JPH01289202A - Voltage-dependent nonlinear resistance element and manufacture thereof - Google Patents

Abstract

PURPOSE:To remove a noise of a low voltage and the like by a method wherein Sr is contained excessively so as to set a ratio of Sr to Ti at 1.001-1.05 and one or more of CeO2, Y2O3 and La2O3 and one or more of SiO2, CuO, Co2O3 and MnCO3 are respectively added to SrTiO3 containing Li and F. CONSTITUTION:An SrTiO3 powder is used as a raw material; Sr is added excessively so as to make 1.001<=Sr/Ti<=1.05; then, a lattice defect is increased; a semiconductor property is promoted; in addition, when another element, e.g., Ce, Y or La, is substituted for Sr, an atomic property is controlled and the semiconductor property is promoted. Then, when SiO2, CuO, Co2O3 and MnCO3 are added, these are segregated at a grain boundary, the grain boundary is made a high resistance and a varistor characteristic is revealed. In addition, when LiF is added and this assembly is fired in a reducing atmosphere or in an atmosphere of nitrogen, a sintering operation is promoted by a liquid sintering operation. By this setup, it is possible to obtain an element which can protect a semiconductor and a circuit from a noise and static electricity.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to abnormal high voltages generated in electronic equipment and electrical equipment,
The present invention relates to a voltage-dependent nonlinear resistor element mainly composed of 5rTiO, which protects semiconductor device circuits from noise, pulses, and static electricity, and a method for manufacturing the same.

Conventional technology Conventionally, abnormal high voltages generated in various electronic devices and electrical devices,
SiC varistors and ZnO-based varistors having varistor characteristics have been used to remove noise, pulses, and static electricity. The voltage-current characteristics of such a varistor can be approximately expressed as in the following equation.

I: (V/C)'' Here, Δ is the current, V is the voltage, C is a constant specific to the varistor, and α is the voltage nonlinear index.

The voltage non-linearity index α of SiC varistor is about 2 to 7, Zn
Some O-type varistors have α as high as 60. Although such varistors have excellent performance in absorbing relatively high voltages, their low dielectric constant and small inherent capacitance make them difficult to absorb low voltages below the varistor voltage or high frequencies. It has almost no effect on Further, the dielectric loss tan δ is as large as 6 to 10%.

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

However, such semiconductor capacitors will be destroyed or will no longer function as a capacitor if a voltage exceeding a certain limit is applied due to a surge or the like. Therefore, in recent years, materials have been developed that contain 5rTiO3i as the main component and have both varistor and capacitor characteristics.

Problem to be Solved by the Invention 5rCapacitive varistors mainly composed of Ti05 have the following problems: high varistor voltage, small voltage nonlinearity index α, apparently small dielectric constant ε, and poor capacitance-temperature characteristics. However, a product that satisfies all of the characteristics simultaneously has not yet been obtained. Furthermore, since the sintering temperature and reoxidation temperature are high, there is a problem in that a large amount of energy is consumed. Therefore, in a capacitive varistor mainly composed of 5rTiO31, the varistor voltage is low, and the voltage nonlinearity index α
It is necessary to simultaneously satisfy the following conditions: a large dielectric constant, a large apparent dielectric constant ε, and good capacitance-temperature characteristics, and furthermore, the firing temperature and reoxidation temperature must be low.

The present invention has been made in view of the above points, and an object of the present invention is to provide a voltage-dependent nonlinear resistor element mainly composed of TrTiO5, which can remove low voltage noise, and a method for manufacturing the same. That is.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention contains an excess of Sr so that the ratio of Sr and Ti is 1,001≦Sr/Ti≦1.05, Furthermore, the total of Li and 1 is o,
SrTiO containing oo'y ~o, soo wt%
3, CeO2, Y2O3, LIL20. At least one of them: i0.1-5.0 mo1%, and 5i
n2. Cub.

The present invention provides a voltage-dependent nonlinear resistor element containing 0.1 to 2.0 nOL% of at least one type of CO205C02O59, and the water-soluble salt contained therein is 0.050 wt% or less. (However, 0wt%
(not including). Further, the present invention uses 5rTiO5 powder with an average particle size of 0.5μ or less as a raw material and 1.001≦Sr
/Ti≦1.05, and 1 Cub2.
Y2O3, La20. At least one type of f
0.1-5.0 mo1%, 8i, Cu, Go.

At least one element of Mn is in the form of any of various forms such as oxides and carbonates, and the amount is 0.1 to 2.
The mixed powder containing 1% C11O is molded and fired at a temperature of 1000 to 14oC in a reducing atmosphere or nitrogen atmosphere, and then a conductive paste that can be baked at a temperature of 500 to 90oC is used to mold the fired element. to form electrodes by baking at SOO~900'C, or heat-treating the fired element in air at 500~1000'C and then baking at SOO~900'C.
To provide a method for manufacturing a voltage-dependent nonlinear resistor element, in which an electrode is formed by baking at 00 to 900°C, and the water-soluble salt contained therein is less than or equal to 0,000% (however, not including 000%). It is something.

Function Generally, in order to convert 5rTiO3e into a semiconductor, forced reduction is performed, or a semiconductor conversion accelerator is added and firing is performed in a reducing atmosphere. However, with this alone, semiconductor formation may not proceed depending on the type of semiconductor formation accelerator. Therefore,
When 5rTiO is made to have an excess of Sr or an excess of Ti compared to the stoichiometry, lattice defects increase and semiconductor formation is promoted. Furthermore, when Sr is replaced with other elements such as Ce, Y, and La, semiconductor formation is promoted through atomization control.

Next, 5in2. OuO, Co2O3, MnC0,f
When added, they segregate at grain boundaries, making the grain boundaries high in resistance and exhibiting varistor properties.

Furthermore, at this time, LiF is added as in the present invention,
When fired in a reducing atmosphere or nitrogen atmosphere, a 5r0-Tio□-LiF-based liquid phase is formed at around 680°C, and sintering is promoted by liquid phase sintering. In addition, S through this liquid phase
rTiO3 dissolves and grain growth occurs. As a result, it is possible to obtain a sintered body element that can be sintered at a low temperature, and the amount of energy for sintering can be reduced.

However, if Ti is excessive here, Li2Tie3 is formed, which suppresses the sinterability of SrTiO3. Therefore, excess Sr is desired. However, if the Sr excess exceeds a certain limit, grain growth is suppressed and sinterability is reduced, and the sintered element contains an excessive amount of water-bathable salt, which affects reliability and life characteristics.

Furthermore, the amount of LiF added to 5rTiO is closely related to the sintering temperature, and for low-temperature sintering, a certain amount or more of LiF must be added.

In this case, the added LiF scatters during firing,
This poses a practical problem in that the firing pod, furnace wall, heating element, etc. are attacked, and reliability and life characteristics are significantly reduced. However, as a result of our research, the present inventors found that by refining the raw material particle size of 5rTiO and using a raw material of 0.5 μm or less, as described later, LiF
It has been found that low-temperature sintering is possible even if the amount of addition is reduced. Therefore, from these reasons, it is possible to suppress the scattering and residual amount of L-work F during firing, and to improve the reliability and life characteristics of the sintered body element.

Next, the temperature of the atmosphere firing was specified to be 1000 to 1400°C.As will be explained later, below 1000°C, the residual amount of Mu soil and 2 contained in the sintered element is 0.500w.
This is because the amount is higher than t%, which affects reliability and electrical characteristics, and because the sintered density is low. Also, 1000℃
This is because if it exceeds this, it becomes porous and the firing density decreases.

Therefore, in 5rTiO with excess Sr, CeO2, Y2O5
゜L! At least one type of L203 and 5in
A sintered body obtained by adding 2°ft of at least one type of OuO, Co2O3, and MnCO3, and at least one type of CeO2, Y2O3, and La2O3 to SrTiO3 with excess Sr, and 5 in2. CuO, Co2
0. .

The sintered body finally obtained by adding at least one type of Mnco3 and LfF has a significantly different microstructure and electrical properties, and is considered to be a completely different composition from each other.

EXAMPLES The present invention will be specifically described below with reference to Examples.

(Example 1) First, 5rTiO, (average particle size 0.5 μm), 5
rCO5゜First component Coo□r Y2O5+ La2
O5 and the second component SiO□ and LiF''f were weighed and mixed so that the composition ratio was as shown in Table 1 below. After drying, a binder of O, Swt% polyvinyl alcohol solution was added, and the mixture was heated for 1 hour. Mixed and granulated. After granulation, 1 t
It was molded into a disk shape of 12φx 1.0 (m*) at a pressure of on/ct4, and then the binder was removed in air at 4oo°C for 1 hour. Thereafter, it was fired for 12 hours at 1000 to 1400'C in a reducing atmosphere of N2:H2=1o:1.

The sintered body 1 shown in FIGS. 1 and 2 obtained in this way
Screen print a conductive material such as mug on both sides of the paper, leaving the outer periphery.
The electrodes 2 and 3 were formed at the same time as the sintered element was reoxidized by baking at 6°C.

In the reducing atmosphere thus obtained, 1300°C, 2
Elements fired for hours (electrodes are made of mug paste at 800℃ for 1 hour)
Electrical properties of (formed by baking under conditions of 5 minutes), remaining amount of Li and 2 contained inside the element, content of water-soluble salts containing Li, F, and Sr atoms also contained inside the element, and reliability test The results are shown in Table 2 below. Here, the content of water-soluble salt contained inside the element was analyzed by the following method. First, the sintered element is crushed and water is added to it for 10 minutes.
After boiling for a minute and filtering, Li and Sr were analyzed by flame atomic absorption.
y was investigated by the ion electrode method. Furthermore, as an evaluation method for reliability tests, the sintered elements were tested at a temperature of 90°C and a humidity of 90°C.
After leaving the device in a humidity-resistant load atmosphere of ~96 inches for 500 hours and leaving it at room temperature for 48 hours, the rate of change in capacity before and after the test was compared.

(Left below) First, let's start with the above 1. To explain Table 2, sample black 1
~9.16.17.22~24.31~33.36,3
7.44 to 62 are comparative examples and are outside the scope of the claims of the present invention. These sintered elements have a density of 3. ．． 5-4.
97i/ctd (67 to 94% of theoretical density), which makes it unsuitable for varistor characteristics, or the capacitance change rate is large, affecting reliability and electrical characteristics, making it unsuitable for varistor characteristics. It is something. In contrast, other samples according to the present invention! 10-15.18
~21.25~30, 34, 35.38~43, the density of the sintered body is 5. It has a high value of og/cM or more (96th coefficient of theoretical density or more), and is suitable for characteristics as a varistor. Furthermore, the capacitance change rate is small, does not affect reliability or electrical characteristics, and is suitable for characteristics as a varistor.

Here, in Figure 3, the average particle size of 5rTiO was changed, and all other conditions such as composition ratio and firing temperature were the same as above sample A10.
3rTiO.

FIG. 2 is a diagram showing the relationship between the average grain size of SrTiO3 and the sintered density of the sintered body element, and when the average grain size of SrTiO3 is 0.6 μm or less, the amount of LiF added is 0.7 mo1%, which is at least low temperature. This shows that sintering is possible.

However, if the average particle size of 5rTiO5 exceeds 0.5 μm, the sintered element will have a low sintered density in low-temperature sintering, making it unsuitable for properties as a varistor.

Also, Li! :The remaining amount of F was determined by Ll and F.
reacts with SrTiOs to form SrO-TiO2-I,
Forms an iF-based liquid phase. Liquid phase sintering has the effect of promoting sinterability, but the remaining amounts of Li and 2 are 0.
If it is less than 007 wt%, the density of the sintered body will not improve and L
This is because the effect of adding iF cannot be obtained.

On the other hand, if the residual amount exceeds o, soo wts, the element becomes porous, the sintered density decreases, and L
This is because the content of water-soluble salts containing i and F atoms increases, which affects reliability and electrical characteristics.

In other words, in the manufacturing process, LiF added
The amount of addition of Li and 2 is naturally regulated based on the remaining amounts of Li and 2. That is, the amount of LiF added is 0.7 to 7.
□mo1%.

Then 5rTiO, tD Sr/Ti ratio 1.0
01 to 1.05 is specified when the Sr/Ti ratio is 1.0.
This is because if it is less than 01, the density of the sintered body does not improve as shown in Samples 1 to 8. This is caused by LiF and 5rT during the sintering process.
iOs reacts to form Li□Tie5 and 5rTi
It is thought that this is to suppress the sinterability of Os.

On the other hand, when the Sr/Ti ratio exceeds 1.05i,
As shown in 62 to 62, the density of the sintered element does not improve. This is because the Sr content increases too much, which suppresses grain growth and reduces sinterability. Furthermore, in this case, the content of water-soluble salts containing Sr atoms inside the element increases, which affects reliability and electrical characteristics.

In addition, the first component 0eO2, Y2O3, La20. The amount of O added was specified because CeO2, Y2O3, and La20° replace Sr in 5rTi05 and have the effect of promoting semiconductor formation through atomization control, but at least one of them is 0.1 mo1 If it is less than %, sample shop 22°23.
This is because, as shown in No. 24, the addition effect is not obtained, the semiconductor formation is suppressed, the dielectric constant ε is deteriorated, and the varistor voltage is high, so the characteristics of high capacitance and low varistor voltage are not exhibited. On the other hand, when s, omo exceeds 1%, sample 431. 3
This is because, as shown in 2.33, semiconducting is suppressed and sinterability is reduced.

Furthermore, the content of water-soluble salts contained inside the element is to, 0.
The reason why it is specified to be 50 wt% or less is because if it exceeds 0.050 wt%, the rate of change in capacity in a humidity-resistant load atmosphere increases as shown in FIG. 4, which affects reliability and electrical characteristics.

Next, the reason why the firing temperature was set at 1000 to 140°C is because, as shown in FIG. This is because the residual amount of F is greater than o, sowt%, which affects reliability and electrical characteristics, and also because the sintered density is low. Moreover, if the temperature exceeds 1400'C, the material becomes porous and the sintered density decreases. This figure 6 shows the firing temperature and L based on sample 36.
l.

This shows the relationship with the remaining amount of F.

(Example 2) Next, the Sr/Ti ratio, LiF, CeO2, Y2O5
゜La20. 5i02 of the second component is fixed.
.

The compositions of CuO, Co2O3, and MnCO3 were changed as shown in Table 3 below, and mixing, granulation, molding, and electrode baking were performed in the same manner as in Example 1 above. Characteristics were measured.

(Left below) First, to explain Tables 3 and 4 above, sample A1
-4, 16-18 are comparative examples and are outside the scope of the claims of the present invention. In contrast, other samples according to the present invention/1
65-14 is 5i02, OuO.

Co20. , MnC0, can be added. Here, the second component 5i02, (uo
, Co20. .

The reason for specifying the amount of MnCO3 added is that when these additives are added, they segregate at the grain boundaries, increase the resistance of the grain boundaries, and exhibit the effect of developing varistor characteristics.
This is because if the mo amount is less than 1%, there is no effect of improving the varistor characteristics as shown in samples 1 to 4. On the other hand, 2.0m
This is because when the amount exceeds 1%, the additive is extremely segregated at the grain boundaries as shown in samples 16 to 18, and the varistor voltage increases and the dielectric constant decreases.

In the examples of the present invention, some combinations were shown, but it was confirmed that other combinations had similar effects. Further, in the examples of the present invention, LIF was used as an additive for Li and F, but it goes without saying that similar effects can be obtained with LiF obtained by adding other Li and F compounds and causing a complex reaction.

Although 5rCO5 was added to create 5rTi051 with excess Sr, it may also be used in the form of oxides or hydroxides, or even in the form of various salts containing Sr to obtain the same effect. Needless to say, it can be done.

Furthermore, (uo, Co20.
.

MnCO3 may also be used in forms other than these oxides and carbonates, for example in the form of hydroxides and various salts.

In the above embodiments, the case where the firing is performed in a reducing atmosphere has been described, but the firing may be performed in a nitrogen atmosphere.

However, when firing in a nitrogen atmosphere, it is somewhat difficult to convert into a semiconductor, so firing at a slightly higher temperature (1300 to 1400°C) is better for characteristics than firing in a reducing atmosphere. is preferable.

Furthermore, in the above example, a conductive paste such as mug base that can be baked at 500 to 900°C is printed on both sides of the sintered body, and the paste is baked at 500 to 900'C to reoxidize the sintered body element. We have described the case where electrodes are formed at the same time as the sintered element, but this is a conventional practice in which the fired element is heat-treated in the air at 500 to 1000°C to form the sintered element. After reoxidation, the conductive paste may be baked at a temperature of 500 to 900° C. to form an electrode.

Here, in the present invention, one of the reasons why the reoxidation treatment of the sintered body element and the electrode formation can be performed simultaneously as shown in the above example is that low temperature sintering is possible due to the addition of LiF. This is because reoxidation tends to occur at low temperatures. Another reason is that the sintered element has many oxygen defects due to the influence of F ions, so reoxidation is likely to occur even if a 5g paste or the like is printed and baked at a low temperature. - The device obtained in this way simultaneously satisfies the characteristics of a relatively low varistor voltage, a large α, a large dielectric constant, and excellent reliability, so it is effective in suppressing noise and static electricity, and has a low dielectric constant. Because of its large value, it exhibits excellent responsiveness even to steep wave pulses with a sharp rise.

Effects of the Invention As described above, according to the present invention, it is possible to simultaneously satisfy the following characteristics: relatively low varistor voltage, large α and dielectric constant, small tan δ, and excellent reliability.

Compared to conventional ZnO-based varistors, the varistor voltage is relatively low and α and dielectric constant are large, so it is extremely effective against steep wave pulses with a sharp rise such as noise and static electricity.

Therefore, according to the present invention, an element capable of protecting semiconductors and circuits from noise and static electricity can be obtained, and its practical effects are extremely large.

In addition, the sintering temperature of the conventional 5rTiO5 varistor is 10
Compared to 00℃ or higher, in the present invention, the temperature was 1000 to 1
Sintering can be performed at a relatively low temperature of 40° C., and it is expected that the amount of energy used in the sintering process will be reduced.

[Brief explanation of the drawing]

FIG. 1 is a top view showing an element according to the present invention, FIG. 2 is a cross-sectional view of the same, and FIG. 3 is a Sr Ti O element for explaining the present invention.
Figure 4 is a diagram showing the relationship between the average particle size and sintered density of , and Figure 4 is a diagram showing the relationship between the content of water-soluble salt and the rate of change in capacity.
FIG. 5 is a diagram showing the relationship between the firing temperature and the remaining amounts of Li and F. 1...Sintered body, 2, 3 Fish--electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 I2172 Figure 3 → Zilifu U stemt)t)n)

Claims (3)

[Claims] (1) The ratio of Sr and Ti is 1.001≦Sr/Ti≦1.
Contains excess Sr so that it becomes 05, and further contains Li and F.
SrT containing 0.007 to 0.500 wt% in total
iO_3, CeO_2, Y_2O_3, La_2O_
0.1 to 5.0 mol of at least one of 3.
% and 0.1 to 2.0 mol% of at least one element among Si, Cu, Co, and Mn in any of various forms such as oxides and carbonates. nonlinear resistor element. (2) The water-soluble salt contained in the voltage-dependent nonlinear resistor element according to claim 1 is 0.050 wt% or less (however, 0 wt%
%)). (3) Using SrTiO_3 powder with an average particle size of 0.5 μm or less as a raw material, add an Sr compound so that 1.001≦Sr/Ti≦1.05, and further add 0.7 to 0.7 μm of LiF.
7.0 mol% and CeO_2, Y_2O_3, La_
0.1 to 5.0 of at least one type of 2O_3
A mixed powder containing 0.1 to 2.0 mol% of at least one element among Si, Cu, Co, and Mn in the form of any of various forms such as oxides and carbonates. Molding, 100% in reducing atmosphere or nitrogen atmosphere
Calcinate at a temperature of 0-1400℃, then 500-90℃
Using a conductive paste that can be baked at 0°C, the fired element is baked at 500 to 900°C to form an electrode, or the fired element is baked at 500 to 1000°C in air.
℃ heat treatment and then baking at 500 to 900℃ to form an electrode, and the water-soluble salt contained inside is 0.050wt.
% (however, 0 wt% is not included).