JP2002164202A - Nonlinear resistance element, its manufacturing method, and liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonlinear resistance element which is suppressed in changeover aging is its voltage-current characteristic caused by the influence of heat, current injection, etc., and is suitably used as a switching element of a liquid crystal display. SOLUTION: This nonlinear resistance element 100 is composed of a nonlinear resistance element (MIM element) 100 constituted of a first conductive film 12, an insulating film 14, and a second conductive film 16 successively laminated upon a substrate 10. The insulating film 14 is the anodic oxide film of the first conductive film 12 and the second conductive film 16 is composed at least of either one of a chromium film and a transparent conductive film. In addition, when a voltage which falls within a prescribed range is impressed upon the MIM element 100, the following equation holds approximately: log(J/J0)=S×t1/m, where S denotes a coefficient of <=3.1×10-3 and t, J, and J0 respectively denote the time (seconds) elapsed after the driving of the element has started, the current density (A/cm2) when the elapsed time t is t seconds, and the current density (A/cm2) when the elapsed time is 1 second. In addition, m denotes a numerical value of >=1, preferably, 5>=.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laptop computer, an engineering workstation (EW).
S) or a non-linear resistance element suitable as a pixel switching element of a liquid crystal display device such as a liquid crystal television, particularly MIM
The present invention relates to an element and a method for manufacturing the same.

[0002]

BACKGROUND OF THE INVENTION In recent years,
In a laptop computer, an EWS, a small television, and the like, conversion from a conventional CRT to a liquid crystal display device has been actively attempted from the viewpoint of reduction in size, weight, and power consumption.

As a pixel switching element of this liquid crystal display device, a three-terminal thin film transistor (TFT) using polysilicon or amorphous silicon, a metal
Two-terminal nonlinear resistance element (MI
M) is used. In the case of a three-terminal device such as a TFT, it is necessary to repeatedly form a thin film from the structure of the device at the time of manufacture. It is easy to occur, and there is a problem that the manufacturing yield is reduced.
On the other hand, a two-terminal element such as an MIM element has a simpler manufacturing process and higher manufacturing yield than a three-terminal element, and has no intersections of signal lines. Attention has been paid to its advantages, and improvements and developments are currently underway.

[0004] The MIM element has a structure in which an insulating thin film is sandwiched between two conductive thin films, and the voltage-current characteristics between the conductive thin films exhibit nonlinearity. Typical MIM element has a structure of Ta-Ta ₂ O ₅ -Cr. This MIM element is usually manufactured by the following method.
That is, first, a Ta thin film is formed on a glass substrate by sputtering, and then etching is performed leaving a timing signal line and a MIM element portion. Next, a Ta ₂ O ₅ insulating film is formed on the surface of the Ta thin film by an anodic oxidation method. The insulating film formed by the anodic oxidation method is advantageous in that a dense film with few pinholes can be formed as compared with an insulating film formed by sputtering, CVD (chemical vapor deposition), or the like. Next, a Cr thin film is formed by sputtering, followed by patterning, and further, an electrode pattern for driving a liquid crystal, which is made of a transparent conductive film of ITO, is formed.

In order to realize high image quality in a liquid crystal panel using such an MIM element, it is generally important to satisfy the following characteristics.

(1) The capacity of the element is sufficiently smaller than the capacity of the liquid crystal. (2) The voltage-current characteristics of the element have a large nonlinearity, and the ratio between the ON current and the OFF current is sufficiently large. (3) The voltage-current characteristics of the element are symmetric on the positive voltage side and the negative voltage side.

As a technique for further pursuing the simplicity of the manufacturing process, there is a technique disclosed in, for example, JP-A-57-122476. In this technique, a transparent conductive film made of ITO (Indium Tin Oxide) is used as an upper electrode. By forming the upper electrode as a transparent conductive film in this manner, the upper electrode can be formed at the same time as forming the transparent electrode film that is a pixel electrode, so that the film formation of the upper electrode and the etching process thereof can be reduced. Can,
The process can be further simplified. However, in the MIM element having the upper electrode made of ITO, the voltage-current characteristics are significantly different between the positive voltage side and the negative voltage side, and it is difficult to obtain good current characteristics.
Such asymmetry of the voltage-current characteristics at the positive and negative applied voltages causes flicker on the display screen of the liquid crystal display device and deterioration of the liquid crystal material.

In order to apply an MIM element using an ITO upper electrode to a liquid crystal display device, for example, a back-to-back connection in which the MIM elements are connected in series in a reverse direction is used.
Back) A technology to obtain a current characteristic that is symmetrical with respect to the positive and negative applied voltages, and to control the driving method to asymmetrical the externally applied voltage value and the waveform itself according to the polarity difference (Katsumi) Aota, et al, SID'9
1 DIGEST, P.A. 219, 1991). However, the former method significantly increases the cost in the manufacturing process of the MIM element,
In the latter case, an increase in the number of external power supplies or driver ICs
Causes an increase in size and cost.

According to the present inventors, the conventional MIM
As another problem in the device, it has been confirmed that voltage-current characteristics of the device change with time due to current injection. When such a change with time of the voltage-current characteristics is large, when the liquid crystal display device is driven by the active matrix method, it may appear as, for example, an afterimage or display unevenness.

An object of the present invention is to provide a switching element of a liquid crystal display device which suppresses a change with time in voltage-current characteristics due to the influence of heat or current injection, in addition to the general characteristics required for the above-described MIM element. An object of the present invention is to provide a suitable nonlinear resistance element and a method for manufacturing the same.

Another object of the present invention is to provide a liquid crystal display device which is constituted by using the above-mentioned nonlinear resistance element and which can maintain high image quality for a long time.

[0012]

A non-linear resistance element according to the present invention is a non-linear resistance element (MIM element) comprising a first conductive film, an insulating film and a second conductive film laminated on a substrate.
In the first conductive film, an element having a valence of 1 or 2 greater than that of the metal as a main component is 0.2 to 6 atomic%.
Wherein the insulating film is an anodic oxide film of the first conductive film.

In this nonlinear resistance element, tantalum, aluminum or the like can be used as a metal constituting the first conductive film, but tantalum is particularly preferred.
The element added to the first conductive film is preferably at least one selected from tungsten, chromium, molybdenum, and rhenium, and particularly preferably tungsten. Tungsten may be added as a compound of tungsten oxide (WO ₃ ).
In addition, as a material constituting the second conductive film, chromium, molybdenum, titanium, aluminum, a transparent conductive film, or the like can be used, but chromium and a transparent conductive film are preferable, and a transparent conductive film made of ITO is particularly preferable. .

Next, the results of a study on how the added element of the first conductive film affects the current characteristics of the nonlinear resistance element of the present invention will be described. Specifically, the first
Tantalum is used as the metal of the conductive film, and tungsten is used as an additive element.
It is an investigation on how the current flowing through the IM element is affected. FIG. 1 shows current characteristics of an element using chromium as the second conductive film, and FIG. 2 shows current characteristics of an element using ITO as the second conductive film.

(Sample) The sample used in this experiment was formed as follows.

First, a first conductive film is formed on a glass substrate by depositing a tantalum thin film having a thickness of about 3500 angstroms or a thin film containing tungsten in tantalum by sputtering. Then, 0.01% by weight
In the citric acid aqueous solution, anodization is performed for 2 hours using a constant voltage method in which the anode voltage is set to 30 V to form an insulating film having a thickness of about 530 angstroms. Then
Annealing is performed at a temperature of 400 ° C. for about 1 hour in a nitrogen gas atmosphere. Then, chromium or ITO is deposited on the insulating film by sputtering to form a second conductive film. At this time, the thickness of the second electrode is 1,50 of chromium.
It is 0 Å and 1000 Å for ITO. Further, at a temperature of 250 ° C.
For one hour. Several kinds of samples having different tungsten concentrations are prepared. The size of the sample is 4 μm × 4 μm. The samples used in each experiment described later were also obtained by the above method.

For each sample, a current value when a voltage of 4 V was applied and a current value when a voltage of 15 V was applied were determined. Normally, in a liquid crystal display device using an MIM element, the voltage applied to the MIM element is
It is 10 to 20 V when selected and 2 to 6 V when not selected.
Therefore, in the present invention, a value approximately at the center of these voltage ranges is selected, and the ON voltage is set to 15V and the OFF voltage is set to 4V.
And the current flowing at that time is defined as an ON current and an OFF current, respectively.

In FIGS. 1 and 2, the curves indicated by A show the results when a voltage of 4 V is applied, and the curves shown by B show the results when a voltage of 15 V is applied. A1 and B1 shown by solid lines show the results when a positive bias voltage is applied to the first conductive film, and A2 and B2 shown by broken lines show the results when a negative bias voltage is applied to the first conductive film. It is shown.

FIG. 1 shows that when tungsten is added in a specific concentration range, the ON current and the OFF current are reduced, and the effect is remarkable especially when the tungsten concentration is low. The range of the concentration of tungsten in which these currents decrease depends on the applied voltage.
The applied voltage is about 3 atomic% or less, and the applied voltage of 15 V is about 3 atomic% or less. Of particular note is the decrease in OFF current. The decrease in the OFF current makes it difficult for the charge to escape in the non-selection period, so that the contrast ratio of the liquid crystal display image increases. FIG.
From this, it can be seen that when the tungsten concentration is greater than about 0.2 atomic%, the voltage-current curves at the positive and negative voltage polarities almost completely match, and the symmetry of the current characteristics is very good.

FIG. 2 shows that the second conductive film is made of ITO.
It was also found that the addition of tungsten in a specific concentration range reduced the ON current and OFF current. Compared to the case where tantalum without addition of tungsten is used as the first conductive film and chromium is used as the second conductive film, the ON current is about 4 atomic% or less and the OFF current is about 4 atomic% or less. It was found that a reduction in current density was observed at 0.5 atomic% or less, and that the effect of reduction was particularly large at a low concentration of 2 atomic% or less. However, when ITO is used as the second conductive film, when the tungsten concentration is lower than when chromium is used, when a positive bias voltage is applied and when a negative bias voltage is applied, It can be seen that there is a difference in current density between and and that the symmetry in voltage polarity is slightly inferior. In particular,
In the OFF current, the concentration of tungsten is about 0.5
Poor symmetry when less than atomic%.

As described above, the insulating film formed by anodizing the tantalum thin film to which tungsten is added lowers the OFF current as compared with the case where no tungsten is contained. When chromium is used as the second conductive film, a maximum of about 3 atomic% is used as the second conductive film.
In the case of using O, the effect of reducing the effect is seen when about 4.5 atomic% of tungsten is added at the maximum. Such a reduction in the OFF current increases the contrast of the liquid crystal display screen, thereby contributing to an improvement in image quality.

The non-linear resistance element according to the present invention is a non-linear resistance element (MIM element) composed of a first conductive film, an insulating film and a second conductive film laminated on a substrate. Is preferably a metal film in which tungsten is added to tantalum as a main component, and the insulating film is
The second conductive film is at least one of a chromium film and a transparent conductive film, and the current density (J) flowing through the element is approximately represented by the following equation (1). The activation energy (E
a) is 0.534 eV or less.

Equation (1) J = Aexp (−Ea / kT) where A is a constant, k is a Boltzmann constant, and T is an absolute temperature.

Normally, the MIM element is sensitive to a change in temperature. For example, the characteristics of the MIM element change due to heating by a backlight of a liquid crystal display device or use in a high-temperature place, causing a decrease in contrast of a displayed image. This is because the current value of the element has a temperature dependency, as can be seen from the equation (1). Further, the current density is also a function of the activation energy (Ea), and it can be said that the temperature dependence increases as the activation energy increases, and the temperature dependence decreases as the activation energy decreases. When the current-voltage characteristics are measured while changing the measurement temperature of the MIM element, and the relationship between the current value and 1 / T is plotted at an arbitrary voltage, the graph becomes almost a straight line, and the activation energy (Ea) is expressed by the straight line. It can be obtained from the slope.

According to the study of the present inventors, room temperature (about 22
If the amount of change in the current density (J) in the actual use range of from 80 ° C. to 80 ° C., particularly the OFF current, is within 1.5 digits, there is no problem in the display characteristics of the liquid crystal display device. It has been confirmed that when the number exceeds 5 digits, the display characteristics, particularly the contrast, are lowered.

Furthermore, the present inventors have found that the activation energy of the insulating film obtained by anodizing the first conductive film in which tungsten is added to tantalum is considerably lower than that in the case where no tungsten is added. I discovered that Therefore, the relationship between the concentration of tungsten added to tantalum and the activation energy was examined by experiments. The results are shown in FIGS. The sample was formed by the same method as described above. FIG.
FIG. 4 shows the case where chromium is used as the second conductive film.
FIGS. 3 and 4 show a case where ITO is used as the conductive film. In FIGS. 3 and 4, E ₄ is an activation when a voltage (OFF voltage) of ₄ V is applied, and E ₁₅ is an activation when a voltage (ON voltage) of ₁₅ V is applied. 4 shows the relationship between energy and tungsten concentration.

3 and 4 that the higher the applied voltage, the lower the activation energy. In addition, each voltage has one peak on the low concentration side of tungsten, and thereafter, the activation becomes gentle. You can see that the energy is decreasing. Then, the ON voltage (15
V) and OFF voltage (4 V), the activation energy is 0.534 eV or less, so that when chromium is used as the second conductive film, the tungsten concentration is about 0.8 atomic% or more. And the second
It has been found that when ITO is used as the conductive film, a tungsten concentration of about 1.2 atomic% or more is required.

By controlling the tungsten concentration in this manner, the activation energy (E
By setting a) to 0.534 eV or less, the change amount of the OFF current that most affects the display characteristics can be kept within about 1.5 digits within the temperature range in which the liquid crystal display device is actually used. Therefore, in a liquid crystal display device using this element, it is possible to suppress a decrease in contrast in an actual operating temperature range.

The non-linear resistance element according to the present invention is a non-linear resistance element (MIM element) composed of a first conductive film, an insulating film and a second conductive film laminated on a substrate, wherein the first conductive film Is preferably a metal film in which tungsten is added to tantalum as a main component, and the insulating film is
An anodic oxide film of a conductive film, wherein the second conductive film is at least one of a chromium film and a transparent conductive film, and after a current is injected into the device at a current density of 1 A / cm ² for 10 seconds; Assuming that the current density when a bias voltage of 10 V is applied is J ₂ and the current density when a bias voltage of 10 V is applied without performing current injection is J ₁ , the following equation (2) is approximately established. In the equation (2), the relation of | B | ≦ 0.2 and n ≦ 0 holds for the constants B and n.

Equation (2) log (J ₂ / J ₁ ) = B × t ^{1 / n} Here, t represents an elapsed time (second) since the application of the bias voltage.

According to the study of the present inventors, under the above conditions, equation (2) approximately holds, and in equation (2), the relationship where the absolute value of the constant B is 0.2 or less and n is 0 or less is satisfied. Holds, it is possible to reduce the difference in luminance between the pixel displayed in the halftone display from the white display and the pixel displayed in the halftone display from the black display, and the difference in the luminance is not recognized by human eyes as an afterimage. Alternatively, it can be a practically acceptable level. Further, it has been confirmed that if the absolute value of the constant B is 0.1 or less, it is not recognized as an afterimage in the case of a moving image display that changes in a short time of, for example, several μsec to several msec.

In a conventional liquid crystal display device using an MIM element, there is a difference in luminance between a pixel changed from white display to halftone display and a pixel changed from black display to halftone display. The difference in luminance was recognized as an afterimage on display, which was one of the major problems. This phenomenon occurs because the current flowing in the MIM element of the pixel that has changed from white display to halftone display is different from the current flowing in the MIM element of the pixel that has changed black display to halftone display. Such a difference in current value is caused, for example, by the fact that electric charges are injected into traps in the insulating film due to current injection into the insulating film for several microseconds to several milliseconds, and the current-voltage characteristics change. it is conceivable that.

Next, the result of an experiment performed on this phenomenon will be described.

FIG. 5 shows the relationship between the time and the current density (shown by b in FIG. 5) when a current of 1 A / cm ² was injected for 10 seconds and then a bias voltage of 10 V was continuously applied. 5 shows the relationship between the time and the current density when a bias voltage of 10 V is continuously applied without performing injection (indicated by a in FIG. 5). From FIG. 5, it can be seen that the value of the current flowing through the element differs between the case where the current injection is performed and the case where the current injection is not performed, and that the difference is remarkable in the early stage of the application of the voltage. Contribute.

FIG. 6 is a plot of the difference (log (J ₂ / J ₁ )) between the two current densities in FIG. 5 with respect to time. FIG. 6 shows that the difference between the current density (logJ ₂ ) when the current injection was performed and the current density (logJ ₁ ) when the current injection was not performed becomes smaller as time passes. Such a relationship exists not only when tantalum is used as the first conductive film and chromium is used as the second conductive film, but also when ITO is used as the second conductive film, and when the first conductive film is made of ITO.
It has been confirmed that the present invention can be applied to each MIM element such as a case where tungsten is added to tantalum as a conductive film.

Taking the logarithm of equation (2), equation (5) when J ₂ > J ₁ log {log (J ₂ / J ₁ )} = log B + 1 / nlo
gt Equation (6) When J ₁ > J ₂ log {−log (J ₂ / J ₁ )} = log (−B) +1
/ Nlogt holds. For example, plotting based on the equation (6) for some samples in which J ₁ > J ₂ holds is shown in FIG.
It is. 7, the horizontal axis logt (s), the vertical axis represents the _{log {-log (J 2 / J} 1)}, the intercept of the vertical axis thus is log (-B), the straight line of slope 1 / n. In FIG. 7, the first conductive film and the second conductive film are made of tantalum-chromium (a) and tantalum-ITO (b).
And tantalum-I containing 0.4 atomic% tungsten
An example of TO (c) is shown. FIG. 7 shows the numerical values of B and n of each sample.

Next, a graph similar to the graph shown in FIG. 7 was created to determine the relationship between the constant B in the above equation (2) and the tungsten concentration. The results are shown in FIGS.
8 and 9, the horizontal axis represents the concentration (atomic%) of tungsten, and the vertical axis represents the constant B. FIG.
FIG. 9 shows the case where chromium is used as the conductive film, and FIG. 9 shows the case where ITO is used as the second conductive film.

FIG. 8 shows that when the second conductive film is chromium, the tungsten concentration must be 0.2 atomic% or more because the absolute value of the constant B in the equation (2) is 0.2 or less. It is sufficient if it is provided, and more preferably 0.3 atomic% or more. According to FIG. 9, when the second conductive film is ITO,
In order for the absolute value of the constant B to be 0.2 or less, the concentration of tungsten needs to be 0.3 atomic% or more, and more preferably 0.6 atomic% or more. In other words, by setting the tungsten concentration of the first conductive film in the above range, the constant in the expression (2) becomes 0.2 or less in absolute value, preferably 0.1 or less, as a result. Does not cause a visually obstructive afterimage.

The non-linear resistance element of the present invention is a non-linear resistance element (MIM element) composed of a first conductive film, an insulating film and a second conductive film laminated on a substrate. Is preferably a metal film in which tungsten is added to tantalum as a main component, and the insulating film is
The second conductive film is at least one of a chromium film and a transparent conductive film, and when a voltage in a predetermined range is applied to the device, the second formula is approximately the following formula (3). Holds, and in this equation (3), the coefficient S is 3.1.
× 10 ⁻³ or less.

Equation (3) log (J / J ₀ ) = S × t ^{1 / m} where t is the elapsed time (second) from the start of driving, J
Is the current density (A / cm ² ) when the elapsed time is t seconds, J ₀ is the current density (A / cm ² ) when the elapsed time t is 1 second, m
Represents 1 or more, preferably 5.

According to the study of the present inventors, when the equation (3) is approximately established in the MIM element and the coefficient S is not more than 3.1 × 10 ⁻³ in the equation (3), Even if the element is driven for a long time, its characteristic change (log (J /
J ₀ )) was about 0.1 or less, and it was confirmed that the display characteristics could be maintained for at least 10,000 hours by a normal driving method such as an active matrix driving method.
More specifically, when the characteristic change is about 0.1 or less, afterimages (burn-in), which is a problem when displaying a long-time still image over several tens of minutes, for example, can be prevented. . This burn-in phenomenon is caused by the fact that the current-voltage characteristics of the selected MIM element change due to long-time driving. Are caused by the fact that the current values flowing through the respective pixels are different, whereby the voltages applied to the two pixels produce different luminance results.

Next, the method of introducing the above equation (3) and the result of studying the relationship between the coefficient in the equation (3) and the tungsten concentration will be described. FIG. 10 shows the relationship between the change in current density and time, with the horizontal axis representing logt and the vertical axis representing log (J / J ₀ ). In this figure, a
The curve shown by indicates the measurement result of an element using tantalum as the first conductive film and chromium as the second conductive film, and the curve shown by b indicates that 0.7 atomic% of tungsten was added to tantalum as the first conductive film. The measurement results of an element using chromium as the second conductive film are shown. And FIG.
Is obtained from the curves a and b shown in FIG. 10. The horizontal axis represents t ^1/5 and the vertical axis represents log (J / J ₀ ). From FIG. 11, it has been confirmed that t ^1/5 and log (J / J ₀ ) have a substantially perfect linear relationship, and that equation (3) holds. In addition, the current density changes over time by adding tungsten to the first conductive film (log (J / J ₀ )).
Was remarkably reduced, and the change in the current characteristics was also extremely reduced.

The “predetermined voltage range” in the precondition of the above equation (3) is a voltage range in which a current density sufficient to drive a liquid crystal display device can be obtained, and varies depending on the current-voltage characteristics of the MIM element. And generally 10 to 20V. Then, the current density of the MIM element definitive this voltage range is generally 1mA / cm ² ~1A / cm ² or so,
Considering the power consumption and the withstand voltage of the driver IC, it is preferably about 1 mA / cm ² .

Then, the relationship between S corresponding to the slope of the straight line in FIG. 11 and the concentration of tungsten added to the first conductive film was examined in further detail. That is, the current density J ₀ in the formula (3) is 1 A / cm ² , 0.1 A / cm ² .
cm ² , 0.01 A / cm ² and 0.001 A / cm ²
The relationship between the coefficient S and the concentration of tungsten added to the first conductive film was determined under the following conditions. The results are shown in FIGS. FIG. 12 shows a case where chromium is used as the second conductive film, and FIG. 13 shows a case where ITO is used as the second conductive film.
Is shown.

FIGS. 12 and 13 show that the coefficient S decreases as the tungsten concentration increases. The coefficient S also depends on the current density, in other words, the magnitude of the applied voltage, and it can be seen that the coefficient S decreases as the applied voltage decreases. Then, when the value of the coefficient S is 3.
In order to be 1 × 10 ⁻³ or less, for example, the current value is 1 mA.
/ Cm ² (d), for example, when the second conductive film is chromium, about 0.3 atomic% or more, and the second conductive film is made of ITO.
In the case of the above, it is understood that it is about 0.7 atomic% or more.

In the above equation (3), the coefficient S is 3.1 × 1.
0 With ^-3, for example a duty ratio of 1/200 to 1/2000 of the liquid crystal display device, driving voltage 10 to 2
When driven under the condition of 0V, the display characteristics of the liquid crystal display device can be maintained satisfactorily for, for example, 10,000 hours without causing burn-in of the pattern due to long-time display.

Further, in the nonlinear resistance element of the present invention, when m is 5 in the above equation (3) and the coefficient S exceeds 3.1 × 10 ^-3 , the following equation (4) is satisfied. It is necessary to perform aging at least for time t seconds. Here, aging means that a voltage in a predetermined range is applied to the MIM element disposed on the entire surface of the substrate for a certain period of time.

Equation (4) log (S / 5) − (4/5) log t <−3.2 Equation (4) is obtained from equation (3) as shown below.

Log (J / J ₀ ) = S × t ^1/5 dlog (J / J ₀ ) / dt = (S / 5) t ^−4/5 Equation (7) log ｛dlog (J / J ₀ ) / Dt｝ = log (S /
5) -4/5 logt FIG. 14 is a graph of the equation (7). That is, in FIG. 14, the horizontal axis indicates logt, and the vertical axis indicates l.
log {d log (J / J ₀ ) / dt}. FIG.
, The intercept (logt = 0) on the vertical axis is log (S /
5) is shown. Therefore, in order for the coefficient S to be 3.1 × 10 ⁻³ , log (S / 5) = log (3.1 × 10 ⁻³ / 5) = −
3.2. The time t required for aging, which satisfies Expression (4), can be obtained from FIG. For example, looking at a straight line d (1 mA / cm ² ) in FIG.
At 1 (second), the value of the equation (7) is about −3.0,
Equation (4) is not satisfied, but at t = 2 (seconds), about-
3.2, thus indicating that an aging time of at least about 2 seconds is required. Thus, the above equation (4)
When the aging is performed for a time t that satisfies the above condition, the above equation (3) can be satisfied in the subsequent driving, so that even if the same pattern is displayed on the same pixel for a long time, pattern burn-in occurs. And good display characteristics can be maintained. According to the study of the present inventors, it has been confirmed that the characteristics obtained by performing such aging can be maintained for a long time in the MIM element of the present invention. Further, it has been confirmed that when tungsten is not added to the first conductive film, the characteristics before aging are restored by being left at room temperature, and it is confirmed that it is difficult to maintain the aging effect.

In the present invention, the activation energy of the thermal stimulation current (TSC current) in the insulating film (the anodic oxide film of the first conductive film) is preferably smaller than 0.7 eV. Energy is 0.
It is preferably 3 eV or less. Further, in order to obtain such a configuration, the first conductive film is formed by adding tungsten to the first conductive film.
It is preferable to add at a ratio of 6 atomic%. The reason why the activation energy of the TSC current is reduced by adding tungsten is not necessarily clear, but it is considered that the trap level in the insulating film is reduced by adding tungsten.

The activation energy of the TSC current is described in J. IEEE Japan, Vol.
8, '88, p. 787-792 "and the approximate formula.

In FIG. 15, the measurement point in the area indicated by a is that of an anodic oxide film having only an insulating film of tantalum, and the measurement point in the area indicated by b is the anode of a film obtained by adding 2 atomic% of tungsten to tantalum. It is of an oxide film.

FIG. 15 shows that the activation energy of the TSC current is significantly reduced in the anodic oxide film to which tungsten is added. Further, the activation energy is almost constant without much depending on the bias temperature. By reducing the activation energy of the TSC current, the value of the constant B in the equation (2) can be reduced. This is because the value of B in the formula (2) depends on the electric charge trapped in the insulating film, and it is possible to form a trap level considerably lower by adding tungsten than in the case where tungsten is not added. Can,
Therefore, it is considered that the charge injected into the insulating film is greatly reduced, and as a result, the value of the constant B can be reduced.

The method for manufacturing a nonlinear resistance element according to the present invention comprises:
(A) A metal film containing an element having a valence of 1 or 2 larger than that of the main component metal at a rate of 0.2 to 6 atomic%, preferably with a thickness of 1500 to 5000 angstroms, is deposited on the substrate to form a first film. Forming a conductive film; (b) forming the first conductive film;
The thickness of the conductive film is preferably 3 nm by anodic oxidation.
Forming an insulating film having a thickness of 100 to 750 angstroms; and (c) forming a second conductive film having a thickness of preferably 300 to 2,000 angstroms on the surface of the insulating film. .

In this manufacturing method, the metal of the first conductive film is preferably tantalum, and the element having a higher valence than tantalum is tungsten, molybdenum, chromium, or the like.
Rhenium, tungsten oxide and the like are preferred, and tungsten is more preferred. Further, the second conductive film is preferably at least one of chromium and a transparent conductive film, and more preferably a transparent conductive film.

In this manufacturing method, it is preferable to perform a first annealing at a temperature of 300 to 400 ° C. after the formation of the insulating film. Further, in this manufacturing method, after forming the second conductive film, the temperature is 230 to 260 ° C.
Then, it is preferable to perform the second annealing treatment in an atmosphere containing at least oxygen.

Particularly, in the first annealing process, the OFF current of the obtained MIM element depends on the processing temperature, so that it is important to appropriately set the temperature range. Usually, the anodic oxide film is stabilized by performing a heat treatment at about 450 ° C. after the anodic oxidation. However, for example, by using inexpensive soda glass instead of the conventional non-alkali glass as the substrate, the manufacturing process can be reduced. In order to reduce costs, it is necessary to reduce the process temperature. However, when the annealing process temperature is lowered, the device is turned off.
The current increases, causing a decrease in contrast in the liquid crystal display device. For example, by lowering the processing temperature from 450 ° C., which is a normal annealing temperature, to 300 ° C., which is less affected by expansion and contraction of glass, cracking, etc., an increase in OFF current of about two digits in a MIM element using tantalum is obtained. Can be seen. However, according to the study of the present inventors, addition of tungsten to tantalum suppresses the increase in the OFF current, that is, even if the processing temperature is reduced from about 450 ° C. to about 300 ° C., the change in the OFF current is suppressed. It was confirmed that it could be within about 1.5 digits and had little effect on display characteristics.

Next, an experiment for demonstrating this will be described. In this experiment, the current densities of a plurality of device samples obtained by changing the concentration of tungsten and the temperature of the first annealing treatment were obtained. FIGS. 16 and 17 show data when chromium is used as the second conductive film, and FIGS. 18 and 19 show data when IT is used as the second conductive film.
Data when O is used. 16 and 18, the horizontal axis represents the concentration of tungsten, and the vertical axis represents the current density (logJ). 17 and 19, the horizontal axis indicates the annealing temperature, and the vertical axis indicates the current density (lo).
gJ).

As shown in FIGS. 16 and 18, by adding tungsten to the tantalum film, the
It can be seen that the F current (bias voltage: 4 V) decreases and the amount of change in current density with respect to the change in annealing temperature decreases.

Specifically, from FIG. 16, when tungsten is added in an amount of 0.2 atomic% or more, the annealing temperature is increased to 450 ° C.
Even when the temperature is lowered from 300 ° C. to 300 ° C., the amount of change in the current density J is about 1.5 digits (close to 2.5 digits when no tungsten is added), and the annealing temperature is lowered from 400 ° C. to 300 ° C. The change in current density is 1
You can see that it fits within the digits.

FIG. 17 shows that the dependence of the OFF current on the annealing temperature can be reduced. Specifically, when tungsten is not added (a), the slope of the curve is large and the current density (logJ) greatly changes with temperature. On the other hand, when tungsten is added to tantalum, the slopes of the curves (b) to (f) decrease, and the slope of the curve decreases as the tungsten concentration increases, resulting in a gentle curve. It turns out that it does not depend much on temperature.

From the above results, by adding tungsten to tantalum at a ratio of about 0.2 atomic% to 6 atomic%, the annealing temperature in the first annealing process is set to 3%.
It can be lowered to about 00 ° C. However, if the annealing temperature is lower than 300 ° C., when the bias voltage is applied to the MIM element, when the polarity changes, asymmetry is observed in the voltage-current characteristics, so that annealing at a temperature lower than this temperature is not preferable. On the other hand, when inexpensive soda glass is used as the substrate, it is preferable to perform annealing at a temperature of 450 ° C. or lower, preferably 400 ° C. or lower at the maximum, in consideration of characteristics such as thermal expansion.

Also, when ITO is used as the second conductive film, the same tendency as when chromium is used as the second conductive film is observed as shown in FIGS. As shown in FIG. 18, when the concentration of tungsten is 0.2 atomic% or more, the amount of change in the OFF current can be suppressed to about 1.5 digits. FIG. 19 shows that when the annealing temperature exceeds about 350 ° C., the slope of the curve becomes gentle, and the amount of change in the OFF current becomes smaller. Therefore, when ITO is used as the second conductive film, the temperature of the first annealing treatment is 300 ° C. or higher, preferably 350 ° C. or higher, and 450 ° C. or lower, preferably 400 ° C. or lower. In order to enable such an annealing treatment, the concentration of tungsten is preferably 0.4 atomic% or more.
However, as can be seen from FIG. 18, if the tungsten concentration is too high, the OFF current increases, so that the tungsten concentration preferably does not exceed, for example, 3 atomic%.

In the manufacturing method of the present invention, the second
In the conductive film forming step (step c), the second conductive film
The thin film of TO has a ratio of oxygen to argon (oxygen / argon) of 5 × 10 ^{−5 to} 1.2 × 1 in volume ratio.
It is preferably formed by sputtering in an atmosphere of 0 ^-2 .

When an ITO thin film is used as the second conductive film, the quality of the film has a great effect on the device characteristics. IT
The film quality of the O film depends on its formation conditions, and is specifically determined by power, gas flow rate, temperature, pressure, and the like in sputtering. According to the study by the present inventors, it has been confirmed that, among these conditions, the gas composition in sputtering greatly affects the MIM element. Specifically, by setting the flow rate ratio between oxygen and argon within the above range, it is possible to make the absolute value of the constant B in the above equation (2) 0.2 or less.

FIG. 20 is a diagram showing data of an experimental example conducted to confirm this. In FIG. 20, the horizontal axis indicates the flow rate ratio between oxygen and argon, and the vertical axis indicates the constant B of the equation (2). In this experiment, the conditions for the sputtering were a power of 1.7 kW and a temperature of 200.
° C, pressure 5 × 10 ^-1 Pa, and gas flow rate (argon: 100 sccm, oxygen: 0 to 10 sccm). FIG. 20 shows that the value of the constant B varies discontinuously depending on the gas flow ratio. And the value of B is 0.2
It can be seen that the flow ratio of oxygen to argon needs to be within the above range in order to achieve the following. Further, by setting the flow rate ratio to 1.6 × 10 ^{−4 to} 1.0 × 10 ⁻² , the value of the constant B can be set to 0.1 or less, which is more preferable.

According to the study by the present inventors, it has been found that the flow ratio of oxygen to argon affects the crystal structure of ITO. Specifically, when the flow ratio of oxygen to argon is within an appropriate range, ITO forms polygonal granular crystals, and the ratio of the long axis to the short axis (long axis / short axis) in a single crystal is large. It was confirmed that it was about 3 to 1 on average. Here, the long axis refers to the longest axis passing through the center of gravity of the crystal shape, and the short axis refers to the shortest axis passing through the center of gravity of the crystal shape.

FIGS. 37 to 40 show electron microscopy of the surface of the ITO film.
A mirror photograph (SEM) is shown. FIG. 37 shows the relationship between oxygen and argon.
Flow ratio of 4.0 × 10^-FourFIG. 38 shows oxygen and argon.
And the flow ratio is 5.0 × 10^-3FIG. 39 shows oxygen and algo
1.0 × 10 ^-2FIG. 40 shows oxygen and
The flow ratio with the gon is 4.0 × 10^-2IT obtained at the time of
It is an electron micrograph of the O film surface. 37 and 38
In this case, the flow ratio of oxygen to argon is in a preferable range.
And clear polygonal granular crystals are observed. Against this
FIG. 39 shows that the flow ratio of oxygen to argon is within the range of the present invention.
Near the boundary of the object and the ratio of the major axis to the minor axis is large.
It was confirmed that the particles were fine and elongated granular crystals. FIG.
The flow ratio of oxygen to argon is greater than the scope of the invention,
It is also an elongated granular crystal with a large ratio of long axis to short axis
It was confirmed that.

In order to comprehensively satisfy the empirical formulas and the conditions of the manufacturing process described above, when the second conductive film is formed of chromium, tungsten added to the first conductive film is required. Is 0.2 to 6 atomic%, preferably 0.3 to 3 atomic%, more preferably 0.1 to 3 atomic%.
8 to 3 atomic%. Further, when the second conductive film is formed of ITO, the concentration of tungsten added to the first conductive film is 0.2 to 6 atomic%, preferably 0.3 to 4.5 atomic%. %, More preferably 0.5-4.
5 atomic%.

Further, according to the present invention, the size dependence of the current characteristics of the MIM element can be reduced. This will be described below.

With the demand for higher definition and larger capacity of liquid crystal display devices, miniaturization of driving MIM elements is also desired. However, the conventional MIM element (first
It has been confirmed by the present inventors that in the case of a device using a tantalum film to which tungsten is not added as the conductive film), the dependency on the device size is large. That is, for example, when comparing the element of the above-described sample size (4 μm × 4 μm) with the element of 2 μm × 2 μm, the latter has a current density smaller by about one digit than the former, and the resistance increases. The reason for this is that the resistance of the flat part and the resistance of the side part of the MIM element are different, and it is more difficult for current to flow in the side part than in the flat part. It is conceivable that the current value becomes smaller as the element becomes finer, because it becomes larger. Therefore, when the size of the element is reduced, it is necessary to devise measures such as increasing the driving voltage or increasing the withstand voltage of the driver IC, which is not preferable in terms of power consumption and cost.

However, in the device of the present invention, the first
It has been confirmed by the present inventors that the above-described size dependence can be significantly reduced by adding tungsten to the conductive film. FIG. 41 shows the relationship between the element area and the current density at the ON voltage (15 V).
In this figure, the ratio of the current density (J _{(S = 16)} ) flowing through the MIM element having the size of 4 μm × 4 μm to the current density (J _S ) of each element is shown. In FIG. 41, one containing no tungsten (line a) and one containing different concentrations of tungsten (lines b to
e) is shown. From this figure, in the case of an element containing no tungsten, the size is changed from 4 μm × 4 μm to 2 μm ×
When the thickness is reduced to 2 μm, the current density is reduced by about one digit. For example, when 2 atomic% of tungsten is added, the reduction in the current density is only about 0.1 even under the same conditions.
It is 05 digits. Further, it can be seen from this figure that the higher the concentration of tungsten, the smaller the decrease in current density due to miniaturization.

As described above, by adding tungsten to the first conductive film, a decrease in current density due to miniaturization of the element can be suppressed.

The liquid crystal display device according to the present invention, wherein a transparent substrate, signal electrodes arranged on the substrate in a predetermined pattern, and connected to the signal electrodes at a predetermined pitch. And a first electrode substrate provided with a pixel electrode connected to the second conductive film of the nonlinear resistor, and a second electrode provided with a counter signal electrode at a position facing the pixel electrode. An electrode substrate, and a liquid crystal layer sealed between the first electrode substrate and the second electrode substrate.

[0075]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below in more detail.

(Example 1) FIG. 23 schematically shows a cross section of an MIM element 100 to which the present invention is applied.
FIG. 24 is a plan view showing one unit of a liquid crystal drive electrode using the MIM element of this embodiment. FIG. 23 is a view along the line AA in FIG.

The MIM element 100 has an insulating and transparent substrate, for example, a substrate 10 made of glass, plastic, or the like, and is formed on the surface of the substrate 10 and contains 0.2 to 6 atomic% of tungsten in tantalum. (In the embodiment, about 2 atomic%), from 1500 to 5000
A first conductive film 12 having a thickness of Å, an insulating film 14 formed on the surface of the first conductive film 12 by anodic oxidation and having a thickness of 300 to 700 Å, Formed, 300
And a second conductive film 16 having a thickness of about 2000 Å.

The MIM element 100 is manufactured by, for example, the following process.

(A) First, a tantalum film containing tungsten at a predetermined concentration is deposited on the substrate 10. The thickness of the tantalum film at this time is selected to be a suitable value depending on the use of the MIM element, and is usually about 1500 to 5000 angstroms (3000 angstroms in this embodiment). As a method for depositing a tantalum film containing tungsten, sputtering using a mixed target, simultaneous sputtering, or the like can be used, and the former is particularly preferable. The mixing ratio of the two in the mixture target of tantalum and tungsten is set in correspondence with the composition ratio of the two in the first conductive film to be formed. As a mixture target, for example, tantalum and tungsten are made into powder having a minute particle size (for example, 500 to 10000 angstroms, preferably 1000 to 3000 angstroms, and in this embodiment, about 2000 angstroms), and both are mixed. Can be used, or a material obtained by melting and alloying tantalum and tungsten can be used. As described above, by using the mixture target as the sputtering target, the first conductive film can be homogenized, more specifically, the tungsten can be localized and the distribution thereof can be made uniform as compared with the simultaneous sputtering using the individual targets. Can be.

Next, the tantalum film is patterned by commonly used photolithography and etching techniques to form the first conductive film 12 and the conductive portion 22a of the timing signal line 22 (see FIGS. 21 and 24). The patterning is achieved, for example, by applying a resist on the entire surface of the substrate 10, exposing and developing using a mask to form a resist pattern, and then performing etching. As an etching method, dry etching using a mixture of CF ₄ gas and O ₂ gas,
For example, wet etching using an etching solution in which hydrofluoric acid and nitric acid are mixed is used.

(B) Next, the upper portion of the first conductive film 12 is oxidized using an anodic oxidation method to form an insulating film 14 and an insulating portion (22b) of the timing signal line 22 (FIG. 2).
2, see FIG. 24). The insulating film 14 also has a preferable thickness depending on its use, and is usually about 300 to 700 angstroms. In this example, anodizing was performed in a 0.01% by weight aqueous citric acid solution at a constant voltage of 30 V for about 2 hours, whereby an insulating film having a thickness of about 530 Å was obtained.

(C) Next, at a temperature of about 300 to 400 ° C.
The first annealing process was performed at (400 ° C. in this embodiment) for 0.5 to 2 hours (1 hour in this embodiment).
This annealing treatment is usually performed in an inert gas atmosphere such as a nitrogen gas or an argon gas, or in an oxygen gas or an argon-hydrogen atmosphere.

By performing this annealing treatment, the chemical structure of the insulating film (anodic oxide film) can be stabilized. In the present embodiment, by adding a specific concentration of tungsten to the first conductive film 12, the temperature of this annealing process can be made considerably lower than a normal temperature (about 450 ° C.). As a result, for example, even when soda glass is used as the substrate, it is possible to make the substrate less susceptible to expansion and contraction due to heat. However, if the annealing temperature is lower than 300 ° C., the symmetry of the current-voltage curve in the MIM element becomes low, which is not preferable.

(D) Then, I
The TO film is laminated with a thickness of about 300 to 2000 Å (1000 Å in this embodiment),
Thereafter, patterning is performed using photolithography and etching techniques to form the second conductive film 16 and the pixel electrode 20 (see FIGS. 23 and 24). The sputtering conditions were as follows: power 1.7 KW, temperature 200 ° C., pressure 5 × 10 ⁻¹ Pa, flow rate ratio of oxygen to argon 5 × 10 ¹
It is ^-3 . As described above, by forming the second conductive film 16 from ITO, the formation of the second conductive film 16 and the formation of the pixel electrode 20 can be performed in the same step, so that the manufacturing process can be further simplified. .

(E) Thereafter, a second annealing treatment was performed at a temperature of 230 to 260 ° C. (250 ° C. in this embodiment) for 0.5 to 4 hours (2 hours in this embodiment). The annealing is preferably performed in an atmosphere containing oxygen at a rate of 5 to 100%, more preferably 50 to 100%. As gases other than oxygen, nitrogen gas,
Argon gas or the like is used.

Next, the results of an experiment on the second annealing process will be described. FIG. 25 is a graph showing the relationship between the annealing temperature and time in the second annealing process and the OMI of the formed MIM element.
The relationship with the FF current is shown. As an experimental sample, conditions other than the second annealing temperature were those manufactured by the process of the present embodiment, and the second annealing treatment was performed in a nitrogen atmosphere containing 50% oxygen. In FIG. 25, a is an OF when annealing is performed at an annealing temperature of 200 ° C., b is 250 ° C., and c is 300 ° C.
It shows the change in the F current. For example, if the annealing temperature is 2
In the case of 00 ° C., the OFF current decreases as the annealing time becomes longer, but the amount of the decrease is small and continues to change with the elapse of time and is not stable. When the annealing temperature is 300 ° C., the OFF current temporarily drops about 20 to 30 minutes after the start of the annealing, and thereafter continues to increase, and does not have a stable current characteristic.
Further, when the annealing temperature is 250 ° C., the OFF current is greatly reduced by the heat treatment for about 1 hour, and thereafter, the numerical value is almost stable thereafter. This tendency is 2
It was confirmed in the range of 30 to 260 ° C.

An experiment performed on the atmosphere in the second annealing process will be described. FIG. 26 shows the relationship between voltage and current when annealing is performed in different atmospheres. In FIG. 26, a shows the result when the annealing was not performed, b shows the result when the annealing was performed in a nitrogen gas atmosphere, and c shows the result when the annealing was performed in an oxygen gas atmosphere. From FIG. 26,
When the annealing is performed, the OFF current of the device is lower than when the annealing is not performed. Even when the annealing is performed, the OFF current is reduced by the annealing in the nitrogen gas atmosphere by the annealing in the oxygen gas atmosphere. It was confirmed that it was further reduced. It is considered that such a reduction in the OFF current is due to oxygen atoms in the atmosphere being diffused to the insulating film and the insulating film-metal interface by the heat treatment to fill the traps in these regions.

The size of the MIM element obtained as described above is selected from the point of use, function and the like, but one side is usually about 1 to 10 μm. MIM element 10 of the present embodiment
In the case of 0, the sizes indicated by S1 and S2 in FIG. 24 are each 4 μm.

Next, results of a characteristic test performed on the MIM element 100 will be described.

(1) Symmetry when voltages of different polarities are applied FIG. 27 shows voltage-current characteristics measured for the MIM element of this example. In FIG. 27, a curve a plotted by a black circle indicates a case where a positive bias voltage is applied, and a curve b indicated by a plot of a white circle indicates a voltage-current density (logJ) curve when a negative applied voltage is applied. . From FIG. 27, it was confirmed that in the MIM element of this example, the voltage-current curves when voltages having different polarities were applied almost completely, and the MIM element had extremely high symmetry.
The reason for obtaining such a result is that by forming an insulating film by anodic oxidation of a metal film in which a specific concentration of tungsten is added to tantalum, the barrier height at the interface between the first conductive film and the insulating film is reduced. It is considered that the barrier height at the interface between the insulating film and the second conductive film became substantially equal.

As a comparative sample, an MIM element was formed in the same manner as in the present embodiment except that tungsten was not added to the tantalum film of the MIM element of the present embodiment. I asked.
FIG. 28 shows the result. From FIG. 28, when tungsten is not added to the tantalum film, the voltage-current curve shifts significantly when a positive bias voltage is applied (line a) and when a negative bias voltage is applied (line b). It was confirmed that good symmetry could not be obtained.

(2) Change in Characteristics in Short Time FIG. 29 is a diagram showing the relationship between time and current corresponding to FIG. 5 obtained by applying the equation (2) to the MIM element of this embodiment. In FIG. 29, the line a is about 1 A for the MIM element.
/ Cm ² current injection for 10 seconds, and then apply an applied voltage of 1
The time-dependent change in the current value when the voltage is maintained at 0 V is shown. The line b shows the time-dependent change in the current value when the applied voltage is maintained at 10 V without performing the above-described current injection. From FIG. 29, it was confirmed that the time-current curves almost completely coincide with the case where the current injection was performed and the case where the current injection was not performed. As a result of examining the experimental results, the constant B in the equation (2) was 0.04 and n was -1.64.

Next, for comparison, the same measurement was performed on an MIM element formed by the same manufacturing method as that of this embodiment except that tungsten was not added to the tantalum film in the MIM element of this embodiment. The result is shown in FIG. FIG.
At 0, line a shows the result when there was current injection, and line b shows the result when there was no current injection. This time-
When the constants B and n in Equation (2) were determined from the current characteristics, B was 0.55 and n was -3.25.
As described above, when the absolute value of the constant B exceeds 0.2, in the active matrix type liquid crystal display device, for example, when displaying a moving image, an afterimage or display unevenness occurs.

(3) Long-term change in characteristics For the MIM element of this example, when the coefficient S was calculated based on the above equation (3), the value was 5.01 × 10 ⁻⁴ . Therefore, in the MIM element of this embodiment, even after driving for 10,000 hours, the change amount of the element characteristics (log (J
/ J ₀ )) is only about 1.63 × 10 ^-2 . Therefore, when this element is used for a liquid crystal display device, no burn-in phenomenon is observed even when driving for a long time. This MIM
According to the element, for example, the duty ratio is 1/200 to 1
Under the driving conditions of / 2000 and a driving voltage of 10 to 20 V, the display characteristics of the liquid crystal display device can be guaranteed for at least 10,000 hours.

For comparison, the coefficient S of the sample containing no tungsten in the tantalum film of this embodiment was 1.41 × 10 ⁻² . In the case of this element, the amount of change in element characteristics after driving for 10,000 hours was about 0.46, and in a liquid crystal display device using this element, the occurrence of image sticking was recognized by driving for a long time.

(4) Aging In the MIM device according to the embodiment of the present invention, when the concentration of added tungsten is low (for example, 0.4 at%),
The value of S in Expression (3) cannot be satisfied,
Its value is 5.62 × 10 ^-3 . Therefore, in this device, it is necessary to perform aging only for a time that satisfies the expression (4). In this case, according to the above equation (4), log (5.62 × 10 ⁻³ / 5) − (4/5) logt
<-3.2 logt> 0.3135 t> 2.06, and aging of at least 2.06 seconds is required. By performing aging for this time, burn-in was not recognized even in the subsequent long-time driving. Even after being left in the actual use temperature range, the characteristics after aging remained. On the other hand, in the case of the comparative example, when the aging time is obtained in the same manner as described above, it is at least 506.7 (seconds). In addition, in this comparative element, burn-in was not recognized at least in the drive immediately after aging.

(5) Activation Energy The activation energy Ea of the MIM element of this embodiment was calculated based on the above equation (1).
It was 0.42 eV at the F voltage. Also, this MI
The activation energy of the thermal stimulation current (TSC current) for the M element was about 0.2 eV.

As described above, when the activation energy in the above equation (1) is 0.534 eV or less, MI
The temperature dependency of the M element can be reduced, so that a liquid crystal display device using this element can maintain stable display characteristics in a wide temperature range, for example, a practical temperature range (room temperature to 80 ° C.). Further, by making the activation energy of the TSC current smaller than 0.7 eV, the MIM element can make the absolute value of the coefficient B in the above formula (2) 0.2 or less, and this element is used in a liquid crystal display device. When used, it is possible to eliminate the afterimage which has been a problem particularly in displaying moving images.

As described above, the MIM element of this embodiment is
Not only are basic characteristics such as non-linearity and symmetry in voltage-current characteristics excellent, but also stable characteristics that are not easily affected by heat or current injection can be maintained for a long time. In this MIM element, the second conductive film is made of ITO.
Therefore, the second conductive film can be formed simultaneously with the pixel electrode, and the process can be simplified.

(Embodiment 2) Since the MIM element of this embodiment has the same basic configuration as that of Embodiment 1, the description of the configuration is omitted. The difference between the MIM element of the present embodiment and the MIM element of the first embodiment is that the electrolytic solution is changed from a citric acid aqueous solution to an ammonium tungstate aqueous solution in forming an insulating film in the manufacturing process. That is, as an electrolyte used in anodization, 0.0
An aqueous solution of 0.01 to 0.05% by weight (0.005% by weight in this embodiment) of ammonium tungstate was used. Other conditions in the anodization are the same as those in Example 1,
That is, anodic oxidation was performed for 0.5 to 4 hours (2 hours in this example) using a constant voltage method of 20 to 40 V (30 V in this example).

It was confirmed that the MIM element of the present example was superior in the steepness of the voltage-current characteristics as compared with the MIM element of Example 1. FIG. 31 shows both voltage-current curves. In FIG. 31, a line a shows a characteristic curve of the present example, and a line b shows a characteristic curve when citric acid is used as an electrolytic solution for anodic oxidation. From FIG. 31, it can be seen that, when an aqueous solution of ammonium tungstate is used in the anodization, the voltage-current curve of the device has a greater steepness (gradient) than in the case where an aqueous solution of citric acid is used, and the writing characteristics to the liquid crystal layer are better. It was confirmed that Further, it has been confirmed that the same characteristics are exhibited even when a phosphoric acid aqueous solution is used as an electrolytic solution used in anodization.

(Embodiment 3) MIM element 400 of this embodiment
Uses a metal film (in this embodiment, a chromium film) of chromium, aluminum, titanium, molybdenum or the like instead of the second conductive film constituting the MIM element of the first embodiment. MI
The formation method and configuration of the first conductive film 12 and the insulating film 14 of the M element 400 (see FIGS. 32 and 33) are the same as those in the first embodiment, and therefore, detailed description thereof will be omitted. The second conductive film 18 has a thickness of 500, for example, by sputtering.
A chromium film having a thickness of about 3000 Å (in this embodiment, 1500 Å) is formed, and thereafter patterned using a commonly used photolithography and etching technique (see FIG. 34). Then I
The thickness of the TO film is 300 to 20 by sputtering or the like.
The pixel electrode 2 is deposited at 00 Å (500 Å in this embodiment), and a predetermined pattern is formed using photolithography and etching techniques.
0 is formed (see FIGS. 34 and 35). The MIM element 400 thus obtained is connected in a state where the second conductive film 18 and the pixel electrode 20 are overlapped.

In this MIM element 400, good results were obtained in each characteristic as in the first embodiment. That is, in this element, the value of the constant B in the equation (2) is 0.001, and n is -0.78. Further, it was confirmed that the value of the coefficient S in the equation (3) was 2.24 × 10 ⁻⁵ . Then, the above formula (1) for the OFF current
Activation energy is 0.40 eV and TS
It was confirmed that the activation energy of the C current was about 0.2 eV.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications can be made within the scope of the invention. For example,
Even when molybdenum, niobium, rhenium, WO ₃ or the like is used instead of tungsten as a substance added to the first conductive film, the same phenomenon as described in the above embodiment occurs.

FIG. 36 shows an equivalent circuit of an active matrix type liquid crystal display device using the MIM type nonlinear resistance element of the present invention. In this equivalent circuit, the MIM element 100 (400) and the liquid crystal cell 200 are connected in series at the intersection of the timing signal line (scanning line) X and the data signal line Y in each pixel region 300. Then, the display operation is controlled by switching the liquid crystal cell 200 to a display state, a non-display state, or an intermediate state based on signals applied to the timing signal line X and the data signal line Y.

The MIM type nonlinear resistance element of the present invention is particularly useful in such an active matrix type liquid crystal display device.

The active matrix type liquid crystal display device to which the non-linear resistance element of the present invention is applied is not particularly limited in its structure, but at least a transparent substrate, and a predetermined pattern provided on this substrate. Signal electrode (timing signal line, data signal line), a nonlinear resistor of the present invention connected to the signal electrode at a predetermined pitch, and a pixel electrode connected to the second conductive film of the nonlinear resistor. A first electrode substrate, a second electrode substrate provided with a counter signal electrode at a position facing the pixel electrode,
The display panel includes a liquid crystal layer sealed between the first electrode substrate and the second electrode substrate, and further includes members such as a polarizing plate and a color filter.

The liquid crystal display device of the present invention can be applied to all types of liquid crystal display devices. For example, when used in display devices such as liquid crystal televisions and video game machines,
An image with high display performance and no afterimage in a moving image can be displayed. Further, even when the liquid crystal display device of the present invention is used for a display means of a personal computer, a workstation, an OA device, or the like, an image with high display performance and no sticking in a fixed pattern can be displayed.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the concentration of tungsten added to a tantalum film and the current density of a MIM element when a chromium film is used as a second conductive film.

FIG. 2 is a diagram showing the relationship between the concentration of tungsten added to a tantalum film and the current density of a MIM element when an ITO film is used as a second conductive film.

FIG. 3 is a diagram showing a relationship between the concentration of tungsten added to a tantalum film and activation energy when chromium is used as a second conductive film.

FIG. 4 is a diagram illustrating a relationship between the concentration of tungsten added to a tantalum film and activation energy when an ITO film is used as a second conductive film.

FIG. 5 is a diagram showing the relationship between the time in constant voltage driving and the current density of the MIM element when current injection is performed or when current injection is not performed.

FIG. 6 is a diagram showing the relationship between the time obtained from the curve in FIG. 5 and the difference in current density.

FIG. 7 is a diagram showing a relationship between time and a difference between current densities for obtaining constants B and n in Expression (2).

FIG. 8 is a diagram showing the relationship between the concentration of tungsten added to a tantalum film and the constant B in equation (2) when chromium is used as the second conductive film.

FIG. 9 is a diagram showing the relationship between the concentration of tungsten added to a tantalum film and the constant B in equation (2) when ITO is used as the second conductive film.

FIG. 10 is a diagram showing a relationship between time and a difference in current density of the MIM element for deriving the equation (3).

FIG. 11 shows a time (t) obtained from the curve shown in FIG.
FIG. 3 is a diagram showing a relationship between ( ^1/5 ) and a difference in current density between MIM elements.

FIG. 12 is a diagram showing the relationship between the concentration of tungsten added to a tantalum film and the coefficient S in equation (3) when chromium is used as the second conductive film.

FIG. 13 is a diagram showing the relationship between the concentration of tungsten added to a tantalum film and the coefficient S in equation (3) when ITO is used as the second conductive film.

FIG. 14 is a diagram showing the relationship between time and the slope of the difference between the current values of MIM elements when 0.4% tungsten is added to a tantalum film.

FIG. 15 is a diagram showing a relationship between bias temperature and activation energy by TSC measurement in an insulating film.

FIG. 16 is a diagram showing the relationship between the concentration of tungsten added to the tantalum film and the current density of the MIM element when the temperature of the first annealing process is changed and chromium is used as the second conductive film. .

FIG. 17 is a diagram showing the relationship between the annealing temperature and the current density of the MIM element obtained from the data shown in FIG.

FIG. 18 is a diagram showing the relationship between the concentration of tungsten added to a tantalum film and the current density of the MIM element when ITO is used as the second conductive film.

FIG. 19 is a diagram showing the relationship between the annealing temperature and the current density of the MIM element obtained from the results of FIG.

FIG. 20 shows a flow rate ratio between oxygen and argon when forming ITO as the second conductive film, and a coefficient B in the above formula (2).
FIG.

FIG. 21 is a cross-sectional view schematically showing a manufacturing process of the MIM element of Example 1.

FIG. 22 is a cross-sectional view schematically showing a manufacturing process of the MIM element of Example 1.

FIG. 23 is a cross-sectional view schematically showing the MIM element of Example 1 (a cross-sectional view along line AA in FIG. 24).

FIG. 24 is a plan view of a unit electrode constituting an active matrix type electrode substrate to which the MIM element of Example 1 is applied.

FIG. 25 is a diagram showing the relationship between the annealing time and the current density when the temperature of the second annealing process is changed in the manufacturing process of the first embodiment.

FIG. 26 is a diagram showing the relationship between voltage and current when the type of gas in the atmosphere is changed in the second annealing process.

FIG. 27 is a diagram showing the relationship between voltage and current density when the polarity of the voltage applied to the MIM element of Example 1 is changed.

FIG. 28 is a diagram showing the relationship between voltage and current density when the polarity of the voltage applied to the MIM element for comparison is changed.

FIG. 29 is a diagram showing the relationship between the time in constant voltage driving and the current density of the MIM element when current injection is performed or when current injection is not performed.

FIG. 30 is a diagram showing the relationship between the time in constant voltage driving and the current density of the MIM element for comparison when current injection is performed or when current injection is not performed.

FIG. 31 is a diagram showing a relationship between voltage and current when an aqueous solution of ammonium tungstate is used as an anodizing electrolytic solution in Example 2.

FIG. 32 is a cross-sectional view schematically showing a manufacturing process according to the third embodiment of the present invention.

FIG. 33 is a cross-sectional view schematically showing a manufacturing process according to the third embodiment of the present invention.

34 is a cross-sectional view schematically showing the MIM element of Example 3 of the present invention (a cross-sectional view along the line BB in FIG. 35).

35 is a plan view schematically showing a unit electrode constituting an electrode substrate using the MIM element shown in FIG. 34.

FIG. 36 is a diagram showing an active matrix driving circuit using the MIM element of the present invention.

FIG. 37 is an electron micrograph of the surface of an ITO film obtained by sputtering with the condition of the flow ratio of oxygen and argon changed.

FIG. 38 is an electron micrograph of the surface of an ITO film obtained by sputtering with the condition of the flow ratio of oxygen and argon changed.

FIG. 39 is an electron micrograph of the surface of the ITO film obtained by sputtering with the condition of the flow ratio of oxygen and argon changed.

FIG. 40 is an electron micrograph of the surface of an ITO film obtained by sputtering with the condition of the flow ratio of oxygen and argon changed.

FIG. 41 is a diagram showing the relationship between the element area and the difference in current density at ON voltage.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Substrate 12 1st conductive film 14 insulating film 16 2nd conductive film 20 pixel electrode 22 timing signal line 22a conductive part 22b insulating part 100 MIM element

 ──────────────────────────────────────────────────続 き Continued on the front page (31) Priority claim number Japanese Patent Application No. 5-106930 (32) Priority date May 7, 1993 (5.7.1993) (33) Priority claim country Japan (JP) (72) Inventor Takashi Inoue 3-3-5 Yamato, Suwa-shi, Nagano F-term in Seiko Epson Corporation (reference) 2H092 JA03 JA13 KA07 KA10 KA18 MA05 MA24 MA29 NA22 5C094 AA02 AA43 AA44 BA04 BA43 CA19 DA14 DA15 EA04 EA07 EB02 FB12 FB14 FB15 5E034 CA10 CB08 CC20 DA02 DA07 DE13 DE16

Claims (22)

[Claims] 1. A non-linear resistance element comprising a first conductive film, an insulating film, and a second conductive film laminated on a substrate, wherein the insulating film is an anodic oxide film of the first conductive film. The second conductive film is at least one of a chromium film and a transparent conductive film, and a current density (J) flowing through the element is approximately represented by the following equation (1). Wherein the activation energy (Ea) is 0.534 eV or less. Equation (1) J = Aexp (−Ea / kT) where A is a constant, k is a Boltzmann constant, and T is an absolute temperature. 2. The non-linear resistance element according to claim 1, wherein the first conductive film is a metal film in which tungsten is added to tantalum as a main component. 3. The nonlinear structure according to claim 1, wherein the second conductive film is formed of chromium, and the concentration of tungsten added to the first conductive film is 0.8 to 6 atomic%. Resistance element. 4. The method according to claim 1, wherein the second conductive film is a transparent conductive film, and the concentration of tungsten added to the first conductive film is 1.2 to 6 atomic%.
A nonlinear resistance element characterized by the following. 5. A non-linear resistance element comprising a first conductive film, an insulating film, and a second conductive film laminated on a substrate, wherein the insulating film is an anodic oxide film of the first conductive film. The second conductive film is at least one of a chromium film and a transparent conductive film, and a 10 V bias voltage is applied to the device after performing a current injection at a current density of 1 A / cm ² for 10 seconds. When the current density is J ₂ , 10 V without current injection
When the current density when a bias voltage is applied to J _1, approximately the following formula (2) is satisfied, in the equation (2), the constant B and the n | B | ≦ 0.2 and n
A non-linear resistance element, wherein a relationship of ≦ 0 is satisfied. Equation (2) log (J ₂ / J ₁ ) = B × t ^{1 / n} Here, t represents an elapsed time (second) after application of the bias voltage. 6. The nonlinear resistance element according to claim 5, wherein the first conductive film is a metal film in which tungsten is added to tantalum as a main component. 7. The nonlinear structure according to claim 5, wherein the second conductive film is formed of chromium, and a concentration of tungsten added to the first conductive film is 0.2 to 6 atomic%. Resistance element. 8. The method according to claim 5, wherein the second conductive film is a transparent conductive film, and the concentration of tungsten added to the first conductive film is 0.3 to 6 atomic%.
A nonlinear resistance element characterized by the following. 9. A non-linear resistance element comprising a first conductive film, an insulating film, and a second conductive film laminated on a substrate, wherein the insulating film is an anodic oxide film of the first conductive film. The second conductive film is at least one of a chromium film and a transparent conductive film, and when a voltage in a predetermined range is applied to the element, the following expression (3) is approximately established. ), Wherein the coefficient S is 3.1 × 10 ⁻³ or less. Equation (3) log (J / J ₀ ) = S × t ^{1 / m} where, t is the elapsed time (second) from the start of driving, and J is the current density (A / cm ² ), and J ₀ is the current density (A / c) when the elapsed time t is 1 second.
m ² ), and m ≧ 1. 10. The nonlinear resistance element according to claim 9, wherein m in Expression (3) is 5. 11. The nonlinear resistance element according to claim 9, wherein the first conductive film is a metal film in which tungsten is added to tantalum as a main component. 12. The method according to claim 9, wherein the second conductive film is formed of chromium, and a concentration of tungsten added to the first conductive film is 0.3 to 6 atomic%. Characteristic nonlinear resistance element. 13. The method according to claim 9, wherein the second conductive film is a transparent conductive film, and the concentration of tungsten added to the first conductive film is 0.7 to 6 atomic%.
A nonlinear resistance element characterized by the following. 14. A nonlinear resistance element formed on a substrate, comprising a first conductive film, an insulating film, and a second conductive film, wherein the insulating film is an anodic oxide film of the first conductive film. The second conductive film is at least one of a chromium film and a transparent conductive film, and the above formula (3) is approximately established when a predetermined voltage is applied to the element. 5 and the coefficient S exceeds 3.1 × 10 ⁻³ ,
Aging is performed for at least time t seconds so as to satisfy the following condition. Equation (4) log (S / 5) − (4/5) log t <−3.2 15. The nonlinear resistance element according to claim 14, wherein the first conductive film is a metal film in which tungsten is added to tantalum as a main component. 16. A non-linear resistance element comprising a first conductive film, an insulating film and a second conductive film laminated on a substrate, wherein the insulating film is an anodic oxide film of the first conductive film. Wherein the second conductive film is at least one of a chromium film and a transparent conductive film, and the activation energy of a thermal stimulation current (TSC current) in the insulating film is lower than 0.7 eV. Resistance element. 17. The nonlinear resistance element according to claim 16, wherein the first conductive film is a metal film in which tungsten is added to tantalum as a main component. 18. The nonlinear resistance element according to claim 16, wherein the activation energy is 0.3 eV or less. 19. The nonlinear structure according to claim 16, wherein the second conductive film is formed of chromium, and a concentration of tungsten added to the first conductive film is 0.2 to 6 atomic%. Resistance element. 20. The method according to claim 16, wherein the second conductive film is a transparent conductive film, and the concentration of tungsten added to the first conductive film is 0.2 to 6 atomic%.
A nonlinear resistance element characterized by the following. 21. The nonlinear resistor according to claim 1, wherein a transparent substrate, signal electrodes arranged on the substrate in a predetermined pattern, and connected to the signal electrodes at a predetermined pitch. An element, a first electrode substrate including a pixel electrode connected to a second conductive film of the non-linear resistance element, a second electrode substrate including a counter signal electrode at a position facing the pixel electrode, A liquid crystal display device comprising: a first electrode substrate and a liquid crystal layer sealed between the second electrode substrate. 22. A liquid crystal display device using the nonlinear resistance element according to claim 1.