JP2697123B2 - Ceramic capacitor and method of manufacturing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally functions as a capacitor to absorb low-voltage noise and high-frequency noise, while providing a varistor function when a high voltage such as a pulse or static electricity enters. The present invention relates to a ceramic capacitor capable of protecting semiconductors and electronic equipment from abnormal voltages such as noise, pulses, and static electricity generated in the electronic equipment and stabilizing their characteristics with respect to temperature, and a method of manufacturing the same. is there.

2. Description of the Related Art In order to realize multifunctional, light, thin and compact electronic devices,
Semiconductor devices such as C and LSI are widely used, and accordingly, the noise immunity of devices is decreasing. In order to ensure the noise immunity of such electronic devices, various ICs and LSIs
In such power supply lines, film capacitors, multilayer ceramic capacitors, semiconductor ceramic capacitors and the like are used as bypass capacitors. However, these capacitors exhibit excellent performance in absorbing low-voltage noise and high-frequency noise, but do not have the function of absorbing high-voltage pulses or static electricity.
When a pulse or static electricity enters, a major problem is that malfunction of equipment, destruction of a semiconductor, and destruction of a capacitor are caused. Therefore, for such applications, in addition to good noise absorption and stability over temperature and frequency, a new type of capacitor with high pulse strength and excellent pulse absorption is used as a SrTiO ₃ based semiconductor. A ceramic capacitor having a varistor function in a ceramic capacitor (hereinafter, referred to as a ceramic capacitor with a varistor function) has been developed and is already provided in Japanese Patent Application Laid-Open Nos. 57-27001 and 57-35303. This ceramic capacitor with a varistor function normally absorbs low-voltage noise and high-frequency noise as a capacitor, but functions as a varistor when a high voltage such as a pulse or static electricity enters, and generates noise and pulse generated in electronic equipment. It has the feature of protecting semiconductors and electronic equipment from abnormal voltages such as static electricity, and its use is being expanded more and more.

On the other hand, in the field of electronic components, lighter, thinner, smaller, and higher performance have been increasingly promoted, and even with this varistor function-equipped ceramic capacitor, demands for smaller size and higher performance have been increasing. However, since the conventional ceramic capacitor with a varistor function is of a single-plate type, if the size is reduced, the area of the electrode is reduced, and as a result, there is a problem that the capacity is reduced and the reliability is reduced. Therefore, as a solution to this, it is expected to expand to a lamination in which the electrode area can be reduced. However, a ceramic capacitor with a varistor function usually has a process of applying an oxide to the surface of a SrTiO ₃ -based semiconductor element and insulating the grain boundary layer by thermal diffusion, so that a commonly used BaTiO ₃ -based multilayer ceramic capacitor is used. In comparison, it has been considered that it is extremely difficult to form a multilayer capacitor with a varistor function (hereinafter, referred to as a multilayer ceramic capacitor with a varistor function) by firing simultaneously with the internal electrodes.

Therefore, as a method of solving the problem of co-firing, JP-A-54-53248 and JP-A-54-53250 are applied, and a ceramic paste with a large amount of organic binder is printed on a portion corresponding to an internal electrode. This part forms a porous layer in the firing process and, after sintering, injects a conductive metal into the porous layer under an appropriate pressure, or forms an internal electrode by plating or melting, and forms a varistor. A method for forming a multilayer ceramic capacitor with a function has been developed and provided. But these are quite difficult in process. It has not yet reached the level of practical use.

JP-A-59-215701 discloses a conductive paste in which a heat diffusion material capable of insulating a grain boundary layer is mixed on a raw sheet made of powder calcined in a non-oxidizing atmosphere. Printing and sintering in an oxidizing atmosphere, and furthermore, JP-A-63-219115 discloses that a pre-semiconductor powder is used as a main component, and an oxidizing agent and a glass component for forming an insulating layer thereon. There has been reported a method in which a molded body obtained by alternately laminating a raw sheet containing a mixed diffusing agent and internal electrodes is fired in air or an oxidizing atmosphere. However, in these methods, the sintering temperature is relatively low at 1000 to 1200 ° C., and sintering of the ceramic is difficult to occur, so that the crystal particles are hardly brought into surface contact, and the completed device has not reached a perfect sintered body. It has the disadvantage that the capacitance is low, the voltage nonlinearity index α, which is a typical characteristic of a varistor, is small, the varistor voltage is unstable, and the reliability is poor. Furthermore, in the latter JP-A-63-219115, since a glass component is added as an additive, a glass phase is precipitated at a crystal grain boundary, and the above-mentioned electric characteristics are easily deteriorated, and the reliability is poor. And has not reached the level of practical use.

As a patent for a multilayer varistor, Japanese Patent Publication No. 58-23921 has already proposed a multilayer voltage non-linear element using ZnO, Fe ₂ O ₃ , and TiO ₂ . However, since this element has almost no capacitance, it exhibits excellent performance against pulses with relatively high voltage and absorption of static electricity, but against noise with low voltage below the varistor voltage and high frequency noise. Have the problem that they show little effect.

Problems to be Solved by the Invention Until now, various compositions and manufacturing methods have been developed and provided for multilayer ceramic capacitors with a varistor function, but as described above, in any case, there are problems in terms of process and completed devices. Has a point and has not reached a practical level. Therefore, development of a new composition and a new manufacturing method for the multilayer ceramic capacitor with a varistor function is expected.

The present invention has been made in view of such a point, and usually functions as a capacitor to absorb low-voltage noise and high-frequency noise, and when a high voltage such as a pulse or static electricity enters, a varistor function is provided. And its characteristics are always stable with respect to temperature, and in terms of process, the ceramic capacitor containing SrTiO ₃ as the main component and the simultaneous firing of the ceramic capacitor material and the internal electrode material and its It is intended to provide a manufacturing method.

Means for Solving the Problems In order to solve the above problems, the present invention provides Sr
Excess Ti so that the molar ratio of Ti is 0.95 ≦ Sr / Ti <1.00
A SrTiO ₃ containing _{a, Nb 2 O 5, Ta 2} O 5, V 2 O 5, W 2 O 5, Dy 2 O 3, Nd
₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , at least one of CeO ₂
5~2.0mol% and, 0.2~5.0mol% in the total amount of MnO ₂ and SiO ₂
And to provide a ceramic capacitor containing 0.05 to 2.0 mol% of Li ₂ SiO ₃ . Further, the present invention relates to Sr
Excess T so that the molar ratio of Ti and Ti is 0.95 ≦ Sr / Ti <1.00.
i the SrTiO ₃ containing _{a, Nb 2 O 5, Ta 2} O 5, V 2 O 5, W 2 O 5, Dy 2 O 3, N
At least one of d ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and CeO ₂ is 0.
05~2.0mol% and, 0.2~5.0mol% in the total amount of MnO ₂ and SiO ₂
And a plurality of layers of internal electrodes are provided in a ceramic containing 0.05 to 2.0 mol% of Li ₂ SiO ₃ so as to reach alternately opposed edges, and external electrodes are provided at both ends of the internal electrodes. The present invention provides a ceramic capacitor characterized in that: Further, the present invention provides that the molar ratio of Sr and Ti is
SrT containing excess Ti so that 0.95 ≦ Sr / Ti <1.00
In iO ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂ O ₅ , W ₂ O ₅ , Dy ₂ O ₃ , Nd ₂ O ₃ , Y ₂ O ₃ , La ₂ O
₃ , 0.05-2.0 mol% of at least one of CeO ₂
And 0.2 to 5.0 mol% of MnO ₂ and SiO ₂ in total, and Li ₂ SiO ₃
Starting from a mixed powder of a composition containing 0.05 to 2.0 mol%, crushing, mixing, and drying the mixed powder, and then calcining in air or a nitrogen atmosphere; The powder thus obtained is dispersed in a solvent together with an organic binder into a raw sheet, and then the internal electrode paste is printed on the raw sheet so as to alternately reach the opposite edges (however,
A process of not printing on the green sheets of the uppermost layer and the lowermost layer), and laminating, pressing and crimping the green sheets on which the internal electrode paste is printed to obtain a molded body, and thereafter, the molded body is aired. Calcining, calcining, baking in a reducing or nitrogen atmosphere, baking, re-oxidizing in air, and after re-oxidizing, applying external electrode paste to both ends exposing the internal electrodes And a baking step. Further, the present invention provides that the internal electrode is formed of at least one kind of metal among Au, Pt, Rh, Pd, and Ni, or an alloy or a mixture thereof. Further, the present invention provides that the external electrode is formed of at least one kind of metal among Pd, Ag, Ni, Cu, Zn or an alloy or a mixture thereof.

Action Generally, in order to convert SrTiO ₃ into a semiconductor, it is necessary to carry out forced reduction or to add a semiconducting accelerator and sinter it in a reducing atmosphere. However, this alone may not make the progress of semiconducting depending on the type of semiconducting accelerator. Therefore, if the stoichiometry of SrTiO ₃ is too large or too much Ti, the number of lattice defects in the crystal increases, and the formation of a semiconductor is promoted. Further, Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂ O ₅ , W ₂ O ₅ , Dy ₂ O ₃ , Nd ₂ O ₃ , Y ₂
Addition of O ₃ , La ₂ O ₃ , and CeO ₂ (hereinafter, referred to as a first component) promotes the formation of a semiconductor by atomization control.

Next, MnO ₂ and SiO ₂ (hereinafter, referred to as a second component) are indispensable substances for forming a laminated structure, and even if one of them is missing, the action is not exhibited. As described above, it has been considered that it is difficult to fabricate an SrTiO ₃ -based multilayer ceramic capacitor with a varistor function. The first reason is that the ceramic capacitor material having a varistor function and the internal electrode material have different functions and properties in the firing process and the re-oxidation process. That is, the former material requires firing in a reducing atmosphere in the firing process, but at this time, since the latter material is formed of metal, it absorbs H ₂ gas in the reducing atmosphere and expands. Further, the latter material is oxidized to a metal oxide during the reoxidation process in the air, and has a function and a property of shielding the reoxidation of the former material.

Also, as the second reason, in order to form the former material as a ceramic capacitor element with a varistor function, after firing in a reducing atmosphere to form a semiconductor, a high-resistance metal oxide (MnO ₂ , CuO ₂ , Bi ₂ O ₃ , Co ₂ O _3, etc.), and re-oxidize in air to selectively diffuse the grain boundaries to make them insulating, that is, a surface diffusion step is required. However, in an element having a structure alternately laminated with the internal electrode material, diffusion of metal oxide is technically difficult.

Then, the present inventors invented the following as a result of research.

First, in addition to the addition of the first component to SrTiO ₃ in excess of Ti, in a material composition in which MnO ₂ and SiO ₂ are added, after firing in a reducing atmosphere, the surface of the element as described above has a high It has been found that a ceramic capacitor having a varistor function can be easily formed only by reoxidizing in air without applying a metal oxide of resistance. It was added with excess Ti
During the sintering process, MnO ₂ and SiO ₂ form a liquid phase of MnO ₂ —SiO ₂ —TiO ₂ system at a low temperature to promote sintering, and at the same time, dissolve and segregate in the grain boundaries. Then, when this is reoxidized in the air, the MnO ₂ —SiO ₂ —TiO ₂ system segregated at the grain boundaries is insulated and easily becomes a ceramic capacitor with a varistor function having a grain boundary insulating structure. Furthermore, Ti
It has also been found that an excessive amount can suppress oxidation and diffusion of the internal electrode. Therefore, in the present invention, for these reasons
We decided to use Ti excess SrTiO ₃ .

Secondly, it has been found that a material composition in which MnO ₂ and SiO ₂ are added to SrTiO ₃ in excess of Ti can be converted into a semiconductor by sintering in a nitrogen atmosphere in addition to a reducing atmosphere. This is the first
As shown in the reason above, in order to form a liquid phase at a low temperature, the added Mn acts as an atomization control agent in addition to forming a liquid phase. At this time, the valence of the Mn atom changes to +2, +4. It is thought that the sinterability is improved due to the effect of being unstable electronically, and the semiconductor is easily converted into a semiconductor even in a nitrogen atmosphere.

Third, if the molded body after degreasing is calcined in the air in advance, the resulting laminated ceramic capacitor with a varistor function has internal electrodes broken, delaminated, cracked, and so on.
It has been found that the occurrence of various problems such as a reduction in sintering density is suppressed as much as possible, and that the electrical characteristics and reliability are significantly improved.

As described above, when such a viewpoint is sufficiently considered, it is possible to easily manufacture a multilayer ceramic capacitor having a varistor function by simultaneously firing a ceramic capacitor material having a varistor function and an internal electrode material.

Further, Li ₂ SiO ₃ (hereinafter, referred to as a third component) contains MnO ₂
Acts as a carrier that uniformly diffuses the liquid phase of -SiO ₂ -TiO ₂ into the grain boundaries, and sharply forms the boundary between the semiconductor crystal and the high-resistance grain boundaries, resulting in temperature characteristics of capacitance and varistor voltage. Is to improve.

Examples Hereinafter, the present invention will be described specifically with reference to examples.

Example 1 First, SrTiO having an average particle size of 0.5 μm or less and a purity of 98% or more.
The powder was adjusted Sr / Ti ratio plus TiO ₂ to ₃ raw material powder, a first component of the Nb ₂ O ₅ as shown in Table 1 ~ Table 15 below, MnO ₂ of the second component, SiO ₂ (provided that The added amount of MnO ₂ and SiO ₂ was assumed to be equal mol%), and the addition amount of Li ₂ SO ₃ as the third component was fixed at 0.5 mol% and mixed. Thereafter, the mixed powder is wet-pulverized by a ball mill or the like, mixed, dried, and then calcined at 600 to 1200 ° C. in air. After calcining, the powder is pulverized again so that the average particle diameter becomes 0.5 μm or less. This was used as a starting material for a laminated ceramic capacitor with a varistor function. The starting material of the fine powder was dispersed in a solvent together with an organic binder such as butyral resin to form a slurry, which was formed into a raw sheet having a thickness of about 50 μm by a doctor blade method and cut into a predetermined size. next,
As shown in FIG. 1, an internal electrode paste 2 made of Pd was screen-printed on the raw sheet 1 obtained as described above according to a predetermined size. As is clear from FIG. 1, the inner electrode paste 2 is not printed on the uppermost and lowermost raw sheets 1. Also, at this time,
The internal electrode paste 2 printed on the raw sheet 1 laminated in the middle was printed so as to reach alternately facing edges as is well known. Thereafter, the raw sheet 1 is laminated in a plurality of layers with the printed direction of the internal electrode paste 2,
Crimped. Next, it was degreased at 400 ° C. in air, and further calcined at 600 to 1250 ° C. in air. Thereafter, firing was performed at 1250 to 1350 ° C. in a reducing atmosphere. After this firing, in air
Reoxidized at 900-1250 ° C.

Then, as shown in FIG. 2, an external electrode paste made of Ag is applied to both ends exposing the internal electrodes 2a, and baked in air at 800 ° C. for 15 minutes, so that a plurality of layers are formed in the ceramic. The multilayer ceramic capacitor 4 with a varistor function was obtained in which the electrodes 2a were alternately provided to the edges, and the external electrodes 3 were provided on both edges of the internal electrode 2a.

The shape of the multilayer ceramic capacitor with a varistor function in the present embodiment is a 5.5 type of 5.70 × 5.00 × 2.00 mm ³ , which is formed by laminating 10 effective layers on which internal electrodes are formed. FIG. 3 shows a manufacturing process of the present invention.

Various electrical characteristics such as the capacitance, tanδ, varistor voltage, voltage non-linear exponent α, series equivalent resistance value ESR, capacitance temperature change rate, and varistor voltage temperature coefficient of the multilayer ceramic capacitor with varistor function thus obtained are described. Are also shown in Tables 1 to 15. However, for each condition such as firing at this time, calcining in air is 1200 ° C for 2 hours,
For details in a reducing atmosphere of N ₂ : H ₂ = 99: 1, 1300 ° C, 2 hours,
Reoxidation was performed at 1100 ° C for 1 hour.

The following measured values are described for various electric characteristics.

容量 Capacitance C is a value at a measurement voltage of 1.0 V and a frequency of 1.0 KHz.

バ リ The varistor voltage V _0.1mA is the value at the measured current 0.1mA.

◇ The voltage non-linear index α was calculated from the values at the measured currents of 0.1 mA and 1.0 _{mA according to} the formula α = 1 / log (V _{1.0 mA} / V _{0.1 mA} ).

直列 Series equivalent resistance value ESR is the resistance value at the resonance point at a measurement voltage of 1.0V.

容量 Capacitance temperature change rate (ΔC / C) is the value between -25 ℃ and 85 ℃.

温度 Temperature coefficient of varistor voltage (ΔV / V) is a value between 25 ° C and 50 ° C.

Next, Tables 1 to 15 will be described. These tables define the Sr / Ti ratio and the amounts of MnO ₂ and SiO ₂ as the second components.

Here, the sample number is marked with * for comparison.
It is outside the scope of the present invention. In other words, these sintered devices have a small capacitance, a small voltage non-linear index α representing varistor characteristics, and a large series equivalent resistance value ESR, so that they absorb low-voltage noise and high-frequency noise as capacitors. Function and the function of absorbing high voltage such as pulse and static electricity as a varistor at the same time, the capacitance temperature change rate and the varistor voltage temperature coefficient are large, and the reliability and electrical characteristics are affected by temperature. It is easy. Therefore, these samples are not suitable as ceramic capacitors with a varistor function for protecting semiconductors and electric equipment from abnormal voltages such as noise, pulses, and static electricity generated in electronic equipment. On the other hand, the other sample numbers have a large capacitance, a large voltage non-linear index α, and a small series equivalent resistance value ESR, so they function to absorb low-voltage noise and high-frequency noise as capacitors. And the pulse as a varistor,
It has both functions of absorbing high voltage such as static electricity at the same time, has a small rate of temperature change of capacitance and a temperature coefficient of varistor voltage, and has a feature that reliability and electric characteristics are hardly influenced by temperature. Therefore, these samples are suitable as ceramic capacitors with a varistor function to protect semiconductors and electronic devices from abnormal voltages such as noise, pulsation, and static electricity generated in the electronic devices.

Here, in the present invention, the Sr / Ti ratio of SrTiO ₃ is specified, when the Sr / Ti ratio is larger than 1.00, Sr becomes excessive, and it is difficult to form a liquid phase of MnO ₂ -SiO ₂ -TiO ₂ system. For this reason, the grain boundary insulating structure is unlikely to be formed, and the internal electrodes are oxidized or diffused, and as a result, electrical characteristics and reliability are reduced. On the other hand, if the Sr / Ti ratio is less than 0.95, the sintered body becomes porous and the sintered density decreases. Furthermore, the average particle size of the starting material for the multilayer varistor function-equipped ceramic capacitor is set to 0.5 μm or less,
If it is larger than m, the powder is agglomerated when the slurry is formed, and the sintered density of the resulting sintered body element is small,
In addition, since it is difficult to form a semiconductor, electric characteristics are also likely to be unstable.

Next, the defining the amount of the sum of MnO ₂ and SiO ₂ of the second component, since the addition amount of the second component can not be obtained the effect of addition is less than 0.1 mol%, MnO ₂ -SiO ₂ - Because it is difficult to form a TiO ₂ -based liquid phase, it is difficult to have a grain boundary insulating structure,
This is because the electrical characteristics and the sintered density are reduced. On the other hand, the second
If the amount of the component exceeds 5.0 mol%, the amount of the high-resistance oxide segregated at the grain boundary increases and the electrical characteristics deteriorate.

Furthermore, the molded body after degreasing is previously heated to 600 to 1250 ° C in air.
Calcination is the most important step in the method of manufacturing a multilayer ceramic capacitor with a varistor function of the present invention,
The result of this step is to substantially determine the electrical characteristics and reliability of the completed multilayer ceramic capacitor with varistor function. The purpose of this process is to strengthen the adhesion between the ceramic capacitor material with varistor function and the internal electrode material,
Further, it is the control of the average particle size of the completed multilayer ceramic capacitor with a varistor function.

Here, the reason why the calcining temperature in the air is set in the range of 600 to 1250 ° C. is that if the calcining temperature is lower than 600 ° C., the effect cannot be obtained. On the other hand, if the calcination temperature exceeds 1250 ° C, sintering of the ceramic capacitor material with a varistor function proceeds. When firing in a reducing or nitrogen atmosphere in this state, stress concentration due to sudden shrinkage will occur in the sintered body, and the resulting multilayer ceramic capacitor with varistor function will have various problems such as delamination and cracking. become.

When Ni is used as the internal electrode material, sintering of the former ceramic capacitor material and oxidation of the Ni internal electrode material occur, and then the sintered body and Ni react, and the diffusion of Ni proceeds.
In the resulting multilayer ceramic capacitor with a varistor function, various problems such as internal electrode breakage, delamination, and cracking occur.

When calcination is performed at a high temperature exceeding 1250 ° C, MnO ₂ -SiO _2-
The liquid phase sintering of TiO ₂ system proceeds rapidly, and the grain growth is promoted, and the density of the sintered body and the packing density decrease remarkably.

Then, if firing in a reducing or nitrogen atmosphere,
Semiconductor conversion is unlikely to occur.

For this reason, electrical characteristics and reliability are significantly reduced.

Further, by adding Li ₂ SiO ₃ as the third component, the capacitance temperature change rate means that the varistor voltage temperature coefficient is improved. That is, the added Na ₂ SiO ₃ is M
This is because it acts as a carrier for uniformly diffusing the nO ₂ —SiO ₂ —TiO ₂ liquid phase into the grain boundaries, and sharply forms the boundary between the semiconductor crystal and the high-resistance grain boundaries.

The multilayer ceramic capacitor with the varistor function obtained in this manner has a larger capacity and more excellent temperature and frequency characteristics than the multilayer varistor reported in Japanese Patent Publication No. 58-23921. While the former simply laminates a varistor material with excellent surge absorption, the present invention provides both a capacitor function with excellent noise absorption and a varistor function with excellent pulse and electrostatic absorption. It is a product obtained by laminating ceramic capacitor materials having a varistor function, which are completely different from each other in function and purpose of use.

Example 2 From Example 1, it was found that the total addition amount of MnO ₂ and SiO ₂ as the second component was required to be 0.2 to 5.0 mol%.
Next, the addition ratio of MnO ₂ and SiO ₂ as the second component was variously changed, the Sr / Ti ratio was 0.97, the addition amount of Nb ₂ O ₅ as the first component was 1.0 mol%, and the third Li ₂ SiO ₃ as a component
Was fixed at 0.5 mol%, and a multilayer ceramic capacitor with a varistor function was manufactured in the same manner as in Example 1. The results are shown in Table 16 below.

Explaining Table 16 above, as is clear from the measurement results, in order to manufacture a multilayer ceramic capacitor with a varistor function, both MnO ₂ and SiO ₂ are required, and even if one of them is missing, it has a varistor function. A multilayer ceramic capacitor cannot be manufactured. That is, only when both components are present, a liquid phase of MnO ₂ —SiO ₂ —TiO ₂ system is formed, dissolves and segregates at the grain boundary, and when reoxidized, the MnO ₂ —SiO ₂ segregated at the grain boundary is insulated. This is because the element easily has a grain boundary insulating structure.

Note that comparing electrical characteristics such as capacity, voltage nonlinearity index α, and ESR, it is preferable that MnO _{2 is} slightly excessive.

Example 3 Next, Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂ O ₅ , W ₂ O ₅ , Dy ₂ O as the first component
₃ , Nd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , to regulate the addition amount of the atomization control agent of CeO ₂ , this was changed variously, the Sr / Ti ratio was 0.97, the addition amount of the second component Of 2.0 mol% of MnO _{2 and} 1.0 mol% of SiO ₂
% And the addition amount of Li ₂ SiO ₃ as the third component were fixed to 0.5 mol%, and a multilayer ceramic capacitor with a varistor function was manufactured in the same manner as in Examples 1 and 2. The results are shown in Tables 17 to 25 below.

Referring to Tables 17 to 25, the addition amount of the first component is specified. As is clear from the measurement results, if the addition amount is less than 0.05 mol%, the addition effect cannot be obtained, and This is because it is difficult to cause the formation. On the other hand, if the total amount of the first component exceeds 2.0 mol%, the formation of a semiconductor is suppressed, desired electrical characteristics cannot be obtained, and the sintered density is further reduced.

It should be noted that the addition of Nb ₂ O ₅ and Ta ₂ O ₅ as the first component makes it possible to use other V ₂ O ₅ , W ₂ O ₅ , Dy ₂ O ₃ , Nd ₂ O ₃ , Y ₂ O ₃ , La _The electrical characteristics were slightly better than the case where ₂ O ₃ and CeO ₂ were added.

Further, with respect to the composition of the mixture of the first component, the electric characteristics were measured for some of the combinations, and as shown in Table 25, the results showed that there was almost no difference in the characteristics between the case where one kind was added and the case where one kind was added. It was not seen. However, also in this case, the addition of Nb ₂ O ₅ and Ta ₂ O ₅ was slightly better in electrical characteristics than the case where other components were added.

On the other hand, when the average particle size of the starting material is larger than 0.5 μm, the effect of the first component tends to be hardly obtained.
It was confirmed that it was necessary to suppress the thickness to 5 μm or less.

(Example 4) Next, in order to regulate the addition amount of Li ₂ SiO ₃ as the third component, this was changed variously, the Sr / Ti ratio was 0.97, and the addition amount of the first component was Nb ₂ O ₅ 0.5 mol. %, Ta ₂ O ₅ 0.5 mol%, and the addition amount of the second component were fixed to MnO ₂ 1.0 mol% and SiO ₂ 1.0 mol%, and a multilayer ceramic capacitor with a varistor function was manufactured in the same manner as in the above-described embodiment. The results are shown in Table 26 below.

As described above Table 26, by adding Li ₂ SiO ₃ of the third component, the capacitance-temperature change rate and the varistor voltage temperature coefficient is improved. This is because the added Li ₂ SiO ₃ is MnO ₂ -S
This is because it acts as a carrier for uniformly diffusing the iO ₂ -TiO ₂ -based liquid phase into the grain boundary portion, and therefore the boundary between the semiconductor crystal and the high-resistance grain boundary is sharply formed. Here, the addition amount of Li ₂ SiO ₃ as the third component is specified because the addition effect of the third component is not obtained when the addition amount of the third component is less than 0.05 mol%, and the capacitance temperature change rate and the Vista voltage temperature coefficient Is difficult to improve. On the other hand, if the added amount of the third component exceeds 2.0 mol%, it acts as a carrier at the grain boundary portion.
This is because the amount of Li ₂ SiO ₃ increases, and as a result, the capacitance and the voltage non-linear index α decrease, the series equivalent resistance value ESR increases, and the firing density decreases, and the mechanical strength decreases.

In addition, Li ₂ O and SiO ₂ were used as additives for the third component Li ₂ SiO _3.
It is conceivable to use _two mixed additives. But,
When this mixed additive of Li ₂ O and SiO ₂ is used, Li ₂ O
Is a very unstable substance, Li ₂ O is easily decomposed during firing, and is scattered and diffused into the atmosphere. It was confirmed that the partially ionized Li ⁺¹ ions migrated under high temperature voltage load, and the characteristics deteriorated. So, Li to Si
By adding the compound with O ₂ , a compound stable in the grain boundary can be provided without impairing the function of Li.

Therefore, it was confirmed that it was necessary to always add the third component in the form of Li ₂ SiO ₃ .

(Embodiment 5) In each of the above embodiments, the case where Pd was used as the internal electrode was described. However, for other Au, Pt, Rh, and Ni, the Sr / Ti ratio was 0.97, and the addition amount of the first component was Nb. ₂ O ₅ 0.5mol%, Ta ₂ O ₅ 0.5m
ol%, the added amount of the second component is MnO ₂ 1.0 mol%, SiO ₂ 1.0 mol
%, The addition amount of Li ₂ SiO ₃ of the third component is fixed at 0.5 mol%,
A multilayer ceramic capacitor with a varistor function was manufactured in the same manner as in the above embodiment. The results are shown in Table 27 below.

As described in Table 27 above, Au, P
It was confirmed that at least one kind of metal among t, Rh, Pd, and Ni, or an alloy or a mixture thereof can be used, and that an effect can be obtained. However, when using Ni
Since oxidation of Ni occurs at a relatively low temperature, oxidation is suppressed by mixing Pd or using SrTiO ₃ with a slight excess of Ti.

As described above, in the embodiments of the present invention, some combinations are shown, but it has been confirmed that similar effects can be obtained with other combinations.

In the embodiment of the present invention, TiO ₂ was added to SrTiO ₃ in producing SrTiO ₂ in excess of Ti. However, Ti may be used in the form of a carbonate, a hydroxide, an organic compound, or the like. Needless to say, the effect is obtained.

Further, in the examples of the present invention, SrTiO ₃ was used as the raw material powder.However, it is a matter of course that the same effect can be obtained even if SrTiO ₃ is prepared from SrO or SrCO ₃ and TiO ₂ as the raw material powder. It is.

Further, it goes without saying that the same effect can be obtained by using MnO ₂ and SiO ₂ as the second component in the form of these carbonates and hydroxides. However, it was confirmed that the use of MnCO _{3 provided a} finer particle size and was easier to decompose, so that a device with stable characteristics could be manufactured, which was suitable for mass production.

Next, in the above embodiment, the case where the baking is performed in a reducing atmosphere has been described, but this may be performed in a nitrogen atmosphere. However, when baking is performed in a nitrogen atmosphere, there is a surface where it is difficult to turn into a semiconductor.
(1450 ° C.) is preferable in terms of characteristics.

Further, in the above-described embodiment, the case where the calcination of the mixed powder is performed in the air has been described. However, it was confirmed that the same effect can be obtained by performing the calcination in the nitrogen atmosphere.

Further, in the above embodiment, the re-oxidation temperature was fixed at 1100 ° C.
It may be performed in a temperature range of 〜1250 ° C. But,
When performing reoxidation at 1200 ° C or higher, not only the grain boundaries but also the crystal grains may be insulated unless the holding time at the maximum temperature is minimized. Regarding the case where Ni is used, when reoxidizing at 1200 ° C. or higher, Ni may be oxidized unless the holding time is minimized.

In addition, although Ag was used as the external electrode in the above example, it was confirmed that similar effects could be obtained with other Pd, Ni, Cu, and Zn. That is, at least one of Pd, Ag, Ni, Cu, and Zn, or an alloy or a mixture thereof may be used as the external electrode. But Pd and Ag
Is difficult to make ohmic contact with the element and the varistor voltage has a slight polarity when used as an external electrode. In this case, however, there is no particular problem in basic performance.

As described above, the average particle size of the multilayer ceramic capacitor with a varistor function obtained by the method shown in the example is 2.0 to 3.0 μm.
It was about. Here, the calcining temperature of the molded body in air
When performed at a temperature higher than 1300 ° C., as described above, MnO ₂ —SiO ₂
-TiO ₂ -based liquid phase sintering progresses rapidly to promote grain growth,
The average particle size is about twice or more. When the average particle size is increased in this way, various problems such as a decrease in the sintered density, a decrease in the voltage nonlinearity index α, an increase in the series equivalent resistance value ESR, and a variation in electric characteristics occur. The electrical characteristics and reliability are remarkably reduced, and are not suitable for practical use.

Further, in the above embodiments, a multilayer ceramic capacitor with a varistor function has been described. The characteristics and varistor characteristics were confirmed to be obtained.

As described above, the device obtained in this way has a large capacity, a large voltage nonlinearity index α, a small varistor voltage, a small series equivalent resistance value ESR, and excellent temperature characteristics, frequency characteristics, and noise characteristics. , Usually acts as a capacitor to absorb low voltage noise and high frequency noise,
On the other hand, when a high voltage such as a pulse or static electricity enters, it exhibits a varistor function, exhibits excellent responsiveness to abnormal voltages such as noise, pulses, static electricity, etc., and their characteristics are always stable with temperature. Therefore, it is expected to replace conventional film capacitors, multilayer ceramic capacitors, and semiconductor ceramic capacitors. Furthermore, the multilayer ceramic capacitor with a varistor function of the present invention has a small size, a large capacity, and a high performance as compared with a conventional single-plate type ceramic capacitor with a varistor function, so that the application as a mounting component is greatly enhanced. It is expected.

Effect of the Invention As described above, according to the present invention, a ceramic capacitor with a varistor function having both a capacitor function and a varistor function can be obtained. The effect is that low-voltage noise acts as a capacitor to absorb high-frequency noise, and when a high voltage such as a pulse or static electricity enters, it functions as a varistor. It has a function of protecting semiconductors and electronic devices from abnormal voltages such as pulses, static electricity and the like. And those characteristics are always stable with respect to temperature. Therefore, as applications, conventional film capacitors, as bypass capacitors for protection of ICs and LSIs used in electronic equipment,
Replaces multilayer ceramic capacitors, semiconductor ceramic capacitors, etc.

Replaces ZnO-based varistors used to prevent damage to equipment and malfunction of equipment due to static electricity, and to absorb inductive load ON-OFF surges.

Application is expected, and the above-mentioned effects can be simultaneously exhibited by one element, and its application is large.

As described above, the reason that the multilayer ceramic capacitor with a varistor function can be easily manufactured in the present invention is that the ceramic capacitor material with a varistor function and the internal electrode material can be simultaneously fired. . Then, simultaneous why firing becomes possible, Ti in excess of SrTiO _2, MnO ₂ and SiO ₂ in addition to adding the semiconducting component
In the composition to which is added, it is possible to easily obtain a grain boundary insulating semiconductor ceramic capacitor only by re-oxidation without passing through the metal oxide surface diffusion step which has been performed so far. Has the greatest feature in the process in this respect.

In addition, the multilayer ceramic capacitor with a varistor function of the present invention is smaller, has a larger capacity, and has higher performance than conventional single-plate type ceramic capacitors with a varistor function. It can also be used as a high-density mounting element for video cameras, communication equipment, and the like.

Therefore, according to the present invention, it is possible to obtain an element that protects semiconductors and electric devices from abnormal voltages such as noise, pulses, and static electricity, and whose characteristics are always stable with respect to temperature. The effect is extremely large.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a ceramic capacitor having a varistor function for explaining an embodiment of the present invention, and is a diagram for explaining shapes of a laminated raw sheet and an internal electrode paste printed thereon. FIG. 2 is a partially cutaway sectional view showing a laminated ceramic capacitor with a varistor function obtained according to an embodiment of the present invention, and FIG. 3 is a process for manufacturing a laminated ceramic capacitor with a varistor function for explaining the embodiment of the present invention. FIG. 1 ... raw sheet, 2 ... internal electrode paste, 2a ... internal electrode, 3 ... end electrode, 4 ... multilayer ceramic capacitor with varistor function.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akihiro Takami 1006 Kadoma, Kazuma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Kimio Kobayashi 1006 Kadoma, Kazuma, Kadoma, Osaka Pref. Inside

Claims (7)

(57) [Claims] A ceramic is provided between electrodes. This ceramic is added to Nb ₂ O ₅ , Ta in SrTiO ₃ containing excess Ti so that the molar ratio of Sr and Ti is 0.95 ≦ Sr / Ti <1.00. ₂ O ₅ , V ₂ O ₅ , W ₂ O
₅ , at least one of Dy ₂ O ₃ , Nd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ is 0.05 to 2.0 mol%, and MnO ₂ and SiO ₂ are 0.2
And ~5.0mol%, ceramic capacitors formed by the Li ₂ SiO ₃ contained 0.05 to 2.0 mol%. 2. An Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂ , SrTiO ₃ containing excess Ti so that the molar ratio of Sr and Ti is 0.95 ≦ Sr / Ti <1.00.
O ₅ , W ₂ O ₅ , Dy ₂ O ₃ , Nd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ at least one or more of 0.05 to 2.0 mol%, MnO ₂ and SiO ₂ In a ceramic containing 0.2 to 5.0 mol% in total and 0.05 to 2.0 mol% of Li ₂ SiO ₃ , a plurality of layers of internal electrodes are provided so as to alternately reach the edges. A ceramic capacitor having external electrodes provided on both ends of the internal electrodes. 3. The ceramic capacitor according to claim 2, wherein the internal electrode is made of at least one of Au, Pt, Rh, Pd, and Ni, or an alloy or a mixture thereof. 4. The external electrode is made of at least one metal of Pd, Ag, Ni, Cu, Zn, or an alloy or mixture thereof.
The ceramic capacitor as described. 5. SrTiO ₃ containing excess Ti such that the molar ratio of Sr and Ti is 0.95 ≦ Sr / Ti <1.00, and Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂
O ₅ , W ₂ O ₅ , Dy ₂ O ₃ , Nd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ at least one or more of 0.05 to 2.0 mol%, MnO ₂ and SiO ₂ Of a composition containing 0.2 to 5.0 mol% in total and 0.05 to 2.0 mol% of Li ₂ SiO ₃ as a starting material, and pulverizing, mixing and drying the mixed powder, and then in air or A step of calcining in a nitrogen atmosphere, and after calcining, the powder ground again is dispersed in a solvent together with an organic binder into a raw sheet, and then, on this raw sheet, the internal electrode paste is alternately applied to opposite edges. A step of printing (but not printing on the raw sheet of the uppermost layer and the lowermost layer), and laminating, pressing, and pressing the printed raw sheet of the internal electrode paste to obtain a molded body, A step of calcining the molded body in the air, a step of calcining and then calcining in a reducing or nitrogen atmosphere, and a step of re-oxidizing in the air after the calcining After reoxidation, the manufacturing method of the ceramic capacitor and having an external electrode paste to both ends to expose the internal electrodes was applied baking process. 6. The method of manufacturing a ceramic capacitor according to claim 5, wherein the internal electrode is formed of at least one of Au, Pt, Rh, Pd, and Ni, or an alloy or a mixture thereof. Method. 7. The external electrode is made of at least one of Pd, Ag, Ni, Cu and Zn, or an alloy or mixture thereof.
The manufacturing method of the ceramic capacitor described in the above.