JPS6266605A - Voltage nonlinear resistance element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a thin film type voltage nonlinear resistance element suitable for overvoltage protection of small electronic devices.

[Prior art and its problems]

Conventionally, voltage nonlinear resistance elements (hereinafter referred to as varistors) such as silicon carbide (SiC), selenium (Se), and silicon (Sl) have been used for overvoltage protection of electronic and electrical equipment. BACKGROUND ART In recent years, a voltage nonlinear resistance element (hereinafter referred to as a ZnO varistor) consisting of a sintered body containing ZnO as a main component, mixed with various additives, molded and fired has been developed. ZnO varistors have low limiting voltage;
Because it has excellent characteristics such as a large voltage non-linearity coefficient, it is suitable for overvoltage protection of equipment made of semiconductor elements with low overvoltage resistance, and is widely used in place of JD, SiC varistors, etc. became.

One of the ZnO varistor shells currently in practical use is ZnO+ Pr6 (111 series), ZnO-Pr6
Oil-based varistors have ZnO as the main component, and cobalt (Co) and magnesium (Mg) as subcomponents in addition to Pr.
), calcium (Ca), potassium ■, chromium ccr>
It is known that it is manufactured by firing a material to which elements or compounds are added (Tokuko Kokō 5
7-42962). Usually, ZnO varistors are often made of a disk-shaped sintered body with a thickness of about 1 m and a diameter of about 105 m, to which electrodes and lead wires are attached, and which is soldered with resin.

On the other hand, with the development of technology to reduce the size and weight of electronic components, various types of small and lightweight consumer electronic devices have been developed, and many IC and L
Since SI is used, these ICs.

Protecting LSIs from abnormal voltages has become an important issue.However, the size of the sintered ZnO varistor described above is not suitable for such applications.

In recent years, alumina (A7zOa) has been used to solve this problem.
Small varistors have been fabricated by forming thin films on insulating substrates such as
(Refer to Publication No.-86704). There are several methods for forming thin films, but sputtering is often used for multi-component oxides such as ZnO varistors because it produces high-quality films.

Figure 1g9 shows an example of a conventional varistor obtained by sputtering.As shown in the cross-sectional view of the main part in Figure 9(a), this device consists of an A7203 substrate l, a platinum film lower electrode. 2
．． The ZnO varistor film 3 and the upper electrode 4 of AIH are laminated on this F@, and the varistor film 3 is 8
A film thickness of #) 5 μmo is obtained by sputtering for a time, and the varistor voltage between the upper electrode 4 and the lower electrode 2 is about 5 V. The varistor voltage is the voltage between the terminals when a 1 mA current is passed through the varistor, and is usually expressed as 1 mA. In the case of this element, when a positive voltage is applied to the upper electrode 4, the current simply flows from top to bottom as indicated by the arrow in Fig. 9(a), so the equivalent circuit is shown in Fig. WJ9(b). ◇ 5 in ) in Figure 9 represents a ZnO varistor 0 In the conventional device configured as above, if you want to further increase the varistor voltage for practical use, the varistor film thickness must be increased, but sputtering equipment Thin film type Zn with desired varistor voltage
K to manufacture the O varistor requires a long time and has the problem of poor manufacturing efficiency.

[Purpose of the invention]

The present invention has been made in view of the above points, and its purpose is to provide a thin film varistor that can obtain a desired varistor voltage with a thin varistor film formed in a short time using a sputtering method. It's about doing.

[Key points of the invention]

The present invention is based on the understanding that most of the current flows perpendicularly to the electrode surface because the ZnO varistor film has excellent voltage non-linearity. The varistor group is sputtered on the sputtered film, and a plurality of electrodes are provided at appropriate distances on the sputtered film to form an element structure. The K is set so that a small thin film varistor with high voltage can be obtained.

[Embodiments of the invention]

The present invention will be explained below based on examples.

FIG. 1 shows an example of a ZnO varistor configured according to the present invention, FIG. 1(a) is a sectional view of the main part, FIG. 1(b) is an equivalent circuit diagram, and FIG. 9(a) and Figure 9(b)
Parts having the same functions as O are denoted by the same reference numerals.The device shown in FIG. 1(a) was manufactured as follows. A platinum film is formed as the lower electrode 2 by sputtering on a mirror-polished Aj 2 OA substrate l, and then the platinum film for the lower electrode 2 is formed using a sintered body containing ZnO as the main component with additions of pr, co, etc. The sputtering device that forms the varistor film 3 on top is a magnetron-type high-frequency sputtering device, and the film forming conditions are: power approximately 4 W/m, gas used A.
Mixed gas with a ratio of r and oxygen of 90:10, gas pressure 0-0
1 Torr, and the substrate temperature was 300°C. In this way, a ZnO varistor film 3 with a thickness of 5 μm is obtained by sputtering for 8 hours, but the film forming rate at that time is approximately 0.6 μm per hour. After the heat treatment, two upper electrodes 4a, 4 of the υAl film are formed on the varistor film 3 by vacuum evaporation using a mask.
b are formed at an appropriate distance as will be described later. Note that when observed using an electron microscope, the grain size of the varistor M3 after the heat treatment was approximately 2 μm. Voltage nonlinearity is determined by heat treatment temperature of 80℃.
It occurs at temperatures above 0℃, but if you consider the surge resistance, it will be 100℃.
It is practical to set the temperature to 0°C or higher. However, when the heat treatment temperature exceeds 1400° C., a portion of the additive in the varistor film 3 evaporates, resulting in a significant decrease in voltage nonlinearity. 1) is an equivalent circuit diagram to be described later.

On the other hand, the upper electrode 4 on the varistor film 3 shown in FIG.
In order to determine the appropriate spacing between upper electrodes 4a and 4b, the spacing between upper electrodes 4a and 4b was varied in the range of 2 to 100 μm using microfabrication technology, and it was confirmed how much current would flow through the device body at this time. FIG. 2 shows a cross section of the element structure and wiring state for this purpose. In FIG. 2, a groove with a width of about 20 μm is provided at the center of the platinum lower electrode 2 to separate the platinum lower electrode 2, and a % current meter A-1 is installed in between. 2 was connected so that a current of 1 mA always flowed. Thus, the two AJ upper electrodes 4a, 4b
The diagram shown in FIG. 3 is obtained as the relationship between the electrode spacing and the current of ammeter A-1. In Figure 3, the varistor film thickness is 5 μm.
It also shows the case where the varistor film thickness is 10 μm as well as the curve A when . From Figure 3, in curve A, the upper electrode spacing is 6.
When the distance between the upper electrodes is 12 μm or more, most of the current flows to the element, and in curve A, it can be seen that when the upper electrode spacing is 12 μm or more, most of the current flows to the element. This is because the ZnO varistor film has an excellent voltage non-linearity coefficient of α=18, so the current greatly depends on the voltage, so the voltage share is 1.
．． If the distance between the electrodes is twice the thickness of the varistor, that is, about 1.2 times the thickness of the varistor film, the current flowing through the surface can be said to be t-.

The difference between Figure 1 (Ik) showing the element configuration of the present invention and the conventional element shown in Figure 9 (a) is that, as is clear from the comparison of the two temperatures, in Figure 1 (a) there are two upper electrodes. 4a and 4b are provided with an interval approximately 1.2 times the varistor film thickness. Thus, when a glass voltage is applied to the upper electrode 4a, the direction of the current flowing is shown by the arrow in FIG. 1(a). Upper electrode 4a, varistor film 3.
Lower electrode 2. Flows in the order of varistor film 3° upper electrode 4b,
The equivalent circuit of this element is shown in FIG. 1(b) in which two ZnO resistors 5 are connected in series, and the lower electrode 2 has the role of a lead wire rather than an electrode.

In the ZnO varistor of the present invention manufactured in this way, the varistor voltage between the two AI upper electrodes 4a and 4b on the varistor film 3 is approximately iov, and the voltage nonlinearity coefficient α is 18. This means that the device of the present invention, which has the same film forming time and varistor film thickness as the conventional device, can obtain twice the varistor voltage compared to the conventional device, and conversely, the conventional device has the same varistor voltage as the present invention. This means that twice the film thickness and twice the film forming time are required.

In addition, as mentioned above, the electrode spacing is about 1 to 2 times the varistor film thickness, so that almost no current flows on the surface. However, if you want the electrode spacing to be within 1.2 times the varistor film thickness, for example, as shown in Figure 1. In the element shown in (a), a groove may be formed between the electrodes 4a and 4b of the varistor film 3 by etching or the like, as shown in FIGS. 4 and 5, so that most of the current flows in the direction of the arrow. Figure 4.

5 are device cross sections corresponding to FIG. 1(a). In FIG. 4, the groove B reaches the lower electrode 2, and in FIG. 5, the groove C does not penetrate to the lower electrode 2. This is the case when some parts are left behind.

Next, FIG. 6 shows a conventional device in which the thickness of the varistor film is 5 μm and the varistor voltage is doubled, that is, 20 V, by the same manufacturing method as shown in FIG. 1 (a) K. FIG. 3 is a cross-sectional view of a main part showing an element configuration that doubles the value. The difference between FIG. 6 and FIG. 1(a) is that three upper electrodes 4c, 4
d, 4e and two lower electrodes 2m, 2b. Since the relationship between the electrode spacing and the varistor film thickness described above is the same for the lower electrode, A!
Between upper electrodes 4c and 4d, between 4d and 4e, platinum lower electrode 2
The electrode spacing between & and 2b must be at least 1.2 times the thickness of the ZnO varistor film 3. In this way, the current flows from the upper electrode 4c to the varistor film 3, as shown by the arrow. Lower electrode 2a, varistor film 3. Upper electrode 4d, varistor film 3. Lower electrode 2b, varistor film 3. Upper electrode 4e
The number of stain flow paths can be increased compared to the case of FIG. 1(a).

FIG. 7 is a cross section of a main part of an element configuration in which a varistor voltage three times that of FIG. 1(a), that is, 30 V, is obtained by the same method as FIG. , 4g
, 4h, 41 and three platinum lower electrodes 20° 2d, 2e, and the electrode spacing is set to 1.
Since the zero current, which is more than twice as large, flows in the direction of the arrow,
In the case of FIG. 6, the number of current paths can be further increased.

As described above, the device of the present invention can increase the varistor voltage while keeping the varistor film thickness constant by appropriately determining the number of electrodes and the electrode spacing. It is preferable to optimize the size within the range of , taking into account ease of separation of electrode formation.

In the examples described above, the left and right ends of the upper electrode are used as terminals, as shown in each figure, but the same effect can be obtained by using the lower electrode as the terminal, as shown in Figure 8, depending on the application of the device. , the current path in this case is as shown by the arrow ◇ Also, in this example, the substrate on which the sputtered film is formed is made of Al2O
Although three plates are used, the substrate is not limited to Al2O3 as long as it is an insulating material that can withstand the heat treatment temperature, and quartz, silicon carbide doped with beryllium (Be), magnesia (MgO), or the like may be used.

The platinum used as the lower electrode material may also be a noble metal that can withstand the heat treatment temperature, such as Au. There are no restrictions on the upper electrode, and in addition to AJ, KAg + Au can be used.
, conductive metals such as Cu can also be used.Furthermore, although the varistor film has been described as a ZnO varistor film, it is not limited to a ZnO varistor film as long as it has voltage nonlinearity (s BJiT103 varistor film,
The effects of the present invention can be observed even when a 5rTi03 varistor film or the like is used.

As described above, the present invention provides a small thin-film varistor that has a desired varistor voltage by simply changing the arrangement of electrodes while maintaining a small varistor film thickness.

〔Effect of the invention〕

Compact, thin-film varistors used for abnormal voltage protection in electronic devices, etc. have traditionally had only one upper and lower electrode in the varistor film, and since current simply flows from top to bottom, it is desirable to use a thin sputtered film. If the varistor voltage of Multiple varistors are connected in series by setting the electrode spacing to about 1.2 times the varistor film thickness and arranging the electrodes so that the current path is upper electrode - varistor film - lower electrode - varistor film - upper electrode. Since it has an electrical equivalent circuit connected to the f
This is a thin film type varistor that can be formed in a short time, has high manufacturing efficiency, and is suitable for reducing the size and weight of the equipment used.

[Brief explanation of drawings]

Fig. 1 shows the ZnO varistor according to the present invention, &) is a cross-sectional view of the main part, (b) is an equivalent circuit diagram, and Fig. 2 is the same as Fig. 1 (a).
Figure 3 is a diagram showing the relationship between the upper electrode interval and the current flowing through the element body; Figures 4 and 5 are diagrams showing the relationship between the upper electrode interval and the current flowing through the element body. In each figure, a groove is provided between the upper electrodes of FIG. 1(a),
Figure 4 shows a groove that penetrates to the lower electrode, Figure 5 is a cross-sectional view of the groove that does not reach the lower electrode, and Figure 6 is a cross-sectional view of the groove that does not reach the lower electrode.
A sectional view showing the structure of an element having double the varistor voltage, FIG. 7 is a sectional view showing the structure of an element having three times the varistor voltage of FIG. 1(a), and FIG. 8 features a lower electrode. A cross-sectional view of the device of the present invention showing an example of the patent, FIG. 9 shows the conventional Zn
An O varistor is shown, in which (a) is a cross-sectional view of a main part, and (b) is an equivalent circuit diagram. 1...Substrate, 2, 2a, 2b, 2c, 2d, 2
e, 2f2g, 2h...lower electrode, 3...
... Varistor membrane, 4° 4a, 4b, 4c, 4d,
4e, 4f, 4g, 4h, 41.4j. 4k... Upper electrode, 5... ZnO varistor, 6... Constant current power supply, A-1, A-2...
...Ammeter, B, C...Groove (Q) Fig. 1 Fig. 2 Fig. 3 Fig. 4 (Q) Fig. 9

Claims (1)

[Claims] 1) A voltage nonlinear resistance element formed by laminating a lower electrode, a varistor film having voltage nonlinearity, and an upper electrode in this order on an insulating substrate, which comprises one or more lower electrodes and an upper electrode. The upper electrode and the lower electrode are provided with two or more upper electrodes, and the upper electrode and the lower electrode are arranged such that the current flows in the order of the upper electrode, the varistor film, the lower electrode, the varistor film, the upper electrode or the lower electrode, the varistor film, the upper electrode, the varistor film, and the lower electrode. A voltage nonlinear resistance element characterized in that it is provided with a voltage nonlinear resistance element. 2) A voltage nonlinear resistance element according to claim 1, characterized in that a ZnO varistor film is used as the varistor film. 3) A voltage nonlinear resistance element according to claim 1, characterized in that a BaTiO_3 film is used as the varistor film. 4) A voltage nonlinear resistance element according to claim 1, characterized in that a SrTiO_3 varistor film is used as the varistor film. 5) A voltage nonlinear resistance element according to claims 1 to 4, characterized in that the upper electrode interval and the lower electrode interval are approximately 1.2 times the varistor film thickness. 6) A voltage nonlinear resistance element according to claims 1 to 4, characterized in that a groove is provided in the varistor film between the upper electrodes.