JPH0784240A - Ferroelectric liquid crystal display device - Google Patents

Abstract

PURPOSE:To realize high-grade continuous gradation display free from flickers by making the layer orientation in the chiral smectic C phase of ferroelectric liquid crystals into C2 uniform orientation. CONSTITUTION:Orientation control layers are formed on at least one substrate of a pair of substrates and at least one of a pair of the substrates are subjected to a rubbing treatment. The layer orientation in the chiral smectic C phase of the ferroelectric liquid crystals is the C2 uniform (C2U) orientation. Voltages of different polarities are applied to the ferroelectric liquid crystals by each of pixels corresponding to scanning electrode groups or signal electrode groups of the first frame of the two continuous display frames having the pixels including the ferroelectric liquid crystals driven by a prescribed number of the scanning electrode groups and the signal electrode groups and voltages of the polarities reverse from the polarities of the first frame are applied to the pixels in the second frame. Namely, the ratio of the transmitted light intensity at the time of applied the positive voltage and at the time of applying the negative voltage is smaller in the CPU orientation than in the C1 uniform (C1U) orientation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric liquid crystal display device. More specifically, the present invention relates to a ferroelectric liquid crystal display device capable of gradation display, and a ferroelectric liquid crystal display device that drives this using an active element such as a thin film transistor.

[0002]

2. Description of the Related Art At present, liquid crystal display devices are used in a wide variety of fields such as timepieces, calculators, office automation equipment such as word processors and personal computers, pocket televisions, etc. Generally, widely used liquid crystal display devices are nematic phase. Is used.

A liquid crystal display device using a nematic phase is a twisted nematic type (Twisted Ne).
TN type liquid crystal display device, Super twisted birefring type
and the like (effect effect, SBE type) liquid crystal display device.

However, the twisted nematic (TN) type liquid crystal display device has a drawback that the driving margin becomes narrower as the number of scanning lines increases and a sufficient contrast cannot be obtained. Therefore, a large-capacity display device is manufactured. It is difficult. In order to improve this TN type liquid crystal display device, super twisted nematic (STN)
Type liquid crystal display device and double layer super twisted nematic (DSTN) type liquid crystal display device have been developed. However, since the contrast and response speed decrease as the number of lines increases, the display capacity of about 800 × 1024 lines is currently the limit. Is. In addition, TN type, STN type, D
A display element using a nematic phase such as STN type has a big drawback that the viewing angle is narrow. Further, neither good contrast nor response speed can be obtained.

On the other hand, a thin film transistor (TF) is formed on the substrate.
An active matrix type liquid crystal display device in which T) is arranged has also been developed, and a large capacity display of 1000 × 1000 lines and the like has become possible and high contrast has been obtained. , There was a problem in terms of response speed.

Therefore, as a device for improving the liquid crystal display device using such a nematic liquid crystal, in 1980, Clarke (NA Clark) and La Gabal (S.T.
Lagerwall) has proposed a liquid crystal display device using a chiral smectic C liquid crystal, that is, a ferroelectric liquid crystal (Japanese Patent Laid-Open No. 56-107216;
U.S. Pat. No. 4,367,924). This liquid crystal display device
Unlike the above-mentioned liquid crystal display device that uses the electric field effect that utilizes the dielectric anisotropy of liquid crystal molecules, a liquid crystal display that uses a rotational force that matches the polarity of the spontaneous polarization of the ferroelectric liquid crystal with the polarity of the electric field. It is a device. The features of this liquid crystal device include bistability, memory property, and high-speed response. That is, when the ferroelectric liquid crystal is injected into a cell having a thin gap, the spiral structure of the ferroelectric liquid crystal is unraveled by the influence of the interface, and as shown in FIG.
A region in which liquid crystal molecules 18 having a direction (perpendicular to the plane of the drawing) are inclined and stabilized with respect to the smectic layer normal 17 by a tilt angle + θ19 and a region in which the liquid crystal molecules 18 are stabilized by being inclined by −θ20 in the opposite direction are bistable. Have sex. By applying a voltage 16 (perpendicular to the paper surface) to the ferroelectric liquid crystal in this cell, the liquid crystal molecules and their spontaneous polarization directions can be made uniform as shown in FIG. 1 (b). it can. In addition, by switching the polarity of the applied voltage, as shown in FIG.
As shown in (c), the orientation of the liquid crystal molecules can be aligned in the opposite direction to that in FIG. 1 (b). With the switching drive, the birefringent light changes in the ferroelectric liquid crystal in the cell, so that the transmitted light can be controlled by sandwiching the cell between two polarizers. Further, as shown in FIG. 1D, even if the voltage application is stopped, the alignment of the liquid crystal molecules is maintained in the state before the voltage application is stopped by the alignment regulating force of the interface, so that the memory effect can be obtained. . In addition, the time required for switching driving is 1/1000 that of the TN type liquid crystal display device because the spontaneous polarization of the liquid crystal and the electric field directly act on it.
It has the following high-speed response, which enables high-speed display.

However, although the display device using the ferroelectric liquid crystal has an advantage that it can display at high speed, it has the drawback that it is difficult to obtain a uniform alignment exhibiting a high contrast, and it is difficult to display gradation. Also holds. Although various methods have been proposed for gradation display in a Clark-Ragabar type display device, one of the promising methods is as follows: JP-A-3-242624, JP-A-3-243915 Mori, et al. 3K111 (1990) Toyota et al., 16th Liquid Crystal Conference, 3K112 (199)
0). Matsui et al., 17th Liquid Crystal Debate, 3F301 (199)
1). K. Nito et al., Proc. IDRC, 179 (199)
1). There is a method disclosed in.

In these methods, an AC voltage is applied to a uni-stable Clarke-Ragaval cell, and the halftone display is performed by uniquely changing the molecular axis direction of liquid crystal molecules according to the magnitude of the voltage. . FIG. 2 shows the principle of this mode. When no voltage is applied, the molecule is at position 101, and when a voltage is applied to it, the molecule moves to the right or left depending on its polarity. When a sufficiently high voltage is applied, the molecule becomes 1
The molecule moves to the 02 or 103 position, but when the voltage is lower than that, the molecule stays at the intermediate position. Therefore, for example, if the polarization axis of one of the polarizing plates is aligned with the position of 101 and the polarization axis of the other polarizing plate is aligned with this, a halftone display can be obtained. It should be noted here that FIG. 2 is a simplified diagram for understanding this mode, and in an actual ferroelectric liquid crystal cell, the molecular axis direction of liquid crystal molecules is from the upper surface of the substrate. It must be mentioned that the bottom surface is not uniform and is twisted. FIG. 3 shows the relationship between the voltage and the tilt angle, and FIG. 4 shows the relationship between the applied voltage and the amount of transmitted light, and it can be seen that halftone display can be performed. It should be noted that according to the techniques disclosed so far, it is described that a uni-stable ferroelectric liquid crystal is used, but half-tone display is possible in either bistable or bistable.
However, in the case of bistable, it is desirable to be uni-stable because it is necessary to control which stable state is returned to when no voltage is applied and the driving method becomes complicated.

[0009]

However, generally, in the halftone display mode so far, an AC voltage is applied to the ferroelectric liquid crystal device. At this time, for example, when the stable state when no electric field is applied forms a certain angle θ from the rubbing direction as shown in FIG. 2, the apparent tilt angle is different between when the positive voltage is applied and when the negative voltage is applied. The size of the touch will be different. Therefore, for example, when a rectangular waveform voltage is applied, the applied voltage dependence of the time-averaged transmitted light intensity is as shown in FIG. 4, but in reality, when a positive voltage is applied and a negative voltage is applied, as shown in FIG. And the transmitted light intensity is different. According to the study by the present inventors, if the frequency of the AC voltage applied to the liquid crystal is about 40 Hz or more, the human eye cannot distinguish the difference in transmitted light intensity between when the positive voltage is applied and when the negative voltage is applied. However, when driving at a frequency of 40 Hz or less, the difference between the two transmitted light intensities is perceived by the human eye as flicker.

Also when actually driving a ferroelectric liquid crystal display device using an active matrix system in which thin film transistors are arranged, as shown in FIG. 5, when the voltage applied to the liquid crystal is positive and when it is negative, The transmitted light intensity is different. Therefore, in this case as well, the frequency of the liquid crystal applied voltage is 40 Hz.
Below (that is, the frame frequency is 80 Hz or less),
You can feel the strong flicker in human eyes. Therefore, the frequency of the liquid crystal applied voltage must be 40 Hz or higher (the frame frequency is 80 Hz or higher) in order to perform the display in which no flicker is felt.

However, when the liquid crystal display is actually used for a television receiver, a display for a personal computer or the like, the frame frequency needs to be 60 Hz. In this case, the frequency of the voltage applied to the liquid crystal is 30 Hz, which causes strong flicker.

Here, for example, Matsui et al., 17th Liquid Crystal Discussion Group, 3F301 (199)
1). K. Nito et al., Proc. IDRC, 179 (19
91). 6, that is, a cell in which the direction of the optical axis of liquid crystal molecules when an electric field is not applied is substantially parallel to the rubbing direction as shown in FIG. 6, a positive voltage is applied when a rectangular wave voltage is applied. The magnitude of the apparent tilt angle deflection of the liquid crystal molecules is the same when the voltage is applied and when the negative voltage is applied. Therefore, the transmitted light intensity is the same when a positive voltage is applied and when a negative voltage is applied, and no flicker is felt even if the frequency of the liquid crystal applied voltage is 40 Hz or less. However, this is only when viewed from the front of the ferroelectric liquid crystal panel,
When this panel is viewed from an oblique direction, the apparent birefringence of the liquid crystal molecules and the angle between the optical axis and the polarization axis of the polarizing plate differ depending on whether a positive voltage is applied or a negative voltage is applied. If the frequency is 40 Hz or less, strong flicker is felt. This flicker is quite strong even when viewed from the front just a few degrees away. Therefore, even using this means, it is extremely difficult to manufacture a display device in which flicker is not felt in a wide viewing angle.

Further, if a method of driving a liquid crystal display device by frequency-converting a video signal originally sent at a cycle of 60 Hz for one frame, the frequency of the AC voltage applied to the liquid crystal becomes 60 Hz. Therefore, human eyes cannot distinguish the difference in transmitted light intensity between when a positive voltage is applied and when a negative voltage is applied, and no flicker is felt. However, the electric circuit for converting the frequency of the video signal is very complicated and expensive, which greatly increases the production cost of the ferroelectric liquid crystal display device.

In order to solve this flicker problem, line inversion drive has been proposed. That is, every time a certain number of lines are driven in one frame, the polarity of the applied AC voltage is changed to drive, or zero or positive voltage is applied to a certain proportion of the pixels on the scanning electrodes. Apply,
Zero or negative voltage is applied to the remaining pixels. At this time, since the adjacent pixels having different polarities of the applied voltage cancel out the change in the transmitted light intensity, there is no flicker even if the frame frequency is 60 Hz. It can be realized. The principle is shown below.

The polarities of the voltages applied to the adjacent line group 1 and line group 2 are the same. Line group 2 both, as shown in FIG. 7, there during the period T ₁ high transmission state, a low transmission state during the period T _2. Therefore, even when the line groups 1 and 2 are viewed at the same time, if the frequency of the applied voltage is 40 Hz or less, flicker is felt by human eyes. However, as shown in FIG. 8, when the polarity of the voltage applied to the line group 1 and line group 2 are different, the line group 1 is a low transmission state during the period in T ₁ high transmission state, the period T ₂ On the other hand, the line group 2 is in the low transmission state in the period T ₁ ,
_{In 2} , it is in a high transmission state. Therefore, when the line groups 1 and 2 are viewed at the same time, the human eye feels that the average transmission intensity P _M of the low transmission state P _L and the high transmission state P _H is obtained during the period T _{1 to} T _2. To be As a result, flicker-free display can be obtained even when the frequency of the applied voltage is 40 Hz or less. Even when this display device is viewed from an oblique direction instead of the front, only the values of P _L , P _H , and P _M change, and flicker is not felt due to the same effect.

The present invention has been made under such a circumstance, and in the SmC * phase (chiral smectic C phase), among the orientations in which the layer structure bends in a V shape, C
By performing line inversion driving using two orientations, a ferroelectric liquid crystal display device in which flicker is extremely unlikely to be felt is realized. Further, in order to make the darkest state when no voltage is applied, it is desirable that the uni-stable state is a uniform orientation having an extinction position. Further, as a means for obtaining unilateral stability, it is preferable to perform asymmetric alignment treatment on the upper and lower substrates. In particular, if a layer for insulation is provided only on one of the substrates, it is easy to obtain monostable. Further, rubbing may be performed substantially parallel to the upper and lower substrates, or may be performed only on the substrate on which the insulating layer is formed. In particular, it is desirable that the ferroelectric liquid crystal used has a C2 uniform orientation.

[0017]

According to the present invention as set forth in claim 1, the ferroelectric liquid crystal is sandwiched between a pair of substrates and the ferroelectric liquid crystal has one stable state when no voltage is applied. , A ferroelectric liquid crystal display device that obtains gradation display by applying an AC voltage to the ferroelectric liquid crystal and controlling the peak value of the AC voltage, and controlling the alignment on at least one of the pair of substrates. A layer is formed, at least one of the pair of substrates is subjected to rubbing treatment, the layer orientation in the chiral smectic C phase of the ferroelectric liquid crystal is C2 uniform orientation, and a predetermined number of scan electrode groups and signal electrode groups are formed. In two consecutive display frames, each of which has a pixel including the ferroelectric liquid crystal driven by, the first frame has a different polarity for each pixel corresponding to the scanning electrode group or the signal electrode group. Voltage is applied to the ferroelectric liquid crystal and that, in the second frame, the first frame of the opposite polarity of the voltage and drives applied to the pixel.

The present invention according to claim 2 is characterized in that the scanning electrode group or the signal electrode group is one scanning electrode or signal electrode.

The present invention according to claim 3 is characterized in that the display frame frequency is 60 Hz.

According to a fourth aspect of the present invention, pixel electrodes are arranged in a matrix on one of the pair of substrates, and scanning electrodes, signal electrodes and active elements are provided corresponding to the pixel electrodes. The other substrate is provided with a counter electrode to perform active matrix driving.

The present invention according to claim 5 is characterized in that, of the pair of substrates, the first substrate contains single crystal silicon as a constituent element, and the second substrate is a transparent substrate. .

The present invention according to claim 6 is characterized in that the pair of substrates are different in alignment treatment.

The present invention according to claim 7 is characterized in that both of the pair of substrates are subjected to rubbing treatment, and the rubbing treatment directions are substantially parallel between the substrates.

The present invention according to claim 8 is characterized in that, of the pair of substrates, only one substrate is subjected to rubbing treatment.

The present invention according to claim 9 is characterized in that an insulating layer is formed only on one side of the pair of substrates.

[0026]

According to the present invention, high-quality continuous gradation without flicker can be obtained even when the driving frequency is low.

[0027]

EXAMPLES Generally, a Clarke-Lagaval type ferroelectric liquid crystal display device subjected to parallel rubbing or one-side rubbing is likely to have alignment defects called zigzag defects (hairpin defects and lightning defects). this is,
Due to the fact that the layer structure bends in the SmC * phase in a "<" shape, the liquid crystal molecules are aligned in the C1 orientation and the C orientation depending on which direction the "<" shape bends with respect to the rubbing direction.
It is divided into two orientations. The definition of C1 orientation and C2 orientation is shown in FIG.
Shown in. Here, FIG. 9A shows a cross-sectional structure of the ferroelectric liquid crystal, and FIG. 9B shows a state of the ferroelectric liquid crystal when viewed from above. Here, there is a C1 orientation within the zigzag defect and a C2 orientation outside it. The C2 orientation may be formed inside and the C1 orientation may be formed outside. Further, the Clark-Ragabar type liquid crystal display device also has two kinds of molecular alignment states called uniform alignment and twist alignment. As shown in FIG. 10, the liquid crystal layer structure has a bookshelf structure and a chevron structure bent in a V shape, and liquid crystal molecules are aligned substantially uniformly between one substrate and the other substrate. The state is called uniform alignment, and the state in which liquid crystal molecules are twisted and aligned between one substrate and the other substrate is called twist alignment. It is generally known that the uniform orientation has an extinction position, and the twist orientation has no extinction position. In the liquid crystal display device described in the present invention, since the darkest state is obtained when no voltage is applied, it is desirable that the liquid crystal display device is in uniform alignment having an extinction position.

That is, among the alignment states showing the chevron layer structure, the liquid crystal alignment state that can be used in the present liquid crystal display device is C1 uniform alignment (C1U alignment).
And the C2 uniform orientation (C2U orientation) is increased.

As a result of repeated studies by the present inventor, when comparing the C1U orientation and the C2U orientation, it is found that the C2U orientation has a smaller ratio of transmitted light intensity when a positive voltage is applied and when a negative voltage is applied. all right. Therefore, flicker is not felt by using the line inversion driving method in the liquid crystal display device having the C2U orientation. In addition, it is possible to provide a display device that does not look uncomfortable even if the display is brought close to the eyes.

That is, when the C1U orientation and the C2U orientation are compared, it is known that the memory angle (the angle between one extinction position and the rubbing direction when no voltage is applied) is smaller in the C2U orientation. . This is explained by comparing the director profiles within the liquid crystal cell. An example of the C1U orientation and C2U orientation array model is shown in FIG.
oden et al. , Jpn. J. Appl. Ph
ys. 31 (1992) 3632). FIG. 11A shows C
The molecular orientation model of 1U orientation, and FIG. 11B is the molecular orientation model of C2U orientation. In a ferroelectric liquid crystal display device, the molecules are never oriented uniformly from the upper surface to the lower surface of the cell. The molecules are regulated at the interface with the substrate and at the surface of the seam of the chevron layer, which necessitates a strained arrangement.
Drawing this with a director profile is as shown in FIG. FIG. 12A shows a C1U orientation, and FIG. 12B shows a C2 orientation.
It is a U-oriented director profile. Here, the vertical axis is the cell thickness, and the horizontal axis is the twist angle (the angle from the layer normal to the director of the liquid crystal molecules when the cell is viewed from above).
θapp is an apparent cone angle. ψ _o is the twist angle at the substrate interface, and ψ _IN is the twist angle at the chevron joint. In the state of FIG. 12, the memory angle is approximately θ _m =
It is given by (ψ _o + ψ _IN ) / 2. Therefore, it is easily understood from FIG. 12 that the memory angle of the C2U orientation is smaller than that of the C1U orientation.

That is, the memory angle 104 in FIG.
This means that the U orientation is smaller than the C1U orientation.
Therefore, the difference between the maximum touch angle 105 when a positive voltage is applied and the maximum touch angle 106 when a negative voltage is applied is smaller in the C2U orientation. In other words, the difference between the transmitted light intensity when a positive voltage is applied and the transmitted light intensity when a negative voltage is applied is C
The 2U orientation is smaller than the C1U orientation.

When the ferroelectric liquid crystal display device is driven in the halftone display mode, it is preferable to use the active matrix drive because it does not have a memory property.
Driving using a thin film transistor is preferable.

FIG. 13 shows an equivalent circuit of an active matrix type liquid crystal display device using a thin film transistor (TFT). Here, a TFT, which is a switching element, is provided at the intersection of the gate electrode Gn from the scan electrode drive circuit D ₁ and the source electrode Sm from the signal electrode drive circuit D ₂ , and the drain electrode and the counter electrode of the TFT (see FIG. Although not shown, it may cover the entire surface of the pixel or may be separated so that it can be driven individually) and the pixel Pn / m in which the ferroelectric liquid crystal is sandwiched is driven.
When driving this device, a signal is sent from the scan electrode drive circuit D ₁ to apply an electric field to the gate electrode Gn to turn on the TFT.
Set to N. When a signal is sent from the signal electrode drive circuit D ₂ to the source electrode Sm in synchronism with this, charges are accumulated in the ferroelectric liquid crystal through the drain electrode, and the liquid crystal responds by the electric field generated by this, and the transmission of the pixel Pn / m is transmitted. The amount of light changes.

Next, FIG. 14 shows changes in the drive waveform and the amount of transmitted light when the ferroelectric liquid crystal display device according to FIG. 13 is driven by active matrix. In the present embodiment, description will be made focusing on _one gate electrode G ₁ and m source electrodes S _m intersecting the gate electrode G ₁ . In FIG. 14, the gate electrode G ₁ , the source electrodes S ₁ and S _2, and the pixels P _1/1 and P
Voltage V _1/1 effectively applied to _1/2, and V _1/2, indicating only the amount of transmitted light T _1/1, change in T _1/2 of that time.

First, for a time t _1, a signal is sent from the scan electrode G ₁ to turn on the TFT. In synchronization with this, a zero or positive voltage corresponding to the display required for the pixels (P _1/1 , P _1/2 , ... P _{1 / m} ) connected to G ₁ is applied from the source electrode Sm. To do. At the next time t ₁ , the gate electrode G
_The signal is sent from ₂ to turn on the TFT, and the signal is sent from the signal electrode in synchronization with this. Thereafter, similarly, the TFTs connected to the respective scanning electrodes are sequentially turned on.

Now, after signals are sent from all the scanning electrodes, signals are sent again from the gate electrode G _{1 at} time t ₁ to turn on the TFTs. In synchronization with this, the gate electrode G ₁
A zero or negative voltage corresponding to the display required for the pixels (P _1/1 , P _1/2 , ... P _{1 / m} ) connected to is applied from the source electrode Sm. At the next time t _1, a signal is sent from the gate electrode G ₂ to turn on the TFT, and in synchronization with this, a zero or negative signal is sent from the source electrode Sm. Thereafter, similarly, the TFTs connected to the respective gate electrodes Gn are sequentially turned on. At this time, a large positive / negative electric field is alternately applied to the pixel P _1/1 for each frame, and this pixel displays white. The voltage applied to the pixel P _1/2 is smaller than the voltage applied to the pixel P _1/1 in the first four frames, so that P _1/2 becomes a darker display than P _1/1 .
A halftone display is obtained. The applied voltage becomes zero in the fifth and sixth frames, and this pixel changes to black display.

Further, as the liquid crystal display device of this embodiment,
A reflection type liquid crystal display device using a single crystal silicon substrate for one side substrate is also preferable.

FIG. 15 shows a sectional structure of a reflective liquid crystal display device. In this example, a silicon gate NMO is formed on the substrate.
This is the case where the S switching circuit is mounted. This device has a single crystal silicon substrate 7 at the bottom, and a field silicon oxide film 6 is formed on the single crystal silicon substrate 7. Part of the field silicon oxide film 6,
In this illustrated example, through holes 6a and 6b are opened at two locations,
Aluminum electrodes 4c and 4b are respectively formed inside the through holes 6a and 6b and on the upper surface portion of the field silicon oxide film 6 around the upper edges of the through holes 6a and 6b while reaching the bottom of the single crystal silicon substrate 7. Has been formed. The single crystal silicon substrate silicon substrate 7 portion below the aluminum electrodes 4c and 4b is a source region 8 and a drain region 9. A gate insulating film 11 and a gate electrode 10 are provided between the above 6a and 6b. The surface of the gate electrode 10 is covered with a silicon oxide film or the like so as not to short-circuit with the aluminum electrodes 4c and 4b. The gate electrode 10 is made of polysilicon in this embodiment, but is not limited to this. A protective film 5 is formed on the aluminum electrodes 4c and 4b and the field silicon oxide film 6. Protective film 5
Is for protecting the switching MOS circuit formed on the single crystal silicon substrate 7. This protective film 5
A through hole 5a is formed in the upper part of the aluminum electrode 4b, and an electrode / reflecting film 4a is formed on the protective film 5 and in the through hole 5a with the bottom reaching the aluminum electrode 4b. In this embodiment, aluminum having a high reflectance is used for the electrode / reflecting film 4a, but the present invention is not limited to this. In addition, the electrode / reflection film 4a is used as the lower electrode 4
In order to reduce the contact resistance with b, the electrode and reflective film 4
Heat treatment is required after the formation of a. At this time, the electrode / reflection film 4
Irregularities occur on the surface of a, and the reflectance is lowered. In this embodiment, the surface of the electrode / reflecting film 4a is smoothed and the surface is polished after the formation of the protective film 5 for the purpose of increasing the reflectance and after the heat treatment performed after the electrode / reflecting film 4a is formed.
Performs smoothing processing. In some cases, an alignment film (not shown) is formed on the electrode / reflection film 4a, and then a transparent counter electrode 2 is formed on the entire lower surface. Then, in some cases, the transparent glass substrate 1 on which the alignment film (not shown) is formed faces. The liquid crystal layer 3 is formed between the transparent glass substrate 1 and the single crystal silicon substrate 7 described above. The transparent glass substrate 1 is used as the light incident side.

Further, in this embodiment, since the single crystal silicon substrate 7 is used, the IC technology can be applied to the liquid crystal display device as it is. In other words, it is possible to apply highly developed advanced technology such as fine processing technology, high quality thin film formation technology, high precision impurity introduction technology, crystal defect control technology, manufacturing technology and equipment, circuit design technology, CAD technology. In addition, since it can be manufactured at the same time as other ICs in the clean room of the existing IC factory, there is an advantage that the new equipment investment is hardly required and the manufacturing cost can be reduced.

Next, a liquid crystal drive circuit for carrying out the present invention will be described. FIG. 16 shows an example of a liquid crystal driving switching circuit. Q ₁ is a transistor for applying a voltage to the liquid crystal, and it is desirable to use a transistor having the performance of showing a substantially linear relationship between the gate potential and the drain potential. Moreover, since a voltage is directly supplied to the liquid crystal, a withstand voltage necessary for switching the liquid crystal is required. Q ₂ is a transistor that supplies a data signal to Q ₁ . It is desirable that this transistor has a small leak current when turned off. Cs is an auxiliary capacitance for holding the data signal of Q ₁ . When a signal is applied to the data line and a voltage is applied to the gate line to turn on Q ₂ , the data signal is applied to Q ₁ .
At the same time, the signal is held in Cs. Q ₁ applies a voltage corresponding to the data signal to the liquid crystal LC to switch the liquid crystal. This ON state of Q ₁ is maintained as it is even after Q ₂ is turned off. As described above, by using the circuit of this embodiment, good display quality can be obtained even when the liquid crystal material has a low resistance value and a large self-polarization rate.

By using the silicon single crystal substrate as described above, a circuit using a plurality of transistors and capacitors can be constructed, and a liquid crystal display device having a function which cannot be realized by a conventional TFT can be realized. Note that FIG.
It is needless to say that the circuit diagram shown in () is for showing the basic concept, and it becomes desirable by adding transistors and other elements.

The use of the ferroelectric liquid crystal device as described above has the following advantages. First, since the one-sided stability is strong, a high contrast is obtained without applying an electric field to the liquid crystal when a black state is required. Secondly, the amount of transmitted light can be changed by changing the voltage applied to each pixel, and gradation display can be easily performed. Thirdly, since the polarity of the applied voltage is switched every frame, it is possible to obtain a highly reliable liquid crystal element having no electric charge bias. Further, it has advantages that the response speed is fast and the viewing angle is wide as compared with an element in which a nematic liquid crystal is combined with a TFT.

As a method of forming the alignment treatment layer, there are a rubbing method, an oblique vapor deposition method and the like, but the rubbing method is advantageous in the case of mass production of a liquid crystal display device having a large screen. In the case of the rubbing method, the rubbing treatment is performed after forming the alignment film, but the parallel rubbing method (a method of laminating both the pair of substrates so that the rubbing directions are the same) and anti-parallel There are a rubbing method (a method of performing rubbing treatment on both of a pair of substrates and laminating them so that the rubbing directions are opposite to each other), and a single rubbing method (method of performing rubbing treatment on only one of the pair of substrates). In the case of the single-sided rubbing of the ferroelectric liquid crystal device of the present invention, it is particularly preferable to perform the rubbing treatment only on the substrate on which the thin film transistor or the circuit made of single crystal silicon is not formed. There are two reasons for this. First of all, the substrate on which the thin film transistor and the circuit are not formed is flat, and uniform rubbing processing can be easily performed. Secondly, when a substrate on which a thin film transistor or a single crystal silicon circuit is formed is subjected to rubbing treatment, the static electricity generated by the treatment tends to change the characteristics of the thin film transistor or the circuit or cause dielectric breakdown between wirings. is there.

Examples will be specifically described below.

Example 1 An insulating film (OCD TYPE2 P-593) was formed on one side of a pair of glass substrates on which a patterned ITO film was formed.
10-SG, manufactured by Tokyo Ohka Co., Ltd., and an alignment film PS is formed on both sides.
IA-X007 (manufactured by Chisso Petrochemical Co., Ltd.) was spin-coated, and only the substrate on the side where the insulating film was formed was rubbed. The pair of glass substrates were bonded together with a cell thickness of 1.3 μm, and the composition 1 shown in the table below was vacuum-injected.

[0046]

[Table 1]

When the produced ferroelectric liquid crystal cell was set in a polarizing microscope and observed, C1U orientation and C2U orientation were observed. Put only C1U part in the field of view of the microscope,
A ± 10 V square wave voltage of Hz was applied to measure the change in transmitted light intensity, and the result is shown in FIG. The ratio I ₊ / I ₋ of the transmitted light intensity I ₊ when a positive voltage is applied and the transmitted light intensity I ₋ when a negative voltage is applied is about 4.3. On the other hand, only the C2U portion was placed in the field of view of the microscope, a ± 10 V rectangular wave voltage of 60 Hz was applied in the same manner, and the change in transmitted light intensity was measured. The results are shown in FIG. The ratio I ₊ / I ₋ of the transmitted light intensity I ₊ when a positive voltage is applied and the transmitted light intensity I ₋ when a negative voltage is applied is about 2.5, which is considerably smaller than the value of the C1U portion.

Example 2 When 30 Hz rectangular wave voltages having different phases were applied to adjacent electrodes of the cell used in Example 1, changes in transmitted light intensity were canceled out by the adjacent electrodes, and flicker was observed. There wasn't.

Therefore, the value of the ratio I ₊ / I _-in the C2U portion is smaller than that in the C1U portion, and by using the C2U portion,
By performing the line inversion drive, a ferroelectric liquid crystal display device with less flicker can be obtained.

Example 3 FIG. 19 shows an example of drive waveforms when the thin film transistor as shown in FIG. 13 is used for driving. In this example, the polarity of the applied voltage is changed every time one line is driven.
Note that, here, for simplicity, from pixel P _1/1 to pixel P
_Paying attention to _3/1, effective applied voltage (V _1/1 , V _2/1 , V _3/1 ) and transmitted light amount (T _1/1 , T _2/1 , Only T _3/1 ) and the source voltage S ₁ are shown.

First, for a time t _1, a signal is sent from the gate electrode G ₁ (scan electrode) to turn on the TFT. In synchronization with this, the pixels (P _1/1 , P) connected to the gate electrode Gn
_2/1 , ... P _{n / 1} ) is applied from the source electrode Sm (signal electrode) with a zero or positive voltage corresponding to the display required. At the next time t _1, a signal is sent from the gate electrode G ₂ to turn on the TFT, and in synchronization with this, the source electrode Sm is synchronized.
Send a signal from. The signal at this time applies a zero or negative voltage corresponding to the desired display. Then, at the next time t ₁ , the signal is sent from the gate electrode G ₃ to the TFT.
Is turned on, and a signal is sent from the source electrode Sm in synchronization with this. The signal at this time applies a zero or positive voltage corresponding to the desired display. Similarly, the TFTs connected to the respective gate electrodes are sequentially turned on, and the voltage corresponding to the display is applied from the source electrode while changing the polarity of the applied voltage for each line.

Now, after sending signals from all the gate electrodes, the signals are sent again from the gate electrodes G _{1 at} time t ₁ to turn on the TFTs. In synchronization with this, the gate electrode G
A voltage corresponding to the display required for the pixels (P _1/1 , P _2/1 , ... P _{n / 1} ) connected to n is applied from the source electrode Sm. The polarity of the applied voltage at this time is opposite to the polarity applied in the previous frame. In this embodiment, zero or negative voltage is applied. Similarly, at the next time t _1, a signal is sent from the gate electrode G ₂ to turn on the TFT, and in synchronization with this, a zero or positive signal is sent from the source electrode Sm. Similarly, the TFTs connected to the scanning electrodes are sequentially turned on and the voltage corresponding to the display is applied from the source electrode while changing the polarity for each line. Pixel P _1/1
, A large positive and negative electric field is alternately applied to each frame, and this pixel displays white. On the other hand, the voltage applied to the pixel P _2/1 is an AC voltage having a phase difference of approximately 180 ° from the voltage applied to P _1/1 . The phase of the voltage applied to the pixel P _3/1 differs from that of the pixel P _2/1 by about 180 °, and is substantially the same as that of the pixel P _1/1 . In response to this,
The change in transmitted light intensity is also different in the phase between the pixel P _3/1 and the pixel P _2/1 or the phase between the pixel P _2/1 and the pixel P _1/1 by about 180 °. Therefore, for example, pixel P _3/1 and pixel P
_{When 2/1} or the pixel P _2/1 and the pixel P _1/1 are viewed at the same time, the temporal changes in the transmitted light intensities are canceled by each other, and the flicker is no longer felt.

Fourth Embodiment A driving method for active matrix driving will be described using the circuits shown in FIGS. The drive circuit used in this embodiment is shown in FIG.

P _{1/1 to} P _1/3 and P _{2/1 to} P _2/3 are pixels formed on the substrate, and each pixel is provided with a circuit for supplying a driving voltage. The circuit configuration is shown in FIG. 8, but is not limited to this. In order to simplify the description, the operation will be described using the matrix shown by the pixels P _{1/1 to} P _1/3 and the pixels P _{2/1 to} P _2/3 , but in reality, the required number of scanning lines is required. And the number of data lines. A plurality of Gates that supply Gate signals in the row direction to each pixel
A plurality of lines and a power supply line for supplying a plurality of power supplies, and a plurality of Data lines for supplying a Data signal in the column direction.

The operation will be described below. An example of driving when this driving circuit is used will be described more specifically. Driving voltage waveforms (V _1/1 , V _1/2 ,
FIG. 21 shows an example of V _1/3 ) and the amount of transmitted light (T _1/1 , T _1/2 , T _1/3 ). Supply voltage of -5V to the power supply 1 and Gate
A +6 V voltage is supplied to 1, and a Data signal for supplying a signal to each pixel is supplied to the Data line. At this time, Dat
The a signal has a positive value. By this scanning, the display data of the first row is written in the pixels. The polarity of the applied voltage corresponding to the data to be written at this time is positive.

Next, the Gate1 is turned off and the Gate2
Turn on. At this time, the voltage supplied to the power supply 2 is -5V and the Gate signal is + 6V. Here, the voltage of the Gate signal may be changed according to the polarity of the power supply.
Data is a positive value. This operation causes the second
The display data is written in the row, but the polarity of the applied voltage corresponding to the display data at this time is negative. Similarly, a pixel with an applied voltage having a positive polarity is written to pixels in an odd-numbered row, and a signal with a negative applied voltage is written to pixels in an even-numbered row.
By performing this operation over the first display frame, necessary display data is written in the first display frame.
The second display frame following the first display frame has the first
Write the display data by inverting the polarities of the display frame and the power supply line. As a result, an alternating voltage is applied to the liquid crystal.

[0057]

By using the ferroelectric liquid crystal element of the present invention, high-quality continuous gradation display without flicker can be realized even when the frequency of the liquid crystal applied voltage is 30 Hz. By driving this display device by active matrix,
It is possible to obtain a liquid crystal display device having a large capacity, a wide viewing angle, a high contrast and an infinite gradation display.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a Clark-Ragabar type ferroelectric liquid crystal display device.

FIG. 2 is a diagram for explaining a halftone display ferroelectric liquid crystal display mode.

FIG. 3 is a diagram showing an applied voltage dependency of an apparent tilt angle in a halftone display ferroelectric liquid crystal display mode.

FIG. 4 is a diagram showing applied voltage dependence of transmitted light intensity in a halftone display ferroelectric liquid crystal display mode.

FIG. 5 is a waveform diagram showing a temporal change in transmitted light intensity according to a conventional technique.

FIG. 6 is a schematic diagram for explaining a switching operation according to a conventional technique when a stable state when no voltage is applied is in a rubbing direction.

FIG. 7 is a waveform diagram for explaining a case where line inversion is not performed according to a conventional technique.

FIG. 8 is a waveform diagram for explaining a case where line inversion is performed according to a conventional technique.

FIG. 9 is a diagram for explaining C1 orientation and C2 orientation.

FIG. 10 is a diagram for explaining uniform orientation and twisted orientation.

FIG. 11 is a diagram illustrating molecular orientation models of C1 uniform orientation and C2 uniform orientation.

FIG. 12 is a diagram showing director profiles of C1 orientation and C2 orientation.

FIG. 13 is a diagram for explaining an active matrix liquid crystal display device.

FIG. 14 is a diagram showing an example of a method of driving each pixel of an active matrix type liquid crystal display device and an amount of transmitted light at that time.

FIG. 15 is a diagram showing a cross-sectional structure of a reflective liquid crystal display device.

FIG. 16 is a diagram showing an example of a switching circuit for each pixel.

FIG. 17 is a waveform diagram showing the change over time in the transmitted light intensity of C1 uniform orientation according to Example 1.

FIG. 18 is a waveform diagram showing the change over time of the intensity of transmitted light in the C2 uniform orientation according to Example 1.

FIG. 19 is a waveform diagram showing the change over time of the transmitted light intensity of the active matrix liquid crystal display device according to Example 3.

FIG. 20 is a diagram showing a drive circuit of an active matrix type liquid crystal display device according to a fourth embodiment.

FIG. 21 is a waveform diagram showing the change over time of the transmitted light intensity of the active matrix liquid crystal display device according to Example 4.

[Explanation of symbols]

 1 Transparent Glass Substrate 2 Transparent Counter Electrode 3 Liquid Crystal Layer 4a Electrode / Reflective Film 5 Protective Film 6 Field Silicon Oxide Film 7 Single Crystal Silicon Substrate 10 Gate Electrode 15 Polarization Direction 16 Voltage Application Direction 17 Smectic Layer Normal Line 18 Liquid Crystal Molecule 19 Tilt angle + θ 20 Tilt angle −θ

Claims (9)

[Claims] 1. A ferroelectric liquid crystal is sandwiched between a pair of substrates, and the ferroelectric liquid crystal has one stable state when no voltage is applied, and an alternating voltage is applied to the ferroelectric liquid crystal. In a ferroelectric liquid crystal display device that obtains gradation display by controlling the peak value of an AC voltage, an alignment control layer is formed on at least one of the pair of substrates, and rubbing is performed on at least one of the pair of substrates. A layer having a C2 uniform orientation in the chiral smectic C phase of the ferroelectric liquid crystal and having a pixel containing the ferroelectric liquid crystal driven by a predetermined number of scan electrode groups and signal electrode groups. In two consecutive display frames, in the first frame, voltages having different polarities are applied to the ferroelectric liquid crystal for each pixel corresponding to the scanning electrode group or the signal electrode group, The frame, the ferroelectric liquid crystal display device, characterized in that the first frame for driving the reverse polarity voltage is applied to the pixel. 2. The scanning electrode group or the signal electrode group,
The ferroelectric liquid crystal display device according to claim 1, wherein the ferroelectric liquid crystal display device comprises one scanning electrode or one signal electrode. 3. The ferroelectric liquid crystal display device according to claim 1, wherein the display frame frequency is 60 Hz. 4. On one of the pair of substrates,
2. The pixel electrodes are arranged in a matrix, scanning electrodes, signal electrodes and active elements are provided corresponding to the pixel electrodes, and a counter electrode is provided on the other substrate to perform active matrix driving. 2. The ferroelectric liquid crystal display device according to item 2 or 3. 5. The method according to claim 1, wherein one of the pair of substrates contains single crystal silicon as a constituent element, and the other substrate is a transparent substrate. Ferroelectric liquid crystal display device. 6. The ferroelectric liquid crystal display device according to claim 1, 2, 3, 4, or 5, wherein the pair of substrates have different alignment treatments. 7. The rubbing treatment is performed on both of the pair of substrates, and the rubbing treatment directions are substantially parallel between the substrates, according to claim 1, 2, 3, 4, 5, or 6. Ferroelectric liquid crystal display device. 8. The ferroelectric liquid crystal display device according to claim 6, wherein only one of the pair of substrates is rubbed. 9. The insulating layer is formed only on one side substrate of the pair of substrates.
The ferroelectric liquid crystal display device according to 4, 5, 6, 7 or 8.