JPH07128689A - Display device - Google Patents

Abstract

PURPOSE:To obtain a nonlinear element showing rectifying characteristics in I-V characteristics and to enable high quality display with high contrast and small cross talk of a display device using this nonlinear element by forming the active layer of an element in each pixel in such a manner that the layer consists of a ZnS film and a semiconductor film having p-type electric conductivity. CONSTITUTION:The nonlinear element consists of a first electrode 2 electrically connected to scanning wiring, second electrode 5 electrically connected to a pixel electrode, and active layer 9 between the first electrode 2 and the second electrode 5. This active layer consists of a ZnS film 3 and a semiconductor film 4 comprising a material except for ZnS formed in such a manner that at least a part of the film 4 is in contact with the ZnS film 3. The semiconductor film 4 is formed by using one or more kinds of material selected from CdS, ZnSe, GaSe, ZnO, TaON, and CdO. Further, the active layer 9 may have a semiconductor film 4 comprising a semiconductor material having p-type electric conductivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type display device using a two-terminal nonlinear element.

[0002]

2. Description of the Related Art With the miniaturization of office automation equipment and personal computers, flat displays have been widely used instead of CRTs for these display devices. The flat display has a structure in which display is performed by applying a voltage between a pair of electrodes sandwiching a display medium having electro-optical characteristics, and liquid crystal, electroluminescence, plasma, electrochromic, or the like is used as the display medium. In particular, a liquid crystal display device using a liquid crystal as a display medium is most practically used because it can display with low power consumption.

As a method for displaying a large amount of characters and images on this liquid crystal display device, there is an active matrix method in which a switching element is provided in each picture element. In an active matrix type liquid crystal display device, picture element electrodes arranged in a matrix and scanning lines passing near the picture element electrodes are electrically connected via a switching element. The switching element may be a 2-terminal non-linear element or a 3-terminal active element. Two
Since the terminal non-linear element has a simpler structure than the three-terminal element, the manufacturing process is simplified. A liquid crystal display device using MIM (Metal Insulater Metal; metal-insulating film-metal) that uses tantalum pentoxide as a two-terminal nonlinear element is disclosed in Japanese Patent Publication No. 61-32673.
It is described in Japanese Patent Publication No. A liquid crystal display device using an amorphous silicon (a-Si) / PIN diode is described in SID84 DIGEST (1984) 324.

[0004]

In the liquid crystal display device using the MIM as the two-terminal nonlinear element, the MIM
The capacity of the LCD is sufficiently smaller than that of the liquid crystal, MIM
In order to realize high image quality, it is necessary that the current-voltage characteristics of (3) are steep and the ratio of ON current to OFF current is large. However, no MIM element that meets these requirements has been developed. Therefore, the problems of flicker and crosstalk have not been solved as a liquid crystal display device.

When zinc sulfide (ZnS) is used for the active layer of the two-terminal nonlinear element, the two-terminal nonlinear element exhibits steep current-voltage characteristics, but the dielectric strength of ZnS is low and reliability is a problem. become.

On the other hand, as a two-terminal nonlinear element, a-Si.
In a liquid crystal display device using a PIN diode, two types of device driving systems, a back-to-back diode system and a diode ring system, have been proposed. However, when considering driving a liquid crystal, the former back-to-back diode method has a problem that the threshold voltage is high and unstable, and the latter diode ring method has a problem that the threshold voltage is low. Therefore, it is difficult for the liquid crystal display devices of the above two types to display a large capacity and high image quality.

The present invention has been made to solve the problems of the prior art. The two-terminal non-linear element has a current-voltage characteristic suitable for display, and a large-capacity, high-quality display is possible. Another object is to provide a display device using such a two-terminal nonlinear element.

[0008]

According to the display device of the present invention, picture element electrodes arranged in a matrix and scanning lines passing near the picture element electrodes are connected through a non-linear element, and the picture elements are connected. In an active matrix type display device in which a display medium having electro-optical characteristics is sandwiched between an electrode and an electrode arranged to face each other, the nonlinear element includes a first electrode electrically connected to the scanning line. A second electrode electrically connected to the pixel electrode, and an active layer disposed between the first electrode and the second electrode, the active layer comprising ZnS
Since the film and the semiconductor film made of a material other than ZnS are provided in contact with at least a part of the ZnS film, the above object is achieved thereby.

In this display device, the semiconductor film is
CdS, ZnSe, GaSe, ZnO, TaON, Cd
It can be formed by using one or more kinds of O.

In the above display device, the active layer may include a semiconductor film made of a semiconductor material having p-type electrical conductivity. The semiconductor film is Cu
It can be formed using one or two or more of S, CdTe, and ZnTe.

In the above display device, the active layer may have a structure having semiconductor films on both sides of the ZnS film or a structure having ZnS films on both sides of the semiconductor film.

Further, in the above display device, an insulating film is formed between the active layer formed on the first electrode and the second electrode, and the insulating film has a through hole, and the through hole is provided. The structure may be such that the second electrode and the active layer are connected.

[0013]

The semiconductor film in contact with the ZnS film of the active layer is
When a semiconductor material having p-type electrical conductivity is used, the current-voltage characteristics of the nonlinear element having the active layer exhibit rectification characteristics, and the threshold voltage in the forward direction is higher than that of the a-Si PIN diode. It becomes higher and the off region can be made wider.

When the semiconductor film is made of a semiconductor other than a semiconductor exhibiting p-type electrical conductivity, a steep current obtained by a nonlinear element having an active layer of ZnS film alone-
In addition to the voltage characteristics, the dielectric strength is higher than that of a non-linear element having an active layer of ZnS film alone, and excellent reliability is imparted to the non-linear element.

By using such a non-linear element in a display device, a high-quality display with a large capacity, a small crosstalk and a high contrast can be realized.

[0016]

EXAMPLES Examples of the present invention will be described below.

(Embodiment 1) FIG. 1A shows the structure of a non-linear element portion of a display device according to the present invention. A display device provided with this non-linear element has pixel electrodes arranged in a matrix on one of a pair of substrates sandwiching a display medium such as a liquid crystal from both sides, a scanning line passing near the pixel electrodes, and a pixel line. Non-linear elements for electrically connecting the element electrodes and the scanning lines are formed.

The non-linear element provided in such a display device includes a first electrode electrically connected to a scanning line, a second electrode electrically connected to a pixel electrode, a first electrode and a second electrode. And an active layer disposed between the ZnS film and the semiconductor layer made of a material other than ZnS and provided at least partially in contact with the ZnS film. The structure will be described below in detail with reference to FIG.

A first electrode 2 composed of a conductive thin film is formed on a glass substrate 1. As the first electrode 2, T
A metal such as a, Ti, Nb, Al, Mo, Pt, Au, Ag, or an alloy thereof, or a transparent conductive material such as ITO is used.

On the first electrode 2, a ZnS film 3 and Zn
An active layer 9 is formed by laminating a semiconductor film 4 made of a material other than S. As a method of forming the active layer 9, a sputtering method, a vacuum deposition method, a CVD method, an M
The BE method or the like is used. As the semiconductor film 4, CuS,
A semiconductor material having p-type electrical conductivity such as CdTe, ZnTe, or other CdS, ZnSe, GaS
e, ZnO, TaON, CdO, etc. are used.

A second electrode 5 made of a conductive thin film is formed on the active layer 9. The same material as the first electrode 2 is used for the second electrode 5.

As another form of the non-linear element thus constructed, as shown in FIG. 1B, a non-linear element in which the insulating film 6 is interposed between the active layer 9 and the second electrode 5 is used. Is also possible. The insulating film 6 is for preventing the first electrode 2 and the second electrode 5 from electrically contacting each other, and specifically, SiO2, Ta2O5, SiNX, AlN, A.
There are l2O3, acrylic, polyimide, polyurea, etc.
Further, the second electrode 5 may be located on the glass substrate 1 and the first electrode 2 may be located on the active layer 9.

Next, the fabrication of the display device of the present invention was performed using ZnS.
A liquid crystal display device using an element in which a semiconductor material having p-type electrical conductivity and a semiconductor material having a p-type conductivity are stacked will be described as an example. Figure 2
(A) is a plan view of a picture element part of the liquid crystal display device,
FIG. 2B is a sectional view taken along the line AA of FIG.

First, a conductive thin film is formed on the glass substrate 1 by a sputtering method, the conductive thin film is patterned into a predetermined shape, and the scanning line 10 and the scanning line 1 are formed.
The first electrode 2 branched from 0 is obtained. In addition, a conductive thin film to be the picture element electrode 7 is formed on the glass substrate 1 and subjected to predetermined patterning to obtain the picture element electrode 7 and a branch portion branched from the picture element electrode 7. In this embodiment, Ta is used for the scanning line 10 and the first electrode 2, and ITO is used for the pixel electrode 7. Further, Ta is sputtered on the branch portion branched from the pixel electrode 7 to form the second electrode 5.

Next, the first electrode 2 branched from the scanning line 10
And in contact with the second electrode 5 branched from the pixel electrode 7, ZnS
The film 3 is formed to a thickness of 5000 angstrom by, for example, a sputtering method.

Next, a semiconductor film 4 having p-type electrical conductivity is formed on the ZnS film 3 by a sputtering method, for example.
The active layer 9 is formed by forming a film having a thickness of 00 angstrom. In this embodiment, CuS is used for the semiconductor film 4.

Next, the active layer 9 composed of the ZnS film 3 and the semiconductor film 4 is patterned into a predetermined shape, and then the insulating film 6 is formed by, for example, a sputtering method,
The insulating film 6 is patterned into a predetermined shape.

Next, after forming a conductive thin film, the conductive thin film is patterned. At this time, the conductive thin film on the active layer 9 formed on the first electrode 2 branched from the scanning line 10 is in contact with the pixel electrode 7 and the second electrode 5 branched from the pixel electrode 7. The conductive thin film on the active layer 9 formed above is in contact with the scan line 10. The former conductive thin film serves as the second electrode 5, and the latter conductive thin film serves as the first electrode 2. In this embodiment, Mo is used for the conductive thin film.

Thus, the non-linear element in which the first electrode 2, the ZnS film 3, the semiconductor film 4 and the second electrode 5 are sequentially laminated on the glass substrate 1, the second electrode 5, the ZnS film 3, the semiconductor film 4 and A non-linear element in which the first electrodes 2 are sequentially stacked is formed.

Then, on the glass substrate 1 in this state,
An alignment film 8 is formed and an alignment treatment is performed to complete one of the pair of substrates.

The other substrate is manufactured as follows. A counter electrode made of a transparent conductive film patterned in a stripe shape is formed on a glass substrate different from the glass substrate 1, and then an alignment film is formed on the glass substrate in such a state, and then an alignment treatment is performed. One substrate is manufactured. Either of the above two substrates may be manufactured first.

Next, after spacers are scattered on one of the two substrates, the two substrates are bonded so that the scanning line and the counter electrode intersect, and liquid crystal is injected into the sealed space between them. The liquid crystal injection port is sealed to complete the liquid crystal display device.

FIG. 2 (c) is an equivalent circuit of the non-linear element in the liquid crystal display device thus manufactured, and FIG. 3 is a current-voltage characteristic of the non-linear element (the present invention).
Are shown in comparison with the current-voltage characteristics (conventional) of the a-Si PIN diode. As can be seen from FIG. 3, the current-voltage characteristics of the nonlinear element of the present invention exhibit good rectification characteristics, and the threshold voltage is higher than the current-voltage characteristics of the a-Si PIN diode. Therefore, a so-called off-voltage region where no voltage is applied to the liquid crystal can be widened.

In the active layer 9 of this embodiment, the ZnS film 3 and the semiconductor film 4 are laminated in this order from the glass substrate 1 side, but the same effect can be obtained even if they are laminated in the reverse order. CuS is used as a semiconductor showing p-type electrical conductivity.
Is used, but instead of this, CdTe, ZnTe
The same effect can be obtained by using the above.

(Embodiment 2) FIG. 4 shows another configuration of the non-linear element in the display device according to Embodiment 2. Figure 4
4A is a plan view of a picture element portion of the liquid crystal display device, and FIG. 4B is a cross-sectional view taken along line BB of FIG. 4A. The configuration of this non-linear element will be described below in the order of manufacturing steps. First, a conductive thin film is formed on a glass substrate 1 by a sputtering method, and the conductive thin film is patterned into a predetermined shape to obtain a scanning line 10 and a first electrode 2 branched from the scanning line 10. In addition, a conductive thin film which becomes the pixel electrode 7 is formed on the glass substrate 1, and a predetermined patterning is performed on this. Ta was used for the scanning line 10 and the first electrode 2, and ITO was used for the pixel electrode 7.

Next, the first electrode 2 branched from the scanning line 10
A ZnS film 3 is formed in a thickness of 1000 angstroms by contacting with, for example, a sputtering method.

Next, a semiconductor film 4 made of a semiconductor material other than ZnS, which does not exhibit p-type electrical conductivity, is formed on the ZnS film 3 to a thickness of 500 angstroms by, for example, a sputtering method, and the active layer is formed. 9 is formed.
ZnO was used for this semiconductor film 4.

Next, after patterning the active layer 9 into a predetermined shape, the insulating film 6 is formed by a sputtering method, and the insulating film 6 is patterned into a predetermined shape.

Next, after forming the conductive thin film, the conductive thin film is patterned so that the conductive thin film on the active layer 9 is in contact with the pixel electrode 7 to form the second electrode 5. Mo was used for the conductive thin film.

Thus, the nonlinear element in which the first electrode 2, the ZnS film 3, the semiconductor film 4, and the second electrode 5 are sequentially laminated on the glass substrate 1 is formed. After forming the element, an alignment film 8 is formed and an alignment treatment is performed to complete the substrate.

The display device is completed by combining the completed substrate with the counter substrate as in the above embodiment.

The element in the display device having such a structure exhibits a steep nonlinear current-voltage characteristic, and moreover, the active layer has a higher withstand voltage as compared with the non-linear element having only the ZnS film, so that the reliability is high. .

In the active layer of the second embodiment, the ZnS film 3 and the semiconductor film 4 (which do not show p-type electrical conductivity) are laminated in this order, but the same effect can be obtained even if they are laminated in the opposite order. To be Further, ZnO is used as the semiconductor film 4 which does not show p-type electrical conductivity, but instead of this, Cd is used.
The same effect can be obtained by using S, ZnSe, GaSe, TaON, CdO or the like.

(Embodiment 3) FIG. 5 shows still another configuration of the non-linear element in the display device according to Embodiment 3.

The structure of the active layer 9 of the nonlinear element of the third embodiment is different from that of the embodiment of FIG. The active layer 9 according to the third embodiment includes the ZnS film 3, the semiconductor film 4 (which does not exhibit p-type electrical conductivity), and ZnS on the first electrode 2.
The film 3 is formed by sequentially forming the film 3 by, for example, a sputtering method. All film thicknesses were 500 angstroms.

As described above, the active layer 9 has the vertically symmetrical three-layer structure having the ZnS films 3 and 3 on both sides of the semiconductor film 4 so that the symmetry of the current-voltage characteristics is improved. In addition, the three-layer structure of the active layer 9 is changed to ZnS.
The same effect can be obtained by using a squad with semiconductor films 4 on both sides of the film 3.

[0047]

As described above in detail, in the display device of the present invention, the active layer of the element provided in each pixel is composed of the ZnS film and the semiconductor film having p-type electrical conductivity. By doing so, the IV characteristic shows a rectifying characteristic, and the threshold voltage becomes higher and the off region can be widened as compared with the rectifying characteristic of the a-Si PIN diode. Also,
When a material that does not exhibit p-type electrical conductivity is used for the semiconductor film, the dielectric strength increases and the reliability of the nonlinear element improves.

Therefore, in the display device using the above-mentioned non-linear element, crosstalk is small and high-quality display with high contrast becomes possible.

[Brief description of drawings]

FIG. 1 is a sectional view showing a basic structure of a non-linear element used in a display device of the present invention.

2A and 2B show a configuration example of a non-linear element in a display device of the present invention, FIG. 2A is a plan view of a pixel portion, and FIG. 2B is a cross-sectional view taken along line AA of FIG. 2A. 2C is an equivalent circuit diagram.

FIG. 3 shows current-voltage characteristics of a non-linear element used in a display device of the present invention and a-Si used in a conventional display device.
-The graph which compared and showed the electric current-voltage characteristic of a PIN diode.

4A and 4B show another configuration of a non-linear element in a display device of the present invention, FIG. 4A is a plan view of a pixel portion, and FIG. 4B is a cross section taken along line BB of FIG. 4A. Fig.

FIG. 5 is a cross-sectional view showing still another configuration of the non-linear element in the display device of the present invention.

[Explanation of symbols]

 1 Glass Substrate 2 First Electrode 3 ZnS Film 4 Semiconductor Film 5 Second Electrode 6 Insulating Film 7 Picture Element Electrode 8 Alignment Film 9 Active Layer 10 Scanning Line

Claims (6)

[Claims] 1. A pixel electrode provided in a matrix,
An active matrix type in which a scanning line passing near the picture element electrode is connected through a non-linear element, and a display medium having electro-optical characteristics is sandwiched between the picture element electrode and an electrode arranged opposite to each other. In the display device, the nonlinear element includes a first electrode electrically connected to the scanning line, a second electrode electrically connected to the pixel electrode, a first electrode and a second electrode. A display device having an active layer disposed between the ZnS film and a semiconductor film made of a material other than ZnS and provided at least partially in contact with the ZnS film. 2. The semiconductor film is CdS, ZnSe, G
1 or 2 of aSe, ZnO, TaON, CdO
The display device according to claim 1, wherein the display device is formed using more than one type. 3. The display device according to claim 1, wherein the active layer has a semiconductor film made of a semiconductor material having p-type electrical conductivity. 4. The semiconductor film is CuS, CdTe, Z
The display device according to claim 3, wherein the display device is formed using one or more of nTe. 5. The display device according to claim 1, wherein the active layer has a structure having semiconductor films on both sides of the ZnS film or a structure having ZnS films on both sides of the semiconductor film. 6. An insulating film is formed between the active layer formed on the first electrode and the second electrode, the insulating film has a through hole, and the second film is formed through the through hole.
The display device according to claim 1, which has a structure in which an electrode and the active layer are connected to each other.