations, in addition to FIG. 21 in the present invention.

FIG. 23 is a waveform diagram showing the timing of applied pulses when displaying 16 gradations in the present invention.

24 is a waveform chart showing the timing of the applied pulse when displaying 16 gray scales, together with FIG. 23 in the present invention.

FIG. 25 is a waveform chart showing the timing of applied pulses when displaying 16 gradations in a form in which the electric fields applied to the liquid crystal are not completely canceled in the present invention.

FIG. 26 is a waveform chart showing the timing of applied pulses in the case of displaying 16 gradations in a form in which the electric fields applied to the liquid crystal are not completely canceled, together with FIG. 25 in the present invention.

FIG. 27 is a cross-sectional structural diagram of a liquid crystal cell.

FIG. 28 is a circuit diagram of a switching element-liquid crystal cell composite element by a sample hold circuit which is substantially equivalent to an element in which a switching element and a liquid crystal cell are combined.

29 is a waveform diagram schematically showing changes in the electric field applied to the liquid crystal when a switching signal and a liquid crystal drive signal are applied to the circuit of FIG. 28.

30 is a waveform diagram showing the timing of pulses applied to the circuit shown in FIG. 28, the current flowing in the liquid crystal cell, and the optical response when the liquid crystal changes from the OFF state to the ON state.

31 is a waveform diagram showing the timing of pulses applied to the circuit shown in FIG. 28, the current flowing through the liquid crystal cell, and the optical response when the liquid crystal changes from the ON state to the OFF state.

32 is a characteristic diagram showing a change in light transmittance of a cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG.

FIG. 33 is a characteristic diagram showing a change in light transmittance of a cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 29.

FIG. 34 is a characteristic diagram showing a change in light transmittance of a cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 29.

FIG. 35 is a waveform diagram showing an electric field applied to a liquid crystal when only a liquid crystal drive signal is applied to the liquid crystal cell and a response of the liquid crystal cell at that time.

FIG. 36 is a characteristic diagram showing a change in light transmittance of a cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 35.

37 is a waveform diagram schematically showing changes in the electric field applied to the liquid crystal when a switching signal and a liquid crystal drive signal are applied to the circuit of FIG.

38 is a characteristic diagram showing a change in light transmittance of a cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 37.

FIG. 39 is a waveform diagram schematically showing changes in the electric field applied to the liquid crystal when a switching signal and a liquid crystal drive signal are applied to the circuit of FIG. 28.

40 is a characteristic diagram showing a change in light transmittance of a cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 39.

41 is a waveform diagram schematically showing changes in the electric field applied to the liquid crystal when a switching signal and a liquid crystal drive signal are applied to the circuit of FIG. 28.

42 is a characteristic diagram showing the relationship between the switching signal and the applied electric field of the cell when the electric field is applied to the liquid crystal cell at the timing shown in FIG. 39.

43A and 43B are schematic diagrams showing changes in the electric field applied to the liquid crystal when a switching signal and a liquid crystal drive signal are applied to the circuit of FIG. 28 at pulse timings such that the display time and the non-display time are equal. It is the wave form diagram shown typically.

44 is a characteristic diagram showing a change in light transmittance of a cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 43.

45 is a liquid crystal in which the switching time and the liquid crystal drive signal are applied to the circuit of FIG. 28 at the timing of the waveform and the pulse in which the display time and the non-display time are equal and the high frequency is superimposed on the non-display time. FIG. 6 is a waveform diagram schematically showing a change in electric field applied to the.

46 is a characteristic diagram showing a change in light transmittance of a cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 45.

FIG. 47 is a schematic diagram showing changes in the electric field applied to the liquid crystal when a switching signal and a liquid crystal drive signal are applied to the circuit of FIG. 28 at the timing of a pulse such that the non-display time is shorter than the display time. It is the wave form diagram shown typically.

48 is a characteristic diagram showing a change in light transmittance of a cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 47.

FIG. 49 schematically shows, for each gradation, the timing of a switching signal and a liquid crystal driving signal applied to the circuit of FIG. 28 for displaying four gradations without canceling the electric field applied to the liquid crystal. It is a waveform diagram.

50 is a characteristic diagram showing a change in light transmittance of cells of each gradation with respect to a switching signal when an electric field is applied to the liquid crystal at the timing shown in FIG. 49.

51 is a timing chart of switching signals and liquid crystal driving signals applied to each gradation for the circuit of FIG. 28 for displaying four gradations with a combination of waveforms that cancel the electric field applied to the liquid crystal. It is the waveform diagram shown typically.

52 is a characteristic diagram showing changes in light transmittance of cells of each gradation with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 51.

FIG. 53 is a view for displaying four gradations by changing the intensity of the illumination light of the liquid crystal in synchronization with the pulse applied to the liquid crystal panel.
9 is a waveform diagram showing a switching signal applied to the circuit of FIG.

54 is a characteristic diagram showing a change in light transmittance of cells of each gradation with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 53.

FIG. 55 is a cross-sectional view of a typical TFT element.

FIG. 56 is a cross-sectional view of a typical TFT element.

FIG. 57 is a perspective view of a typical TFT element.

[FIG. 58] TF in the case where a high frequency is superimposed on a non-display time
FIG. 6 is a waveform diagram showing timings of signals applied to gates, sources and common electrodes of a T panel and electric fields applied to liquid crystals.

59 is a characteristic diagram showing a change in light transmittance of a cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 58.

FIG. 60: TF when non-display time is longer than display time
FIG. 6 is a waveform diagram showing timings of signals applied to gates, sources and common electrodes of a T panel and electric fields applied to liquid crystals.

FIG. 61 is a characteristic diagram showing a change in light transmittance of a cell with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 60.

FIG. 62 shows timings of switching signals and liquid crystal driving signals applied to the gate, source and common electrodes of a TFT panel for displaying four gradations without canceling the electric field applied to the liquid crystal, for each gradation. It is the waveform diagram shown typically.

63 is a characteristic diagram showing changes in light transmittance of cells of each gradation with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 62.

FIG. 64 is a timing chart of a switching signal and a liquid crystal driving signal applied to the gate, source and common electrodes of a TFT panel for displaying four gradations with a combination of waveforms that cancel the electric field applied to the liquid crystal. FIG. 6 is a waveform diagram schematically showing each gradation.

65 is a characteristic diagram showing changes in light transmittance of cells of each gradation with respect to a switching signal when an electric field is applied to the liquid crystal cell at the timing shown in FIG. 64.

FIG. 66 is an equivalent circuit diagram of an active matrix liquid crystal display device applied to the present invention.

[Explanation of symbols]

 LC liquid crystal S 3 terminal switching element P 2 terminal switching element

Claims (7)

[Claims] 1. A method for driving an active matrix liquid crystal display device, comprising: switching elements connected to scan lines and data lines; and pixel electrodes for applying an electric field to liquid crystal through the switching elements are arranged in a matrix. A liquid crystal with spontaneous polarization is used as the liquid crystal, and the switching element is energized for a time shorter than the response time of the liquid crystal to charge the liquid crystal, thereby driving the liquid crystal molecules, and at the same time, the liquid crystal of the pixel electrode corresponding to all scan lines. Driving one line at a time to form one field, and combining a plurality of fields continuously to form one screen to obtain a screen of a plurality of gradations. Driving an active matrix liquid crystal display device. Method. 2. The method for driving an active matrix liquid crystal display device according to claim 1, wherein the scanning times of the fields forming one screen are equal to each other. 3. The method of driving an active matrix liquid crystal display device according to claim 1, wherein the scanning times of the fields forming one screen are different from each other. 4. A screen is formed by n fields, and 2 fields are formed.
^The method of driving an active matrix liquid crystal display device according to claim 3, wherein a screen with ⁿ gradations is obtained. 5. The method of driving an active matrix liquid crystal display device according to claim 1, wherein the polarities and magnitudes of the electric fields applied to the liquid crystal are set so as to cancel each other out within the display time of one screen. 6. The method of driving an active matrix liquid crystal display device according to claim 1, wherein the polarities and magnitudes of the electric fields applied to the liquid crystal are set so as to cancel each other out within a display time of a plurality of screens. 7. The method of driving an active matrix liquid crystal display device according to claim 1, wherein a high frequency pulse having a period shorter than the response time of the liquid crystal is applied to the liquid crystal so that the electric field applied to the liquid crystal is canceled.