JPH09236788A - Liquid crystal display - Google Patents

Abstract

(57) Abstract: A liquid crystal display device capable of storing halftone image information in each pixel, having high image quality, high reliability, and low power consumption. After writing image information, a switch 10 is turned on and terminals B and C are set to a ground potential. AC voltage symmetrical to the ground potential is applied to the terminal A. The voltage is divided by the liquid crystal layer 2 and the memory element 6 connected in parallel. The parallel structure of the memory elements 6 has CV characteristics that are symmetrical with respect to the ground potential. For this reason,
The voltage change at the terminal E is also symmetrical. As a result, the divided AC voltage is applied to the liquid crystal layer 2.

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 device having a memory device for storing image information on the display device.

[0002]

2. Description of the Related Art In recent years, new display devices which replace conventional CRTs have been actively developed. Among them, the liquid crystal display device is thin and can operate at low power consumption, so that there are great expectations in the market of home appliances and OA equipment.

Liquid crystal display devices are classified into a simple matrix type and an active matrix type using active elements, depending on the driving method. The active matrix type is excellent in display performance and is a mainstay of liquid crystal display devices.

The structure of an active matrix type liquid crystal display device is shown in FIG. A thin film transistor 1 is provided in each pixel. When the switching signal of the thin film transistor 1 is supplied by the scanning line 3 and a pixel is selected, image information is sent from the signal line 4 to the liquid crystal layer 2 through the thin film transistor in the ON state. When not selected, the state of the liquid crystal is held by the capacitance of the liquid crystal layer 2 itself and the auxiliary capacitance 5. However, it is inevitable that the image information changes with time due to the movement of charges inside the liquid crystal layer 2 and the auxiliary capacitor 5. Therefore, the image information is refreshed with a cycle of about 1/60 seconds.

However, mobile information devices and OA devices often display still images. According to the conventional method, it is necessary to frequently refresh image information that does not change even when displaying a still image. This poses a problem that it becomes a major obstacle to the reduction of power consumption.

As a means for solving this problem, it is conceivable to give the pixel a memory property. Ferroelectric liquid crystal is known as a means for realizing a memory property, but there is a problem in operation stability. Further, since only two states of light on and off can be selected, it is necessary to use spatial modulation for halftone display, and there is a problem that the resolution is lowered.

Further, Japanese Patent Laid-Open No. 5-119298 discloses an example in which a ferroelectric substance is incorporated in each pixel as a memory element and each pixel is provided with an image information storage function. The equivalent circuit is shown in FIG. In this example, an AC voltage is applied to the counter electrode, and the thin film transistor 1 in which the ferroelectric layer 8 is connected to the gate electrode is turned on or off depending on the state of the ferroelectric layer 8. As a result, the terminal A takes a constant potential or a floating state, and two states can be selected as the AC voltage applied to the liquid crystal layer 2. However, even in this example, halftone cannot be displayed, and it is necessary to use spatial modulation for halftone display. Also, there is a state in which the terminal A is floated,
There is concern about instability in operation.

On the other hand, an example using a memory type thin film transistor is disclosed in Japanese Patent Application Laid-Open No. 3-89391. The equivalent circuit is shown in FIG. In this example, the voltage divided by the thin film transistor 1 and the memory thin film transistor 15 in which the image information is written is output to the terminal A and applied to the liquid crystal layer 2. With this method, analog gradation control is possible, but the voltage applied to the liquid crystal layer 2 has a DC component. It is known that the presence of the DC component causes deterioration of the liquid crystal layer 2, and there is a problem that the reliability of the display is uncertain.

[0009]

As described above, in the conventional active matrix type liquid crystal display device, it is necessary to rewrite an image frequently even when displaying a still image.
There is a problem that power consumption increases. Further, in a liquid crystal display device using a ferroelectric liquid crystal or a conventional ferroelectric substance, it is technically difficult to store and display a halftone as image information without impairing reliability, resulting in a decrease in display resolution. was there.

In view of the above problems, the present invention provides a liquid crystal display device capable of storing halftone image information in each pixel, high image quality, high reliability and low power consumption.

[0011]

In order to solve the above problems, the present invention according to claim 1 provides a liquid crystal display device in which a liquid crystal is sandwiched between a first electrode and a second electrode. A voltage applying unit that applies an AC voltage to the first electrode or the second electrode, and a display signal that is connected to the second electrode and holds the display signal, and the AC voltage is applied to the first electrode or the second electrode. Memory means for AC-dividing the AC voltage in response to the display signal. Here, the first electrode is, for example, a counter electrode, and the second electrode is, for example, a pixel electrode. The AC voltage may be applied to either the counter electrode or the pixel electrode.

The liquid crystal is a guest-host type liquid crystal, which is 9
A material rotated by 0 to 360 degrees, an amorphous guest-host type in which the orientation is random, and the like are effective in enhancing the contrast and reflectance. Also, it may be a TN type or a selective reflection-transmission mode using a cholesteric liquid crystal,
Ferroelectric liquid crystal, antiferroelectric liquid crystal, polymer dispersed liquid crystal, O
CB mode liquid crystal or the like may be used. The display system is also free, and in terms of classification of optical changes, any of those that obtain transmission-absorption, those that obtain transmission-scattering, and those that obtain scattering-absorption may be used. Since the number of pixels is large, a reflective type in which an insulating film is provided on the elements to form pixel electrodes is preferable, but a transmissive type is also possible depending on the pixel size.
Naturally, it does not matter whether it is monochrome or color display. The liquid crystal layer may be a single layer or multiple layers.

The alternating current applied by the voltage applying means may be a sine wave or the like in addition to the pulse, and may have a period for writing the display signal periodically.

The display signal may be applied to the memory means from the signal line through the TFT, for example. In addition to TFT,
A display pixel may be written by selecting a writing pixel by using a switching element such as MIM.

As the memory means, for example, a metal electrode, a ferroelectric layer, a laminated structure of a semiconductor layer, a structure in which an insulator is provided between the ferroelectric layer and the semiconductor layer, and a structure between the ferroelectric layer and the semiconductor layer are provided. A structure in which a metal electrode and an insulator are provided and connected in parallel and with opposite polarities can be used. However, when an AC voltage is applied to the first electrode, an AC voltage is generated according to a display signal. Any type may be used as long as it has a function of dividing the voltage in an AC manner.

Ferroelectric materials include PZT and LiNb
An inorganic compound such as O ₃ , BaTiO ₃ , PMN, or Bi ₄ Ti ₃ O ₁₂ may be used, or an organic thin film of polyvinylidene fluoride subjected to orientation treatment may be used.

According to the present invention, it is possible to store a display signal as halftone image information in each pixel in the liquid crystal display device. As a result, frequent image refreshing with respect to still image display can be omitted, which is extremely effective in reducing power consumption.

Further, according to the present invention, for any image information in the memory element, a voltage corresponding to the image information can be applied to the liquid crystal in an analog manner. As a result, halftone image information can be stored and displayed, and a liquid crystal display device with extremely high image quality can be realized.

According to a second aspect of the present invention, in a liquid crystal display device in which a liquid crystal is sandwiched between a first electrode and a second electrode, an AC voltage is applied to the first electrode or the second electrode. A voltage applying means for applying is connected to the second electrode to form a capacity connected in series with the capacity of the liquid crystal, holds a display signal as the magnitude of the capacity, and A memory capacitor having a capacitance change characteristic that is substantially symmetrical or asymmetrical about a specific voltage.

When the liquid crystal capacitance is asymmetric with respect to the positive and negative of the applied voltage, the memory capacitance element having a capacitance change characteristic asymmetric with respect to the applied voltage is used. In this case, the AC voltage applied to the first electrode is correspondingly asymmetric.

According to a third aspect of the present invention, in a liquid crystal display device in which a liquid crystal is sandwiched between a first electrode and a second electrode, an AC voltage is applied to the first electrode or the second electrode. A voltage applying means for applying a voltage, a first polar memory element connected to the second electrode and having a capacitance change characteristic asymmetric with respect to the applied voltage, and the first polar memory element in parallel. And a second polar memory element connected to the second electrode so as to have opposite polarities and having an asymmetric capacitance change characteristic with respect to an applied voltage; and the first and second polar memory elements. And a signal applying means for applying a display signal.

The polar memory element is a laminated structure of the metal electrode, the ferroelectric layer and the semiconductor layer described above, a structure in which an insulator is provided between the ferroelectric layer and the semiconductor layer, the ferroelectric layer and the semiconductor layer. It refers to a structure in which a metal electrode and an insulator are provided between them.

The signal applying means applies display signals of mutually opposite polarities to the first and second polar memory elements, respectively.

[0024]

FIG. 1 is a diagram showing a basic configuration of the present invention. In FIG. 1A, the terminals B and C are normally kept at the same potential. The two memory elements 6 are shown in FIG.
As shown in (c), it has a laminated structure (MFS structure) of a metal electrode 7, a ferroelectric layer 8 and a semiconductor layer 9. An MFIS structure in which an insulator is provided between the ferroelectric layer 8 and the semiconductor layer 9 or an MFMIS structure in which a second metal electrode and an insulator are provided between the ferroelectric layer 8 and the semiconductor layer 9 may be used. .

FIG. 1D shows the capacitance-voltage characteristic (CV characteristic) when amorphous silicon is used as the semiconductor layer 9 in the structure of FIG. 1C. Common metal −
In the insulator-semiconductor structure (MIS structure), when a positive voltage is applied to the metal, charges are accumulated at the interface between the semiconductor and the insulator at a voltage equal to or higher than the threshold voltage.
The capacity increases as shown in a. When the ferroelectric substance in the memory element 6 is used as in this embodiment, the residual polarization Pr generated when an electric field larger than the coercive electric field is generated in the ferroelectric substance. It is known that the characteristic shifts to the left and right as indicated by 11c.

As described above, this structure has an asymmetric C-
Since it has V characteristics, as shown in FIG. 1B, the polarities of the memory element will be shown by adding arrows to the terminals on the electrode side. Here, consider a structure in which the polarities of the MFS structure described above are connected in parallel with each other. It is assumed that the CV characteristics of each memory element are the same. The remanent polarization of the ferroelectric substance in each memory element 6 is generated by applying an electric field higher than the coercive electric field between terminals B and C shown in FIG. When viewed from the terminals B and C, the polarities of the memory element 6 are in the same direction. The CV characteristic of each memory element 6 shifts due to the occurrence of remanent polarization, but the amount is the same in the two memory elements 6.

Next, as shown in FIG. 2 (c), terminals B and C are connected and a new terminal D is considered. At this time, the polarities of the memory elements 6 viewed from the terminals A and D are opposite to each other. The C-V characteristic between the terminals A and D is a characteristic in which the C-V characteristics of the two memory elements are superposed in the opposite direction.
As shown in (a), a C-V characteristic symmetrical about the vertical axis (ground potential) is obtained. Moreover, since the threshold voltages of both memory elements 6 change by the same amount as indicated by the dotted line in the figure according to the magnitude of the remanent polarization, the spread of the CV curve changes without losing symmetry. The present invention relates to C- shown in FIG.
The purpose is to control the voltage applied to the liquid crystal by utilizing the V characteristic.

FIG. 1A shows the memory device 6 shown in FIG.
And the liquid crystal layer 2 is connected in series. In this figure, a switch 10 is provided to simplify the description.

To write image information, a voltage is applied between terminals B and C with switch 10 turned off. The voltage is set to such a level that an electric field higher than the coercive electric field is generated in the ferroelectric substance in the memory element 6 and remanent polarization corresponding to image information is generated. If the structure of each memory element 6 is the same, the remanent polarization generated is also the same in each memory element 6.

When the writing of the image information is completed, the switch 10 is turned on and the terminals B and C are set to the ground potential. On the other hand, a symmetrical AC voltage with respect to the ground potential is applied to the terminal A. The voltage is divided by the liquid crystal layer 2 and the memory element 6 connected in parallel. At this time, an electric field higher than the coercive electric field is prevented from being generated in the ferroelectric substance in each memory element 6. Since the parallel structure of the memory elements 6 has a C-V characteristic that is symmetrical with respect to the ground potential, the voltage change at the terminal E is also symmetrical. As a result, the divided AC voltage is applied to the liquid crystal layer 2.

The symmetry point of the CV characteristic does not have to be the ground potential. If the voltage between the terminals B and C and the terminal A is shifted according to the amount of deviation of the symmetry point of the CV characteristic from the ground potential, an AC voltage is applied to the liquid crystal layer 2.

The fact that an AC voltage can be applied to the liquid crystal layer 2 means that
Very effective against deterioration of liquid crystal. When a direct current component is present in the voltage applied to the liquid crystal, deterioration of the liquid crystal called image sticking occurs due to localization of charges in the liquid crystal alignment film and the like. However, in the present invention, since a complete AC voltage can be applied to the liquid crystal layer 2, deterioration of the liquid crystal does not occur at all, and an extremely reliable display device can be realized.

Further, in the present invention, by changing the threshold voltage of each memory element 6, the voltage applied to the liquid crystal layer 2 can be controlled in an analog manner. As shown in FIG. 2A, if the region in which the CV curve gradually changes according to the voltage and the horizontal portions before and after the region are used as the operating range of the memory device 6, the threshold voltage of the memory device 6 is The capacity of the memory element 6 changes accordingly. As a result, the voltage applied to the liquid crystal layer 2 can be changed in an analog manner without changing the voltage applied to the terminal A. Moreover, since the symmetry of the CV characteristics in the parallel structure of the memory element 6 is maintained, no DC voltage component is applied to the liquid crystal layer 2.

The state of the ferroelectric substance in the memory element 6 in each state will be described with reference to the hysteresis curve of the ferroelectric substance shown in FIG.

When the electric field is set to zero after the electric field equal to or higher than the coercive electric field Ec is generated, the remanent polarization Pr is generated. If there is already stored information, it is sufficient to generate an electric field of coercive electric field −Ec or less to reset the memory function and then generate an electric field of Ec or more. The magnitude of Pr depends on the magnitude of the applied voltage. In the image display state, since only the electric field below the coercive electric field is generated in the ferroelectric substance in the memory element 6, Pr does not change, and its operating range is the portion shown in FIG. In the present invention, gradation control is performed using the magnitude of Pr. Since Pr is held very stably in the ferroelectric substance, it is also excellent in the memory property of halftone.

According to the present invention, once the image information is stored in the pixel, the image is displayed only by applying a common AC voltage to the liquid crystal layer, and frequent screen rewriting is not necessary, so that the image is particularly stationary. When displaying images, it is possible to significantly reduce power consumption.

Further, if the AC voltage applied to the terminal A is cut off, that is, the liquid crystal display device is turned off, if the AC voltage is applied to the terminal A again, the image information stored in the memory element 6 is displayed again. Therefore, reduction in power consumption can be expected also in this respect.

In the present invention, the C of the memory element is
It is sufficient that the region where the −V characteristic is symmetric and the capacitance gradually changes with respect to the applied voltage, or this region and the horizontal portions before and after the region can be used as the operating range. Therefore, the C-V characteristic of the memory element 6 alone is not limited to the characteristic shown in FIG. 2, and may be V-shaped as shown in FIG. Such characteristics are obtained when the generation of carriers in the semiconductor layer follows the measurement frequency. Also in this case, as described above, by using the structure in which parallel connection is made with the reverse characteristics,
It is possible to obtain symmetrical C-V characteristics.

[0039]

【Example】

(Embodiment 1) FIG. 5 is a circuit diagram of one pixel of a liquid crystal display device according to the first embodiment of the present invention. Two selection thin film transistors 1 are provided for each pixel, and the gate electrodes thereof are connected to the scanning lines 3. Each thin film transistor 1
The drain electrodes of a and 1b are connected to the signal lines 4a and 4b, respectively. Further, the source electrodes of the thin film transistors 1a and 1b are connected to the memory elements 6a and 6b using the ferroelectric substance.

The memory elements 6a and 6b have different polarities with respect to the source electrodes of the thin film transistors 1a and 1b. Further, the source electrode of each thin film transistor 1 is provided with auxiliary capacitances 5a and 5b having a liquid crystal capacitance or more with respect to the ground. Auxiliary capacitors 5a and 5b
Have the same capacity.

One electrode of the liquid crystal layer 2 is connected between the memory elements 6a and 6b, and the other electrode of the liquid crystal layer 2 (corresponding to the terminal A in the figure) is a counter electrode. An alternating voltage centered on the ground potential is applied to the counter electrode.

First, the case of writing image information in the memory element 6 will be described.

Since the immediately preceding image information has already been written in the memory element 6, a voltage of reverse polarity is applied to reset. Specifically, a voltage is externally applied to the ferroelectric substance in the memory element 6 so that an electric field equal to or lower than the coercive electric field −Ec is generated. At this time, if the voltage applied to the memory element 6 is -Vc, a switching signal of the thin film transistor 1 is sent to the scanning line 3 to turn on the thin film transistor 1, and -Vc is applied to the signal line 4a and Vc is applied to the signal line 4b. To do. Due to the symmetry of the circuit, -Vc is applied to each memory element 6, and the immediately preceding image information is reset.

Next, an electric field is generated in the ferroelectric substance in the memory element 6 to the extent that remanent polarization corresponding to image information is generated at a coercive electric field Ec or more. At this time, when the voltage applied to the memory element is Va, Va is applied to the signal line 4a and -Va is applied to the signal line 4b while the thin film transistor 1 is in a conductive state.
Is applied. Due to the symmetry of the circuit, V is applied to each memory element 6.
a is applied and the image information is stored equally in the memory elements 6a, 6b. The terminal A, that is, the counter electrode is shown in FIG.
An AC voltage centered on the ground is applied like
A period for writing image information may be specially provided in the voltage waveform of the counter electrode as shown in FIGS.
In the same figure (b), the voltage of the writing time is set to ground. In this case, since no voltage is applied to the liquid crystal layer 2 during writing, high image quality can be realized. In the same figure (c), the voltage of the writing time is set to a constant voltage ± Vs for reversing the polarity. That is, the voltage applied to the liquid crystal during the writing time is Vs
I have to.

When the image information is rewritten for the other pixels in which the gate electrode of the thin film transistor 1 is connected to the scanning line 3 which has sent the switching signal, the data may be rewritten by the above method. If it is not necessary to rewrite the image information, a voltage in the range where the information in the memory element 6 does not change may be applied to the signal line 4.
As a result, it becomes possible to rewrite image information of an arbitrary pixel.

Next, the behavior of the liquid crystal when writing image information will be described.

The equivalent circuit of one pixel shown in FIG. 5A is symmetrical, and in principle the voltage between the two memory elements 6 is equal to the ground potential during writing. However, the voltage between the two memory elements 6 may slightly fluctuate due to a slight difference between the left and right characteristics or a slight shift in signal timing. However, while the time required for writing the image information is several tens of μsec, the response speed of the liquid crystal is several tens of msec, and the influence of the voltage variation between the two memory elements 6 has almost no influence on the display characteristics. do not do. Next, a case of displaying the image information written in the memory element 6 will be described.

The switching signal of the scanning line 3 is stopped and the thin film transistor 1 is turned off. This state is shown in Figure 5.
It is represented by the equivalent circuit of (b). An alternating voltage centered on the ground potential is applied to the terminal A. Auxiliary capacity 5
Since the voltage dependence of the combined capacitance of a total of four elements a, 5b and the memory elements 6a and 6b has a symmetrical characteristic with respect to the ground potential, the liquid crystal layer 2 also has the auxiliary capacitance 5 and the memory element 6.
A considerable AC voltage divided by is applied. Moreover, there is no DC component in the voltage applied to the liquid crystal layer 2, and the liquid crystal does not deteriorate.

As described above, according to this embodiment, it is possible to realize a liquid crystal display device which can apply an AC voltage to the liquid crystal layer 2 and can also store an analog gradation.

In the present embodiment, as shown in FIG. 2A, in the CV characteristic of the memory element 6, a region in which the capacitance gradually changes according to the voltage or a horizontal portion before and after this region. Area will be used. Therefore, the wider the area, the easier the control of the voltage applied to the liquid crystal layer 2. Therefore, as shown in FIG. 6, if the memory element 6 and a plurality of sub-capacitances 11 are connected in series and further those connected in parallel are used as a new memory element, the sub-capacitance 11
It is possible to widen the range by dividing the capacity with.

(Embodiment 2) FIG. 9A is an equivalent circuit diagram of one pixel of a liquid crystal display device according to a second embodiment of the present invention.

Three thin film transistors are provided for each pixel. Polysilicon is used for the thin film transistor, and n-type thin film transistor 13 for pixel selection and 2
It is composed of individual p-type transistors 14a and 14b. The gate electrode of each thin film transistor is connected to the scanning line 3. The drain electrode of the n-type transistor 13 is connected to the signal line 4. The source electrode of the n-type thin film transistor 13 is connected to the memory elements 6a and 6b using the ferroelectric substance with the polarity shown in FIG. It is also connected to the drain electrode of the p-type thin film transistor 14b, and the source electrode of the thin film transistor is grounded. Two memory elements 6
The drain electrode of the p-type transistor 14a is connected between a and 6b.

One electrode of the liquid crystal layer 2 is connected to the source electrode of the p-type thin film transistor 14a, and the other electrode (corresponding to terminal A in the figure) of the liquid crystal layer 2 of the liquid crystal is a counter electrode. An alternating voltage centered on the ground potential is applied to the counter electrode.

First, the case of writing image information in the memory element 6 will be described.

Since the immediately preceding image information has already been written in the memory element 6, a voltage of opposite polarity is applied to reset. Specifically, a voltage is externally applied to the ferroelectric substance in the memory element 6 so that an electric field equal to or lower than the coercive electric field −Ec is generated. At this time, if the voltage applied to each memory element is -Vc, a switching signal of the thin film transistors 13 and 14 is sent to the scanning line 3 to turn on the n-type thin film transistor 13 and turn off the p-type transistor 14. Then, −2 × Vc is applied to the signal line 4. -Vc is applied to each memory element 6, and the immediately preceding image information is reset.

Next, an electric field is generated in the ferroelectric substance in the memory element 6 to the extent that remanent polarization corresponding to image information is generated at a coercive electric field Ec or more. Assuming that the voltage applied to the memory element at this time is Va, 2 × Va is applied to the signal line 4 while the switching signal is being sent to the scanning line 3. Since the p-type thin film transistor 14a is in the off state, the liquid crystal layer 2 is not affected by being applied to the memory element, Va is applied to each memory element 6, and the image information is equal to that of the memory elements 6a and 6b. Remembered. The p-type thin film transistor 14b is also in the off state, and the source electrode and the drain electrode of the n-type thin film transistor 13 are kept at the same potential. An AC voltage centered on the ground is applied to the terminal A, that is, the counter electrode as shown in FIG. 8A. However, as shown in FIGS. 8B and 8C, the counter electrode has a period for writing image information. It may be specially provided in the voltage waveform. In the same figure (b), the voltage of the writing time is set to ground.
In the same figure (c), the voltage of the writing time is set to a constant voltage ± Vs for reversing the polarity.

Next, the case of displaying the image information written in the memory element 6 will be described.

By stopping the switching signal of the scanning line 3,
The n-type thin film transistor 13 is turned off and the p-type transistors 14a and 14b are turned on. The equivalent circuit of the pixel in this state is shown in FIG. 9 (b). An alternating voltage centered on the ground potential is applied to the terminal A. Since the voltage dependency of the combined capacitance of the two memory elements 6a and 6b in total is symmetrical with respect to the ground potential, the liquid crystal layer 2 also has a corresponding AC voltage divided by the memory element 6. Will be applied. Moreover, there is no DC component in the voltage applied to the liquid crystal layer 2, and the liquid crystal does not deteriorate.

As described above, according to this embodiment, it is possible to realize a liquid crystal display device which can apply an AC voltage to the liquid crystal layer 2 and can also store an analog gradation.

[0060]

As described above, according to the present invention, a liquid crystal display device capable of storing halftone image information in each pixel and having high image quality, high reliability and low power consumption is provided. It becomes possible to provide.

[Brief description of drawings]

FIG. 1 is a diagram showing an equivalent circuit of a liquid crystal display device according to the present invention and characteristics of a memory element.

FIG. 2 is a diagram showing characteristics and configuration of a memory element according to the present invention.

FIG. 3 is an equivalent circuit diagram showing an example of a conventional liquid crystal display device.

FIG. 4 is a characteristic diagram showing an operating range of a ferroelectric layer according to the present invention.

FIG. 5 is a diagram showing an equivalent circuit of the liquid crystal display device of the first embodiment.

FIG. 6 is a diagram showing an equivalent circuit of another memory element according to the present invention.

FIG. 7 is a diagram showing characteristics of another memory element according to the present invention.

FIG. 8 is a diagram showing an example of applied voltages in the first and second embodiments.

FIG. 9 is a diagram showing an equivalent circuit of the liquid crystal display device of the second embodiment.

FIG. 10 is an equivalent circuit diagram showing an example of a conventional liquid crystal display device.

DESCRIPTION OF SYMBOLS 1 thin film transistor 2 liquid crystal layer 3 scanning line 4 signal line 5 auxiliary capacitance 6 memory element 7 metal electrode 8 ferroelectric layer 9 semiconductor layer 10 switch 13 n-type thin film transistor 14 p-type thin film transistor 15 memory thin film transistor

Claims (3)

[Claims] 1. A liquid crystal display device in which a liquid crystal is sandwiched between a first electrode and a second electrode, wherein voltage applying means for applying an AC voltage to the first electrode or the second electrode, Memory means connected to the second electrode for holding a display signal and for AC-dividing the AC voltage according to the display signal when an AC voltage is applied to the first electrode or the second electrode A liquid crystal display device comprising: 2. A liquid crystal display device in which a liquid crystal is sandwiched between a first electrode and a second electrode, wherein voltage applying means for applying an AC voltage to the first electrode or the second electrode, The capacitor is connected to the second electrode to form a capacitor that is connected in series with the capacitor of the liquid crystal, holds a display signal as the size of the capacitor, and is centered around a specific voltage with respect to the applied voltage. A liquid crystal display device, comprising: a memory capacitor having symmetrical or asymmetrical capacitance change characteristics. 3. A liquid crystal display device in which a liquid crystal is sandwiched between a first electrode and a second electrode, wherein voltage applying means for applying an alternating voltage to the first electrode or the second electrode, A first polar memory element that is connected to the second electrode and has a capacitance change characteristic that is asymmetric with respect to an applied voltage; and a first polar memory element that is in parallel with and has an opposite polarity to the first polar memory element. A second polar memory element connected to the second electrode and having a capacitance change characteristic asymmetric with respect to an applied voltage; and a signal for applying a display signal to the first and second polar memory elements. A liquid crystal display device comprising: an applying unit.