JPH01289206A - Voltage-dependent nonlinear resistance element and manufacture thereof - Google Patents

Abstract

PURPOSE:To remove noise of a low voltage and the like by a method wherein Sr is contained excessively and one or more of CeO2, Y2O3 and La2O3, one or more of Si, Cu, Co and Mn and one or more of Sn and Zr 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, 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. When another element, e.g., Sn or Zr, is substituted for Ti, a strain is caused in a crystal structure, 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 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 SrTiO3 that protects semiconductors and 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.

r=(v7c)α Here, engineering is current, vB voltage, C is a constant specific to the varistor, and α is a 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.

Such varistors have excellent performance in absorbing relatively high voltages, but due to their low dielectric constant and small inherent capacitance, they are difficult to absorb low voltages below the varistor voltage or high frequencies. shows 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 break down or cease to function as a capacitor when a voltage or current exceeding a certain limit is applied due to a surge or the like. Therefore, in recent years, materials containing 5rTiO5 as a main component and having both varistor and capacitor characteristics have been developed.

Problem to be Solved by the Invention 5r Capacitive varistors whose main component is TiOx 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 the characteristics at the same time 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 whose main component is 5rTiO5, the varistor voltage is low, 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 5rTiOs, which can eliminate 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 includes a method that contains excess Sr so that the ratio of Sr and Ti (7) is 1,001≦Sr/Ti≦1.05. 0g of SrTi containing a total of 0.007 to 0,500 wt% of Li and F.
and at least one of CeO2゜Y2O3 and La2O5 at 0, 1 to 5. Omo1%, Si, C
At least one element among u, Coo, and MnO is made into any of various forms such as oxides and carbonates, and the content is 0.1 to 2. Omo1%, Sn, Zr
0.1"-1.0mo1% of at least one element among the above in the form of any of various forms such as oxides
The present invention provides a voltage-dependent non-linear resistor element containing a water-soluble salt of 0.05%.
The present invention provides a voltage-dependent nonlinear resistor element having a voltage dependency of 0 wt% or less (excluding Owt%). Furthermore, the present invention provides 5rT105 with an average particle size of O0Sμm or less.
Using the powder as a raw material, an Sr compound was added so that 1.001≦Sr/Ti≦1.05, and LiF was further added to 0.7
~ Omo1%, aeo2, Y2O3, La2O5
At least one kind of 0.1 to 5. □ mo1
%, Si, Cu.

At least one element among Go and Mn is made into any of various forms such as oxides and carbonates.
．． Molding a mixed powder in which 1% to 2.0IIO and 0.1 to 1.0 mol% of at least one or more elements among Sn and Zr are added in the form of any of various forms such as oxides, 100 in a reducing atmosphere or nitrogen atmosphere
Calcinate at a temperature of 0~1400℃, then 500~9o
Using a conductive paste that can be baked at 0°C, bake the fired element at 500 to 900°C to form an electrode, or heat the fired element in air at 600 to 100°C.
℃ heat treatment and then baking at 500-900℃ to form an electrode, and the water-soluble salt contained inside is 0.05oW.
The present invention provides a method for manufacturing a voltage-dependent nonlinear resistor element having a voltage dependence of t% or less (excluding 0 wt%).

Function Generally, in order to convert 5rTiOs into a semiconductor, it is either forcedly reduced or a semiconductor conversion accelerator is added and fired in a reducing atmosphere. However, with this alone, semiconductor formation may not proceed depending on the type of semiconductor formation accelerator. Therefore,
When 5rTiOs is made to have an excess of Sr or 1 excess of Sr than the stoichiometry, lattice defects increase and semiconductor formation is promoted. Furthermore, when Sr is replaced with other elements such as Oe, τ, and La, semiconductor formation is promoted through atomization control. Furthermore, when T1 is replaced with an element such as Sn or Zr, the crystal structure is distorted and semiconductor formation is promoted.

Next, 5i02, CuO, Co2O3, MncOs
When added, these segregate at the 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 SrO-TiO2-LiF system liquid phase is formed at around 580C, and sintering is promoted by liquid phase sintering. 5 through the liquid phase with
rriO5 is dissolved 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 T1 is excessive here, Li2TiO3 is formed, which suppresses the sinterability of 5rT103. Therefore, excess Sr is desired. However, if Sr excess exceeds a certain limit.

Grain growth is suppressed and sinterability is reduced, and the sintered element contains an excessive amount of water-soluble salt, which affects reliability and life characteristics.

Furthermore, the amount of LiF added to SrTiO5 is related to the sintering temperature and density, and for low-temperature sintering, a certain amount of LiF must be added.

In this case, the added LiF scatters during firing,
This poses a practical problem in that the firing pod, the heating element of the furnace wall 9, etc. are attacked, and the reliability and life characteristics are significantly reduced. However, as a result of our research, the present inventors found that by reducing the raw material particle size of SrTiO5 and using a raw material of O-5 μm or less, as described later, Li
It has been found that low-temperature sintering is possible even when the amount of F added is reduced. Therefore, from these reasons, it is possible to suppress LiF scattering and residual 1 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 10oO to 1400°C, as will be described later.

Below ℃, the remaining amount of Li and F contained in the sintered element is o.
, 6o0 Wt%, which affects reliability and electrical properties, and also because the sintered density is low. Also,
This is because when the temperature exceeds 1,400°C, it becomes porous and the fired density decreases.

Jutte, CeO2, Y2O5 to SrTiO3 with excess Sr
+At least one type of La2O3 and 5in2
゜A sintered body obtained by adding at least one kind among CuO, Co2O3, and MnCO3 and at least one kind among 5n02 and ZrO2, and a sintered body obtained by adding at least one kind among CuO, Co2O3, and MnCO3;
rTiOs with at least one kind of CeO2, Y2O5+ Il&205, 5i02, CuO, C
At least one or more of o2O3 and Mn005,
The sintered body finally obtained by adding at least one of 5n02, ZrO2, and LiF has significantly different fine grooves 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, SrTiO5 (average particle size 0.6 μm),
5rCO3, first component CeO2, Y2O5l La2
O3 - second component 8102, third component ZrO2 and I
, iF were weighed to have the composition ratio shown in Table 1 below,
Mixed. After drying, a binder of o,ts wt% polyvinyl alcohol solution was added to this, and the mixture was mixed for 1 hour and granulated.

After granulation, 12φX 1, O(
mm), and then heated in air at 400°C for 1
Time binder removal was performed. Then N2:H2=1o
:1000 to 1400°C for 2 hours in a reducing atmosphere. FIG. 1 obtained in this way.

A conductive paste such as wheat was screen printed on both sides of the sintered body 1 shown in Fig. 2, leaving the outer periphery.
Baking was performed at ~900°C for 10~6°C to reoxidize the sintered element and at the same time form electrodes 2°3.

In the reducing atmosphere thus obtained, at 130°C,
The element was fired for 2 hours (the electrodes were made of mug paste at 80°C,
(formed by baking in 15 minutes), the remaining amounts of Li and y contained inside the element, the content of water-soluble salts containing Li, F, and Sr atoms also contained within the element, and the results of reliability tests. 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 was crushed, water was added to it, it was boiled for 10 minutes, it was filtered out, Li and Sr were examined by flame atomic absorption, and F was examined by the ion electrode method. Furthermore, as an evaluation method for reliability testing, the sintered element was heated at 90°C.

After leaving the device in a humidity-resistant load atmosphere with a humidity of 90 to 96% for 600 hours and leaving the device 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 point 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. In these sintered elements, the density is a, es ~ a
,s,! //cd (67-94% of theoretical density), which is not suitable for varistor characteristics, or has a large capacitance change rate, which affects reliability and electrical characteristics, and is not suitable for varistor characteristics. It's something that doesn't exist. On the other hand, the sample quality according to the present invention of the candy was 10 to 15.18.
~21.25~30, 34, 35.38~43, the density of the sintered body is as high as 5-0 g/i or more (96% or more of the theoretical density), 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 FIG. 3, the average particle size of SrTiO5 is changed, and the conditions such as the composition ratio of the pond and the firing temperature are all the same as the above sample A10.
FIG. 2 is a diagram showing the relationship between the average particle size of 5rTiO5 and the sintered density of the sintered element when the 5rTiO5
When the average particle size of iOs is 0.5 μm or less, LiF
The amount added is 0.7 mo1%, which indicates that at least low-temperature sintering is possible. However, if the average particle size of SrTiO5 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.

In addition, the remaining amounts of Li and F were specified because Li and F are S
It reacts with rTiO5 to form a SrO-TiO2-LiF system liquid phase. Liquid phase sintering has the effect of promoting sinterability, but the residual amount of Li and F is 0.007
This is because if the amount is less than wt%, the density of the sintered body will not improve and the effect of adding LiF will not be obtained. On the other hand, the remaining amount is 0.5
If it exceeds 00 wt%, the element becomes porous, the sintered density decreases, and the content of water-soluble salts containing Li and F atoms increases inside the element, which affects reliability and electrical characteristics. It is.

In other words, in the manufacturing process, LiF added
The amount of addition of Li and F is naturally regulated based on the remaining amounts of Li and F. That is, the amount of LiF added is 0.7 to 7.
It becomes 0 mol%.

Next, the Sr/Ti ratio of SrTiO5 was set to 1.001 to 1.
The reason why it is specified as 05 is that when the Sr/Ti ratio is less than 1-001, the density of the sintered body does not improve as shown in sample points 1 to 8. This is caused by LiF (!: Srτ
105 reacts, Li2Ti0. form 5rT103
This is thought to be due to the suppression of sinterability. On the other hand, Sr/
When the Ti ratio exceeds 1.05, the density of the sintered element does not improve as shown at sample points 44 to 62. This is because the Sr content increases too much, which suppresses grain growth and reduces sinterability. Further, in this case, the content of water-soluble salts containing Sr atoms inside the element increases, which affects reliability and electrical characteristics.

In addition, M11-formed CeO2, 7203, 1,1L2Q4
The amount of addition was specified in G'02. Y2O3, La
2O5 substitutes for Sr in SrTiO3 and exhibits the effect of promoting semiconductor formation through atomization control, but at least one type is 0. I less than 1101%, sample &22
, 23 and 24, the addition effect is not obtained, the semiconductor formation is suppressed, the dielectric constant ε deteriorates, and the varistor voltage is high, so the characteristics of high capacitance and low varistor voltage are not exhibited. On the other hand, 5. Q: If it exceeds 1%, the sample &
This is because, as shown in 31.32.33, semiconductor formation is suppressed and sinterability is reduced.

Furthermore, the content of water-soluble salts contained inside the element is o, o
The eso wt% or less stipulated is 0.050wt%.
This is because if the value exceeds 100%, the rate of change in capacity under humidity-resistant load increases as shown in FIG. 4, which affects reliability and electrical characteristics.

Next, the firing temperature was set at 1000 to 140°C because, as shown in Figure 5, below 1000°C, the residual amount of Li and 2 contained in the sintered element becomes greater than 0 to 500 wt%. , affecting reliability and electrical characteristics;
This is because the sintered density is low.

Further, if the temperature exceeds 1000°C, the material becomes porous and the sintered density decreases. This FIG. 6 shows the relationship between the firing temperature and the remaining amounts of Li and F based on the sample point 36.

(Example 2) Next, the Sr/Ti ratio, LiF, Ce102, 72
03. The amount of La2O5 added was fixed, and the second component 5i02, CuO, Co2O3,
The composition of MnCO3 was changed and the pond was mixed in the same manner as in Example 1 above.

Granulation, molding, and electrode baking were performed, and various properties were measured as shown in Table 4 below.

(Left below) First, to explain Table 31M4 above, sample point 1
-4.16-18 are comparative examples and are outside the scope of the claims of the present invention. In contrast, 7% of the sample according to the present invention in that pond
5-14 are 5i02, CuO.

The effect of adding co2o5 and MnCO3 can be obtained. Here, the second component 8102, OuO, C
o2O3.

The reason for specifying the amount of MnC05 added is that when these additives are added, they segregate at the grain boundaries, make the grain boundaries high in resistance, and have the effect of developing varistor properties.
This is because if the mo is less than 1%, there is no effect of improving the varistor characteristics as shown in samples A1 to A4. On the other hand, 2.0
This is because when the mol% is exceeded, this additive is extremely segregated at the grain boundaries as shown in samples &16 to 1B, and the varistor voltage increases and the dielectric constant and sintered density decrease.

(Example 3) Next, the Sr/Ti ratio, LiF, and the first component CaO2.

τ205 + "205 + 5i02 of the second component,
CuO, Co2O3.

The amount of MnCO3 added was fixed, and the compositions of the third component 5n02 and ZrO2 were changed as shown in Table 6 below, but otherwise mixing, granulation, molding, and electrodes were carried out in the same manner as in Example 1.2 above. Baking was performed and various properties were measured as shown in Table 6 below.

(Left below) First, let's start with the above 6. To explain Table 6, sample &1
-2.9 to 10 are comparative examples and are outside the scope of the claims of the present invention. In contrast, other samples &3~ according to the present invention
B is 5n02, which provides the effect of adding ZrO2. Here, the addition amount of the third component 5n02 and ZrO2 was specified because when these additives are added,
Replaced with 1 in 5rTiOg.

It is expected that this will cause distortion in the crystal structure and promote semiconducting, resulting in an increase in the dielectric constant.

This is because if O-1mol is less than 1%, there is no effect of increasing the dielectric constant as shown in samples /a1 and /a2. On the other hand, 1.0m
When it exceeds ol%, semiconductor formation and grain growth are suppressed, as shown in sample points 9 to 1o, and the dielectric constant decreases.

This is because properties such as tan δ and sintered density deteriorate.

In addition, although some combinations were shown in the examples of the present invention, it was confirmed that a similar effect could be obtained with a combination of ponds. Furthermore, in the examples of the present invention, LiF was used as an additive for Li and F, but what about other Li? It goes without saying that similar effects can be obtained with LiF in which a compound is added and a complex reaction is carried out.

Then, when creating 5rT105 with excess Sr,
Although 5rCO5 is added, it goes without saying that it may be used in the form of oxides or hydroxides, and even in the form of various salts containing Sr, similar effects can be obtained.

Furthermore, CuO and Co2O3 as the second component.

MnC03, 5n02 as the third component, ZrO2
It may be used in a form other than these oxides and carbonates, for example, in the form of a hydroxide or 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 14oC) is better for characteristics than firing in a reducing atmosphere. is preferable.

Furthermore, in the above example, a conductive paste such as Ag paste that can be baked at 500 to 900°C is printed on both sides of the sintered body, and the sintered body element is reoxidized by baking at 600 to 900°C. We have explained the case where electrodes are formed at the same time, but this is commonly done in the past.
The fired element may be heat treated in air at 500 to 1000°C to reoxidize the sintered element, and then the conductive paste may be baked at 500 to 900°C to form the electrode. It is something.

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 problem is that due to the influence of y ions, the sintered element has many oxygen defects, so re-oxidation is likely to occur even if Ag 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 size, it exhibits excellent responsiveness even to steep wave pulses with a sharp rise.

Effects of the Invention As shown above, according to the present invention, it is possible to simultaneously satisfy the characteristics of 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, it is possible to obtain an element that can protect semiconductors and circuits from noise and static electricity.
Its practical effects are extremely large.

In addition, the sintering temperature of the conventional 5rTiO5 varistor is 14
Compared to 00'C or more, the present invention has a temperature of 10oO~
Since sintering can be performed at a relatively low temperature of 14oO<0>C, it is expected that the amount of energy 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 sectional view thereof, and the fJcs diagram is a 5rTiO
Figure 4 is a diagram showing the relationship between the average particle size and sintered density of No. 5, and Figure 4 is a diagram showing the relationship between the content of water-soluble salt and the rate of change in capacity.
Figure 6 also shows the firing temperature and Li. It is a figure showing the relationship with the residual amount of F. 1... Sintered body, 2.3... Electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person

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.
%, 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, and 0.1 to 2.0 mol% of Sn, Zr. A voltage-dependent nonlinear resistor element containing 0.1 to 1.0 mol% of at least one element among them in the form of any of various forms such as oxides. (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%
A voltage-dependent nonlinear resistor element characterized in that: (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
Sn,
0.1 to 1.0 mol% of at least one element of Zr in any of various forms such as oxides
The added mixed powder is molded and fired at a temperature of 1000 to 1400°C in a reducing atmosphere or nitrogen atmosphere, and then
Using a conductive paste that can be baked at 00-900℃,
The fired element is baked at 500 to 900°C to form an electrode, or the fired element is heated at 500°C in air.
After heat treatment at ~1000°C, the electrode is baked at 500~900°C, and the water-soluble salt contained inside is reduced to 0.
A method for manufacturing a voltage-dependent nonlinear resistor element, characterized in that the voltage is 0.050 wt% or less (excluding 0 Wt%).