JPS59124319A - Image display device - Google Patents

Abstract

PURPOSE:To lower the dark level in the dark display of an image display and to obtain a large contrast ratio by installing directly or via an insulating film, etc. a thin film for decreasing reflected light on the observer's side of a conductor wiring or thin conductor film. CONSTITUTION:A gate insulating film is formed on a gate electrode, a gate bus 3 and an image display electrode 2, and a semiconductor layer 5 is formed in an island shape thereon. A source bus 4 and a drain electrode 6 are formed. An image display electrode 2 and a drain electrode 6 are electrically connected by a contact hole 7. A thin film 13 for decreasing reflected light is installed directly on the image observer's side L of the surce electrode and source bus 4 and the drain electrode 6. The reflectivity on the surface of the wiring is thus decreased and the dark level in the dark display of the image is lowered and therefore a large contrast ratio is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image display device using a liquid crystal or the like, and relates to, for example, a liquid crystal display device driven by an active matrix array.

Conventional Structures and Problems Thereinafter, a liquid crystal display device driven using a thin film field effect transistor as a semiconductor element will be explained as a representative example.

FIG. 1 is a schematic diagram of a drive array section of a liquid crystal display device.

A picture element is composed of a thin film field effect transistor 1 and an image display electrode 2 formed of a transparent electrode or the like. The image display electrode 2 for driving the liquid crystal maintains electrical contact with the drain electrode 6 of the transistor 1. Furthermore, a gate insulating film 3 and a source bus 4 are required to connect the picture elements to each other to form a drive matrix/nox array.

FIG. 2 is a plan view of the picture element portion. The thin film field effect transistor 1 is shown inside the circle. A gate insulating film is formed over the entire surface of the gate electrode, gate bus 3, and image display electrode 2, and an island-shaped semiconductor layer 5, which becomes the channel region of the transistor, is formed through the gate insulating film, and the source electrode Also, a source bus 4 and a drain electrode 6 are formed. The image display electrode 2 is in electrical contact with the drain electrode 6 through a contact hole.

FIG. 3 is a sectional view taken along line A--A' in FIG. 2.

In FIG. 3, the same parts as in FIGS. 1 and 2 are given the same numbers. 8 is a gate insulating film, and 9 is a substrate. A transparent electrode is installed as a counter electrode 16 on a glass substrate 16 on the side of the image viewer, and the liquid crystal 14 is arranged between the driving array section on the substrate 9 and the counter electrode 16. Furthermore, FIG. 3 shows the state of reflected light 10b caused by incident light 10a from the side of the display panel image viewer.

The gate electrode and gate bus 3, the source electrode and source bus 4, and the drain electrode 6 are wiring or thin films made of conductors such as Al, Cr, Ni, Mo, other metals, and silicide transparent electrodes. The following discussion will focus on reflective liquid crystal display devices. When displaying an image, for example, if the entire surface is displayed in black, the reflected light from these conductor wirings and conductor thin films 1
Contrast processing is used because 0b becomes the background of light on the image display surface. There is a drawback that N/■OFF (dynamic range) is inhibited. ION has a white display light.

■. FF indicates black display light. In fact, the image display light in a unit picture element can be approximated as follows.

However, IO is the intensity of light incident on the image display surface, S is the area of the unit picture element in Figure 2, Sm is the area p of the conductor surface other than the image display electrode within the unit picture element, and Rm is the area of the conductor surface within the unit picture element. Reflectance of conductor surfaces other than image display electrodes.

RLCOFF and RLCON are the reflectances of the image-display section controlled by the liquid crystal when the liquid crystal is OFF and ON, respectively (in equations (1) and (2), the reflectances of areas other than the conductor portion are used). In equations (1) and (2), the first term is from the conductor surface, and the second term is when the liquid crystal is OFF and OFF.
This is the contribution of the reflected light from the image display section at the time of N. Not yet (1
), From equation (2), the contrast ratio ION/I. FF
becomes as follows.

FIG. 4 illustrates the relationship between the contrast ratio and the reflectance of the conductor surface. However, the area ratio of the conductor in the unit picture element Sm/S
−〇． 2, and in the ideal case where there is no reflection from the conductor surface, that is, when Rm==○, the contrast ratio is 1ON/1OF
F: RLCON/RLCON-15 As can be seen from Figure 4, when the reflectance of the conductor surface is large, the contrast chemical ON/OFF is extremely reduced. For example, in a structure in which the conductor KAl is used and the A1 surface is exposed to the liquid crystal, - is 0.8 or more, while normal RLON is 0.8.
Since the contrast ratio was about 6, the contrast ratio was extremely small at 2.3. Therefore, in order to obtain a good image, it is necessary to reduce the reflectance of the conductor surface and improve the contrast ratio lON/IOFF of image display.

FIG. 5 shows a conventional example in which a metal film 12 is provided with an insulating film 11 interposed therebetween for light shielding. This is because the photoconductivity of the semiconductor layer 5 is high, and the leakage current increases when the transistor is in the OFF state due to direct light irradiation to the semiconductor layer 5 or photoconduction due to light transmission, and the writing state of the liquid crystal cell changes from the next writing state. This is a conventional and common method that is used to improve the drawback that it cannot be held at one time. In this case as well, there is a possibility that the light 10b is reflected by the installed metal film 12, which has the disadvantage of impairing the contrast ratio of image display.

In this way, it is clear that in image display elements that have image display electrodes and semiconductor elements arranged regularly, and that have conductor wiring and conductive thin films, reflection from the conductive wiring and conductive thin films has an extremely large adverse effect. It became.

OBJECTS OF THE INVENTION Accordingly, the present invention has been made to improve the above-mentioned conventional drawbacks. In other words, the present invention prevents reflected light from conductor wiring or conductor thin films with high reflectivity such as metals other than image display electrodes, lowers the dark level in dark display of image display, and obtains a large contrast ratio to produce good images. The purpose is to obtain.

Structure of the Invention In the present invention, an image display electrode for driving a liquid crystal and a semiconductor element as a switch element are formed for each picture element on a substrate, and each picture element is connected to an IJ node from the semiconductor element. Conductor wiring exists to configure the structure. Of course, the semiconductor element itself also has conductor wiring or conductor thin films formed as electrodes.

In such an image display device, the present invention provides a reflected light reducing thin film on the image viewer side of the conductor wiring or conductive thin film, and a reflected light reducing thin film is installed on the image viewer side of the conductive wiring or conductive thin film. Install directly or via an insulating film, etc.

Description of examples Hereinafter, the present invention will be explained in detail with reference to Examples.

Embodiment 1 FIG. 6 is a sectional view of one substrate side of a liquid crystal image display device according to a first embodiment of the present invention. The reflected light reducing thin film 13 in the present invention is installed directly on the source electrode, the source bus 4, and the drain electrode 6 on the side facing the image viewer.

The numbers and names in other figures are the same as in FIG.

Usually, Al is used for the source electrode, the source bus 4, and the drain electrode 6, or a conductor wiring in which Al is placed on another conductor is used. Therefore, when 84 is used, a black thin film or black alumite is formed on the surface of Al on the two image observation side using a blackening agent of Al to form the reflection reducing thin film 13. As a result, the reflectance of Al increased from about 0.9 to about 0.02, and the contrast ratio greatly improved from 2.3 to over 12, as is clear from FIG.

Embodiment 2 In FIG. 6, Cr is used for the source electrode, source bus 4, and drain electrode, or conductor wiring in which Cr is placed on another conductor is used. Next, by forming Cr 203 on the image observation side surface to form a reflected light reducing thin film, reflected light can be reduced to a greater extent. As a result, the reflectance of the wiring surface decreases from about 0.6 to about 0.002, and the contrast ratio decreases from about 3 to 13, similar to the blackening of AI.
Improved to above.

Example 3 As another example, the antireflection thin film 13 in FIG.
Non-single crystal semiconductors (Si, Si:H) have a large diameter of 10 to 1 ocm or more in the visible light region.

5i1-xNx, Si1. -xCx, Si1-xGex
, 5i1-xSn, Ge, etc.). If more than 20008 of these non-single-crystal semiconductors mainly composed of group III are deposited, more than 90% of the incident light will be absorbed, resulting in reflected light reduction thin film 1.
3 is very effective. Also, ■ such as boron and phosphorus,
When a non-single-crystal semiconductor whose main component is a group III element doped with a group III element as an impurity is used as the reflected light reducing thin film 13, its absorption coefficient α increases by more than one digit on the long wavelength side of about 0.7 μm. It's even more effective. Especially T in Figure 6.
The semiconductor layer 5 forming the channel portion of the PT is a non-single-crystal semiconductor whose main component is a group III element, and the reflected light reducing thin film 13 of the present invention is applied to the semiconductor layer 5 as in this embodiment.
If it is formed from a non-single-crystal semiconductor whose main component is a group Ⅰ element, which is the same material as that of Very effective.

Embodiment 4 FIG. 7 shows yet another embodiment of the present invention. In this embodiment, the reflected light reducing thin film 13 of the present invention is applied to a region other than the image display electrode 2 via an insulating film 14 in a non-single crystal semiconductor device whose main component is a group Ⅰ element. This makes it possible to reduce not only the reflection of light from the source electrode, the source bus 4 and the drain electrode 6, but also the reflection of light from the gate bus 3. Further, the reflected light reducing thin film 13B, T
It also serves to block the direct incident light 10a to the semiconductor layer 6 forming the channel portion of the PT, and also serves to eliminate leakage current due to photocurrent when the transistor is OFF, and is also effective as a photoblocking film. .

Embodiment 5 FIG. 8 is a sectional view showing a third embodiment of the present invention. This is done by replacing the light-shielding metal film 12 shown in FIG. 5 with TPT.
This was done in contrast to the conventional example in which a light shield was placed on the semiconductor layer 6 forming the channel portion of the device. In FIG. 8, the reflected light reducing thin film 13 of the present invention selectively contains a group III element such as amorphous silicon as a main component in the area of the image display electrode 2 excluding the area that effectively contributes to the image. Non-single crystal semiconductor devices. As a result, source electrodes and source buses 4. Gate electrode and gate bus3. A reflected light reducing thin film 13 is formed directly or via an insulating film on the image viewer side of a part or all of the conductive wiring and conductive thin film of the drain electrode 6 and the light-shielding metal film 12. Reflected light from part or all of the light can be significantly reduced.

Of course, as the reflected light reducing thin film 13, boron, phosphorus, etc.
Even when a non-single-crystal semiconductor whose main component is a group Ⅰ element doped with a group or V group element as an impurity was used, the effect was poor.

Effects of the Invention As described above, the present invention is particularly effective in preventing reflected light from conductive wiring or thin films other than display electrodes and obtaining good images.

Although the present invention has been described above with a focus on an image display device that drives a liquid crystal using a thin film field effect transistor as a semiconductor element, the present invention is not limited to this, and the present invention is not limited to this. This method is effective for image display devices having large conductive wiring or thin conductive films, in which case the contrast ratio during image display is impaired.

[Brief explanation of the drawing]

Fig. 1 is a schematic plan view of the image display device, Fig. 2 is a schematic plan view of a unit pixel constituting the image display device, and Fig. 3 is a cross-sectional view of the unit pixel taken along line A-A' in Fig. 2. , Figure 4 is a diagram of the relationship between contrast ratio and reflectance, and Figure 5 is a diagram showing the relationship between contrast ratio and reflectance, and Figure 5 is a diagram showing the relationship between contrast ratio and reflectance. A cross-sectional view of a main part of the image display device, FIGS. 1...--Semiconductor elements such as thin film field transistors,
2... Image display electrode, 3-... Gate electrode and gate bus, 4... Source electrode and source bus, 5...
...Semiconductor layer, 6--Drain electrode, 9--Substrate, 13--Reflected light reduction thin film, 14--Liquid crystal. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 6 @ Figure 4 Kawarakugihira Rtn Figure 5.廿10α Figure 7 L ■ 8th Figure well

Claims (5)

[Claims] (1) Picture elements having image display electrodes and semiconductor elements are regularly arranged on one main surface of the substrate, and conductive wiring that connects the semiconductor elements with each other and extends on the one main surface of the substrate , an image display device comprising: a conductive thin film connecting the semiconductor element and the image display electrode; and a reflected light reducing thin film formed on a part or all of the conductive wiring and the conductive thin film on the image viewer side. 0 (2) The image display according to claim 1, wherein the conductor wiring or the conductor thin film is made of aluminum, and the reflected light reducing thin film is a black thin film formed with an aluminum blackening agent or black alumite. Device. (3) The image display device according to claim 1, wherein the conductive wiring and the conductive thin film are made of chromium metal, and the reflected light reducing thin film is made of chromium oxide. (4) Claim 1, characterized in that the reflected light reducing thin film is a non-single-crystal semiconductor whose main component is a group III element.
The image display device described in Section 1. (5) The reflected light reducing thin film is a non-single-crystal semiconductor doped with a group III or group III element such as boron or phosphorus as an impurity and whose main component is a group III element. The image display device according to item 1.