JPS6189602A - Voltage non-linear 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 Industrial Application) The present invention relates to a voltage non-linear resistance element, and particularly to a voltage non-linear resistance element such as a varistor mainly made of tin oxide.

('Prior Art) It is well known that a varistor is constructed using a semiconductor ceramic having voltage non-linear resistance characteristics. As this type of semiconductor ceramic, tin oxide (Sn
O2) type products are often used.

FIG. 1 is a diagram illustrating an example of a chip-shaped firmware using a semiconductor ceramic mainly based on tin oxide, which is the background of the present invention. The chip type varistor 10 is mainly made of tin oxide.
It includes a semiconductor ceramic body 12 as a body. Electrodes 14 are formed on both main surfaces of the ceramic body 12, respectively. These electrodes 14 are formed, for example, by printing and applying an electrode paste of silver, zinc, or copper, and then baking it.

(Problems to be Solved by the Invention) When evaluating the V-I characteristics of the above-mentioned varistor, it was found that there were large variations in the characteristics, and when measured again after soldering the lead wire to the electrode 14, Threshold voltage V
, mA changed by about -10 to 30%. This is because when printing and baking the electrode 14 on the ceramic body 12, a barrier vr was created at the interface between the ceramic body 12 and the electrode 14, as shown in FIG. V' r is formed by the ceramic body 12 and exhibits voltage nonlinearity like the star VR, but its nonlinear coefficient is inferior to the characteristics of the ceramic body. When an electrode is formed on a semiconductor G toceraminok body like this, the overall nonlinear coefficient is 1
It gets smaller. If the barrier vr remains present, the varistor characteristics as a whole will vary widely, and the threshold voltage will change significantly before and after the processing for attaching the lead wires.

In addition, /8 method, vacuum deposition method, sputtering method,
A similar problem occurs when non-ohmic electrodes are formed by electroless plating or the like. Furthermore, the same applies to a laminated type varistor in which molten metal constituting the internal electrode is injected into a semiconductor ceramic body and solidified.

In order to avoid the influence of the barrier vr as described above, it is conceivable to form a so-called ohmic electrode that does not create a barrier at the interface with the semiconductor ceramic body. Such an ohmic electrode generally has a two-layer structure including an ohmic electrode layer and, for example, a silver electrode layer formed thereon. However, ohmic electrodes have the disadvantage that they are difficult to solder and have poor moisture resistance, such as their characteristics varying due to moisture absorption. Therefore, as mentioned above, attempts have been made to form a thin solderable and moisture-resistant electrode on top of the Ohm 1 raw electrode, but this method is not only expensive but also difficult to process. There are problems such as poor sex.

Furthermore, since the conventional ohmic electrode has a two-layer structure, the ohmic electrode layer and the metal electrode layer must be formed accurately to avoid misalignment. this is,
This is because if a positional shift occurs between the two layers, variations in characteristics will be further aggravated. Therefore, another problem with the ohmic electrode of the conventional structure is that the process becomes complicated in order to process it with high precision.

Therefore, an object of the present invention is to provide a voltage nonlinear resistance element mainly based on tin oxide, which is simpler and cheaper and can avoid the influence of barriers.

(Means for Solving the Problems) This invention involves forming a non-ohmic metal electrode on a semiconductor ceramic mainly made of tin oxide and having voltage non-linear resistance characteristics, and then applying a pulse voltage to the semiconductor ceramic. This is a voltage nonlinear resistance element in which the metal electrode is formed as an electrode exhibiting ohmic or nearly ohmic properties by destroying the barrier formed at the interface between the metal electrode and the semiconductor ceramic.

(Effects of the Invention) According to the present invention, when forming an electrode, the barrier formed between the semiconductor ceramic body and the electrode is electrically forcibly destroyed. Even if the metal electrode is ohmic, the electrode will be ohmic or nearly ohmic. Therefore, the obtained voltage nonlinear resistance element will remain stable even after subsequent processing, such as attaching lead wires. Characteristics can be maintained.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description with reference to the drawings.

(Example) A semiconductor ceramic body 12 similar to that shown in FIG. 1 is prepared. This ceramic body 12 is a semiconductor ceramic mainly composed of tin oxide and having voltage nonlinear resistance characteristics. Then, an electrode paste of silver, copper, or zinc is printed on the ceramic body 12 and baked to form a baked electrode 14 (Fig. 1).
form.

Thereafter, an appropriate pulse voltage is applied to the electrode 14 once or multiple times in both the positive and negative directions. The current density at this time is
It is chosen to have a density sufficient to destroy the barrier vr (FIG. 2) and a size that does not destroy the ceramic body 12 itself. According to experiments conducted by the inventors of the present invention, the current density is IA/cII for the material and size.
! The barrier cannot be destroyed below 100A/a+1
In this case, the inherent voltage nonlinear resistance of the ceramic body itself has been lost.

After that, lead wires are soldered to electrodes 1.1.

In this way, a voltage nonlinear resistance element such as a varistor using a semiconductor ceramic mainly composed of tin oxide is completed.

In addition to baking, the electrode 14 may be formed by a thermal spraying method, a vacuum evaporation method, a sputtering method, or an electroless plating method. This applies to all types of varistors in which a barrier vr is formed between them.

Tin oxide (Sn02) and semiconducting agent (In203, S
b203, Ta205, 'Nb2.05, etc.) and a trace amount of sintering aid, and has a diameter of 10 mm and a wall thickness of 0.
．． A non-ohmic silver paste with excellent solderability and moisture resistance is applied to both main surfaces of a 5mm semiconductor ceramic body.
Baking is performed to form a silver electrode. 1 such sample
00 pieces were created. 50 of these remain as they are.
After measuring electrical characteristics such as mI characteristics, lead wires were attached to the electrodes by soldering, and then the electrical characteristics were measured again. For the remaining 50 pieces, 8 x 20μse
After applying a pulse voltage with a waveform of c and a peak value of 200V,
Electrical characteristics such as v-r characteristics were measured, and after attaching a Riet wire by soldering, the electrical characteristics were measured again.

The results are shown in Tables 1 and 2. Table 1 and Table 2
V, mA, and α are obtained from each V-1 characteristic, and ■.

mA is the voltage across the sample (threshold) when a direct current of 1 mA is passed through the sample. Table 1 shows the soldering before, and Table 2 shows the after soldering. In the table, σ indicates the variation, and α indicates the current of 10 mA.
This is a nonlinear coefficient determined from the voltage at 1 mA and the voltage at 1 mA.

(Leaving space below) Table 1 (Soldering before) Table 2 (Soldering after) As is clear from Tables 1 and 2, apply a pulse to forcibly destroy the barrier VR (Figure 2). By soldering, it is possible to significantly reduce variations in the threshold voltage and non-linear coefficient before and after soldering, and it is possible to obtain a voltage non-linear resistance device (for example, a varistor) with stable characteristics.

In this embodiment, the present invention is applied to a ring-shaped varistor 20 shown in FIG. Here, the ring-shaped varistor 20 will be briefly explained with reference to FIG.

The ring-shaped varistor 20 includes a flat donut-shaped ring-shaped semiconductor ceramic body 22, and on one main surface of the ceramic body 22, three divided electrodes 24 are formed of, for example, silver.

It had the same composition as Example 1 and an outer diameter of 11 mm.

Inner diameter 7. Three divided electrodes as shown in FIG. 1 are formed on a ring-shaped semiconductor ceramic body with a thickness of 1.9 mm and a thickness of 1.9 mm. This electrode is formed by applying a non-ohmic silver paste with excellent solderability and moisture resistance and burning it to form an i'v electrode. Such a sample was prepared as +OO(II).

After measuring the electrical characteristics of these 50 pieces as they were, lead wires were attached to the electrodes by soldering, and then the electrical characteristics were measured again. For the remaining 50 pieces, the waveform is 8 x 20 lI S e c and the peak value is 200.
After applying the pulse voltage (2), the electrical characteristics were measured, and after attaching a Riet wire by soldering, the electrical characteristics were measured again. The results are shown in Tables 3 and 4.

Table 3 (Soldering is done before) Table 4 (Soldering is done after) Tables 3 and 4 show that, as in Example 1, the barrier is destroyed and the threshold voltage and nonlinear coefficient vary. It can be seen that the amount decreases.

In each of the above embodiments, for example, a pulse voltage was applied after the electrodes were formed on the semiconductor ceramic body. However, it goes without saying that after forming the electrodes and attaching the lead wires, for example, a pulse voltage may be applied between the lead wires.

Furthermore, in each of the above embodiments, the chip type varistor 10 with electrodes formed on both sides of the ceramic body 120 and the ring type varistor 20 with divided electrodes 24 formed on the surfaces of the ceramic bodies 2, 2 have been explained. The invention is also applicable to varistors having structures as shown in FIGS. 4 and 5.

In the example shown in FIG. 4, electrodes 14 are formed on both sides of a semiconductor ceramic body 12 mainly made of tin oxide, and an intermediate electrode 16 is further formed inside the ceramic body 12. Also,
The example shown in FIG. 5 is called a multilayer varistor, in which an internal electrode 18 is formed and electrically connected to an electrode 14 on the side surface of a semiconductor ceramic body 12 whose living body is tin oxide.

By applying a pulsed voltage to the electrodes 14, the respective intermediate electrodes 16. The barrier between the internal electrode 18 and the ceramic body 12 can be broken.

Note that the internal mold 1a18 is made of, for example, Pb, Sn, etc.
A! The metal is melted and the electrode 18 is formed into a void layer (
A base metal may be injected into the seepage pore layer of the ceramic body 12 which is a porous layer.

[Brief explanation of the drawing]

Figure 1 shows the background of this invention and the structure of the Naro chip type varistor.
It is a structural diagram illustrating an example. FIG. 2 is an equivalent circuit showing that a barrier is formed at the interface between the electrode and the ceramic body. FIG. 3 is a schematic sectional view of a link type varistor as another embodiment of the invention. FIG. 4 is a schematic cross-sectional view of another chip-type varistor. FIG. 5 is a schematic cross-sectional view of a multilayer chip type varistor. In the figure, 12.22 is a semiconductor ceramic body, 14.
24 is an electrode, 16 is an intermediate electrode, and 18 is an internal electrode. Patent applicant Murata Sosakusho Co., Ltd. Representative Patent attorney Oka [1 Zen Kei (1 idiot)

Claims (1)

[Scope of Claims] A semiconductor ceramic body having a voltage non-linear resistance characteristic mainly based on tin oxide, and a non-ohmic metal electrode formed on the semiconductor ceramic body, the semiconductor ceramic body and the metal electrode A voltage nonlinear resistance element in which the barrier between the