JP2725357B2 - 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 which exhibits semiconductor characteristics, protects semiconductors and electronic devices from abnormal voltages such as noise, pulses, and static electricity generated in the electronic devices, and furthermore, its characteristics are stable with respect to temperature and a method of manufacturing the same. .

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 grain boundary insulating semiconductor ceramic capacitor having a varistor function in a ceramic capacitor (hereinafter referred to as a varistor function-equipped ceramic capacitor) has been developed, and has already been disclosed in Japanese Patent Application Laid-Open Nos. Provided. 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, the ceramic capacitor with varistor function, usually coated with oxide on the surface of the SrTiO ₃ based semiconductor device, since a step of insulating the grain boundary layer by thermal diffusion, BaTiO ₃ based layered ceramic generally used 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 at the same time as the internal electrodes as compared with the capacitor.

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. Then, this part forms a porous layer in the sintering process, and after sintering, a method of injecting a conductive metal into the porous layer under an appropriate pressure, or forming an internal electrode by a plating method or a melting method, A method for forming a multilayer ceramic capacitor with a varistor function was developed.
Provided. However, these are quite difficult in terms of process and have 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. Further, Japanese Patent Application Laid-Open No. 63-219115 discloses that an oxidizing agent and a glass component for forming an insulating layer on a powder containing a semiconductor previously formed as a main component. There has been reported a method of firing a molded body in which a raw sheet containing a diffusing agent containing the same and internal electrodes are alternately laminated, in the air or in 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 element 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. Sr _(1-X) Ca _X TiO ₃ (These characteristics are stable at all times with respect to temperature, and the process enables simultaneous firing of ceramic capacitor material and internal electrode material. ₎ However, 0.001 ≦
X ≦ 0.2) and a method for manufacturing the same.

Means for Solving the Problems To solve the above problems, the present invention provides
_(1-X) Sr containing excess Ti so that the molar ratio of Ca _X and Ti is 0.95 ≦ Sr _(1-X) Ca _X /Ti<1.00, and 0.001 ≦ X ≦ 0.2
_(1-X) Ca _X TiO ₃ with Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂ O ₅ , W ₂ O ₅ , Dy ₂ O ₃ , Nd ₂ O ₅ ,
Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ at least one or more of 0.05 ~
And 2.0 mol%, and 0.2～5.0Mol% of MnO ₂ and SiO ₂ in a total amount, A
The l ₂ O ₃ is to provide a ceramic capacitor comprising moistened 0.1~1.5mol%. Further, the present invention provides Sr _(1-X) Ca _X
The molar ratio of Ti is contained excess Ti such that _{0.95 ≦ Sr (1-X)} Ca X /Ti<1.00 with a _{0.001 ≦ X ≦ 0.2 Sr (1} -X) Ca X
To _{TiO 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 to 2.0 mol% of at least one or more of the CeO ₂
And MnO ₂ and SiO ₂ in a total amount of 0.2 to 5.0 mol%, and Al ₂ O ₃ in 0.1.
A plurality of layers of internal electrodes are provided in a ceramic containing from 01 to 1.5 mol% so as to alternately reach the edges, and external electrodes are provided on both ends of the internal electrodes. To provide a ceramic capacitor. Further, the present invention, the molar ratio of Sr _(1-X) Ca _X and Ti is 0.95
Sr _(1-X) Ca _X TiO ₃ which contains an excessive amount of Ti such that ≦ Sr _(1-X) Ca _X /Ti<1.00, and Nb ₂ O ₅ , Ta
_{At least one of 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 is 0.05 to 2.0 mol% , and a 0.2～5.0Mol% of MnO ₂ and SiO ₂ in a total amount, and the mixed powder starting material of a composition comprising a Al ₂ O ₃ contained 0.01～1.5Mol%, grinding the mixed powders, mixed, dried And then calcining in air or nitrogen atmosphere, and after calcining, disperse the ground powder again in a solvent together with an organic binder to form a raw sheet, and then alternately apply the internal electrode paste on this raw sheet. Printing (but not printing on the uppermost and lowermost raw sheets) so as to reach the edge facing the above, and laminating, pressing and crimping the printed raw sheets of the internal electrode paste Obtaining a molded body, and then calcining the molded body in the air;
After calcination, a step of firing in a reducing or nitrogen atmosphere, a step of re-oxidizing in air after firing, and a step of applying and baking external electrode paste on both ends exposing the internal electrodes after re-oxidation. It is intended to provide a method for manufacturing a ceramic capacitor characterized by having the above. 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 external electrodes are Pd, A
It is provided that it is formed of at least one or more metals of g, Ni, Cu, and Zn or alloys or mixtures thereof.

Action Generally, in order to convert Sr _(1-X) Ca _X TiO ₃ into a semiconductor, it is necessary to forcibly reduce it, or to add a semiconducting accelerator and fire it in a reducing atmosphere. However, this alone may not make the progress of semiconducting depending on the type of semiconducting accelerator. Therefore, from the stoichiometry of Sr _(1-X) Ca _X TiO ₃ , Sr _(1-X) C
a _X excess (hereinafter referred to as excess A-site), or when the Ti-rich, increases lattice defects in the crystal, semiconductor is promoted. In addition, Ca enters the Sr site and has an effect of suppressing grain growth. Further, Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂ O ₅ , W ₂ O ₅ , Dy ₂ O ₃ , Nd ₂ O
Addition of ₃ , Y ₂ 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. Since Al ₂ O ₃ (hereinafter referred to as a third component) forms a solid solution in the crystal and lowers the resistance of the crystal by controlling the valence, the series equivalent resistance value ESR is reduced, and the voltage non-linear index α
Has the effect of improving. As mentioned above, Sr
It was thought that it was difficult to fabricate a TiO 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 a 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 Sr _(1-X) Ca _X TiO ₃ in excess of Ti, the material composition in which MnO ₂ and SiO ₂ are added,
After firing in a reducing atmosphere, a ceramic capacitor with a varistor function can be easily formed simply by re-oxidizing in air without applying the high-resistance metal oxide to the element surface as described above. Was found. This is MnO ₂ and SiO ₂ was added an excess of Ti sintering process, MnO ₂ -SiO ₂ -Ti at low temperatures
A sintering is promoted by forming an O ₂ -based liquid phase, and at the same time, it is dissolved and segregated in the grain boundary portion. Then, when this was reoxidized in air, MnO ₂ -SiO ₂ -TiO ₂ segregated at the grain boundary part
This is because the system becomes insulated and becomes a ceramic capacitor with a varistor function that easily has a grain boundary insulating structure. Furthermore, it has been found that an excessive amount of Ti can suppress oxidation and diffusion of the internal electrode. Accordingly, in the present invention, it was decided to use a Ti excess _{Sr (1-X) Ca X} TiO 3 these reasons.

_Second , MnO ₂ and SiO ₂ are added to Ti-excess Sr _(1-X) Ca _X TiO _3.
It has been found that, in the material composition to which is added, a semiconductor can be formed even in a crystal in a nitrogen atmosphere in addition to a reducing atmosphere. This is because the liquid phase is formed at a low temperature as described in the first reason, and the added Mn acts as an atomization control agent in addition to forming the liquid phase. It is considered that the sinterability is improved due to the effect of changing to +2 and +4 and being unstable electronically, and the semiconductor is easily formed into a semiconductor even in a nitrogen atmosphere.

Third, if the molded body after degreasing is calcined in the air in advance, the internal electrodes of the completed multilayer ceramic capacitor with a varistor function are cut, 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.

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

(Example 1) First, Sr having an average particle size of 0.5 μm or less and a purity of 98% or more.
TiO ₂ was added to _(1-X) Ca _X TiO ₃ raw material powder, and the powder having the adjusted Sr _(1-X) Ca _X / Ti ratio (hereinafter referred to as A / B ratio ₎ was added to the following Tables 1 to As shown in Table 15, the first component Nb ₂ O ₅ and the second component MnO
₂ , SiO ₂ (however, MnO ₂ and SiO _{2 to be} added are assumed to be equimol%) by variously changing the addition amount of Al ₂ O ₃ as the third component to 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.
m or less, and 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, Pd was placed on the raw sheet 1 obtained as described above.
The internal electrode paste 2 was screen-printed according to a predetermined size. In addition, as is clear from FIG.
Internal electrode paste 2 is applied to raw sheets 1 of the uppermost and lowermost layers.
Shall not be printed. At this time, the internal electrode paste 2 printed on the raw sheet 1 to be laminated in the middle is used.
Was printed so as to reach alternately facing edges as is well known. Thereafter, the raw sheet 1 was laminated in a plurality of layers while keeping the printed direction of the internal electrode paste 2 and pressed and pressed.
Next, degrease at 400 ° C in air, and then 600 ~
Calcination was performed at 1250 ° C. After that, 1250 ~
Fired at 1350 ° C. After firing, 900 ~ 1250 ℃ in air
And reoxidized.

Thereafter, 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 to form the inside of the grain boundary insulating semiconductor ceramic. Then, a multilayer ceramic capacitor 4 with a varistor function was obtained in which a plurality of layers of internal electrodes 2a were provided so as to alternately reach the ends, and external electrodes 3 were provided at both ends of the internal electrodes 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 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,
Firing in a reducing atmosphere of N ₂ : H ₂ = 99: 1 is performed at 1300 ° C for 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 / 1og (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 Varistor voltage temperature coefficient (ΔV / V) is the value between two points of 25 ° C and 50 ° C.

Next, Tables 1 to 15 will be described. These tables show that the A / B ratio of Sr _(1-X) Ca _X TiO ₃ and MnO _{2 of} the second component
And the amount of SiO ₂ added.

Here, the sample number is marked with * for comparison.
It is outside the scope of the present invention. That is, in these crystal elements, since the capacitance is small, the voltage non-linear index α representing the varistor characteristic is small, and the series equivalent resistance value ESR is large, it absorbs low-voltage noise and high-frequency noise as a capacitor. It does not have both the function and the function as a varistor to absorb high voltage such as pulse and static electricity. Furthermore, the capacitance temperature change rate and the varistor voltage temperature coefficient are large, and the reliability and electric characteristics are easily affected by temperature. Things. Therefore, these samples are not suitable as ceramic capacitors with a varistor function for protecting semiconductors and electronic devices from abnormal voltages such as noise, pulses, and static electricity generated in the electronic devices. 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, pulses, and static electricity generated in the electronic devices.

Here, in the present invention, the A / B ratio of Sr _(1-X) Ca _X TiO ₃ is defined because when the A / B ratio is larger than 1.00, the A site becomes excessive, and MnO ₂ -SiO ₂ -TiO _{2 This is because the two} -phase liquid phase is not easily formed, so that it is difficult to form a grain boundary insulating structure, and the internal electrodes are oxidized or diffused, and as a result, electrical characteristics and reliability are reduced. On the other hand, if the A / B ratio is less than 0.95, the crystal becomes porous and the sintering density decreases.
Further, the average particle size of the starting material for the ceramic capacitor with a multilayer varistor function was specified to be 0.5 μm or less.
If the particle size is larger than 0.5 μm, the powder is agglomerated when the slurry is formed, the sintered density of the resulting sintered body element is low, and it is difficult to convert the element into a semiconductor.

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 electrical characteristics and reliability of the multilayer ceramic capacitor with a varistor function obtained as a result of this process are almost determined. 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 rapid shrinkage occurs in the sintered body, and the resulting multilayer ceramic capacitor with a varistor function causes various problems such as delamination and cracking. Will be.

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.

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. And a varistor ceramic material having a varistor function, which is completely different in function and purpose of use.

Example 2 Next, the composition ratio of Sr and Ca corresponding to the A site of the perovskite structure represented by ABO ₃ was variously changed,
_(1-X) The A / B ratio of Ca _X TiO ₃ was fixed at 0.97, and the addition amount of Nb ₂ O ₅ as the first component was fixed at 1.0 mol%, and the varistor function lamination was performed in the same manner as in Example 1 above. A ceramic capacitor was manufactured. The results are shown in Table 16 below.

Explaining the above Table 16, when Ca is not added, there is nothing to suppress the crystal grain growth, the crystal grain size varies widely, and the tan δ and the temperature characteristics deteriorate.
On the other hand, when the added amount of Ca is increased and the value of X exceeds 0.2, oxidation is apt to proceed, the capacity is reduced, and the varistor characteristics are degraded. Therefore, the substitution rate X of Ca that partially substitutes for Sr at the A site is desirably 0.001 ≦ X ≦ 0.2.

(Example 3) Example 1, the total amount of MnO ₂ and SiO ₂ as the second component was found to be necessary 0.2~5.0mol%. Next, the addition ratio of MnO ₂ and SiO ₂ as the second component was variously changed, and the A / B ratio of Sr _(1-X) Ca _X TiO ₃ was changed.
0.97, X = 0.10, the addition amount of Nb ₂ O ₅ as the first component is 1.0 mol%, and the addition amount of Al ₂ O ₃ as the third component is 1.0 mol
%, And a multilayer ceramic capacitor with a varistor function was manufactured in the same manner as in Example 1 above. The results are shown in Table 17 below.

Explaining Table 17 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 in the grain boundary component, and when reoxidized, the MnO ₂ —SiO ₂ segregated in the grain boundary part 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 4) Next, Nb ₂ O ₅ as a first _{component, 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 , in order to regulate the addition amount of the atomization control agent of CeO ₂ , this was changed variously, the A / of Sr _(1-X) Ca _X TiO ₃ The B ratio is 0.97, X = 0.10, the addition amount of the second component is MnO ₂ 1.0 mol%,
The total amount of SiO ₂ 1.0 mol% was fixed at 2.0 mol%, and the addition amount of Al ₂ O ₃ as the third component was fixed at 1.0 mol%.
A multilayer ceramic capacitor with a varistor function was manufactured in the same manner as in the above. The results are shown in Tables 18 to 26 below.

Explaining the above Tables 18 to 26, the addition amount of the first component is specified because, as is clear from the measurement results, if the addition amount is less than 0.05 mol%, the addition result 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 mixture composition of the first component, the electric characteristics were measured with respect to a part of the combinations, and as shown in Table 26, the results showed that there was almost no difference in the characteristics from 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 5) Next, in order to regulate the addition amount of Al ₂ O ₃ as the third component, the amount was changed variously, and the A / B ratio of Sr _(1-X) Ca _X TiO ₃ was set to 0.9.
7, X = 0.10, the addition amount of the first component was Nb ₂ O ₅ 1.0 mol%,
The total amount of components added was 1.0 mol% of MnO _{2 and} 1.0 mol% of SiO ₂
1%, 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 Table 27 below.

With describes the Table 27, by adding _{Al 2 O 3, Al 2 O} 3 was dissolved in the crystal lowers the resistance of the crystal by the valence control, thereby improving the ESR and voltage nonlinearity index α . However, the added amount of Al ₂ O ₃ increases, and 1.5 mol
%, It precipitates at the grain boundaries, and the voltage non-linear index α and the temperature characteristics deteriorate. Therefore, the addition amount of Al ₂ O ₃ is suitably 0.01 to 1.5 mol%.

(Embodiment 6) 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, Sr _(1-X)
The A / B ratio of Ca _X TiO ₃ is 0.97, X = 0.10, the amount of the first component added
Nb ₂ O ₅ 0.5 mol%, Ta ₂ O ₅ 0.5 mol%, the amount of the second component added to MnO
₂ 1.0 mol%, fixed to 1.0 mol% SiO ₂ , and as the third component Al ₂ O
_With the addition amount of ₃ fixed at 1.0 mol%, a multilayer ceramic capacitor with a varistor function was produced in the same manner as in the above example. The results are shown in Table 28 below.

As described in Table 28 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 the oxidation of Ni takes place at a relatively low temperature, or mixing Pd, preferable to use the Ti excess of _{Sr (1-X) Ca X} TiO 3 slightly suppressed oxidation.

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, Ti excess Sr _(1-X) Ca _X TiO ₃
TiO ₂ was added to Sr _(1-X) Ca _X TiO ₃ in the production of Ti, but it goes without saying that the same effect can be obtained by using Ti in the form of carbonate, hydroxide, organic compound, etc. No. In the embodiment of the present invention, it was used _{Sr (1-X) Ca X} TiO 3 in the raw material _{powder, SrO, SrCO 3, CaCO 3} , CaO, titanates, and the like TiO ₂ Sr _{(1-X It} goes without saying that the same effect can be obtained even if Ca _X TiO ₃ is prepared as a raw material powder.

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 MnCo ₃ was more suitable for mass production because MnCo ₃ had a finer particle size and was easier to decompose, so that a device with stable characteristics could be manufactured.

Similar effects can be obtained by using nitrate or carbonate for the third component Al ₂ O ₃ .

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,
If reoxidation is performed at 1200 ° C. or more, care must be taken because not only the grain boundaries but also the crystal grains may be insulated unless the holding time at the maximum temperature is minimized. Also, in the case where Ni is used as the internal electrode, when reoxidizing at 1200 ° C. or higher, Ni may be oxidized unless the holding time is kept as short as possible.

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 manner, various problems such as a decrease in the sintering density, a decrease in the voltage nonlinearity index α, an increase in the series equivalent resistance value ESR, and variations 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 and static electricity, and its 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. As a function, the capacitor normally acts to absorb low-voltage noise and 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 an application, conventional film capacitors, as bypass capacitors for protection of ICs and LSIs used in electrical 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 _3, MnO ₂ and SiO ₂ in addition to adding the semiconducting component
In the composition to which is added, it is possible to easily form a grain boundary insulated semiconductor ceramic capacitor simply by re-oxidation without going through the metal oxide surface diffusion step which has been performed so far. The invention has the greatest feature in terms of 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 which protects semiconductors and electric equipment from abnormal voltages such as noise, pulses, static electricity and the like, and whose characteristics are stable with respect to temperature. 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 multilayer ceramic capacitor with a varistor function obtained according to an embodiment of the present invention, and FIG. 3 is a view showing a manufacturing process of the multilayer 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 ... external electrode, 4 ... multilayer ceramic capacitor with varistor function.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-56-74913 (JP, A) JP-A-62-282411 (JP, A) JP-A-59-215701 (JP, A) 25999 (JP, B1)

Claims (7)

(57) [Claims] A ceramic is provided between electrodes, and the ceramic has a molar ratio of Sr _(1-X) Ca _X to Ti of 0.95 ≦ Sr _(1-X) Ca _X / Ti
<1.00 containing an excess of Ti so as to be <1.00.
Sr _(1-X) Ca _X TiO ₃ with 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 is 0.05 to 2.0 mol%, and MnO ₂ and SiO ₂ are 0.2 to 5.0 mol in total amount.
A ceramic capacitor containing l% and 0.01 to 1.5 mol% of Al ₂ O ₃ . 2. The method according to claim 1, wherein the molar ratio of Sr _(1-X) Ca _X to Ti is 0.95 ≦ Sr _(1-X) C
a Excess Ti is contained so that _X / Ti <1.00, and 0.001 ≦ X
Sr _(1-X) Ca _X TiO ₃ ≤ 0.2, Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂ O ₅ , W
_{At least one of 2} O ₅ , Dy ₂ O ₃ , Nd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , and CeO ₂ is 0.05 to 2.0 mol%, and MnO ₂ and SiO ₂ are in total amount. 0.
In a ceramic containing _{2 to} 5.0 mol% and 0.01 to 1.5 mol% of Al ₂ O ₃ , a plurality of layers of internal electrodes are provided so as to alternately reach the edges facing each other. A ceramic capacitor having external electrodes provided at both ends. 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. The method according to claim 1, wherein the molar ratio of Sr _(1-X) Ca _X to Ti is 0.95 ≦ Sr _(1-X) C
a Excess Ti is contained so that _X / Ti <1.00, and 0.001 ≦ X
Sr _(1-X) Ca _X TiO ₃ ≤ 0.2, Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂ O ₅ , W
_{At least one of 2} O ₅ , Dy ₂ O ₃ , Nd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , and CeO ₂ is 0.05 to 2.0 mol%, and MnO ₂ and SiO ₂ are in total amount. 0.
And 2～5.0Mol%, the mixed powder as a starting material composition obtained by the Al ₂ O ₃ contained 0.01～1.5Mol%, grinding the mixed powder,
After mixing and drying, a step of calcining in air or a nitrogen atmosphere, and after calcining, dispersing the powder ground again in a solvent together with an organic binder into a raw sheet, and then, on this raw sheet, an internal electrode A step of printing the paste so as to alternately reach the opposing edges (but not printing on the raw sheet of the uppermost layer and the lowermost layer), and laminating, pressing, Crimped to obtain a molded body,
Thereafter, a step of calcining the molded body in the air, and after calcining,
The method has a step of firing in a reducing or nitrogen atmosphere, a step of re-oxidizing in air after firing, and a step of applying and firing an external electrode paste on both ends of the internal electrode exposed after re-oxidation. Method for manufacturing a ceramic capacitor. 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.