JP2707707B2 - Grain boundary insulating semiconductor 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. To protect semiconductors and electronic equipment from abnormal voltages such as noise, pulses, and static electricity generated in electronic equipment, and furthermore, a grain boundary insulated semiconductor ceramic capacitor whose characteristics are stable with respect to temperature. The present invention relates to the manufacturing method.

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, resulting in a problem that the volume 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 ceramic capacitor with varistor function is 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 multilayer ceramic capacitors that are commonly 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 sintering process, and after sintering, a conductive metal is injected into the porous layer under an appropriate pressure, or an internal electrode is formed by plating or melting to form a varistor. A method for forming a multilayer ceramic capacitor with a function has been developed and 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, 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. In addition, these characteristics are always stable with temperature, and in terms of process, the grain boundary insulation type containing SrTiO ₃ as a main component enables simultaneous firing of ceramic capacitor material and internal electrode material. It is an object of the present invention to provide a semiconductor ceramic capacitor and a method for manufacturing the same.

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 , and CeO ₂ at least one of 0.05 to 2.0 mol%, and Mn and Si as MnO ₂ and SiO ₂ , respectively.
0.2 to 5.0 mol% in total, and NaAlO ₂ in 0.05 to
An object of the present invention is to provide a grain boundary insulating semiconductor ceramic capacitor containing 4.0 mol%. In addition, the present invention relates to
Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂ O ₅ , W ₂ O ₅ , and Dy are added to SrTiO ₂ containing excess Ti so that the molar ratio of is 0.95 ≦ Sr / Ti <1.00.
_At least one of 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 Mn and Si are replaced by MnO ₂ and Si, respectively.
And 0.2～5.0Mol% in a total amount in terms of O _2, the NaAlO ₂ 0.05
A plurality of layers of internal electrodes are provided in a grain boundary insulated semiconductor ceramic containing up to 4.0 mol% so as to reach alternately opposed edges, and external electrodes are provided on both ends of the internal electrodes. It is another object of the present invention to provide a laminated type grain boundary insulated semiconductor ceramic capacitor. Further, the present invention relates to SrTiO ₃ containing excess Ti such that the molar ratio of Sr and Ti satisfies 0.95 ≦ Sr / Ti <1.00, and Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂ O ₅ ,
At least one of W 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 Mn and Si are each
And 0.2～5.0Mol% in a total amount in terms of MnO ₂ and SiO _2, NaAlO
Starting from a mixed powder of a composition containing 0.05 to 4.0 mol% of ₂ and pulverizing, mixing and impressing the mixed powder,
Calcining in air or nitrogen atmosphere, and after calcining,
The crushed powder is dispersed in a solvent together with an organic binder in a solvent to form a raw sheet, and then the internal electrode paste is printed on the raw sheet so as to alternately reach opposite edges (provided that the uppermost layer and the lowermost layer have different shapes). A step of laminating, pressing, and pressing a printed green sheet of the internal electrode paste to obtain a molded body, and then calcining the molded body in the air; After that, 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 of manufacturing a multilayer grain boundary insulating semiconductor ceramic capacitor characterized by the following. And the internal electrode is A
It is provided that it is formed of at least one or more metals among u, Pt, Rh, Pd, and Ni or alloys or mixtures thereof. Further, the external electrodes are Pd, Ag, N
It is provided that it is formed of at least one kind of metal among i, Cu, and Zn or an alloy or a mixture thereof.

In general, in order to convert SrTiO ₃ into a semiconductor, it is necessary to forcibly reduce it, or to add a semiconductor-promoting 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, 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. Furthermore, Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂ O ₅ , W ₂ O ₅ , Dy ₂ O ₃ , Nd ₂
Addition of O 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 (the second component to be obtained) are indispensable substances for forming a laminated structure in the firing process, and even if one of them is lacking, 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 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 SrTiO ₃ in excess of Ti, in the material composition to which the second component is added, after firing in a reducing atmosphere, the surface of the element with the above-described high resistance Even without applying metal oxide, just re-oxidize in the air,
It has been found that a ceramic capacitor with a varistor function is easily formed. This is due to the second Ti added with excess Ti.
During the sintering process, the components form a MnO ₂ —SiO ₂ —TiO ₂ system liquid phase at a low temperature to promote sintering and, at the same time, dissolve and segregate at the grain boundary. 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, it has been found that an excessive amount of Ti can suppress oxidation and diffusion of the internal electrode. Therefore, in the present invention, SrTiO ₃ in excess of Ti is used for these reasons.

Second, it has been found that a material composition in which the second component is added to SrTiO ₃ in excess of Ti can be converted into a semiconductor by sintering in a nitrogen atmosphere as well as in 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, Na atoms in NaAlO ₂ (hereinafter, referred to as a third component) act as a carrier for uniformly diffusing the MnO ₂ —SiO ₂ —TiO ₂ system liquid phase into the grain boundary portion, and the semiconductor crystal and the high-performance semiconductor crystal are mixed with each other. The boundary of the resistance grain boundary is sharply formed, and as a result, the temperature characteristics of the capacitance and the varistor voltage are improved. Further, Al atoms in the third component form a solid solution in the crystal to lower the resistance of the crystal grains, thereby improving the voltage non-linear index α and lowering the series equivalent resistance value ESR.

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.
₃₎ TiO ₂ was added to the raw material powder, and the powder having the adjusted Sr / Ti ratio was added to the first component Nb ₂ O ₅ and the second component as shown in Tables 1 to 15 below.
Component MnO ₂ , SiO ₂ (However, added MnO ₂ , SiO ₂ is equimol%
) Was varied, and the amount of NaAlO ₂ added as the third component was fixed at 1.0 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 to be 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.

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 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,
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.

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

◇ Varistor voltage V _0.1mA is the value at measurement 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 by the equation α = 1 / log (V _{1.0 mA} / V _{0.1 mA} ).

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

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

◇ The 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 define the Sr / Ti ratio and the addition amounts of the second components MnO ₂ and SiO ₂ .

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 affect the temperature. It is easy to receive. 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 capacitance temperature change rate and a small varistor voltage temperature coefficient, and has a characteristic that its 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 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 total addition amount of MnO ₂ and SiO ₂ of the second component is specified because the addition effect of MnO ₂ -SiO _2-is not obtained if the addition amount of these second components is less than 0.2 mol%. 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 rapid shrinkage occurs in the sintered body, and in the resulting multilayer ceramic capacitor with varistor function, problems such as delamination and cracking occur. 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 reacts with Ni, and the diffusion of Ni proceeds. In the obtained 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 -Ti
The liquid phase sintering of the O ₂ system proceeds rapidly, and the grain growth is promoted, and the density of the sintered body and the packing density decrease remarkably.

Thereafter, when firing is performed in a reducing or nitrogen atmosphere, the semiconductor is less likely to be formed.

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

Further, by adding NaAlO ₂ as the third component, the rate of change in capacitance with temperature and the temperature coefficient of varistor voltage are improved. In other words, Na atoms in the added NaAlO ₂ act as carriers for uniformly diffusing the liquid phase of the MnO ₂ -SiO ₂ -TiO ₂ system into the grain boundaries, and the boundary between the semiconductor crystal and the high-resistance grain boundaries is formed. This is due to the sharp formation. Furthermore, by adding NaAlO ₂ , the voltage non-linear index α is improved, and the series equivalent resistance value ES
R decreases. This is of NaAlO in ₂ added Al:
This is because atoms dissolve in the crystal and lower the resistance of the crystal particles.

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. This is a laminate of ceramic capacitor materials with a varistor function having the following characteristics, and is completely different in terms of its 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 NaAlO ₂ as a component
Was fixed at 1.0 mol%, and a multilayer ceramic capacitor having 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, dissolved at the grain boundary, segregated, and reoxidized, MnO ₂ -SiO ₂ segregated at the grain boundary is formed. This is because the element is insulated and 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 as a first component,
In order to regulate the addition amount of the atomization controlling agent for Dy ₂ O ₃ , Nd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , and CeO ₂ , these were variously changed, and the Sr / Ti ratio was changed to 0.9.
7. The addition amount of the second component is MnO ₂ , 1.0 mol%, SiO ₂ , 1.0 mol%
2.0 mol% of the total amount of NaAlO ₂ as the third component is 1.0 m
ol%, and a multilayer ceramic capacitor with a varistor function was produced 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.

The addition of Nb ₂ O ₅ and Ta ₂ O ₅ as the first component is better for the other V ₂ O ₅ , W ₂ O ₅ , Dy ₂ O ₃ , Nd ₂ O ₃ , Y ₂ O ₃ and La ₂ O ₃ . ₂ O ₃ , CeO
_It was slightly better in electrical properties than in the case of adding ₂ .

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, the amount of NaAlO ₂ as the third component was changed variously in order to regulate the addition amount, the Sr / Ti ratio was 0.97, the addition amount of the first component was Nb ₂ O ₅ 0.5 mol%, ₂ O ₅ 0.5mol%, add 2nd component
MnO ₂ was fixed at 1.0 mol% and SiO _{2 was at} 1.0 mol%, and a multilayer ceramic capacitor having 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 in Table 26 above, as a first feature, it can be understood that the capacity temperature change rate and the varistor voltage temperature coefficient are improved by adding NaAlO ₂ as the third component. This is because Na atoms in the added NaAlO ₂ are MnO ₂ -SiO ₂ -Ti
This is because it acts as a carrier for uniformly diffusing the O 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.

Also, as a second feature, the addition of NaAlO ₂ improves the voltage non-linear index α and increases the series equivalent resistance value ES.
R decreases. This is because the Al atoms in the added NaAlO _{2 form a} solid solution in the crystal and lower the resistance of the crystal particles. Here, the reason why the addition amount of NaAlO ₂ as the third component is specified is that if the addition amount of the third component is less than 0.05, the addition effect cannot be obtained, and the capacity temperature change rate and the varistor voltage temperature coefficient are not improved. This is because the voltage non-linear index α does not improve and the series equivalent resistance ESR does not further decrease. On the other hand, if the addition amount of the third component exceeds 2.0 mol%, the amount exceeds the solid solution limit in the crystal, so that extra NaAlO ₂ precipitates at the grain boundary part and lowers the resistance of the grain boundary, resulting in the capacity and voltage. This is because the non-linear index α suddenly decreases, the series equivalent resistance value ESR increases, the firing density further decreases, and the mechanical strength decreases.

In addition, Na ₂ O and Al ₂ O ₃ were used as additives of the third component, NaAlO _2.
It is conceivable to use a mixed additive of. However, when this mixed additive of NaO and Al ₂ O ₃ is used, since Na ₂ O is a very unstable substance, Na ₂ O is easily decomposed during firing and becomes Almost no Na atoms are present in the sintered element created due to scattering and diffusion, and partially ionized Na ⁺¹ ions move under high temperature voltage load.
It was confirmed that characteristic deterioration occurred. Therefore, Na is converted to NaAlO ₂
By adding in the form of, it is possible to provide a stable substance in the grain boundary without impairing the function of Na.

Therefore, it was confirmed that NaAlO ₂ was always required as the third component.

(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
% And the addition amount of NaAlO ₂ as the third component were fixed at 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 result is the following 27th
It is described in the table.

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.

Then, when in the embodiment of the present invention to produce a SrTiO ₃ of Ti-rich, the SrTiO ₃ was added TiO _2, carbonates and Ti, hydroxides, may be used in the form of organic compounds, 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,
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 thus obtained 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. These characteristics are always stable with respect to temperature. Therefore, as an application, it replaces conventional film capacitors, multilayer ceramic capacitors, semiconductor ceramic capacitors and the like as bypass capacitors for protection of ICs and LSIs used in electronic devices.

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 electronic 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 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.

Continued on the front page (72) Inventor Kaori Okamoto 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd.

Claims (7)

(57) [Claims] 1. An SrTiO ₃ containing excess Ti so that the molar ratio of Sr and Ti is 0.95 ≦ Sr / Ti <1.00, 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, and 0.05 to 2.0 mol% of at least one or more of the CeO _2, Mn and Si Is converted to MnO ₂ and SiO ₂ respectively, and the total amount is 0.2 to 5.0 mol%
And a grain boundary insulated semiconductor ceramic capacitor containing 0.05 to 4.0 mol% of NaAlO ₂ . 2. An SrTiO ₃ containing excess Ti such that the molar ratio of Sr to 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, and 0.05 to 2.0 mol% of at least one or more of the CeO _2, Mn and Si Is converted to MnO ₂ and SiO ₂ respectively, and the total amount is 0.2 to 5.0 mol%
And a plurality of layers of internal electrodes are provided in a grain boundary insulating semiconductor ceramic containing NaAlO _{2 in an amount} of 0.05 to 4.0 mol% so as to reach alternately opposed edges, and both end edges of the internal electrodes. A multilayer grain boundary insulating semiconductor ceramic capacitor characterized by having external electrodes provided thereon. 3. The multilayer grain boundary according to claim 2, wherein the internal electrode is formed of at least one or more of Au, Pt, Rh, Pd, and Ni, or an alloy or a mixture thereof. Insulated semiconductor ceramic capacitor. 4. The external electrode is made of at least one metal of Pd, Ag, Ni, Cu, Zn, or an alloy or mixture thereof.
A multilayer grain boundary insulating semiconductor ceramic capacitor as described in the above. 5. An 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, and 0.05 to 2.0 mol% of at least one or more of the CeO _2, Mn and Si Is converted to MnO ₂ and SiO ₂ respectively, and the total amount is 0.2 to 5.0 mol%
A mixed powder of a composition containing 0.05 to 4.0 mol% of NaAlO ₂ as a starting material, pulverizing, mixing and drying the mixed powder, and then calcining in air or a nitrogen atmosphere;
After the calcination, the re-ground powder 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 opposite edges (however, the uppermost layer and A step of printing without printing on the lowermost green sheet), laminating, pressing and pressing the green sheet on which the internal electrode paste is printed to obtain a molded body, and then calcining the molded body in the air Process, calcining, firing in a reducing or nitrogen atmosphere, firing, re-oxidizing in air, and after re-oxidizing, applying and baking external electrode paste on both ends exposing the internal electrodes. And a method for manufacturing a multilayer grain boundary insulating semiconductor ceramic capacitor. 6. The multilayer grain boundary according to claim 5, wherein 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. A method for manufacturing an insulated semiconductor ceramic capacitor. 7. The external electrode is made of at least one of Pd, Ag, Ni, Cu and Zn, or an alloy or mixture thereof.
A method for manufacturing the multilayer grain boundary insulated semiconductor ceramic capacitor according to the above.