JPH11233852A - Two-terminal type nonlinear element, manufacture thereof and liq. crystal display panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of eliminating the burning of a liq. crystal display panel by providing a method of reducing the voltage-current characteristic shift of a two-terminal type nonlinear element. SOLUTION: The two-terminal type nonlinear element comprises a first conductive film 22, oxide film 24 and second conductive film 26 laminated on a substrate 30. After forming the oxide film 24, and it is heat treated in a water vapor atmosphere at 220-300 deg.C to add water content to only the surface of the oxide film 24, thereby making the water content on the oxide film 24 surface more than that on the interface of the first conductive film 22 and oxide film 24. As the result, by the heat treatment of a second oxide film 24b, no water content passes, hence the film quality degradation can be avoided and the shift is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-terminal non-linear element serving as a switching element used in a liquid crystal display device or the like.

[0002]

2. Description of the Related Art In an active matrix type liquid crystal display device, a liquid crystal is filled between an active matrix substrate in which a non-linear element is provided for each pixel area to form a matrix array and a counter substrate in which a color filter is provided. ,
The predetermined state is displayed by controlling the alignment state of the liquid crystal in each pixel region. Generally, a three-terminal element such as a thin film transistor (TFT) or a two-terminal element such as a thin-film diode (TFD) is used as a switching element. However, a switching element using a two-terminal element has no crossover short circuit. It is excellent in that the manufacturing process can be shortened.

As a technique for reducing the characteristic fluctuation of a two-terminal nonlinear element, for example, an internationally published PCT / J
P94 / 00204 (International Publication Number WO94 / 1860)
0) has been proposed. In this technique, since the first conductive film of the two-terminal nonlinear element is changed to tantalum and is made of an alloy film of tantalum and a specific element such as tungsten, short-term temporal change and symmetry of voltage-current can be reduced. The improvement has made it impossible to recognize afterimages. However, even with this technique, there is a problem that burn-in occurs depending on the display pattern.

[0004] Here, "afterimage" is a phenomenon in which when a certain image is displayed for several minutes and then a different image is displayed, the previously displayed image is recognized. Further, "burn-in" means that when a certain pixel is displayed for several hours and then a different image is displayed, the previously displayed image is recognized.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a two-terminal type non-linear element having sufficiently small fluctuations in voltage-current characteristics, and a high quality liquid crystal display panel using the same. To provide.

Another object of the present invention is to provide a method for manufacturing a two-terminal nonlinear element having the above-mentioned excellent characteristics.

[0007]

A two-terminal nonlinear element according to the present invention includes a first conductive film, an oxide film, and a second conductive film laminated on a substrate, wherein the oxide film is a first conductive film. From the conductive film side, a first oxide film containing moisture, a second oxide film containing no moisture, and a third oxide film containing moisture, wherein the moisture content of the third oxide film is Is larger than the water content of the first oxide film.

[0008] In the two-terminal nonlinear element according to the present invention, the second conductive film is not limited to a metal but includes a transparent conductive film such as an ITO film.

In the present invention, since water is added only to the surface of the oxide film by the heat treatment, water and hydroxyl groups pass through the second oxide film so that the crystallinity does not fluctuate. Fluctuations in current characteristics are reduced.

The first conductive film is preferably made of tantalum or an alloy of tantalum. Further, the oxide film is
Preferably, the first conductive film is an anodic oxide film.

The method for manufacturing a two-terminal nonlinear element according to the present invention includes: (1) a step of forming a first conductive film on a substrate;
(2) forming an oxide film on the first conductive film;
(3) a step of heat-treating the substrate on which the first conductive film and the oxide film are formed at 220 to 300 ° C. in an atmosphere containing moisture; and (4) a second conductive film on the oxide film. And forming a.

According to this manufacturing method, the above-described two-terminal nonlinear element according to the present invention can be obtained by performing a simple heat treatment step.

In the above heat treatment, the concentration of water is preferably 0.001 mol% or more based on the whole processing gas.
More preferably, it is 0.014 to 2 mol%. The two-terminal nonlinear element thus manufactured has a configuration in which three oxide films having different conduction band energy levels are joined.

When the oxide film is formed by anodic oxidation of the first conductive film, a first oxide film containing water or a hydroxyl group is formed near an interface between the first conductive film and the oxide film. Is done. Further, by the heat treatment, a third oxide film is formed with the surface of the oxide film containing moisture or a hydroxyl group. At this time, if the heat treatment temperature is 300 ° C. or less, moisture or a hydroxyl group does not enter the first oxide film in the heat treatment step. That is, moisture and hydroxyl groups do not pass through the second oxide film in the heat treatment step.

Further, a liquid crystal display panel according to the present invention is characterized in that the above-described two-terminal type nonlinear element is provided as a switching element.

According to this liquid crystal display panel, high-quality images can be displayed since image sticking is unlikely to occur, and the liquid crystal display panel can be applied to a wide range of applications.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

(Two-Terminal Nonlinear Element and Liquid Crystal Display Panel) FIG. 1 is a plan view schematically showing one unit of a liquid crystal drive electrode using the two-terminal nonlinear element of the present invention.
FIG. 2 is a cross-sectional view schematically showing a portion along line AA ′ in FIG. 1.

The two-terminal nonlinear element 20 includes an insulating and transparent substrate, for example, a substrate (first substrate) 30 made of glass, plastic, or the like;
An insulating film 31 formed on the surface of the first conductive film 22, a first conductive film 22 made of tantalum or a tantalum alloy, and an oxide film 2 formed on the surface of the first conductive film 22 by anodic oxidation
4 and a second conductive film 26 formed on the surface of the oxide film 24. The first conductive film 22 of the two-terminal nonlinear element 20 is connected to the signal line (scanning line or data line) 12, and the second conductive film 26 is connected to the pixel electrode 3.
4 is connected.

The insulating film 31 is made of, for example, tantalum oxide. The insulating film 31 has a purpose of preventing separation of the first conductive film 22 due to heat treatment performed after the deposition of the oxide film 24 and preventing diffusion of impurities from the substrate 30 to the first conductive film 22. Since it is formed, it is not always necessary if these do not matter.

The first conductive film 22 may be tantalum alone or an alloy film containing tantalum as a main component and containing an element belonging to Group 6, 7, or 8 in the periodic table.
Preferable examples of the element added to the alloy include tungsten, chromium, molybdenum, rhenium, yttrium, lanthanum, and dysprosium. In particular, tungsten is preferable as the additive element, and its content is preferably, for example, 0.1 to 6 atomic%.

The oxide film 24 is preferably formed by anodic oxidation in a chemical conversion solution and then heat-treated at a temperature of 220 to 300 ° C. in an atmosphere containing moisture.

As described above, the first conductive film 22 and the oxide film 24
FIG. 7 shows a cross-sectional view of a film on which a heat treatment is performed at a temperature of 220 to 300 ° C. As shown in FIG. 7, the oxide film 24 is divided into three layers, and the first oxide film 24a is a layer formed by forming an anodic oxide film on a layer containing excess oxygen atoms and hydrogen atoms. The second oxide film 24b is an oxide film having a stoichiometric composition, and the third oxide film 2b
4c is a layer containing excess oxygen and hydrogen atoms.

A third oxide film is formed by performing a heat treatment in a steam atmosphere of 220 ° C. or higher, and an oxygen is passed through the second oxide film by performing a heat treatment in a steam atmosphere of 300 ° C. or lower. No atoms or hydrogen atoms are added to the first oxide film. This prevents atoms from moving in the second oxide film in the heat treatment, so that deterioration of the film quality can be prevented. As a result, even when an AC voltage is applied to the completed two-terminal nonlinear element, the fluctuation of the current value is reduced.

That is, the reason for performing the heat treatment at a temperature of 220 to 300 ° C. is to form the third oxide film 24 c by adding hydrogen atoms and oxygen atoms only to the surface layer of the oxide film 24.

Although the second conductive film 26 is not particularly limited,
Usually made of metal such as chrome or aluminum. The pixel electrode 34 is formed of a transparent conductive film such as an ITO film when used for a transmissive liquid crystal display panel, and has a reflectance of Al or Ag when used for a reflective liquid crystal display panel. It is composed of a large metal film.

Next, an example of a liquid crystal display panel using the two-terminal nonlinear element 20 will be described.

FIG. 3 shows an example of an equivalent circuit of an active matrix type liquid crystal display panel using a two-terminal nonlinear element 20. The liquid crystal display panel 10 includes a scanning signal driving circuit 100 and a data signal driving circuit 110.
The liquid crystal display panel 10 is provided with signal lines, that is, a plurality of scanning lines 12 and a plurality of data lines 14.
2 is driven by the scanning signal driving circuit 100, and the data lines 14 are driven by the data signal driving circuit 110. Then, in each pixel region 16, the two-terminal nonlinear element 20 and the liquid crystal display element (liquid crystal layer) 4 are provided between the scanning line 12 and the signal line 14.
0 are connected in series. In FIG. 3, the two-terminal nonlinear element 20 is connected to the scanning line 12 side and the liquid crystal display element 40 is connected to the data line 14 side. The liquid crystal display element 40 may be provided on the scanning line 12 side on the line 14 side.

FIG. 4 is a perspective view schematically showing an example of the structure of the liquid crystal display panel according to the present embodiment. The liquid crystal display panel 10 has two substrates, that is, a first substrate 3
0 and a second substrate 32 are provided facing each other, and liquid crystal is sealed between these substrates 30 and 32. First substrate 3
On 0, the insulating film 31 is formed as described above. On the surface of the insulating film 31, signal lines (scanning lines) 12
Are provided. Then, on the second substrate 32,
A plurality of data lines 14 are formed in a strip shape in a direction intersecting the scanning lines 12. Further, the pixel electrode 34 is connected to the scanning line 12 via the two-terminal nonlinear element 20.

Then, based on signals applied to the scanning lines 12 and the signal lines 14, the liquid crystal display element 40 is displayed,
The display operation is controlled by switching to a non-display state or an intermediate state. As a control method of the display operation, a generally used method can be applied.

FIGS. 5 and 6 are plan views schematically showing one unit of a liquid crystal drive electrode using a two-terminal type non-linear element. FIG. 6 is a view taken along a line BB 'in FIG. It is sectional drawing which shows typically.

The two-terminal type nonlinear element 40 has a
It is different from the above-described two-terminal type nonlinear element 20 in having a back-to-back structure. That is, the two-terminal nonlinear element 40 has a structure in which the first two-terminal nonlinear element 40a and the second two-terminal nonlinear element 40b are connected in series with opposite polarities.

More specifically, a substrate having insulating and transparent properties, for example, a substrate (first substrate) 30 made of glass, plastic or the like, an insulating film 31 formed on the surface of the substrate 30, a tantalum or A first conductive film 42 made of a tantalum alloy, an insulating film 44 formed on the surface of the first conductive film 42 by anodic oxidation, and two second conductive films formed on the surface of the insulating film 44 and separated from each other. Of the conductive films 46a and 46b. The second conductive film 46a of the first two-terminal nonlinear element 40a is connected to a signal line (scanning line or data line) 48,
The second conductive film 46b of the two-terminal non-linear element 40b is connected to the pixel electrode 45. The thickness of the insulating film 44 is set to be smaller than that of the insulating film 24 of the two-terminal nonlinear element 20 shown in FIGS. The specific characteristics and configuration of each component such as the first conductive film 42, the oxide film 44, and the second conductive films 46a and 46b are the same as those of the two-terminal nonlinear element 20 described above. Therefore, description is omitted. As described above, even if the thickness of the oxide film 44 becomes thin,
The structure in the oxide film is divided into three layers by a heat treatment in a steam atmosphere at 220 to 300 ° C. after the formation of 4.

(Manufacturing Process of Two-Terminal Nonlinear Element) Next, a method of manufacturing the two-terminal nonlinear element shown in FIG. 2 will be described.

The two-terminal type nonlinear element 20 is manufactured, for example, by the following process.

(A) First, an insulating film 31 made of tantalum oxide is formed on a substrate 30. The insulating film 31 can be formed by, for example, a method of thermally oxidizing a tantalum film deposited by a sputtering method, or a sputtering or co-sputtering method using a target made of tantalum oxide. The insulating film 31 is provided to improve the adhesion of the first conductive film 22 and to prevent diffusion of impurities from the substrate 30.
It is formed with a thickness of about 50 to 200 nm.

Next, a first conductive film 22 made of tantalum or a tantalum alloy is formed on the insulating film 31. A suitable value is selected for the thickness of the first conductive film depending on the use of the two-terminal nonlinear element, and is usually 100 to 500 nm.
Degree. The first conductive film can be formed by a sputtering method or an electron beam evaporation method. As a method for forming the first conductive film made of a tantalum alloy, a sputtering method using a mixed target, a co-sputtering method, an electron beam evaporation method, or the like can be used. As the element contained in the tantalum alloy, an element belonging to Groups 6, 7, and 8 in the periodic table, preferably, the above-mentioned elements such as tungsten, chromium, molybdenum, and rhenium can be selected.

The first conductive film 22 is patterned by commonly used photolithography and etching techniques. Then, the signal lines (scanning lines or data lines) 12 are formed in the same process as the formation process of the first conductive film 22.
Is formed.

(B) Next, the surface of the first conductive film 22 is oxidized using an anodic oxidation method to form an insulating film 24. At this time, the surface of the signal line 12 is simultaneously oxidized to form an insulating film. The preferred thickness of the insulating film 24 is selected depending on its use, and is, for example, about 20 to 70 nm.

The chemical conversion solution used for the anodic oxidation is not particularly limited. For example, a citric acid aqueous solution of 0.01 to 0.1% by weight can be used.

(C) Next, heat treatment is performed to introduce water into the oxide film 24 to divide the structure into three layers. This heat treatment is performed in a steam atmosphere at a constant temperature of 220 to 300 ° C., preferably 260 to 300 ° C. for 10 to 120 minutes, and then to 200 ° C. or lower in the same atmosphere for 5 to 300 minutes. The temperature is reduced over time. The water concentration in the steam atmosphere is preferably 0.001 mol% or more, more preferably 0.014 mol%, based on the entire processing gas.
~ 2 mol%. Further, after performing a heat treatment at 300 ° C. or more in an inert gas such as nitrogen or argon, in a temperature lowering process, when the temperature in the heat treatment furnace becomes 300 ° C. or less, a similar result is obtained even in a steam atmosphere. Can be

By performing heat treatment at a temperature of 220 ° C. or more, moisture is added to the oxide film 24 to form a third oxide film,
By setting the temperature to 300 ° C. or lower, water was not added to the first oxide film, and the current value fluctuation during voltage application was reduced. Further, by setting the heat treatment temperature to 260 ° C. or higher, the steepness of the voltage-current characteristics of the two-terminal nonlinear element was increased.

(D) Next, a metal film of chromium, aluminum, titanium, molybdenum, or the like is deposited by, for example, a sputtering method, so that the second conductive film 26 is formed.
Is formed. The second conductive film has a thickness of, for example, 50 to 30.
It is formed to a thickness of 0 nm and then patterned using commonly used photolithography and etching techniques. At this time, no matter what method is used to form the second conductive film, the secondary ion mass spectrum confirms that the oxide film 24 contains the elements constituting the second conductive film. Next, in the transmission type liquid crystal display panel, ITO is used.
In the reflection type liquid crystal display panel, an Al film is deposited to a thickness of 30 to 200 nm by a sputtering method or the like, and a pixel electrode 34 having a predetermined pattern is formed by using a commonly used photolithography and etching technique.

The above-described effect is the same in the cross-type two-terminal nonlinear element as shown in FIG. 1 and in the back-to-back type element as shown in FIG.

[0045]

The present invention will be described in more detail with reference to specific examples and comparative examples of the present invention.

(Embodiment 1) In this embodiment, the structure of the oxide film is divided into three layers, and the heat treatment at 220 to 300 ° C. in a steam atmosphere after the formation of the oxide film 24 is the third.
It was confirmed from the thermal desorption spectrum that water was only added to the oxide film of No. 1.

First, measurement by the thermal desorption spectrum (TDS) method will be described. This measurement was performed using a thermal desorption spectrum measuring apparatus 500 shown in FIG.

This thermal desorption spectrum measuring apparatus 500
The vacuum chamber 510 is provided with a quadrupole mass spectrometer 502 and an infrared heater 504. The sample is heated from the back side of the sample 520 by the infrared heater 504, and the sample 52 is heated.
The gas coming out from zero is measured by a quadrupole mass spectrometer 502 to obtain a thermal desorption spectrum. The temperature of the sample 520 was controlled using the thermocouple TC1 on the back surface side of the sample 520 due to the problem of controllability. In order to measure the surface temperature of the sample 520, a thermocouple T is also provided on the surface side of the sample 520.
C2 was provided. Since the substrates 522 and 532 used for the sample 520 had poor heat conduction and were as thick as 1.1 mm, a difference occurred between the temperatures of the thermocouples TC1 and TC2. However, the temperature in the actual two-terminal nonlinear element forming process is almost the same as the temperature in the thermocouple TC2. T
For the measurement of DS, quartz glass or a silicon wafer is used as a substrate. This is because the heat resistant temperature of the substrate was increased in order to perform measurement up to a high temperature of 1000 ° C.
It has been confirmed that the voltage-current characteristics of the two-terminal nonlinear element are the same even when the substrate is changed to ordinary alkali-free glass.

Two types of samples 520 were prepared in this embodiment. Each sample is described below.

(Sample 1) Sample 1 used for measurement is shown in FIG.
As shown in the figure, first, a quartz substrate 522 having a thickness of 1.1 mm
A 200 nm-thick tantalum film (containing 0.2 atomic% of tungsten) 524 is formed thereon by a sputtering method, and the tantalum pentoxide film 526 is formed to a thickness of 85 nm at 50 V by anodizing the tantalum film. After heat treatment at 320 ° C. in a nitrogen atmosphere,
After cooling to 1.0 ° C. in a moisture atmosphere at a rate of 1.0 ° C./min, the laminate was taken out of the heat treatment furnace to prepare Sample 1 for measuring thermal desorption spectrum.

(Sample 2) The sample 2 used for the measurement is shown in FIG.
0, a silicon wafer 5 having a thickness of 1.1 mm
32, a tantalum pentoxide film 536 is formed to a thickness of 85 nm by an RF sputtering method.
After heat treatment at 0 ° C., the sample was cooled to 180 ° C. at a rate of 1.0 ° C./min in a moisture atmosphere, and then the laminate was taken out of the heat treatment furnace and used as a sample for thermal desorption spectrum measurement.

Using these samples 1 and 2, the thermal desorption spectrum was measured. FIG. 11 shows the results of Sample 1 and FIG. 12 shows the results of Sample 2. 11 and 12, the horizontal axis indicates temperature and indicates the temperature of the thermocouple TC2 for measuring the surface temperature, and the vertical axis indicates the intensity of the measured value of the gas at (H ₂ O) corresponding to water.

In the spectrum shown in FIG. 11, three peaks P1 to P3 are obtained. When the surface temperature of the sample 1 is obtained, the thermocouple TC2 at the peaks P1 to P3
Were about 120, 220 and 410 ° C., respectively. Further, the manufacturing method of the tantalum pentoxide film 526 is changed to RF.
The same thermal desorption spectrum as that of FIG. 11 was obtained for a sample made to have the same structure except that the thickness was 85 nm by sputtering. In other words, the same spectrum can be obtained if the structure is the same even if the film manufacturing method is different.

In the spectrum shown in FIG. 12, two peaks P4 and P5 are obtained. When the surface temperature of the sample 2 was determined, the temperatures of the peaks P4 and P5 by the thermocouple TC2 were about 120 and 300 ° C., respectively.

When it is considered from Sample 1 that P1 is moisture adsorbed on the surface, it can be imagined that there are two water desorption regions in the tantalum pentoxide film formed on the tantalum film.
At a temperature between P2 and P3, almost no water is desorbed, so P2 is desorbed from the surface layer of the oxide film, and P3 is desorbed from the interface with the first conductive film. If the oxide film in between has a layer that does not contain moisture,
Inferred from the results.

When it is considered from Sample 2 that P4 is moisture adsorbed on the surface, it can be imagined that there is only one water desorption region from the tantalum pentoxide film formed on the silicon wafer. In this case, it is assumed that no water distribution occurs in the tantalum pentoxide film.

From the above results, if there is a metal under the tantalum pentoxide film, the moisture in the tantalum pentoxide film is separated into two and exists only at the interface between the surface layer and the first metal film. become. In other words, after the tantalum pentoxide film is formed,
When heat treatment is performed at a temperature of 300 ° C. or more in a water atmosphere, the water added thereto is separated into two parts. Therefore, if the heat treatment temperature is set to 300 ° C. or less, the first
No water is added to the interface with the conductive film, and water is added only to the surface layer. As a result, the moisture content of the third oxide film becomes larger than that of the first oxide film.

(Embodiment 2) In this embodiment, using the cross-type two-terminal nonlinear element shown in FIGS. 1 and 2, how the element resistance changes depending on the direction in which current flows is investigated. did. Specifically, a 100-nm-thick tantalum oxide film was deposited over a glass substrate by a sputtering method, a 150-nm-thick tantalum film was further deposited, and further patterning was performed to form a first conductive film. Then, using a 0.05% by weight aqueous solution of citric acid as a chemical conversion solution, a constant current electrolysis was performed at a current density of 0.04 mA / cm ² until the voltage reached 30 V, and then the voltage was maintained at 30 V and left for 2 hours for tantalum. Anodization of the film was performed. as a result,
A tantalum oxide film having a thickness of about 55 nm was formed. Further, a heat treatment was performed for 30 minutes at various temperatures in a steam atmosphere (heat treatment A). At this time, the water concentration was 1.2 mol% with respect to the whole processing gas. Furthermore, the film thickness 1
A second conductive film was formed by depositing a 00-nm chromium film by a sputtering method and performing patterning. Further, a heat treatment was performed at 250 ° C. for 1 hour in a nitrogen atmosphere (heat treatment B).

FIG. 13 shows how the resistance changes when 4 V is applied to the formed two-terminal nonlinear element at each temperature in the heat treatment A. In FIG.
Ta (+) is a resistance value of a current flowing when a positive DC voltage is applied to the first conductive film side, and Ta (−) is a resistance value of a current flowing in the opposite direction. It can be seen that when the heat treatment temperature is in the range of 220 to 300 ° C., the resistance value differs depending on the direction of voltage application, and the resistance value of Ta (+) increases. This can be explained by the fact that the third oxide film contains more oxygen atoms and hydrogen atoms than the first oxide film. That is, as shown in FIG.
It is presumed that the energy level of the conduction band of the oxide film 24c is smaller than that of the first oxide film 24a. When a voltage is applied in the direction of Ta (+),
The difference in the energy level between the oxide film 24 and the second conductive film 26 is related to the difference in the energy level between the third oxide film 24c and the second oxide film 24b. The resistance is larger than the electrical conduction in the Ta (−) direction, which is determined substantially by the difference in energy level between the first conductive film 22 and the oxide film 24.

When the heat treatment temperature is lower than 220 ° C.,
Since it is lower than the P2 temperature of the thermal desorption spectrum of FIG.
Water cannot be added to the oxide film 24, the third oxide film 24c is not formed, and the resistance of the two-terminal nonlinear element becomes low, so that the liquid crystal cannot be driven.

(Embodiment 3) In this embodiment, the relationship between the resistance value and the shift value of a two-terminal nonlinear element will be described.
In order to observe the change over time in the current-voltage characteristics with a two-terminal nonlinear element, a shift value as an index of the change over time was obtained. Incidentally, the shift value, when applying a square wave voltage changes polarity every second in a two-terminal type non-linear element, is defined by the value I _S represented by the following formula. At this time, the applied voltage is 1 × 1 per pixel of the liquid crystal display panel.
It is set so that 0 ^-7 A flows.

I _S = {(I ₁₀₀ −I ₀ ) / I ₀ } 100 (%) In this equation, I ₀ represents the absolute value of the initial (1 second) current value, and I ₁₀₀ is the value after 100 seconds. Indicates the absolute value of the current value. In practice, the shift value is desirably in the range of -5 to + 5%, more preferably -2 to + 2%, in order to prevent image sticking.

FIG. 15 shows that the two-terminal type nonlinear element has four axes on the horizontal axis.
The resistance value when a voltage of V was applied was taken, and the shift value was plotted on the vertical axis. A straight line 801 shows the relationship between the resistance value and the shift value of the two-terminal nonlinear element of the present invention, and a straight line 802 shows the relationship between the resistance value and the shift value when the heat treatment after forming the anodic oxide film is performed in a steam atmosphere exceeding 300 ° C. Shows the relationship. As the structure, a two-terminal nonlinear element having a back-to-back structure shown in FIGS. 5 and 6 was used. Specifically, a 100 nm-thick tantalum oxide film is deposited on a glass substrate by a sputtering method, and a 150 nm-thick tantalum film (containing 0.2 wt% of tungsten atoms) is further deposited.
Further, patterning was performed to form a first conductive film.
Subsequently, heat treatment was performed at 350 ° C. for 30 minutes in a nitrogen atmosphere, and the temperature was lowered to 200 ° C. or less while maintaining the nitrogen atmosphere (pre-annealing). Next, using a 0.05% by weight aqueous citric acid solution as a chemical conversion solution, anodization (around 15 V) was performed at various voltages to anodize the tantalum film. Further, the data of the straight line 801 is 2 in a steam atmosphere.
Heat treatment A was performed at 20 to 300 ° C. for 30 minutes, and then cooled to 180 ° C. in the same atmosphere. The data of the straight line 802 shows another heat treatment A at 320 ° C. or more for 30 minutes in a steam atmosphere.
And then cooled to 180 ° C. in the same atmosphere. Only the heat treatment is different in the manufacturing process.
Further, a 100-nm-thick chromium film was deposited by a sputtering method, and was also patterned to form a second conductive film. Further, a heat treatment was performed at 250 ° C. for 1 hour in a nitrogen atmosphere (heat treatment B).

Normally, when a liquid crystal panel is driven using a two-terminal nonlinear element, the resistance value when 4 V is applied to the two-terminal nonlinear element is preferably 5 × 10 ¹¹ to 1 × 10 ¹³ Ω. Here, the reason why the optimum resistance value differs is that it is limited by the type of liquid crystal used and the application of the liquid crystal panel. As can be seen from FIG. 15, the straight line 8 obtained by the present invention
In the case of 01, the shift value becomes -2 to 1% in the above range of the resistance value, and it is possible to make the image sticking of the liquid crystal display panel inconspicuous without any special measures. On the other hand, the shift value of the straight line 802 is 1 to 4% in the above-described range of the resistance value, and the burn-in can be made inconspicuous by devising a driving method and a liquid crystal panel manufacturing method. From the above, the temperature of the heat treatment A after forming the oxide film 24 is 3
It is desirable that the temperature be not higher than 00 ° C.

(Embodiment 4) In this embodiment, the relationship between the heat treatment temperature after the formation of the anodic oxide film and the β value of the two-terminal nonlinear element will be described. The current-voltage characteristics of the two-terminal nonlinear element were actually measured and plotted as a Pool Frenkel plot, and the slope obtained from the values when the applied voltage was 6 V and 8 V was defined as the nonlinear coefficient (β value).

The two-terminal type nonlinear element was manufactured by the manufacturing method described in Example 2, and the processing temperature of the heat treatment A was used as a parameter. FIG. 16 shows the processing temperature of the heat treatment A on the horizontal axis and the β value on the vertical axis. It is understood that the β value increases when the heat treatment is performed at 220 ° C. or higher, and further increases when the heat treatment is performed at 280 ° C. or higher.

Example 5 Characteristics of Liquid Crystal Display Panel Further, when a liquid crystal display panel was produced using the two-terminal nonlinear element of the present invention, a contrast of 100 or more was obtained in a temperature range of 0 to 50 ° C. No display unevenness or image sticking was observed.

[Brief description of the drawings]

FIG. 1 is a plan view showing a main part of a liquid crystal display panel to which a two-terminal nonlinear element of the present invention is applied.

FIG. 2 is a sectional view taken along the line AA in FIG.

FIG. 3 is a diagram showing an equivalent circuit of the liquid crystal display panel of the present invention.

FIG. 4 is a perspective view showing a liquid crystal display panel of the present invention.

FIG. 5 is a plan view showing a main part of a liquid crystal display panel to which the two-terminal nonlinear element of the present invention is applied.

FIG. 6 is a sectional view taken along line BB in FIG. 5;

FIG. 7 is a cross-sectional view showing elements excessively contained in an oxide film of the two-terminal nonlinear element of the present invention.

FIG. 8 is a diagram schematically showing an apparatus for obtaining a thermal desorption spectrum.

FIG. 9 is a diagram schematically showing a sample for obtaining a thermal desorption spectrum.

FIG. 10 is a diagram schematically showing a sample for obtaining a thermal desorption spectrum.

FIG. 11 is a diagram showing a thermal desorption spectrum obtained for an oxide film of a two-terminal nonlinear element.

FIG. 12 is a diagram showing a thermal desorption spectrum obtained for an oxide film of a two-terminal nonlinear element.

FIG. 13 is a diagram illustrating a relationship between a heat treatment temperature after forming an anodic oxide film of a two-terminal nonlinear element and a resistance value when 4 V is applied.

FIG. 14 is a band diagram of a two-terminal nonlinear element.

FIG. 15 is a diagram illustrating a relationship between a resistance value and a shift value when a voltage of 4 V is applied to a two-terminal nonlinear element.

FIG. 16 is a diagram illustrating a relationship between a heat treatment temperature and a β value after forming an anodic oxide film of a two-terminal nonlinear element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Liquid crystal display panel 12, 48 Scan line 14 Data line 16 Pixel area 20 Two-terminal nonlinear element 22, 42, 524 First conductive film 24, 44, 526, 536 Oxide film 24a First oxide film 24b Second Oxide film 24c Third oxide film 26, 46 Second conductive film 30 First substrate 31 Insulating film 32 Second substrate 34, 45 Pixel electrode 40 Liquid crystal element 100 Scanning signal driving circuit 110 Data signal driving circuit 522 Quartz substrate 532 silicon wafer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seki ▲ Taku ▼ Mino 3-3-5 Yamato, Suwa City, Nagano Prefecture Inside Seiko Epson Corporation

Claims (5)

[Claims] A first conductive film, an oxide film, and a second conductive film laminated on a substrate, wherein the oxide film includes a first oxide film containing moisture from a side of the first conductive film; In a two-terminal nonlinear element having a configuration of a second oxide film containing no moisture and a third oxide film containing moisture, the moisture content of the third oxide film is reduced by the moisture content of the first oxide film. A two-terminal nonlinear element characterized by having a higher content than the content. 2. The two-terminal nonlinear element according to claim 1, wherein said first conductive film is made of tantalum or an alloy of tantalum. 3. The two-terminal non-linear element according to claim 1, wherein the oxide film is an anodic oxide film for the first conductive film. 4. A process for forming a first conductive film on a substrate, a process for forming an oxide film on the first conductive film, and a process for forming an oxide film on the first conductive film. And the substrate on which the oxide film is formed is placed in an atmosphere containing moisture for 220 to 30 minutes.
A method for manufacturing a two-terminal nonlinear element, comprising: a heat treatment at 0 ° C .; and (4) a step of forming a second conductive film on the oxide film. 5. A liquid crystal display device comprising the two-terminal nonlinear element according to claim 1 as a switching element.