JPH038761A - Production of voltage-dependent nonlinear resistor porcelain composition and varistor - Google Patents

Abstract

PURPOSE:To reduce varistor voltage and increase voltage-current nonlinear index and extent of surge resistance by constructing a varistor from a composition composed of Ca-substituted SrTiO3 which is a principal component, the second and third components of specific metal oxide groups and the fourth component of SrTiO3-SiO2 in a specified proportion. CONSTITUTION:A varistor is produced by calcining a composition composed of a mixture of 100 pts.wt. principal component containing (1) 90.000-99.998mol% Sr1-xCaTiO3 (0.001<=x<=0.300), (2) 0.001-5.000mol% one or more of Nb2O5, Ta2O5, etc., and (3) 0.001-5.000mol% one or more of Al2O3, Sb2O3, etc., with 0.001-10.000 pts.wt. additive prepared by calcining (4) a mixture of 60.000-32.500mol% SrTiO3 with 40.000-67.500mol% SiO2 at >=1200 deg.C. The resultant element has a low varistor voltage, a high dielectric constant and voltage-current nonlinear index due to a large particle diameter, a homogeneous flow of surge current due to small dispersion in particle diameter and a great extent of surge resistance due to effectively increased resistance of grain boundaries with Ca.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a voltage having capacitor characteristics and varistor characteristics to protect semiconductors and circuits of equipment from abnormal high voltages, noise, static electricity, etc. generated in electrical equipment and electronic equipment. The present invention relates to a dependent nonlinear resistor ceramic composition and a method for manufacturing a varistor.

Conventional technology Conventionally, SiC varistors and Z
nO type varistors are used. The voltage-current characteristics of such a varistor can be approximately expressed as in the following equation.

1=(V/C) α Here, ■ is a current, ■ is a voltage, C is a constant specific to the varistor, and α is a voltage-current nonlinear index.

The α of SiC varistors is about 2 to 7, and the α of some ZnO-based varistors is as high as 50. Such varistors have excellent performance in absorbing relatively high voltages, but due to their low dielectric constant and small inherent capacitance, they have little ability to absorb relatively low voltages below the varistor voltage. It has no effect, and the dielectric loss tan δ is as large as 5 to 10%.

On the other hand, semiconductor capacitors with an apparent dielectric constant of about 5×10 4 and a tan δ of about 1% are used to remove these low voltage noises.

However, when a voltage or current exceeding a certain limit is applied to such a semiconductor capacitor due to a surge or the like, the capacitance decreases or the semiconductor capacitor is destroyed, and the capacitor no longer functions as a capacitor.

Therefore, recently, a product that has SrTiO3 as its main component and has both varistor and capacitor properties has been developed, and it
It is used to protect semiconductor devices such as SI.

Problems to be Solved by the Invention The above-mentioned 5rTiCh-based element that functions as both a varistor and a capacitor has a dielectric constant about 10 times higher than that of a ZnO-based varistor, but its α and surge resistance are small (
However, the varistor voltage had the disadvantage that the characteristics tend to deteriorate if the varistor voltage is lowered.

Therefore, the present invention provides a voltage-dependent nonlinear resistor ceramic composition that has a large dielectric constant, a low varistor voltage (α), and a large surge withstand capacity, and a method for manufacturing the varistor. .

Means for Solving the Problems In order to solve the above problems, in the present invention, S r+-
xCaxT i 03 (0.001≦x≦0.300)
(hereinafter referred to as the first component) from 90.000 to 99.998
mol%, Nb2O5, Ta205°WO2, DV20
3. Y2O3, L a203. CeO2゜Sm20s,
At least 11 or more of Pr1BO11, Nd2O3 (hereinafter referred to as the second component) from 0.001 to 5.0OOi
o1%, At! 203. S b203. Bad.

Bed, Pb0. B2O3, Cr203. F e203
゜Cd O, Ni2O, Ca O, C0203, Cu O
, CtJ20L i2O, L i F, MgO, MnO
2, MoO3゜Na2O, NaF, Nip, Rh2O3
,5ee2°Ag2O,5i02. SiC, SrO, T
e203゜Th0z, T iCh, V2O5, B 12
03. ZnO.

Zrch, at least one type of 5n02 (
0.001 to 5.000 mol of
100 parts by weight of the main component containing S rT i
03 60.000-32.500 mol%.

SiC240. ○A voltage-dependent nonlinear resistor consisting of 0.001 to 10.000 parts by weight of an additive (hereinafter referred to as the fourth component) obtained by firing a mixture consisting of OO to 67.500 mol% at 1200 to 1300'C. The aim is to solve the problem by obtaining a porcelain composition.

Further, a method for producing a varistor in which the above composition is fired at 1100°C or higher, or the above composition is fired at 1100°C or higher, then fired at 1200°C or higher in a reducing atmosphere, and then 900°C or higher in an oxidizing atmosphere. This paper proposes a method for manufacturing a varistor that is fired at a temperature of ~1300°C.

Effect In the above invention, the first component is the main component, and 5i
By substituting a portion of Sr in Ti03 with Ca, a high resistance layer formed at grain boundaries becomes strong against surges. Second
The components are mainly metal oxides that promote semiconducting of the first component. Further, the third component contributes to improving the dielectric constant, α, and surge resistance, and the fourth component is effective in reducing the varistor voltage and improving the dielectric constant. In particular, since the fourth component has a relatively low melting point of 1230 to 1250° C., when fired at a temperature around the melting point, it turns into a liquid phase, which promotes the reactions of the other components and the growth of particles. Therefore, the third component is more likely to segregate at the grain boundaries and break down, making it easier for the grain boundaries to have a high resistance, thereby improving the varistor function and capacitor function. Furthermore, since grain growth is promoted, the varistor voltage is lowered, and the uniformity of the grain size is improved, resulting in improved stability of characteristics, and in particular, improved surge resistance.

Example The present invention will be specifically explained below with reference to Examples.

First, SrTiO3 and Si02 are weighed at various composition ratios as shown in Table 1 below, and mixed for 208r using a ball mill or the like. Next, after drying, the mixture is calcined at various temperatures as shown in Table 1 below, pulverized again for 20 hours using a ball mill, etc., and then dried to obtain the fourth component. Next, the first component, second component, third component, and fourth component were weighed to have the composition ratio shown in Table 1 below, mixed in a ball mill for 248 r, dried, and mixed with polyvinyl alcohol, etc. After adding 10 wt% of organic binder and granulating, 10φX with a press pressure of 1 (t/cI+?)
It was molded into a disk shape of 1000℃ (mm) for 10H at 1000℃.
r to remove the binder. Next, as shown in Table 1, it is fired for 4 hours at various temperatures (first firing), and then fired for 4 hours at various temperatures in a reducing atmosphere, for example, a gas of N2:N2 = 9:1. 2nd firing).

Furthermore, after that, 3H was prepared at various temperatures in an oxidizing atmosphere.
Perform r firing (third firing).

A conductive paste such as Ag was applied by screen printing or the like, leaving the outer periphery on both planes of the sintered body 1 shown in FIGS. 1 and 2 obtained in this way.
The electrodes 2 and 3 are formed by firing. Next, the lead wires are attached using solder or the like, and a resin such as epoxy is applied.

The characteristics of the device thus obtained are shown in Table 2 below.

Note that the apparent permittivity is calculated from the capacitance at 1KHz, and α is α= 1 / L o g (VIOm^/V 11
1A) (However, VInA * VlOmA is 1mA,
This is the voltage across the device when a current of 10 mA is applied. ) was evaluated. Further, the surge resistance is evaluated based on the maximum pulse current value when the rate of change in VliA after applying the pulse current is within ±10%.

(Margin below) Also, the first component S r 1-XCaxT i○3
The reason for specifying the range is that if X is smaller than 0.001, there will be no effect, and if Because it precipitates as a single phase, the structure becomes non-uniform and VIm
This is because A becomes too high and the characteristics deteriorate. Furthermore, if the second component is less than ○, OO 1 mol%, it will not show any effect, and if it exceeds 5.000 mol%, it will segregate to the grain boundaries, suppress the high resistance of the grain boundaries, and form a second phase at the grain boundaries. The characteristics deteriorate. Also, the third component is O1O○I I
ll ol? If it is less than jr, it will not show any effect; 5. ○○O
If it exceeds mol%, it segregates at grain boundaries and forms a second phase, resulting in deterioration of properties. And the fourth component is Sr
In the binary phase diagram for TiO3 and SiO2, 5rTi○
3 mol%, 5i0240.000-67.500 mo
Those within the 1% range are substances with the lowest melting point, and those outside this range have a higher melting point. Also,
If the amount of the fourth component added is less than 0.001 parts by weight, no effect will be shown, and if it exceeds 10.000 parts by weight, the resistance of the grain boundaries will be high (although the width of the grain boundaries will become thicker, so the capacitance will increase). As the VlmA decreases, the VlmA increases, making it vulnerable to surges.Also, the firing temperature for the fourth component was specified because the temperature at which the fourth component with a low melting point is synthesized is 1200°C or higher. The reason for specifying the temperature for the first firing is that the melting point of the fourth component is 1230 to 1250°C, so if fired at a temperature of 1100°C or higher, the fourth component will be in a state close to a liquid phase. This is because sintering is promoted, and 11
This is because the fourth component has no liquid phase sintering effect below 00°C. In addition, the temperature for the second firing was regulated at 1200°C.
This is because if the temperature is less than 0.degree. C., the sintered body after the first firing will not be sufficiently reduced, resulting in deterioration of both the varistor characteristics and the capacitor characteristics.

The temperature of the third firing was specified because the resistance of grain boundaries cannot be sufficiently increased below 900°C, so VlfflA is low (
This is because the varistor characteristics deteriorate too much, and 1300
This is because if the temperature exceeds ℃, the capacitance becomes too small and the capacitor characteristics deteriorate. Furthermore, it was confirmed that the same effect can be obtained whether the atmosphere for the first firing is an oxidizing atmosphere or a reducing atmosphere.

In addition, as the second component, two or more types may be used in combination in an amount within the above range.

Further, as the third component, in addition to the components mentioned in the above examples, Sb20wl, Bad, Cab, and LiF are used.

Na2O, NaF, Rh203, 5i02Sr○, Th
02, T i02 , and V205Z00.5no2 can be used, and similarly to the second component, two or more types may be used in combination in an amount within the above-mentioned range. Furthermore, although only some of the combinations of these additives are shown in the above examples, it has been confirmed that similar effects can be obtained with other combinations.

Effects of the Invention As shown above, according to the present invention, the varistor voltage is low due to the large particle size, and the dielectric constants ε and α are large (and the variation in particle size is small, so surge current flows uniformly through the element. Furthermore, since the grain boundaries are effectively made to have a high resistance by Ca, the effect of increasing the surge resistance can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view showing an element according to the present invention, and FIG. 2 is a sectional view showing the element according to the present invention. 1... Sintered body, 2, 3... Electrode.

Claims (3)

[Claims] (1) Sr_1_-_xCa_xTiO_3(0.00
1≦x≦0.300) from 90.000 to 99.998m
ol%, Nb_2O_5, Ta_2O_5, WO_3,
Dy_2O_3, Y_2O_3, La_2O_3, Ce
O_2, Sm_2O_3, Pr_6O_1_1, Nd_
At least one type of 2O_3 from 0.001 to 5
．． 000mol%, Al_2O_3, Sb_2O_3,
BaO, BeO, PbO, B_2O_3, Cr_2O_
3, Fe_2O_3, CdO, K_2O, CaO, Co
_2O_3, CuO, Cu_2O, Li_2O, LiF
, MgO, MnO_2, MoO_3, Na_2O, Na
F, NiO, Rh_2O_3, SeO_2, Ag_2O
, SiO_2, SiC, SrO, Tl_2O_3, Th
O_2, TiO_2, V_2O_5, Bi_2O_3,
100 parts by weight of a main component containing 0.001 to 5.000 mol% of at least one of ZnO, ZrO_2, and SnO_2, and SrTiO_360.000 to
32.500mol%, SiO_240.000~67
．． 1. A voltage-dependent nonlinear resistor ceramic composition comprising 0.001 to 10.000 parts by weight of an additive obtained by firing a mixture of 500 mol % at 1200° C. or higher. (2) Sr_1_-_-_xCa_xTiO_3(0.
001≦x≦0.300) from 90.000 to 99.99
8mol%, Nb_2O_5, Ta_2O_5, WO_
3, Dy_2O_3, Y_2O_3, La_2O_3,
CeO_2, Sm_2O_3, Pr_6O_1_1, N
0.001 of at least one type of d_2O_3
~5.000mol%, Al_2O_3, Sb_2O_
3, BaO, BeO, PbO, B_2O_3, Cr_2
O_3, Fe_2O_3, CdO, K_2O, CaO,
Co_2O_3, CuO, Cu_2O, Li_2O, L
iF, MgO, MnO_2, MoO_3, Na_2O,
NaF, NiO, Rh_2O_3, SeO_2, Ag_
2O, SiO_2, SiC, SrO, Tl_2O_3,
ThO_2, TiO_2, V_2O_5, Bi_2O_
3. 100 parts by weight of a main component containing 0.001 to 5.000 mol% of at least one of ZnO, ZrO_2, and SnO_2, and SrTiO_360.00
0~32.50mol%, SiO_240.000~6
A method for manufacturing a varistor, characterized in that a composition comprising 0.001 to 10.000 parts by weight of an additive is obtained by firing a mixture of 7.500 mol % at 1200°C or higher and firing at 1100°C or higher. (3) Sr_1_-_xCa_xTiO_3(0.00
1≦x≦0.300) from 90.000 to 99.998m
ol%, Nb_2O_5, Ta_2O_5, WO_3,
Dy_2O_3, Y_2O_3, La_2O_3, Ce
O_2, Sm_2O_3, Pr_6O_1_1, Nd_
At least one type of 2O_3 from 0.001 to 5
．． 000mol%, Al_2O_3, Sb_2O_3,
BaO, BeO, PbO, B_2O_3, Cr_2O_
3, Fe_2O_3, CdO, K_2O, CaO, Co
_2O_3, CuO, Cu_2O, Li_2O, LiF
, MgO, MnO_2, MoO_3, Na_2O, Na
F, NiO, Rh_2O_3, SeO_2, Ag_2O
, SiO_2, SiC, SrO, Tl_2O_3, Th
O_2, TiO_2, V_2O_5, Bi_2O_3,
100 parts by weight of the main component containing 0.001 to 5.000 mol% of at least one of ZnO, ZrO_2, and SnO_2, and SrTiO_360.000 to
32.500mol%, SiO_240.000~67
．． A composition consisting of 0.001 to 10.000 parts by weight of an additive obtained by firing a mixture of 500 mol% at 1200°C or higher is fired at 1100°C or higher, and then fired at 1200°C or higher in a reducing atmosphere. , and then firing at 900 to 1300°C in an oxidizing atmosphere.