JPH0713192A - Thin-film transistor driving liquid crystal display element - Google Patents

Abstract

PURPOSE:To obviate the generation of linear defects in an abnormal longitudinal direction even in severe environment affected by strong vibrations and impact by forming a mechanically secure insulating film on the inside surface of the common transparent electrode of a substrate so as to evade points to be formed as pixels for display. CONSTITUTION:Patterns of black matrix films BM which prevent the exposure of thin-film transistors TFTs to external light and the consequent conducting thereof and help to improve the contrast by suppressing the reflection of the external light, color filters FILs, etc., are formed on the inside surface (liquid crystal side) of an upper transparent glass substrate SUB2. The surfaces thereof are coated with a protective film PSV2 and further, the common transparent electrode ITO2 (COM) covers thereon over the entire surface. Further, the mechanically secure insulating film PSV3, for example, a silicon nitride film, is formed on the inside surface of the common electrode ITO2 (COM) by evading the points to be formed as the pixels for display. As a result, the front ends of conductive foreign matter are blocked by the PSV3 and cannot come into contact with the common transparent electrode ITO2(COM) any more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a drain electrode of a thin film transistor (hereinafter referred to as a TFT) formed thereon and is opposed to another portion of a glass substrate on which a TFT is formed by a step difference due to electrode formation (a common transparent electrode is To prevent accidents where abnormal vertical lines appear in the displayed image even in an environment where the part that is formed (relatively high) to the substrate side approaches the opposite substrate side under strong vibration or shock. Did T
The present invention relates to an FT drive liquid crystal display element.

[0002]

2. Description of the Related Art A liquid crystal display element of an active matrix drive system in which a switching element (and a capacitor element as required) is provided corresponding to each of a large number of pixels arranged in a matrix to form a display image Are driven independently of each other, the crosstalk phenomenon is prevented, and the capacitance effect between the opposing pixel electrodes helps to keep the signal voltage almost constant during one frame period. In principle, the duty ratio is 10 without being restricted by the number of scan electrodes, which is a problem when performing time division driving.
A liquid crystal display close to 0% static drive can be realized.
Therefore, display performance such as contrast and response is remarkably excellent, there is no crosstalk phenomenon, and there is a single point of view for color display on a large screen, and in recent years, it has been favorably adopted for portable OA devices and the like. There is. In practice, TFTs are widely used as the switching element.

[0003]

However, a TFT in which TFTs are arranged in a matrix on a liquid crystal display element substrate having an extremely large area as compared with a normal semiconductor element chip.
As is well known, there are many difficulties in manufacturing a driving liquid crystal display device, and many efforts are made to improve the yield. An active matrix type liquid crystal display element using a thin film transistor is disclosed in, for example, Japanese Patent Application Laid-Open No. 63-309921 or “12.5 type active matrix type color liquid crystal display employing a redundant structure” Nikkei Electronics, December 1986. 1
It is also described in the 5th issue, pages 193-210.

As a result of various improvement efforts, a color liquid crystal display device having a considerably large size and a high definition has been commercially available in recent years, but it is not found in a normal inspection condition, and a severe vibration or shock is applied. It has been recently discovered that only in the environment, sometimes a linear defect occurs, in which an abnormal vertical line, which should not be displayed originally, appears.

It is an object of the present invention to provide a TFT drive liquid crystal display device which prevents such an accident.

[0006]

In order to solve the above problems, according to the present invention, a thin film transistor driving liquid crystal display element is provided without a thin film transistor, and a transparent conductive film electrode common to each pixel is entirely formed on an inner surface of a substrate. It was decided to form a mechanically firm insulating film on the inner surface of the common transparent electrode of the existing substrate, avoiding the portion which becomes the display pixel.

[0007]

The present inventor has conducted a detailed investigation on a defective product in which it has been confirmed that an abnormal vertical line, which should not be originally displayed, appears for a short time under a severe environment where strong vibration or shock is applied. A hard conductive foreign substance adheres to a portion where the drain electrode of the TFT is formed and which projects relatively higher than the other portion of the glass substrate on which the TFT is formed toward the counter substrate by a step due to the formation of the drain electrode. Then, the drain electrode is short-circuited to the common transparent conductive film electrode on the opposite substrate side (where the common transparent electrode is formed), and in the neighboring pixels vertically connected to the same signal electrode line (data line), the It was found that the display voltage could not be applied.

The fact that a considerably large amount of conductive foreign matter as described above exists in the work chamber (after all, foreign matter is similar to dust and dust and lacks cleanliness in the work chamber) cannot be overlooked. On the other hand, considering that the area of the liquid crystal substrate on which the TFT is formed is extremely large compared to the chip area of a normal semiconductor element, even if the number of man-hours increases, a means to prevent accidents is a symptom. Even if it is a therapeutic measure, it is better to execute it to improve the yield.

Since the above-mentioned means is adopted in the present invention, the TFT
Even if the drain electrode of the present invention approaches the counter substrate side together with the transparent glass substrate when it is subjected to vibration or impact and tries to contact the common transparent conductive film electrode of the counter substrate through the attached conductive foreign matter, the present invention Is blocked by a newly provided mechanically firm insulating film such as a silicon nitride (Si ₃ N ₄ ) film,
No short circuit accident will occur.

FIG. 3 is a simplified sectional view for explaining the present invention. In the case of the conventional device, FIG. 3A shows that the conductive foreign material MD adheres to the drain electrode SD2 of the TFT of one pixel during the processing of the lower transparent glass substrate SUB1 and the protective film is formed on the TFT without noticing it. Formed PSV1,
Since the foreign matter MD is large, it is not completely covered with the protective film PSV1, and the tip of the foreign matter MD further projects from the protective film PSV1 and the tip thereof is in direct contact with the liquid crystal LC of the upper transparent glass substrate SUB2. ORI2 shows the state just about to be touched. However, in this state, since the orientation film ORI2 is an insulating film, no abnormal display appears. In order to keep the gap between the upper and lower transparent glass substrates to a predetermined length, plastic beads (not shown) having a diameter substantially equal to the predetermined length are dispersed and sealed inside the liquid crystal cell. When the liquid crystal display element is subjected to strong vibration or impact, the tip of the conductive foreign matter MD may be received. Penetrates the relatively soft (mainly plastic in recent years) alignment film ORI2 and contacts the common transparent pixel electrode ITO2 (COM) formed on the entire inner surface of the upper transparent glass substrate SUB2 to contact the lower transparent glass substrate SU.
A plurality of short-circuits are formed between the transparent pixel electrode ITO1 on B1 and the same data line (vertical (column) direction signal line transmitting a video signal) as the pixel in which this TFT is arranged. Even in the pixel of, the upper and lower transparent pixel electrodes are short-circuited,
The display voltage cannot be applied to the liquid crystal of those pixels.
Therefore, in the case of a transmissive element, light continues to pass in the vertical direction for a short period when the upper and lower transparent pixel electrodes are short-circuited by foreign matter, and in the case of a reflective element, during the above period, A column of a plurality of pixels that keeps blocking light in a certain direction is generated, and a so-called line abnormality occurs.

It should be noted that FIG. 3 is for illustration purposes only, and the detailed description is greatly simplified.

[0012]

FIG. 1 is a sectional view of the essential part of an embodiment of the present invention. On the lower transparent glass substrate SUB1 (liquid crystal side), T
The gate electrode GT, the gate insulating film GI, the drain electrode SD2, the source electrode SD1 of the FT, the transparent pixel electrode ITO1 connected to the source electrode SD1, and the protective film PS made of silicon oxide or silicon nitride that covers each member of the TFT.
V1, an alignment film ORI1 and the like formed by rubbing a polymer film of polyimide or the like to orient the long molecules of the liquid crystal LC in a desired direction. The i-type semiconductor layer AS used as a channel formation region is formed on the gate electrode GT between the drain electrode SD2 and the source electrode SD1 via the gate insulating film GI. Inner surface of upper transparent glass substrate SUB2 (liquid crystal side)
In addition, the black matrix film BM and the color filter FI which prevent the TFT from being brought into a conductive state by being exposed to external light and also suppress the reflection of external light to improve the contrast.
A pattern such as L is formed, a protective film PSV2 covers it, and a common transparent electrode ITO2 (C
OM) completely covers it. Conventionally, above that (on the liquid crystal side)
All of them were directly covered with the alignment film ORI2. However, in the present invention, by avoiding a portion to be a display pixel on the inner surface of the common transparent electrode ITO2 (COM), the mechanical A solid insulating film PSV3, for example, a silicon nitride film is formed. FIG. 2 is a plan view showing a portion where the insulating film PSV3 is formed, and the insulating film PSV3 is formed in a shaded portion while avoiding a portion which becomes a pixel. As shown in the figure, the drain electrode SD2 has a considerably large step from the surface of the lower transparent glass substrate SUB1 and the upper transparent glass substrate S.
It is getting excited towards UB2. Therefore, if a considerably large conductive foreign matter MD as shown in FIG. 3 adheres to the drain electrode SD2, a strong vibration is conventionally generated even if there is no problem in a normal inspection state performed in a relatively mild environment. In an environment subject to impact or shock, the tip of the conductive foreign matter MD penetrates through the relatively soft alignment film ORI2 and contacts the common transparent electrode ITO2, and between the upper and lower transparent electrodes of a plurality of pixels connected to the same data line. Was short-circuited, that is, the voltage could not be applied, and an abnormal vertical line appeared for a short time. However, when the solid insulating film PSV3 according to the present invention is formed, the tip of the conductive foreign matter MD is still above the insulating film PSV3 even under the above environment.
Therefore, the common transparent electrode ITO2 (COM) cannot be contacted and the abnormal vertical line appears unlike the conventional case.

In the present invention, the upper transparent glass electrode SU
On the inner surface of B2, the common transparent electrode ITO2 (COM) is left on the entire surface as it is, and on the inner surface of the same, avoiding a portion to be a display pixel, and avoiding a short circuit accident even if a conductive foreign matter MD adheres. Then, the insulating film PSV3 was formed. Instead of this, the conductive foreign matter MD of the common transparent electrode ITO2 (COM)
It is also possible to cut out a part that may cause a contact short circuit accident, but this is common transparent electrode ITO2 (C
(OM) sheet resistance value is increased, which may lead to deterioration of image quality, which is not preferable.

[0014]

As described above, according to the present invention, even when a large conductive foreign substance adheres to the drain electrode of the TFT that is raised above the lower transparent glass substrate surface, unlike the conventional device. Even under a severe environment with strong vibration or shock, there is no fear of displaying abnormal vertical lines, and a thin film transistor drive liquid crystal display device with good vibration resistance and shock resistance can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of an embodiment of the present invention.

FIG. 2 is a plan view showing a formation location of a solid insulating film according to the present invention to be formed on an inner surface of a common transparent electrode inside an upper transparent glass substrate.

FIG. 3 is a schematic cross-sectional view for explaining the present invention.
FIG. 3A is a diagram showing a state in which a large conductive foreign substance is attached to the drain electrode of the TFT of the conventional element, and an abnormal vertical line is likely to appear when subjected to vibration or shock.
FIG. 3B is a diagram showing a state in which even if the conductive foreign matter is attached, the effect of the solid insulating film according to the present invention eliminates the possibility that an abnormal vertical line will appear.

[Explanation of symbols]

SUB1 ... Lower transparent glass substrate, GT ... Gate electrode,
GI ... Gate insulating film, SD1 ... Source electrode, SD2
... Drain electrode, AS ... i-type semiconductor layer, ITO1 ...
Transparent pixel electrode, PSV1 ... Protective film covering TFT, O
RI1 ... Alignment film on the lower substrate side, MD ... Conductive foreign matter,
SUB2 ... Upper transparent glass substrate, BM ... Black matrix film, FIL ... Color filter, PSV2 ... Protective film covering color filter and black matrix on inner surface of upper substrate, ITO2 ... Common transparent electrode, ORI2 ... Alignment film on upper substrate side, PSV3 ... A solid insulating film according to the present invention, LC ... Liquid crystal.

Claims (1)

[Claims] 1. A thin film transistor driving liquid crystal display element, wherein a thin film transistor is not provided and a transparent conductive film electrode common to each pixel is entirely formed on the inner surface of the substrate, and a display pixel is formed on the inner surface of the common transparent electrode. A thin film transistor drive liquid crystal display element, characterized in that a mechanically strong insulating film is formed so as to avoid the area where