JP2548299B2 - Manufacturing method of voltage-dependent nonlinear resistor element - Google Patents

Description

TECHNICAL FIELD The present invention relates to an abnormal voltage generated in an electronic device or an electric device,
To protect semiconductors and circuits from noise and static electricity,
The present invention relates to a method for manufacturing a voltage-dependent nonlinear resistance element using a sintered body containing SrTiO ₃ as a main component.

2. Description of the Related Art A voltage-dependent nonlinear resistor element has a resistance value that changes non-linearly depending on the voltage applied between the electrodes provided on the surface of the sintered body, and the resistance changes when the applied voltage exceeds a certain voltage. It has the property that the value sharply decreases. Utilizing this property, it is widely used to erase sparks of DC motors of electronic devices, noise removal, noise removal and protection of relay contacts, IC and LSI protection and malfunction prevention, and discharge absorption of CRT circuits of television receivers. Has been.

As a conventional voltage-dependent nonlinear resistor element, ZnO-based,
SnO ₂ series, Fe ₂ O ₃ series, SiC series, TiO ₂ series, etc. are known. Of these, the SnO ₂ series and the Fe ₂ O ₃ series are linear resistors, and a special electrode is added to this to form an energy barrier between the sintered body and the electrodes. , Has gained varistor characteristics. Further, since ZnO-based and TiO ₂ -based ones have varistor characteristics at grain boundaries, and SiC-based ones have varistor characteristics at contact surfaces between particles, no particular electrode is selected. On the other hand, in terms of characteristics, ZnO-based and SiC-based have a large non-linearity and show an excellent effect on absorption of a relatively high voltage, but have a small dielectric constant and show almost no effect on absorption of a relatively low voltage. SnO ₂ series, F
The e ₂ O ₃ system and the TiO ₂ system have small non-linearity and insufficient energy absorption. Therefore, recently, an SrTiO ₃ system having a large dielectric constant and being effective in absorbing a relatively low voltage has been developed.

DISCLOSURE OF INVENTION Problems to be Solved by the Invention However, the above-mentioned conventional voltage-dependent nonlinear resistance element has a small permittivity and a high varistor voltage, and therefore has no effect on absorption of a surge or noise of a relatively low voltage. Since the problem of the sintered body itself and the contact between the sintered body and the electrode are non-ohmic, a kind of rectifying action occurs at the interface between the sintered body and the electrode. There is a problem with the combination of the sintered body and the electrode that the excellent non-linearity is not effectively utilized. In addition, depending on the application, the element is used without being coated with resin, so it is easily affected by the surrounding atmosphere, etc., and when a relatively large amount of power is applied, the element heats up and the electrodes are likely to deteriorate. However, it had a problem of poor reliability.

The present invention is to solve such problems, to fully exhibit the excellent characteristics of the sintered body, strong adhesion of the electrode to the sintered body, excellent solderability, corrosion resistance and reliability Moreover, it is an object of the present invention to provide a voltage-dependent non-linear resistance element having an electrode structure with low material cost.

Means for Solving the Problems In order to solve the above problems, the present invention provides an ohmic electrode by firing a paste containing Cu as a main component in a sintered body containing SrTiO ₃ as a main component in the air. Further, a paste containing silver as a main component is fired in a non-oxidizing atmosphere to provide a double electrode. In addition, part of Sr in SrTiO ₃ is replaced with C
The main component of the sintered body is one obtained by substituting one or more elements of a, Ba and Mg.

Function When a normal electrode is applied to a sintered body containing SrTiO ₃ as a main component, the electrode comes into non-ohmic contact with the sintered body, and a rectifying action occurs at the interface between the sintered body and the electrode. The excellent varistor characteristics that I have are slowed down,
The original characteristics cannot be fully exhibited. Therefore, it must have ohmic contact with SrTiO ₃ as an electrode. As the electrode that makes ohmic contact,
In-Ga alloy is considered. However, In-Ga alloy is not suitable for mass production due to its high cost, and there are only methods such as rubbing or ultrasonic brazing to attach the In-Ga alloy to the sintered body, and it is necessary to adhere the electrode to the sintered body. The force is weak, and defective electrode peeling easily occurs. In addition, the melting point of In-Ga alloy is low, and it is difficult to solder the lead wire.

Therefore, in the present invention, as a result of studying a method of forming an electrode that is simple and the cost of the electrode material is relatively low, as a method of forming the electrode, air firing is adopted and
Cu is adopted. Conventionally, Cu had a surface that was easily oxidized when fired in air and was difficult to use for electrodes.However, by appropriately selecting and using a paste containing Cu as a main component, such as the particle size of Cu, The ohmic electrode containing the main component can be easily formed. In addition, a silver electrode layer was provided to improve the corrosion resistance and reliability of the electrode. These are significantly cheaper than In-Ga alloys, are highly mass-producible, have a very strong adhesive force between the sintered body and the electrodes, and prevent electrode peeling defects from occurring easily. It is extremely easy to perform, etc., it has excellent corrosion resistance and its change over time is small,
It is possible to provide a highly reliable and inexpensive SrTiO ₃ -based voltage-dependent nonlinear resistor element.

Examples The present invention will be specifically described below with reference to examples.

First, SrCO ₃ and TiO ₂ are weighed so as to have a ratio of SrTiO ₃ , wet mixed with a ball mill for 20 hours, dehydrated and dried, calcined at 1100 ° C. for 4 hours, and again wet milled with a ball mill for 20 hours. Then, it is dehydrated and dried to synthesize SrTiO ₃ . 0.5 mol part of Nb ₂ O ₅ and CuO were added to 100 mol parts of SrTiO ₃ thus obtained.
Is weighed and 0.25 mol of MnO ₂ is weighed, and wet-mixed in a ball mill for 20 hours, and dehydrated and dried. Next, 10 wt% of an organic binder such as PVA (polyvinyl alcohol) is added and granulated to form a donut shape with a hole in the center. After firing this molded body in air at 1100 ° C for 2 hours, it was fired in a reducing atmosphere of N ₂ : H ₂ = 9: 1 at 1450 ° C for 8 hours, and further in air at 1025 ° C for 12 hours. First
A sintered body 1 as shown in FIGS. 2 and 3 is prepared. Next, a paste containing lead borosilicate glass frit and resin as a main component and containing Cu as a main component is applied to a region (three places in this embodiment) of the sintered body 1 by screen printing or the like. After that, it is dried and baked in air at 200 ° C. for 5 minutes to form an ohmic electrode 2 containing Cu as a main component on the sintered body 1. Here, Cu has an average particle size of 3 μm.
m was used. Next, a paste containing silver as a main component is applied onto the ohmic electrode 2 by screen printing or the like, and then baked at 400 ° C. for 10 minutes in a non-oxidizing atmosphere to provide the silver electrode 3.

In this way, a voltage-dependent nonlinear resistance element having the ohmic electrode 2 and the electrode 3 containing silver as a main component is obtained.

In addition, as a method of forming the electrode 3 containing silver as a main component,
It may be formed by any method other than screen printing.

Further, in this embodiment, only the doughnut-shaped element is shown, but other shapes (for example, a disk shape, a cylinder shape, a square plate shape) may be used. Further, the electrodes may be on one side or both sides of the device. Then, a part of Sr, which is the main component of the sintered body, may be replaced with one or more elements of Ca, Ba, and Mg, and the same result can be obtained regardless of the additive component. I was confirmed.

EFFECTS OF THE INVENTION As described above, according to the present invention, the obtained electrode is in ohmic contact with the sintered body, and there is no rectifying action at the interface between the sintered body and the electrode. The voltage non-linearity which it has can be fully exhibited. Further, since the adhesive strength between the sintered body and the electrode is very strong, defects such as electrode peeling are unlikely to occur, and the reliability is extremely high. Moreover, by superposing the electrode containing silver as the main component on the ohmic electrode, the connection with the external electrode becomes extremely easy,
Moreover, it has excellent corrosion resistance, little change over time, and stable characteristics. Further, the electrode material cost is very low compared to the case of using an In-Ga alloy, and the effect that it is suitable for mass production can be obtained.

[Brief description of drawings]

FIG. 1 is a top view showing an embodiment of an element obtained by the manufacturing method of the present invention, and FIG. 2 is a sectional view of the same. 1 ... Sintered body, 2 ... Ohmic electrode, 3 ... Silver electrode.

Claims (2)

(57) [Claims] 1. A paste containing Cu as a main component is applied to a sintered body containing SrTiO ₃ as a main component and baked in air to provide an ohmic electrode, and a paste containing silver as a main component is further formed on the ohmic electrode. Is applied and fired in a non-oxidizing atmosphere, and electrodes are provided so as to overlap each other. 2. The sintered body according to claim 1, wherein a main component of the sintered body is one obtained by replacing a part of Sr of SrTiO ₃ with one or more elements of Ca, Ba and Mg. Manufacturing method of voltage-dependent nonlinear resistor element.