JPS6410085B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a voltage nonlinear resistor with extremely low rise 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 that generate surges, 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, ZnO was used as these surge protection elements.
ZnO voltage nonlinear resistors (hereinafter referred to as varistors) are known, which are obtained by adding and sintering trace amounts of additives such as Bi ₂ O ₃ , Co ₂ O ₃ , and MnO ₂ . ZnO varistors are stable against surges and exhibit excellent surge protection ability. However, ZnO varistors utilize the non-ohmic nature of grain boundaries in sintered bodies, which makes it difficult to obtain one for low pressure. That is, since the rising voltage is proportional to the number of grain boundaries inserted in series between the electrodes, in order to obtain a low rising voltage, the thickness of the element must be reduced.
However, since the particle size of ZnO particles is from several μm to 10-odd μm, when trying to obtain one for low pressure, the thickness must be increased several times.
Although it needs to be 100 μm or less, 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, a film made of bismuth oxide, cobalt oxide, rare earth oxide, alkaline earth oxide, etc. was formed by sputtering on a substrate mainly composed of ZnO, and A varistor with a ZnO film layered thereon by sputtering has also been reported. These varistors have a low rise voltage and are suitable for surge protection of low-voltage semiconductors. However, a constant that expresses the performance of these elements as a varistor, a voltage nonlinear index, α (α is defined as I = (V / C) 〓, where I: current, V: voltage, C: constant ) is not that large. 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 drawing shows 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 other metal oxides, and 3 is an electrode. With this configuration, an energy barrier is formed at the interface between the ZnO main component layer and the layer containing cobalt oxide and other metal oxides, and this energy barrier exhibits non-ohmic properties, resulting in an effect as a varistor. It will be done. 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 powder with a diameter of 40
mm, thickness 20mm, put in a SiC mold and heated to 1200℃
Pressure firing was performed in air for 10 hours while applying a pressure of 200 kg/cm ² . The obtained sintered body was cut into a disk with a thickness of 0.5 mm, mirror-polished using fine alumina powder, and then thoroughly washed with an organic solvent. next,
The oxide composition powder shown in Table 1 is dispersed in an organic binder and an organic solvent to form a paste.
Coated on a 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 board was heated to 400℃ at a temperature of 750℃.
Pressure firing was performed in air for 1 hour while applying a pressure of Kg/cm ² , and then Al was deposited on the ZnO substrate on both sides of the device.
A vapor-deposited electrode was provided, the chip was cut into 1 mm square chips, and the electrical properties were measured. Table 1 shows the voltage nonlinearity index α and the rising voltage (terminal voltage when a current of 1 mA/mm ² is applied) in the region of 0.1 to 1 mA/cm ² for each element. Composition No. 1 in Table 1
-34 are examples within the scope of the present invention, and No. 34 is marked with 〓.
35 to 38 are shown as comparative examples. From Table 1, convert cobalt oxide into the form of Co ₂ O ₃ ,
99.96 mol% to 45 mol%, bismuth oxide 0.01 to 54.97 mol% in the form of Bi ₂ O ₃ , praseodymium oxide 0.01 to 54.97 mol % in the form of Pr ₂ O ₃ , barium oxide to BaO Convert to the form of 0.01~
54.97 mol% and at least one or more of manganese, antimony, boron, nickel, and lithium, each converted into the form of MnO ₂ , Sb ₂ O ₃ , B ₂ O ₃ , NiO, and Li ₂ O, from 0.01 to 20.0 Mol%, 0.01-5.0
Mol%, 0.01-10.0 Mol%, 0.01-20.0 Mol%,
By using a composition containing 0.001 to 0.5 mol%,
It can be seen that a good low-voltage varistor with α of 15 or more and a rise voltage of 8V or less can be obtained.

【table】

[Table] * indicates a comparative example (Example 2) Among the compositions used in Example 1, the composition shown in No. 28 of Table 1 was used to examine the effect of manufacturing conditions. Table 2 shows the relationship between the firing temperature and electrical properties when laminating and pressurizing firing, and shows the relationship between the firing temperature and electrical characteristics when laminated and pressure fired.
Good properties were obtained at a firing temperature of . In addition,
When firing at a temperature lower than 500°C, the adhesive strength of the laminated portion was weak and a practical product could not be obtained.

[Table] In this example, lamination and pressure firing was carried out at a pressure of 400 Kg/cm ² , but the effect of the pressure at that time was further investigated. As a result, when the pressure was less than 50 Kg/cm ² , sufficient adhesion strength between the ZnO substrate and the layer containing cobalt oxide and other metal oxides could not be obtained when taken out after firing. On the other hand, firing at a pressure higher than 1000 Kg/cm ² was not suitable as many cracks appeared in the ZnO substrate. 50Kg/ ^cm2 ~
Those fired at a pressure of 1000 kg/cm ² showed almost the same electrical properties and had no problems in terms of adhesive strength or cracking. From the above results, it was found that a lamination pressure of 50 to 1000 Kg/cm ² is appropriate. Next, we investigated the effect of firing time in laminated pressure firing. As a result, it was found that if the material was kept at the firing temperature for 10 minutes or more, there were no significant changes in the electrical properties. Next, we investigated the firing conditions for the ZnO substrate used as the substrate. The firing pressure was varied between 0 and 1500 Kg/cm ² and the firing temperature was varied between 700°C and 1500°C, and the effects thereof were investigated. As a result, the pressure during firing was 50Kg/cm ²
If it is less than that, there will be many pores on the surface of the ZnO substrate after polishing, and therefore only those with extremely unstable characteristics can be obtained. When firing at a pressure of 50Kg/cm2 or ^more , good results are obtained at any pressure.
A ZnO substrate was obtained. If the pressure is too high, other problems will occur, such as the equipment becoming expensive, so there is no point in increasing the pressure too much, especially if there is no significant effect. The firing pressure for ZnO substrate is 50~
1500Kg/cm ² was appropriate. When the firing temperature was less than 800°C, sintering was insufficient, and when the firing temperature was higher than 1400°C, ZnO grain growth progressed too much, resulting in problems such as weakening of mechanical strength. Therefore, a suitable firing temperature is 800°C to 1400°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 other metal oxides is stacked on two ZnO substrates in a sandwich pattern, and on top of this, another layer containing cobalt oxide and other metal oxides is stacked on two ZnO substrates. layer,
Furthermore, if ZnO substrates are laminated, the varistor effect of the present invention occurs at the interface between the layer containing cobalt oxide and other metal oxides and the ZnO substrate, as described at the beginning of the example, and therefore, the effect of Example 1 can be improved. 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. Note that although a ZnO substrate was used in this example, ZnO
Various additives that control the specific resistance of the substrate, such as trivalent elements such as aluminum and gallium, and
It is also possible to change the properties in various ways by adding a valence element such as lithium, so the present invention is not limited to pure ZnO substrates. In addition, when forming a layer containing cobalt oxide and other metal oxides, in this example, Co 2 O 3 and Co ₂ O ₃ , respectively
Pr ₂ O ₃ , MnO _{2 ,} etc. were used, but CoO, Co ₃ O ₄ ,
Similar results were obtained using MnO and the like. Therefore, the present invention is not limited only to the oxides shown in this example. As described above, the present invention was obtained for the first time through a skillful combination of material composition and method, and the device obtained from the present invention is useful for improving the reliability of electronic devices using semiconductor devices. It is a thing.

[Brief explanation of drawings]

The drawing is a sectional view showing the structure of an embodiment of the present invention. 1... ZnO main component layer, 2... Layer containing cobalt oxide and other metal oxides, 3... Electrode.

Claims (1)

[Claims] 1. 45 to 99.96 mol% of cobalt in the form of cobalt oxide (Co ₂ O ₃ ) and 0.01 to 54.97 mol % of bismuth in the form of bismuth oxide (Bi ₂ O ₃ ). , 0.01 to 54.97 mol% of praseodymium in the form of praseodymium oxide (Pr ₂ O ₃ ), and barium in the form of barium oxide (BaO).
0.01 to 54.97 mol%, and at least one or more of manganese, antimony, boron, nickel, and lithium, MnO ₂ , Sb ₂ O ₃ , B ₂ O ₃ , NiO,
0.01 to 20.0 mol%, 0.01 to 5.0 mol%, 0.01 to 10.0 mol%, and 0.01 to 0.01 to 20.0 mol%, respectively, in terms of _Li2O form.
A region containing 20.0 mol% and 0.001 to 0.5 mol% is sandwiched between two regions containing zinc oxide as the main component in a sandwich-like pattern, and one or more sets of these are stacked to form a laminate, and both the front and back sides of this laminate are stacked. A voltage nonlinear resistor characterized by having electrodes on its main surface. 2. The voltage nonlinear resistor according to claim 1, wherein the region containing zinc oxide as a main component is a polycrystalline sintered body. 3. All of cobalt oxide, bismuth oxide, praseodymium oxide, and barium oxide, and manganese oxide, antimony oxide, boron oxide, nickel oxide, and lithium oxide are respectively deposited on the main surfaces of at least two zinc oxide-based substrates. After forming a film containing one or more of the above, and laminating the substrate and the film so that the substrate and the film are arranged alternately and the outermost layer is the substrate containing the zinc oxide as a main component, heat treatment is performed while applying pressure. 1. A method for manufacturing a voltage nonlinear resistor, comprising: bonding the laminate with a laminate, and forming electrodes on both the front and back principal surfaces of the obtained laminate. 4. As a substrate, powder containing zinc oxide as the main component is molded and heated to 50 to 1500 kg/cm ² in air at 800 to 1400°C.
4. The method of manufacturing a voltage nonlinear resistor according to claim 3, characterized in that a sintered body obtained by firing while applying pressure is used. 5 While applying a pressure of 50 to 1000Kg/ ^cm2 ,
4. The method of manufacturing a voltage nonlinear resistor according to claim 3, wherein the laminate is bonded by heat treatment at 950°C.