JPS5917207A - Voltage nonlinear resistor and method of producing same - 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 The present invention relates to a voltage nonlinear resistor with an extremely low \γ-1 voltage and a method for manufacturing the same. - In recent years, semiconductor elements have come to be widely used in various electrical and electronic devices. However, these semiconductor devices are generally susceptible to surges (abnormal overvoltage). Therefore, when semiconductor devices are used in circuits where surges occur, one of two methods is used: select one with a high withstand voltage, or use a surge absorber to protect against surges. There is. Usually, the latter method is used because the former method is not sufficient to counter nage, and also because it increases the height of one song.

Conventionally, as these surge protection elements, Bi2 was added to ZnO.
The 0ZnQ varistor, which is known as a ZnO voltage nonlinear resistor (hereinafter referred to as a varistor) obtained by adding and sintering a small amount of additives such as O3, C020C02O32, is stable against surges and has excellent surge protection. Demonstrate ability. However, the ZnO varistor utilizes the non-ohmic nature of the grain boundaries of the sintered body, and therefore it is difficult to obtain one for low pressure. That is, since the rise voltage is proportional to the number of grain boundaries inserted in series between the electrodes, the thickness of the element must be reduced in order to obtain a low break-through voltage.

However, the particle size of ZnO particles ranges from several 11 meters to several tens of feet.
m, so if you want to obtain one for low pressure, the thickness should be reduced to several 1
001 tm or less, but it is extremely difficult to obtain such a thin material due to mechanical strength. Therefore, suitable varistors for protecting semiconductor devices such as integrated circuits have not been available.

In order to eliminate the drawbacks of these sintered varistors,
Bismuth oxide on a substrate mainly composed of ZnO.

A varistor has been reported in which a film made of cobalt oxide, rare earth oxide, alkaline oxide, etc. is formed by sputtering, and a ZnO film is further superimposed thereon by sputtering. These baristas
The rise voltage is low, making it suitable for surge protection of low-voltage semiconductors. However, the constant that expresses the performance of these elements as a varistor, the voltage nonlinearity index, α (a is l−(, v, , '
c) Fixed in a. However, ■=current, ■: voltage I C+1 constant] is not so large.

The present invention aims to improve these drawbacks, and embodiments thereof will be described in detail below, in which a voltage nonlinear resistor with a low rise voltage and a large a is realized.

The drawing shows the basic structure of the element according to the present invention, in which 1 is a layer containing ZnO as a main component, 2 is a layer containing cobalt oxide, and 3 is an electrode. With such a configuration, an energy barrier is formed at the interface between the Z and nO main component layer and the layer containing cobalt oxide, and this energy barrier exhibits non-ohmic properties, resulting in an effect as a varistor. Since the energy barrier is formed at each of the two interfaces, it operates in the same way for both positive and negative voltages, so the element with this structure exhibits positive-negative symmetrical voltage nonlinearity.

(Example 1) ZnO powder was molded into a diameter of 40 mm and a thickness of 20 mm using a normal molding method, and placed in a SiC mold at 1200° C. while applying a pressure of 200 Kg/ca in air.
Pressure fired for hours. The obtained sintered body was cut into a disk having a thickness of 0.5 mm, mirror-polished using fine alumina powder, and thoroughly washed with an organic solvent. Next, the oxide composition powder shown in Table 1 was dispersed in an organic binder and an organic solvent to form a paste, and the paste was applied onto the Znoi surface substrate. Two sets of substrates with coated films thus obtained were stacked so that the coated films were in contact with each other. This laminated substrate was pressure-fired in air for 1 hour at a temperature of 750°C while applying a pressure of 400 kg/c, and then ZnO on both sides of the element was fired.
An At vapor-deposited electrode was provided on the substrate, and the chip was cut into a 1 mm square chip and its electrical characteristics were measured. Table 1 shows the voltage non-linearity index α and rise' voltage (1 mA/mm2
(terminal voltage when current flows through).

Compositional forms 1 to 62 in Table 1 are examples within the scope of the present invention,
Flats 63 to 66 marked with * are shown as comparative examples. From Table 1, cobalt oxide is converted to 99.98 to 46 moles in the form of CO2O3, and bismuth oxide (, B
1203), rare earth oxide (A203: However, 1.
Ai rare earths), metal oxides (BO: where B is Ba, Sr
Bi2O
3, A203. 0.01 to 54.9 when converting to BOO type
By using a material composition with 9 molar addition, a becomes 15
From the above, it can be seen that a good low-voltage varistor with a rising voltage of 8.5 cm or higher can be obtained.

In this example, praseodymium oxide, neodymium oxide, and zamariulium oxide were used as rare earth oxides.
Although an example has been shown, it is clear that similar effects can be obtained by using other rare earth oxides due to the co-jT+ chemical properties of rare earth elements.

(Hereinafter referred to as Kinshiro) (Example 2) Among the compositions used in Example 1, the composition shown in A2 of Table 1 was used to examine the effects of manufacturing conditions. Table 2 shows the relationship between firing temperature and electrical properties when laminated and pressure fired, and good properties are obtained at firing temperatures of 600°C to 950'C.

In addition, when firing at a temperature lower than 600°C, the adhesive strength of the laminated portion was weak, making it impossible to obtain a practical product.

Table 2 In this example, lamination and pressure firing was carried out at a pressure of 400 Kg/cnj, but we further examined the effect of the pressure at that time. As a result, at pressures below 50 K7/cnj, the ZnO substrate and oxide co-contaminated when taken out after firing.
It was not possible to obtain sufficient adhesive strength for the layer containing the core. - Firing at a pressure greater than 1000 Kg/ctrt often causes cracks in the ZnO substrate, which is not appropriate. For this, 50 Kg/
Those fired at a pressure of crl~1000 Kg/ol showed almost the same electrical properties and had no problems in terms of adhesive strength and cracking. From the above results, it was found that 60 to 1000 Kg/cnf is appropriate as the lamination pressure.

Next, we investigated the effect of firing time in laminated pressure firing. As a result, it was found that if the sintering temperature was maintained for 10 minutes or more, no significant change appeared in the electrical properties.

Next, the firing conditions for the ZnO substrate used as the substrate were studied. Firing pressure: ○~1500 Kg/cnf
.

The firing temperature was varied between 700°C and 1500'C, and the effect was investigated. As a result, the pressure during firing was 50°C to 90°C.
If it was less than /cJ, there would be many pores on the surface of the ZnO substrate after polishing, and therefore only those with extremely unstable characteristics could be obtained. When firing under a pressure of 50 Kg/crl or more -J-, a good ZnO substrate was obtained at any pressure. If the pressure is increased too much, the equipment becomes expensive and other problems arise, so there is no point in increasing the pressure too much if there is no particularly significant effect.

The firing pressure for ZnO substrate is 60 to 1500 N/c.
〃; was appropriate.

If the firing temperature is less than 800°C, sintering is insufficient,
When the temperature was higher than 1400°C, ZnO grain growth progressed too much, resulting in problems such as a decrease in mechanical strength. Therefore, a suitable firing temperature is 80°C to 140°C. It was found that a sufficiently dense ZnO substrate could be obtained with a firing time of one hour or more. In this example, one layer containing cobalt oxide was formed by two ZnO substrates.
Although nO substrates are laminated in a sandwich-like manner, if another layer containing cobalt oxide is further provided on top of this and a ZnO substrate is laminated on the other side, the varistor effect of the present invention can be obtained as described at the beginning of the embodiment. is a layer containing cobalt oxide and Z
Considering that this occurs at the interface of the nO substrate, it is clear that the same effect can be obtained by connecting two varistors in series with each other in Example 1, and by increasing the number of laminated layers in this way. Therefore, a higher voltage varistor can be obtained.

Although a ZnO substrate was used in this example, various additives that control the resistivity of the ZnO substrate, such as trivalent elements such as aluminum and gallium, and monovalent norium, such as lithium, may be added. In addition, it is also possible to vary the properties (7) Therefore, the present invention is not limited to pure ZnO substrates.

Indeed, when forming a layer containing cobalt oxide, in this example, CO2O3, Pr2O3, etc. were used, and /ζ was used, but CaO, (-o s○4.Pr601□, etc.) were used to obtain similar results. Therefore, the present invention is not limited only to the oxides expressed in this example.

As described above, the present invention was obtained for the first time through a skillful combination of nanomaterial composition and manufacturing method, and the device obtained by the present invention improves the reliability of electronic devices using semiconductor devices. It is useful for.

[Brief explanation of drawings]

The drawings are sectional views showing the structure of one embodiment of the present invention. 1... Zno main component layer, 2... Layer containing cobalt oxide, 3... Electrode.

Claims (1)

[Claims] (1) Cobalt has a mole ratio of 45 to 99.98 in terms of cobalt oxide (C02o3), and bismuth oxide (C02o3).
B1203), red earth oxide (A203-where A is rare earth), metal oxide (BO: where B is Ba, Sr or P
b) Regions each containing 0.01 to 54.99 mol of ``2'' in two or more of the three groups are sandwiched by two regions containing zinc oxide as the main component. 1. A voltage nonlinear resistor characterized in that a laminate is formed by stacking at least one set of scissors, and electrodes are formed on both the front and back sides of the laminate. (2) Voltage nonlinear resistor 0 according to claim (1), characterized in that at least one oxide selected from praseodymium oxide, neodymium oxide, and samarium oxide is used as the rare earth oxide. (3) Oxidized lIF
1. The voltage nonlinear resistor according to claim 1, wherein the region containing lead as a main component is a polycrystalline sintered body. (4) Cobalt oxide, bismuth oxide, rare earth oxide, and metal oxide () < oxide of lithium, strontium, or lead) on the main surfaces of at least two substrates mainly composed of zinc oxide. After forming a film containing two or more types of components and stacking the substrates and the films alternately so that the outermost layer is the substrate containing zinc oxide as the main component, heat treatment is performed without applying pressure. and glue [7,
A method for manufacturing a voltage nonlinear resistor, comprising providing electrodes on both the front and back principal surfaces of the obtained laminate. (5) As a substrate, mold powder mainly composed of zinc oxide and heat it in air at 800 to 14 oO
(6) A method for manufacturing a voltage nonlinear resistor according to claim (4), characterized in that a sintered body obtained by firing while applying a pressure of Kg/cni is used. ) The laminate is bonded by heat treatment at 500 to 950°C while applying a pressure of 50 to 1000 kg/err.
4) A method for manufacturing a voltage nonlinear resistor as described in item 4).