JPH07159807A - Active matrix liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a film structure to efficiently apply an electric field on a liquid crystal layer in a liquid crystal display device of a transverse electric field system by using tantalum oxide (Ta2O5) having high relative dielectric const. as a protective film of a pixel electrode. CONSTITUTION:The pixel part consists of a glass substrate 1 in a TFT side, scanning electrode (Cr) 2, gate insulating film (silicon nitride film) 3, semiconductor film (amorphous silicon film) 4, signal electrode (Cr) 5, pixel electrode (Cr) 6, protective film 7 for the pixel electrode, lower oriented film 8, liquid crystal layer 9, upper oriented film 10, counter electrode (Cr) 11, and counter glass substrate 12. In this film structure, tantalum oxide (Ta2O5) having rather high relative dielectric const. is used for the protective layer 7 of the pixel electrode. Since tantalum oxide has high relative dielectric const. as 23 to 27, reduction of voltage in the tantalum oxide film is decreased, and thereby, an electric field can be efficiently applied on the liquid crystal layer. As a result, the response speed is improved and the display quality of the liquid crystal display is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low cost and high image quality active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art In a conventional active matrix type liquid crystal display device, transparent electrodes, which are formed on the interface between two substrates and face each other, are used as electrodes for driving a liquid crystal composition layer.
This is because a display system represented by a twisted nematic (TN) display system, which operates by making the direction of the electric field applied to the liquid crystal composition layer substantially perpendicular to the substrate interface, is used. . Hereinafter, a display system in which the main electric field direction applied to the liquid crystal composition layer is a direction substantially perpendicular to the substrate interface will be referred to as a vertical electric field system.

Further, a method of applying an electric field to a liquid crystal composition layer using a comb-teeth-shaped electrode pair formed on one substrate has been proposed, for example, in Japanese Patent Publication No. 63-21907. The comb-teeth-shaped electrode pair referred to here is one in which two electrodes having the shape of comb teeth as shown by 32 and 33 in FIG. 5 are arranged so that their teeth do not overlap and mesh with each other. Is. In this case, the electrode that drives the liquid crystal composition layer does not need to be transparent, and an opaque metal electrode can be used. Hereinafter, a display system in which the main electric field direction applied to the liquid crystal composition layer is substantially parallel to the substrate interface is referred to as a lateral electric field system. Here, the horizontal electric field method has a wider viewing angle than the vertical electric field method, and thus high image quality can be obtained. This is because in the horizontal electric field system, the long axis of the liquid crystal molecule is almost parallel to the substrate,
This is because it does not stand up, and therefore the change in brightness is small when the viewing angle direction is changed.

[0004]

In the above-mentioned lateral electric field system,
Considering a liquid crystal display of the 10 ″ class, the distance between the pixel electrode and the counter electrode is several tens of μm, so it is important to efficiently apply an electric field to the liquid crystal layer. Normally, the voltage V _SB applied between the pixel electrode and the counter electrode causes a voltage drop between the protective film and the alignment film of the pixel electrode, so that the voltage applied to the liquid crystal layer is V _SB. Particularly, since the silicon nitride film conventionally used as a protective film for a pixel electrode has a low relative dielectric constant of 6 to 7, a voltage drop generated between the silicon nitride films becomes large. Is to provide a film structure for efficiently applying an electric field to a liquid crystal layer in a horizontal electric field type liquid crystal display device. Distance between electrode and counter electrode Since 10μm a following, the problem described above can be ignored.

[0005]

In order to achieve the above object, the present invention provides a pair of substrates, at least one of which is transparent, a liquid crystal composition layer sandwiched between the substrates, and one of the substrates. A plurality of scanning wirings and signal wirings arranged in a matrix on the surfaces facing each other, a pair of pixel electrodes, active elements connected to the pixel electrodes, the scanning wirings and the signal wirings, and the scanning wirings. In a liquid crystal display device including a scanning wiring driving unit connected to the signal wiring driving unit and a signal wiring driving unit connected to each of the signal wirings, the pair of pixel electrodes has a strip shape, and one of the electrodes The long side direction is substantially parallel to the long side direction of the other electrode, and the scanning line and the signal line other than the connection terminal portion with the external module, the pixel electrode, and the active element are made of tantalum oxide. Are covered with Ta ₂ O _5).

[0006]

In the above film structure, tantalum oxide (Ta ₂ O ₅ ) is used for the protective film of the pixel electrode. Here, since the relative permittivity of tantalum oxide is as high as 23 to 27, the voltage drop generated between the tantalum oxide films is small. Therefore, it becomes possible to efficiently apply an electric field to the liquid crystal layer. In the present invention, since tantalum oxide (Ta ₂ O ₅ ) is used for the protective film of the pixel electrode, an electric field can be efficiently applied to the liquid crystal layer, and as a result, the response speed is improved and the display quality of the liquid crystal display is improved. improves.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a sectional structure of a pixel portion when the present invention is used. In the figure, 1 is a glass substrate on the TFT side,
2 is Cr (scan electrode), 3 is a silicon nitride film (gate insulating film), 4 is an amorphous silicon film (semiconductor film), 5 is Cr
(Signal electrode), 6 Cr (pixel electrode), 7 Ta ₂ O
₅ (protective film for pixel electrode), 8 lower alignment film, 9 liquid crystal layer, 10 upper alignment film, 11 Cr (counter electrode), 1
Reference numeral 2 is a counter glass substrate, and 13 is a direction of an electric field applied to the liquid crystal. Here, an electrical equivalent circuit between the pixel electrode 6 and the counter electrode 11 is, as shown in FIG. 2, a capacitor 21 of a protective film of the pixel electrode / a capacitor 22 of a lower alignment film / a liquid crystal capacitor 23 / a capacitor 24 of an upper alignment film. It becomes the series capacity of. In the film structure of the present invention, Ta ₂ O ₅ having a relatively high dielectric constant is used for the protective film of the pixel electrode. Here, since the relative permittivity of tantalum oxide is as high as 23 to 27, the voltage drop generated between the tantalum oxide films is small. Therefore, it becomes possible to efficiently apply an electric field to the liquid crystal layer. As a result, the response speed is improved and the display quality of the liquid crystal display is improved.

FIG. 3 shows an embodiment of a plane pattern of a pixel portion when the present invention is used. As shown in the figure, an electric field is mainly applied to the liquid crystal layer provided between the pixel electrode 6 and the counter electrode 11 substantially in parallel to the substrate interface.
Although not shown in the figure, tantalum oxide is deposited on the entire surface of the pixel portion as a protective film for the scanning wiring, the signal wiring, the pixel electrode, and the active element.

FIG. 4 shows a second embodiment of the sectional structure of the pixel portion when the present invention is used. This embodiment is an embodiment in which a thin film diode composed of metal / insulating film / metal is used as an active element. Also in this embodiment, as shown in the figure, tantalum oxide 7 is used as a protective film for the pixel electrode. Therefore, it is possible to efficiently apply an electric field to the liquid crystal layer for the reasons described above. As a result, the response speed is improved and the display quality of the liquid crystal display is improved.

[0010]

According to the present invention, in a horizontal electric field type liquid crystal display device, tantalum oxide (Ta ₂ O ₅ ) having a high relative dielectric constant is used for a protective film of a pixel electrode. This reduces the voltage drop in the protective film of the pixel electrode,
An electric field can be efficiently applied to the liquid crystal layer, and as a result, the display quality of the liquid crystal display is improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a pixel portion of the present invention.

FIG. 2 is an equivalent circuit diagram between a pixel electrode and a counter electrode.

FIG. 3 is an explanatory diagram of a plane pattern of a pixel portion of the present invention.

FIG. 4 is a sectional view of a second embodiment of the pixel portion of the present invention.

FIG. 5 is an explanatory diagram of a conventional pixel.

[Explanation of symbols]

1 ... TFT side glass substrate, 2 ... Cr (scan electrode), 3 ...
Silicon nitride film (gate insulating film), 4 ... Amorphous silicon film (semiconductor film), 5 ... Cr (signal electrode), 6 ... Cr (pixel electrode), 7 ... Ta ₂ O ₅ (TFT protective film), 8 ... Alignment film, 9 ... Liquid crystal, 10 ... Alignment film, 11 ... Cr (counter electrode), 12 ... Counter glass substrate, 13 ... Direction of electric field.

Claims (2)

[Claims] 1. A pair of substrates, at least one of which is transparent, a liquid crystal composition layer sandwiched between the substrates, and a plurality of scans arranged in a matrix on facing surfaces of one of the substrates. Wirings and signal wirings, paired pixel electrodes, active elements connected to the pixel electrodes, the scanning wirings and the signal wirings, scanning wiring driving means connected to the scanning wirings, and the signal wirings. In a liquid crystal display device including a signal wiring driving unit connected to the pair of pixel electrodes, the paired pixel electrodes have a strip shape, and the long side direction of one of the electrodes is substantially parallel to the long side direction of the other electrode. a is, especially in that the scanning wiring and the signal wiring other than the connection terminal portion with the external module, the pixel electrode, the active element is covered with tantalum oxide (Ta ₂ O ₅₎ Active matrix liquid crystal display device according to. 2. The active element according to claim 1,
An active matrix liquid crystal display device which is a thin film transistor or a diode composed of metal / insulating film / metal.