JPH09218429A - Active matrix substrate, its production and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid crystal display panel without burning in which an active matrix substrate with an MIM nonlinear elements is used, by electrically connecting a wiring film and the MIM nonlinear element with the same material as used for pixel electrodes. SOLUTION: A wiring film and an MIM nonlinear element are electrically connected with the same material as used for pixel electrodes, and moreover, the structure of the contact film from the wiring film to the pixel electrodes is made symmetric. For example, the MIM nonlinear element is formed to have a back-to-back structure of two elements connected in series with the opposite polarities to each other. In this MIM nonlinear optical element, a metal film 12 consists of a metal film which can be anodically oxidized such as tantalum, aluminum, titanium or an alloy film of these, and is formed as a part of the wiring film and the first metal film of the MIM nonlinear element. The second metal film 14 of the MIM nonlinear element consists of chromium, titanium, tantalum or an alloy of these. The ITO film 15 is formed as a part of the pixel electrode and the wiring film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix substrate, a method of manufacturing the same, and a liquid crystal display device.

[0002]

2. Description of the Related Art In an active matrix type liquid crystal display device, a liquid crystal is provided between a substrate on one side on which a non-linear element is provided in each pixel region to form a matrix array and a substrate on the other side on which color filters are formed. After filling, the alignment state of the liquid crystal in each pixel area is controlled to display predetermined information. As a non-linear element, a three-terminal element such as a thin film transistor or two such as a MIM type non-linear element
Although terminal elements are used, MIM is required to meet the demands for larger screens and lower costs for liquid crystal display elements.
The method using the non-linear element is advantageous because the manufacturing process is short. Moreover, when the MIM type non-linear element is used, the scanning line can be provided on the substrate on one side where the matrix array is formed and the signal line can be provided on the substrate on the other side. There is also an advantage that a crossover short circuit between the scanning line and the signal line, which is the cause, does not occur. On the other hand, the thin film transistor has advantages such as excellent image quality because it has excellent writing characteristics and holding characteristics, and enables high density of pixels.

In an active matrix type liquid crystal display panel using MIM type non-linear elements, as shown in FIG. 7 which is an equivalent circuit of the liquid crystal display panel, each pixel region 3
The MIM type non-linear element 1 (indicated by a varistor symbol in the drawing) and the liquid crystal display element 2 (indicated by a capacitor symbol in the drawing) are connected in series between each scanning line 71 and each signal line 72. The liquid crystal display element 2 is switched between a display state and a non-display state or an intermediate state thereof based on a signal applied to the scanning line 71 and the signal line 72 to control the display operation.

As shown in FIG. 8A, in the MIM type non-linear element 1, a voltage VNL applied to the first metal film and the second metal film of the MIM type non-linear element and between the above two metal films. Has a non-linear relationship with the current INL flowing through the.
Assuming that the threshold voltage of the MIM type nonlinear element 1 is Vth, the threshold voltage of the liquid crystal display element 2 is Vb, and the potential in the display state is (Vb + ΔV), as shown in FIG. Then, by setting the potential difference V (applied voltage to the unit pixel) between the scanning line 71 and the signal line 72 in the predetermined pixel region 3 to (Vb + Vth), the liquid crystal display element 2
Can be hidden, and the scanning line 71 and the signal line 72
By setting the potential difference V between and to (Vb + Vth + ΔV), the liquid crystal display element 2 can be brought into a display state. On the other hand, the potential V applied to the unit pixel in the non-selection period
Is set to be substantially close to the potential remaining on the liquid crystal display element 2 and the difference is equal to or less than the threshold voltage Vth of the MIM type non-linear element, the MIM type non-linear element 1 is always in the non-selection period. The cutoff state is maintained, and the state set in the selection period is maintained as it is.

The above is an ideal M in which the capacitance of the MIM type non-linear element is sufficiently small, the non-linearity of the voltage-current characteristic is sufficiently high, and the current value flowing in the direction of voltage application is the same.
This is the most basic operation example in the case where the IM type nonlinear element 1 can be obtained and the resistance of the wiring that gives a signal to the MIM type nonlinear element can be made sufficiently low.

FIG. 6 (a) which is a plan view of a MIM type non-linear element and FIG. 6 (b) which is a cross-sectional view of AA 'have a general structure as described in JP-A-52-149090. I will describe using. The MIM type non-linear element 1 includes a transparent substrate 61.
A first metal film 62 which is formed on the front surface side of Ta and is conductively connected to the scanning circuit side through the scanning line 71 and has Ta atoms as a main component.
A metal oxide film 63, which is an insulating film on the surface side thereof, and a second metal film 64 made of Cr, which is formed on the surface side thereof and electrically conductively connects to the pixel electrode 65. The metal oxide film 63 is formed on the surface of the Ta film so that the first metal film 6 has a uniform film thickness and is formed without pinholes.
2 is formed by anodic oxidation.

[0007]

However, in the liquid crystal display panel using the conventional MIM type non-linear element 1, the same picture is displayed for several hours, and then the entire surface of the panel is displayed in the same color. There was a problem that the picture looked thin. Hereinafter, this phenomenon will be referred to as burn-in.

As a means for solving this problem, Japanese Patent Laid-Open No. 196588/1982 discloses a method of depositing an oxide film of a MIM type non-linear element by oxygen plasma treatment while keeping it at 300 ° C. or higher. . This method is not so preferable because the uniformity of the film thickness within the substrate cannot be obtained. Japanese Unexamined Patent Publication No. 63-48528 discloses a method of forming the second metal film after removing the upper layer portion of the anodic oxide film, but it is difficult to uniformly remove the oxide film within the substrate. However, the removal of these oxide films requires dry etching, which damages the glass substrate and is not a preferable technique.

Further, as shown in Japanese Patent Laid-Open No. 58-34428, there is shown a method of arranging the structures of MIM type non-linear elements in series so that the polarities are opposite to each other. Since the contact resistance between the pixel electrode film and the pixel electrode film has a polarity difference in that the value of the current that flows depends on the direction in which the voltage is applied, the burn-in phenomenon inevitably remains.

It is an object of the present invention to provide a non-burn-in liquid crystal display panel using an active matrix substrate using MIM type non-linear elements.

Another object of the present invention is to provide an MIM type non-linear element in which the value of current flowing is the same depending on the direction of voltage application.

[0012]

An active matrix substrate of the present invention is an MIM type non-linear element having a first metal film, an insulating film formed of an anodized film of the first metal film, and a second metal film structure. In the active matrix substrate used, the conductive connection between the wiring film and the MIM type nonlinear element is made through the same material as the pixel electrode.

Further, the active matrix substrate of the present invention is an active matrix using an MIM type non-linear element having a first metal film-an insulating film formed of an anodized film of the first metal film-a second metal film structure. In the substrate, the structure of the contact film from the wiring film to the pixel electrode is symmetrical.

Furthermore, the active matrix substrate of the present invention is the same as the active matrix substrate described above, in which M
The IM type non-linear element is characterized by having a back-to-back structure in which the polarities are reversed and the polarities are connected in series.

Further, in the active matrix substrate of the present invention, in these active matrix substrates, the area for making conductive connection with the pixel electrode and the first or second metal film is S1, and the wiring film made of the same material as the pixel electrode is used. And the first
Alternatively, if S2 is an area for making a conductive connection with the second metal film, the relationship of 0.4S1 ≧ S2 ≧ 2.5S1 is satisfied.

Further, the active matrix substrate of the present invention is the same as the active matrix substrate according to the above-mentioned S.
The areas of 1 and S2 are three times or more the area of the MIM type non-linear element.

A method of manufacturing an active matrix substrate according to the present invention is the method of manufacturing an active matrix substrate according to claim 3, wherein a) a step of forming a first metal film, and b) a first metal. A step of depositing an anodic oxide film on the film, c) a step of processing the first metal film into an island shape, d) a step of forming a second metal film, and e) a pixel electrode and a wiring film and an element. And the step of simultaneously forming the connection film of.

Further, the liquid crystal display device of the present invention comprises:
The active matrix substrate according to claim 5 is used.

Further, the liquid crystal display device of the present invention is characterized in that a liquid crystal display panel manufactured by the method for manufacturing an active matrix substrate according to claim 6 is manufactured.

[0020]

As a cause of burn-in of the liquid crystal display panel using the MIM type non-linear element as the switching element, the applicant investigated the voltage-current characteristics of the MIM type non-linear element and found that there were two factors.

One is that it is related to that the current increases with the application time when the voltage is continuously applied between the first metal layer and the second metal layer of the MIM type nonlinear element. did. In other words, the voltage-current characteristics of the MIM type non-linear element differ between the part that has been displayed on the liquid crystal display panel for a long time (1 hour or more) and the part that has not been displayed, and even if the same color is output, the contrast is different and it is recognized as burn-in. It will be.

The other is that even if a plus and minus same voltage is applied to the MIM type non-linear element as a drive waveform, the current value flowing in the MIM type non-linear element differs depending on the polarity, so that it is applied to the liquid crystal depending on the polarity. It was confirmed that the applied voltage was different and the DC component was constantly applied to the liquid crystal to cause deterioration, and the liquid crystal display panel recognized it as burn-in. Conventionally, it was considered that a direct current component would not be applied to the liquid crystal if the polarity difference of the MIM type non-linear element itself was eliminated. However, even if the polarity difference of the MIM type non-linear element is eliminated, a polarity difference occurs in the contact resistance between the second metal film and the pixel electrode such as the ITO film, so that it is found that a DC component is applied to the liquid crystal. It was

In the present invention, the second factor is to prevent burn-in which occurs when a DC component is applied to the liquid crystal.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments.

1 and 2 are top views of an active matrix substrate using the MIM type nonlinear element of the present invention. FIG. 1 shows a back-to-back structure in which two MIM type non-linear elements are connected in series so that their polarities are opposite to each other. FIG. 2 shows one MIM type non-linear element.

The configuration of FIGS. 1 and 2 will be described. 12 is
It is made of anodizable metal film of tantalum, aluminum, titanium, tungsten, rhenium, niobium, vanadium or the like, or an alloy film thereof, and is a part of the wiring film or the first metal film of the MIM type non-linear element. 14 is MIM
Is a second metal film of the non-linear element, which is made of a metal such as chromium, titanium, tantalum, aluminum, molybdenum, or an alloy film thereof, and 15 is an ITO film which is a part of the pixel electrode and the wiring film, The line width of the ITO film is preferably thicker than that of the metal film forming 12 in order to reduce pixel defects due to disconnection. Further, when it is desired to reduce the resistance of the wiring film, the film used for the second metal film 14 may be formed on the wiring film.

Although the pixel electrode is an ITO film here,
This is a case of considering a transmissive liquid crystal display panel, and in the case of a reflective pixel electrode also serving as a reflector, a metal film such as aluminum or magnesium may be used. In the following description, assuming that a transmissive liquid crystal display panel is used, the pixel electrode is ITO.
Think of it as a film. Further, even in the case of the transmissive type, the pixel electrode may use not only the ITO film but also another transparent conductive film.

In FIG. 1, the area of the contact portion between the second metal film 14 and the pixel electrode 15 is S1, and the area of the contact portion between the wiring film and the second metal film 14 is S2. In FIG. 2, when the current flow path is the wiring film, the first metal film, the anodic oxide film, the second metal film, and the pixel electrode as shown in FIG. Metal film 14 and pixel electrode 1
The area of the contact portion with 5 is S1, and the area of the contact portion between the wiring film and the first metal film 12 is S2. In addition, FIG.
When the current flow path is such as the wiring film, the second metal film, the anodic oxide film, the first metal film, and the pixel electrode, the first metal film 12 and the pixel electrode 15 The area of the contact portion is S1, and the area of the contact portion between the wiring film and the second metal film 14 is S2.

FIG. 4 shows a sectional view of the element structure when the MIM type nonlinear element has a back-to-back structure as shown in FIG. FIG. 4 is a sectional view taken along the line AA ′ of FIG. 4A shows the length of the area S1 of the contact portion between the second metal film and the pixel electrode along the line AA ′, and similarly b shows the length of S2.

[Embodiment 1] First, the reason why the wiring film and the MIM type non-linear element should be connected through the same material as the pixel electrode will be described.

FIG. 9 shows an equivalent circuit diagram of one pixel.
(A) is a figure regarding this invention, (b) is a conventional figure. 91 is a scanning line and 92 is a signal line. Now, when a direct current is applied to the liquid crystal, the liquid crystal display panel causes image sticking due to deterioration of the liquid crystal. The DC component at this time is MI
This is caused when the selection pulse is applied to the M-type non-linear element, the voltage required to flow a predetermined current varies depending on the voltage application direction. The predetermined current varies depending on the displayed color, but if the cell gap of the liquid crystal is 5 μm in a 100 μm square pixel, 1 × 10 ^{−8 A} to 1 × 10
^-7 A. Further, generally, when a predetermined current is passed through the MIM type non-linear element, the required voltage varies depending on the direction of the current flow. The voltage difference at this time is defined as the polarity difference. If the polarity difference when the above-mentioned predetermined current is passed is eliminated, even if there is a voltage difference when the current in the liquid crystal holding state is passed through the MIM type non-linear element, it will almost affect the image quality of the liquid crystal display panel. Don't give.

The relationship between the polarity difference of the MIM type non-linear element and the burn-in of the liquid crystal display panel using the element is as shown in FIG. The horizontal axis is the polarity difference and the vertical axis is an arbitrary unit indicating the amount of image sticking. There is a visual result by the human eye that the polarity difference needs to be 0.1 V or less in order to recognize the burn-in. It only needs to be within the range of the arrow in FIG. When the polarity difference is around 0.1 V, the image sticking amount changes with a slight change in the polarity difference, so it is desirable to reduce the polarity difference as much as possible.

To eliminate the polarity difference of the MIM type non-linear element, the anodizing chemical solution is adjusted, the polarities of the element structure are reversed, and the elements are connected in series, or the first metal film and the second metal film are connected. It is possible if the material of the film is the same. However,
As shown in FIG. 9B, in the conventional method, a polarity difference occurs in the current flowing between the metal film and the ITO film forming the pixel electrode, so that even if the polarity difference of the MIM type nonlinear element is eliminated, A direct current component was applied to the liquid crystal. Metal film and ITO
When a current flows from the ITO film to the metal film, the resistance value of the film will be ² to 10 MΩ depending on the contact situation and the kind of metal, if the contact area is 200 μm ² , but it changes from the metal film to the ITO film. When a current flows, it is below 1 MΩ. For example, when a current of 1 × 10 ⁻⁷ A necessary for writing a pixel flows in one pixel, the resistance of the MIM type non-linear element is about 100 MΩ, and the polarity difference of the contact resistance between the metal film and the ITO film is maximum. When it becomes 10 MΩ, a maximum DC component of about 0.3 V is applied to the liquid crystal. When such a DC component is applied to the liquid crystal, it is easy to recognize the burn-in of the liquid crystal display panel, as can be seen from FIG.

Therefore, as shown in FIG. 9 (a), the contact resistance between the metal film and the ITO film is set between the wiring film and the MIM type non-linear element so that the contact portion between the second metal film and the ITO film has a polarity. If you put it in the opposite way, the polarity difference of the element part will be eliminated,
The direct current component is not applied to the liquid crystal, and the burn-in of the liquid crystal display panel is eliminated. At this time, the area of S1 and S2 at the contact portion between the metal film and the ITO film shown in FIGS. By doing so, the difference in polarity from the wiring film to the pixel electrode is within 0.1 V at maximum, and the liquid crystal display panel does not burn. Ideally, the areas of S1 and S2 should be equal. Since the width of the second metal film is constant in the direction perpendicular to the alternate long and short dash line AA ′ in FIG. 1 when controlling the area of S1 and S2, the length in the AA ′ direction, that is, the lengths of a and b in FIG. It should be equal. Therefore, if the area of S1 and S2 is set to be three times or more the area of the MIM type non-linear element (the size of one element in the case of the back-to-back structure), it shifts in the AA 'direction by the size of the element size. Also, the area ratio between S1 and S2 is 2.5.
It will be less than double. In addition, considering the margin of the manufacturing process,
The area of S1 and S2 is 1 of the area of the MIM type non-linear element.
It is better to make it 0 times or more. [Embodiment 2] A method of manufacturing an active matrix substrate when the MIM type non-linear element has a back-to-back structure will be described with reference to FIG.

As shown in FIG. 5A, after processing the first metal film 12 into a predetermined shape, a metal oxide film 13 for the first metal film 12 is deposited by an anodic oxidation method. After that, as shown in FIG. 5B, the second metal film 14 is processed into a predetermined shape. At this time, the second metal film 14 may be processed so as to be a wiring film so that the film is left in the wiring film portion of the metal film 12. Next, as shown in FIG. 5C, the first metal film 12 is separated into a portion where an element is formed and a portion where a wiring film is formed. Finally, the IT that forms the pixel electrode and the wiring film
The O film 15 is deposited. For example, when the second metal film 14 is used as the wiring film, the ITO film having high resistance may not be used as the wiring film. That is, even if the ITO film is used as the wiring film, the wiring resistance hardly changes. that way,
The area of the ITO film of the pixel electrode can be increased, which leads to improvement of the aperture ratio of the liquid crystal display panel. At this time, I
The contact area between the ITO film and the second metal film that can be the wiring film needs to be considerably larger than the contact area S1 between the TO film 15 and the second metal film 14. At a minimum, in order to prevent the polarity difference from becoming a problem, it is necessary to make it 10 times or more, preferably 20 times or more of S1. The equivalent circuit corresponding to one pixel at this time is shown in FIG.
It is like (a). Further, the MIM type non-linear element also has a symmetrical shape and no polarity difference occurs.

This method has the same manufacturing process as the case where the same material as the pixel electrode is not interposed between the conventional wiring film and the MIM type non-linear element as shown in FIG. 3, and the manufacturing cost does not change and the display quality is improved. Can be improved.

[Third Embodiment] As shown in the second embodiment, the MIM
If the structure of the non-linear element is a back-to-back structure, the contact film from the wiring film to the pixel electrode as described in claim 2 has an ITO film-second metal film-metal oxide film-first metal film. -Metal oxide film-Second metal film-ITO film, which has a symmetrical film structure around the first metal film. Another one
As one method, the materials of the first metal film and the second metal film may be the same. By doing so, the current values that flow are equal regardless of the voltage application direction, and no polarity difference occurs. Further, according to this structure, even if the voltage-current characteristics of the element and the resistances of the contact portions S1 and S2 vary within the same liquid crystal display panel, the variation is self-compensated, so that there is no difference in polarity. Variations within the panel are eliminated.

There is also a method of making the second metal film and the ITO film which is the pixel electrode the same, but if the structure of the MIM type non-linear element becomes the structure of the first metal film-metal oxide film-ITO film. Unless the metal content of the ITO film is increased to reduce the transmittance, the current value changes greatly when a voltage is applied, and this phenomenon causes image sticking of the liquid crystal display panel. In addition, if the fluctuation of the current value during voltage application is suppressed, the ITO
The amount of metal components in the inside increases and the transmittance decreases, resulting in a dark liquid crystal display panel, and the advantage of being bright is lost. Therefore, this method is not preferable because it deteriorates the display quality of the liquid crystal display panel in any case.

[Embodiment 4] As a method of conducting the conductive connection between the wiring film and the MIM type non-linear element through the same material as the pixel electrode, the structure of the MIM type non-linear element has a back-to-back structure as shown in FIG. There are the following differences between the method of forming the structure and the cross-type structure as shown in FIG. 2 (including the case where the first metal film and the second metal film are made of the same material).

In the cross type structure, as compared with the method of manufacturing the back toe back structure shown in FIG.
(B) In either structure, when the contact portion between the first metal film 102 and the pixel electrode 105 is formed, the metal oxide film 10 is formed.
3 needs to be removed, which increases the number of steps by one. However, since the area of the MIM type non-linear element is smaller than that of the back-to-back structure, the aperture ratio of the active matrix substrate can be increased, which is suitable for a bright liquid crystal display panel.

[Embodiment 5] As described above, if the direct current component is not applied to the liquid crystal through the MIM type non-linear element, not only the burn-in is reduced but also the flicker which makes the screen rough is suppressed. The LCD panel is easy to see.

[0042]

[0043]

As described above, since the conductive connection between the wiring film and the MIM type non-linear element is made through the same material as the pixel electrode, the direct current component is not applied to the liquid crystal and the burn-in does not occur. A liquid crystal display panel can be provided without increasing the number of manufacturing processes.

Further, by making the structure of the contact film from the wiring film to the pixel electrode symmetrical, the MI in the same liquid crystal display panel can be improved.
Since the polarity difference of the M-type non-linear element can be always zero, a liquid crystal display panel with high yield can be provided.

[0045]

[Brief description of drawings]

FIG. 1 is a plan view of a MIM type non-linear element of the present invention.

FIG. 2 is a plan view of a MIM type non-linear element of the present plane.

FIG. 3 is a plan view of a conventional MIM type nonlinear element.

FIG. 4 is a sectional view of the MIM type non-linear element of the present invention.

FIG. 5 is a cross-sectional view showing a manufacturing process of the MIM type nonlinear element of the present invention.

6A and 6B are a plan view and a cross-sectional view of a conventional MIM type nonlinear element.

FIG. 7 is an equivalent circuit diagram of an active matrix liquid crystal display device.

8A is a diagram showing a relationship between an applied voltage and a current value of a conventional MIM type non-linear element. FIG. FIG. 5B is a diagram showing the relationship between the voltage applied to the unit pixel of the liquid crystal display element and the brightness. FIG. 6B is a diagram showing the formation temperature of the anodic oxide film and the ratio of the oxide film thickness of the anion species contained in the oxide film.

9A is an equivalent circuit diagram of one pixel of the present invention. FIG. Figure b
The equivalent circuit diagram of the conventional one pixel.

FIG. 10 is a diagram showing the polarity difference of the MIM type nonlinear element and the burn-in of the liquid crystal display panel.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 MIM type non-linear element 2 Liquid crystal display element 3 Pixel region 10,60 Transparent substrate 11,61 TaOX film 12,62 First metal film 13,63 Metal oxide film 14,64 Second metal film 15,65 Pixel electrode 71 , 91 scanning lines 72, 92 signal lines

Claims (8)

[Claims] 1. An active matrix substrate using a MIM type non-linear element having a first metal film, an insulating film made of an anodized film of the first metal film, and a second metal film structure, wherein a wiring film and the MIM are provided. An active matrix substrate, characterized in that the conductive connection with the non-linear element is made through the same material as the pixel electrode. 2. An active matrix substrate using a MIM type non-linear element having a first metal film, an insulating film formed of an anodized film of the first metal film, and a second metal film structure, from a wiring film to a pixel electrode. The active matrix substrate is characterized in that the contact film has a symmetrical structure. 3. The active matrix substrate according to claim 1, wherein the MIM type non-linear element has a back-to-back structure in which polarities are opposite to each other and which are connected in series. . 4. The active matrix substrate according to claim 1, 2 or 3, wherein an area for conductively connecting the pixel electrode to the first or second metal film is S1, and a wiring film made of the same material as the pixel electrode. And the first
Alternatively, if an area for making conductive connection with the second metal film is S2, then the relationship of 0.4S1 ≧ S2 ≧ 2.5S1 is satisfied. 5. The active matrix substrate according to claim 4, wherein the areas of S1 and S2 are three times or more the area of the MIM type non-linear element. 6. The method for manufacturing an active matrix substrate according to claim 3, comprising: a) forming a first metal film, and b) depositing an anodic oxide film on the first metal film. , C) a step of processing the first metal film into an island shape, d) a step of forming a second metal film, and e) a step of simultaneously forming a connection film between a pixel electrode and a wiring film and an element. A method of manufacturing an active matrix substrate, comprising: 7. A liquid crystal display device using the active matrix substrate according to any one of claims 1 to 5. 8. A liquid crystal display device manufactured by the method for manufacturing an active matrix substrate according to claim 6.