JPH02148802A - Thin film type voltage-dependent nonlinear resistor - Google Patents

Abstract

PURPOSE:To provide a thin film type voltage-dependent nonlinear resistor having a large nonlinear coefficient, excellent characteristic stability, small size and high practical utility by incorporating predetermined contents of cobalt, antimony in first and second zinc oxide thin film layers and a predetermined content of manganese in a lead oxide thin film layer. CONSTITUTION:In a thin film type voltage-dependent nonlinear resistor, a lower electrode layer 2 made of a thin metal film is formed on a board 1, at least one set of a first zinc oxide (ZnO) thin film layer 3a and a zinc oxide (PbO) thin film layer 4 are sequentially laminated on the electrode layer, a second zinc oxide thin film layer 3b is formed on the laminate, and an upper electrode layer 5 is formed on the thin film layer. Cobalt and antimony of 0.1-0.5mol-% and 0.05-0.1mol-% in terms of CoO and Sb2O3 are contained in the first and second zinc oxide layer, and manganese of 0.05-0.1mol-% in terms of MoO is further contained in the zinc oxide layer.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a symmetrical voltage that can be obtained by laminating a thin film mainly composed of zinc oxide and an insulating film mainly composed of lead oxide on a substrate. The present invention relates to a thin film type voltage nonlinear resistor exhibiting current characteristics, and in particular to a small thin film type voltage nonlinear resistor with excellent stability of characteristics.

[Prior Art] A voltage non-linear resistor (hereinafter referred to as a varistor) usually exhibits a non-ohmic symmetrical voltage-current characteristic expressed by the following formula [I].

I/1=(V/V-)" - [I] Here, ■ is the current value flowing through the element, ■ is the voltage applied to the element, and the voltage V when the current is i ampere is called the rising voltage. Usually This value is the voltage value at 1 mA.α is called a nonlinear coefficient, and it can be said that the larger this value is, the better the characteristics are.

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.

The baristas known so far have zinc liquefied as the main component, and various additives such as B i 203,
Coo, MnO, Sb2O3゜Cr2O3,,N!
O, B203, PI)O.

By adding and mixing a small amount of SiO2 etc. and sintering,
Varistors that exhibit excellent voltage nonlinearity are obtained, and among these, varistors using Bi2O3 as an additive are particularly well known. The varistor that can be raised to 1Q using this method is the first one made of ceramic sintered bodies that can be raised to 1Q, and utilizes the properties of zinc oxide grain boundaries. That is, during sintering, along with the growth and sintering of ZnO crystal grains, which are n-type semiconductors, for example, B! By generating a liquid phase of 203 and segregating various additives therein, the phenomenon of forming a potential barrier against electrons at the grain boundaries of zinc oxide is utilized. Therefore, until now, excellent voltage nonlinear resistors have only been available in bulk type ceramic sintered bodies.

Considering the application of electrons to devices, it is desirable to form a voltage nonlinear resistor on a substrate by using a thin film or a thick film.

Various attempts have been made to fabricate a voltage nonlinear resistor (varistor) using a thin film or a thick film on a substrate.

However, since varistors using thick films also utilize zinc oxide crystal grains and grain boundaries, the thickness of the varistor varies from crystal grain size 5 to
A diameter several times larger than 10 microns is required. Even with the method of forming parallel electrodes on the surface of a thick film, it is necessary to provide a spacing between the electrodes that is several times the size of the ZnO crystal grains (50 to 100 microns), and there is a limit to miniaturization. There are also problems in that it is difficult to increase surge resistance and is susceptible to surface contamination.

In addition, the liquid phase of Bi2O3 is extremely reactive and reacts with most oxides and metals, so even if it can be formed into a thick film, the interface with the substrate will be severely altered, reducing the portion that can effectively function as a device. There is also the problem. Problems arise such as reactions between bismuth and wiring metal materials during the rough fabrication 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 rising 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.

Attempts to produce varistors in the form of thin films were made in 1979, for example.
Journal of Applied Physics, Volume 50, pp. 555-558 (Journalof
Applied Physics, vol, 50. p
, 555-558 (1979)), a zinc metal film of about 10% was deposited on a fused silica substrate by sputtering.
By depositing a film of 0000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 type-form type type-form type type-form type type-form type type by layering on top of the ZnO thin film and Bi2O3 thin film. It has been revealed that the device can be obtained. This device consists of ZNOI film and B
12 (Using the interface of the hl film, Z
B which is an insulator with nO! 203, which utilizes the so-called semiconductor-insulator interface phenomenon.

[Problems to be solved by the invention] However, these elements have asymmetric voltage-current characteristics, have a small nonlinear coefficient, cannot control the rise voltage, cannot be made thin, and cannot be made small to about 100 microns or less. However, the scope of application was limited due to problems such as difficulty and lack of stability of properties.

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 an extremely wide range of applications and be highly practical. As mentioned above, it can be easily inferred that in order to manufacture a thin film type varistor, a stacked structure in which a Bi2O3 thin film is sandwiched between upper and lower ZnO thin films is sufficient. However, even with this structure, the above-mentioned problems could not be solved. Considering the cause of this, B! It is thought that z03 has a low melting point of 880'C, easily undergoes crystal transformation, and changes due to the heat generated during varistor operation, resulting in only results lacking in stability of properties.

The characteristic change of the varistor is the rising voltage (VllIIA)
V11I after applying a DC voltage of about 80% of
The rate of change of IA, that is, Δv11IIA/v1□. Te is evaluated. Is this value practically desired to be within ±10%?
For thin film varistors with a small flat structure, this value is ±10
There was only one that exceeded %.

The present invention has been made in order to solve the conventional problems as described above, and provides a thin film voltage nonlinear resistor that has a large nonlinear coefficient, excellent stability of characteristics, and is small and highly practical. The purpose is to

[Means for solving the problems] In order to solve the various problems of thin film varistors,
Sufficient consideration must be given to the properties of the ZnO thin film as a semiconductor, the control of the interface between ZnO and the insulator, the stability of the insulator layer, and the stability of the electrode material used. As a result of examining various materials to replace B12O3, which is highly unstable, the present inventor found that a thin film varistor that solved the various problems described above could be realized by having the following predetermined configuration. reached.

That is, the present invention provides a lower mold (
*A layer is formed, and a first zinc oxide (ZnO) layer is formed on the electrode layer.
) At least one set of thin film layers and lead oxide (PbO) thin film layers are sequentially laminated, a second zinc oxide thin film layer is formed on the laminate, and an upper electrode layer made of a metal thin film is formed on the thin film layer. A thin film type voltage nonlinear resistor comprising a thin film type voltage nonlinear resistor, in which cobalt and antimony are contained in the first and second zinc oxide thin film layers in terms of CoO and Sb2O3, respectively.
．． 1 to 0.5 mol% and 0.05 to 0.1 mol% of manganese were contained, and the lead oxide thin film layer contained 0.05 to 0.1 mol% of manganese in terms of MnO. This is a thin film type voltage nonlinear resistor characterized by the following.

The structure of the thin film type varistor of the present invention is as shown in FIG. 1, which also serves as an example and shows its basic configuration. FIG. 1(a) is a cross-sectional view, and FIG. 1(b) is a plan view. be. The cross-sectional view in FIG. 1(a) is taken along the line A-A'' in FIG. 1(b).

In FIG. 1(a), the underlying substrate 1 is made of a material that has good surface flatness and can withstand the subsequent process conditions of film formation in an oxidizing atmosphere of up to 400'C, such as glass, alumina, or It is not particularly limited as long as it is made of sapphire or the like. The lower electrode layer 2 applied first must be able to withstand similar atmospheric conditions, and is suitably made of, for example, gold, platinum, palladium or ruthenium metal. The reason why the above-mentioned materials are suitable as electrode film materials is partly due to the difference in work function between the zinc oxide thin film layer 3a (first zinc oxide thin film layer) and the metal material, or because the zinc oxide thin film This may also be due to the presence or absence of an oxide film layer on the metal surface just before layer 3a is formed.

In short, it seems that any material that is stable and exhibits low resistance in an oxidizing atmosphere is sufficient.

Next, cobalt is converted to CoO and is 0.1 to 0.5 mol%.
and 0.05 to 0 when antimony is converted to Sb2O3
．． The zinc oxide thin film layer 3a to which 1 mol% is added is formed by preparing a target in advance so as to have the same composition and using a sputtering method or the like. 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.

Next, manganese is converted into M n Q and is 0.05 to 0.
．． The ¥43 oxide thin film layer 4 containing 1 mol % and the zinc oxide thin film layer 3b (second zinc oxide thin film layer) meeting the same conditions as above may be formed by sputtering.

At this time, conditions were suitable such that the additives cobalt and antimony were slightly mutually diffused and mixed into the lead oxide thin film layer 4 from near the surfaces of the zinc oxide thin film layers 3a and 3b. That is, it seems that good electrical characteristics can be obtained by optimizing the concentration change near the interface between the zinc oxide thin film layers 3a and 3b and the lead oxide thin film layer 4. It is necessary to increase the concentration of cobalt and antimony in the zinc oxide thin film, and conversely, to increase the concentration of manganese in the lead oxide thin film. Any method that can be expected to produce such a phenomenon in a thin film is not limited to sputtering, 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 layer 5 as long as it does not particularly deteriorate the characteristics.

[Example] Next, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic sectional view and a plan view of an embodiment of the present invention, and the manufacturing method thereof is as follows.

First, as the substrate 1, fused silica and sapphire substrates were used. When using palladium or platinum as the lower electrode layer 2, in consideration of adhesion to the substrate, Ti was applied in advance by magnetron sputtering on only 500 people, and then palladium or platinum was deposited on 3000 people using the same sputtering method. . On the other hand, when ruthenium (Ru) was used as the lower electrode layer 2, a film was formed directly on the substrate to a thickness of 3000 nm.

Oxide powder with a purity of 99.9% LX was used as C00 and 5b2o3, and this powder was mixed with Zno powder, which also had a purity of 99.9% or higher, using pure water using a ball mill method. 15 cm in diameter at a pressure of Cm2,
A sintered body formed to a thickness of 1 cm and sintered at 1200'C for 1 hour was used as a sputter target for a zinc oxide thin film layer. The zinc oxide thin film layer 3a containing cobalt and antimony was formed to a thickness of 5000 mm by high frequency magnetron sputtering at a substrate temperature of 300°C.

The lead oxide layer 4 was formed to a thickness of 2000 mm in the same manner as described above using a sputtering target in which MnO was mixed with PbO powder and compacted at 2 tons/cm2.

Furthermore, 5,000 people successively laminated and formed a zinc oxide thin film layer 3b containing cobalt and antimony under the same conditions as above. Finally, a gold electrode was deposited to a thickness of 3000 mm using an electron beam heating vapor deposition method to form the upper electrode layer 5.

The electrical characteristics of the obtained device were evaluated by measuring the voltage-current characteristics using a curve tracer and direct current.

The nonlinear coefficient was calculated from the measured voltage 1IIIv1111A and vlomA values at current values of 1 mA and 10 mA according to the above formula [11].

The results of measuring the nonlinear coefficient (α) when varying the amount of cobalt and antimony added in the zinc oxide thin film layer are shown in the second table.
As shown in the figure. Further, FIG. 3 shows the results of measuring the nonlinear coefficient (α) when the amount of manganese added in the lead oxide thin film layer was changed. Note that the dependence on each additive was measured under conditions in which the amounts of the other two additives were set to the optimum amounts, and both values are shown in amounts converted to oxides.

As is clear from FIGS. 2 and 3, the thin film varistor according to the present invention has excellent nonlinearity.

Table 1 shows the rate of change in vllIIA △v11 after applying a DC voltage of 80% of the rising voltage (V1) for 100 hours.
Il8/v1mA is shown. Table 1 shows the characteristics of a conventional example in which bismuth oxide was used instead of lead oxide in the present invention. As can be seen from the table, the nonlinear coefficient and the rate of change in VlmA clearly show better characteristics in the case of the present invention.

Table 1 Note that in this example, only the thin film varistor having the structure shown in FIG. Needless to say, a thin film varistor with excellent stability can be obtained.

[Effects of the Invention] As described above, the thin film varistor according to the present invention is a highly practical element that has excellent not only nonlinear characteristics but also stable characteristics, and can be easily formed on various substrates. Because of this, it can be easily fabricated not only into ultra-small varistor arrays, but also into 10-micron sizes, such as those required for liquid crystal display elements, by using photolithographic microfabrication technology, and a wide range of applications are possible.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view and a plan view of an embodiment of the present invention,
FIGS. 2 and 3 are characteristic diagrams showing the dependence of the nonlinear coefficient on the amount of additives. 1... Substrate 2... Lower electrode layer 3a,
3b...Zinc oxide thin film layer

Claims (1)

[Claims] (1) A lower electrode layer made of a metal thin film is formed on the substrate, at least one set of a first zinc oxide thin film layer and a lead oxide thin film layer are sequentially laminated on the electrode layer, and a second A thin film type voltage non-linear resistor comprising: a zinc oxide thin film layer formed thereon, and an upper electrode body made of a metal thin film formed on the thin film layer; , cobalt and antimony respectively as CoO and Sb_
0.1 to 0.5 mol% and 0.0 in terms of 2O_3
A thin film type voltage nonlinear resistor characterized in that the lead oxide thin film layer contains 0.05 to 0.1 mol% of manganese in terms of MnO. vessel.