JPH0444012A - Active matrix liquid crystal display element - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a printing phenomenon and an after-image phenomenon by setting the film thickness of a liquid crystal orienting film to 200-3000Angstrom . CONSTITUTION:This active matrix liquid crystal display element consists of a base plate 1 provided with a transparent electrode 4, an orienting film 6, and a base plate 2 provided with a black matrix 9, a transparent electrode 5, an active element such as a transistor (TR), an electric conductor 3, and an orienting film 7, and a liquid crystal layer 8. The orienting films which orient liquid crystal molecules on the surfaces of the substrates at a 3-4 deg. tilt angle, i.e. orienting films which are 200-3000Angstrom thickness are provided by sintering a polyimide precursor whose carbon number is 12 for a cyclobutabutadiene ring and a terminal alkyl group. Consequently there is no discrimination due to an electric field from the electric conductor and neither the printing phenomenon nor the after-image phenomenon is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display element, and particularly to an active matrix liquid crystal display element in which each display element has active elements such as transistors and diodes.

[Conventional technology]

An active matrix liquid crystal display element has a structure in which a glass substrate having an active element and a glass substrate having a transparent electrode are stacked on top of each other, and nematic liquid crystal is injected in between. The liquid crystal is oriented so that the long axis direction of the liquid crystal molecules is twisted by about 90" by the alignment films on both glass substrates, and constitutes a TN (twisted nematic) type liquid crystal element.

Liquid crystal display elements that do not have active elements have fewer irregularities on the substrate, whereas active matrix display elements have fewer irregularities on the substrate.
Because there are semiconductor layers, insulator layers, and wiring layers that constitute active elements, the substrate surface has many irregularities.

If there are many irregularities, the alignment of the liquid crystal is disturbed, a phenomenon occurs in which the direction of rotation of the liquid crystal is reversed (reverse twist), and a boundary with the normally oriented portion (disclination) is formed, making it easy to cause alignment defects.

In order to prevent this reverse twist from occurring, in conventional active matrix liquid crystal display elements, the liquid crystal on the substrate is tilted back and forth by 1° from the substrate surface (referred to as a tilt angle of around 1°).
An alignment film was used that was rotated for alignment. As such an alignment film, a polyimide using an aliphatic tetracarboxylic dianhydride as shown in FIG. 3 has been used.

[Problem to be solved by the invention]

In active matrix liquid crystal display elements with a tilt angle of about 1°, alignment defects do not occur in a stopped state such as when the switch is turned off or in an OFF state where a low voltage is applied to the display pixels. Next, the case of an ON state in which a high voltage is applied to a display pixel will be described. FIG. 4 is a cross-sectional view of a conventional example, in which transparent electrodes 41. Orientation film 61. A substrate 11 provided with a black matrix 91 and a transparent electrode 51
゜Wiring 31. It is composed of a substrate 21 provided with an alignment film 71 and a liquid crystal layer 81.

In the ON state, an electric field is applied between the transparent electrode 41 and the transparent electrode 510, so that the liquid crystal molecules 81a near the center of the liquid crystal layer 81 are substantially perpendicular to the electrodes. On the other hand, the liquid crystal molecules 81b located near the substrate are determined by the influence of the alignment film 71. It has a tilt angle (about 1°) and is almost parallel to the electrode.

Here, a voltage for driving an active element such as a transistor is applied to the wiring 31, but due to the influence of the electric field from the wiring, the liquid crystal molecules 81c near the wiring 310
are aligned with a tilt angle different from that of the liquid crystal molecules 81b,
A phenomenon occurs in which a tissue clination 100, which is a discontinuous boundary between the orientations of the molecules of both liquids, occurs. Because of this phenomenon, bright lines are generated within the pixels, which are either fixed or change over time, resulting in problems such as burn-in and afterimage phenomena that make the display look faint even when the display is changed. Ta.

[Means to solve the problem]

The active matrix liquid crystal display element of the present invention is produced by baking an alignment film in which liquid crystal molecules on the substrate surface are aligned with a tilt angle of 3 to 4 degrees, that is, a polyimide precursor having a cyclobutane ring and a terminal alkyl group with 12 carbon atoms. Thickness is 20
It is an active matrix liquid crystal display device having an alignment film of 0 to 3000 layers.

Further, the active matrix liquid crystal display device is characterized in that the orientation film firing temperature is 150 to 200°C.

The active matrix liquid crystal display element is characterized in that it uses a liquid crystal composition containing as a component a liquid crystal compound having a fluorine-substituted skeletal ring or a fluorine substituent at its terminal.

〔Example〕

Next, the present invention will be explained using the drawings.

FIG. 1 shows the structure of a polyimide having a cyclobutane ring and a terminal alkyl group having 12 carbon atoms used in the present invention. FIG. 2 is a cross-sectional view of the active matrix liquid crystal display element of the present invention, in which transparent electrodes 4. The alignment film 6. A substrate 1 provided with a black matrix 9, a transparent electrode 5. Active elements such as transistors (omitted in the figure), wiring3. It is composed of a substrate 2 provided with an alignment film 7 and a liquid crystal layer 8.

The liquid crystal alignment film 6 was formed on each substrate by a printing method and then baked at 170° C. to a film thickness of 800°C. Further, a liquid crystal material NR, -5042LB manufactured by Chisso Petrochemical Co., Ltd., which was composed of a liquid crystal compound having a structure having a fluorine-substituted skeleton ring and a fluorine substituent at the end, was injected into the liquid crystal element.

In the ON state, an electric field is applied between the transparent electrode 4 and the transparent electrode 5, so that the liquid crystal molecules 8 near the center of the liquid crystal layer 8
a is perpendicular to the electrode. On the other hand, the liquid crystal molecules 8b located near the substrate are oriented almost parallel to the electrodes, more precisely at a tilt angle of 3.7 degrees, due to the influence of the alignment film.

Even if an electric field of the same strength as in the conventional example is applied from the wiring 3, the liquid crystal molecules 8c near the wiring 30 will not shift to a metastable state different from that of the liquid crystal molecules 8b because of the large tilt angle.
No disclination occurred, and no burn-in or afterimage phenomenon occurred when an alignment film material with a tilt angle of 1° having the structure shown in FIG. 3 was used.

In this example, the orientation film firing temperature was 170°C, and the film thickness was 800°C.
However, when the orientation film firing temperature was 150 to 200 DEG C. and the film thickness was within the range of 200 to 3,000 people, no burning or afterimage phenomenon occurred at all, as in the above results.

Note that when the film thickness is less than 200 Å or more than 3000 Å, there is a drawback that the alignment becomes slightly unstable immediately after the liquid crystal is injected, and some disclination occurs during the ON state.

Furthermore, if the firing temperature is below 150°C, the film is not sufficiently cured, resulting in peeling of the film due to rubbing, and the alignment becomes slightly unstable immediately after liquid crystal injection. As in the case of , some disclination occurred during the ON state. Furthermore, when the firing temperature is 200° C. or higher, there is a drawback that the characteristics of the transistor shift and sufficient display characteristics cannot be obtained.

In this example, liquid crystal material NR-5042LE manufactured by Chisso Petrochemical Company Ltd. was used as the liquid crystal material. Liquid crystal material ML (
, -2003, etc., it was confirmed that no burn-in phenomenon or afterimage phenomenon occurred at all even when many liquid crystal materials were used.

〔Effect of the invention〕

As explained above, the present invention has the advantage that disclination does not occur due to the influence of electric fields from wiring, and therefore burn-in and afterimage phenomena do not occur.

[Brief explanation of drawings]

Fig. 1 is a diagram of the structural formula of the alignment film of the present invention, Fig. 2 is a cross-sectional view of an embodiment of the present invention, Fig. 3 is a diagram of the structural formula of a conventional liquid crystal alignment film, and Fig. 4 is a conventional example. FIG. 3... Wiring, 4, 5... Transparent electrode, 6
, 7 alignment film, 8... liquid crystal layer, 8a, 8b, 8c
・・・・・・Liquid crystal molecules. Agent: Patent Attorney Susumu Uchihara

Claims (3)

[Claims] (1) The number of carbon atoms in the cyclobutane ring and the terminal alkyl group is 1
The polyimide precursor of 2 was fired and used as a liquid crystal alignment film,
An active matrix liquid crystal display element characterized in that the thickness of the liquid crystal alignment film is 200 to 3000 Å. (2) The active matrix liquid crystal display element according to claim 1, wherein the alignment film firing temperature is 150 to 200°C. (3) The active matrix liquid crystal according to claim 1, which uses a liquid crystal composition containing as a component a liquid crystal compound having a fluorine-substituted skeletal ring or a fluorine substituent at the end. display element.