JPH01177020A - Active matrix display device - Google Patents

Abstract

PURPOSE:To lower the resistance of a gate bus wiring and to improve an image grade by bringing a light shielding film into contact with the gate bus wiring of a transistor, thereby making double wirings. CONSTITUTION:The light shielding film 8 which shields the projection of incident light to allow transmission of a liquid crystal to a semiconductor thin film 5 is formed in said film; in addition, the light shielding film 8 is brought into contact with the gate bus wiring 7. Since the light shielding film 8 shields the irradiation of the incident light to the semiconductor thin film 5 and, therefore, the decrease of the off resistance of the thin-film transistor (TFT) which has the thin film 5 as a part of the constitution is prevented. Since the gate bus wiring 7 is double-wired, the resistance of the gate bus wiring is lowered. The large-sized active matrix display device having the high image grade is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an active matrix display device, and particularly to a transmissive liquid crystal display device using thin film transistors as switching elements.

[Prior Art] In recent years, amorphous silicon (hereinafter referred to as a-Si) has been used as a thin film material for thin film transistors (hereinafter referred to as TPT) used in Swiss-Sochi elements of liquid crystal display devices.
Its operational characteristics have been attracting attention.

FIG. 5 is a schematic cross-sectional view of a conventional active matrix display device using this thin film transistor, FIG. 6 is an enlarged cross-sectional view of a part thereof, and FIG. 7 is a schematic cross-sectional view showing the area around the transparent electrode. FIG.

The conventional configuration will be described below with reference to FIGS. 5 to 7.

On the side receiving the backlight 39, the polarizing plate 2
A glass substrate 9 is prepared as a transparent insulating substrate with 2 formed on one side thereof, an insulating film 18 is formed on the opposite side, and a gate electrode 3 patterned thereon is integrally formed with the gate bus wiring 7. It is formed. Gate electrode 3
A gate insulating film 20 is formed on the entire surface of the insulating film 18 so as to cover the gate bus wiring 7, and a transparent electrode 1 and a TP as a switching element connected to the transparent electrode 1 are formed thereon.
A T is formed. TPT includes a drain electrode 2 connected to a transparent electrode 1, a thin a-St layer 5 formed above the gate electrode 3 by connecting the source electrode 4 and the drain electrode 4, the gate electrode 3, and the gate electrode 3. It consists of an insulating film 20.

A source bus wiring 6 is formed integrally connected to the source electrode 4 to establish electrical conduction with the outside. Transparent electrodes 1 and T
A protective film 40 is formed on the gate insulating film 20 so as to cover the PT, and a liquid crystal alignment film 42 for aligning the crystal orientation of the liquid crystal is further formed on the entire surface thereof.

On the other hand, on the opposite side to the surface irradiated by the backlight 39, a glass substrate 36 having a polarizing plate 38 formed on one side is also prepared, and on the opposite side, a color filter 34 is placed at a position corresponding to the transparent electrode 1. It is formed in a quantity corresponding to . A transparent electrode 32 is formed on a glass substrate 36 so as to cover the color filter 34, and a protective film 2 is further formed on the entire surface thereof.
8 is formed.

The glass substrate 9 and the glass substrate 36 configured in this manner are arranged to face each other, and the liquid crystal 26 is enclosed in the space between them, surrounded by the frame 30, thereby forming an active matrix display device.

The display operation of the active matrix display device configured as described above will be briefly described.

When no voltage is applied to the liquid crystal 26, the crystal molecules of the liquid crystal 26 are oriented in a predetermined direction by the liquid crystal alignment film 24, so that the light incident on the liquid crystal 26 is polarized in a predetermined direction while passing through the liquid crystal. transmitted to the outside. However, when a predetermined voltage is applied to the gate electrode 3 via the gate bus wiring 7, the conductivity type of the a-3t layer 5 above the electrode 3 is reversed, and the source electrode 4 and the drain electrode 2 are in a conductive state. becomes. Since a predetermined voltage is always applied to the source electrode 2 via the source bus wiring 6, the O of this TPT
A voltage is applied to the transparent electrode 1 due to N.

Therefore, an electric field is generated between the transparent electrode 1 and the transparent electrode 32 that face each other via the liquid crystal 26, so that the orientation of the liquid crystal molecules of the liquid crystal 26 is changed by this electric field, and the light incident on the backlight 39 is directed to the polarizing plate 38. The direction of polarization differs, and the light is not transmitted to the outside. Looking at this display operation from the side opposite to the backlight 39 side, that is, from the display side, when the TPT is ON, the picture element portion is in a dark state;
When PT is OFF, the picture element portion is in a bright state and is displayed in a color corresponding to the coloring of the color filter 34. Based on this principle, a desired image or information can be displayed by individually operating a large number of picture elements arranged in a matrix across the screen.

[Problems to be Solved by the Invention] In the conventional active matrix display device as described above, since the thin film semiconductor layer of the TPT receives incident light, this light reception causes a change in the operating characteristics of the TPT, resulting in a change in the display. There is a problem in that the image quality of the device is degraded.

FIG. 8 is a diagram showing the current-voltage characteristics of this TFT.

In the figure, the horizontal axis represents the gate voltage (VG) of the TPT, and the vertical axis represents the source/drain current (1).

When VG > 0, the current-voltage characteristics are the same regardless of whether or not the backlight is illuminated, but when VG is 0,
The current values are different when the backlight is not irradiated (solid line indicated by a in the figure) and when it is irradiated (broken line indicated in the figure). During backlight irradiation, the current value decreases less, that is, the OFF resistance of the TPT decreases. This reduction in OFF resistance can be demonstrated by the phenomenon that electrons are generated in the thin film semiconductor layer when light is incident on the thin film semiconductor layer. This means that when an attempt is made to turn off the TPT to bring the pixel into a bright state, the electric field applied to the liquid crystal 26 is not completely released, and the pixel does not become completely bright, resulting in the image being distorted. It affects the contrast.

Incidentally, the decrease in the OFF resistance of the TPT due to the incidence of light can occur not only due to backlight irradiation but also due to external light from the display side.

However, in a display device with a color filter as shown in Fig. 5, the influence of external light on the TPT can be made negligible by forming a black stripe made of a metal film or the like surrounding the color filter. Is possible. On the other hand, the backlight irradiation is performed by the polarizing plate 22.
Although the irradiation amount is attenuated by about 40%, the effect on the reduction of the OFF resistance of TPT is still not negligible.

This invention has been made to solve such problems, and has a structure in which the OFF resistance of the TPT is less reduced by the backlight, and the light shielding film is brought into contact with the gate bus wiring.
It is an object of the present invention to provide a large active matrix display device with high image quality by reducing the resistance of gate bus wiring as double wiring.

[Means for Solving the Problems] An active matrix display device according to the present invention has a light shielding film formed therein to shield the semiconductor thin film from being irradiated with incident light that passes through the liquid crystal, and the light shielding film is This is to make contact with the gate bus wiring.

[Function] In this invention, since the light shielding film blocks the irradiation of incident light to the semiconductor thin film, the T.
Prevents decrease in PT OFF resistance. Furthermore, since the gate bus wiring is double wiring, it is possible to reduce the resistance of the gate bus wiring.

[Example 1] FIG. 1 is a plan view showing an example of the present invention, and T
It shows the arrangement relationship of each component around the PT, and the second
The figure is a sectional view taken along the line ■-■ in Figure 1, and Figure 3 is the
−■ It is a sectional view.

The configuration will be described below with reference to FIGS. 1 to 3.

An insulating film 16 for an etching stopper is formed on a glass substrate 9 as a transparent insulating substrate, and furthermore, a film 16 is patterned in a predetermined shape at a predetermined position on the insulating film 16, for example, A(l).
, Tf, Mo, or the like is formed. An insulating film 18 serving as a similar etching stopper is formed on the insulating film 16 so as to cover the light shielding film 8, and a gate electrode is further patterned in a predetermined shape above the light shielding film 8. 3 is formed.

The gate insulating film 20 covers the insulating film 1 so as to cover the gate electrode 3.
Further, an a-8i layer 5 is formed as a semiconductor thin film in a predetermined shape above the gate electrode 3 . Also, a predetermined distance Millf from the a-8i layer 5
Similarly, a transparent electrode 1 serving as a picture element is formed on the gate insulating film 20 at the same position.

One side of the a-3i layer 5 and the transparent electrode 1 are n" a-3
connected by the drain electrode 2 through the i layer 12, and a
- A source electrode 4 is formed on the opposite side of the Si layer 5 via an n''a-8i layer 14. A source bus wiring 6 is formed integrally connected to the source electrode 4, and a gate electrode 3 is formed on the opposite side of the Si layer 5. A gate bus wiring 7 is integrally connected to each of the gate bus lines 7 and is electrically connected to the outside.In this embodiment, not only a light shielding film 8 is provided below the a-3i layer 5, but also
A light shielding film 8 is also provided below the gate bus wiring 7. The light shielding film 8 below the gate bus wiring 7 is connected to the insulating film 1 above it.
A contact 9 consisting of an opening formed at a predetermined position of 8,
It is electrically connected to the gate bus wiring 7 via 10.

The display operation of the active matrix display device configured as described above is the same as the conventional one, so a description thereof will be omitted here.
The light shielding film 8 has a significant effect on the operating characteristics of T. FIG. 4 is a diagram showing the current-voltage characteristics of TPT, which shows this effect.

In the figure, the horizontal axis represents the gate voltage (VG) of the TPT, and the vertical axis represents the source/drain current (1). In the figure, the solid line indicated by a when TPT is OFF (Vc < 0) indicates the case when there is no backlight irradiation, the broken line indicated by b indicates the case of the conventional example when the backlight is irradiated, and the dashed line indicated by C indicates the case when the backlight is irradiated. The cases of the embodiments of this invention are shown respectively.

These results show that by installing a light shielding film, the TPT characteristics hardly change even during backlight irradiation, and the 0N
It was found that the 10FF ratio could be maintained at an extremely large value of 10'' or more, and it was confirmed that the image quality was not degraded.

The light shielding film 81 formed under the gate bus wiring 7 was originally formed to prevent a step from forming at the connection between the gate electrode 3 and the gate bus wiring 7, but as shown in FIG. By making conduction with the gate bus wiring 7 through the contact 9.10, it brings about an effect that can also contribute to reducing the gate wiring resistance between the contacts 9 and 10, and as the display screen becomes larger. This is useful for increasing the wiring length of the gate bus wiring 7.

In the above example, an a-Si layer is used as the semiconductor thin film, but other semiconductor thin films may be similarly applied as long as the current characteristics of the TPT change due to light irradiation. Needless to say, the same effect can be achieved.

Further, in the above embodiments, the electrodes have a matrix-type electrode shape, but it goes without saying that the present invention can be similarly applied to a liquid crystal display device having a segment-type electrode shape.

[Effects of the Invention] As explained above, this invention forms a light shielding film for shielding the semiconductor thin film of the TPT from being irradiated with incident light, so that the operating characteristics of the TPT are changed even when the incident light is irradiated. First, since the light shielding film is brought into contact with the gate bus wiring to form a double wiring, it is possible to obtain an active matrix display device with low resistance of the gate bus wiring and high image quality.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the line ■-■ in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line ■-■ in FIG.
FIG. 4 is a TPT showing the effect of one embodiment of this invention.
FIG. 5 is a schematic cross-sectional view of a conventional active matrix display device, FIG. 6 is an enlarged cross-sectional view of a part of FIG. 5, and FIG. 7 is a diagram showing the current-voltage characteristics of FIG. FIG. 8 is a schematic plan view showing the area around the transparent electrode, and is a diagram showing the current-voltage characteristics of a conventional TPT. In the figure, 1 is a transparent electrode, 2 is a drain electrode, 3 is a gate electrode, 4 is a source electrode, 5 is an a-8i layer, 8 is a light shielding film, 20 is a gate insulating film, and 26 is a liquid crystal. In each figure, the same reference numerals indicate the same or corresponding parts. No. 11.27 67-st:, Jindo Otsu 6 Act name 2 (2) 14, n”a-5t, 4 Envy 3 no Mata 9 Figure 5 Tea 6 (2)

Claims (1)

[Scope of Claims] In an active matrix display device that performs display by applying a driving voltage to a liquid crystal using a thin film transistor as a switching element and modulating incident light, there is provided a light shielding device that shields a semiconductor thin film of the thin film transistor from the incident light. 1. An active matrix display device characterized in that a film is interposed therebetween, and the light shielding film is in contact with a gate bus wiring of the transistor to form a double wiring.