JPH0990915A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate a multi-level display and to enable low voltage drive by providing a photoconductor element as a switch selecting a unit pixel when the display data are written. SOLUTION: This device is provided with the photoconductor element (optical switching element) 21 being a switching element of each unit pixel, a scanning line light source 22 for irradiating light on the optical switching element 21, a signal electrode 23 for imparting the display data and a liquid crystal layer 24 held between counter electrodes. Further, the photosensitive part of the optical switching element 21 is confronted with the scanning line light source 22, and the optical switching element 21 is connected between the signal electrode 23 and one side (unit electrode) 25 of the counter electrodes holding the liquid crystal layer 24 in-between. Further, the other side of the counter electrode holding the liquid crystal layer 24 in-between is made a common electrode 26. Then, respective photoconductor element 21 of the whole unit pixels on the selected scanning line are irradiated by the light simultaneously. Thus, respective photoconductors 21 are made a conductive state, and the whole unit pixels on the scanning line are selected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device using liquid crystal used in, for example, a television or a CRT of a computer terminal.

[0002]

2. Description of the Related Art The above-mentioned liquid crystal display device, that is, a liquid crystal display (LCD) has been attracting attention in recent years because it can be made thin and lightweight and has low power consumption. The LCD includes a large number of horizontal electrodes (scan electrodes) corresponding to the scanning lines and a large number of vertical electrodes (signal electrodes) called data lines, and a liquid crystal layer is provided between the scanning electrodes and the signal electrodes. It is arranged. The light transmittance of the liquid crystal of the unit pixel cell changes depending on the magnitude of the potential difference between the selected scan electrode and the signal electrode corresponding to the unit pixel on the scan line. In many cases, one scanning line is selected, and display data is simultaneously supplied to each unit pixel on the scanning line, that is, a line-sequential driving system is adopted. In this line-sequential driving method, one scan electrode is selected and set to have a predetermined potential, and the unit pixel at each intersection of the scan electrode and all signal electrodes has a light transmittance corresponding to each write data. A voltage is applied to each signal electrode so that

Since the scanning electrodes, the signal electrodes, and the liquid crystal layer form a capacitor, sufficient electric charge is stored to give a voltage necessary for the liquid crystal layer to maintain the light transmittance of the unit pixel. After that, even if the circuit on the scan electrode side is cut off by a method such as increasing the impedance of some elements of the circuit thereafter, the light transmittance will be maintained for some time (time until the next frame or field). Can be maintained. In this way, the entire screen can be displayed by the process of supplying and writing the display data to the signal electrode for each scanning line, then switching to a new scanning line and repeating the same.

LCDs of this kind are roughly classified according to the drive system of the liquid crystal, and a simple matrix drive system LCD,
There is an active matrix drive type LCD. In a simple matrix driving type LCD, each unit pixel remains connected to a unit pixel on a number of other scan lines through a signal electrode, so that the light transmittance is affected by the voltage applied to the other unit pixels. There is a drawback that the image quality deteriorates due to crosstalk that changes from the initial value. On the other hand, in the active matrix driving type LCD, the switching element is provided for each unit pixel so that the crosstalk which the above-mentioned simple matrix driving type LCD does not occur. The LCD of the active matrix drive system has a MIM (Metal) due to the difference in the switching elements.
-Insulator-Metal), a method using a two-terminal element such as a diode or a varistor, or a TFT (Thi
n-Film-Transistor) and other three-terminal devices are used.

[0005]

SUMMARY OF THE INVENTION
Among matrix drive type LCDs, an LCD using a two-terminal element is, for example, as shown in the plan view of FIG.
A switch element 1 of each unit pixel, a scan electrode 2 for sending a scan line selection signal, a signal electrode 3 for giving display data, and a liquid crystal layer 4 sandwiched between counter electrodes are provided. The switch element 1 is provided between the scan electrode 2 and the signal electrode 3.
And a counter electrode sandwiching the liquid crystal layer 4 are connected in series. M
The IM method utilizes the nonlinear characteristic of the tunnel effect that occurs when a thin insulator film is sandwiched between metals. This M
In the IM method, the influence of variations in element characteristics is large, there is a voltage dependency of the element capacitance, and because the switch is turned on / off by the write data that is a feature of the two-terminal element method, it is There is a drawback that the key display is difficult.

Diode method (Back-to-Bac
(k method, diode ring method, etc.) is a combination of a plurality of diodes in series or in parallel in the reverse direction. The reverse characteristics of the diodes (Zener effect), that is, when a reverse voltage equal to or higher than a threshold value is applied, the Ze
A characteristic that a ner current flows or a forward characteristic, that is, a characteristic that a voltage drops due to a forward current is used. This diode method also has a drawback that multi-gradation display is difficult because the influence of variations in element characteristics is large and the switch is turned on / off by write data, which is a characteristic of the two-terminal element method. . The varistor method is an element whose electric resistance changes according to the applied voltage, such as Zn.
Utilizes O ceramics. In this varistor method, the threshold voltage is as high as 34V to 36V, so low voltage driving cannot be performed, and the switch is turned on / off by the write data, which is a characteristic of the two-terminal element method, so that multi-gradation display is possible. Has the drawback of being difficult.

LCD with active matrix drive
Among them, the LCD using the three-terminal element is, for example, as shown in the plan view of FIG.
1 and a scanning electrode 12 for transmitting a scanning line selection signal,
A signal electrode 13 for giving display data and a liquid crystal layer 14 sandwiched between counter electrodes are provided. Switch element 1
The driving unit of No. 1 is connected to the scanning electrode 12, and one side (unit electrode) 15 of the counter electrode sandwiching the signal electrode 13 and the liquid crystal layer 14
The switch element 11 is connected between the and. And
The other side of the counter electrodes sandwiching the liquid crystal layer 14 is a common electrode 16. Although the TFT method is currently under development, it has a drawback that the structure is complicated and the manufacturing process is complicated because a transistor is formed for each unit pixel, and defects are likely to occur. Further, each component of each switching element with respect to a unit pixel is also reduced in size, and there is a drawback that the yield in manufacturing is further deteriorated.

The present invention has been made to solve the above problems, and it is an object of the present invention to provide a liquid crystal display device which can easily perform multi-gradation display, can be driven at a low voltage, and has a simple structure. Has an aim.

[0009]

SUMMARY OF THE INVENTION In the present invention, the above object is to provide a photoconductive film as a switch for selecting a unit pixel when writing display data in a liquid crystal display device driven by an active matrix driving system. This is achieved by including a body element.

According to the above structure, since the photoconductor element is used for the switch for connecting the signal electrode and each unit pixel, the photoconductor element for all the unit pixels on the selected scanning line is selected. By simultaneously irradiating light to each photoconductor element, all the unit pixels on the scanning line can be selected.

[0011]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Although the embodiments described below are preferred specific examples of the present invention, various technically preferable limitations are given. However, the scope of the present invention is not limited to the following description. It is not limited to these forms unless otherwise stated.

The liquid crystal display device of the present invention is applied to an active matrix drive type LCD in which a switch connecting an electrode for applying a light transmittance control voltage of a liquid crystal cell and a control circuit is provided for each unit pixel. The present invention is applied to an LCD using a line-sequential driving method in which one scanning line is selected and each unit pixel on the scanning line is simultaneously supplied with respective display data. FIG. 1 is a plan view showing an embodiment of the liquid crystal display device of the present invention. This liquid crystal display device includes a photoconductor element (optical switch element) 21 which is a switch element of each unit pixel, and an optical switch element 21.
A scanning line light source 22 for irradiating light to the light source, a signal electrode 23 for giving display data, and a liquid crystal layer 24 sandwiched between counter electrodes are provided. The photosensitive portion of the optical switch element 21 is opposed to the scanning line light source 22, and is connected to the signal electrode 23 and the liquid crystal layer 2.
The optical switch element 21 is connected to one side (unit electrode) 25 of the counter electrodes sandwiching 4 therebetween. The other side of the counter electrodes sandwiching the liquid crystal layer 14 is a common electrode 26. A polarizing plate, a light-shielding mask, a control unit, etc. are omitted.

FIG. 2 is a plan view showing another embodiment of the liquid crystal display device of the present invention. This liquid crystal display device has the same basic configuration as that of the liquid crystal display device shown in FIG. 1, but the signal electrode 23 and one side (unit electrode) 25 of the counter electrodes sandwiching the liquid crystal layer 24 are connected to each other, and the liquid crystal layer The optical switch element 21 is connected between the other side of the counter electrodes sandwiching 14 and the common electrode 26. In the liquid crystal display device having the above-described configuration, the scanning line light source 22 irradiates the optical switch element 21 for each unit pixel with light, so that the counter electrodes 25 and 26 and the signal electrode 23 of each unit pixel are electrically connected. And the voltage corresponding to the display data is applied via the signal electrode. Therefore, all the optical switch elements 21 for each unit pixel on the same scanning line are
By irradiating light at the same time, these unit pixels can be driven simultaneously. It should be noted that instead of the scanning line light source 22, a shutter using liquid crystal or the like, for example, a ferroelectric liquid crystal that takes a binary state, may be used. In this case, a control unit for controlling on / off of the shutter, a backlight, or the like. Is required.

FIG. 3 is a plan view showing a concrete example of one mode of the liquid crystal display device of the present invention, and FIG. 4 is a side view taken along line XX thereof. In this liquid crystal display device, a transparent electrode 35 that is a unit electrode for each unit pixel is formed on a transparent glass plate 37, and a photoconductor layer 31 that is an optical switch element is formed on the transparent electrode 35. The signal electrode 33 is formed on the photoconductor layer 31. Also, a transparent glass plate 3
A transparent electrode 36, which is a common electrode, is formed on the electrode 8.
The liquid crystal 34 is sandwiched between a glass plate 37 on which the transparent electrode 35 is formed and a glass plate 38 on which the transparent electrode 36 is formed. The scanning line light source 32 is arranged on the surface opposite to the surface of the glass plate 37 on which the transparent electrode 35 is formed.

Here, for example, an a-Si: H film is used as the photoconductor layer 31, an ITO film is used as the transparent electrodes 35 and 36, and a Cr film is used as the signal electrode 33. Used. And, these are normal film forming apparatus, for example, vapor deposition apparatus, sputtering apparatus,
A film is formed by a plasma CVD device or the like, processed by an element forming device such as a contact proximity exposure device, a stepper device, or the like, and etched by an etching device such as a plasma etching device or a plasma ashing device.

An operation example of such a configuration will be described. First, when light is emitted from the scanning line light source 32 (A), all the photoconductor layers 31 of each unit pixel on the scanning line light source 32 (A) are turned on, and the respective signal electrodes 33 and unit electrodes 35 ( A-1, A-2, A-3, ...) and electric charges start to flow, and eventually the liquid crystal 34 has the same potential.
Each voltage is applied to. Next, the scanning line light source 32
The irradiation of light from (A) is stopped, and the scanning line light source 32 (B)
When the light is emitted from the scanning line light source 32 (A), the photoconductor layer 31 of each unit pixel is turned off, and the photoconductor layer 31 of each unit pixel on the scanning line light source 32 (B) is turned off. Are all turned on, and the respective signal electrodes 33 and unit electrodes 35 are turned on.
(B-1, B-2, B-3 ...) Conduct electricity and electric charges start to flow, and eventually they become the same potential, and respective voltages are applied to the liquid crystal 34.

At this time, the unit electrodes 35 (A-1, A-2,
(A-3 ...) And the electric charge accumulated between the common electrode 36 cannot escape, so that the voltage applied to each unit pixel is maintained. In reality, since there is a slight off resistance, the charge flows and the voltage drops, but the off resistance and the like may be adjusted so that the voltage drops to the extent that there is no problem until the next writing. In this way, writing can be performed for each scanning line. Then, those data are stored until the next field or frame.
That is, the data is retained until the next data is written.

[0018]

As described above, according to the present invention, the influence of variations in device characteristics is small, multi-gradation display is easy, low voltage driving is possible, and the structure is simple and the manufacture is easy. Therefore, an inexpensive liquid crystal display device can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a liquid crystal display device of the present invention.

FIG. 2 is a plan view showing another form of the liquid crystal display device of the present invention.

FIG. 3 is a plan view showing a specific example of one mode of the liquid crystal display device shown in FIG.

FIG. 4 is an X of a specific example of one mode of the liquid crystal display device shown in FIG.
-X-ray sectional side view.

FIG. 5 is a plan view showing an example of a conventional liquid crystal display device.

FIG. 6 is a plan view showing another example of a conventional liquid crystal display device.

[Explanation of symbols]

 21 Optical Switch Element 22, 32 Scanning Line Light Source 23, 33 Signal Electrode 24 Liquid Crystal Layer 25 Unit Electrode 26 Common Electrode 31 Photoconductive Layer 34 Liquid Crystal 35, 36 Transparent Electrode 37, 38 Glass Plate

Claims (6)

[Claims] 1. A liquid crystal display device driven by an active matrix driving method, comprising a photoconductor element as a switch for selecting a unit pixel when writing display data. 2. The liquid crystal display device according to claim 1, further comprising a light source that controls irradiation of light to the photoconductor element. 3. The liquid crystal display device according to claim 1, further comprising a shutter that controls transmission / blocking of irradiation light to the photoconductor element. 4. The liquid crystal display device according to claim 1, wherein the display data is written by a line-sequential driving method. 5. The liquid crystal display device according to claim 1, wherein selection of the unit pixel at the time of writing the display data is performed by irradiating light to the photoconductor elements of all the unit pixels on the scanning line at the same time. . 6. The photoconductor element connects a signal electrode for supplying the display data to each of the unit pixels.
3. The liquid crystal display device according to 1.