JPH04240826A - Transmission type liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the flow of a light excitation leak current into a TFT by preventing from being irradiated the TFT with illuminating light. CONSTITUTION:A TFT substrate 2 formed a display electrode 6 and the TFT 7 on a glass substrate 5, and a color filter substrate 3b formed a color filter 10, a lattice form of a light shielding film 9 and a counter electrode 11 in a matrix state on a glass substrate 8 are arranged to face each other with a liquid crystal layer 4. Here the TFT 7 is so as to be covered with the light shielding film 9 and a back light 12 is arranged at the back of the color filter substrate 3.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission type liquid crystal display device, and more particularly to an active matrix transmission type liquid crystal display device using thin film transistors.

0002

2. Description of the Related Art FIG. 3 is a sectional view of a conventional transmission type liquid crystal display device of this type. As shown in the figure, the liquid crystal panel 1
is composed of a TFT substrate 2, a counter electrode substrate 3c, and a liquid crystal layer 4 sandwiched between these two substrates. Here, T
The FT substrate 2 includes a glass substrate 5, display electrodes 6 made of a transparent conductive film formed in a matrix on the surface thereof, and thin film transistors connected to each display electrode to control whether or not a voltage is applied to the display electrodes. (hereinafter referred to as TFT) 7, and the counter electrode substrate 3c is composed of a glass substrate 8 and a counter electrode 11 made of a transparent conductive film formed entirely on the surface thereof. Although not shown in FIG. 4, polarizing plates are arranged on the upper and lower surfaces of the liquid crystal panel 1, respectively.

In the conventional liquid crystal display device, a backlight 12 is arranged on the back side of the TFT substrate 2, and illumination light a is made incident on the liquid crystal panel 1 through this. Light incident on the liquid crystal panel 1 via the inner polarizing plate passes through the liquid crystal layer 4 between the display electrode 6 and the counter electrode 11, but the rotation of the plane of polarization is affected by the presence or absence of voltage applied to the display electrode 6. controlled. As a result, the light that has passed through the liquid crystal panel 1 either passes through the outer polarizing plate as it is or is blocked there.

FIG. 4 is an enlarged view of the TFT portion of the TFT substrate 2. As shown in FIG. In the figure, 7a is a gate electrode made of Cr, etc., 7b is a gate insulating film, 7c is a semiconductor layer made of amorphous silicon, etc., 7d is a source electrode whose one end is connected to the display electrode 6, and 7e is a drain wiring. This is a drain electrode formed integrally. Here, the gate electrode 7a
plays the role of a light-shielding film that prevents the illumination light a from entering the semiconductor layer 7.

[0005]

[Problems to be Solved by the Invention] In the above-mentioned conventional liquid crystal display device, illumination light is shielded by a Cr film which is the gate electrode, so this film must be made thicker in order to obtain sufficient light shielding properties. However, if the Cr film is made thicker, the drain wiring (signal wiring) formed perpendicular to the gate wiring (scanning wiring) will be more likely to break, so it is difficult to make this film as thick as necessary for light shielding. could not. Furthermore, in the conventional example, there is a portion of the semiconductor layer that is not shielded from light by the gate electrode. Therefore, in the conventional example, the light shielding property for the semiconductor layer is not sufficient, and a photoexcited leakage current occurs, causing the TFT to
As a result, the voltage applied to the display electrodes deviated from the planned value, causing light leakage.

[0006]

[Means for Solving the Problems] A transmissive liquid crystal display device of the present invention comprises a TFT substrate on which display electrodes and TFTs are formed, and a counter electrode substrate (or A color filter substrate (on which a light shielding film, a color filter, and a counter electrode are formed) are opposed to each other with a liquid crystal layer interposed therebetween, and illumination light is incident from the counter electrode substrate (or color filter substrate) side. and,
The TFTs on the TFT substrate are shielded from this illumination light by a light shielding film on the counter electrode substrate (or color filter substrate).

[0007]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing one embodiment of the present invention. The liquid crystal panel 1 of this embodiment is composed of a TFT substrate 2, a counter electrode substrate 3a, and a liquid crystal layer 4 provided between these two substrates, but the TFT substrate is different from that of the conventional example shown in FIG. Since they are similar, their explanation will be omitted. Although not shown in FIG. 1, polarizing plates are arranged on the upper and lower surfaces of the liquid crystal panel 1, respectively.

The counter electrode substrate 3a in this embodiment includes a glass substrate 8 and a light shielding film 9 selectively provided on the surface of the glass substrate 8.
and a counter electrode 11 formed over the entire surface. The light shielding film 9 on the counter electrode substrate 3a is formed to completely cover the TFT 7, and the light shielding film 9 on the counter electrode substrate 3a is formed so as to completely cover the TFT 7.
a is arranged on the backlight 12 side.

In this embodiment, the TFT 7 receives illumination light a.
Since it is further shielded by the light shielding film 9, the generation of leakage current due to optical excitation in the TFT is suppressed.

FIG. 2 is a sectional view showing another embodiment of the present invention. In this embodiment, a color filter substrate 3b is used in place of the counter electrode substrate 3a in the previous embodiment, but other points are the same as in the previous embodiment.

Color filter substrate 3b in this embodiment
consists of a glass substrate 8, a color filter 10 formed in a matrix on the surface thereof, a light shielding film 9 formed in a lattice shape surrounding the color filter 10, and a light shielding film 9 and a color filter 10 formed entirely on the light shielding film 9 and the color filter 10. and a counter electrode 11 formed in the opposite direction. Also in this embodiment, the light shielding film 9 is formed so as to sufficiently shield the TFT 7 from the illumination light a.

In this embodiment, the illumination light a, which is white light, is polarized by an inner polarizing plate (not shown) and then passes through a color filter 10 to be converted into R, G, and B monochromatic light. Thereafter, the plane of polarization is rotated by the voltage applied to the display electrode, or the light is emitted from the liquid crystal panel without being rotated, and its transmission or blocking is controlled by the outer polarizing plate.

[0013]

As explained above, in the liquid crystal display device of the present invention, a light shielding film having a shape that completely covers the TFTs on the TFT substrate is provided on the substrate on the side where the counter electrode is formed, so that illumination light can be blocked. Since the light is incident from the substrate side where the counter electrode is formed, the semiconductor layer of the TFT can be completely shielded from the illumination light. Therefore, according to the present invention, leakage current due to photoexcitation of the semiconductor layer can be suppressed, and T
The characteristics of the FT can be made as designed values. Therefore, according to the present invention, a predetermined voltage can be applied to the display electrodes, and light leakage can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of the present invention.

FIG. 2 is a sectional view showing another embodiment of the present invention.

FIG. 3 is a sectional view of a conventional example.

FIG. 4 is a detailed view of a portion of FIG. 3;

[Explanation of symbols]

1.LCD panel 2 TFT substrate 3a, 3c Counter electrode substrate 3b Color filter board 4 Liquid crystal layer 5, 8 Glass substrate 6 Display electrode 7 Thin film transistor (TFT) 9. Light shielding film 10 Color filter 11 Counter electrode 12 Backlight a Illumination light

Claims (2)

[Claims] 1. A first glass substrate, a light shielding film selectively formed on the surface of the first glass substrate, and a light shielding film selectively formed on the surface of the first glass substrate;
a counter electrode formed entirely on the surface of the glass substrate; a second glass substrate; and a display electrode formed in a matrix on the surface of the second glass substrate. , a plurality of thin film transistors each connected to one of the display electrodes, the display electrode facing the counter electrode on the counter electrode substrate, and the thin film transistor formed on the counter electrode substrate. A TFT substrate arranged to overlap with the light shielding film, a liquid crystal layer provided between the counter electrode substrate and the TFT substrate, and a lighting means arranged behind the counter electrode substrate. Transmissive liquid crystal display device. 2. A first glass substrate, a color filter formed in a matrix shape on the first glass substrate, and a lattice shape formed on the first glass substrate so as to surround the color filter. a color filter substrate having a light-shielding film, a counter electrode formed entirely on the first glass substrate; a second glass substrate; and a plurality of thin film transistors each connected to one of the display electrodes, wherein the display electrode faces a counter electrode on the color filter substrate, and the thin film transistor is connected to the color filter substrate. a TFT substrate arranged to overlap with the light shielding film on the substrate, a liquid crystal layer provided between the color filter substrate and the TFT substrate, a lighting means arranged behind the color filter substrate, A transmissive liquid crystal display device comprising: