JPH05346593A - Liquid crystal display device and its production - Google Patents

Abstract

PURPOSE:To improve the display quality of the liquid crystal display device and to improve its reliability by decreasing the variations in the threshold voltage of a MIM element and current value at the time of writing. CONSTITUTION:The liquid crystal display device and the process for production of the device consist in providing an intermediate layer 17 consisting of a simple substance metal, such as indium, tantalum, chromium or titnium, or the alloy thereof on the rear surface of the pixel electrode layer of the MIM (metallic layer-insulator layer-metallic layer) element formed with a line electrode 13, an anodically oxidized layer 14 and the pixel electrode 15 consisting of the transparent electrode layer on a substrate 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a liquid crystal display device for controlling liquid crystal by controlling MIM (metal layer-insulator layer-metal layer) elements, which are nonlinear elements arranged in a matrix, and a structure thereof. And a manufacturing method for forming.

[0002]

2. Description of the Related Art M formed by using two photomasks
The one using the IM element as the switching element is 1
991, SID DIGEST, p219. The MIM element described in this document will be described with reference to the sectional view of FIG. 5 and the circuit diagram of FIG.

As shown in FIGS. 5 and 6, a row electrode 13 is formed on one substrate 12, a pixel electrode 15 is formed on an anodized layer 14, and a plurality of MIM elements 32 are arranged.
The scanning electrode 31 is formed on the other substrate, and the liquid crystal 33 is injected between the two substrates, so that the MIM element 3 serving as a switching element is formed.
2 is controlled to display an image.

A method of manufacturing the MIM element having the conventional structure is described below.
This will be described with reference to FIG.

A tantalum layer having a thickness of 200 nm is formed on a substrate 12 made of glass by a sputtering method, and a dry etching method is performed by using a first photoresist.
The tantalum layer is etched to form the row electrode 13.

After that, an anodic oxide layer 14 having a film thickness of 80 nm is formed on the surface of the row electrode 13 by an anodic oxidation method.

Further, a transparent electrode film made of, for example, indium tin oxide having a film thickness of 50 nm is formed by a sputtering method.
After that, the transparent conductive film is etched using the second photoresist to form the pixel electrode 15.

In this way, the MIM element is formed by the two photomasks. After that, heat treatment is performed in a nitrogen atmosphere to stabilize the device characteristics, and M
Form an IM device.

[0009]

However, the element characteristics of the above-described conventional MIM structure largely depend on the conditions for forming the transparent electrode film to be the pixel electrode 15 and the subsequent heat treatment conditions, and the threshold voltage of the MIM element is The variation becomes large. This variation in the threshold voltage causes problems such as display unevenness, deterioration of display quality, and shortened operating life of the MIM element.

With respect to the conditions for forming the transparent electrode film, for example, the voltage value when the on-state current value of the MIM element is 10 ⁻⁸ A when the amount of oxygen introduced into the sputtering apparatus is changed by 3% to 15%. Fig. 7 shows the variation of a certain threshold voltage.
Shown in.

In the graph of FIG. 7, the horizontal axis represents the amount of oxygen introduced into the sputtering apparatus when forming the transparent electrode layer, and the vertical axis represents the variation in the threshold voltage of the MIM element. A solid line 51 in FIG. 7 shows the maximum value of the threshold voltage,
The broken line 52 shows the minimum value of the threshold voltage. For the sputtering at this time, an indium oxide target containing 8% tin oxide was used.

As shown by the solid line 51 and the broken line 52 in FIG. 7, it can be seen that the variation of the threshold voltage sharply increases when the amount of oxygen introduced exceeds 5%.

Further, in the above-mentioned heat treatment in the nitrogen atmosphere, if the heat treatment is carried out in an atmosphere in which the residual oxygen concentration in the heat treatment apparatus exceeds 500 ppm, the threshold voltage varies as in the data shown in FIG. Was revealed by the experiment.

These causes are caused by the anodized layer 1 shown in FIG.
It is considered that this is because oxygen diffuses from the outside to the interface between the pixel electrode 15 and the pixel electrode 15 or the interface between the row electrode 13 and the anodized layer 14 to form an electrical barrier layer at these interfaces.

The object of the present invention is to solve the above problems by
An object of the present invention is to provide a configuration of a liquid crystal display device capable of suppressing variations in threshold voltage of IM elements and a manufacturing method thereof.

[0016]

In order to achieve the above object, the present invention employs the following MIM element structure and its manufacturing method.

The MIM element structure of the present invention comprises a lower electrode layer, an insulator layer and a transparent electrode layer formed on a substrate.
In a liquid crystal display device using an element, an intermediate metal layer is provided between the insulating layer and the transparent electrode layer.

According to the method of manufacturing an MIM element of the present invention, a lower electrode layer is formed on the entire surface of a substrate, a first photoresist is formed on the lower electrode layer, and the lower electrode is used as a mask. Patterning to form row electrodes, and
The step of removing the photoresist, the step of forming the anodized layer by anodizing the surface of the row electrode, the intermediate metal layer and the transparent electrode layer are sequentially formed on the entire surface to form the second photoresist. Etching the transparent electrode and the intermediate metal layer using the second photoresist as a mask to form a pixel electrode, and removing the second photoresist.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing the structure of the liquid crystal display device of the present invention and the manufacturing process thereof, and FIG. 2 is a plan view showing the liquid crystal display device of the present invention. First, the MIM of the liquid crystal display device of the present invention
The element structure will be described with reference to FIG.

The MIM element structure in the present invention is shown in FIG.
As shown in (d), a row electrode 13, an anodized layer 14, and a pixel electrode 15 are sequentially provided on a substrate 12, and an intermediate metal having a role of an oxygen diffusion barrier layer is formed under the pixel electrode 15 formed of a transparent electrode layer. The layer 17 is provided.

The intermediate metal layer 17 having the role of the oxygen diffusion barrier layer of the present invention is made of a metal having a high chemical activity, such as indium, tantalum, chromium or titanium. By providing this intermediate metal layer 17, the oxygen from the outside is trapped by the intermediate metal layer 17, and the variation of the threshold voltage due to the influence of oxygen can be reduced.

Next, a method for manufacturing the liquid crystal display device of the present invention will be described.
This will be described with reference to FIGS. 1 (a) to 1 (d) and FIG.

First, as shown in FIG. 1A, a tantalum film having a thickness of 200 nm is formed as a lower electrode layer on a substrate 12 made of glass by a sputtering method.

After that, a photoresist is formed on the entire surface by a coating method, exposed and developed using a first photomask, and the photoresist is patterned to form a first photoresist 21.

Then, using the first photoresist 21 as an etching mask, the tantalum film is etched by a dry etching method to pattern the row electrodes 13. The plane pattern shape of the row electrode 13 is shown by the solid line 23 in FIG.

Then, the first used as an etching mask
The photoresist 21 is removed.

Next, as shown in FIG. 1 (b), the surface of the row electrode 13 was anodized in a 0.1% citric acid solution to obtain 80 n.
Tantalum oxide, which is the anodized layer 14 having a thickness of m, is formed.

Next, as shown in FIG. 1 (c), 100% argon gas was introduced into the sputtering chamber at 100 cc / min, and indium as the intermediate metal layer 17 was removed by a sputtering method in which the sputtering pressure was controlled to 1 mTorr.
It is formed on the entire surface with a film thickness of 5 to 10 nm, and the pixel electrode 1
As a fifth material, a transparent electrode layer made of indium tin oxide is continuously formed with a film thickness of 50 nm.

After that, a photoresist is formed on the entire surface by a coating method, exposed and developed using a second photomask, and the photoresist is patterned to form a second photoresist 22.

As the intermediate electrode layer 17, in addition to indium, tantalum, chromium, titanium, or an alloy containing these materials as a main component can be applied.

After that, the transparent electrode layer and the intermediate metal layer 17 are etched by dry etching or wet etching using the second photoresist 22 as an etching mask to form the pixel electrode 15.

A plane pattern shape of the pixel electrode 15 and the intermediate metal layer 17 is shown by a chain line 25 in FIG.

After that, the second photoresist 22 is removed. After that, heat treatment is performed in a nitrogen atmosphere at a temperature of 350 ° C. for 1 hour to stabilize the MIM element characteristics. In this way, the MIM element is formed by the two photomasks.

A sectional view of FIG. 4 shows a liquid crystal display device according to another embodiment of the present invention.

The difference between the structure shown in FIG. 4 and the structure shown in FIG. 1D lies in the pattern shape of the intermediate metal layer 17. That is, in the first embodiment shown in FIG. 1D, the intermediate metal layer 17 has the same pattern shape as the pixel electrode 15, but in the second embodiment shown in FIG. It has the same pattern shape.

FIG. 3 shows the relationship between the amount of oxygen introduced and the variation in the threshold voltage of the MIM element when the pixel electrode 15 which is the transparent electrode layer of the MIM element formed by the manufacturing method of the present invention is formed.
Is shown in the graph.

The horizontal axis of the graph of FIG. 3 represents the amount of oxygen introduced into the sputtering apparatus when the transparent electrode layer is formed, and the vertical axis represents the variation of the threshold voltage of the MIM element. Furthermore, the solid line 53 in the graph of FIG.
4 indicates the minimum value of the threshold voltage.

As is clear from the graph of FIG. 3, the variation in the threshold voltage of the MIM element of the present invention is smaller than that of the conventional one.

This is because, in the MIM element of the present invention, by providing the intermediate metal layer 17, the oxygen from the external atmosphere is trapped by the intermediate metal layer 17 and the diffusion of oxygen into the anodized layer 14 is prevented. The variation in threshold voltage is small.

The MIM element structure of the present invention is not easily affected by the oxygen partial pressure when the pixel electrode 15 made of the transparent electrode layer is formed, and the variation in the threshold voltage of the MIM element is reduced even if the amount of oxygen introduced increases. , Margin of MIM element manufacturing conditions,
That is, the process window can be widened. Further, it also has an effect of reducing variations in current value at the time of writing.

[0041]

As is apparent from the above description, in the liquid crystal display device of the present invention, by forming an intermediate metal layer between the anodized layer and the transparent electrode layer, the threshold voltage of the MIM element is increased. Variation and current value variation during writing are reduced. Further, it becomes possible to significantly widen the process window of the transparent electrode layer forming condition and the heat treatment condition, the display quality of the liquid crystal display device is improved, and the reliability is improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structure of a liquid crystal display device and a manufacturing method thereof according to an embodiment of the present invention.

FIG. 2 is a plan view showing a liquid crystal display device in an example of the present invention.

FIG. 3 is a graph showing the relationship between the amount of oxygen introduced and the variation in threshold voltage when manufacturing an MIM element in an example of the present invention.

FIG. 4 is a sectional view showing a liquid crystal display device according to another embodiment of the present invention.

FIG. 5 is a cross-sectional view showing an MIM element in a conventional liquid crystal display device.

FIG. 6 is a circuit diagram showing an equivalent circuit of a liquid crystal display device using MIM elements.

FIG. 7 is a graph showing the relationship between the amount of oxygen introduced and variation in threshold voltage when manufacturing a conventional MIM element.

[Explanation of symbols]

 12 Substrate 14 Anodized Layer 15 Pixel Electrode 17 Intermediate Metal Layer

Claims (3)

[Claims] 1. A metal layer formed by forming a lower electrode layer, an insulator layer, and a transparent electrode layer on a substrate-insulator layer-insulator layer of a liquid crystal display device using a MIM element having a metal structure and transparent. A liquid crystal display device comprising an intermediate metal layer provided between the electrode layer and the electrode layer. 2. The liquid crystal display device according to claim 1, wherein the intermediate electrode layer is formed of a single metal made of indium, tantalum, chromium, or titanium, or an alloy containing these substances as a main component. .. 3. A row electrode in which a lower electrode layer is formed on the entire surface of a substrate, a first photoresist is formed on the lower electrode layer, and the lower electrode layer is patterned using the first photoresist as a mask. And removing the first photoresist, a step of anodizing the surface of the row electrode to form an anodized film, an intermediate metal layer and a transparent electrode layer are sequentially formed on the entire surface, and Forming a photoresist, forming a pixel electrode by etching the transparent electrode layer and the intermediate metal layer using the second photoresist as a mask, and removing the second photoresist. Method for manufacturing liquid crystal display device.