JPH0553148A - Active matrix liquid crystal panel - Google Patents

Abstract

PURPOSE:To suppress the off-current of TFT elements and to improve the characteristic to hold a signal voltage by lowering the incident level of reflected light on the amorphous silicon films (a-Si films) of the TFT element. CONSTITUTION:This liquid crystal panel is formed by disposing a TFT substrate A which is constituted by forming gate electrodes 102, gate insulating films 103, a-Si films 104, insulating films 110, (n) type a-Si films 105, drain electrodes 106, source electrodes 107, picture element electrodes 109, etc., on a glass substrate 101 and a counter electrode substrate B which is constituted by forming a black matrix 122, color filters 124, an over coat 125, counter electrodes 126, etc., on a glass substrate 121. Chromium oxide films 108, 123 are provided on the source and drain electrodes and/or the black matrix of the above-mentioned panel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display active matrix liquid crystal panel, and more particularly to a structure of a metal film such as electrode wiring.

[0002]

2. Description of the Related Art FIG. 4 is a sectional view of a conventional liquid crystal panel of this type. As shown in the figure, an active matrix liquid crystal panel using TFT elements is composed of a TFT substrate A, a counter electrode substrate B, and a liquid crystal sandwiched between both substrates.

The TFT substrate A is formed on the glass substrate 401 by
A gate electrode 402 formed integrally with the scanning line and a gate insulating film 403 covering the entire surface thereof are provided, and an amorphous silicon film (hereinafter referred to as a-Si film) 4 is formed thereon.
04, an insulating film 410 serving as an etching stopper, a P-doped amorphous silicon film for contact (hereinafter referred to as n-type a-Si) 405, a drain electrode 406 integrally formed with a signal line, a source electrode 407, a source electrode Four
Pixel electrode 409 made of transparent conductive material connected to 07
Is formed, and the protective film 411 and the alignment film 4 are formed on the entire surface.
And 12 are formed. In the same substrate, the gate electrode 402, the gate insulating film 403, the a-Si film 404,
n-type a-Si film 405, source / drain electrodes 407,
A TFT element C is formed by 406.

The counter electrode substrate B is a glass substrate 42.
A color filter 424 facing the pixel electrode of the TFT substrate and a black matrix 422 having an opening at a color filter forming portion are formed on the first substrate 1, and an overcoat 425 and a counter electrode 426 made of a transparent conductive material are formed on the entire surface thereof.
The alignment film 427 is formed.

The alignment films provided on both substrates are subjected to an alignment treatment so that the liquid crystal molecules are in a predetermined alignment state when no voltage is applied. A voltage is supplied to the drain electrode (signal line) 406, and this voltage is applied to the TFT element C.
When transmitted to the pixel electrode 409 via the
9 and a counter electrode 426 generate a potential difference, and the alignment state of the liquid crystal molecules changes accordingly, and display becomes possible. The voltage supplied to the pixel electrode is retained even after the TFT element C is turned off. Maintaining this voltage above a certain value is extremely important for display quality, but the state of holding this voltage is determined mainly by the leakage current (off current) when the TFT element is off and the capacitance of the pixel electrode. It

The black matrix 422 provided on the counter electrode substrate B mainly has the following functions. Since the signal voltage is not applied to the portion other than the pixel electrode, the alignment state of the liquid crystal molecules in that portion cannot be controlled by the signal voltage. The light leaking from the region where the liquid crystal does not sufficiently function as an optical shutter is shielded to improve the contrast between the bright state and the dark state of the liquid crystal display device. The TFT element is prevented from being irradiated with light, and an increase in off current due to photocurrent is suppressed.

[0007]

The active matrix liquid crystal panel has a high brightness backlight. The incident light a, b, c from this backlight is directly (a),
After reflecting on the surface of the black matrix which is a metal film (b) or after multiple reflection (c), the a-Si film 4 is formed.
Incident on 04. Further, when the liquid crystal panel is used in a bright environment, ambient light also passes through the counter electrode substrate and is incident on the a-Si film 404 after multiple reflection.

Since a-Si, which is the active region of the TFT element, is a material having high photoconductivity, when the reflected light is incident as described above, the element current is increased by photoconduction. FIG. 5 shows a dark state and a brightness of 40 in a conventional liquid crystal panel.
FIG. 9 is a characteristic diagram showing a relationship between a gate voltage and a drain current in an actual use state using a backlight of 00 cd / m ² . As is clear from the figure, in the conventional liquid crystal panel, the current when the transistor is turned off by light irradiation,
That is, the off current increases by two digits or more as compared with the dark state.

In the conventional liquid crystal panel, the increase in the off-current causes a large decrease in the holding voltage held in the capacitance of the pixel electrode, which deteriorates the display characteristics.

In order to prevent such an increase in off-current due to light, a light-shielding film is provided [eg, Proc. Japan Displa
y (1983) 352], and a method of reducing the film thickness of the a-Si film [for example, Appl. Phys. A41 (1986) 311] have been tried, but in the former, the number of processes is increased and the manufacturing cost is increased. In the latter case, there is a drawback that the yield decreases because the conditions for the uniformity and reproducibility of the film thickness become strict in the latter case.

[0011]

An active matrix liquid crystal panel of the present invention comprises a counter electrode substrate in which a black matrix made of a metal film and a counter electrode made of a transparent conductive material are formed on a glass substrate, and a glass substrate is provided. Source / drain electrode wiring for a thin film transistor including a plurality of thin film transistors and a metal film is formed.
An FT substrate and a liquid crystal sandwiched between the counter substrate and the TFT substrate, wherein at least one surface of the black matrix and the source / drain electrode wiring has a metal oxide film. It is characterized by being covered with.

[0012]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a partial cross-sectional view showing a first embodiment of the present invention. Also in this embodiment, the liquid crystal panel is composed of the TFT substrate A, the counter electrode substrate B, and the liquid crystal sandwiched between them, as in the conventional example.

To manufacture the TFT substrate of this embodiment, the gate electrode 1 connected to the scanning line is formed on the glass substrate 101.
02 is formed, a silicon nitride film is formed as the gate insulating film 103 to a thickness of 5000 Å, and an a-Si film 104 is formed to a film thickness of 2
A silicon nitride film having a thickness of 2000 Å is continuously formed as an insulating film 110 serving as an etching stopper at a thickness of 2000 Å by a glow discharge decomposition method.

After patterning the insulating film 110 into a predetermined shape, an n-type a-Si film 105 for obtaining ohmic contact between the a-Si film 104 and the electrode is deposited to a thickness of 500 Å by glow discharge decomposition method. To do. Then n-type a-S
The i film 105 and the a-Si film 104 are patterned into a predetermined shape.

After the pixel electrode 109 is formed of ITO (indium tin oxide), chromium is formed to a thickness of 2000 Å and chromium oxide (Cr ₂ O ₃ ) film 108 is formed to a thickness of 500 Å.
Are deposited by the sputtering method. next,
A drain electrode 106 integrally formed with the signal line and a source electrode 107 connected to the pixel electrode are formed through a photolithography process. At this time, chromium and chromium oxide can be wet-etched with the same etching solution (for example, cerium ammonium nitrate / perchloric acid aqueous solution), and even when the dry etching method is used,
The same etching gas (for example, a mixed gas of carbon tetrachloride and oxygen) can be used for etching. Therefore, it is possible to continuously etch both films without adding a new photolithography process.

After that, the protective film 11 made of silicon nitride is formed.
1 and the alignment film 112 are formed to complete the manufacture of the TFT substrate A.

Regarding the counter electrode substrate, the glass substrate 12
After depositing a chromium film and a chromium oxide film 123 on 1 by sputtering, a black filter 122 is formed by opening holes in the color filter forming portion.

After the color filter 124 is formed by a conventional method, a silicon nitride film is deposited and the overcoat 125 is formed.
Further, the counter electrode 126 made of ITO and the alignment film 1
27 are formed to complete the counter electrode substrate B.

The completed TFT substrate A and counter electrode substrate B are adhered and fixed at a distance of 5 μm, liquid crystal is injected between both substrates, and then the injection port is sealed. Thereafter, although not shown in the figure, polarizing plates are attached to the outer surfaces of both substrates in order to impart a display function.

FIG. 2 shows the reflectance of the chromium film and the chromium oxide / chromium laminated film in the visible light region. As shown, the reflectance of the laminated film is 1/4 to 1 / the reflectance of the chromium film.
It is 5.

Since the incident light on the TFT after the multiple reflection in the liquid crystal cell is exponentially lowered due to the decrease of the reflectance, the incident light due to the multiple reflection is provided by providing the oxide film on the black matrix and the electrode surface. Drastically reduced. When the TFT device characteristics in the liquid crystal cell according to the structure of this embodiment were actually measured, the off-current during light irradiation was reduced by one digit compared with the TFT device according to the conventional structure.

FIG. 3 is a sectional view of the TFT substrate A of the second embodiment of the present invention. In order to manufacture the TFT substrate of this embodiment, after the scanning line and the gate electrode 302 integrated with the scanning line are formed on the glass substrate 301, the gate insulating film 30 is formed.
3 as a silicon nitride film with a thickness of 5000 Å, aS
The i film 304 has a thickness of 3000 Å and the n-type a-Si film 30
5 is continuously deposited in a thickness of 500 Å by the glow discharge decomposition method. Then, after patterning the a-Si film 304 and the n-type a-Si film 305 into a predetermined shape,
ITO having a film thickness of 800 Å is deposited by a sputtering method and patterned into a predetermined shape to form a pixel electrode 309.

Next, a chromium film 306a having a film thickness of 500Å,
307a, an aluminum film 306b having a film thickness of 1500Å,
307b, 300 Å film thickness aluminum oxide (Al ₂ O
₃ ) A film 308 is deposited by a sputtering method respectively, and this laminated film is patterned to form a drain electrode 306 and a source electrode 307 having an oxide film on the surface. Subsequently, the unnecessary n-type a-Si film 305 on the gate electrode 302 is removed by etching.

Next, a silicon nitride film is deposited as a protective film 311 to a thickness of 2000 Å by glow discharge decomposition method. Although the subsequent steps and the structure other than the above are not shown, they are the same as those in the first embodiment.

In the second embodiment, since aluminum, which has a lower resistance than chromium, is used as the signal line, the signal delay due to the wiring resistance can be reduced. Although aluminum is a highly reactive metal, n-type aS
i film 305, pixel electrode 309, and aluminum film 30
6b and 307b between the chrome films 306a and 307a
The interfacial reaction does not adversely affect these films.

Although the preferred embodiments have been described above, the present invention is not limited to these embodiments and various modifications can be made. For example, titanium (Ti) or titanium oxide (TiOx) can be used instead of chromium or chromium oxide. Further, the oxide film can be provided only on one substrate side rather than being provided on both electrodes of the TFT substrate and the counter electrode substrate. Further, although the oxide film is not formed on the gate electrode (scan line) in the embodiment, the oxide film can be formed on this electrode as necessary.

[0027]

As described above, according to the present invention, the TFT
Since the metal oxide film is provided on the electrode wiring of the substrate and on the black matrix of the counter electrode substrate, according to the present invention, the reflected light of the electrode wiring and the black matrix of the backlight light and the ambient environment light is increased. Can be attenuated. Therefore, the reflected light a-Si of the TFT
The incident level on the film can be suppressed low, and the off current of the TFT can be suppressed. Therefore, according to the present invention, the voltage holding characteristic of the liquid crystal panel can be improved and the display characteristic can be dramatically improved by a relatively simple means.

[Brief description of drawings]

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

FIG. 2 is a diagram showing reflectance characteristics of a chromium film and a chromium oxide / chromium laminated film.

FIG. 3 is a sectional view of a second embodiment of the present invention.

FIG. 4 is a sectional view of a conventional example.

FIG. 5 is a diagram showing TFT characteristics of a conventional example.

[Explanation of symbols]

101, 301, 401 ... Glass substrate 102, 302, 402 ... Gate electrode (scanning line) 103, 303, 403 ... Gate insulating film 104, 304, 404 ... Amorphous silicon film (a
-Si film) 105, 305, 405 ... P-doped amorphous silicon film (n-type a-Si film) 106, 306, 406 ... Drain electrode (signal line) 107, 307, 407 ... Source electrode 306a, 307a ... Chromium film 306b , 307b ... Aluminum film 108 ... Chromium oxide film 308 ... Aluminum oxide film 109, 309, 409 ... Pixel electrodes 110, 410 ... Insulating films (etching stoppers) 111, 311, 411 ... Protective films 112, 412 ... Alignment films 121, 421 ... Glass substrates 122, 422 ... Black matrix 123 ... Chromium oxide films 124, 424 ... Color filters 125, 425 ... Overcoat 126, 426 ... Counter electrodes 127, 427 ... Alignment film A ... TFT substrate B ... Counter electrode substrate C ... TFT element

Claims (3)

[Claims] 1. A counter electrode substrate in which a black matrix made of a metal film and a counter electrode made of a transparent conductive material are formed on a glass substrate, and a source / drain for a plurality of thin film transistors and a thin film transistor made of a metal film on the glass substrate. An active matrix liquid crystal panel comprising: a TFT substrate on which electrode wiring is formed; and liquid crystal filled between the counter substrate and the TFT substrate, wherein the black matrix and the source / drain electrode wiring are An active matrix liquid crystal panel, wherein at least one surface is covered with a metal oxide film. 2. The active matrix liquid crystal panel according to claim 1, wherein a part or all of the electrode wiring is composed of a multilayer metal film. 3. The gate electrode wiring formed on the TFT substrate is covered with a metal oxide film.
The active matrix liquid crystal panel described.