CN101261892A - Zinc Oxide Based Low Voltage Thin Film Varistors - Google Patents

Abstract

The invention discloses a low-voltage thin-film voltage-sensitive resistor based on zinc oxide, which is formed by the series connection of two or more basic units that are deposited on an insulating substrate and composed of metal electrode-zinc oxide film-metal electrode; wherein, the zinc oxide film is height C-axis orientation columnar crystal film; the threshold voltage of the resistor is controllable, the manufacturing technology is simple and the adaptability is strong.

Description

Zinc Oxide Based Low Voltage Thin Film Varistors

technical field

The invention relates to a protection element for a low-voltage electronic circuit, in particular to a zinc oxide-based low-voltage film varistor.

Background technique

Zinc oxide varistor is a polycrystalline semiconducting ceramic element with zinc oxide as the main body, which has the advantages of large flow capacity, fast response speed, no freewheeling, and nonpolarity. However, the threshold voltages of commercially available varistors are all fixed. For example, the O402 chip varistors of AVX Company have specifications of 5.6V, 9V, 14V and 18V. Different circuits often require different varistors for protection, which brings inconvenience to actual use. Zinc oxide low-voltage varistors with adjustable threshold voltage have not been developed yet.

Contents of the invention

The object of the present invention is to provide a zinc oxide-based low-voltage film varistor for the deficiencies of the prior art. In the present invention, different threshold voltages can be obtained by selecting different electrodes (that is, pins), so as to meet the needs of different protection voltages.

The purpose of the present invention is achieved by the following technical solutions: a zinc oxide-based low-voltage film varistor, which consists of two or more basic metal electrodes-zinc oxide film-metal electrodes Units are connected in series. In addition, pins connected to the metal electrodes are also included. The columnar zinc oxide film is a columnar crystal film with a high c-axis orientation; the metal electrode is a metal aluminum film.

The beneficial effects of the present invention are: the present invention only needs to simply control the thickness of the film in the unit, so that the thickness is less than the grain size of zinc oxide under specific preparation conditions, and the threshold voltage of the entire piezoresistor can be determined by the The number is easily controlled.

Description of drawings

Fig. 1 is the cross-sectional view of the basic unit of the zinc oxide-based low-voltage film varistor of the present invention;

2 is a cross-sectional view of a zinc oxide-based low-voltage film varistor composed of four basic units connected in series according to an embodiment of the present invention;

FIG. 3 is a graph showing the relationship between the threshold voltage and the number of layers of the ZnO-based low-voltage thin film varistor shown in FIG. 2 .

Detailed ways

The zinc oxide low-voltage varistor of the present invention is composed of two or more basic units consisting of metal electrodes-zinc oxide film-metal electrodes connected in series, wherein the zinc oxide film is a columnar crystal film with a high c-axis orientation. The basic unit of a metal electrode-zinc oxide film-metal electrode is shown in Figure 1, which consists of an upper electrode 1, a columnar zinc oxide film 2, and a lower electrode 3.

Typical zinc oxide varistors are composed of metal-zinc oxide-metal. There are grain boundaries between zinc oxide grains. Due to the bending of the surface energy band, a back-to-back Schottky barrier pair is formed at the grain interface, and the breakdown of the barrier leads to the varistor phenomenon. In ordinary varistors, the thickness of the zinc oxide layer is relatively large, so the thickness direction of the zinc oxide film can be regarded as a series connection of many crystal grains, so the threshold voltage of the varistor is relatively high. However, if the zinc oxide film is a c-axis-oriented columnar film, there is only one crystal grain in the thickness direction, so that a very low threshold voltage can be obtained. Assuming that the varistor threshold voltage of such a basic unit is V _m , then, if two such units are connected in series, a varistor whose threshold voltage is twice as high as V _m can be obtained, and so on. If N such By connecting the cells in series, a varistor with a threshold voltage N times higher than V _m can be obtained.

Example

Referring to Figure 2, we have fabricated a 4-unit zinc oxide film varistor. The zinc oxide thin film was prepared by reactive direct current magnetron sputtering method, and the substrate temperature was 400°C during deposition. XRD test showed that the zinc oxide thin film under this deposition condition was a columnar film with a film thickness of 80nm. The upper and lower electrodes are metal aluminum films deposited by DC magnetron sputtering, each with a thickness of 50nm, and each metal electrode is connected to a pin 4, 5, 6, 7, 8 respectively.

The threshold voltages tested between different electrode pairs are shown in Table 1. It can be seen that the threshold voltage has a simple linear relationship with the number of cells between the electrodes. The fitting results show that the threshold voltage increases by about 3.3 volts for each additional unit, as shown in Figure 3.

Table 1

Claims (4)

1. A low-voltage film varistor based on zinc oxide is characterized in that it is mainly composed of two or more basic units formed by metal electrodes-zinc oxide film-metal electrodes connected in series. 2 . The zinc oxide-based low-voltage film varistor according to claim 1 , wherein the columnar zinc oxide film is a highly c-axis oriented columnar crystal film. 3. The zinc oxide-based low-voltage thin film varistor according to claim 1, wherein the metal electrode is a metal aluminum film. 4. The zinc oxide-based low-voltage thin film varistor according to claim 1, further comprising pins connected to the metal electrodes respectively.

Images