JPH0574608A - Manufacture of voltage-dependent nonlinear resistor - Google Patents

Abstract

PURPOSE:To increase crystal grain diameter because, in the case where varistor voltage is lowered for a low voltage circuit use, the thickness of a resistor must be 0.1-0.2mm, and the strength is insufficient when zinc oxide crystal grain diameter is 10-20mum. CONSTITUTION:By reducing the quantity of admixture forming the grain boundary of zinc oxide crystal grain, the crystal grain diameter can be made large without deteriorating voltage nonlinearity. That is, the following values are set; the total loadings of at least one of Pr and La is 0.08-2.0atomic%, the total loadings of at least one of Mg and Ca is 0.001-2.0atomic%, the total loadings of at lest one of K, Cs, and Rb is 0.001-0.5atomic%, and the loading of Cr is 0.001-0.5atomic%. By performing baking in the atmosphere wherein oxygen partial pressure is 40% or higher, the baking temperature is lowered and the irregularities of characteristics are reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a voltage non-linear resistor which contains zinc oxide (ZnO) as a main component and is used for overvoltage protection particularly in a low voltage circuit.

[0002]

2. Description of the Related Art Electronic devices, electric devices, especially semiconductor devices
Overcurrent of equipment such as those with small overcurrent capability
A varistor mainly composed of ZnO is suitable for protection against pressure.
It is known that The main component is such ZnO
Among the baristas listed above,
As disclosed in Japanese Patent Application Laid-Open No. 1-25205, containing zinc oxide as a main component,
The total amount of at least one rare earth element as an accessory component
0.08 to 5.0 atomic%, cobalt 0.1 to 10.0 atomic%,
0.01 to at least one of gnesium and calcium
5.0 atomic%, less of potassium, cesium, and rubidium
At least one kind 0.01-1.0 atomic% in total and 0.01 in chromium
~ 1.0 atomic%, boron 5 × 10^-Four~ 1 x 10 ^-1Atomic% and
And aluminum, gallium, and indium
1 x 10 in total^-Four~ 5 x 10^-2Add in atomic% range
The voltage non-linear resistor made by firing
Has a large non-linearity, high long-wave surge withstand capability, and voltage life
It has excellent characteristics.

[0003]

[Problems to be Solved by the Invention]
Addition of rare earth elements such as aluminum and lanthanum, cobalt, etc.
Zinc oxide varistors made by sintering after mixing with other objects
As for linearity, praseodymium, lanthanum, etc. are crystallized by sintering.
It is thought to be caused by precipitation at grain boundaries.
The varistor voltage per grain boundary layer of a practical varistor is
Is almost constant, so the varistor voltages of the elements are opposite
It is determined by how many layers of grain boundaries exist between the electrodes.
Varistors for high-voltage circuits have a large varistor voltage.
Increase element thickness or crystal to
The particle size may be reduced. On the contrary, targeting low voltage circuits
In the case of a device, reduce the device thickness or crystal
It is necessary to make the particle size sufficiently large. The varistor voltage is
Terminal voltage V at 1mA current _1mAIs defined by
For example, V commonly used for DC12V circuits_1mA= 22V
With a varistor, the varistor voltage per grain boundary layer is approximately 2V.
Therefore, the particles that may exist between the terminal electrodes of the varistor
The world has about 11 layers. Manufacture ZnO varistor by conventional method
Then, since the crystal grain size is 10 to 20 μm,
In order to set the lister voltage to 22V, the device thickness should be 0.1-
Must be 0.2 mm. However, the ZnO varistor
Such a sintered body has a mechanical strength of 0.1 to 0.2 mm.
It is weak and cracks, making it unusable. Therefore, the crystal grain size
Ensuring the element thickness is sufficiently large and the varistor voltage is high.
It is effective to lower the amount, but the conventional composition and manufacturing method
In order to promote sufficient grain growth, the method
Higher temperature is required, and in that case voltage / current
There was a problem that the linearity was not sufficient. Also, ZnO particles
Using ZnO varistor powder as a core particle,
Also known is a method of manufacturing a low voltage varistor by molding and firing.
However, this method causes large variations in product characteristics and
There is a problem in childbirth.

The object of the present invention is to solve the above-mentioned problems,
It is an object of the present invention to provide a method for manufacturing a voltage non-linear resistor which is suitable especially when the varistor voltage is small.

[0005]

In order to achieve the above object, the present invention comprises zinc oxide as a main component, to which at least one of praseodymium and lanthanum, at least one of magnesium and calcium, and potassium. At least one of cesium and rubidium, chromium, boron and aluminum are added to the raw material powder, which is mixed and shaped, and then fired. The total amount of at least one of these
It shall be 0.08 to 2.0 atomic%. Further, the total addition amount of at least one of magnesium and calcium in all the constituent metal elements is 0.001 to 2.0 atom%, the total addition amount of at least one of potassium, cesium and rubidium is 0.001 to 0.5 atom%, or the addition of chromium. It is effective to set the amount to 0.001 to 0.5 atom%. It is also effective to carry out the firing in an atmosphere having an oxygen partial pressure of 40% or more.

[0006]

[Function] When the research on the addition amount of the constituent element of the above-mentioned known zinc oxide voltage non-linear resistor was advanced, the crystal grain growth was suppressed when the total addition amount of at least one of praseodymium and lanthanum exceeded 2.0% by weight. In fact, the total amount of addition of at least one of magnesium and calcium is 2.
0 atomic%, the total amount of at least one of potassium, cesium and rubidium added is 0.5 atomic%, and the amount of chromium added is 0.5 atomic%.
It has been found that the voltage / current non-linearity of a voltage non-linear resistor for low-voltage circuits decreases when the content of each exceeds 0.5 atom%. This is considered to be due to the following reasons.

Praseodymium or lanthanum is an important additive in forming grain boundaries during sintering and exhibiting voltage non-linearity. Further, magnesium, calcium, potassium, etc. are present in the crystal grain boundaries and in the vicinity of the grain boundaries, and are effective in increasing the voltage nonlinear coefficient, especially in the large current region. However, when only magnesium, calcium, potassium, etc. are added, the resistance of the resistor becomes high and the limiting voltage rises greatly. Therefore, the limiting voltage is suppressed to an appropriate value by adding chromium. As mentioned above, in manufacturing zinc oxide varistor for low voltage circuit, it is effective to increase the crystal grain size, and the element thickness is 0.7mm or more as a practical varistor.
The particle size is preferably 50 μm or more. For that purpose, it is desirable to reduce the amount of subcomponents other than zinc oxide, which is the main component, especially the grain boundaries and the amount of elements existing near the grain boundaries.
In this case, the proportion of grain boundaries in the sintered body is smaller than that of zinc oxide varistors for medium and high voltage circuits, so the voltage non-linearity can be reduced even if the amount of sub-component elements existing at grain boundaries and near the grain boundaries is reduced. Sex is not impaired.

Furthermore, after the zinc oxide varistor powder according to the present invention is mixed and shaped, it is fired in an atmosphere having an oxygen partial pressure of 40% or more, so that a predetermined crystal grain size is obtained as compared with firing in the air. It has been found that the firing temperature required for obtaining the zinc oxide varistor can be greatly reduced and a zinc oxide varistor with less variation in characteristics can be provided. 14 in the atmosphere
Although a firing temperature of 00 ° C or higher is required, it is difficult to obtain a homogeneous sintered body under such conditions, and reproducibility such as control of characteristics is difficult, and it is difficult to obtain a product for practical use.

[0009]

EXAMPLES Pr ₆ O ₁₁ in ZnO _{powder, Co 3 O 4, MgO,} K 2
Co ₃ , Cr ₂ O ₃ , B ₂ O ₃ , and Al ₂ O ₃ powders were added and mixed sufficiently to prepare a raw material powder. The amount of addition is the ratio of the number of atoms to the total number of atoms of each component metal element in the raw material,
0.08 to 2.0% for Pr, 0.1 to 1.0 for Co
%, 0.001 to 2.0 atomic% for Mg, and 0 for K.
001 to 0.5 atomic%, 0.001 to 0.5% for Cr, 5 × 10 ^-4 to 1 × 10 ^-1 % for B, and 1 for Al.
It was set to be in the range of × 10 ^{-4 to} 5 × 10 ^-2 %. And
The raw material powder is calcined in the temperature range of 500 to 1000 ° C for several hours, and the calcined product is sufficiently crushed.
m, 1.2mm thick, pressed into a disc and molded at 1400-1500 ℃
Sintered bodies were obtained by sintering in the temperature range of 2 hours in air. The average crystal grain size of the sintered body thus obtained was measured, and electrodes were baked on both sides of the sintered body to measure the electrical characteristics. As a result, a crystal grain size of 50 μm or more was observed, and a DC12V circuit varistor with V _1mA = 22V was obtained. Such results are obtained even if some or all of Pr in the above raw material powder is replaced with La, some or all of Mg is replaced with Ca, and some or all of K is replaced with Rb or Cs or both. I was able to get it.

The sintered product obtained by firing the above-mentioned molded product in the temperature range of 1200 to 1400 ° C. for 2 hours in the atmosphere of oxygen partial pressure of 40 to 100% has the same crystal grain size and electrical property. The characteristics were obtained, and the variation could be reduced.

[0011]

According to the present invention, the crystal grain size can be increased without impairing the voltage non-linearity by reducing the amount of the additive element existing in the crystal grain boundary and in the vicinity thereof. It has become possible to reduce the varistor voltage without reducing the thickness. In addition, the oxygen partial pressure of 40
%, The sintering temperature can be lowered, and a zinc oxide voltage non-linear resistor for low voltage circuits with less variation in characteristics can be manufactured.

Claims (5)

[Claims] 1. A main component is zinc oxide, to which at least one of praseodymium and lanthanum, at least one of magnesium and calcium, at least one of potassium, cesium and rubidium, chromium, boron and aluminum are added. In the method for manufacturing a voltage nonlinear resistor, in which the added raw material powder is mixed and shaped, and then fired, the total amount of at least one of praseodymium and lanthanum in all the metal elements is added.
A method for manufacturing a voltage non-linear resistor, which comprises 0.08 to 2.0 atomic%. 2. The total addition amount of at least one of magnesium and calcium in all the constituent metal elements is 0.001 to
The method for producing a voltage nonlinear resistor according to claim 1, wherein the content is 2.0 atomic%. 3. The total addition amount of at least one of potassium, cesium and rubidium in all the metallic elements is 0.
The method for producing a voltage nonlinear resistor according to claim 1 or 2, wherein the content is 001 to 0.5 atom%. 4. The addition amount of chromium in all the metallic elements is 0.00
The method for producing a voltage non-linear resistor according to claim 1, 2 or 3, wherein the content is 1 to 0.5 atom%. 5. The method for producing a voltage non-linear resistor according to claim 1, wherein the firing is performed in an atmosphere having an oxygen partial pressure of 40% or more.