JPH07311393A - Liquid crystal display device using nonlinear driving element - Google Patents

Abstract

PURPOSE:To improve the driving ability of a liquid crystal compared to a conventional nonlinear element, and to obtain higher display quality of a liquid crystal display device using this element. CONSTITUTION:The liquid crystal display device is an active matrix type device using a two-terminal MIM diode having a structure of lower metal/insulating film/upper metal as a nonlinear driving element. Metal tantalum, tantalum oxide, and a transparent conductive film are used for the lower metal 2, the insulating film 3, and the upper metal 4, respectively. The tantalum oxide as the insulating film 3 is an oxide of metal tantalum as the lower metal 2. The concentration of hydrogen atom in the metal tantalum and the tantalum oxide which constitute the nonlinear element is <1 atomic %.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an active matrix type liquid crystal display device using a two-terminal type MIM diode having a lower metal / insulating film / upper metal structure as a non-linear driving element.

[0002]

2. Description of the Related Art A conventional structure of a two-terminal type MIM diode having a lower metal / insulating film / upper metal structure is shown in a sectional view of FIG.

As shown in FIG. 1, on a glass substrate 1, metal tantalum / tantalum oxide / transparent conductive film using metal tantalum as a lower metal 2, tantalum oxide as an insulating film 3 and transparent conductive film 4 as an upper metal 4, respectively. An active type liquid crystal display device using a two-terminal type non-linear liquid crystal display element having a structure as a driving element is a thin film transistor or a metal tantalum /
The structure is simpler than that using a two-terminal type non-linear element having a tantalum oxide / metal film / transparent conductive film structure.

Therefore, the manufacturing cost is low, the element defect rate is low, and it is possible to supply a cheaper and higher quality liquid crystal display device.

[0005]

The metal tantalum film of the lower electrode 2 of the non-linear driving element having the structure shown in FIG. 1 is usually formed by physical vapor deposition. In the film of the lower electrode 2,
It was found that a large amount of hydrogen atoms, which are supposed to originate from the residual water in the film forming atmosphere, are contained.

The thermal desorption spectrum represents the amount of emission of a certain molecule (vertical axis, arbitrary scale) from a certain sample at a certain temperature (horizontal axis). FIG. 2 shows a metal tantalum film formed by the DC magnetron sputtering method. 3 is a temperature programmed desorption spectrum of hydrogen molecules in FIG.

FIG. 2 shows that a large amount of hydrogen is released from the metal tantalum film of the lower electrode 2 at a temperature of 400 ° C. or higher.

Further, hydrogen contained in the metal tantalum film as a raw material remains as it is also in the film of tantalum oxide which is the insulating film 3 formed by anodizing the metal tantalum of the lower electrode 2. Can be guessed.
The mechanism of this hydrogen remaining is unknown.

Although the mechanism is unknown, the hydrogen atoms in the film have a drawback that the leakage current characteristics of the MIM diode in the low voltage region are poor and the ability as a driving element of the liquid crystal display device is suppressed to be low. Occur.

An object of the present invention is to solve the above-mentioned problems and to provide a liquid crystal display using a non-linear driving element capable of forming a non-linear driving element having a good leak current characteristic in a low voltage region and a high driving ability. It is to provide a configuration of the device.

[0011]

In order to achieve the above object, a liquid crystal display device using a non-linear driving element of the present invention adopts the structure described below.

A liquid crystal display device using a non-linear driving element according to the present invention is an active matrix type liquid crystal display device using a two-terminal type MIM diode having a lower metal / insulating film / upper metal structure as a non-linear driving element. Metal tantalum is used as the insulating film, tantalum oxide is used as the insulating film, and a transparent conductive film is used as the upper metal. Tantalum oxide as the insulating film is an oxide of the metal tantalum that is the lower metal. And the hydrogen atom concentration contained in is less than 1 atom%.

[0013]

In the physical vapor deposition method, the residual gas pressure is usually in the range of 10 ^-2 to 10 ^-5 Pa, and water is the main component.

Therefore, the metal tantalum film formed by the conventional method inevitably contains a considerable amount of water, although there are some differences depending on the film forming conditions and the atmosphere.

Among them, water contained in the film is desorbed from the film at a relatively low temperature of 200 ° C. or lower, as is known from the thermal desorption spectrum shown in FIG. On the other hand, hydrogen has a temperature of 400 degrees or more.

Since hydrogen is not contained in the metal tantalum film forming raw material, it is considered that the origin of this hydrogen is that the residual water taken in during the film formation becomes hydrogen by the decomposition reaction.

By removing hydrogen in the film and reducing the concentration of hydrogen atoms contained in metal tantalum and tantalum oxide to less than 1 atom%, the electrical characteristics of the non-linear element are improved and the driving capability is enhanced, resulting in higher It is possible to manufacture a liquid crystal display device having high quality display performance.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of a liquid crystal display device using a non-linear driving element in an embodiment of the present invention will be described below with reference to the drawings.

The structure of the non-linear driving element in the present invention is as follows.
As shown in FIG. 1, on a glass substrate 1, a metal tantalum / tantalum oxide / transparent conductive film structure is used in which metal tantalum is used as a lower metal 2, tantalum oxide is used as an insulating film 3, and a transparent conductive film is used as an upper metal 4. .

3 to 7 are sectional views showing a manufacturing method for forming the structure of the liquid crystal display device of the nonlinear liquid crystal display element of the present invention.

As shown in FIG. 3, metal tantalum 12 is formed on the glass substrate 1 by the DC sputtering method.
Ultra high-purity argon is used as the sputtering gas, and the substrate is heated at a temperature of 150 to relax the stress of the metal tantalum film.
A film is formed by heating to ~ 350 ° C. The film thickness of the metal tantalum film is 80 to 300 nm.

Subsequently, the metal tantalum 12 is vacuum fired using a vacuum heat treatment apparatus. The heating temperature of the glass substrate 1 is 425 ° C., and the heating time is 2 hours.

At this time, in order to sufficiently release hydrogen in the film and prevent the metal tantalum from being oxidized by oxygen and moisture contained in the atmosphere, the vacuum chamber is evacuated to 10 ^-4 Pa or less. The sputtering film forming apparatus may be used as it is as the vacuum heat treatment apparatus, and the heat treatment may be continuously performed after the film formation.

Next, as shown in FIG. 4, the metal tantalum 12 is patterned by a photolithography process and an etching process. The metal tantalum is etched by reactive ion etching using a mixed gas of argon, oxygen and CF4. It is possible to form a tantalum pattern with high uniformity within and between substrates by an end point detection method that monitors light emission from plasma.

After removing the resist film used for forming the pattern of the metal tantalum 12, as shown in FIG. 5, the surface of the patterned metal tantalum is oxidized by the anodic oxidation method to form the tantalum oxide 13.

Citric acid with a concentration of 0.01 to 1% is used as the chemical conversion solution, and the applied voltage is 20 to 100V. As a result, the film thickness of the obtained tantalum oxide 13 is 30 to 1
It is 50 nm.

A transparent conductive film 14 is formed on the entire surface of the anodized substrate as shown in FIG. A film is formed by a direct current reactive sputtering method targeting indium oxide containing tin oxide. The sputtering gas is a mixed gas of oxygen / argon. The thickness of the transparent conductive film 14 formed here is 80 to 3
00 nm.

Finally, as shown in FIG. 7, the transparent conductive film 14 is patterned by a photolithography process and an etching process. This forms the nonlinear element shown in the figure.

The etching of the transparent conductive film 14 is performed by a wet etching process using an etching solution containing potassium dichromate.

The voltage-current characteristic of the non-linear element is proportional to the area of the element. In order to realize high display quality without display unevenness in a liquid crystal display device, it is necessary to suppress variations in electric characteristics of drive elements, that is, variations in element area.

By optimizing the over-etching time according to the cross-sectional shape of the metal tantalum / tantalum oxide pattern of the nonlinear element portion 10 and the film thickness of the transparent conductive film,
It is possible to form a non-linear element with a small variation in element area.

The graph of FIG. 8 compares the current-voltage characteristics of the non-linear element, which is obtained by subjecting the metal tantalum to the heat treatment described above, and that which is not subjected to the heat treatment. As shown in the graph of FIG. 8, the heat treatment reduces the leakage current in the low voltage region.

When the leak current of the non-linear element is reduced in this manner, the write data retention characteristics are improved, the liquid crystal driving capability is increased, the contrast ratio is increased, and the display quality of the liquid crystal display device is improved.

The active type liquid crystal display device produced by using the non-linear element formed of metal tantalum heat-treated in vacuum by the manufacturing method shown in FIGS. 3 to 7 showed a large contrast ratio and high display quality.

Although the hydrogen atom concentration in the metal tantalum film changes depending on the heat treatment temperature and the heat treatment time, the current-voltage characteristics of the non-linear element hardly change when the hydrogen concentration is 1 atom% or more, and the leakage occurs when the hydrogen concentration is less than 1 atom%. The current decreases, and it becomes almost saturated from 0.1 atomic% to 0 atomic%.

A vacuum firing furnace is the most general method for heat-treating metal tantalum, but it is difficult to finely control the hydrogen atom concentration, and a flash lamp heating method is preferable for controlling the concentration.

[0037]

As is apparent from the above description, the non-linear liquid crystal display device including the metal tantalum and tantalum oxide having the features described in the present invention can reduce the leak current in the low voltage region. Is.

As a result, the driving capability of the liquid crystal can be improved as compared with the conventional non-linear element, and the liquid crystal display device using the non-linear element of the present invention exhibits higher display quality.

By adopting the manufacturing process of the continuous heat treatment after forming the metal tantalum film, it is possible to suppress the cost increase and manufacture a high quality active type liquid crystal display device at a low cost.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a non-linear display element according to an embodiment of the present invention and a conventional example.

FIG. 2 is a thermal desorption spectrum diagram showing hydrogen release from a metal tantalum film of a non-linear display element according to an example of the present invention.

FIG. 3 is a cross-sectional view showing the manufacturing method for forming the structure of the non-linear liquid crystal display element in the example of the present invention.

FIG. 4 is a cross-sectional view showing the manufacturing method for forming the structure of the non-linear liquid crystal display element in the example of the present invention.

FIG. 5 is a cross-sectional view showing the manufacturing method for forming the structure of the non-linear liquid crystal display element in the example of the present invention.

FIG. 6 is a cross-sectional view showing the manufacturing method for forming the structure of the nonlinear liquid crystal display element in the example of the present invention.

FIG. 7 is a cross-sectional view showing the manufacturing method for forming the structure of the nonlinear liquid crystal display element in the example of the present invention.

FIG. 8 is a graph showing electric characteristics of a non-linear liquid crystal display device according to an example of the present invention.

[Explanation of symbols]

 2 Lower metal 3 Insulating film 4 Upper metal 12 Metal tantalum 13 Tantalum oxide 14 Transparent conductive film

Claims (1)

[Claims] 1. An active matrix type liquid crystal display device using a two-terminal type MIM diode having a lower metal / insulating film / upper metal structure as a non-linear driving element, has a lower metal of tantalum, an insulating film of tantalum oxide, and an upper metal. The transparent conductive film is used for each, and tantalum oxide as an insulating film is an oxide of metal tantalum which is a lower metal,
A liquid crystal display device using a non-linear driving element, characterized in that the concentration of hydrogen atoms contained in tantalum oxide and tantalum oxide constituting the non-linear element is less than 1 atom%.