JPH0996838A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the flow of photocurrent to a semiconductor layer of a switching element by forming the front layers of a black mask, which layers face one transparent substrate, of a material having low reflectivity. SOLUTION: The black mask 33 having prescribed patterns including the regions facing thin-film transistors(TFTs) 25 disposed on a lower glass substrate 21 is formed on the rear surface of an upper glass substrate 22. Color filters 34 are arranged in the parts enclosed heretofore by the black mask 33 on the rear surface of an upper glass substrate 22. The black mask 33 is constituted by successively laminating three layers; a chromium oxide layer 33A, chromium layer 33B and chromium oxide layer 33C toward the opposite inner side direction from the upper glass substrate 22 and the upper and lower front layers are formed of a material having low light reflectivity. The light reflection is suppressed by the surface of the chromium oxide layer 33C in case the diagonal incident light between the upper and lower glass substrates 21 and 22 is reflected by, for example, source electrodes 29 and drain electrodes 30 and is made incident on the black mask 33 and, therefore, the incidence of the light on the semiconductor layer 28 is suppressed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art As a conventional liquid crystal display element, there is known one having a structure shown in a sectional view of an essential part of FIG. In this liquid crystal display element, a pair of lower glass substrate 1 and upper glass substrate 2 facing each other are bonded via a sealing material (not shown), and a liquid crystal is formed in a gap formed between the lower glass substrate 1 and the upper glass substrate 2. It is generally configured by enclosing (not shown). A thin film transistor (TFT) 3 and a pixel electrode 4 made of, for example, ITO and connected to the thin film transistor are formed on the inner surface of the lower glass substrate 1 facing each other, and an alignment film 5 covering them is formed thereon. Has been formed.
On the other hand, on the inner surface of the upper glass substrate 2 facing the TFTs formed on the lower glass substrate 1, a black mask 8 patterned in a matrix is arranged, and at a position facing the pixel electrodes 4. A color filter 9 is formed on the. A common electrode 10 made of, for example, ITO is formed on the surfaces of the black mask 8 and the color filter 9.
Are formed over the entire display area, and an alignment film 11 is formed on the common electrode 10. Further, the lower polarizing plate 12 is provided on the facing outer surface (lower surface) of the lower glass substrate 1, and the upper polarizing plate 13 is provided on the facing outer surface (upper surface) of the upper glass substrate 2.

Generally, the above-mentioned black mask 8 is composed of two layers, a chromium oxide layer 6 adhered to the upper glass substrate 2 and a chromium layer 7 formed on the chromium oxide layer 6 (lower in the figure). ing. In the thin film transistor 3 described above, the gate electrode 14, the gate insulating film 15, the semiconductor layer 16 made of, for example, amorphous silicon, the source electrode 17 made of a metal material, and the drain electrode 18 patterned on the inner surface of the lower glass substrate 1 facing each other. Etc.

[0004]

In the above-mentioned conventional liquid crystal display device, the chromium oxide layer 6 of the black mask 8 is used.
Is a low-reflection material, it has a structure that suppresses the reflection of light that enters the black mask 8 from the outside of the upper glass substrate 2. However, it does not reflect the light that enters obliquely between the upper and lower glass substrates 1 and 2. It is not structured to suppress multiple reflections. That is, light from the direction perpendicular to the upper glass substrate 2 does not enter the thin film transistor 3 portion, but light from the oblique direction due to multiple reflection in the liquid crystal cell cannot be avoided. Specifically, as shown in FIG. 5, since the chromium layer 7 forming the black mask 8 is formed on the inner side opposite to the chromium oxide layer 6, when the light is obliquely incident on the source electrode 17. However, there is a problem that the light reflected by the source electrode 17 is further reflected by the chrome layer 7 and enters the semiconductor layer 16.
Since the semiconductor layer 16 has photoconductivity, in such a case, a problem such as an increase in off current of the thin film transistor 3 occurs. As a liquid crystal display element, when a so-called light leak current occurs in the thin film transistor as described above, there is a problem that the contrast is lowered and crosstalk occurs.

An object of the present invention is to provide a liquid crystal display element having a high display performance in which the amount of light incident on the semiconductor layer of the thin film transistor connected to each pixel electrode is suppressed.

[0006]

According to the first aspect of the present invention,
A pixel electrode and a switching element having a semiconductor layer portion, which is connected to the pixel electrode, are arranged on the inner surface of the pair of transparent substrates facing each other, which face each other, and the other transparent substrate is provided. In a liquid crystal display device including a black mask facing at least the switching element on the facing inner surface, at least the surface layer facing the one transparent substrate of the black mask is formed of a material having a low reflectance. , As a solution. In the invention according to claim 1, since the surface layer located on the liquid crystal side of the black mask is made of a material having a low reflectance, light incident from a diagonal direction between the transparent glass substrates is reflected by the surface layer of the black mask. Has the effect of suppressing the incident on the semiconductor layer. Therefore, it is possible to prevent the photocurrent from flowing through the semiconductor layer of the switching element.

The invention according to claim 2 is characterized in that an antireflection layer made of a material having a low reflectance is disposed around the switching element. According to the second aspect of the present invention, the antireflection layer arranged around the switching element can prevent reflection of light that is obliquely incident between the transparent substrates and reduce light incident on the black mask.

According to a third aspect of the present invention, the switching element is an inversely staggered type thin film transistor, and a surface layer of the source / drain electrode of the thin film transistor facing the other transparent substrate is made of a material having a low reflectance. It is characterized by being formed.

According to the third aspect of the invention, since the switching element is a thin film transistor having an inverted stagger type structure, light is likely to be incident on the semiconductor layer between the source and drain, but the surface layer of the black mask is reflected. Since it is formed of a material having a low ratio or an antireflection layer is formed around the thin film transistor, light incidence on the semiconductor layer can be suppressed. Therefore, off current can be prevented from being generated in the thin film transistor, which can prevent reduction in contrast and generation of crosstalk.

Further, since the surface layer (on the liquid crystal side) of the source / drain electrodes of the thin film transistor facing the other transparent substrate is made of a material having a low reflectance, it is incident between the transparent substrates in an oblique direction. Prevents reflection of light,
It is possible to prevent light from entering the semiconductor layer due to multiple reflection. Therefore, off current can be prevented from being generated in the thin film transistor, which can prevent reduction in contrast and generation of crosstalk.

The invention according to claim 4 is characterized in that an antireflection layer made of the same material as the semiconductor layer of the thin film transistor is arranged around the thin film transistor. In the invention according to claim 4, since the antireflection film is made of the same material as the semiconductor layer of the thin film transistor, the antireflection film can be formed at a time, so that it is not necessary to add a step of forming the antireflection film.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the liquid crystal display device according to the present invention will be described below with reference to the embodiments shown in the drawings. (Embodiment 1) FIG. 1 is a sectional view of an essential part of Embodiment 1 of the present invention. In the figure, reference numeral 20 denotes a liquid crystal display element, in which a lower glass substrate 21 as one transparent substrate and an upper glass substrate 22 as the other transparent substrate are arranged so as to face each other, and a liquid crystal (not shown) is provided between both substrates. Is included. A lower polarizing plate 23 is provided on the lower surface of the lower glass substrate 21. Further, on the upper surface of the lower glass substrate 21 (inside surface facing the upper glass substrate 22), a pixel electrode 24 made of ITO, a thin film transistor 25 as a switching element connected to the pixel electrode 24, a gate line and a drain not shown Lines are formed.

The thin film transistor 25 is composed of the lower glass substrate 2
1. A gate electrode 26 patterned on the inner surface facing each other
A gate insulating film 27 deposited on the gate electrode 26 and the lower glass substrate 21, a semiconductor layer 28 made of amorphous silicon patterned on the gate insulating film 27 so as to face the gate electrode 26, and a semiconductor layer. Source / drain electrodes 2 provided separately on 28
The reverse stagger type structure, which is roughly composed of 9 and 30, is adopted. Note that the pixel electrode 24 is the thin film transistor 2
5 and is patterned on the gate insulating film 27. Then, the source electrode 2 of the thin film transistor 25
The end portion 9 is formed so as to overlap the peripheral portion of the pixel electrode 24. Further, a lower alignment film 31 is formed on the entire surface of the liquid crystal display area where the thin film transistors 25 and the pixel electrodes 24 are formed.

On the upper surface of the upper glass substrate 22, the upper polarizing plate 3
2 are provided. Further, on the lower surface of the upper glass substrate 22 (the inner surface facing the lower glass substrate 21), the black mask 3 having a predetermined pattern including a region facing the thin film transistor 25 provided on the lower glass substrate 21.
3 are formed. Further, a color filter 34 is arranged in a portion surrounded by the black mask 33 on the lower surface of the upper glass substrate 22. A common electrode 35 made of ITO is formed on the lower surfaces of the black mask 33 and the color filter 34 over the entire liquid crystal display area, and an upper alignment film 36 is provided on the lower surface of the common electrode 35 over the entire liquid crystal display area. There is.

In this embodiment, the black mask 33 is
A chromium oxide layer 33A, a chromium layer 33B, and a chromium oxide layer 33 are sequentially provided from the upper glass substrate 22 toward the opposite inner side.
It is configured by laminating three layers of C, and the upper and lower surface layers are formed of a material having a small light reflectance. As shown in FIG. 1, when light obliquely incident between the upper and lower glass substrates 21 and 22 is reflected by, for example, the source electrode 29 or the drain electrode 30 and incident on the black mask 33, on the surface of the chromium oxide layer 33C. Since light reflection is suppressed, it is possible to suppress light from entering the semiconductor layer 28. Further, even when multiple reflections other than the light reflection shown in FIG. 1 occur, the black mask 33 can suppress the light reflection of the incident light. Therefore, in this embodiment,
It is possible to prevent the off current of the thin film transistor 25 from increasing. Further, by preventing the increase of the off current, it is possible to prevent the deterioration of contrast and the occurrence of crosstalk.

(Embodiment 2) FIG. 2 is a cross-sectional view of essential parts showing Embodiment 2 of the present invention. In describing the present embodiment, the same parts as those in the above-described first embodiment are designated by the same reference numerals and the description thereof will be omitted. This embodiment is characterized in that the surface layer of the source / drain electrodes of the thin film transistor as the switching element is formed of a material having a low light reflectance.

In the present embodiment, as shown in FIG. 2, the source electrode 29 and the drain electrode 30 of the inverted staggered thin film transistor 25 have a three-layer structure. The source electrode 29 is formed by sequentially stacking a chromium layer 29A, an aluminum layer 29B, and a chromium oxide layer 29C from the lower layer. Similarly, the drain electrode 30 is also formed by sequentially stacking a chromium layer 30A, an aluminum layer 30B, and a chromium oxide layer 30C from the lower layer. The chrome layers 29A and 30A have a function as a barrier metal and an ohmic layer. Aluminum layers 29B, 30
B has a low resistance as a wiring. The chromium oxide layers 29C and 30C are materials having a low light reflectance, and when light obliquely enters between the upper and lower glass substrates 21 and 22, the light reflection is suppressed and the light is incident on the semiconductor layer 28. Has a function to prevent. The other configurations in the present embodiment are the same as those in the first embodiment. In the present embodiment, the surface layer of the facing inner surface (the surface on the liquid crystal side) of the black mask 33 provided on the upper glass substrate 22 side is the chromium layer 3.
3B, the source and drain electrodes 29,
Since the surface layer of 30 has a low light reflectance, light incident on the semiconductor layer 28 can be effectively suppressed.

(Embodiment 3) FIG. 3 is a cross-sectional view of essential parts showing Embodiment 3 of the present invention. In this embodiment, the black mask 33 provided on the upper glass substrate 22 has the same configuration as that of the first embodiment described above, and the source and drain electrodes 29 and 30 of the thin film transistor 25 provided on the lower glass substrate 21 side are the same as those described in the above embodiment. The configuration is the same as that of 2. That is, the black mask 33 is sequentially formed on the chromium oxide layer 3
3A, a chromium layer 33B, and a chromium oxide layer 33C are laminated. Also, the source and drain electrodes 29, 3
0 is a chromium layer (29A, 30A), an aluminum layer (29B, 30B), a chromium oxide layer (29C,
30C) is sequentially laminated. Therefore, in the present embodiment, when light is incident between the upper and lower glass substrates 21 and 22 in an oblique direction, the semiconductor layer 28 due to the reflection of light.
It is possible to more effectively prevent light from entering.

(Embodiment 4) FIGS. 4A and 4B.
[FIG. 8] A sectional view of a main portion, which shows Embodiment 4 of the present invention. 4 (A) is an enlarged plan view showing the thin film transistor 25 and the pixel electrode 24, and FIG. 4 (B) is AA of FIG. 4 (A).
It is sectional drawing. In this embodiment, as shown in the plan view of FIG. 4A, the antireflection layer 3 is formed around the thin film transistor 25.
7 is formed. The antireflection layer 37 is divided into four parts via the groove 37A, and is formed so that the source electrode 29 and the drain electrode 30 do not form a transistor other than the thin film transistor 25. In FIG. 4A, reference numeral 38 indicates a gate line and 39 indicates a drain line. Further, the other configuration of this embodiment is the same as that of the above-described third embodiment.

The antireflection layer 37 formed around the thin film transistor 25 is made of the same material as that of the semiconductor layer 28 forming the thin film transistor 25 and is patterned at the same time. The etching process can be formed simply by changing the pattern mask. In this embodiment, since the antireflection layer 37 is made of amorphous silicon having high absorbance, incident light can be absorbed well. According to this embodiment, as shown in FIG. 4B, when light is obliquely incident on the source electrode 29 (or the drain electrode 30), light reflection can be prevented as in the third embodiment. At the same time, since the antireflection layer 37 can absorb the light incident from the oblique direction, the influence of the light can be suppressed as much as possible. Furthermore, the upper glass substrate 2
Since the surface of the black mask 33 on the second side also has an antireflection effect, it is possible to reliably prevent light from entering the semiconductor layer 28. Therefore, it is possible to suppress the occurrence of leakage current of the thin film transistor 25, reliably prevent the deterioration of contrast and the occurrence of crosstalk, and obtain a liquid crystal display element having good display performance.

Although the first to fourth embodiments have been described above, the present invention is not limited to these, and various design changes associated with the gist of the configuration can be made. For example, in each of the above-described embodiments, the surface layer of the black mask 33 on the liquid crystal side, the source / drain electrodes 29, 3,
Although chromium oxide was used as the material for the surface layer of No. 0, it is not limited to this as long as it is a material having a low light reflectance.

In the fourth embodiment, the antireflection layer 37 is composed of four parts, but both the source and drain electrodes 29 and 30 must be a constituent part to form a transistor. For example, the number and shape can be changed appropriately. The groove 37A existing between the antireflection layers 37 has a function of promoting light absorption by repeating reflection of incident light in the groove. Further, the antireflection layer 37 does not have to intervene under the electrodes 29 and 30 as long as it is disposed around the source and drain electrodes 29 and 30.

Furthermore, in each of the above-mentioned embodiments,
Although the thin film transistor is applied as the switching element in the description, it is of course possible to apply various switching elements including a semiconductor layer.

[0024]

As is apparent from the above description, according to the present invention, it is possible to prevent the photocurrent from being generated in the switching element connected to the pixel electrode, so that the drive control of the liquid crystal can be ensured. Has the effect. In particular, when a thin film transistor is used as a switching element, light incident on the semiconductor layer can be suppressed, so that it has an effect of preventing an increase in off-state current of the thin film transistor. Also,
By forming the antireflection layer around the switching element, it becomes possible to prevent light from entering the semiconductor layer without increasing the number of steps.

[Brief description of drawings]

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

FIG. 2 is a sectional view of a main part showing a second embodiment of the present invention.

FIG. 3 is a sectional view of an essential part showing a third embodiment of the present invention.

FIG. 4A is an enlarged plan view of an essential part showing Embodiment 4 of the present invention, and FIG. 4B is a sectional view taken along line AA of FIG.

FIG. 5 is a cross-sectional view of a main part of a conventional liquid crystal display element.

[Description of Reference Signs] 21 upper glass substrate 22 lower glass substrate 25 thin film transistor 28 semiconductor layer 29 source electrode 30 drain electrode 33 black mask 33C chrome oxide layer 37 antireflection layer

Claims (4)

[Claims] 1. A pixel electrode, a switching element having a semiconductor layer portion connected to the pixel electrode, on one of inner surfaces of the pair of transparent substrates facing each other, the inner surface facing the transparent substrate.
In the liquid crystal display element provided with a black mask facing at least the switching element on the opposite inner surface of the other transparent substrate, at least the surface layer of the black mask facing the one transparent substrate is reflective. A liquid crystal display element characterized by being formed of a material having a low rate. 2. The liquid crystal display element according to claim 1, wherein an antireflection layer made of a material having a low reflectance is arranged around the switching element. 3. The switching element is a thin film transistor having an inverted staggered structure, and a surface layer of the source / drain electrode of the thin film transistor facing the other transparent substrate is formed of a material having a low reflectance. The liquid crystal display element according to claim 2. 4. The liquid crystal display element according to claim 3, wherein an antireflection layer made of the same material as the semiconductor layer of the thin film transistor is arranged around the thin film transistor.