JPH02303003A - Non-linearity voltage resistance element - Google Patents

Abstract

PURPOSE:To increase the non-linearity index alpha by a method wherein the title non-linearity voltage resistance element is provided with a substrate an electrode layer formed thereon, a composite layer comprising a ZnO layer held between two metallic oxide layers on the electrode layer and another electrode layer on the topmost part of the composite layer. CONSTITUTION:A lower electrode 3 is formed by evaporating nickel on a glassy substrate 1 and then a metallic oxide layer 4 is formed on the electrode 3 using a sintered body comprising a praseodymium oxide and a cobalt oxide as a target. Furthermore, a ZnO layer 5 in almost 1mum thick is formed using a ZnO sintered body as another target; next, another metallic oxide layer 6 is formed using the said sintered body comprising the praseodymium oxide and the cobalt oxide as the other target; next an upper electrode 7 is formed by evaporating nickel. Through these procedures, the flatness of the ZnO layer 5 can be enhanced by forming the layer 5 after forming the metallic oxide layer 4, consequently the unfavorable effect on the non-linearity in the current voltage characteristics can be averted thereby enabling the non-linearity index alpha to exceed 30.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is a means for protecting relay contacts, protecting semiconductor elements such as ICs and LSIs against static electricity, and absorbing discharges in color TV cathode ray tube circuits. This invention relates to improvements in voltage nonlinear resistance elements used as such.

(Conventional technology) Conventionally, voltage nonlinear resistance elements (hereinafter also referred to as varistors)
As shown in FIG. 3, Au, AJ, etc. are vacuum-deposited on a glass or ceramic substrate 12 to form a lower electrode (electrode layer) 13, and a Zn0 layer 14 is formed on this lower electrode 13 by sputtering or the like. Then, praseodymium oxide (Pr2
03) and cobalt oxide (CO203), a Zn0 layer 16 is formed on this metal oxide layer 15 by sputtering, etc., and then Au is formed on this Zn0 layer 16.

A varistor 11 is known in which an upper electrode (electrode layer) 17 is formed by vapor-depositing A1 or the like.

Further, the varistor 11 having the above structure has the ZnO layer 14.
The characteristics (varistor voltage) are determined by the potential barriers 14a and 16a formed at the interface between the metal oxide layer 16 and the metal oxide layer 15.

In the varistor 11 having the above configuration, when a voltage is applied so that the upper electrode 17 becomes positive with respect to the lower electrode 13, the potential barrier 16a is biased in the opposite direction, and the lower electrode 13 becomes positive with respect to the upper electrode 17. When a voltage is applied so that is 1
0).

(Problems to be Solved by the Invention) In the varistor (voltage nonlinear resistance element) as described above, after forming a lower electrode, a ZnO layer is formed on the lower electrode by sputtering or the like.

However, as shown in Figure 4, ZnO has the property of being predominantly oriented along the C-axis (perpendicular to the substrate), so when a film is formed on a crystalline metal electrode, unevenness occurs at the interface of the ZnO layer and this height difference occurs. H1 can hold up to 1000 people. This height difference reduces the flatness of the ZnO layer and adversely affects the nonlinearity in current-voltage characteristics, resulting in a nonlinearity index α
This results in the problem that the performance cannot be improved because it cannot be made larger.

In addition, when forming a conductive pattern on the upper electrode by etching, ZnO is an amphoteric oxide and is soluble in both acid and alkali, so it partially dissolves together with the removed portion of the upper electrode, resulting in the same current-voltage characteristics as above. Another problem arises in that a conductive pattern cannot be easily formed because it adversely affects the nonlinearity of the conductive pattern.

The present invention solves the above problems, improves the flatness of the ZnO layer, does not adversely affect the nonlinearity in current-voltage characteristics, increases the nonlinearity index α, and allows a conductive pattern to be easily formed on the upper electrode by etching. An object of the present invention is to provide a voltage nonlinear resistance element that can form a voltage nonlinear resistance element.

[Configuration of the Invention (Means for Solving the Problems) The present invention provides a base material, an electrode layer formed on the base material,
It is characterized in that it has at least one composite layer formed of a ZnO layer sandwiched between metal oxide layers on the electrode layer, and has an electrode layer on the top of the composite layer.

(Function) As described above, by having a composite layer in which a ZnO layer sandwiched between metal oxide layers is formed on an electrode layer (lower electrode) formed on a base material, the flatness of the ZnO layer is improved. Furthermore, a conductive pattern can be easily formed on the upper electrode by etching.

(Example) An example of a voltage nonlinear resistance element (hereinafter referred to as a varistor) according to the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view of a varistor according to the invention.

The varistor 1 shown in the figure includes a substrate (base material) 2 (a glass substrate is shown in the examples) made of, for example, glass, alumina (an insulating substrate), a conductive substrate such as aluminum, zinc, etc.
A lower electrode (electrode layer) 3 made of, for example, nickel (Ni), a metal oxide layer 4 made of, for example, praseodymium oxide (Pr203) and cobal oxide 1' (CO203), and a metal oxide layer 4 mainly made of ZnO. Zn0 layer 4
and further the same as above, for example, praseodymium oxide (Pr20
i) and a metal oxide layer 6 made of cobalt oxide (CO203), and an upper electrode (electrode layer) 7 made of, for example, nickel (Ni). Incidentally, the composite layer referred to in the present invention refers to the metal oxide layer 4, Z
It is composed of an n0 layer 5 and a metal oxide layer 6. Further, 5a and 5b in the figure are potential barriers formed at the interface between the metal oxide layer 4 and the ZnO layer 5.

Next, a method for manufacturing the varistor 1 will be explained.

First, nickel (Ni) is formed on the glass substrate 2 to a thickness of 0.5 μm by vapor deposition to form the lower electrode 3, and this lower electrode 3 is coated with a sintered material made of praseodymium oxide (Pr203) and cobalt oxide (CO2o,'). A metal oxide layer 4 is formed by sputtering using the compact as a target at the temperature of the glass substrate 2 of 250° C. in a sputtering argon (Ar) atmosphere at an input power of 120 W, and using the ZnO sintered compact as a target, in the same manner as above. A Zn0 layer 5 of approximately 1 μm thick is formed, then a metal oxide layer 6 is formed in the same manner as above using a sintered body consisting of praseodymium oxide (pr2o3) and cobal oxide 1'(CO203') as a target, and then a nickel oxide layer 6 is formed in the same manner as above. (Ni) is formed by vapor deposition to a thickness of 0.5 μm to form the upper electrode 7.
Then, the varistor 1 is obtained.

As mentioned above, in the varistor 1, since the metal oxide layer 4 is formed and then the Zn0 layer 5 is formed, the height difference H0 of the unevenness at the interface of the ZnO layer is 200 at the highest value as shown in FIG. The flatness of the ZnO layer is improved. As a result, the nonlinearity in the current-voltage characteristics was not adversely affected, and the nonlinearity index α could be set to 30.

Furthermore, when a conductive pattern is formed by etching on the upper electrode 7 of the varistor 1 having the above structure, since the Zn0 layer 5 is sandwiched between the metal oxide layers 4 and 6, the ZnO is dissolved together with the removed portion of the upper electrode 7. Therefore, a conductive pattern can be easily formed without adversely affecting nonlinearity in current-voltage characteristics, as described above.

As detailed above, according to the present invention, the flatness of the ZnO layer can be improved, the nonlinearity index α can be increased (and the upper electrode can be easily A varistor that can form a conductive pattern can be provided.

The present invention is not limited to the above-mentioned embodiments, and various modifications can be made. For example, within the scope of the present invention, the metal used for the electrode may be Au, A1, etc., and the metal oxide of the metal oxide layer may be bismuth oxide (Bi203), cobalt monooxide (C0203), etc.
), praseodymium oxide (pr2o3), and their mixtures, etc., and the ZnO layer is not only ZnO alone, but also a variety of ZnO layers with additives such as aluminum (AJ2), gallium (Ga), and indium (In) added to ZnO. The inert gas in the sputtering atmosphere is not limited to argon (Ar), and may be other gases.

Furthermore, in this example, the electrodes were formed by vapor deposition and other films were formed by sputtering, but CVD (Chemical Vapor Deposition) was used.
Other film forming methods such as porDeposition (chemical vapor deposition) may also be used.

[Effects of the Invention] As described above, according to the present invention, the flatness of the ZnO layer can be improved, the nonlinearity index α can be increased without adversely affecting the nonlinearity in the current-voltage characteristics, and the upper electrode can be easily attached to the ZnO layer. A voltage nonlinear resistance element that can form a conductive pattern can be provided.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a varistor (voltage non-linear resistance element) according to the present invention, Figure 2 is a diagram for explaining the flatness of the ZnO layer of the varistor according to the present invention, and Figure 3 is a cross-sectional view of a conventional varistor. FIG. 4 is a square diagram for explaining the flatness of the ZnO layer of a conventional varistor. 1... Varistor (voltage nonlinear resistance element), 2...
Glass substrate (base material), 3... lower electrode, 4.6...
Metal oxide layer, 5...ZnO layer, 5a, 5b...
Potential barrier, 7... Upper electrode, Ho... Difference in height of unevenness at the interface of ZnO layer.

Claims (1)

[Claims] It has at least one composite layer formed of a base material, an electrode layer formed on the base material, and a ZnO layer sandwiched between metal oxide layers on the electrode layer; A voltage nonlinear resistance element characterized by having an electrode layer on top.