JPS5914603A - 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 an extremely low voltage nonlinear resistor with a rising voltage of 9, 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, either one of two methods is used: select one with a high withstand voltage, or use a surge absorber to protect against surges. The latter method is usually used because the former method of surge protection is not sufficient and is also expensive.

Conventionally, as these surge protection elements, Bi2 was added to ZnO.
The 02nO varistor, which is known as a ZnO voltage nonlinear resistor (hereinafter referred to as a varistor) obtained by adding a small amount of additives such as O3'+ CO2O3 and MnO2 and sintering, is stable against surges and has an excellent Indicates surge protection 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. In other words, the rise voltage is proportional to the number of grain boundaries inserted in series between the electrodes, so in order to obtain a low rise voltage, the thickness of the element must be reduced.However, the grain size of the ZnO particles The thickness ranges from several micrometers to several micrometers, so if you want to obtain one for low pressure, the thickness will need to be several hundreds of micrometers.
It is necessary to make the thickness smaller than μm, but it is extremely difficult to strengthen it mechanically. 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, Z
nOf: Bismuth oxide on the substrate as the main component.

A film made of cobalt oxide, rare earth oxide, alkaline earth oxide, etc. is formed by sputtering, and then Z
Varistors on which an nO film is similarly deposited by sputtering have been reported. These varistors have a low rise voltage and are suitable for surge protection of low-voltage semiconductors. However, a constant representing the performance of these elements as a varistor, the voltage nonlinearity index α (α, is fixed as I = (Vlo f).

However, engineering: current, v2 voltage, C: constant, each is not large.

In addition, as a method for obtaining a low-pressure varistor with a laminated structure, Zn
A method is known in which an ohmic layer mainly composed of O and a non-ohmic layer containing barium oxide are laminated. According to this method, a low voltage varistor can be obtained by using a thin non-ohmic layer. However, in this horizontal path, the rising voltage should be proportional to the thickness of the non-ohmic layer, so if there is a distribution in the thickness of the non-ohmic layer, the current will concentrate at the thinnest part, resulting in extremely unstable characteristics. Or you can only get something that is extremely weak against surges.

The present invention improves these drawbacks by realizing a voltage nonlinear resistor with a low rise voltage and a large α. Examples thereof will be described in detail below.

The drawings show the basic structure of the device according to the present invention, in which 1 is a layer mainly composed of ZnO, 2 is a layer containing cobalt oxide and a metal oxide MO (where M is barium, strontium, or lead). , 3 are electrodes. With such a configuration, an energy barrier is formed at the interface between the ZnO main component layer and the layer containing cobalt oxide and metal oxide, and this energy barrier exhibits non-ohmic properties, providing 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 voltage nonlinearity with positive and negative symmetry.

(Example 1) ZnO powder was molded into a diameter of 40 mm and a thickness of 20 mm by a normal molding method, and placed in a SiC mold at 1200° C. while applying a pressure of 200 Kt/c and a in air. The obtained sintered body, which was pressure-fired for 10 hours, was cut into disks with a thickness of 0.6 mm, mirror-polished using alumina fine 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 powder was coated on the ZnO mirror 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 760°C while applying a pressure of 4 o, o Ky/cd, and then a mulch vapor deposition electrode was provided on the ZnO substrate on both sides of the element, and a 1W square chip was formed. It was cut out and its electrical properties were measured. , Table 1 shows the voltage non-linearity index α and the rising voltage (terminal voltage when a current of 1 mm/11s2 is passed) in the range of 01 to 1 mm/cJ for each element. Compositions A1 to 16 in Table 1 are examples within the scope of the present invention, and 71fli17 marked with an *
-20 are shown as comparative examples. From Table 1,
99.9 in terms of Co203 form
9 to 46 mol%, 0.0 in terms of metal oxide iMo (where M is lithium, strontium, or lead)
By using a composition containing 1 to 66 mol%, α is 11
From the above, it can be seen that a good low voltage (no risk) can be obtained with a rising voltage of 8 V or less.It can also be seen that the same effect can be obtained even if BaO, SrO, and PbO are added at the same time.

(Margin below) Table 1: Comparative example (Example 2) Among the compositions used in Example 1, the composition shown in A3 of Table 1 was used to investigate the effect of manufacturing conditions.Table 2 This shows the relationship between firing temperature and electrical properties when laminated and pressure fired. 1) Good properties were obtained at firing temperatures of 500°C to 960°C. case,
The adhesive strength of the laminated portion was weak, and a practical product could not be obtained.

Table 2 In this example, lamination and pressure firing was carried out at a pressure of 400 h/cA, but the effect of the pressure at that time was further investigated. As a result, at a pressure lower than s O”tlc4,
When taken out after firing, sufficient adhesion strength between the ZnO substrate and the layer containing cobalt oxide and metal oxide could not be obtained. On the other hand, firing at a pressure as high as 1000 Kp/d often caused cracks in the ZnO substrate, which was not appropriate.

Against this, 50'&/ca ~ 1000 Ky,/c
The products fired at pressure A showed almost the same electrical properties and had no problems in terms of adhesive strength and cracking, which was a result of 0 or more, so the lamination pressure was 50 to 1000'C1.
/lU was found to be appropriate.

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 0~1tsoo++; p/c, A
The firing temperature was varied between 700°C and 1500°C, and the effects thereof were investigated. As a result, the pressure during firing is 60 /
If it was less than c4, 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 was performed under a pressure of 60'&/ca or higher, good ZnO substrates were obtained at any pressure. If the pressure is too high, other problems such as the equipment will become expensive, so there is no point in raising the pressure too high. The appropriate firing pressure for the ZnO substrate was 50 to 15001j/c'.

If the firing temperature is less than 800°C, sintering will be insufficient;
When the temperature was higher than 400° C., ZnO grain growth progressed too much, causing problems such as weakening of mechanical strength. Therefore, a suitable firing temperature is 80°C to 140°C. It was also found that a sufficiently dense ZnO substrate could be obtained if the firing time was one hour or more.

In this example, one layer containing cobalt oxide and a metal oxide is laminated in a sandwich manner between two ZnO substrates, and on top of this, another layer containing cobalt oxide and a metal oxide is provided. Furthermore, if ZnO substrates are laminated, the varistor of Example 1 can be stacked, considering that the varistor action of the present invention occurs at the interface between the layer containing cobalt oxide and metal oxide and the ZnO substrate, as described at the beginning of the example. It is clear that the same effect as when two varistors are connected in series can be obtained, and by increasing the number of laminated layers in this way, a higher voltage varistor can be obtained.

Although a ZnO substrate was used in this example, various additives that control the specific resistance of the ZnO substrate, such as trivalent elements such as aluminum and gallium, and monovalent elements such as lithium, may be added to improve the characteristics. Various variations are possible, so the invention is not limited to pure ZnO substrates.

In addition, when forming a layer containing cobalt oxide and metal oxide, CO2O3 was used in this example, but Coo,
Similar results were obtained using 0o504 and the like. Therefore, the present invention is not limited only to the oxides expressed in this example.

Among the devices obtained by the material composition and method of the present invention, the layer containing cobalt oxide and metal oxide exhibited an ohmic resistance value. That is, powder consisting of cobalt oxide and metal oxide mixed within the composition range used in the present invention was fired in the temperature range used in the present invention, and the voltage-current characteristics were measured.・Exhibited ohmic resistance characteristics of the mouth. Moreover, Zn used in the present invention
As a result of measuring the resistance value of the O substrate, a value of approximately 1 Ω·m was obtained. Since the thickness of the layer containing cobalt oxide and metal oxide in the device of the present invention was approximately o, o sw, 11
The resistance of the entire element in the case of a 1B chip is approximately SO
OΩ to 6Ω. However, the resistance obtained from the voltage-current characteristics below the rising stain pressure of the element was about 1 MΩ. Therefore, the cause of this high resistance is due to another cause, and as a result of investigation, an energy barrier is formed at the interface between the ZnO layer and a layer containing cobalt oxide and metal oxide, and this energy barrier is responsible for the high resistance. It was found that this is because it has a non-ohmic property that allows current to flow rapidly when the voltage exceeds a certain level. This means that the reciprocal of the square of the capacitance is proportional to the bias voltage.

Therefore, the rising voltage of the device of the present invention hardly depends on the thickness of the layer containing cobalt oxide and metal oxide, but depends on the energy barrier formed at the interface between it and the ZnO layer. Therefore, even if the thickness of the layer containing cobalt oxide and metal oxide varies, the device of the present invention has a current concentration i
Shows good surge characteristics. In fact, one person, one
Almost no deterioration was observed even when an impulse current of 0x100 μB was applied. Moreover, even when many samples were made, they showed almost the same characteristics and were extremely stable. Such properties have never been observed with a non-ohmic layer sandwiched between ZnO layers.

As described above, the present invention was first obtained through a skillful combination of material composition and manufacturing method, and the voltage nonlinear resistor according to the present invention is useful for improving the reliability of electronic equipment using semiconductor elements. It is something.

[Brief explanation of the drawing]

The drawings are cross-sectional views showing the structure of an embodiment of the present invention.01...ZnO main component layer,2...layer containing cobalt oxide and metal oxide,3... ···electrode. Name of agent: Patent attorney Toshio Nakao and one other person f 13-

Claims (1)

[Claims] (1) 45 to 99.99 mol% x of cobalt oxidized (CO2O3) and one or more of barium, strontium, and lead as an oxide MO (however,
A region containing 0.01 to 66 mol% in terms of barium, strontium or lead (M is barium, strontium or lead) is sandwiched between two regions containing zinc oxide as the main component, and these are stacked in pairs or more. A voltage nonlinear resistor comprising a laminate, and electrodes are formed on both front and back surfaces of the laminate. (Effectiveness) A film containing at least one of cobalt oxide and barium, strontium, or lead oxide is formed on the main surfaces of at least two substrates containing zinc oxide as a main component, and After laminating the films in such a way that they are arranged alternately and the outermost layer is the substrate mainly composed of zinc oxide, they are bonded by heat treatment while applying pressure, and electrodes are placed on both the front and back surfaces of the resulting laminate. (3) A method for manufacturing a voltage nonlinear resistor, characterized in that the laminate is bonded by heat treatment at 500 to 960°C while applying a pressure of 50 to 1000% = /cJ. The method of manufacturing a voltage non-linear resistor according to Claim No. @) = 81 (4 substrates are molded from powder containing zinc oxide as a main component, A method for manufacturing a voltage nonlinear resistor according to claim (2), characterized in that a sintered body obtained by firing while applying a pressure of 16004/c4 is used.