JPH0276204A - Zno thin film varistor - Google Patents

Abstract

PURPOSE:To improve a surface flatness of a ZnO layer and a nonlinearity in a current-and-voltage characteristic by constituting the ZnO layer by a polycrystal film which is not dominantly oriented to a C axis. CONSTITUTION:A ZnO layer 11 is a polycrystal film which is not dominantly oriented to a C axis. The ZnO layer is formed by using an opposed type sputter in which targets face to each other. Ions come in from the plasma between the targets, forming the film. Since the film is a polycrystal film which is a random aggregate of minute single crystals which are aligned in different directions, the surface of the ZnO layer 11 is made flat. By this, a nonlinearity in a current-and-voltage characteristic can be improved.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention provides a method for forming a flat surface of the ZnO layer by forming the ZnO layer with a polycrystalline film that is not predominantly oriented along the C-axis. , relates to a ZnO thin film varistor with improved nonlinearity.

[Prior Art] Conventionally, a ZnO thin film varistor having a structure as shown in FIG. 3 is known. That is, Au is deposited on a glass or ceramic substrate 1.

Ni or the like is vacuum-deposited to form the lower electrode 2, and a Zn0 layer 3 is formed on the lower electrode 2 by sputtering.
A metal oxide layer 4 is formed on the layer 3 by sputtering to form a potential barrier 5 at the bonding interface of the Zn0 layer 3, and Au, Ni, etc. are vacuum deposited on the metal oxide layer 4 to form an upper electrode 6. That is. When a voltage is applied so that the upper electrode 6 is positive with respect to the lower electrode 2, the potential barrier 5 is biased in the positive direction, and when a voltage is applied in the opposite direction, it is biased in the reverse direction, and the current flows in the positive and reverse directions. Different voltage characteristics.

Moreover, its current-voltage characteristics are non-linear.

[Problem to be Solved by the Invention 1] The sputtering method in the above sputtering is high frequency sputtering or high frequency magnetron sputtering. When the Zn0 layer 3 is formed by these sputtering methods in which the target and the substrate face each other, ZnO has the property of being predominantly oriented along the C axis, that is, in the direction perpendicular to the substrate. Therefore, as shown in FIG. 3(b), unevenness occurs in the level of columnar growth, and unevenness occurs on the surface of the Zn0 layer 3 (the height difference is 1,000 at most). Such poor surface flatness adversely affects nonlinearity in current-voltage characteristics.

That is, the nonlinear index α cannot be increased.

In order to improve the surface flatness, physical methods such as polishing can be considered, but this is physically impossible for a thin film thinner than 1 μm.

This invention was made with the aim of solving the problems of the prior art.

[Means for Solving the Problems] Means for solving the above problems will be explained below using FIG. 1 corresponding to the embodiment. In the present invention, as shown in FIG. 1, the Zn0 layer 11 is composed of polycrystals that are not predominantly oriented along the C axis.

[Function] With this structure, the surface flatness of the Zn0 layer 11 is improved.

[Example] FIG. 1 is a diagram showing an embodiment of the present invention.

In FIG. 1, 11 is a ZnO layer, and 4 is Bi and O.

5 is a potential barrier.

As shown in FIG. 1(b), the Zn0 layer 11 is a polycrystalline film that is not predominantly oriented along the C-axis. The Zn0 layer 11 is formed by using facing type sputtering in which targets are opposed to each other, as shown in FIG.

Ions randomly fly in from the plasma between the targets and form a film. Since the film is a polycrystalline film, which is a disorderly collection of minute single crystals with different alignment directions, the first
As shown in FIG. Therefore, the nonlinearity in the current-voltage characteristics was improved, and the nonlinearity index α increased from 10 to 30 in the conventional case.

[Effects of the Invention] As explained above, in the present invention, the ZnO layer is composed of a polycrystalline film in which the C-axis is not dominantly oriented. Therefore, the surface flatness of the ZnO layer is improved. Therefore, according to the present invention, it is possible to obtain the effect that nonlinearity in current-voltage characteristics is improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, (a) is a cross-sectional view, (b) is an enlarged cross-sectional view of a ZnO layer, FIG. 2 is a diagram showing facing type sputtering, and FIG. In the figure showing (a)
is a cross-sectional view, and Φ) is an enlarged cross-sectional view of the ZnO layer. ■... Substrate, 2... Lower electrode, 4... Metal oxide layer, 5... Potential barrier, 6... Lower electrode, 3.11.
...ZnO layer patent applicant: TDC Co., Ltd.; Figure 1 (Q) (b) Figure 2

Claims (1)

[Claims] 1. A ZnO thin film varistor characterized in that the ZnO layer is composed of a polycrystalline film that is not predominantly oriented along the C axis.