JPH02119203A - Thin-film type voltage nonlinear resistor - Google Patents

Abstract

PURPOSE:To obtain a symmetric type resistor whose nonlinear coefficient is large, whose threshold voltage can be controlled, which is thin and can be reduced in size and enables stability of characteristics to be obtained by a method wherein a resistor has a laminated film consisting of a thin zinc oxide film layer, a thin lead oxide film layer and a thin zinc oxide film layer wherein a specific amount of manganese oxide is added to the thin zinc oxide film layers. CONSTITUTION:A resistor has a laminated thin film structure consisting of an insulating substrate 1, a lower electrode thin film layer 2 formed on the insulating substrate 1, a laminated film consisting of a thin zinc oxide film layer 3, thin load oxide film layer 4 and a thin zinc oxide film layer 3 laminated sequentially on a required portion on the lower electrode thin film layer 2 and the insulating substrate 1, and an upper electrode thin film layer 5 formed on the laminated film, wherein manganese oxide has been added to the thin zinc oxide film layers 3 by 0.5 to 1.0mol.% expressed in terms of MnO. For example, fused quartz, sapphire, etc., may be used in the substrate 1 and gold, platinum, palladium, etc., may be used in the electrode thin film layers 2, 5. In addition, the thin zinc oxide film layer 3 and the thin lead oxide film layer 4 containing manganese oxide are molded by means of high frequency magnetron sputtering at substrate temperature of 300 deg.C.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a thin film type voltage nonlinear resistor, in particular a thin film mainly composed of zinc oxide and an insulating film mainly composed of lead oxide are laminated on a substrate. This invention relates to a thin film voltage nonlinear resistor that exhibits symmetrical voltage-current characteristics obtained by

[Conventional technology]

A voltage nonlinear resistor (hereinafter referred to as a varistor) is usually (1
) indicates a non-ohmic symmetrical voltage-current characteristic as expressed by the percentage of the equation.

I/i − (V/Vi) α (1)
(2) is the current value flowing through the element, (2) is the voltage applied to the element, and the voltage Vi when the current is i ampere is called the rising stain pressure. Usually, this value takes the voltage value at 1 mA. α is called a nonlinear coefficient, and it can be said that the larger the value, the better the characteristics.

Generally, a varistor is used by being inserted into an electric circuit as a surge absorbing element, an abnormal voltage suppressor, or a voltage stabilizing element for the purpose of protecting the electric circuit from abnormal voltage.

Until now, zinc oxide has been the main component, and various additives have been added to it, such as B1103, CoO, MnO, sb, o,
.

It has been shown that a varistor exhibiting excellent voltage nonlinearity can be obtained by adding and sintering a small amount of Cr2O3, NiO, B2O3, PbO, and 5i02#.

The varistor obtained by this method is the first to be obtained as a ceramic sintered body, and utilizes the properties of zinc oxide grain boundaries. That is, during sintering, ZnO, which is an n-type semiconductor,
As the crystal grains grow and sinter, Bi2O3 forms at the grain boundaries of the crystal grains.
By generating a liquid phase and segregating various additives therein, the phenomenon of forming potential barriers against electrons at the grain boundaries of zinc oxide is utilized. Therefore, until now,
Excellent voltage nonlinear resistors have only been obtained using bulk-type ceramic sintered bodies.

Considering application to electronic equipment, it is desirable to form a voltage nonlinear resistor on a substrate using a thin film or a thick film. Many attempts have been made to fabricate a voltage nonlinear resistor (varistor) using a thin or thick film on a substrate. However, since varistors using thick films also utilize zinc oxide crystal grains and grain boundaries, the thickness is limited to crystal grain sizes of 5 to 10 mm.
Several times the micron size or more is required. Even in the method of forming parallel electrodes on the surface of a thick film, it is necessary to provide an electrode interval several times the size of the ZnO crystal grains (50 to 100 microns) between the electrodes, and there is a limit to miniaturization. Another problem is that it is susceptible to surface contamination.

Furthermore, the liquid phase of BIt's is extremely reactive and reacts with most oxides and metals, so even if it can be formed into a thick film, there is a problem in that the interface with the substrate is severely altered. Furthermore, problems arise such as reactions between bismuth and wiring metal materials during the production of wiring patterns and devices, and wiring breakage at steps with a thickness of 10 microns or more. Further, there were problems in that it was difficult to control the rise voltage, the shape and dimensions could not be reduced to 100 microns or less because it was dependent on printing technology, and the nonlinear coefficient could only be about 10 at most.

An attempt to fabricate a varistor in the form of a thin film was made, for example, in the Journal of Applied Physics, Vol. 50, pp. 555-558, published in 1979.
Applied Phys+cs, vol, 50.
A zinc metal film is deposited on a fused silica substrate using a spunter method for approximately 10 min as described in J.P., 555-p, 558 (1979).
00 angstrom film was formed, and a ZnO thin film and B
It has been revealed that an asymmetric voltage nonlinear element with a rise voltage of 2 to 3 volts can be obtained by sequentially stacking 1103 thin films of approximately 6000 angstroms each and attaching 2000 angstroms of Ag as electrodes thereon. There is. This device consists of a ZnO thin film and a Bi
It uses the interface of a 2O3 thin film, and the semiconductor Zn
The interface between O and the insulator Bi2O3, the so-called semiconductor
This utilizes the interfacial phenomenon of insulators.

[Problem to be solved by the invention]

However, these devices have asymmetric voltage-current characteristics, small nonlinear coefficients, cannot control the rise voltage, cannot be made thin, are difficult to downsize to 100 microns or less, lack stability in characteristics, etc. However, the problem was that the scope of application was limited. If a symmetrical thin-film varistor could be realized, it would be possible to provide an ultra-small varistor array at low cost, which would have a wide range of applications and high practicality. To make a thin film type varistor, as mentioned earlier (Hit
It can be easily inferred that the 03 thin film may be formed into a laminated structure in which the ZnO thin film is sandwiched between the upper and lower layers. However, even with this structure, the above-mentioned problems could not be solved. Considering the cause of this, Bi2O5 is 880
It is thought that the low melting point (°C) makes it easy to undergo crystal transformation, which changes due to the heat generated during the operation of the varistor, resulting in only unstable characteristics.

Varistor characteristics change is the rise voltage (VlmA)
■11n after applying a DC voltage of approximately 80% for a certain period of time
The rate of change in A is evaluated by ΔvlIuA/'vlfnA.

Practically speaking, this value is desired to be within ±10%. In the thin film varistor having the structure described above, this value only exceeded ±10%.

The purpose of the present invention is to eliminate the above-mentioned conventional drawbacks, and to provide a thin film type voltage that is symmetrical, has a large nonlinear coefficient, can control rising stain pressure, can be made thin and compact, and has stable characteristics. The purpose of the present invention is to provide a non-linear resistor.

[Means to solve the problem]

The thin film type voltage nonlinear resistor of the present invention is formed by sequentially laminating an insulating substrate, a lower electrode thin film layer formed on the insulating substrate, and the lower electrode thin film layer and the required portions on the insulating substrate. It has a laminated thin film structure consisting of a laminated film consisting of a zinc oxide thin film layer, a lead oxide thin film layer, and a zinc oxide thin film layer, and an upper electrode thin film layer formed on the laminated film, and the zinc oxide thin film layer contains oxide. Manganese is 0.0 in terms of M n O.
It is characterized by being added in an amount of 5 to 1.0 mol%.

[Effect]

In order to solve the various problems faced by thin-film varistors, we must study the properties of the ZnO thin film as a semiconductor, the control of the interface between ZnO and the insulator, and the stability of the insulator layer, as well as the stability of the electrode materials used. Consideration is required. The present inventor investigated various materials to replace Bi2O5, which is highly unstable, and arrived at the structure of the present invention.

Next, the main points of the present invention will be explained in more detail with reference to the drawings. FIGS. 1A and 1B are a cross-sectional view and a plan view showing the structure of a thin film varistor according to an embodiment of the present invention.
In Figure (a), the underlying substrate 1 is a material with good surface flatness that can withstand the subsequent process conditions of film formation in an oxidizing atmosphere at a maximum temperature of 400 degrees C, such as glass, alumina, or sapphire. If so, there are no particular limitations. The lower electrode film layer 2, which is first applied, also needs to be able to withstand similar atmospheric conditions. As will be described in the examples, gold, platinum, palladium or ruthenium metals were suitable. Although the details of this reason are unclear, it may be due to the difference in work function between the zinc oxide layer 3 and the metal material, or the presence or absence of an oxide film layer on the metal surface just before the zinc oxide layer 3 is formed. There is a possibility that it is something. It seems that any material that is stable and exhibits low resistance in an oxidizing atmosphere is suitable. Next, a zinc oxide layer 3 to which 0.5 to 1.0 mol % of manganese oxide is added in terms of Lin0K is formed using a sputtering method using a target prepared in advance so as to have the same composition. A normal powder metallurgy method can be used to prepare the target, and the target may be prepared by mixing and firing powder raw materials.

The lead oxide thin film layer 4 may also be formed by sputtering. At this time, conditions were suitable such that MnO as an additive was slightly mixed into the lead oxide film 4 near the surface of the zinc oxide film layers 3 and 3'. That is, it seems that good electrical characteristics can be obtained by slowing down the concentration change near the interface between the zinc oxide thin film layers 3 and 3' and the lead oxide film layer 4. Any method that can be expected to produce such a phenomenon is not limited to the sputtering method, and may also be a vapor deposition method using an ion beam or plasma. Alternatively, heat treatment may be performed after film formation is completed. Any material may be used for the upper electrode 5 as long as it does not particularly deteriorate the characteristics.

〔Example〕

Fused silica and sapphire substrates were used as substrates. When using palladium or platinum as the lower electrode, a 500 oz.
After applying Ti by magnetron sputtering, palladium was deposited to a thickness of 3000 angstroms by sputtering. Other ruthenium (Ru) metal electrodes were formed directly on the substrate to a thickness of 3000 angstroms.

f'vl n O was prepared by mixing a baride powder with a purity of 99.9% or more with a ZnO powder also with a purity of 99.9% or more by a whole mill method using pure water, and a diameter of 1
Molded into 1 senna with a thickness of 5 cm at a pressure of 2 tons/d, 1
The sintered body sintered at 200'O for 1 hour was used as a sputtering target for a zinc oxide thin film layer. A zinc oxide thin film layer containing manganese was formed to a thickness of 5000 angstroms by high frequency magnetron sputtering at a substrate temperature of 300 degrees Celsius.

The lead oxide layer was similarly formed to a thickness of 2000 angstroms using PbO powder compacted with 2 ton/L:rIl as a target.

Furthermore, a zinc oxide thin film layer containing manganese was applied again to 5,000 ml.
A laminated film was formed under the same conditions for angstroms.

Finally, the gold electrode was deposited using an electron beam heating method.
The film was formed to a thickness of angstroms.

The electrical characteristics of the obtained device were evaluated by measuring the voltage-current characteristics using a Kerr 7 tracer and direct current. Non-linear coefficient is 1m
Measured voltage V1mA at a current value of A and 10mA
and V10mAO value according to formula (1).

The stability of the characteristics was evaluated by the rate of change after applying a DC voltage of 80% of the stain pressure for 100 hours.

The results are shown in FIGS. 2(a) and 2(b), which show the dependence of the non-M line coefficient on the amount of manganese oxide added. Figure 2 (al, (b)
As is clear from the above, the thin film varistor of the present invention has excellent nonlinearity.

Table 1 shows the rate of change ΔV in vlrrA after applying a DC voltage of 80% of the rising stain pressure (vlrnA) for 100 hours.
1aIA/VII! Indicates LA. Table 1 shows the characteristics of a product using bismuth oxide as a conventional example. Regarding the non-linear coefficient and the rate of change of 1llllA, the one according to the present invention clearly shows better characteristics.

〔Effect of the invention〕

As described above, the thin film varistor of the present invention is a highly practical element that has excellent not only nonlinear characteristics but also stability of its characteristics. Not only arrays but also 10 micron size required for liquid crystal display elements can be easily processed by using microfabrication technology using photophosphorography, and a wide range of applications are possible.

It goes without saying that by repeating the structure of the present invention many times to form a laminated film, a thin film varistor with a high rise voltage and excellent stability can be easily obtained.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are a sectional view and a plan view showing the structure of a thin film varistor according to an embodiment of the present invention, and FIG. 2(a)
. (b) is a diagram showing the relationship between the nonlinear coefficient and the rising stain pressure with the additive. 1... Insulating substrate, 2... Lower electrode thin film layer, 3.3'
. . . Zinc oxide thin film layer containing additives, 4 . . . Lead oxide thin film layer, 5 . . . Upper electrode thin film layer.

Claims (1)

[Claims] An insulating substrate, a lower electrode thin film layer formed on the insulating substrate, a zinc oxide thin film layer, a lead oxide thin film layer, and a zinc oxide thin film layer formed by sequentially laminating the lower electrode thin film layer and required parts on the insulating substrate. It has a laminated thin film structure consisting of a laminated film made of thin film layers and an upper electrode thin film layer formed on the laminated film, and the zinc oxide thin film layer contains manganese oxide of 0.5 to 1 in terms of MnO. A thin film type voltage nonlinear resistor characterized in that .0 mol% is added.