JP2001051304A - Liquid crystal display element and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal drive method which does not depend upon gate selection time, the response time of spontaneous polarization liquid crystals and the magnitude of the spontaneous polarization of the spontaneous polarization liquid crystals and a liquid crystal display element using the spontaneous polarization liquid crystals. SOLUTION: This liquid crystal display element has liquid crystals which have the spontaneous polarization, electrodes (b) for impressing electric field to the liquid crystals, a first switching element 16 which has input and output terminals and is constituted by connecting a data signal line 15 to this input terminal and connecting a control signal line 17 to the control gate, a second switching element 13 which has the input and output terminals and the control gate and is constituted by connecting a charge supply line 12 to this input terminal, connecting the output terminal to an electrode 22 (b) for electric field impression and connecting the output terminal of the first switching element 16 to the control gate, and a timer circuit for gate control which is connected to the control gate of the second switching element 13 and is made non-conducting after the conduction of the second switching element 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display element used for a notebook PC, a monitor, and the like, and more particularly to a method of driving a spontaneously polarized liquid crystal suitable for high-speed driving, and a high-quality image using the spontaneously polarized liquid crystal. The present invention relates to a liquid crystal display element capable of displaying a.

[0002]

2. Description of the Related Art A conventional liquid crystal display (LCD) is mainly composed of a nematic liquid crystal and a thin film transistor (TFT). For example, Japanese Patent Application Laid-Open No. 7-64051 discloses the operation of the above method as a conventional example. That is, a selection signal is applied to the gate of the TFT for a certain period of time (gate selection time),
A voltage corresponding to the image signal is applied to the liquid crystal and the storage capacitor through T and the pixel, and charges corresponding to the applied voltage are accumulated. The nematic liquid crystal is driven by a dielectric interaction between the electric field due to the accumulated charge and the nematic liquid crystal. When an electric field of the same polarity is continuously applied to the pixel, ionic impurities are adsorbed on the interface between the liquid crystal and the alignment film, and so-called burning occurs. To prevent this, the liquid crystal is usually driven by an inversion driving method in which the polarity of the applied electric field is inverted every frame. As described above, since the driving of the nematic liquid crystal is based on the dielectric interaction,
The torque applied to the liquid crystal is proportional to the square of the electric field strength and is independent of the polarity of the electric field. Therefore, even if the response of the liquid crystal is not completed within one frame display time and the polarity of the applied electric field is reversed, the torque applied to the liquid crystal does not change and continues to respond.

For this reason, the response time of the nematic liquid crystal, that is, the time required for switching the optical characteristics of the liquid crystal, is one time.
Even if it is longer than the frame display time, it is possible to drive the nematic liquid crystal by writing an image signal with a relatively short gate selection time. However, if the change of the image is fast, the response time of the liquid crystal itself is long, so that the liquid crystal cannot follow the image. In addition, there is a problem that the viewing angle is narrow. In contrast, in recent years,
Spontaneously polarized liquid crystal, for example, a surface stable ferroelectric liquid crystal (SSFL)
C), an antiferroelectric liquid crystal (AFLC), a thresholdless antiferroelectric liquid crystal (TLAFLC), a helical structure-variable ferroelectric liquid crystal (DHFLC), a short pitch bistable ferroelectric liquid crystal (SBFLC), or a mixture thereof. It is also known to form a liquid crystal display element using either a polymer stable type or polymer dispersed type liquid crystal. Such a liquid crystal display element drives the liquid crystal by the interaction between spontaneous polarization and an electric field. Therefore, the response time is usually shorter than the one-frame display time, and a high-speed response is possible. Attention has been paid to high-quality images, such as a wide viewing angle that can be widened because it is basically parallel to the screen before and after the response.

[0004]

However, when the spontaneously polarized liquid crystal moves due to the interaction with an electric field, the permittivity of the liquid crystal portion is greatly increased, so that the voltage applied to the liquid crystal must be maintained. Requires extra accumulated charge to compensate for this increase. In order to supply such stored charges, the switching TFT also needs to have a high driving capability, and in particular, needs several times to several tens of times the power of TN driving of the nematic liquid crystal. In addition, the gate selection time of a TFT tends to be shortened in accordance with the recent trend toward higher definition. The gate selection time can be obtained by dividing the reciprocal of the frame frequency (one frame display time) by the number of gate lines. For example, the frame frequency is 60 Hz and the definition is VG.
A (640 × 480 pixels) SVGA (800 × 600 pixels) XGA (1024 × 768 pixels), the gate selection time is about 34.7, 26.0, 21.
7 μs, and the wiring delay is about several μs, so that the effective gate selection time is further shortened, and the time during which voltage is actually applied to the liquid crystal is shortened.

[0005] However, although a high-speed response is possible as compared with a nematic liquid crystal, the response speed of a spontaneously polarized liquid crystal is usually several tens μs.
Since the response of the spontaneously polarized liquid crystal is not completed within the gate selection time longer than the gate selection time,
An auxiliary capacitor that supplies extra charge until completion is required. In addition, unlike a nematic liquid crystal, in the case of a spontaneously polarized liquid crystal, the interaction with the electric field due to the accumulated charge is a direct interaction with the spontaneous polarization Ps, so that the torque applied to the liquid crystal is the product of the magnitude of the spontaneous polarization and the electric field strength. Proportionally, the direction of the torque changes when the polarity of the electric field changes. Therefore, if the response of the liquid crystal is not completed within one frame display time and the polarity of the applied electric field is reversed, the liquid crystal starts to move in the opposite direction. Therefore, when the spontaneously polarized liquid crystal is driven by inversion driving, the response must be completed within one frame display time.

For example, the operation speed is sufficiently higher than that of a nematic liquid crystal.
As a response, a thresholdless response with a full drive and a response speed of 100 μs
Consider the case where a ferroelectric liquid crystal is required. Achieve this
The magnitude of the spontaneous polarization is determined by setting the rotational viscosity of the spontaneously polarized liquid crystal to mPa ·
1 [n] even if reduced to the order of s (millipascal seconds)
C / cm^Two] Is necessary. The response speed is 10
0 μs, spontaneous polarization is 1 [nC / cm^Two] Thresholdless antiferroelectric
Full driving of liquid crystal by inversion driving method with applied voltage of about 5V
Is necessary to achieve a voltage holding ratio of 99%.
The auxiliary capacitance is about 9 pF.
Realized with an insulating film structure of about 0Å (angstrom)
For this purpose, several hundred μm square (100000 μm ^TwoDegree)
Area is required and becomes larger than a normal pixel.
Not practical.

Actually, even if the response time is 100 μs, the response time is longer than the above-mentioned gate selection time, and the response time may increase in the case of halftone display instead of full driving.
In order to drive the spontaneously polarized liquid crystal, it is advantageous to further increase the spontaneous polarization and make the response faster. However, if the spontaneous polarization is increased, the necessary auxiliary capacity becomes huge. Further, when the resolution of the pixel is increased to obtain a high-quality image, the gate selection time is further shortened, so that it is difficult to realize the conventional inversion drive using the auxiliary capacitance.

Therefore, in order to drive the spontaneously polarized liquid crystal, it is necessary to increase the applied voltage to shorten the response time or to increase the gate selection time. However, when the applied voltage is increased, the breakdown voltage of the liquid crystal display element and the driving circuit must be increased. Further, even if the applied voltage is increased, it is difficult to realize a response time of 30 μs or less as a material property of the spontaneously polarized liquid crystal, and it is impossible to cope with an increase in definition of the display element. As a driving method for increasing the gate selection time, a method of lowering the frame frequency, a gate division driving method and a thinning driving method are known. However, when the frame frequency is reduced, a problem occurs that flicker is easily recognized.

The gate division drive method is a drive method in which a plurality of drive circuits are prepared and different places on the screen are driven simultaneously. If the number of divisions is n, the gate selection time can be increased by n times. However, practically, it is limited to about two divisions, and when the definition of the display element increases, insufficient writing occurs. In the thinning drive (for example, the operation is described in Japanese Patent Application Laid-Open No. 9-185039), n non-write lines are prepared for one write line, and the gate selection time for the non-write line is set to one. With the driving method used for the write lines, the gate selection time can be n + 1 times (when writing every other line with n = 1, it is called interlace driving). However, since writing is not performed on the 1 / (n + 1) portion of the screen, n
If the value is set to a large value, the image quality deteriorates. Therefore, as in the case of the gate division driving, it is not possible to cope with an increase in the definition of the display element.

On the assumption that the response of the spontaneously polarized liquid crystal does not end within one frame display time (reciprocal of the frame frequency), a driving method in which a voltage of the same polarity is continuously applied (DC driving method)
Is also provided (for example, see Japanese Patent Application Laid-Open No. 10-13317).
No. 6), the high-speed response of the spontaneously polarized liquid crystal is not utilized,
In addition, since a voltage of the same polarity is continuously applied, there is a problem that seizure easily occurs. There is also provided a driving method using two TFTs and using a capacitor for controlling the second TFT so that a voltage is continuously applied to the liquid crystal even after the gate selection time is over (see, for example, Japanese Unexamined Patent Application Publication No. -64051
Publication), which specializes in driving a surface-stabilized ferroelectric liquid crystal with an AC voltage, and cannot generally be applied to driving a spontaneously polarized liquid crystal.

As described above, when driving a spontaneously polarized liquid crystal which is expected to be able to display high-definition and high-quality images at high speed, a short gate selection time for high definition and a large gate response for high-speed response are required. Various problems associated with spontaneous polarization occur, and the conventional technology cannot cope with it.

In order to solve the above problems, the present invention provides a liquid crystal driving method that does not depend on the gate selection time, the response time of the spontaneously polarized liquid crystal, the magnitude of the spontaneously polarized liquid crystal, and a liquid crystal display using the spontaneously polarized liquid crystal. It is intended to provide an element.

[0013]

In order to achieve the above object, the present invention provides (1) a liquid crystal having spontaneous polarization;
(2) an electrode for applying an electric field to the liquid crystal;
A first switching element having an input / output terminal (node) and a control gate, a data signal line connected to the input terminal, and a control signal line connected to the control gate; (4) an input / output terminal and control A second terminal having a gate, an input terminal connected to a charge supply line, an output terminal connected to the electrode for applying an electric field, and an output terminal of the first switching element connected to a control gate; A switching element;
(5) A liquid crystal display element comprising a gate control timer circuit connected to the control gate of the second switching element and turned off after the second switching element is turned on. The spontaneously polarized liquid crystal targeted in the present invention includes, for example, a surface stable ferroelectric liquid crystal (SSFLC),
Antiferroelectric liquid crystal (AFLC), thresholdless antiferroelectric liquid crystal (TLA)
FLC), helical structure-variable ferroelectric liquid crystal (DHFL)
C), short-pitch bistable ferroelectric liquid crystal (SBFLC), or liquid crystal of either polymer stable type or polymer dispersed type thereof. However, the type of liquid crystal is not particularly limited as long as the function or effect of the present invention can be obtained, and various liquid crystals other than those described above can be used.

In the present invention, the magnitude of the spontaneous polarization is 1
Provided is a liquid crystal display device using a spontaneously polarized liquid crystal of [nC / cm ² ] or more.

In the present invention, the magnitude of the spontaneous polarization is 1
[NC / cm ² ] or more, and the response time, that is, the time at which the optical property of the liquid crystal is switched, is longer than the conduction time of the first switching element and shorter than the frame display time. A display element is provided.

The present invention further provides the liquid crystal display device, wherein the gate control timer circuit is equivalently constituted by a parallel circuit of a capacitor and a resistor.

Further, in the present invention, there is provided a method of driving the liquid crystal display element, wherein the gate control timer circuit controls a conduction time of the second switching element to change a voltage applied to the liquid crystal. provide.

Further, in the present invention, the magnitude of the spontaneous polarization is 1 [nC / cm ² ] or more, the response time is longer than the conduction time of the first switching element, and the time interval (frame) at which the screen display information is switched. The present invention provides a method for driving the liquid crystal display element, wherein a spontaneously polarized liquid crystal shorter than (time) is used, the frame time is divided into a plurality of subframes, and an image is not displayed or black is displayed in a certain subframe. I do.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The concept, operation principle and operation and effect of the present invention will be described below with reference to examples. For example, the present invention is used in a configuration of a light valve portion as shown in FIG. However, the application field is not limited to this. In FIG. 2, a spontaneously polarized liquid crystal 24 is sandwiched between a pair of glass substrates 23 provided with an alignment film 21 having been subjected to an alignment process and a transparent electrode 22. The transmission axis of the polarizing plate 25 is adjusted to the display mode of the liquid crystal to be used.
When LC is used, one of the transmission axes of the polarizing plate 25 is parallel to the helical axis, and the other is perpendicular. One transparent electrode 22
(A) is a counter electrode, and its potential is a reference potential Vcom. The accumulated charge is supplied from the other transparent electrode 22 (b). However, one of the transparent electrodes may be a metal electrode also serving as a reflector or a scattering plate. The liquid crystal display element has a configuration in which a switching transistor and a pixel electrode are provided for each pixel, and the pixel electrode portion corresponds to the light valve portion shown in FIG. In this liquid crystal display element, the data signal,
That is, the image signal is written into the liquid crystal as the amount of accumulated charge to be charged. FIG. 1A schematically shows an example of a circuit element configuration provided in each pixel of the present liquid crystal display element.

The liquid crystal display element shown in FIG. 1A has a light valve section 11 using spontaneously polarized liquid crystal, and a charge supply line 12 connected to a charge supply source for charging the liquid crystal.
A switching element 13 (second switching element) for connecting the transparent electrode 22 (b) of the light valve section 11 and the charge supply line 12, for example, an n-channel transistor or the like; and a gate for controlling the switching element 13 A control timer circuit 14, an image signal line 15 (data signal line), and a switching element 16 (first switching element) for connecting the timer circuit 14 and the image signal line 15, for example, an n-channel transistor or the like. And a gate line 17 (control signal line) for controlling the switching element 16. In such a configuration, the switching circuit 16 operates the timer circuit 1 within the gate selection time.
4, a signal for designating a time τ at which the switching element 13 connects the charge supply line 12 and the transparent electrode 22 (b) of the light valve unit 11 is written, and the gate control timer circuit 14 designates a time designated by the gate control timer circuit 14. When the switching element 13 connects the charge supply line 12 and the transparent electrode 22 (b) by τ, the amount of charge charged in the liquid crystal is controlled.

If the stored charge can be supplied to the liquid crystal 24 for a time τ specified by a data signal such as an image signal, the time for supplying the liquid crystal 24 with the time τ as an input signal is controlled. In addition, a pulse current generation circuit or a pulse voltage generation circuit can be applied. Further, as the gate control timer circuit, a circuit capable of turning on the second switching element for a predetermined time and then turning off the second switching element can be used. For example, the gate control timer circuit has an appropriate capacity and a magnitude of leakage current. A circuit including a capacitor and the like can be used, and specific examples thereof will be described in Examples described later. However, the configuration is not limited to this example, and another configuration may be adopted.

The response time of a spontaneously polarized liquid crystal is usually several tens μs to
The response time is longer than the gate selection time because the writing of the image signal and the response of the liquid crystal can be independently controlled in the liquid crystal display element of the present invention. Can drive the spontaneously polarized liquid crystal having In addition, a large spontaneous polarization of 1 [nC / cm ² ] is generally required for a spontaneously polarized liquid crystal to respond at high speed.
In a liquid crystal display element, a large auxiliary capacitance and a high TFT charging capacity are required due to a large spontaneous polarization. In the liquid crystal display element of the present invention, the writing of the image signal and the response of the liquid crystal are made independent, and therefore, 1 [nC / cm ² ], which is required for high-speed response, does not require a particularly large auxiliary capacitance or a charging capability of the TFT.
The spontaneously polarized liquid crystal having such a large spontaneous polarization can be driven, and a high-quality image can be displayed.

In the liquid crystal display device of the present invention, it is not necessary to change the voltage of the charge supply line 12 in accordance with a display image, and a fixed voltage can normally be applied.
Therefore, even if a plurality of signal lines 12 and 15 exist, the load on the circuit side is small. Further, in the liquid crystal display element of the present invention, the charge supply line is set at an arbitrary stage when the charging of the accumulated charges of all the pixels in the display screen is completed, for example, at the stage when the charging of the liquid crystal of all the pixels connected to the final gate line is completed. The polarity of the twelve voltages with respect to the reference potential Vcom can be inverted, and it is possible to apply a voltage whose polarity has been inverted to the liquid crystal for each frame (inversion driving). Therefore, it is possible to display a high-quality image without burning. In this case, the maximum charging time τ _m [s] of the charge stored in the liquid crystal is f [Hz], the gate selection time is t _g [s], and the number of gate lines written in one frame is G [lines].

[0024]

(Equation 1)

It is desirable to satisfy the following condition.

Hereinafter, the principle of the liquid crystal driving method according to the present invention will be briefly described. When the spontaneous polarization of the spontaneously polarized liquid crystal moves in the direction of the electric field due to the interaction with the electric field E due to the fixed amount of accumulated charge Q, the relative permittivity ε of the liquid crystal increases. Electric field E applied to liquid crystal
Is expressed by E = Q / εε ₀ S (ε ₀ is the dielectric constant of vacuum, S is the pixel area). As the relative dielectric constant ε increases, E decreases, and the driving force for driving the liquid crystal also decreases. , And finally stabilized in a state determined by the accumulated charge amount Q.

Therefore, instead of applying the voltage applied to the spontaneously polarized liquid crystal itself as an image signal to the liquid crystal and driving the liquid crystal, the accumulated charge amount required to drive the liquid crystal to a target alignment state is represented by Q, A current flowing through a switching element connecting the source and the liquid crystal is represented by I (t).

[0028]

(Equation 2)

The liquid crystal can be driven by writing an image signal designating a time τ determined by the above.

Here, an experiment confirming that the spontaneously polarized liquid crystal is driven by the accumulated charge amount will be described. Size 50X5
A polyimide orientation film is spin-coated on the ITO side of a glass substrate (electrode area is 19.6 mm ^{2) having} a thickness of 0 mm ² and a thickness of 1.1 mm (electrode area is 19.6 mm ² ), dried, rubbed with a nylon cloth, and the ITO electrode is placed inside. And bonded together with a 2 μm gap with a resin spacer. The polarizing plate is placed on both sides of the DHFLC-injected element in the gap. To form a light valve portion of a liquid crystal display element. FIG. 6 shows the dependence of the transmitted light intensity when the pulse width is changed when a pulse-type current power supply is connected to the light valve unit and a rectangular current is applied at a constant wave height of 10 μA. Thus, it was possible to drive the spontaneously polarized liquid crystal by controlling the amount of accumulated charge.

In the conventional method of writing the voltage applied to the spontaneously polarized liquid crystal itself as an image signal, if the movement of the liquid crystal does not end within the time for writing the signal, the voltage of the liquid crystal element is increased by the movement of the liquid crystal which occurs even after the writing ends. Fluctuates greatly. However, according to the liquid crystal driving method of the present invention, since the image signal is given not by the voltage to be applied to the spontaneously polarized liquid crystal but by the time τ that specifies the amount of accumulated charge to be charged in the liquid crystal, the signal writing time is reduced. Independent of the response time of the liquid crystal, a high-quality image can be obtained even with a short writing time.

For example, a thresholdless antiferroelectric liquid crystal having a response speed of 100 μs and a spontaneous polarization of 1 [nC / cm ² ] is set to 5 V
When the full driving is performed by the inversion driving method with the applied voltage of about 16.5 μs and the gate selection time, the voltage holding ratio is about 87% without the auxiliary capacitance in the conventional driving method. Only about 87% respond,
According to the driving method of the present invention, the spontaneously polarized liquid crystal can supply an amount of electric charge necessary for completely responding to a target state, and the response rate to an image signal can be almost 100%.

Another example of a liquid crystal display element driven by controlling the amount of accumulated charge is shown below. Size 370X4
A counter electrode composed of an ITO electrode is formed on one of two glass substrates having a thickness of 70 mm ² and a thickness of 1.1 mm, and a TFT and a pixel electrode (one pixel is 100 × 300 μm ² ) are formed on the other by a usual method. , A gate line and a source line matrix were formed. After transferring the polyimide alignment film to the electrode side of these two glass substrates, drying and rubbing with a nylon cloth, the electrodes are opposed so that the electrodes are on the inside, and the distance between the pixel electrode and the counter electrode is set by the resin spacer. A polarizing plate was attached on both sides of the device in which DHFLC was injected into the gap, so that one of the transmission axes was in the direction of the helical axis of DHFLC and the other was perpendicular to it. A constant voltage power supply was connected to the source line, and a pulse power supply capable of changing the pulse width and wave height was connected to the gate line, thereby forming a liquid crystal display element.
Shows the relationship between the current i _D and the gate voltage V _G flowing through the TFT in FIG. The off voltage was −5 V, and the on current was 10 μA. FIG. 8 shows a relationship between an applied pulse width of a pulse power supply (maximum 10 V and a minimum of -5 V in a rectangular wave) and a transmittance of the liquid crystal display element. Thus, a liquid crystal display element driven by controlling the amount of accumulated charge was obtained.

In the liquid crystal display device described above, DH
A liquid crystal display element using TLAFLC instead of FLC was produced. The transmission axis of the polarizing plate was stretched so as to be perpendicular to the direction normal to the layer of the TLAFLC. TLA used
The minimum response time of FLC was 30 μs and the maximum was 2 ms. The output pulse width of the pulse power supply was written from a computer. This writing time was 1 μs or less. FIG. 9 shows the relationship between the applied pulse width of a pulse power supply (maximum 10 V, minimum -5 V for a rectangular wave) of the liquid crystal display element and the transmittance of the liquid crystal display element. As described above, a liquid crystal display element driven even though a signal writing time from the computer to the pulse power supply is shorter than a response time of the liquid crystal was obtained.

In the liquid crystal display device described above, the SSFL having a spontaneous polarization magnitude of 20, 50 [nC / cm ² ]
C and liquid crystal display devices using 100, 150, 240 [nC / cm ² ] TLAFLC were produced. SS
In the case of a liquid crystal display device using FLC, the transmission axis of the polarizing plate is S
The extinction position of one of the two stable states of the SFLC was stretched to be orthogonal to it. When all the manufactured liquid crystal display elements were driven by the same method as described above, a liquid crystal display element driven by accumulated charge control regardless of the magnitude of spontaneous polarization was obtained.

In the present liquid crystal display device, the gate selection time can be set short regardless of the response time of the liquid crystal.
For example, by dividing one frame into two sub-frames, displaying an image in one sub-frame, and erasing the image in the other sub-frame, the same effect as intermittent lighting can be obtained, and a hold-type afterimage of a moving image is obtained. And a high-quality moving image can be displayed.

Further, by using a simple circuit composed of a parallel circuit of a capacitor and a resistor as shown in FIG. 1B as a timer circuit, it is possible to suppress a decrease in aperture ratio and a decrease in yield. The element or circuit shown in FIG. 1B can be manufactured by using, for example, a dielectric thin film. The operation when the equivalent circuit is shown in FIG. 1B will be described. The first switching element 16 connects the image signal line 15 and the gate control timer circuit 14 for the gate selection time t _g by the signal of the gate line 17, and charges the capacitor 18 with the charge for the timer circuit that specifies the charge supply time τ. Charge. The time constant τ _CR of the timer circuit is represented by τ _CR = C · R by a resistor 19 connected in parallel (C is the capacitance [F] of the capacitor 18 and R is the resistance value [Ω] of the resistor 19). Assuming that the image signal voltage is V _S , the voltage V _{C of the} capacitor 18 is

[0038]

(Equation 3)

Is represented by At this time, a sufficiently large voltage V _C
Τ _CR <5t _g , more preferably τ _CR
<It is desirable to satisfy the 3t _g.

The timer power stored in the capacitor 18
Voltage V due to load_CTurns on the switching element 13
And a light valve unit 11 using spontaneously polarized liquid crystal and
Signal line 1 connected to a charge supply for charging the liquid crystal
2 and the charge of the stored charge to the liquid crystal is started.
You. Voltage V of capacitor 18_CAre parallel as shown in FIG.
Time constant τ by the resistor 19 connected to_CR= C · R
Decay. When the switching element 13 is
In order to connect the lube section 11 and the signal line 12, τ _CR> 5
μs is desirable.

Since the gate voltage V _G of the switching element 13 is the voltage V _{C of the} capacitor 18, the value of the charging current i _D to the spontaneously polarized liquid crystal changes with time according to the characteristics of the switching element 13 as shown in FIG. Go. If the potential of the timer circuit after a sufficient time has passed (the potential on the opposite side of the switching element 13 of the capacitor 18) is taken as the off voltage _Vgl of the switching element 13,

[0042]

(Equation 4)

Is accumulated in the liquid crystal element.

[0044]

An embodiment of the present invention using a timer circuit for gate control will be described below. Embodiment 1 FIG. As a gate control timer circuit, FIG.
An example in which the method shown in FIG. Timer circuit is Si
_A time constant τ _CR of about 50 can be obtained by forming a very thin 3N ₄ film.
μs. The capacitance component 18 is formed by the capacitance of the Si ₃ N ₄ film itself and the capacitance parasitic to the Si ₃ N ₄ film. For the liquid crystal display device having such a configuration, the frame frequency is set to 60H.
z, the gate selection time was 16.5 μs, and the video of the accumulated charge supply signal line was inverted with respect to the common potential Vcom (5.5 V) 4 ms after the final gate line writing was completed to display a moving image. As a result, a high-quality full-color moving image with almost no image sticking or afterimage could be obtained.

Embodiment 2 FIG. Next, FIG. 3 illustrates an example in which a CMOS transistor including a p-channel transistor and an n-channel transistor is used as the first switching element. In FIG. 3, the first switching element has a p-channel transistor 16a having a gate connected to the control signal line 17 and an input terminal connected to the data signal line, a gate connected to the control signal line 17, and an input terminal. , P-channel transistor 16a, and an n-channel transistor 16b whose output terminal is connected to the control gate of second transistor element 13. The timer circuit for gate control is constituted by a parallel circuit of a resistor 19 and a capacitor 18. The capacitor 18 is connected to a common node of the transistors 16a and 16b, and the resistor 19 is connected to an output terminal of the transistor 16b. Have been. The rest is common to the configuration of FIG. When such a CMOS transistor element is used, while the switching transistor 16a (p-channel FET) is turned on and the capacitor 18 is charged, the switching transistor 16b (n-channel FET) is turned off, so that the capacitor 18 is turned off. Can be charged up to V _C = V _{S in} 1 μs or less regardless of the size of the resistor 19. That is, since the discharge due to the resistance does not occur during the charging, the charging can be performed at a high speed.
Specifically, a size of 370 × 470 mm ² and a thickness of 1.1
On one of the two glass substrates, a counter electrode made of an ITO electrode and a color filter are formed, and on the other, a TFT and a pixel electrode (having an area of 100 × 300) are formed by a normal method.
μm ² ), a matrix of gate lines (control signal lines), image signal lines (data signal lines), charge supply lines, and a gate control timer circuit were formed. The timer circuit is a capacitor 18
Was formed by a Ta ₂ O ₅ film, and the resistor 19 was formed by thinly forming a Si ₃ N ₄ film to have a time constant τ _CR of about 50 μs. To be precise, the Si ₃ N ₄ film also has a capacitance component, but since the Ta ₂ O ₅ film has a large resistance and capacitance, the circuit configuration is a circuit schematically shown in FIG. 3 (first and second circuits). TFTs are used as transistors constituting the switching elements).

The polyimide alignment film was transferred to the electrode side of these two glass substrates, dried, rubbed with a nylon cloth, opposed so that the electrodes came inside, and a 2 μm gap was formed with a resin spacer. TL
Polarizing plates were adhered on both sides of the device into which the AFLC was injected, so that the transmission axis was perpendicular to the liquid crystal layer on one side and perpendicular to the other. The number of pixels was set to 1024 × 768 (XGA) in units of three RGB colors. The spontaneous polarization of the TLAFLC used was 100 [nC
/ Cm ² ], the minimum response time is 30 μs, and the maximum is 1.5
ms. With respect to such a liquid crystal display element, the frame frequency is set to 60 Hz, the gate selection time is set to 16.5 μs, and the voltage of the signal line for supplying stored charges is set to the common potential Vcom (5.5 V) 4 ms after the end of writing the final gate line.
And inverting drive.

FIG. 10 shows the relationship between the writing voltage (image signal) to the timer circuit and the amount of accumulated charges. In this way, it was found that the amount of accumulated charge could be controlled by the image signal. When a moving image was displayed using this liquid crystal display element,
A high-quality full-color moving image with almost no afterimage was obtained.

Embodiment 3 FIG. In the liquid crystal display element of the second embodiment, the frame frequency is set to 60 Hz, one frame is divided into two sub-frames, the gate selection time is set to 8.2 μs in the first sub-frame, and an image signal is written. In the second sub-frame, an image signal of 0 gradation (black display) is written, and the voltage of the charge supply line is changed to the common potential Vco 4 ms after the end of writing the final gate line.
m (5.5 V) for inversion drive. When a moving image was displayed by this driving method, intermittent lighting was performed, and further, because of the reversal driving, a high-quality full-color moving image free from image sticking and afterimages could be obtained.

[0049]

As described above, according to the present invention,
(1) a liquid crystal having spontaneous polarization; (2) an electrode for applying an electric field to the liquid crystal; and (3) an input / output terminal and a control gate. A first switching element having a gate connected to a control signal line, (4) an input / output terminal and a control gate, a charge supply line connected to the input terminal, and an output terminal connected to the electrode for applying an electric field. And the control gate is connected to the first
A second switching element to which the output terminal of the second switching element is connected; and (5) a gate control connected to the control gate of the second switching element, which is turned off after the second switching element is turned on. Since the liquid crystal display element has a timer circuit and a liquid crystal display element, the liquid crystal drive with the inconvenience of the conventional driving method, which is caused by the response time of the spontaneously polarized liquid crystal and the magnitude of the spontaneous polarization, can be performed, and a high-quality image can be obtained. Can be provided.

In particular, the magnitude of spontaneous polarization is 1 [nC
/ Cm ² ] or more, a liquid crystal display element capable of ensuring high-speed response and displaying a high-quality image can be provided.

The magnitude of the spontaneous polarization is 1 [nC / cm
² ], the spontaneous polarization liquid crystal whose response time is longer than the conduction time of the first switching element and shorter than the time interval (frame time) at which the screen display information is switched is used, so that the spontaneous polarization longer than the gate selection time is used. Since polarized liquid crystal can be used, problems with conventional liquid crystal display elements due to the response time being longer than the gate selection time can be avoided, and liquid crystals capable of displaying high-quality images despite the response time being longer than the gate selection time. A display element can be provided.

The gate control timer circuit is equivalently constituted by a parallel circuit of a capacitor and a resistor, so that a large-screen, high-definition, high-quality moving image can be displayed with a simple driving circuit configuration. An element can be provided.

Further, since the voltage applied to the liquid crystal is changed by controlling the time during which the second switching element is in the conductive state by the gate control timer circuit, the response of the spontaneously polarized liquid crystal is reduced. It is possible to provide a driving method of a liquid crystal display element in which the inconvenience of the conventional driving method due to time and the magnitude of spontaneous polarization is improved.

The magnitude of the spontaneous polarization is 1 [nC / cm
² ] and using a spontaneously polarized liquid crystal whose response time is longer than the conduction time of the first switching element and shorter than the time interval (frame time) at which the screen display information is switched, and dividing the frame time into a plurality By dividing into sub-frames, displaying images in certain sub-frames, and not displaying images in other frame times,
The same effect as intermittent lighting can be obtained, and a high-quality moving image can be obtained by preventing a hold-type afterimage of a moving image and making use of the high speed of the spontaneously polarized liquid crystal.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an example of a driving circuit of a liquid crystal display element according to the present invention.

FIG. 2 is a schematic view of a cross section of a light valve portion used in the liquid crystal display element of the present invention.

FIG. 3 is a schematic diagram illustrating an example of a driving circuit of a liquid crystal display element according to the present invention.

[4] Time-dependent illustration of the capacitor voltage V _C in the specific example of the gate control timer circuit used in the driving circuit of the liquid crystal display device of the present invention.

FIG. 5 is a schematic view illustrating switching element characteristics of a drive circuit of a liquid crystal display element according to the present invention.

FIG. 6 is an explanatory diagram showing the dependence of the transmittance of a light valve used in an embodiment of the present invention on the pulse width of an applied current.

FIG. 7 is a circuit diagram of a driving circuit of a liquid crystal display element according to the present invention.
FIG. 4 is an explanatory diagram illustrating switching element characteristics.

FIG. 8 is an explanatory view illustrating the dependency of the transmittance of the liquid crystal display element on the applied voltage pulse width in the present invention.

FIG. 9 is an explanatory view illustrating the dependency of the transmittance of the liquid crystal display element on the applied voltage pulse width in the present invention.

FIG. 10 is an explanatory diagram showing the dependence of the amount of charge stored in the spontaneously polarized liquid crystal on the capacitor voltage of the timer circuit in the liquid crystal display element according to the embodiment of the present invention.

[Explanation of symbols]

11 Light valve unit using spontaneously polarized liquid crystal, 12
Charge supply line, 13 second switching element, 14
Gate control timer circuit, 15 image signal line (data signal line), 16 first switching element, 16
a p-channel transistor, 16b n-channel transistor, 17 gate line (control signal line), 18
Capacitor, 19 resistor, 21 alignment film, 22
(A) Transparent electrode (counter electrode), 22 (b) Transparent electrode (pixel electrode), 23 glass substrate, 24 spontaneously polarized liquid crystal, 25 polarizing plate.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kasuko Wakita 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. (72) Inventor Tetsuyuki Kurata 2-3-2 Marunouchi, Chiyoda-ku, Tokyo 3 F term (reference) in Ryo Electric Co., Ltd. EE19 EE29 FF11 JJ02 JJ03 JJ05 JJ06

Claims (6)

[Claims] 1. A liquid crystal having (1) a spontaneous polarization, and (2)
A first electrode having an electrode for applying an electric field to the liquid crystal, (3) an input / output terminal and a control gate, a data signal line connected to the input terminal, and a control signal line connected to the control gate. A switching element, (4) an input / output terminal and a control gate, a charge supply line connected to the input terminal, an output terminal connected to the electrode for applying an electric field, and a first switching connected to the control gate. A second switching element to which an output terminal of the element is connected; and (5) a gate control timer circuit which is connected to a control gate of the second switching element and is turned off after the second switching element is turned on. A liquid crystal display device comprising: 2. The magnitude of spontaneous polarization is 1 [nC / cm ² ].
2. A liquid crystal display device according to claim 1, wherein said spontaneously polarized liquid crystal is used. 3. The liquid crystal display device according to claim 1, wherein a spontaneously polarized liquid crystal having a response time of the liquid crystal longer than a conduction time of the first switching element and shorter than a frame display time is used. 4. The liquid crystal display device according to claim 1, wherein the gate control timer circuit is equivalently constituted by a parallel circuit of a capacitor and a resistor. 5. The liquid crystal display element driving method according to claim 1, wherein the gate control timer circuit controls the conduction time of the second switching element to change the voltage applied to the liquid crystal. A method for driving a display element. 6. The method of driving a liquid crystal display element according to claim 1, wherein the magnitude of the spontaneous polarization is 1 [nC / cm ² ] or more, and the first switching element when the response time of the liquid crystal is driven. Using a spontaneously polarized liquid crystal longer than the conduction time and shorter than the frame display time, dividing the frame time into a plurality of sub-frames, and displaying no image in a certain sub-frame or displaying black. A method for driving a display element.