JPH11305257A - Liquid crystal display device utilizing ferroelectric substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption on half tone display by constituting a MOS transistor(TR) as vertical structure for allowing a carrier to run in the film thickness direction of a semiconductor layer formed on a substrate. SOLUTION: Ferroelectric controlling electrodes and signal electrodes are formed like a matrix by a thin film semiconductor process and a MOS type switch element is formed on an intersecting part of respective wirings. The switch element has vertical thin film TR structure and allows a carrier to run in the film thickness direction of the semiconductor layer formed on the substrate. In this case, a silicon active layer 9 is deposited on signal electrodes 10 formed like strips and a ferroelectric film 7 is deposited on the layer 9. Ferroelectric controlling electrodes 8, 11, 13 are also patterned so as to intersect with the electrodes 10 while leaving the film 7 like a comb. Then connection holes to be connected to the lower silicon active layer 9 are formed on a display pixel electrodes and a silicon active layer 6 is deposited again so as to fill the holes. Then a display electrode 5 is formed on the layer 6 in each pixel to obtain an array substrate.

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 using a ferroelectric material which realizes low power consumption in a halftone display state.

[0002]

2. Description of the Related Art A liquid crystal display device is used as a light-weight and low-power-consumption display device as represented by a notebook personal computer and a portable TV. TF among liquid crystal display devices
In a T-LCD, a TFT (thin film transistor) as a switch element is provided at an intersection of wirings formed in a matrix, and a TFT is turned on by sequentially inputting a line-sequential scanning signal from one of the wirings. A predetermined signal is written in the liquid crystal material by supplying a video signal synchronized with the above to the corresponding pixel electrode through the on-state TFT from the other orthogonal wiring, and the liquid crystal material is displayed by the signal. Is displayed. FIG. 11 illustrates the matrix circuit, and a circuit S (i, j) within a broken line indicates a pixel circuit. FIG. 12 is an equivalent circuit of the circuit S (i, j) within the broken line. Reference numeral 124 denotes a switching element for applying a video signal to the liquid crystal layer, 121 denotes a liquid crystal capacitor, and 123 denotes an auxiliary capacitor.

[0003] In this conventional display device, 1 / 60th is usually used.
Since the image is refreshed by sequential scanning every second and the image is constantly rewritten, for example,
Even if you do not need to rewrite the video in still image display,
Since the driving of the sequential scanning is performed, the power consumption is largely consumed for the driving.

Therefore, a display device having a memory characteristic has been considered by using a ferroelectric material having a PE hysteresis characteristic as shown in FIG. 9 as a capacitor material. As shown in FIG. 10, a pixel is formed by connecting a switch element 103, a liquid crystal capacitor 101, and a ferroelectric capacitor 102 in series. By writing a signal to the connected ferroelectric capacitor 102 until the saturation electric field intensity is reached, a memory state is obtained in which the directions of spontaneous polarization of the ferroelectric are uniform. This memory state of the capacitor compensates for the charge due to the leak current generated in the switch element, so that the fluctuation of the potential applied to the liquid crystal can be reduced.

However, in a display in which refresh is frequently performed, a large amount of electric charge is written into the capacitor 102 and a driving voltage is increased due to the series connection of the capacitors. . Further, when the display device is formed of a liquid crystal material having a large leak current, the charge compensation in the serially connected capacitors 102 as shown in FIG. 10 cannot be completely performed, and there is a possibility that display unevenness or the like may occur. As a countermeasure, a method of using a 1-bit type memory circuit instead of the switch element of FIG. 12 has been considered (Japanese Patent Laid-Open No. Hei 3-077922). By storing ON and OFF of the switch element in a 1-bit memory and driving Vsig with an AC signal having an appropriate cycle (up to 60 Hz), a display corresponding to ON / OFF of the switch can be performed. By storing the switch state, in the case of a still image display, it is not necessary to rewrite the storage information of the switch, so that the power consumption required for rewriting the serially inserted capacitor 102 in FIG. 10 is very small. However, when halftone display is performed using this device, since only binary on / off control can be performed for the switch characteristics, a large number of display pixels are combined and gradation display is performed based on the display area. It can be executed only by the method of performing the area gray scale display, and the capacitor is fully charged in the ON state, so that the power consumption cannot be reduced in the halftone display state.

[0006]

Although a conventional liquid crystal display device using a ferroelectric for a switching element can reduce power consumption as compared with a case where it is not used, in a halftone display, the switching element is turned on. Will charge the capacitor fully. Therefore, the power consumption cannot be reduced in the halftone display state.

The present invention has been made in view of the above problems, and has as its object to provide a liquid crystal display device using a ferroelectric having switching elements capable of reducing power consumption even in a halftone display state. And

[0008]

According to a first aspect of the present invention, there is provided a liquid crystal display device using a ferroelectric material, comprising: a substrate having an insulating surface; and a gate insulating film formed on the substrate. A MOS transistor using a ferroelectric,
A liquid crystal using a ferroelectric having a pixel electrode whose charge injection amount is controlled by the MOS transistor, a counter electrode facing the pixel electrode, and a liquid crystal layer formed between the counter electrode and the pixel electrode. In the display device, the MOS transistor has a vertical structure in which carriers run in a thickness direction of a semiconductor layer formed on the substrate.

According to a second aspect of the present invention, there is provided a liquid crystal display device using a ferroelectric, a substrate having an insulating surface, a MOS transistor formed on the substrate and using a ferroelectric for a gate insulating film, and a MOS transistor. Liquid crystal display device using a ferroelectric having a pixel electrode whose charge injection amount is controlled by a type transistor, a counter electrode facing the pixel electrode, and a liquid crystal layer formed between the counter electrode and the pixel electrode Wherein the MOS transistor includes a first semiconductor film formed on the substrate, a comb-shaped gate insulating film formed on the first semiconductor film, and a comb formed on the gate insulating film. A gate electrode having a shape, and a second semiconductor film covering the gate insulating film and the gate electrode, wherein carriers run in a thickness direction of the first semiconductor layer.

According to a third aspect of the present invention, in the liquid crystal display device using a ferroelectric, the gate electrode controls the amount of the carrier by changing the interval between the comb-shaped teeth. And

According to a fourth aspect of the present invention, there is provided a liquid crystal display device using a ferroelectric substance according to the second aspect, wherein the gate electrode and the second semiconductor film are electrically insulated by an insulating film. .

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a liquid crystal display device in which a ferroelectric material is used for a gate insulating film of a MOS transistor, the whole structure of the transistor is vertical, and this device is used as a pixel switching device. The main point.
Since this switching element has a linear characteristic in which the drain current gradually increases with respect to the drain voltage, the switching element can operate stably in an intermediate state other than the on / off binary value. By using this switching element as a pixel switch element of a liquid crystal display device, the charge amount of the pixel electrode in a halftone state can be reduced as compared with the conventional transistor which can only fully turn on the charge amount. As a result, power consumption in the halftone display state can be reduced.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to embodiments. (Embodiment 1) Hereinafter, Embodiment 1 of the liquid crystal display device of the present invention will be described.
Is shown.

FIG. 1 is a sectional view of a display device according to the present invention.
A ferroelectric control electrode and a signal electrode are formed in a matrix by a thin film semiconductor process.
An OS-type switch element is formed. This switch element has a structure of a vertical thin film transistor as shown in FIG.

First, a silicon active layer 9 is deposited on a strip-shaped signal electrode 10, and a ferroelectric film 7 is deposited thereon. The ferroelectric film 7 is left in a comb shape by etching corresponding to the display pixels, and the ferroelectric control electrodes 8, 11, and 13 are also patterned so as to be orthogonal to the signal electrode 10 (the electrodes are formed on the ferroelectric film. Also formed in a comb shape). Patterning can be performed collectively after depositing the ferroelectric film and the control electrode film. 12 is an interlayer insulating film, and 1 is a glass substrate. Instead of this glass substrate, a semiconductor substrate can be used as the substrate. In this case, the surface may be coated with an insulating film.

Next, a connection hole to the lower silicon active layer 9 is formed by an appropriate etching method at an arbitrary position on a display pixel signal electrode described later, and the silicon active layer 6 is deposited again so as to fill the hole. Let it. At this time, if the adjacent distance of the pixel electrode 5 to be deposited later is short, there is a possibility that noise between adjacent pixels may cause a problem. Therefore, the silicon active layer is further etched like an island like a ferroelectric. It is desirable (not shown in the figure).

Further, the display electrodes 5 are formed for each pixel on the silicon active layer 6, and the array substrate is completed. The array substrate and the opposing substrate 2 on which the opposing electrode 3 is formed are assembled in a conventional cell process, and a liquid crystal layer 4 is interposed between the substrates 1 and 2 to form a liquid crystal display device.

In FIG. 1, the ferroelectric control electrodes 8, 11, 1
3 is electrically connected to the wiring 13 disposed in the lowermost layer via the wirings 8 and 11 formed in the contact holes, but is simply connected to the silicon active layer 6 so as to be orthogonal to the signal electrode wiring. , 9 may be formed. The ferroelectric control electrodes 8, 11, and 13 function as an address line of the liquid crystal display device or a gate electrode of the MOS transistor 100. The signal electrode 10 and the pixel electrode 5 also function as the source / drain of the MOS transistor 100. The reason for adopting the configuration as shown in FIG. 1 is to limit the region where the silicon active layers 6 and 9 operate as switch elements, and to prevent malfunctions as parasitic elements. As the expected parasitic element, in FIG.
An element formed between 3 and the silicon active layers 6, 9 and the signal electrode 10 and an element formed between the ferroelectric control electrodes 8, 11, 13 and the silicon active layer pixel electrode 5 are expected. . As a countermeasure, as described above, the silicon active layer 6,
It is considered that it is better to form elements 9 in an island shape for each display pixel to achieve element isolation. When the active layers 6 and 9 are separated into islands, the reliability of element operation is improved by providing an interlayer insulating film in consideration of the reliability of the next process. I do. The active layers 6, 9 and the ferroelectric control electrodes 8, 11, 13 are Schottky-bonded to restrict the flow of current to some extent. By providing one layer of insulating film before the formation, it is possible to reliably insulate. The above-described gate electrode can control the amount of carriers flowing through the channel by changing the interval between the comb-shaped teeth, and can control the display range of halftone.

The temperature process that can be used for manufacturing the above-described wiring board 1 differs depending on the material of the board material used. For example, when a silicon wafer is used, since the ULSI technology can be used, a high-quality wiring board can be manufactured with its controllability, processability, and reliability. On the other hand, a-SiTF
The process of about 400 ° C. represented by T has an advantage that a large glass substrate can be used.

Further, polysilicon, which is currently attracting attention,
The process consists of a high mobility TFT on a large glass substrate
It is in the limelight to be able to form devices. In this process, a TFT having a high mobility can be formed by depositing and patterning an a-Si thin film and then polycrystallizing it by an ELA (excimer laser annealing) process. Since the mobility required for the switch element of the pixel display unit is a mobility of 10 to 10 V · s / cm 2, it is sufficient to appropriately select the process timing of performing the ELA in the manufacturing process. Is optimized.

As a simple method of applying ELA, ELA is performed after the deposition of the second silicon active layer. Silicon on the electrode is rapidly cooled by reflection of metal electrodes and diffusion of heat, so that crystal grains become fine. On the other hand, in the portion connected to the lower silicon layer through the penetrating portion, heat is absorbed in the depth direction and gradually cooled, so that the crystal grains become larger and more homogenous than on the electrode. As a result, the size and homogeneity of the crystal grains corresponding to the channel portion of the vertical TFT can be realized, so that the performance of the switch element can be improved and the leakage characteristics of the switch element other than the channel portion can be suppressed low.

To achieve the same effect, a method of performing ELA immediately after patterning the ferroelectric control electrode before depositing the second silicon layer is also conceivable. in this way,
The first silicon layer becomes p-Si, and the second silicon layer remains a-Si. In this step, charge transfer by the electric field of the first layer is easier than that of the second layer, so that control of the electric field or electric charge can be performed by the a-Si layer of the second layer. Therefore, a switch element in which the loss due to the second silicon layer is suppressed to a low level can be formed. Also, E
When performing LA, the laser beam is normally irradiated perpendicularly to the substrate surface, but the size and shape of the through-holes forming the first and second silicon layers and the irradiation angle of the ELA laser beam are optimized. By doing so, it is possible to control the electric field distribution of the channel portion at the time of device operation by distributing the state of ELA activation.

The characteristics of the vertical MOS transistor incorporated in the reflection type liquid crystal display device manufactured in this step will be described. In a conventional flat TFT (where the carrier runs in a direction parallel to the substrate surface), the current at the drain voltage is saturated at the drain voltage of about 10 to 15 V as shown in FIG. Although suitable for binary control, it is difficult to stop in this intermediate state, but in the element formed this time, as shown in FIG.
It can be seen that the voltage can be controlled linearly even at about 15 V, and the current control region based on the drain voltage is widened. From the above, it is not necessary to use the switch element as a simple on / off switch, but to control the charge or the partial voltage for multi-gradation display, the element characteristics shown in FIG. 2 are required. . In this regard, it can be said that this element having improved charge or electric field control has high controllability.

By using such a switching element as a pixel switch element of a liquid crystal display device, the charge amount of the pixel electrode in a halftone state can be only fully turned on compared to a conventional transistor which can only turn on fully. By reducing the amount, power consumption in the halftone display state can be reduced.

In the first embodiment described with reference to FIG.
An example in which a switch element is formed under the entire surface is shown. This is because the structure is applied to a reflective display device in which a reflective metal electrode is formed on a pixel electrode. In consideration of implementation in a transmissive display device, it is conceivable to dispose a switch element at an end of a pixel electrode. As an example of the arrangement, it is conceivable to form switch elements at the corners, four corners, one side, the periphery, the center, and the like of the pixel electrode. Although this arrangement method is determined based on requirements such as the amount of drive current, controllability (uniformity), operation stability, and easiness of process, it does not prevent application of this arrangement method to a reflection-type device.

In FIG. 1, a pixel electrode is provided as a reflection electrode. However, a silicon active layer and a ferroelectric control electrode can be used as a light scattering or absorption layer.
When the pixel electrode is eliminated, the orientation of the liquid crystal is determined by the lines of electric force emitted from the through portion. Therefore, the interval between the penetrating portions needs to be an interval of at least several tens of microns or less. In order to increase the spacing, the resistance is reduced by lightly doping only the top of the silicon active layer in order to homogenize the lines of electric force, and the uniformity of display is achieved by making the interface with the liquid crystal an equipotential surface. Can be secured.

In the above, the specific structure of the liquid crystal display device has been described.
Although the configuration and the manufacturing process of the wiring board have been described, a specific circuit configuration and a driving method will be described below. FIG. 5 shows an equivalent circuit of one pixel 50 in FIG. Micro-switch elements formed of patterned ferroelectric layers are connected to three-terminal elements 521, 5
22, 523, and 524. A display electrode is provided to collect the output signals of these elements, and drives the liquid crystal sandwiched between the counter electrodes. 51 is a liquid crystal capacitance.

FIG. 4A shows an example of the drive signal. The drive signals of the switch elements 521, 522, 523, 524 are
It consists of a reset signal and a set signal. As a simple configuration, a new signal is generally written and displayed immediately after reset. As the reset signal, a pulse (Vfe-Vsig) that becomes a bias voltage corresponding to the point C of the hysteresis curve in FIG. 9 is applied. Thereafter, by applying a voltage of the opposite sign to the ferroelectric, the open / close state of the switch is controlled. Signals An ON state can be set by a combination of FIGS. 4B and 4C, and an OFF state can be set by a combination of FIGS. 4B and 4D. In order to perform multi-gradation display from binary control, it is necessary to initialize a hysteresis curve. In this case, an attenuation signal as shown in FIG. 4A is supplied in advance as a reset signal, and the characteristic is returned near the origin of the curve in FIG. This initialization enables multi-gradation display by a hysteresis loop with a small signal. It is thought that it is possible to write a signal to this ferroelectric in a few microseconds or less, and it is faster than the conventional method of sequentially scanning switch elements and writing signals to the pixel capacitance and auxiliary capacitance. It is considered that scanning is possible. Therefore, in a blanking period between scans, it is possible to apply a correction signal for the fluctuation of the Vsig signal also used as a reference signal during this period (blanking period). This is to make uniform the occurrence of display unevenness by inputting a correction signal, because the effective voltage of Vsig with respect to Vcom in FIG. 5 is different depending on the video signal, and by imbalance of the effective voltage of the Vsig signal. Display unevenness can be corrected. As a correction method, a moving charge amount between the reference potential and the input signal Vsig may be integrated for a fixed scanning time, and a potential corresponding to the integrated charge amount may be applied as a pulse.

As can be understood from the above description, in a still image display or the like, rewriting for refreshing the switch element provided in the pixel becomes unnecessary. Also, like before,
In driving by an auxiliary capacitor connected in parallel to the liquid crystal capacitor, rewriting must be performed for liquid crystal refreshing. Therefore, the charge transfer for “liquid crystal capacitor + switch element capacitance + auxiliary capacitance + array side wiring capacitance” is several μm. Needed to be completed in seconds. On the other hand, in the present display device, only the movement of the charges corresponding to “liquid crystal capacitance + opposite electrode side wiring capacitance” causes the driving cycle to be 6
About 0 Hz is sufficient. The power consumption P is the capacitance C of the element to be driven, the signal voltage V to be written, and the frequency F of the signal.
Since P = C × V × V × F, the power consumption at the time of refreshing by AC driving of the liquid crystal is ideal because the capacitance is about 1/10 and the driving frequency F is about 1 / 1,000. Can be reduced by a factor of 10,000.

According to the present embodiment, according to the present invention, when there is a counter electrode, a switch element for continuously controlling an AC drive signal supplied from a signal electrode is provided for each display pixel. By controlling the amount of electric charge transferred or the electric field, multi-gradation display is realized, and when refreshing is not required, scanning of the switch element and rewriting of signals are not required, greatly reducing power consumption. A display device can be realized. In addition, when there is a counter electrode, a switch element that continuously controls an AC drive signal supplied from a signal electrode is provided for each display pixel, and a charge transfer amount or an electric field of an applied drive signal is controlled to achieve multi-gradation. When display is realized and refreshing is not required, scanning of switch elements and signal rewriting are not required, thereby realizing a display device in which power consumption in a halftone display state is significantly reduced.

(Embodiment 2) Next, Embodiment 2 will be described.
In the following embodiments, description of the same manufacturing method, driving method, and the like as in the first embodiment will be omitted.

FIG. 2 shows that a large taper angle is given to the ferroelectric control electrode 31 corresponding to the gate electrode, so that the ELA
This is an example in which the channel section is controlled by activation. In the channel region, the ELA activation is not sufficiently performed because the taper portion 32 of the semiconductor layer just on the control electrode 31 is activated, and only the connection portion 34 between the signal electrode 30 and the pixel electrode 25 is E-type.
LA will be activated. Only the tapered part is a-
By being left as the Si layer 32, signal writing to the ferroelectric film is performed from the signal electrode to the p-Si (polycrystalline) layer portion 34.
Through which the electric charge can be injected. The written charge (ferroelectric) has a low mobility, but the a-Si (amorphous) layer 32 with a very small off-leakage current operates as a switch element, so that it becomes a high-performance memory switch element. . 22 is a counter substrate, 23 is a counter electrode,
24 is a liquid crystal layer, 26 is an interlayer insulating film, and 33 is a ferroelectric film. In FIG. 2, the signal electrodes 30 are provided on both sides of the switch element 200, and the switch element (the channel portion is a-Si
Although the signal writing capability of the (amorphous) layer 32) is enhanced, a signal electrode may be formed on only one side. The structure of the present switch element is characterized in that the non-ELA part 32 formed on the side wall part of the gate electrode is used as a channel part of the switch element. By narrowing the interval controlled by the channel, even without a pixel electrode, It is possible to apply a charge and an electric field to the liquid crystal.

As described above, it has been shown that the silicon layer can be optimized by the laser beam irradiation method. However, since the modification of the ferroelectric film quality can be realized at the same time, the ELA method including the upper electrode is used for the device. It is possible to further improve the performance.
As for the other effects, the same effects as those of the first embodiment can be obtained also in the liquid crystal display device of the second embodiment.

(Embodiment 3) Further, Embodiment 3 will be described. In this embodiment, since the configuration of the entire liquid crystal display device is the same as that of the first embodiment, the following description focuses on the characteristic circuits, such as the equivalent circuit and the driving method. FIG. 6 shows a circuit example that realizes the symmetry of the drive signal and the refresh drive at an arbitrary position. Reference numerals 601 and 602 in the figure are equivalent to the circuit 50 indicated by the broken line in FIG. 5, and the charge or electric field applied to the liquid crystal is controlled by the switch element controlled by the charge held by the ferroelectric. ing.

In the first embodiment, the counter electrode is a sheet-like electrode. However, in the display device shown in FIG.
Wiring is formed in a comb shape in a direction orthogonal to the wiring of the ferroelectric control electrode. The wiring is arranged so as to correspond to each display pixel. The operation is similar to the memory element write operation shown in FIG. 5, but switch elements 611 and 612 are added to increase the write accuracy of the write signal to the pixel switch elements in 601 and 602, and 601. , 6
02, the switches are closed only when selected, and the scanning signals Vfe1 and Vfe2 are selected so that a predetermined ferroelectric control voltage is applied. The signal was not applied to 601 and 602. In addition, the switch 613 is
02 when the control signal is written,
1, 602 can be independently controlled. After writing the control signal, the switch 613 is closed so that a drive signal can be supplied to the liquid crystal. The liquid crystal drive signal is displayed by supplying a rectangular signal to Vcom1 and Vcom2, but in order to reduce power consumption, it is desirable to supply a symmetric rectangular wave with GND as a symmetric axis. Switch elements 611, 6
12 is the same control signal or the logical NOT of the signal (N
It can be driven by using OT). In the example of FIG. 6, the circuit configuration emphasizes the symmetry of the element characteristics, and a pair of memory type display elements is associated with one liquid crystal capacitor. FIG.
Is possible. In the circuit of FIG. 7, a circuit corresponding to 602 is only the liquid crystal capacitor 73, and a circuit other than the circuit corresponding to 602 is a circuit indicated by 71. The charge or electric field is controlled by a switch element in the 601 circuit. I have.
Reference numeral 72 denotes a transistor for applying an alternating current to the liquid crystal layer.

The driving signal for the liquid crystal is supplied by supplying a symmetrical rectangular wave to Vcom1 and Vcom2, similarly to the driving of the circuit of FIG. 7 is a more simplified description of the circuit operation of FIG. 7, and as shown in FIG. 8, the switch element 811 controlled by the electric field (charge) held in the ferroelectric and the refresh timing of the holding state of the switch element are controlled. It comprises a switch 812. Reference numeral 82 denotes the vertical MOS transistor described in the first embodiment. The switch 83 controlled by Vfe1 in the figure may be an on / off control switch. In the above embodiment, other effects can be the same as those of the first embodiment.

[0037]

According to the above configuration, the present invention can reduce the power consumption in the halftone display state.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a first embodiment of the present invention.

FIG. 4 is a diagram for explaining the operation of the first embodiment of the present invention;

FIG. 5 is an equivalent circuit diagram of one pixel according to the first embodiment of the present invention.

FIG. 6 is an equivalent circuit diagram of Embodiment 3 of the present invention.

FIG. 7 illustrates a third embodiment of the present invention.

FIG. 8 is a diagram illustrating a third embodiment of the present invention.

FIG. 9 illustrates characteristics of a ferroelectric liquid crystal.

FIG. 10 illustrates a conventional liquid crystal display device.

FIG. 11 illustrates a conventional liquid crystal display device.

FIG. 12 illustrates a conventional liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 2 Substrate 3 Counter electrode 4 Liquid crystal layer 5 Pixel electrode 6 Silicon active layer 7 Ferroelectric film 8, 11, 13 Ferroelectric control electrode 9 Silicon active layer 10 Signal electrode 12 Interlayer insulating film

Claims (4)

[Claims] 1. A substrate having an insulating surface, a MOS transistor formed on the substrate and using a ferroelectric material for a gate insulating film, and a pixel electrode whose charge injection amount is controlled by the MOS transistor. And a liquid crystal display device using a ferroelectric material having a counter electrode facing the pixel electrode and a liquid crystal layer formed between the counter electrode and the pixel electrode, wherein the MOS transistor is formed on the substrate. A liquid crystal display device using a ferroelectric material, wherein the liquid crystal display device has a vertical structure in which carriers run in the thickness direction of the formed semiconductor layer. 2. A substrate having an insulating surface, a MOS transistor formed on the substrate and using a ferroelectric for a gate insulating film, and a pixel electrode whose charge injection amount is controlled by the MOS transistor. And a liquid crystal display device using a ferroelectric material having a counter electrode facing the pixel electrode and a liquid crystal layer formed between the counter electrode and the pixel electrode, wherein the MOS transistor is formed on the substrate. A first semiconductor film, a comb-shaped gate insulating film formed on the first semiconductor film, a comb-shaped gate electrode formed on the gate insulating film, the gate insulating film and the gate electrode And a second semiconductor film covering the first semiconductor layer, wherein carriers run in a thickness direction of the first semiconductor layer. 3. The liquid crystal display device using a ferroelectric according to claim 2, wherein the gate electrode controls the amount of the carrier by changing the interval between the comb-shaped teeth. 4. The semiconductor device according to claim 1, wherein the gate electrode and the second semiconductor film are
3. The liquid crystal display device according to claim 2, wherein the liquid crystal display device is electrically insulated by an insulating film.