JPH01289207A - 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 at least one or more of Nb2O5 and Ta2O5 are 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., Nb or Ta, is substituted for Ti, an atomic property is controlled and the semiconductor property is promoted. Then, when LiF is added and this assembly is fired in a reducing atmosphere or in an atmosphere of nitrogen, an SrO-TiO2- LiF-based liquid phase is formed and sintering operation is promoted by a liquid sintering operation. By this setup, it is possible to obtain an element whose varistor voltage is comparatively low, whose alpha and permittivity are large, whose tan delta is small, which can simultaneously satisfy a characteristic of excellent reliability and 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 varisque 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.

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

The voltage non-linearity index α of the 13i0 varistor is about 2 to 7, Z
Some nO-based 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 6×1Q 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 level is applied due to a surge or the like. Therefore, in recent years, materials have been developed that have 8rTiO,f as the main component and have both varistor and capacitor characteristics.

Problem to be Solved by the Invention 5 The capacitive varistor mainly composed of rTiO has 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 of high energy consumption. It is necessary to simultaneously satisfy the following conditions: a large linear index α, 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 these points, and uses 5rTiO that can remove low voltage noise.

It is an object of the present invention to provide a voltage-dependent nonlinear resistor element having as a main component and a method for manufacturing the same.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention contains excess Sr so that the Sr to TiO ratio is 1.001≦Sr/Ti≦1.06, and The sum of Li and 1 is o,
SrT containing o o y ~ o, so o wt%
iO3, Nb, 05. The present invention provides a voltage-dependent nonlinear resistor element containing at least one type of Ti2O5 in an amount of 0.1 to 5.01101%. Another object of the present invention is to provide a voltage-dependent nonlinear resistor element in which the water-soluble salt contained therein is 0.050 wt% or less (excluding 0 wt%). Furthermore, the present invention uses SrTiO3 powder with an average particle size of 0.5 μm or less as a raw material and adjusts SrTiO3 so that '1.001≦Sr/Ti≦1,06.
Add the compound and further add LiF from 0.7 to 7.0110
1% and Wb206. A mixed powder containing 0.1 to 5.0 mo1% of at least one type of Ti2O5 is molded to form a powder of 1000 to 5.0 mo1 in a reducing atmosphere or nitrogen atmosphere.
Calcinate at a temperature range of 1400″C, then 600~9
Using a conductive paste that can be baked at 00°C, the fired element is baked at 500 to 900°C to form an electrode, or the fired element is baked at 500 to 100°C in air.
After heat treatment at 0'C, the electrode is formed by baking at SOO~900°C, and the water-soluble salt contained inside is 0. Os
The present invention provides a method for manufacturing a voltage-dependent non-linear resistor element having a concentration of 0wt% or less (excluding Qwt%).

Function Generally, 5rTiO can be converted into a semiconductor by forced reduction or by adding a semiconductor conversion accelerator and firing in a reducing atmosphere. However, depending on the type of semiconducting accelerator, semiconducting may not progress with this alone.
When 5rTi03 is made in excess of Sr or Ti in excess of the stoichiometry, lattice defects increase and semiconductor formation is promoted.

Furthermore, when Ti is replaced with other elements such as Wb or Ta, semiconductor formation is promoted through atomization control.

Next, at this time, when LiF is added as in the present invention and fired in a reducing atmosphere or nitrogen atmosphere, a 5rO-TiO2-LiF system liquid phase is formed at around 680°C, and liquid phase sintering forms a 5rO-TiO2-LiF system liquid phase. Sintering is promoted. In addition, Sr
TiO3 dissolves and grains grow.

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, Li2T
ie, 5rTiO to form .

'sinterability is suppressed. Therefore, excess Sr is desired. However, when excess Sr 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 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 it damages the pod during firing, the heating element of the furnace wall 2, etc., and significantly reduces reliability and life characteristics. However, as a result of our research, the present inventors found that 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 remaining of LiF during firing, and to improve the reliability and life characteristics of the sintered element.

Next, the temperature of the atmosphere firing was specified to be 1oOo to 14oOoC because, as described later, below 1ooOoC, the residual amount of Ll and F contained in the sintered element is greater than o, so0 wt%. affecting the properties and electrical properties,
This is because the sintered density is low. In addition, if the temperature exceeds 1400'C, it becomes porous and the firing density decreases.

Therefore, in 5rTiO with excess Sr, Nb2O5, Ta2
A sintered body obtained by adding at least one kind of O, , and Sr-excess SrTiO3 and Wb205. Ti
The sintered body finally obtained by adding at least one type of 2O5 and LiF 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. First, 5rTiO (average particle size 0.5 μm).

5rCO,, Nb2O5, Ti2O5. Li F t
-Weighed and mixed so that the composition ratio shown in Table 1 below was achieved. After drying, this was ground in an automatic mortar. After that, o,
A binder of swt% polyvinyl alcohol solution was added, mixed for 1 hour, and granulated. After granulation, 1 ton/coi
Formed into a disc shape of 12φ x 1.0 (w) at a pressure of
Next, the binder was removed in air at 400°C for 1 hour.

Thereafter, it was fired at 100° C. to 1400° C. for 12 hours in a reducing atmosphere of N2:H2=10:1. 5 g of conductive paste was screen printed on both sides of the thus obtained sintered body 1 shown in FIGS. 1 and 2, leaving the outer periphery. Baking was performed for 60 minutes to reoxidize the sintered element and at the same time, the electrode 2.
3 was formed.

130°C12 in the reducing atmosphere thus obtained.
Elements fired for hours (electrodes are made of mug base at 800°C for 1 hour)
The electrical properties of the product (formed by baking under conditions of 5 minutes), the residual amount of Ll and F contained inside the device, the content of water-soluble salts containing Li, F, and Sr atoms also contained within the device, and reliability tests. 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, water is added to it, it is boiled for 10 minutes, and after filtration, Li and Sr are determined by flame atomic absorption.
y was investigated by the ion electrode method. Furthermore, as an evaluation method for reliability testing, the sintered element was tested at a temperature of 90'C and a humidity of 90°C.
After leaving the device in a humidity-resistant load atmosphere of 0 to 96% 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.

(The following is a margin) <Table 1> The main part is a comparative example, and the uninvented 1ilI Eikoku Shigai-(The main part is a comparative example and is outside the scope of the claims of the present invention.

The umbrella part is a comparative example and is outside the scope of the present invention.

This part is a comparative example and is outside the scope of the present invention.

First, let's start with the above 1. To explain Table 2, sample locus 1
~9,16,17,25,26,31.32°35,
38 and 43 to 61 are comparative examples and are outside the scope of the claims of the present invention. These sintered elements have a density of 3.5~
Because it is as low as 4.9 f/ad (67 to 94% of the theoretical density), it is not suitable for characteristics as a varistor, or the capacitance change rate is large, affecting reliability and electrical characteristics.
It is not suitable for characteristics as a varistor. In contrast, other samples 8110 to 15 according to the present invention.
18~24.27~30°33.34.37~42, the density of the sintered body is 6.0f/a11 or more (9 of the theoretical density)
6% or more), which 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 grain size of SrTiO5 was changed, and all other conditions such as composition ratio and firing temperature were set to the above sample Ph1.
5 is a diagram showing the relationship between the average grain size of SrTiO3 and the sintered density of the sintered element when the diameter is the same as 5.
When the average particle size of rTiO is 0.5 μm or less, L
The amount of iF added was 0.71101%, which indicates that at least low temperature sintering is possible.

However, if the average particle size of 5rTiO 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 amount of Ll and 1 was specified because Ll and F are 5
It reacts with rTiO to form a 5rO-TiO2-LiF system liquid phase, which has the effect of promoting sinterability by liquid phase sintering, but if the remaining amount of Li and 1 is less than 0.007 wt%, sintering This is because the density of the solids does not improve and the effect of adding LiF cannot be obtained. On the other hand, if the residual amount exceeds o, so0 wt%, the element becomes porous, the sintered density decreases, and there is Ll inside the element.

This is because the content of water-soluble salts containing F atoms increases, which affects reliability and electrical characteristics.0 In other words, LiF added during the manufacturing process
The amount of addition is also naturally regulated based on the remaining amounts of Ll and F. That is, the amount of LiF added is 0.7 to 7
．． 0 gmo1%.

Next, Sr/Ti ratio f of 5rTi03: 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 samples Nagi 1 to 8. During the sintering process, LiF and 8rTi05
reacts to form Li2Tie, SrTiO3
This is thought to be due to the suppression of sinterability. On the other hand, 1.05
If it exceeds this, the density of the sintered element will not improve as shown in sample holes 44-61. 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.

Also, Nb 205r T! The amount of L 20 s added was determined as follows: Nb 20 s * Ta 20 s is added to replace Ti in 5rTj-0 and promote semiconductor formation by controlling atomization, but Nb2O5
, at least one type of Ta 20 s is 0.1 mo
If it is less than 1%, as shown in samples 1'h25 and 26, the addition effect cannot be obtained, the semiconductor formation is suppressed, the dielectric constant ε deteriorates, and the varistor voltage is high, so the characteristics of high capacity and low varistor voltage are This is because it does not show. On the other hand, 5.0 mo
This is because if it exceeds 1%, semiconductor formation will be suppressed and the sintered density will decrease as shown in samples Fh31 and Fh32.

Furthermore, the content of water-soluble salts contained inside the element was reduced to 0.0.
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 specified to be 1000 to 1400'C is because as shown in Figure 6, below 1000°C, the residual amount of Ll and F contained in the sintered element is greater than 0% by weight. This is because the reliability and electrical characteristics are affected, and the sintered density is low. Further, if the temperature exceeds 1400°C, the material becomes porous and the sintered density decreases. This figure 6 shows the firing temperature and Li, using sample Nagi 16 as a pace.
This shows the relationship with the remaining amount of F.

In addition, although some combinations were shown in the examples of the present invention, it was confirmed that other combinations had similar effects. Furthermore, in embodiments of the present invention, Li, F
Although LiFi was used as the additive, it goes without saying that the same effect can be obtained with LiF obtained by adding other Li and F compounds and causing a complex reaction.

In preparing 5rTiO with excess Sr, 5
Although rCO5 is added, it goes without saying that it may be used in the form of oxides or hydroxides, or even in the form of various salts containing Sr to obtain the same effect.

In the above embodiment, the case where the firing is performed in a reducing atmosphere has been described, but the firing may also 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 (130Q to 1400°C) is better than firing in a reducing atmosphere. The above is preferred.

Furthermore, in the above example, a conductive paste such as mug base that can be baked at 600 to 900 °C is printed on both sides of the sintered body, and the paste is baked at SOO to 900 °C to prevent reoxidation of the sintered body element. The case where the electrodes are formed at the same time as the sintered body is formed by heat-treating the fired element in air at 500 to 1'OOO''C, as is conventionally done in boat fishing. After reoxidizing the element, the conductive paste may be baked at 500-900°C to form the electrode.

In the present invention, the reoxidation treatment of the sintered element and the electrode formation can be performed at the same time as shown in the above example. One reason is that low-temperature sintering is made possible by 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 re-oxidation is likely to occur even if a mug paste or the like is printed and baked at a low temperature.

The device of the present invention obtained in this way satisfies the following properties: a relatively low varistor voltage, a large α and dielectric constant, and excellent reliability, and is therefore effective in suppressing noise and static electricity. Due to its large dielectric constant, it exhibits excellent response 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 a relatively low varistor voltage, a large dielectric constant (a, 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 S rTio system varistor is 1
Compared to 400'C or more, the present invention has a temperature of 1oOo
Sintering can be performed at a relatively low temperature of ~140.0'C, and a reduction in the amount of energy in the sintering process is expected.

[Brief explanation of the drawing]

FIG. 1 is a top view showing a device according to the present invention, FIG. 2 is a cross-sectional view of the device according to the present invention, and FIG. 3 is a diagram showing the relationship between the average grain size and sintered density of SrTiO3 for explaining the present invention. FIG. 4 is a diagram similarly showing the relationship between the water-soluble salt content and the rate of change in capacity, and FIG. 5 is a diagram similarly showing the relationship between the firing temperature and the remaining amounts of Li and F. 1... Sintered body, 2, 3... Electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 3

Claims (1)

[Claims] (1) The ratio of Sr and Ti is 1.001≦Sr/Ti≦1.
06, and further contains Li and F.
SrT containing 0.007 to 0.500 wt% in total
A voltage-dependent nonlinear resistor element comprising iO_3 containing 0.1 to 5.0 mol% of at least one of Nb_2O_5 and Ta_2O_5. (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.
A mixed powder containing 7.0 mol% and 0.1 to 5.0 mol% of at least one of Nb_2O_5 and Ti_2O_5 is molded, fired at a temperature of 1000 to 1400°C in a reducing atmosphere or nitrogen atmosphere, and then ,500
Using a conductive paste that can be baked at ~900°C, bake the above fired element at 500~900°C to form an electrode, or heat the fired element in air at 500~100°C.
000°C heat treatment and then baking at 500 to 900°C to form an electrode, and the voltage is characterized in that the water-soluble salt contained inside is 0.050wt% or less (however, 0wt% is not included). A method for manufacturing a dependent nonlinear resistor element.