JPH0443606A - Manufacture of voltage-dependent nonlinear resistor ceramic composition and varistor - Google Patents

Abstract

PURPOSE:To improve characteristics of permittivity, varistor voltage, surge yield strength, etc. by preparing ceramic composition by using the respective specified quantities of component wherein a part of Sr of SrTiO3 is substituted by Ba, component composed of two kinds of different metal oxide, and component wherein MgTiO3 and SiO2 are mixed and baked. CONSTITUTION:Main component is constituted by containing the following; 90.000-99.998 mol% of (Sr1-xBax)aTiO3 (0.001<=x<=0.300, 0.950<=a<1.000), 0.001-5.000 mol% of at least one or more kinds out of Nb2O5, Ta2O5, WO3, etc. and 0.001-5.000 mol% of at least one or more kinds out of Al2O3, Sb2O3, BaO, etc. Admixture is made by baking, at 1200 deg.C or higher, mixture composed of 60.000-32.500 mol% of MgTiO3 and 40.000-67.5 mol% of SiO2. Ceramic composition is prepared by using 100 wt.% of the main component and 0.001-10.000 wt.% of the admixture. Thereby varistor voltage is lowered; stability of characteristics is increased because the uniformity of grain diameter is improved; especially surge yield strength is improved.

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 voltage, 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.

α r − (V/C) Here, ■ is current, ■ is voltage, C is a constant specific to the varistor, and α is the voltage-current nonlinear index. There are some with α as high as 50. Although such varistors have excellent performance in absorbing relatively high voltages, they have a low dielectric constant and
Since the inherent capacitance is small, it is hardly effective in absorbing a relatively low voltage below the varistor voltage, 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' 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 voltage or the like, the capacitance decreases or breaks down, and the capacitor no longer functions as a capacitor.

Recently, products containing 5rTiO as the main component and having both varistor and capacitor properties have been developed, and ICs and L
It is used to protect semiconductor devices such as SI.

Problems to be Solved by the Invention The above-mentioned 5rTiOs-based element, which functions as both a varistor and a capacitor, has a dielectric constant that is about 10 times higher than that of a Zr+O-based varistor, but its α and surge resistance are small, making it difficult to use as a varistor. This had the disadvantage that when the voltage was lowered, the characteristics deteriorated.

Therefore, an object of the present invention is to provide a voltage-dependent nonlinear resistor ceramic composition that has a large dielectric constant, a low varistor voltage, a large 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, the present invention provides (Srl-
Jaw) @Ti0i (0,001≦x≦0.300.
0.950≦a<1. ooo) (hereinafter referred to as the first component)
90.000~99.998so1$S Nb1O1
, TazOsJOs, DyzOx, YzO*, LazO
At least one of xCeOl, Sagos, Pr60+ zNdxox (hereinafter referred to as the second component) is 0
．． 001 to 5.000 molχ, A1. Os, 5bzO
s, BaO, BeO, PbO, BzO, CrzO3F
e, 03. CdO, KzO, CaO, Co, 03. Cu
O, Cu2O, LirO, l-il-1F, gate nJ, M
00z, NazO, NaF, NiO, Rh2O3,5e
02. AgJsio,, sic, SrO, Tlt
o3. The2. Til□, V2O5, Ri p
ot, Zn0ZrOz, and 5nOz, each of which has one type of base (hereinafter referred to as the third component) is o, oo+ to 5.
Contains OOOmolχ, main component 100!1 part, M
gTlOs 60.000-32.500 PengO1χ,
SiO□ 40.000-67.5m. Additive obtained by firing a mixture consisting of 1χ at 1200 to 1300°C (hereinafter referred to as the fourth component) 0.001 to 10.000
The present invention attempts to solve this problem by obtaining a voltage-dependent nonlinear resistor ceramic composition consisting of parts by weight.

In addition, a composition consisting of the above main ingredients and additives was added to 1100
A method for manufacturing a varistor fired at a temperature of 'C or higher, further comprising firing at a temperature of 1200°C or higher in a reducing atmosphere after firing,
The present invention attempts to provide a method for manufacturing a varistor which is then fired at 900 to 1300°C in an oxidizing atmosphere.

Effect In the above invention, the first component is the main component, and 5r
By replacing a portion of Sr in TiO with Ba, a high resistance layer formed at grain boundaries becomes strong against surges. In addition, by making the stoichiometric ratio of A sites such as Sr and Ba and the stoichiometric ratio of B sites such as Ti excessive,
It is possible to lower the resistance inside the grains and increase the dielectric constant of the dielectric formed at the grain boundaries.

Further, the second component is mainly a metal oxide that promotes the semiconductor formation 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, it becomes a liquid phase when fired at a temperature around the melting point, which promotes the reaction of the other components and the growth of particles. Therefore, the third component is likely to be segregated in the grain boundary portion, and the resistance of the grain boundary is likely to be increased, thereby improving the varistor function and the capacitor function. In addition, 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, 5ift of MgTiOs was weighed at various composition ratios as shown in Table 1 below, and 5ift was weighed using a ball mill or the like.
Mix for 4 hours. 1st Next, after drying, the mixture is baked at various temperatures as shown in Table 1 below, and ground again for 24 hours using a ball mill, etc., and then dried to form the fourth component. The first, second, third, and fourth components were weighed to have the composition ratio shown in Table 1 below, mixed for 22 hours using a ball mill, etc., dried, and mixed with an organic binder such as polyvinyl alcohol. After adding 10-tχ and granulating, 10φ×lt(
■) Formed into a disc shape and baked at 0°C for 10 days 6) 1r to remove the binder 9 Next, bake at various temperatures and times as shown in Table 1 (first baking). , and then fired in a reducing atmosphere, for example, a 9:1 ratio of N, :) l, at varying temperatures and times (second firing). Furthermore, after that, firing was performed at various temperatures and times in an oxidizing atmosphere (third stage).
firing).

(Hereinafter, blank space) A conductive paste such as Ag is 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 as described above. 610
6 times to form electrode 2.3 by firing at 4 m1n at
A lead wire (not shown) is attached using solder or the like, and a resin such as epoxy (not shown) is applied. The characteristics of the device thus obtained are shown in Table 2 below.

In addition, in Table 2, the dielectric constant is calculated from the capacitance at 1 cell in l, and α is a = 1 / log (V IO + sA / V II
IJ (However, ■, □, ■1゜, A is l mA, 10
This is the voltage applied across the device when a current of s+A flows through it. ) was evaluated. Further, the surge resistance is evaluated based on the maximum pulse current value when the rate of change of Vl and A after applying the pulse current is within ±10%.

(Hereinafter, blank space) In the present invention, the first component (Srl-xBaJaTi
The reason for specifying the range of X in 03 is that if X is smaller than 0.001, there will be no effect, and if This is because Ba precipitates as a single phase, resulting in a non-uniform structure and an excessively high VlmA, deteriorating the properties. The range of a was specified because if it becomes smaller than 0.950, crystals of Ti alone will precipitate and the structure will become non-uniform, resulting in deterioration of characteristics, and if it exceeds i, ooo, the dielectric constant of the dielectric will become small. It is. Furthermore, the second component is 0.001
No effect is shown below molχ; 5. If it exceeds OOOmolχ, it will segregate at the grain boundaries, suppress the increase in resistance of the grain boundaries, and form a second phase at the grain boundaries, resulting in deterioration of properties. Further, the third component exhibits no effect if it is less than 0.001 molχ, and if it exceeds 5.000 mol %, it segregates at grain boundaries and forms a second phase, resulting in deterioration of properties. The fourth component is a substance having the lowest melting point in the phase diagram of the binary system of MgTiOs and SiO□, and has a high melting point outside of this range. Furthermore, if the amount of the fourth component added is less than 0.0 OIffi part, no effect will be shown, and if it exceeds the io, ooo overlapping part, the grain boundary resistance will be high (
However, since the width of the grain boundary becomes thicker, the capacitance becomes smaller and VlmA becomes higher, making the material vulnerable to surges. Furthermore, the firing temperature of the fourth component was specified because the temperature at which the fourth component with a low melting point was synthesized was 1200''C. This is because the melting point of the component is 1230 to 1250°C, so when fired at a temperature of 1100°C or higher, the fourth component becomes close to a liquid phase and sintering is accelerated.
This is because there is no liquid phase sintering effect of the fourth component below 0"C. Also, the temperature of the second firing was specified at 1200"C.
This is because if it is less than C, the sintered body after the first firing will not be sufficiently reduced, and both the varistor characteristics and the capacitor characteristics will deteriorate.

Furthermore, the temperature for the third firing was specified because if it is less than 900°C, the resistance of the grain boundaries will not increase sufficiently, resulting in VlmA becoming too low and the varistor characteristics deteriorating.
This is because if the temperature exceeds 00°C, 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, in this example, regarding the combination of additives, (Sr+-Jax) and TiO* (0,0
01≦x≦0.300.0.950≦a<1.000)
, NbzOs-DingazOsWOs, Dy as the second component
zOs, YtO3+LazOj, Ce0z, third component L 7AIzOs, PbO, Crt03. CdO,K
J, CJO3, Cll0Cu, O, MnO,, MoOs
, NiO, AgtO, SiC, TlzO3, ZnO, Z
rO,, only MgTiOi and SiO□ are shown as the fourth component, but in addition, Ss! as the second component! 03.
Pr60+++NdtOz, 5bzOs as the third component
, Bad, Bed, BtOx, Feto3+
Ca0LizO, LiF, MgO, NatO, NaF,
RhtO3,5eOz,5iO1,5rOThO1,T
rOt, VtOs, BIzO! It was confirmed that similar effects could be obtained by combining compositions using +5nO1. Furthermore, it was also confirmed that two or more types of the second and third components may be used in combination within a predetermined range. In addition, simply by first firing the first component, second component, third component, and fourth component, the fourth component becomes a liquid phase, which promotes the reaction of the other components and the growth of particles. It was confirmed that the third component is more likely to segregate in the grain boundary portion, the grain boundaries are more likely to have a high resistance, and the varistor function and capacitor function are improved.

Effects of the Invention As described above, according to the present invention, due to the liquid phase sintering effect of the fourth component, the particle size is large, so the varistor voltage is low, the dielectric constants C and α are large, and the variation in particle size is reduced. Because it is small, surge current flows uniformly through the element, and B
Since grain boundaries are effectively made to have a high resistance by a, the effect of increasing surge resistance can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a top view showing an element according to the invention, and FIG. 2 is a sectional view showing the element according to the invention. 1... Sintered body, 2.3... Electrode. Name of agent: Patent attorney Shigetaka Awano

Claims (3)

[Claims] (1) (Sr_1_−_xBa_x)_aTiO_3(
0.001≦x≦0.300, 0.950≦a<1.0
00) to 90.000 to 99.998 mol%, Nb_
2O_5, Ta_2O_5, WO_3, Dy_2O_3
, Y_2O_3, La_2O_3, CeO_2, Sm_
0.001 to 5.000 mol of at least one of 2O_3, Pr_6O_1_1, Nd_2O_3
%, 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, C
uO, Cu_2O, Li_2O, LiF, MgO, Mn
O_2, MoO_3, Na_2O, NaF, NiO, R
h_2O_3, SeO_2, Ag_2O, SiO_2,
SiC, SrO, Tl_2O_3, ThO_2, TiO
_2, V_2O_5, Bi_2O_3, ZnO, ZrO
_2, at least one type of SnO_2 0.0
100 parts by weight of the main component containing 01 to 5.000 mol% and MgTiO_3 60.000 to 32.500
mol%, SiO_2 40.000-67.5 mol
% and 0.001 to 10.000 parts by weight of an additive obtained by firing a mixture consisting of (2) (Sr_1_−_xBa_x)_aTiO_3(
0.001≦x≦0.300, 0.950≦a<1.0
00) to 90.000 to 99.998 mol%, Nb_
2O_5, Ta_2O_5, WO_3, Dy_2O_3
, Y_2O_3, La_2O_3, CeO_2, Sm_
0.001 to 5.000 mol of at least one of 2O_3, Pr_6O_1_1, Nd_2O_3
%, 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, C
uO, Cu_2O, Li_2O, LiF, MgO, Mn
O_2, MnO_2, Na_2O, NaF, NiO, R
h_2O_3, SeO_2, Ag_2O, SiO_2,
SiC, SrO, Ti_2O_3, ThO_2, TiO
_2, V_2O_5, Bi_2O_3, ZnO, ZrO
_2, at least one type of SnO_2 0.0
100 parts by weight of the main component containing 01 to 5.000 mol% and MgTiO_3 60.000 to 32.500
mol%, SiO_2 40.000-67.5 mol
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 10% and 10% by weight at 1200°C or higher, and a composition comprising 0.001 to 10.000 parts by weight of an additive is fired at 1100°C or higher. (3) (Sr_1_−_xBa_x)_aTiO_3(
0.001≦x≦0.300, 0.950≦a<1.0
00) to 90.000 to 99.998 mol%, Nb_
2O_5, Ta_2O_5, WO_3, Dy_2O_3
, Y_2O_3, La_2O_3, CeO_2, Sm_
0.001 to 5.000 mol of at least one of 2O_3, Pr_6O_1_1, Nd_2O_3
%, 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, C
uO, Cu_2O, Li_2O, LiF, MgO, Mn
O_2, MoO_3, Na_2O, NaF, NiO, R
h_2O_3, SeO_2, Ag_2O, SiO_2,
SiC, SrO, Tl_2O_3, ThO_2, TiO
_2, V_2O_5, Bi_2O_3, ZnO, ZrO
_2, at least one type of SnO_2 0.0
100 parts by weight of the main component containing 01 to 5.000 mol% and MgTiO_3 60.000 to 32.500
mol%, SiO_2 40.000-67.5 mol
A composition consisting of 0.001 to 10.000 parts by weight of an additive obtained by firing a mixture consisting of
Calcinate at 00℃ or higher, then heat to 900℃ or higher in an oxidizing atmosphere.
A method for manufacturing a varistor, characterized by firing at 1300°C.