JPH08262500A - Solid-state device having nonlinear element - Google Patents

Abstract

PURPOSE: To make it possible to improve the stability of current-current characteristics with lapse of time, etc., by independently constituting nonlinear elements without using the wiring layers of a solid-state device as constituting elements. CONSTITUTION: The nonlinear element 20 of a MIM type is composed of a Ta electrode layer 22 conducted and connected to a scanning circuit (driving circuit) side via a scanning line, a Ta2 O5 film 23 (anodically oxidized film) formed by anodic oxidation in an aq. citric acid soln. on the surface of this Ta electrode layer 22 and a Cr electrode layer 25 formed on the front surface side of this anodically oxidized film 23. The MIM nonlinear element 20 is conducted and connected via this Cr electrode layer 25 to a pixel electrode 24 consisting of ITO on its signal supply circuit side. Namely, the nonlinear element 20 does not include the pixel electrode 24 as its constituting element but is independently composed of the Ta electrode layer 22, the Ta2 O5 film 23 and the Cr electrode layer 25. Then, the selection of the Cr layer, etc., in preference to the operating characteristics as the nonlinear element 20 is possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state device having a non-linear element, and more particularly to a technique for stabilizing the switching operation of the non-linear element.

[0002]

2. Description of the Related Art In an active matrix type liquid crystal display panel, which is a typical solid-state device provided with a non-linear element, a non-linear element is provided for each pixel area to form a matrix array, and a color filter is formed. Liquid crystal is filled between the substrate and the other substrate, and the alignment state of the liquid crystal in each pixel region is controlled to display predetermined information. Here, a three-terminal element such as a TFT or a two-terminal element is used as the non-linear element, but a method using the two-terminal element is used in order to meet the demand for a larger screen and lower cost of the liquid crystal display panel. Is advantageous.
Moreover, when the two-terminal element is used, the scanning lines can be provided on the substrate on one side where the matrix array is formed, and the signal lines can be provided on the substrate on the other side. Therefore, the crossover between the scanning lines and the signal lines is possible. There is also an advantage that a short circuit does not occur.

In an active matrix type liquid crystal display panel using such a two-terminal element, as shown in FIG. 2, each scanning line 11 and each signal line 1 in each pixel region 1a.
2 and a non-linear element 2 (indicated by a varistor symbol in the figure) and a liquid crystal display element 3 (indicated by a symbol in the figure) are connected in series.
Based on the signal applied to the signal line 12, the liquid crystal display element 3 is switched between the selected state (display state) and the non-selected state (non-display state) to control the display operation. That is, as indicated by the solid line 31 in FIG.
Since the applied voltage V _NL and the current I _NL have a non-linear relationship, the threshold voltage of the nonlinear element 2 is V _th , the potential at which the liquid crystal display element 3 is in the non-display state is V _a , and the display state is Assuming that the potential is (V _a + ΔV),
As shown in (b), the potential difference V (applied voltage to the unit pixel) between the scanning line 11 and the signal line 12 in the predetermined pixel region 1a is set to (V _a + V _th ), whereby the nonlinear element 2 Is cut off to bring the liquid crystal display element 3 into a non-selected state, while the potential difference V between the scanning line 11 and the signal line 12 is
_{Is set} to (V _a + V _th + ΔV), the non-linear element 2 is brought into conduction and the liquid crystal display element 3 is brought into a selected state.

Here, as shown in FIG. 5, the non-linear element 2 is conventionally formed on the front surface side of the transparent substrate 51 and conductively connected to the scanning circuit (driving circuit) side via the scanning line 11. Ta electrode layer 52 and Ta ₂ O ₅ on the surface side thereof
The diode type non-linear element 50 includes a film 53 and a pixel electrode 54 made of ITO formed on the surface side of the film 53. Here, the Ta ₂ O ₅ film 53 is formed by anodizing the Ta electrode layer 22 so that the Ta ₂ O ₅ film 53 is formed on the surface of the Ta electrode layer 22 with a uniform film thickness and without pinholes. An aqueous solution of citric acid is used as the electrolytic solution for anodic oxidation.

[0005]

However, in the liquid crystal display panel using the non-linear element 50, an afterimage is more likely to occur after displaying a still image, etc.
There is a problem that the display performance is low. The cause has not been known so far, but as a result of investigating the relationship between each constituent element of the matrix array and the display performance, the present inventor found that the cause was the stability of the current-voltage characteristics of the nonlinear element 50 with time. I confirmed there was a problem.

That is, in the nonlinear element 50, the relationship between the applied voltage V _NL and the current I _NL is as shown in FIG.
This is because the relationship indicated by the solid line 31 in (a) shifts over time as indicated by the broken line 32 or the alternate long and short dash line 33. Here, the applied voltage V _NL and the current I _NL
When the relationship between the scanning line 11 and the signal line 1 is changed from the display state to the non-display state,
The potential difference V from 2 is (V _a + V _th + ΔV) to (V _a + V
Even if it is switched to _th ), the non-linear element 50 cannot be switched and controlled from the conductive state to the cutoff state, and an afterimage is generated. The same applies to the case of the reverse display operation.

In order to solve such a problem, the inventor of the present application changed Ta ₂ by changing the current density and the liquid temperature in the anodic oxidation among the conventional anodic oxidation conditions and further by using another organic acid. An O ₅ film was formed, and the temporal stability of the relationship between the applied voltage V _NL and the current I _NL in each nonlinear element was examined. To improve the stability of any Ta ₂ O ₅ film, It didn't come.

In view of the above problems, the object of the present invention is to:
An object of the present invention is to realize a solid-state device including a non-linear element that can stabilize the relationship between the applied voltage and the current characteristics with time while ensuring the cost advantage of using the non-linear element.

[0009]

In order to solve the above-mentioned problems, the means taken in the solid state device according to the present invention is such that a non-linear element formed on the front surface side of a substrate is conductively connected to one circuit side thereof. The first metal electrode layer, the anodic oxide film formed on the surface of the metal electrode layer, and the second metal electrode layer formed on the surface side of the anodic oxide film are included in the second metal electrode layer. The non-linear element is conductively connected to the other circuit side through the metal electrode layer.

[0010]

In the present invention, the non-linear element is conductively connected to the other circuit side through the second metal electrode layer, and the circuit is formed by the first metal electrode layer, the anodic oxide film and the second metal electrode layer. It has become independent from the side. Therefore, since the wiring layer and the pixel electrode on the other circuit side are not constituent elements of the non-linear element, the material of the second metal electrode layer and the like can be selected so as to suit the operating characteristics of the non-linear element.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a solid-state device having a nonlinear element according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[Embodiment 1] FIG. 1 is a sectional view showing a configuration of a non-linear element of a solid-state device according to Embodiment 1 of the present invention.
The operation of the non-linear element of this example is similar to that of the conventional non-linear element, and its operation characteristics and the like will be described with reference to FIGS. 2 and 3.

As shown in FIG. 1, the MIM type non-linear element 2 of the present example (hereinafter referred to as the MIM type non-linear element 20).
Is a Ta electrode layer 22 (first metal electrode layer) that is conductively connected to the scanning circuit (driving circuit) side via the scanning line 11, and the surface of the Ta electrode layer 22 is anodized in an aqueous citric acid solution. The formed Ta ₂ O ₅ film 23 (anodized film),
Cr electrode layer 2 formed on the surface side of this anodic oxide film 23
5 (second metal electrode layer), and the MIM non-linear element 20 via the Cr electrode layer 25.
Is the pixel electrode 2 made of ITO which is the signal supply circuit side.
4 is conductively connected. That is, the nonlinear element 2 does not include the pixel electrode 24 as its constituent element but Ta element.
Electrode layer 22, Ta ₂ O ₅ film 23, and Cr electrode layer 25
Is independently configured by.

Therefore, as the second metal electrode layer, the Cr layer or the like can be selected without giving priority to the configuration of the solid-state device and giving priority to the operating characteristics as the non-linear element. is there. For example, the MI of this example
In the M-type non-linear element 20, the applied voltage V _NL and the current I
The relationship with _NL is shown by the solid line 31 in FIG.
The relationship shown in FIG. 3 holds the relationship of the solid line 31 even after the electric potential is applied for a long time.
There is no shift to the relationship indicated by the broken line 32 or the alternate long and short dash line 33 in (a). Therefore, for example, even in the case of the circuit configuration shown in FIG. 2, the MIM nonlinear element 20 is surely brought into the conducting state or cut off based on the signals applied to the scanning line 11 and the signal line 12, respectively. The state is switched and controlled. Therefore, this MIM type non-linear element 20
The solid-state device using is highly reliable in operation.

Second Embodiment Next, a liquid crystal display panel (solid state device) according to a second embodiment of the present invention and a method for manufacturing the same will be described. Here, the structure and operation of the matrix array are the same as those of the MIM type nonlinear device 20 of the first embodiment.
Since it is the same as the above, the description will be made similarly with reference to FIG. 1, but the corresponding portions are denoted by the same reference numerals. Moreover, since the operation thereof is similar to that of the conventional non-linear element, the same operation as in FIG.
And it demonstrates with reference to FIG.

In the active matrix type liquid crystal display panel (solid-state device) according to this example, as shown in FIGS. 1 and 2, a scanning circuit (driving circuit) is provided via a scanning line 11 for each pixel region 1a of the matrix array. A Ta electrode layer 22 (first metal electrode layer) conductively connected to the circuit side, and Ta formed on the surface of the Ta electrode layer 22 by anodic oxidation.
_The MIM is composed of a ₂ O ₅ film 23 (anodic oxide film) and a Cr electrode layer 25 (second metal electrode layer) formed on the surface side of the anodic oxide film 23 and conductively connected to the pixel electrode 24 made of ITO. Type nonlinear element 2 (hereinafter referred to as MIM type nonlinear element 20).

) Is configured. That is, the MIM type non-linear element 20 does not include the pixel electrode 24 as its constituent element but is independently provided by the Ta electrode layer 22, the Ta ₂ O ₅ film 23, and the Cr electrode layer 25 (second metal electrode layer). It is configured.

Here, inside the Ta ₂ O ₅ film 23, V
A borate anion is doped as a doping material containing a group element in its composition. Therefore, in the MIM nonlinear element 20 of the present example, the relationship between the applied voltage V _NL and the current I _NL is shown by a solid line 31 in FIG. The relationship shown in FIG. 3 holds the relationship of the solid line 31 even after the potential is applied for a long time to display a still image, for example.
There is no shift to the relationship indicated by the broken line 32 or the alternate long and short dash line 33 in (a). The stability is extremely high even when compared with the MIM type nonlinear element of the first embodiment. Therefore, the scanning line 11 and the signal line 12 generated based on the signals applied to the scanning line 11 and the signal line 12, respectively.
The potential difference generated between the liquid crystal display element 3 and the liquid crystal display element 3 can reliably switch the liquid crystal display element 3 between the selected state and the non-selected cutoff state to control the display operation. That is, as shown in FIG. 3B, by setting the potential difference V between the scanning line 11 and the signal line 12 to (V _b + V _th ), the MIM type non-linear element 20 is turned off, and the liquid crystal display element is displayed. 3 is set to the non-display state (non-selected state), while the potential difference V between the scanning line 11 and the signal line 12 is set to (V _b + V _th + ΔV), the MIM type nonlinear element 20 is set to the conductive state. When the liquid crystal display element 3 is brought into the display state (selected state), the MI
Since the relationship between the applied voltage V _NL of the M-type non-linear element 20 and the current I _NL is extremely unlikely to shift depending on the usage history, it follows the changes in the signals from the scanning line 11 and the signal line 12 and the The orientation state changes. Therefore, the liquid crystal display panel has no afterimage and the display quality is high.

A method of manufacturing a liquid crystal display panel having such a structure will be described below.

First, a Ta layer is formed by sputtering on the surface side of the transparent substrate 21 on which the Ta oxide layer 21a and the like are formed in advance, and then the Ta layer is patterned to form a Ta electrode layer 22. The Ta electrode layer 22 also extends to the scanning circuit to form the scanning line 11.

Next, the Ta electrode layer 22 is anodized to form a surface layer of the Ta ₂ O ₅ film 23. Here, an aqueous solution of boric acid is used as the anodizing electrolyte. First, the transparent substrate 21 on which the Ta electrode layer 22 is formed is immersed in the anodizing electrolyte solution, and the current value of the constant current / constant voltage power source is set so that the initial current density is 0.1 mA / cm ^2. Then, anodization is performed under constant current conditions. At this time, the set voltage of the constant current constant voltage power supply is set to a voltage value corresponding to a predetermined film thickness, usually 30 to 40 v. here,
When anodic oxidation is performed for about 15 minutes under constant current conditions, Ta ₂
The power supply voltage rises with the growth of the O ₅ film, and after the power supply voltage reaches the set voltage, a constant voltage anodization process occurs and the leakage current attenuates. In this state, hold for about 2 hours to make the thickness of 500 Å on the surface of the Ta electrode layer 22.
Then, a Ta ₂ O ₅ film 23 is formed. The liquid temperature of the anodizing electrolyte is room temperature.

Thereafter, Cr is sputtered on the surface of the Ta ₂ O ₅ film 23 and patterned to form a Cr electrode layer 25. The Ta electrode layer 22, the Ta ₂ O ₅ film 23 and the Cr electrode layer 25 are separated from each other. The MIM type non-linear element 20 is formed. Here, as shown in FIG. 1, when the pixel electrode 24 is formed below the Cr electrode layer 25,
It is formed before the step of forming the Cr electrode layer 25, but the order of the step of forming the pixel electrode 24 is as follows.
It is arbitrarily set depending on the relationship with the etchant species that etches it.

In the MIM type non-linear element 20 formed by such an anodizing process, since boric acid is mixed as an anion species in the anodizing electrolyte solution, Ta ₂ O ₅ is added in the anodizing process. With growth, borate anions penetrate into the Ta ₂ O ₅ film 23. Further, it can be presumed that the invasion affects the stabilization of the grain boundaries of the Ta ₂ O ₅ film 23, the crystallinity, or the like. Therefore, in order to modify the Ta ₂ O ₅ film 23, it is possible to dope the borate anion by using the step of forming the Ta ₂ O ₅ film 23 without using a process such as ion implantation. Therefore, since the number of steps is not increased, the cost merit of using the MIM type non-linear element 20 in the matrix array of the liquid crystal display panel is not sacrificed.

Now, the result of studying the relationship between the liquid composition (boric acid concentration) of the anodizing electrolyte solution and V _th of the MIM type non-linear element 20 among the anodizing conditions will be described.

In this example, (NH ₄ ) ₂ B ₄ 0 ₇ .4H
_A predetermined amount of water was added to 85 wt% ammonium tetraborate tetrahydrate represented by 20, to prepare various anodizing electrolyte solutions, and the ammonium tetraborate concentration and
The relationship with the stability of V _th of the MIM type non-linear element 20 was examined. Here, the relationship between the applied voltage and the current in the MIM type nonlinear element is generally expressed by the following equation.

I = αVexp (βV ^1/2 ) where α is a conductivity coefficient and β is a non-linear coefficient, which is expressed by the following equation.

Α = (nμq / d) exp (−φ / kT) β = (1 / kT) (q ³ / πε ₁ ε ₀ d) ^1/2 where n: carrier density, μ: carrier , Q: electron charge amount d: film thickness, φ: trap depth, k: Boltzmann constant,
T: Ambient temperature ε ₁ , ε ₀ : Permittivity Therefore, when log (I / V) is plotted against V ^1/2 , it is represented by a substantially straight line as shown by a solid line 41 in FIG. In the examination in this example, as the threshold voltage V _th , the applied voltage value when a current value of 10 mA / cm ² flows is V _th1 , and the applied voltage value when a current value of 10 μA / cm ² flows is V _th2 . Based on these values, the stability of V _th of the MIM type non-linear element 20 was evaluated. That is, the applied voltage value V corresponding to the predetermined current value
_th1 or V _th2, in the conventional MIM nonlinear device, between time and a potential is applied, a voltage [Delta] V _th where V _th1 or V _th2 is shifted, as shown by the solid line 42 in FIG. 4 (b) It has been confirmed that there is a relation and that it causes a decrease in display stability.
Then, the same potential was applied to the MIM type non-linear element of this example, and ΔV _th after a predetermined time passed was compared.
Therefore, it is preferable that the value of ΔV _th is small.

(Relationship Between Anodic Oxidation Electrolyte Composition and Initial _Vth ) First, the composition of the anodic electrolyte solution is [(NH ₄ ) ₂ B
₄ 0 ₇ 4H ₂ 0] / [(NH ₄ ) ₂ B ₄ 0 ₇ 4H ₂ 0 + H ₂
[0] wt% is changed to form the MIM type non-linear element 20, and the relationship between the composition of the electrolytic solution for anodization and the initial V _th1 or V _th2 of each MIM type non-linear element 20 is shown in Table 1. . Table 1 shows the case where the Ta electrode layer 22 has a positive potential with respect to the Cr electrode layer 25 and the Ta electrode layer 22.
With respect to the Ta electrode layer 22, the composition of the anodizing electrolyte solution and V _th1 , V
The relationship with _th2 is shown.

[0029]

[Table 1]

As shown in Table 1, as the concentration of boric acid in the anode electrolyte solution was increased, V _th1 and V th
Both _th2 tend to decrease. This trend is
The same applies regardless of the direction in which the potential is applied. Therefore, in the MIM type non-linear element 20 of the present example, it is possible to improve the display operation as follows by utilizing the fact that the low voltage is sufficient to pass the same current. For example,
In the Ta ₂ O ₅ film 23 of this example, the values of V _th1 and V _th2 are small even if the film thickness is the same as the film thickness of the Ta ₂ O ₅ film formed in the conventional citric acid aqueous solution. ,
This shows that the driving voltage can be lowered. On the contrary, when the values of V _th1 and V _th2 of the MIM type non-linear element 20 of the present example are made the same as the values of V _th1 and V _th2 of the conventional MIM type non-linear element, the Ta ₂ O ₅ film 23 is formed. The film thickness can be increased to, for example, about 1000Å. Therefore, the generation of microscopic pinholes can be prevented, and at the same time, the Ta ₂ O
_Since the capacitance component of the _five film 23 can be reduced, it is possible to prevent display point defects, crosstalk, and the like, and improve the initial display quality.

(Relationship Between Anodic Oxidizing Electrolyte Composition and _Vth Shifted Value) Next, with respect to the MIM type non-linear element 20 used in the above-described examination, the change with time of _Vth2 was investigated. In this study, first, after measuring V _th2 , 6 vDC is applied for 300 seconds, V _th2 after the application is measured, the shifted value ΔV _th2 is obtained, and the magnitude is compared. As boric acid concentration in the anode electrolyte solution obtained in the study of the present example _{[(NH 4) 2 B 4 0} 7 · 4H 2
0] / [(NH ₄ ) ₂ B ₄ 0 ₇ 4H ₂ 0 + H ₂ 0] wt%
And the relationship between ΔV _th2 and ΔV _th2 are shown in Table 2. Table 2 also shows the case where the Ta electrode layer 22 has a positive potential with respect to the Cr electrode layer 25 and the Ta electrode layer 22 has a negative potential applied to the Cr electrode layer 25.

[0032]

[Table 2]

As shown in Table 2, as the concentration of boric acid in the electrolytic solution for the anode is increased, ΔV _th2 is reduced accordingly. This tendency is the same regardless of the direction in which the potential is applied.

As described above, in the liquid crystal display panel of this example, when forming the Ta ₂ O ₅ film 23 of the MIM type non-linear element 20 forming the matrix array, an aqueous solution of boric acid is used as the anodizing electrolyte. By M
The change in V _th of the IM-type nonlinear element 20 with time is suppressed to stabilize the switching operation. Therefore, the change in the alignment state of the liquid crystal used in the liquid crystal display panel follows the change in the potential difference V between the scanning line 11 and the signal line 12. As a result, in the liquid crystal display panel,
Even when the fixed pattern is displayed for a long period of time, high quality display is possible without occurrence of afterimages and flicker.

The effect of the invaded boron or borate anion is derived from the results of repeated experiments, so the mechanism has not been elucidated. For example, particles of the Ta ₂ O ₅ film 23 It is also considered that it influences the relation with the stabilization of the field or the relation with the crystallization of the Ta ₂ O ₅ film 23. Therefore, the anion which can be obtained by adding the doping material, that is, the anodizing electrolyte solution, is not limited to the borate anion,
It can be envisioned that it may be a group oxyanion.
Further, although these anion species may be used alone, a plurality of anion species may be used at the same time, or may be blended in the anodizing electrolytic solution together with other components such as ammonium.

In this example, the relationship between the composition of the phosphoric acid-based anodic oxidation electrolyte solution and the effect of suppressing the V _th shift of the MIM type nonlinear element 20 over time is as shown in Table 2. Not limited to this, it shifts depending on the current density and liquid temperature at that time. Thus, in Table 2, _{[(NH 4) 2 B 4 0} 7 ·
4H ₂ 0] / [(NH ₄ ) ₂ B ₄ 0 ₇ · 4H ₂ 0 + H ₂ 0] w
t% is about 0.215 wt% or more, especially about 1.0 wt%
Although the remarkable effect is obtained as described above, when the current density at the time of anodic oxidation is further increased, the region where the effect is exhibited tends to be further expanded. Therefore, the concentration condition of the composition is set to the optimum condition depending on the current density and the liquid temperature.

Further, in this example, the chromium layer was used as the second metal electrode layer, but the present invention is not limited to this, and a titanium layer, an aluminum layer, or the like can also be used without limitation.

Further, although the tantalum layer is used as the first metal electrode layer, the present invention is not limited to this, and any metal capable of forming an insulating layer by utilizing anodizing treatment and forming a non-linear element can be used. It may be another metal layer.

[0039]

As described above, in the present invention, the non-linear element formed on the surface side of the substrate is formed on the first metal electrode layer conductively connected to one circuit side and on the surface of this metal electrode layer. And a second metal electrode layer formed on the surface side of the anodic oxide film, and the non-linear element is connected to the other circuit side via the second metal electrode layer. It is characterized in that it is conductively connected. Therefore, according to the present invention, since the non-linear element is configured independently without using the wiring layer of the solid-state device as a component,
A metal layer suitable for a non-linear element can be used as the second metal electrode layer. Therefore, it is possible to improve the temporal stability of the current-current characteristics.

[Brief description of drawings]

FIG. 1 is an MIM according to a first embodiment or a second embodiment of the present invention.
It is sectional drawing which shows the structure of a non-linear element.

FIG. 2 is an equivalent circuit diagram of an active matrix type liquid crystal display panel.

FIG. 3A is a graph showing the relationship between applied voltage and current of a non-linear element forming a matrix array of a liquid crystal display panel, and FIG. 3B shows the relationship between applied voltage to a unit pixel and display brightness. It is a graph figure which shows.

FIG. 4A is a graph diagram in which log (I / V) is plotted with respect to V ^1/2 as a relationship between applied voltage and current of a MIM type non-linear element forming a matrix array of a liquid crystal display panel; (B) is a graph showing the relationship between the time when a potential is applied to the MIM type non-linear element and the shifted value of V _th .

FIG. 5 is a cross-sectional view of a conventional diode type non-linear element.

[Explanation of symbols]

1 ... Liquid crystal display panel 1a ... Pixel area 2 ... Non-linear element 3 ... Liquid crystal display element 11 ... Scan line 12 ... Signal line 20 ... MIM type non-linear element 21, 51 ... ..Transparent substrate 22, 52 ... Ta electrode layer (first metal electrode layer) 23, 53 ... Ta ₂ O ₅ film (anodized film) 24, 54 ... Pixel electrode 25 ... Cr Electrode layer (second metal electrode layer) 50 ... Non-linear element of diode type

Claims (1)

[Claims] 1. A non-linear element formed on a front surface side of a substrate, and a first metal electrode layer conductively connected to one circuit side,
It is composed of an anodized film formed on the surface of the metal electrode layer and a second metal electrode layer formed on the surface side of the anodized film, and via the second metal electrode layer, A solid-state device having a non-linear element, wherein the non-linear element is conductively connected to the other circuit side.