JPH03218602A - Manufacture of porcelain composition for voltage dependent nonlinear resistor and varistor - Google Patents

Abstract

PURPOSE:To increase permittivity, to lower varistor voltage, and to increase alphaand resistance to surge by a method wherein the title composition consists of the specific main component and the additive of 0.001 to 10.000 pts.wt. formed by firing the mixture of SrTiO3 and SiO2 at 1200 deg.C. CONSTITUTION:The title composition consists of the main component of 100 pts.wt., containing Si1-xMaxTiO3 (0.001<=x<=0.300) (first component) of 90.000 to 99.998mol%, at least one or more (second component) selected from Nb2O5, Ta2O5, WO3, Dy2O3, Y2O3, La2O3, CeO2, Sm2O3, Pr6O11 and Nd2O3 of 0.001 to 5.000mol%, at least one or more (third component) selected from Al2O3, Sb2O3, BaO, BeO and the like of 0.001 to 5.000mol%, and the additive (fourth component) which is formed by firing the mixture, consisting of SrTiO3 of 32.500 to 60.000mol% and SiO2 of 40.000 to 67.500mol%, at 1200 to 1300 deg.C. As a result, varistor voltage can be lowered, permittivity epsilon and alpha can be increased, and resistance to surge can be increased.

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 expressed approximately as follows. 1= (V/C) Here, ■ is the current, ■ is the voltage, C is a constant specific to the varistor, and α is the 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. Although such varistors have excellent performance in absorbing relatively high voltages, they have a low dielectric constant.
Since the inherent capacitance is small, it has little effect on 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 5X10' 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 breaks down, and the capacitor no longer functions as a capacitor. Therefore, recently, a material containing SrTi03 as a main component and having both varistor and capacitor properties has been developed and is used to protect semiconductor elements such as ICs and LSIs in electronic devices such as computers. Problems to be Solved by the Invention The above-mentioned SrTiOi-based element that functions as both a varistor and a capacitor has a dielectric constant that is about 10 times higher than that of a ZnO-based varistor, but its α and surge resistance are small, making it difficult to use as a varistor. It had the disadvantage that its characteristics tended to deteriorate when the voltage was lowered. Therefore, the present invention aims 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 producing the varistor. Means for Solving the Problems In order to solve the above problems, in the present invention, Sr+-Jg
xTiOs (0.001≦X≦0.300) (hereinafter referred to as the first component) from 90.000 to 99.998 mo
lX, NbgOs+TaiOs+WOs+DyzOs
+ YtOs+ LaxOz+ CeOx+ Sago
ff, PriO+ l l NdzOz (hereinafter referred to as the second component) at least one type of 0.001
~5.000mo1χ, ^IzOi+SbzOs+Ba
O, Be(L pbo, BzO3+ CrlOs +
Feze2+ CdO+ K! 01 CaO+ Co
t's l Cuo+ Cute, Li, ol Lt
F + MgO+ MnOz + MoOs+ Naz
O+ NaP + Nr O+RhzOs + Se
O t+ AgzO+ Stow + SICI Sr
O+ TIzOi lThaw + Tt Ot +V
zOs+Bt! 03+ Zn(L ZrOt+ S
100 parts by weight of the main component containing 0.001 to 5.000 molχ of at least one type of now (hereinafter referred to as the third component);
2.500molχ, Sing 40.000 ~6
Additive obtained by firing a mixture consisting of 7.5 molχ at 1200 to 1300°C (hereinafter referred to as the fourth component) 0
．． The object of the present invention is to solve the problem by obtaining a voltage-dependent nonlinear resistor ceramic composition comprising 0.001 to 10.000 parts by weight.

Effect In the above invention, the first component is the main component, and S
By replacing part of Sr in rTiOs with Mg,
The high-resistance layer formed at grain boundaries becomes resistant to surges.
The second component is mainly a metal oxide that promotes 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, the fourth component has a relatively low melting point of 1,230 to 1,250°C, so when fired at a temperature around the melting point, it becomes a liquid phase, which promotes the reaction of the other components and the growth of particles. Therefore, the third component is more likely to segregate at the grain boundaries, making the grain boundaries more likely to have high resistance, thereby improving the varistor and capacitor functions. In addition, grain growth is promoted, which lowers the varistor voltage, and the uniformity of grain size improves, resulting in better stability of characteristics, and in particular, improved surge resistance. EXAMPLES The present invention will be specifically explained below with reference to Examples. SrTiOs, St (h) was weighed at various composition ratios as shown in Table 1 below, and mixed for 24 hours using a Pall mill.Next, after drying, the mixture was heated at various temperatures as shown in Table 1 below. Change the color and fire it again for 24 hours using a pole mill etc.
After pulverizing, it is dried and used as the fourth component. Then the first
Weigh the components, second component, third component, and fourth component so that they have the composition ratio shown in Table 1 below, and grind them using a ball mill etc.
After mixing for 0 hours, drying, adding 10 tχ of an organic binder such as polyvinyl alcohol and granulating, 1
(t/cd) press pressure 10φ×1t (II11)
It was molded into a disk shape and baked at 1100°C for 4 hours to remove the binder. Next, firing was performed at various temperatures and times as shown in Table 1 (first firing), and then in a reducing atmosphere.
For example, firing is performed in a gas of Hz:Hz=9:l at various temperatures and times (second firing). After that, it is fired in an oxidizing atmosphere at various temperatures and times (third firing).
do.

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 l shown in FIGS. 1 and 2 obtained in this way.
The electrodes 2 and 3 are formed by firing for 5 minutes. Next, although not shown, the lead wires are attached using solder, etc., and a resin such as epoxy is applied. The characteristics of the device thus obtained are shown in Table 2 below. The dielectric constant is calculated from the capacitance at IKHz, and α is α=1/Log (Vta+aa/VlmA
) (However, V lam % V + sma4;! 1
mA, lO+sA (7) This is the voltage applied to both ends of the element when current is passed. ) was evaluated. Further, the surge resistance is evaluated based on the maximum pulse current value when the rate of change in VlaA after applying the pulse current is within ±10%. In the following margin, in the present invention, the first component Srr-xMgxTl
(The reason for specifying the range of X in 1+ is that if X is smaller than 0.001, it will not be effective, while if it exceeds 0.300, lattice defects will be less likely to occur, so semiconductor formation will not be promoted.
This is because Mg precipitates as a single phase at the grain boundaries, resulting in a non-uniform structure and an excessively high VIIIA, resulting in deterioration of properties. Furthermore, if the second component is less than 0.001 molχ, it does not show any effect, and if it exceeds 5.000 molχ, it segregates at the grain boundaries, suppresses the high resistance of the grain boundaries, and forms a second phase at the grain boundaries, which deteriorates the characteristics. It deteriorates. Further, the third component does not show any effect if it is less than 0.001 molχ. OO
If it exceeds Omolχ, it will segregate at grain boundaries and form a second phase, resulting in deterioration of properties.

The fourth component is a substance with the lowest melting point in the phase diagram of the two-component system of SrTi03 and SiOz, and has a high melting point outside of this range. Further, if the amount of the fourth component added is less than 0.001 parts by weight, no effect will be shown.
If the amount exceeds 10.000 parts by weight, the grain boundary resistance increases, but the width of the grain boundaries increases, so the capacitance decreases and the vl. This is because A becomes higher and becomes weaker against surges. Furthermore, the firing temperature of 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. In addition, the temperature of the first firing was determined by
Since the melting point of the fourth component is 1230-1250°C,
This is because when fired at a temperature of 1100°C or higher, the fourth component enters a state close to a liquid phase, promoting sintering.
This is because there is no liquid phase sintering effect due to the fourth component below °C. In addition, the temperature for the second firing was regulated at 1200°C.
This is because if the temperature is below 10°C, the sintered body after the first firing will not be sufficiently reduced, resulting in deterioration of both varistor and capacitor properties.
Furthermore, the temperature of the third firing was specified because if it is less than 900°C, the resistance of grain boundaries cannot be sufficiently increased. A
This is because the varistor characteristics deteriorate if the value becomes too low, and 1
This is because when the temperature reaches 300°C, the capacitance becomes too small and the capacitor characteristics deteriorate. It was also confirmed that the first firing had the same effect whether it was an oxidizing atmosphere or a reducing atmosphere. In this example, regarding the combination of additives, Sr. ,+Mg,ITi
Os (0.001≦X≦?.300), NbzOs+TazOs+is+DVzOi+YtOs as the second component
+LatOs+CeOz, Sa+tOs+PrhO+
++NdzOs, Alg02, PbO as the third component
, BgOi+ CrzOz+ Fezes, cdo
．． KtO+ Cot03 lCub, CutO+
Li*0. MgO, MnOx + Moss +
Nip, SeOz, AgxO+SiC+ThOs
+BizO3+ZrOz, S r T as the fourth component
Although only iO s + SiO■ is shown, other third components include Sb103, BaO, BeO.
CaO iF, NaxO, NaF. RbzOz+Si0
i+ SrO+ Tho. , TiOz+ VxOs+
It was confirmed that similar effects could be obtained by combining compositions using ZnO+ Snug. In addition, the first component,
It has been confirmed that simply performing the first firing of the second, third, and fourth components is effective in lowering the varistor voltage and increasing the dielectric constant ε.

Effects of the Invention As shown above, according to the present invention, the particle size is large due to the liquid phase sintering effect of the fourth component, so the varistor voltage is low, the dielectric constants ε and α are large, and the variation in particle size is small. The surge current flows uniformly through the device, and Mg effectively increases the resistance of the grain boundaries, resulting in increased surge resistance.

[Brief explanation of drawings]

FIG. 1 is a top view showing an element according to the present invention, and the figure is a sectional view showing the element according to the present invention. 1...Sintered body,
2, 3... Electrode. Name of agent: Patent attorney Shigetaka Awano and one other person Figure 2

Claims (3)

[Claims] (1) Sr_1_-_xMg_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_2, O_5, Bi_2O_3
, ZnO, ZrO_2, SnO_2 at least one
100 parts by weight of the main component containing 0.001 to 5.000 mol% of SrTiO_360.000
~32.500mol%, SiO_240.000~6
A voltage-dependent nonlinear resistor ceramic composition comprising 0.001 to 10.000 parts by weight of an additive obtained by firing a mixture comprising 7.5 mol % at 1200° C. or higher. (2) Sr_1_-_xMg_xTiO_3 (0.00
1≦x≦0.300) from 90.000 to 99.998m
ol%, Nb_2O_3, Ta_2O_5, WO_3,
Dy_2O_3, Y_2O_3, La_2O_3, Ce
O_2, SmO_3, Pr_6O_1_1, Nd_2O
_0.001 to 5.0 of at least one type of 3
00mol%, Al_2O_3Sb_2O_3, BaO
, BeO, PbO, B_2O_3, Cr_2O_3, F
e_2O_3, CdO, K_2O, CaO, Co_2O
_3, CuO, Cu_2O, Li_2O, LiF, Mg
O, MnO_2, MoO_3, Na_2O, NaF, N
iO, Rh_2O_3, SeO_2, Ag_2O, Si
O_2, SiC, SrO, Tl_2O_3, ThO_2
, TiO_2, V_2, O_5, Bi_2O_3, Zn
100 parts by weight of the main component containing 0.001 to 5.000 mol% of at least one of O, ZrO_2, and SnO_2, and SrTiO_360.000 to 32
．． 500mol%, SiO_240.000~67.5
1. A method for producing 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 consisting of mol % at 1200°C or higher, and firing at 1100°C or higher. (3) Sr_1_-_xMg_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, A1_2O_3, Sb_2O_3, B
aO, BeO, PbO, B_2O_3, Cr_2O_3
, Fe_2O_3, CdO, KzO, CaO, Co_2
O_3, CuO, Cu_2O, Li_2O, LiF, M
gO, MnO_2, MoO_3, Na_2O, NaF,
NiO, Rh_2O_3, SeO_2, Ag_2O, S
iO_2, SiC, SrO, Tl_2O_3, ThO_
2, TiO_2, V_2, O_5, Bi_2O_3, Z
100 parts by weight of the main component containing 0.001 to 5.000 mol% of at least one of nO, ZrO_2, and SnO_2, and SrTiO_360.000 to 3
2.500 mol%, 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 5 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.