Method of manufacturing a voltage-nonlinear resistor

A method of manufacturing a voltage-nonlinear resistor which has a substantially symmetrical voltage-current characteristic and a large voltage-nonlinearity coefficient and which is thus well resistant to surge voltage. The method comprises: preparing a ZnO-based composition containing metal zinc, at least one metal oxide such as bismuth oxide and at least one spinel type crystalline compound such as spinel type crystalline chromium compound, shaping the ZnO-based composition to form a body, and sintering the body of composition in the air at 1,000.degree. C. or more.

BACKGROUND OF THE INVENTION 
This invention relates to a method of manufacturing a voltage-nonlinear 
resistor, and more particularly a method wherein a ZnO (zinc oxide)-based 
starting composition containing a small amount of metal zinc is shaped and 
then sintered. 
In recent years semiconductor elements and semiconductor circuits such as 
transistors, thyristors, and ICs have been rapidly improved. Their 
characteristics thus improved, the semiconductor elements and circuits are 
used in increasing numbers in measuring devices, control devices, 
communication devices and power supply devices. Provided with such 
semiconductor elements and semiconductor circuits, the devices are 
successfully miniaturized and come to have a high efficiency. On the other 
hand, however, these devices and their parts cannot be said to be 
sufficiently resistant against high voltage, surge voltage and noise. It 
is therefore demanded that these devices or their parts be protected 
against an abnormally high voltage or an abnormally large noise. That is, 
the circuit voltage of the devices or their part should be stabilized. 
Voltage-nonlinear resistors meet the demand. Thus it is required that 
there should be developed voltage-nonlinear resistors which has an 
excellent voltage-nonlinearity, a large discharge capacity, a long life, 
and a highly resistant characteristics against an abnormally high voltage 
or noise. 
Hitherto, to stabilize the circuit voltage of measuring devices, control 
devices, communication devices and power supply devices, use has been made 
of voltage-nonlinear resistors such as SiC varistors and Si varistors. 
Zener diodes have been also used for the same purpose. Recently developed 
is a varistor made of a ZnO-based composition containing a few additives. 
The voltage-current characteristic of a varistor is generally determined by 
the following formula: 
EQU I=(V/C).sup..alpha., 
where V is the voltage across the varistor, I the current flowing through 
the varistor, C a constant, and .alpha. a nonlinearity coefficient. When 
.alpha.=1, the varistor is an ordinary resistor covered by the Ohm's law. 
The larger is .alpha., the better voltage-nonlinearity. Generally, the 
varistor characteristic is determined by C and .alpha.. Here, the varistor 
characteristic is expressed by .alpha. and a starting voltage V.sub.1 mA 
at 1 mA. 
Known SiC varistors are made by sintering SiC particles bonded together by 
a ceramic binder. The voltage-nonlinearity of the SiC varistors is 
determined by the dependancy of the contact resistance of SiC particles on 
the voltage applied to them. Thus, the value of C can be controlled by 
changing the thickness of the varistor, measured in the direction in which 
current flows through the varistor. But the nonlinearity coefficient of 
SiC varistors is relatively small, usually 3 to 7. Further, to manufacture 
an SiC varistor it is necessary to sinter an SiC mass in a non-oxidizing 
atmosphere. 
Si varistors, whose voltage-nonlinearity owes to p-n junctions formed in an 
Si mass. The value of C cannot therefore be controlled over a broad range. 
Similarly, the voltage-nonlinearity of Zener diodes owes to p-n junctions 
formed in them. Despite their very good voltage-nonlinearity, Zener diodes 
cannot make resistor elements for a high voltage. They are disadvantageous 
also in that they are not sufficiently resistant against a surge voltage. 
Other known voltage-nonlinear resistors are ceramic varistors made of a 
ZnO-based composition containing bismuth oxide, cobalt oxide, manganese 
oxide, antimony oxide and the like. These are rather varistors of new 
type. They exhibit an excellent voltage-nonlinearity which owes to the 
sintered masses of ZnO-based composition themselves. But the rate at which 
their V.sub.1 mA varies in positive direction when a large impulse current 
flows through them much differs from the rate at which their V.sub.1 mA 
varies in negative direction when a large impulse current flows through 
them. That is, ceramic varistors do not exhibit a symmetrical 
voltage-current characteristic. Thus they are not sufficiently stable and 
therefore not sufficiently reliable. 
Other ceramic varistors are known which are made of a ZnO-based composition 
containing nickel oxide, barium oxide and the like or a ZnO-based 
composition containing rare earth element and cobalt oxide, but not 
containing bismuth oxide. Indeed these ceramic varistors exhibit a 
voltage-current characteristic less asymmetrical than that of the ceramic 
varistors made of a ZnO-based composition containing bismuth oxide among 
other additives. Further, their V.sub.1 mA varies but very little. But 
they are less resistant against a surge voltage. In addition, they do not 
function for a sufficiently long time. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a method of manufacturing a 
voltage-nonlinear resistor which exhibits a substantially symmetrical 
voltage-current characteristic and which is highly resistant against a 
surge voltage. 
According to this invention there is provided a method of manufacturing a 
voltage-nonlinear resistor made of a sintered ZnO-based composition body 
which exhibits a voltage-nonlinearity. The method comprises steps of 
preparing a ZnO-based composition containing at least 0.001 to 20 mol% of 
metal zinc and at least one metal oxide selected from the group consisting 
of 1 mol% or less of bismuth oxide, 1 mol% or less of cobalt oxide and 1 
mol% or less of manganese oxide; shaping the ZnO-based composition in the 
form of a plate or a rod; sintering the body of composition thus shaped at 
1,000.degree. C. or more in an oxidizing atmosphere; and forming 
electrodes on the body of composition thus sintered so as to be 
electrically connected to the sintered body. 
Another method of manufacturing a similar resistor according to this 
invention comprises steps of preparing a ZnO-based composition containing 
at least 0.01 to 20 mol% of metal zinc, at least one metal oxide selected 
from the group consisting of 1 mol% or less of bismuth oxide, 1 mol% or 
less of cobalt oxide and 1 mol% or less of manganese oxide, and at least 
one spinel type crystalline compound selected from the group of 0.001 to 
10 mol% of spinel type crystalline compound of antimony, 0.001 to 10 mol% 
of spinel type crystalline compound of titanium, 0.001 to 10 mol% of 
spinel type crystalline compound of chromium and 0.001 to 10 mol% of 
spinel type crystalline compound of tin; shaping the ZnO-based composition 
in the form of a plate or a rod; sintering the body of composition thus 
shaped at 1,000.degree. C. or more in an oxidizing atmosphere; and forming 
electrodes on the body of composition thus sintered so as to be 
electrically connected to the sintered body.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now this invention will be described in detail with reference to several 
examples. 
EXAMPLE 1 
Three ZnO-based compositions were prepared. These compositions contained 
bismuth oxide, cobalt oxide, manganese oxide and metal zinc. But each 
contained these additives in a different mol percentage. Zinc oxide and 
the additives had been thoroughly mixed. Several discs having a diameter 
of 20 mm and a thickness of 0.5 mm were made of the first composition for 
providing resistors with V.sub.1 mA of 100 V. Several discs having a 
diameter of 20 mm and a thickness of 1 mm were made of the second 
composition for providing resistors with V.sub.1 mA of 200 V. Several 
discs having a diameter of 20 mm and a thickness of 1.5 mm were made of 
the third composition for providing resistors with V.sub.1 mA of 300 V. 
All the discs were sintered in the air at 1,000.degree. C. or more. The 
discs thus sintered were provided with electrodes, by Ag paint fusing, 
vapor deposition of silver or spraying of aluminum, whereby 
voltage-nonlinear resistors were manufactured. 
Further manufactured were voltage-nonlinear resistors which were the same 
as those of Example 1, except that the starting compositions did not 
contain metal zinc. These resistors will hereinafter be called "Control 
1". Also manufactured were voltage-nonlinear resistors which were the same 
as those of Example 1, except that the ZnO-based compositions contained 
only nickel oxide and barium oxide. These resistors will hereinafter be 
called "Control 2". 
The sintering temperatures and compositions of Example 1 and Controls 1 and 
2 were as shown in the following Table 1: 
TABLE 1 
__________________________________________________________________________ 
V.sub.1 mA 100V V.sub.1 mA 200V 
V.sub.1 mA 300 V 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,250.degree. C. 
temp. 1,200.degree. C. 
temp. 1,150.degree. C. 
__________________________________________________________________________ 
Example 1 
Bi.sub.2 O.sub.3 
0.7 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
Zn 3 mol % 
Zn 3 mol % 
Zn 1 mol % 
ZnO 95.3 mol % 
ZnO 95.5 mol % 
ZnO 97.5 mol % 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,250.degree. C. 
temp. 1,200.degree. C. 
temp. 1,150.degree. C. 
__________________________________________________________________________ 
Control 1 
Bi.sub.2 O.sub.3 
0.7 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol% 
MnO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
ZnO 98.3 mol % 
ZnO 98.5 mol % 
ZnO 98.5 mol % 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,300.degree. C. 
temp. 1,200.degree. C. 
temp. 1,150.degree. C. 
__________________________________________________________________________ 
Control 2 
NiO 1 mol % 
NiO 1 mol % 
NiO 1 mol % 
BaO 1 mol % 
BaO 1 mol % 
BaO 1.5 mol % 
ZnO 98 mol % 
ZnO 98 mol % 
ZnO 97.5 mol % 
__________________________________________________________________________ 
The sintered discs of Example 1 and Controls 1 and 2 exhibited a 
nonlinearity. That is, their V.sub.1 mA varied in proportion to their 
thickness. However, Example 1, Control 1 and Control 2 showed different 
V.sub.1 mA-.alpha. relationships as illustrated in FIG. 1. In FIG. 1, 
curve 1 indicates the V.sub.1 mA-.alpha. relationship of Example 1, curve 
2 that of Control 1 and curve 3 that of Control 3. As FIG. 1 clearly 
shows, the resistors of Example 1 had a nonlinearity coefficient greater 
than Control 1 and Control 2. Further, as curve 1 shows, the resistors of 
Examiner had a large nonlinearity coefficient .alpha. over a broad range 
of V.sub.1 mA. This is a characteristic very important to a voltage 
nonlinear resistor. 
The resistors of Example 1 and Control 1, whose V.sub.1 mA was 200 V, were 
tested to ascertain their impulse current characteristic, their D.C. load 
characteristic and their temperature-humidity cycle characteristic. On the 
resistors a surge current of 500 A was applied 10,000 times, thus 
recording the impulse current characteristic, i.e. variation of V.sub.1 mA 
in positive and negative directions. This test was conducted to see if the 
voltage-nonlinear resistors could work stably as surge voltage absorbing 
elements. Further, a load of 2 watts was applied on the resistors 
continuously for 500 hours at 85.degree. C., thereby recording the D.C. 
load characteristic of the individual resistors, i.e. variation of V.sub.1 
mA in positive and negative directions. Moreover, the ambient temperature 
of these resistors was changed from -40.degree. C. to 85.degree. C. 
exactly 100 times, while applying a load of 2 watts on the resistors and 
maintaining the ambient humidity at 95%, thereby recording the 
temperature-humidity cycle characteristic of the individual resistors in 
terms of variation of V.sub.1 mA in positive and negative directions. The 
results of these tests were as shown in the following Table 2. 
TABLE 2 
______________________________________ 
Control 1 Example 1 
Positive 
Negative Positive Negative 
direction 
direction 
direction direction 
______________________________________ 
Impulse +5% -18% +3% +3% 
current 
characteristic 
D.C. load +3% -26% +2% +1.5% 
characteristic 
Temp.-humidity 
+4% -20% +2% +2% 
cycle 
characteristic 
______________________________________ 
As Table 2 clearly shows, the resistors of Example 1 exhibited better 
impulse current, D.C. load and temperature-humidity characteristics than 
those of Control 1. Table 2 further shows that the resistors of Control 1, 
i.e. known voltage-nonlinear resistors, had their V.sub.1 mA varied very 
much at a high temperature. 
The resistors of Control 2, whose V.sub.1 mA was 200 V, were put to the 
same tests. The results were that their V.sub.1 mA varies more in negative 
direction than in positive direction by 4 to 5% in terms of variation of 
V.sub.1 mA. In view of this, the resistors made of ZnO-based composition 
containing nickel oxide and barium oxide showed better impulse current, 
D.C. load and temperature-humidity cycle characteristics than those of 
Control 1, though their nonlinearity coefficient .alpha. was 35 at most as 
shown in FIG. 1. 
The resistors of Example 1, i.e. voltage-nonlinear resistors according to 
this invention, had an excellent voltage-nonlinearity. What is more, they 
exhibited good impulse current, D.C. load and temperature-humidity cycle 
characteristics in positive and negative directions. That is, they had a 
symmetrical voltage-current characteristic. They can therefore function 
stably for a long time. This impart them a high reliability and a high 
practical value. 
The ZnO-based composition, of which the resistors of Example 1 were made, 
contained bismuth oxide, cobalt oxide, manganese oxide and metal zinc. Of 
course, these oxide additives may be replaced by bismuth, cobalt and 
manganese so long as these metals are oxidized during the sintering 
process. The optimum sintering temperature may differ according to the 
amount of the additives contained in the ZnO-based composition. If the 
composition is sintered at less than 1,000.degree. C., it would not be 
sintered sufficiently, and the sintered products would not exhibit so good 
characteristics as shown in Table 2. The highest sintering temperature may 
be raised so long as the sintered products do not expand or are not 
deformed. 
A number of ZnO-based compositions were prepared, which contained metal 
zinc in different amounts, as well as bismuth oxide, cobalt oxide and 
manganese oxide in such amount as shown in Table 1. Using these 
compositions, a number of voltage-nonlinear resistors were manufactured. 
The resistors were tested, thereby recording their impulse current 
characteristic. The results were as shown in FIG. 2. As shown in FIG. 2, 
metal zinc should be contained in the ZnO-based composition in an amount 
of 0.001 mol% to 20 mol%. When it was contained in an amount outside this 
range, V.sub.1 mA of the resultant products varied in negative direction 
to the same extent as did V.sub.1 mA of Control 1. Preferably, metal zinc 
should be used in an amount of 0.01 mol% to 10 mol% in order to minimize 
the variation of V.sub.1 mA, as clearly understood from FIG. 2. 
The resistors of Example 1 were made of ZnO-based composition containing 
bismuth oxide, cobalt oxide, manganese oxide and metal zinc. They may 
contain other additives in a small amount. Such additives may be added to 
zinc oxide or be dispersed into the ZnO-based composition during the 
sintering process. Alternatively, a portion of them may be added to zinc 
oxide and the remaining portion may be dispersed into the ZnO-based 
composition during the sintering process. 
EXAMPLE 2 
Three ZnO-based compositions were prepared. Each of them contained 1 mol% 
or less of bismuth oxide, 1 mol% or less of cobalt oxide, 1 mol% or less 
of manganese oxide, 0.001 to 20 mol% of metal zinc and 0.001 to 10 mol% of 
a spinel type crystalline chromium compound. Zinc oxide and these 
additives had been thoroughly mixed. Several discs having a diameter of 20 
mm and a thickness of 0.5 mm were made of the first composition for 
providing resistors with V.sub.1 mA of 100 V. Several discs having a 
diameter of 20 mm and a thickness of 1 mm were made of the second 
composition for providing resistors with V.sub.1 mA of 200 V. Similarly, 
several discs having a diameter of 20 mm and a thickness of 1.5 mm were 
made of the third composition for providing resistors with V.sub.1 mA of 
300 V. All these discs were sintered in the air at 1,000.degree. C. or 
more. They were provided with electrodes in the same method as employed to 
manufacture the resistors of Example 1, whereby voltage-nonlinear 
resistors were manufactured. 
Also manufactured were voltage-nonlinear resistors which were the same as 
those of Example 2, except that the starting compositions did not contain 
metal zinc. These resistors will hereinafter be called "Control 3". 
The sintering temperatures and compositions of Example 2 and Control 3 were 
as shown in the following Table 3: 
TABLE 3 
__________________________________________________________________________ 
V.sub.1 mA 100V V.sub.1 mA 200V 
V.sub.1 mA 300V 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,250.degree. C. 
temp. 1,200.degree. C. 
temp. 1,150.degree. C. 
__________________________________________________________________________ 
Example 2 
Bi.sub.2 O.sub.3 
0.7 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Cr compound 
1 mol % 
Cr compound 
1 mol % 
Cr compound 
3 mol % 
Zn 6 mol % 
Zn 2 mol % 
Zn 4 mol % 
ZnO 91.3 mol % 
ZnO 95.5 mol % 
ZnO 91.5 mol % 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,250.degree. C. 
temp. 1,200.degree. C. 
temp. 1,150.degree. C. 
__________________________________________________________________________ 
Control 3 
Bi.sub.2 O.sub.3 
0.7 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub. 2 O.sub.3 
0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Cr compound 
1 mol % 
Cr compound 
1 mol % 
Cr compound 
3 mol % 
ZnO 97.3 mol % 
ZnO 97.5 mol % 
ZnO 95.5 mol % 
__________________________________________________________________________ 
The resistors of Example 2 exhibited V.sub.1 mA-.alpha. relationship which 
was substantially identified with curve 1 shown in FIG. 1. And the 
resistors of Control 3 showed V.sub.1 mA-.alpha. relationship which was 
substantially identified with curve 2 shown in FIG. 1. 
The resistors of Example 2 and Control 3, whose V.sub.1 mA was 200 V, were 
tested to ascertain their impulse current, D.C. load and 
temperature-humidity cycle characteristics, exactly in the same way as 
those of Example 1 and Controls 1 and 2 were tested. The results of the 
test were as shown in the following Table 4: 
TABLE 4 
______________________________________ 
Control 3 Example 2 
Positive 
Negative Positive Negative 
direction 
direction 
direction direction 
______________________________________ 
Impulse +4% -15% +3% +3% 
current 
characteristic 
D.C. load +3% -21% +2% +2% 
characteristic 
Temp.-humidity 
+4% -16% +2% +1.5% -cycle 
characteristic 
______________________________________ 
A number of ZnO-based compositions were prepared, which contained metal 
zinc in different amounts, as well as bismuth oxide, cobalt oxide, 
manganese oxide and spinel type crystalline chromium compound in such 
amounts as shown in Table 3. Using these compositions, a number of 
voltage-nonlinear resistors were manufactured. The resistors were tested, 
and their impulse current characteristic was recorded. The results were 
substantially the same as shown in FIG. 2. That is, they exhibited 
substantially the same impulse current characteristic as that of Example 
1. Thus, metal zinc should be contained in the ZnO-based composition in an 
amount of 0.001 mol% to 20 mol%. 
Further, a number of ZnO-based compositions were prepared, which contained 
spinel type crystalline chromium compound in different amounts, as well as 
bismuth oxide, cobalt oxide, manganese oxide and metal zinc in such 
amounts as shown in Table 3. Using these compositions, a number of 
voltage-nonlinear resistors of Example 2 were manufactured. The resistors 
were tested, and their temperature-humidity cycle characteristics were 
recorded. The results were as shown in FIG. 3. As FIG. 3, shows, spinel 
type crystalline chromium compound should be contained in the ZnO-based 
composition in an amount of 0.001 mol% to 10 mol%. When it was contained 
in an amount outside this range, V.sub.1 mA of the resultant products 
varied in negative direction to such extent that their characteristics 
would be deteriorated. Preferably, spinel type crystalline chromium 
compound should be used in an amount of 0.01 mol% to 5 mol%. 
EXAMPLE 3 
Three ZnO-based compositions were prepared, which were identical with those 
used in Example 2 and shown in Table 3, except that they contained spinel 
type crystalline tin compound instead of spinel type crystalline chromium 
compound. Several resistors with V.sub.1 mA of 100 V were made of the 
first composition, several resistors with V.sub.1 mA of 200 V were made of 
the second composition, and several resistors with V.sub.1 mA of 300 V 
were made of the third composition--all in the same method as those of 
Example 2. 
Also manufactured were voltage-nonlinear resistors which were identical 
with those of Example 3, except that the starting compositions did not 
contain metal zinc. These resistors will hereinafter be called "Control 
4". 
The sintering temperature and compositions of Example 3 and control 4 were 
as shown in the following Table 5: 
TABLE 5 
__________________________________________________________________________ 
V.sub.1 mA 100V V.sub.1 mA 200V 
V.sub.1 mA 300V 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,250.degree. C. 
temp. 1,200.degree. C. 
temp. 1,150.degree. C. 
__________________________________________________________________________ 
Example 3 
Bi.sub.2 O.sub.3 
0.7 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
tin compound 
1 mol % 
tin compound 
2 mol % 
tin compound 
5 mol % 
Zn 6 mol % 
Zn 4 mol % 
Zn 3 mol % 
ZnO 91.3 mol % 
ZnO 92.5 mol % 
ZnO 90.5 mol % 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,250.degree. C. 
temp. 1,200.degree. C. 
temp. 1,150.degree. C. 
__________________________________________________________________________ 
Control 4 
Bi.sub.2 O.sub.3 
0.7 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
tin compound 
1 mol % 
tin compound 
2 mol % 
tin compound 
5 mol % 
ZnO 97.3 mol % 
ZnO 97.5 mol % 
ZnO 93.5 mol % 
__________________________________________________________________________ 
The resistors of Example 3 and Control 4, whose V.sub.1 mA was 200 V, were 
tested to ascertain their impulse current, D.C. load and 
temperature-humidity cycle characteristics, exactly in the same way as 
those of Example 1 and Controls 1 and 2 were tested. The results of the 
test were as shown in the following Table 6: 
TABLE 6 
______________________________________ 
Control 4 Example 3 
Positive 
Negative Positive Negative 
direction 
direction 
direction direction 
______________________________________ 
Impulse +6% -13% +4% +3.5% 
current 
characteristic 
D.C. load +4% -21% +3% +3% 
characteristic 
Temp.-humidity 
+5% -16% +3% +2.5% 
cycle 
characteristic 
______________________________________ 
A number of ZnO-based compositions were prepared, which contained metal 
zinc in different amounts, as well as bismuth oxide, cobalt oxide, 
manganese oxide and spinel type crystalline tin compound in such amount as 
shown in Table 5. Using these compositions, a number of voltage-nonlinear 
resistors of Example 3 were manufactured. The resistors were tested, and 
their impulse current characteristics were recorded. The results were as 
shown in FIG. 4. 
Also prepared a number of ZnO-based compositions which contained spinel 
type crystalline tin compound in different amounts, as well as bismuth 
oxide, cobalt oxide, manganese oxide and metal zinc in such amounts as 
shown in Table 5. Using these compositions, resistors of Example 3 were 
manufactured. The resistors were tested, and their temperature-humidity 
cycle characteristics were recorded. The results were as shown in FIG. 5. 
As Tables 5 and 6 and FIGS. 4 and 5 show, the resistors of Example 3 
exhibited substantially the same characteristics as those of Examples 1 
and 2. 
EXAMPLE 4 
Three ZnO-based compositions were prepared, which were identical with those 
used in Example 2 and shown in Table 3, except that they contained spinel 
type crystalline antimony compound instead of spinel type crystalline 
chromium compound. Several resistors with V.sub.1 mA of 100 V were made of 
the first composition, several resistors with V.sub.1 mA of 200 V were 
made of the second composition, and several resistors with V.sub.1 mA of 
300 V were made of the third composition--all in the same method as were 
those of Example 2. 
Also manufactured were voltage-nonlinear resistors which were identical 
with those of Example 3, except that the starting compositions did not 
contain metal zinc. These resistors will hereinafter be called "Control 
5". 
The sintering temperature and compositions of Example 4 and Control 5 were 
as shown in the following Table 7: 
TABLE 7 
__________________________________________________________________________ 
V.sub.1 mA 100V V.sub.1 mA 200V 
V.sub.1 mA 300V 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,250.degree. C. 
temp. 1,200.degree. C. 
temp. 1,150.degree. C. 
__________________________________________________________________________ 
Example 4 
Bi.sub.2 O.sub.3 
0.7 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Sb compound 
1 mol % 
Sb compound 
1 mol % 
Sb compound 
4 mol % 
Zn 6 mol % 
Zn 3 mol % 
Zn 3 mol % 
ZnO 91.3 mol % 
ZnO 94.5 mol % 
ZnO 91.5 mol % 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,250.degree. C. 
temp. 1,200.degree. C. 
temp. 1,150.degree. C. 
__________________________________________________________________________ 
Control 5 
Bi.sub.2 O.sub.3 
0.7 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Sb compound 
1 mol % 
Sb compound 
1 mol % 
Sb compound 
4 mol % 
ZnO 97.3 mol % 
ZnO 97.5 mol % 
ZnO 94.5 mol % 
__________________________________________________________________________ 
The resistors of Example 4 and Control 5 whose V.sub.1 mA was 200 V, were 
tested to ascertain their impulse current, D.C. load and 
temperature-humidity cycle characteristics, exactly in the same way as 
those of Example 1 and Controls 1 and 2 were tested. The results of the 
test were as shown in the following Table 8: 
TABLE 8 
______________________________________ 
Control 5 Example 4 
Positive 
Negative Positive Negative 
direction 
direction 
direction direction 
______________________________________ 
Impulse +6% -10% +4% +4% 
current 
characteristic 
D.C. load +5% -20% +3% +2.5% 
characteristic 
Temp.-humidity 
+5% -15% +3% +3% 
cycle 
characteristic 
______________________________________ 
A number of ZnO-based compositions were prepared, which contained metal 
zinc in different amounts, as well as bismuth oxide, cobalt oxide, 
manganese oxide and spinel type crystalline antimony compound in such 
amounts as shown in Table 7. Using these compositions, voltage-nonlinear 
resistors of Example 4 were manufactured. The resistors were tested, and 
their impulse current characteristics were recorded. The results were 
substantially the same as those illustrated in FIG. 4. 
Further, a number of ZnO-based compositions were prepared, which contained 
spinel type crystalline antimony compound in different amounts, as well as 
bismuth oxide, cobalt oxide, manganese oxide and metal zinc in such 
amounts as shown in Table 7. Using these compositions, voltage-nonlinear 
resistors of Example 4 were manufactured. The resistors were tested, and 
their temperature-humidity cycle characteristics were recorded. The 
results were substantially the same as those illustrated in FIG. 5. 
EXAMPLE 5 
Three ZnO-based compositions were prepared, which were identical with those 
used in Example 2 and shown in Table 3, except that they contained spinel 
type crystalline titanium compound instead of spinel type crystalline 
chromium compound. Using these compositions, voltage-nonlinear resistors 
whose V.sub.1 mA were 100 V, 200 V and 300 V were manufactured in the same 
method as were those of Example 2. 
Also manufactured were voltage-nonlinear resistors which were identical 
with those of Example 5, except that the starting compositions did not 
contain metal zinc. These resistors will hereinafter called "Control 6". 
The sintering temperature and compositions of Example 5 and Control 6 were 
as shown in the following Table 9: 
TABLE 9 
__________________________________________________________________________ 
V.sub.1 mA 100V 
V.sub.1 mA 200V 
V.sub.1 mA 300V 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,250.degree. C. 
temp. 1,200.degree. C. 
temp. 1,150.degree. C. 
__________________________________________________________________________ 
Example 5 
Bi.sub.2 O.sub.3 
0.7 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Ti compound 
1 mol % 
Ti compound 
1 mol % 
Ti compound 
3 mol % 
Zn 5 mol % 
Zn 2 mol % 
Zn 3 mol % 
ZnO 92.3 mol % 
ZnO 95.5 mol % 
ZnO 92.5 mol % 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,250.degree. C. 
temp. 1,200.degree. C. 
temp. 1,150.degree. C. 
__________________________________________________________________________ 
Control 6 
Bi.sub.2 O.sub.3 
0.7 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Ti compound 
1 mol % 
Ti compound 
1 mol % 
Ti compound 
3 mol % 
ZnO 97.3 mol % 
ZnO 97.5 mol % 
ZnO 95.5 mol % 
__________________________________________________________________________ 
The resistors of Example 5 and Control 6, whose V.sub.1 mA was 200 V, were 
tested to ascertain their impulse current, D.C. load and 
temperature-humidity cycle characteristics, exactly in the same way as 
those of Example 1 and Controls 1 and 2 were tested. The results of the 
test were as shown in the following Table 10: 
TABLE 10 
______________________________________ 
Control 6 Example 5 
Positive 
Negative Positive Negative 
direction 
direction 
direction direction 
______________________________________ 
Impulse +5% -10% +4% +3.5% 
current 
characteristic 
D.C. load +4% -20% +2% +1.5% 
characteristic 
Temp.-humidity 
+3% -14% +3% +2.5% 
cycle 
characteristic 
______________________________________ 
A number of ZnO-based compositions were prepared, which contained metal 
zinc in different amounts, as well as bismuth oxide, cobalt oxide, 
manganese oxide and spinel type crystalline titanium compound in such 
amounts as shown in Table 9. Using these compositions, voltage-nonlinear 
resistors of Example 5 were manufactured. The resistors were tested, and 
their impulse current characteristics were recorded. The results were 
substantially the same as those illustrated in FIG. 4. 
Further, a number of ZnO-based compositions were prepared, which contained 
spinel type crystalline titanium compound in different amounts, as well as 
bismuth oxide, cobalt oxide, manganese oxide and metal zinc in such 
amounts as shown in Table 9. Using these compositions, voltage-nonlinear 
resistors of Example 5 were manufactured. The resistors were tested, and 
their temperature-humidity cycle characteristics were recorded. The 
results were substantially the same as those illustrated in FIG. 5. 
EXAMPLE 6 
Three ZnO-based compositions were prepared, which were similar to those 
used in Example 2, except that they contained spinel type crystalline 
antimony compound in addition to spinel type crystalline chromium 
compound. Using these compositions, voltage-nonlinear resistors whose 
V.sub.1 mA were 100 V, 200 V and 300 V were manufactured in the same 
method as were those of Example 2. 
Also manufactured were voltage-nonlinear resistors which were identical 
with those of Example 6, except that the starting compositions did not 
contain metal zinc. These resistors will hereinafter be called "Control 
7". 
The sintering temperature and compositions of Example 6 and Control 7 were 
as shown in the following Table 11: 
TABLE 11 
__________________________________________________________________________ 
V.sub.1 mA 100V V.sub.1 mA 200V 
V.sub.1 mA 300V 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,250.degree. C. 
temp. 1,200.degree. C. 
temp. 1,200.degree. C. 
__________________________________________________________________________ 
Example 6 
Bi.sub.2 O.sub.3 
0.7 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Sb compound 
0.5 mol % 
Sb compound 
1.0 mol % 
Sb compound 
2.0 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Cr compound 
0.5 mol % 
Cr compound 
1.0 mol % 
Cr compound 
1.0 mol % 
Zn 2 mol % 
Zn 2 mol % 
Zn 6 mol % 
ZnO 95.5 mol % 
ZnO 94.5 mol % 
ZnO 89.5 mol % 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,250.degree. C. 
temp. 1,200.degree. C. 
temp. 1,200.degree. C. 
__________________________________________________________________________ 
Control 7 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Sb compound 
0.5 mol % 
Sb compound 
1.0 mol % 
Sb compound 
2.0 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Cr compound 
0.5 mol % 
Cr compound 
1.0 mol % 
Cr compound 
1.0 mol % 
ZnO 97.5 mol % 
ZnO 96.5 mol % 
ZnO 95.5 mol % 
__________________________________________________________________________ 
The resistors of Example 6 and Control 7, whose V.sub.1 mA was 200 V, were 
tested to ascertain their impulse current, D.C. load and 
temperature-humidity cycle characteristics, exactly in the same way as 
those of Example 1 and Controls 1 and 2 were tested. The results of the 
test were as shown in the following Table 12: 
TABLE 12 
______________________________________ 
Control 7 Example 6 
Positive 
Negative Positive Negative 
direction 
direction 
direction direction 
______________________________________ 
Impulse +6% -10% +4% +4% 
current 
characteristic 
D.C. load +4% -20% +3% +2.5% 
characteristic 
Temp.-humidity 
+5% -14% +3% +3% 
cycle 
characteristic 
______________________________________ 
A number of ZnO-based compositions were prepared, which contained metal 
zinc in different amounts, as well as bismuth oxide, cobalt oxide, 
manganese oxide and the two spinel type crystalline compounds in such 
amounts as shown in Table 11. Using these compositions, voltage-nonlinear 
resistors of Example 6 were manufactured. The resistors were tested, and 
their impulse current characteristics were recorded. The results were 
substantially the same as those illustrated in FIG. 4. 
Further, a number of ZnO-based compositions were prepared, which contained 
the two spinel type crystalline compounds in different amounts, as well as 
bismuth oxide, cobalt oxide, manganese oxide and metal zinc in such 
amounts as shown in Table 11. Using these compositions, voltage-nonlinear 
resistors of Example 6 were manufactured. The resistors were tested, and 
their temperature-humidity cycle characteristics were recorded. The 
results were substantially the same as those illustrated in FIG. 5. 
EXAMPLE 7 
Three ZnO-based compositions were prepared, which were similar to those 
used in Example 3, except that they contained spinel type crystalline 
antimony compound in addition to spinel type crystalline tin compound. 
Using these compositions, voltage-nonlinear resistors whose V.sub.1 mA 
were 100 V, 200 V and 300 V were manufactured in the same method as were 
those of Example 2. 
Also manufactured were voltage-nonlinear resistors which were identical 
with those of Example 7, except that the starting compositions did not 
contain metal zinc. These resistors will hereinafter be called "Control 
8". 
The sintering temperature and compositions of Example 7 and Control 8 were 
as shown in the following Table 13. 
TABLE 13 
__________________________________________________________________________ 
V.sub.1 mA 100V V.sub.1 mA 200V 
V.sub.1 mA 300V 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,250.degree. C. 
temp. 1,200.degree. C. 
temp. 1,200.degree. C. 
__________________________________________________________________________ 
Example 7 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Sb compound 
0.5 mol % 
Sb compound 
1.0 mol % 
Sb compound 
1.0 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Sn compound 
0.5 mol % 
Sn compound 
1.0 mol % 
Sn compound 
2.0 mol % 
Zn 2 mol % 
Zn 2 mol % 
Zn 6 mol % 
ZnO 95.5 mol % 
ZnO 94.5 mol % 
ZnO 89.5 mol % 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,250.degree. C. 
temp. 1,200.degree. C. 
temp. 1,200.degree. C. 
__________________________________________________________________________ 
Control 8 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Sb compound 
0.5 mol % 
Sb compound 
1.0 mol % 
Sb compound 
1.0 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Sn compound 
0.5 mol % 
Sn compound 
1.0 mol % 
Sn compound 
2.0 mol % 
ZnO 97.5 mol % 
ZnO 96.5 mol % 
ZnO 95.5 mol % 
__________________________________________________________________________ 
The resistors of Example 7 and Control 8, whose V.sub.1 mA was 200 V, were 
tested to ascertain their impulse current, D.C. load and 
temperature-humidity cycle characteristics, exactly in the same way as 
those of Example 1 and Controls 1 and 2 were tested. The results of the 
test were as shown in the following Table 14: 
TABLE 14 
______________________________________ 
Control 8 Example 7 
Positive 
Negative Positive Negative 
direction 
direction 
direction direction 
______________________________________ 
Impulse +6% -10% +4% +3.5% 
current 
characteristic 
D.C. load +5% -20% +3% +2.5% 
characteristic 
Temp.-humidity 
+5% -15% +3% +3% 
cycle 
characteristic 
______________________________________ 
A number of ZnO-based compositions were prepared, which contained metal 
zinc in different amounts, as well as bismuth oxide, cobalt oxide, 
manganese oxide and the two spinel type crystalline compounds in such 
amounts as shown in Table 13. Using these compositions, voltage-nonlinear 
resistors of Example 7 were manufactured. The resistors were tested, and 
their impulse current chracteristics were recorded. The results were 
substantially the same as those illustrated in FIG. 4. 
Further, a number of ZnO-based compositions were prepared, which contained 
the two spinel type crystalline compounds in different amounts, as well as 
bismuth oxide, cobalt oxide, manganese oxide and metal zinc in such 
amounts as shown in Table 13. Using these compositions, voltage-nonlinear 
resistors of Example 7 were manufactured. The resistors were tested, and 
their temperature-humidity cycle characteristics were recorded. The 
results were substantially the same as those illustrated in FIG. 5. 
EXAMPLE 8 
Three ZnO-based compositions were prepared, which were similar to those 
used in Example 4, except that they contained spinel type crystalline 
chromium compound and spinel type crystalline titanium compound in 
addition to spinel type crystalline antimony compound. Using these 
compositions, voltage-nonlinear resistors whose V.sub.1 mA were 100 V, 200 
V and 300 V were manufactured in the same method as were those of Example 
2. 
Also manufactured were voltage-nonlinear resistors which were identical 
with those of Example 8, except that the starting compositions did not 
contain metal zinc. These resistors will hereinafter be called "Control 
9". 
The sintering temperature and compositions of Example 8 and Control 9 were 
as shown in the following Table 15: 
TABLE 15 
__________________________________________________________________________ 
V.sub.1 mA 100V V.sub.1 mA 200V 
V.sub.1 mA 300V 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,250.degree. C. 
temp. 1,200.degree. C. 
temp. 1,200.degree. C. 
__________________________________________________________________________ 
Example 8 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O3 
0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Sb compound 
0.5 mol % 
Sb compound 
1.0 mol % 
Sb compound 
2.0 mol % 
Spinel type Spinel type Spinel type 
Cr compound 
0.5 mol % 
Cr compound 
1.0 mol % 
Cr compound 
1.0 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Ti compound 
0.5 mol % 
Ti compound 
1.0 mol % 
Ti compound 
1.0 mol % 
Zn 2 mol % 
Zn 2 mol % 
Zn 6 mol % 
ZnO 95.0 mol % 
ZnO 93.5 mol % 
ZnO 88.5 mol % 
__________________________________________________________________________ 
Sintering Sintering Sintering 
temp. 1,250.degree. C. 
temp. 1,200.degree. C. 
temp. 1,200.degree. C. 
__________________________________________________________________________ 
Control 9 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
Bi.sub.2 O.sub.3 
0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
CoO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
MnO 0.5 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Sb compound 
0.5 mol % 
Sb compound 
1.0 mol % 
Sb compound 
2.0 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Cr compound 
0.5 mol % 
Cr compound 
1.0 mol % 
Cr compound 
1.0 mol % 
Spinel type Spinel type Spinel type 
crystalline crystalline crystalline 
Ti compound 
0.5 mol % 
Ti compound 
1.0 mol % 
Ti compound 
1.0 mol % 
ZnO 97 mol % 
ZnO 95.5 mol % 
ZnO 94.5 mol % 
__________________________________________________________________________ 
The resistors of Example 8 and Control 9, whose V.sub.1 mA was 200 V, were 
tested to ascertain their impulse current, D.C. load and 
temperature-humidity cycle characteristics, exactly in the same way as 
those of Example 1 and Controls 1 and 2 were tested. The results of the 
test were as shown in the following Table 16: 
TABLE 16 
______________________________________ 
Control 9 Example 8 
Positive 
Negative Positive Negative 
direction 
direction 
direction direction 
______________________________________ 
Impulse +5% -9% +3.5% +3.5% 
current 
characteristic 
D.C. load +5% -20% +3% +2.5% 
characteristic 
Temp.-humidity 
+4% -14% +2.5% +2.5% 
cycle 
characteristic 
______________________________________ 
A number of ZnO-based compositions were prepared, which contained metal 
zinc in different amounts, as well as bismuth oxide, cobalt oxide, 
manganese oxide and the three spinel type crystalline compounds in such 
amounts as shown in Table 15. Using these compositions, voltage-nonlinear 
resistors of Example 8 were manufactured. The resistors were tested, and 
their impulse current characteristics were recorded. The results were 
substantially the same as those illustrated in FIG. 4. 
Further, a number of ZnO-based compositions were prepared, which contained 
the three spinel type crystalline compounds in different amounts, as well 
as bismuth oxide, cobalt oxide, manganese oxide and metal zinc in such 
amounts as shown in Table 15. Using these compositions, voltage-nonlinear 
resistors of Example 8 were manufactured. The resistors were tested, and 
their temperature-humidity cycle characteristics were recorded. The 
results were substantially the same as those illustrated in FIG. 5. 
Spinel type crystalline tin compound, for example, is prepared in the 
following way. First, zinc oxide, magnesium carbonate and tin oxide are 
mixed, each used in such an amount as to form spinel crystals together 
with the other ingredients. The mixture thus provided is heated at 
1,300.degree. C. for 6 hours. After this heat treatment, the mixture is 
subjected to wet grinding. Other spinel type crystalline compounds 
selectively used in Examples 2 to 8 are prepared in a similar method.