Ceramic electronic device

A ceramic electronic device includes a multilayer structure in which each of a plurality of dielectric layers and each of a plurality of internal electrode layers are alternately stacked. A relationship of “IA/IB>0.30” is satisfied and a peak current value IB is 100 pA/mm2 or less in a TSDC in which a polarizing temperature is 150 degrees C., a polarizing electric field is 15 V/μm to 20 V/μm, a polarizing time is 60 minutes, and an increasing speed of temperature is 10° C./minute, when a peak current of a low temperature side of a temperature range of 160 degrees C. or more and less than 230 degrees C. is IA and a peak current of a high temperature side of a temperature range of 230 degrees C. or more and 350 degrees C. or less is IB.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2020-111709, filed on Jun. 29, 2020 and the prior Japanese Patent Application No. 2021-064015, filed on Apr. 5, 2021, the entire contents of which are incorporated herein by reference.

FIELD

A certain aspect of the present invention relates to a ceramic electronic device.

BACKGROUND

There is a report in which an insulation degradation occurs when oxygen vacancies in a dielectric layer are accumulated in a cathode because of electric field and an electrical resistance in an interface between the cathode and the dielectric layer is reduced in a ceramic electronic device such as a multilayer ceramic capacitor, and a time until the accumulation determines a lifetime of the ceramic electronic device (for example, see “dc-Electrical Degradation of the BT-Based Material for Multilayer Ceramic Capacitor with Ni internal Electrode: Impedance Analysis and Microstructure, Jpn J Appl Phys, 40(2001) pp. 5624-5629”).

There is disclosed a technology in which reliability such as the lifetime or resistance to voltage can be improved by reducing an amount of the oxygen vacancies (for example, see Japanese Patent Application Publication No. 2004-356305 hereinafter referred to as Document 1 and Japanese Patent Application Publication No. 2014-165447 hereinafter referred to as Document 2). In Document 1 and Document 2, a concentration of the oxygen vacancies is quantified with use of a TSDC (Thermally Stimulated Depolarization Currents).

SUMMARY OF THE INVENTION

In Document 1 and Document 2, the amount of the oxygen vacancies is estimated from an integral value of a current of the TSDC data. However, it is a part of the oxygen vacancies moving to the cathode over a crystal grain boundary of the dielectric layer that largely influences on the lifetime of the ceramic electronic device. Neither Document 1 nor Document 2 discloses the fact.

According to an aspect of the present invention, there is provided a ceramic electronic device including: a multilayer structure in which each of a plurality of dielectric layers and each of a plurality of internal electrode layers are alternately stacked, a main component of the plurality of dielectric layers being a ceramic, wherein a relationship of “IA/IB>0.30” is satisfied and a peak current value IBis 100 pA/mm2or less in a TSDC in which a polarizing temperature is 150 degrees C., a polarizing electric field is 15 V/μm to 20 V/μm, a polarizing time is 60 minutes, and an increasing speed of temperature is 10° C./minute, when a peak current of a low temperature side of a temperature range of 160 degrees C. or more and less than 230 degrees C. is IAand a peak current of a high temperature side of a temperature range of 230 degrees C. or more and 350 degrees C. or less is IB.

According to another aspect of the present invention, there is provided a ceramic electronic device including: a multilayer structure in which each of a plurality of dielectric layers and each of a plurality of internal electrode layers are alternately stacked, a main component of the plurality of dielectric layers being a ceramic, wherein a relationship of “(J170−J150)/J150≥0” is satisfied in a TSDC in which a polarizing time is 60 minutes, a polarizing electric field is 10 V/μm, a polarizing temperature is 150 degrees C. or 170 degrees C., the plurality of dielectric layers are polarized, an increasing speed of temperature is 10° C./minute after cooling to 130 degrees C., when a peak current value of a polarization at 150 degrees C. among peak currents in a case of a temperature rise to 350 degrees C. is J150 and a peak current value of a polarization at 170 degrees C. among the peak currents is J170.

DETAILED DESCRIPTION

A description will be given of an embodiment with reference to the accompanying drawings.

(First embodiment) A description will be given of an outline of a multilayer ceramic capacitor.FIG.1illustrates a perspective view of a multilayer ceramic capacitor100in accordance with an embodiment, in which a cross section of a part of the multilayer ceramic capacitor100is illustrated. As illustrated inFIG.1, the multilayer ceramic capacitor100includes a multilayer chip10having a rectangular parallelepiped shape, and a pair of external electrodes20aand20bthat are respectively provided at two end faces of the multilayer chip10facing each other. In four faces other than the two end faces of the multilayer chip10, two faces other than an upper face and a lower face of the multilayer chip10in a stacking direction are referred to as side faces. The external electrodes20aand20bextend to the upper face, the lower face and the two side faces of the multilayer chip10. However, the external electrodes20aand20bare spaced from each other.

The multilayer chip10has a structure designed to have dielectric layers11and internal electrode layers12alternately stacked. The dielectric layer11includes ceramic material acting as a dielectric material. The internal electrode layers12include a base metal material. End edges of the internal electrode layers12are alternately exposed to a first end face of the multilayer chip10and a second end face of the multilayer chip10that is different from the first end face. In the embodiment, the first end face faces the second end face. The external electrode20ais provided on the first end face. The external electrode20bis provided on the second end face. Thus, the internal electrode layers12are alternately conducted to the external electrode20aand the external electrode20b. Thus, the multilayer ceramic capacitor100has a structure in which a plurality of dielectric layers11are stacked and each two of the dielectric layers11sandwich the internal electrode layer12. In the multilayer chip10, the internal electrode layer12is positioned at an outermost layer. The upper face and the lower face of the multilayer chip10that are the internal electrode layers12are covered by cover layers13. A main component of the cover layer13is a ceramic material. For example, a main component of the cover layer13is the same as that of the dielectric layer11.

For example, the multilayer ceramic capacitor100may have a length of 0.25 mm, a width of 0.125 mm and a height of 0.125 mm. The multilayer ceramic capacitor100may have a length of 0.4 mm, a width of 0.2 mm and a height of 0.2 mm. The multilayer ceramic capacitor100may have a length of 0.6 mm, a width of 0.3 mm and a height of 0.3 mm. The multilayer ceramic capacitor100may have a length of 1.0 mm, a width of 0.5 mm and a height of 0.5 mm. The multilayer ceramic capacitor100may have a length of 3.2 mm, a width of 1.6 mm and a height of 1.6 mm. The multilayer ceramic capacitor100may have a length of 4.5 mm, a width of 3.2 mm and a height of 2.5 mm. However, the size of the multilayer ceramic capacitor100is not limited.

A main component of the internal electrode layers12is a base metal such as nickel (Ni), copper (Cu), tin (Sn) or the like. The internal electrode layers12may be made of a noble metal such as platinum (Pt), palladium (Pd), silver (Ag), gold (Au) or alloy thereof.

The dielectric layers11are mainly composed of a ceramic material that is expressed by a general formula ABO3and has a perovskite structure. The perovskite structure includes ABO3-a, having an off-stoichiometric composition. For example, the ceramic material is such as BaTiO3(barium titanate), CaZrO3(calcium zirconate), CaTiO3(calcium titanate), SrTiO3(strontium titanate), Ba1-x-yCaxSryTi1-zZrzO3(0≤x≤1, 0≤y≤1, 0≤z≤1) having a perovskite structure. For example, the dielectric layers11are formed by firing ceramic raw material powder of which a main component is a ceramic material having a perovskite structure.

In the multilayer ceramic capacitor100, the insulation degradation occurs, when the oxygen vacancies in the dielectric layer11are accumulated in an interface between the internal electrode layer12and the dielectric layer11because of the electrical field of the internal electrode layer12acting as a cathode and reduces the electrical resistance in the interface. There is a report that a time until the accumulation determines the lifetime. The report is accepted widely. It is known that the reliability such as the lifetime or resistance to voltage can be improved when the amount of the oxygen vacancies is reduced in accordance with the model. For example, it is possible to estimate a movement amount of the oxygen vacancies by TSDC (Thermal Stimulation Depolarization Current).

For example,FIG.2AtoFIG.2Eillustrate a method for estimating the movement amount of the oxygen vacancy with use of the TSDC.FIG.2Aillustrates a cross sectional view of the dielectric layer11sandwiched by the internal electrode layer12connected to one of the external electrodes and the internal electrode layer12connected to the other of the external electrodes. As illustrated inFIG.2A, oxygen vacancies14exist in the dielectric layers11. For example, the oxygen vacancies14are evenly distributed in the dielectric layers11.

FIG.2Bpartially illustrates the multilayer ceramic capacitor100in which a direct current voltage is applied to a part between the two internal electrode layers12next to each other and the part is heated. The oxygen vacancies14distributed evenly in the dielectric layer11are unevenly distributed on the side of one of the internal electrode layers12(minus electrode side inFIG.2B), when the unloaded multilayer ceramic capacitor100is heated and the direct current voltage is applied between the two internal electrode layers12next to each other. In this case, the temperature is, for example, 200 degrees C. The electric field strength applied to the dielectric layer11is, for example, 10 V/μm.

FIG.2Cillustrates a case where the condition of the multilayer ceramic capacitor100under a high temperature load is returned to the unloaded condition at a room temperature (25 degrees C.). Even if the voltage is canceled after the temperature is returned to the room temperature (25 degrees C.), the oxygen vacancies14are still unevenly distributed on the side of the one (the minus electrode side).

When the multilayer ceramic capacitor100is equipped with a current meter and the multilayer ceramic capacitor100is re-heated, the oxygen vacancies14unevenly distributed on the side of the one of the internal electrode layers12(the minus electrode side) in the dielectric layer11gradually moves toward the other of the internal electrode layers12, as illustrated inFIG.2D. The oxygen vacancies14act as carriers. Thus, a current flows. The current is called a thermally stimulated current. The temperature after the re-heating is approximately 300 degrees C. As illustrated inFIG.2E, the thermally stimulated current occurs until the polarization caused by the oxygen vacancies14is canceled. Therefore, a time-integration of the current until the polarization is canceled is a total amount Q of the carrier charge in the dielectric layer11.

The measured charge Q is divided by a charge per one oxygen vacancy14and the volume of the dielectric layer11. Thus, the oxygen vacancy concentration in the multilayer ceramic capacitor100is calculated. The charge per one oxygen vacancy is 2×1.6×10−19coulombs. An absolute value of the charge is expressed by Vo′ as a minus fixed charge. Therefore, an absolute value of the charge is twice as elementary electrical charge. In this manner, it is possible to estimate the amount of the oxygen vacancy from the integral of the current value.

A description will be given of a moving of the oxygen vacancy during occurring of the thermal stimulation current.FIG.3Aillustrates the moving of the oxygen vacancy. As illustrated inFIG.3A, the dielectric layer11includes a plurality of crystal grains15. A crystal grain boundary16is formed between two of the crystal grains15. As illustrated in an upper part ofFIG.3A, the oxygen vacancy14moves in the crystal grain15. As illustrated in a middle part ofFIG.3A, the oxygen vacancy14crosses over the crystal grain boundary16. The oxygen vacancy14crossing over the crystal grain boundary16of the dielectric layer11largely influences on the lifetime of the multilayer ceramic capacitor100.

FIG.3Billustrates a relationship between a temperature and the thermal stimulation current in a TSDC in a case where a polarizing temperature is 150 degrees C., an electric field is 15 V/μm to 20 V/μm, a polarizing time is 60 min, an increasing speed of temperature is 10 is 10 C°/min, and a temperature is increased to 350 degrees C. As illustrated inFIG.3B, a plurality of current peaks appear in the TSDC data. Two typical main peaks coarsely appear at a temperature of 160 degrees C. or more. One of the peaks is a low temperature side peak (peak A) of a temperature range of 160 degrees C. or more and less than 230 degrees C. and a high temperature side peak (peak B) of a temperature range of 230 degrees C. or more and 350 degrees C. or less. In the method ofFIG.2AtoFIG.2E, the amount of the oxygen vacancy is estimated from an integrated value of the current peaks. The polarizing temperature is a temperature at which the dielectric layers11are polarized. The electric field of the polarizing is intensity of the electric field needed for polarizing the dielectric layers11. The polarizing time is a time for polarizing the dielectric layers11. The peaks are local maximum values in a case where the current value is expressed in a graph.

InFIG.3B, a difference between the solid line and the dotted line appears because of the oxygen vacancies in the dielectric layers11. The peak A of low temperature side in the temperature range of 160 degrees C. or more and less than 230 degrees C. and the peak B of high temperature side in the temperature range of 230 degrees C. or more and 350 degrees C. or less appear in the solid line and the dotted line. And two or more of the TSDC peaks appear in the temperature range of 130 degrees C. or more and 350 degrees C. or less. Three or more of the TSDC peaks may appear in the temperature range.

Only the integrated value does not associate actual reliability of the multilayer ceramic capacitor100with the TSDC data. This is because the oxygen vacancy14crossing over the crystal grain boundary16in the dielectric layer11largely influences on the reliability of the multilayer ceramic capacitor100, as mentioned above. The current of the peak B indicates the moving of the oxygen vacancy14crossing over the crystal grain boundary16. On the other hand, the current of the peak A indicates the oxygen vacancy which moves in the crystal grain15but does not cross over the crystal grain boundary16. The influence of the peak A on the lifetime of the multilayer ceramic capacitor100is smaller than the influence of the peak B on the lifetime. Therefore, it is favorable that the peak B is small, from a viewpoint of improvement of the reliability.

The present inventors have found that a ratio of the peak current value IAof the peak A with respect to the peak current value IBof the peak B (IA/IB) is important for control of the reliability. In concrete, the present inventors have found that long lifetime can be achieved even if a relatively high electric field is applied, when the relationship of “IA/IB>0.30” is satisfied and the peak current value IBis 100 pA/mm2or less in the TSDC in which the polarizing temperature is 150 degrees C., the polarizing electric field is 15 V/μm to 20 V/μm, the polarizing time is 60 min, and the increasing speed of temperature is 10° C./min. With the method, it is possible to estimate the reliability of the multilayer ceramic capacitor100in a short time.

In the multilayer ceramic capacitor100of the embodiment, at least one of the dielectric layers11has a structure in which IA/IBis more than 0.30, and IB≤100 pA/mm2. It is preferable that all of the dielectric layers11have the structure in which IA/IBis more than 0.30 and IB≤100 pA/mm2.

For example, it is possible to make the structure in which IA/IBis more than 0.30 and IB≤100 pA/mm2, by adjusting the composition, the crystal grain diameter, the firing condition and so on of the dielectric layers11. From a viewpoint of improving the reliability, it is preferable that IA/IBis 0.50 or more. It is preferable that IA/IBis more than 0.50. It is preferable that IA/IBis 0.70 or more. It is preferable that IA/IBis more than 1.0. It is preferable that IA/IBis 2.00 or more. It is preferable that TBis 95 pA/mm2or less. It is preferable that TBis 90 pA/mm2or less. It is preferable that TBis 85 pA/mm2or less. It is preferable that TBis 80 pA/mm2or less. It is preferable that TBis 50 pA/mm2or less. The unit of the current value is A/mm2. The unit indicates a current value per a unit area. The value can be obtained by diving the current value measured with respect to the multilayer ceramic capacitor100by a total area of areas in which all internal electrode layers of the multilayer ceramic capacitor100face each other through a dielectric layer.

For example, IA/IBgets larger, when the number of crystal grain boundary crossing electrical field or a thickness of the crystal grain boundary is enlarged. When TBis smaller, the reliability of the product is improved. When TBis close to zero, IA/IBmay be a very large value.

When the dielectric layers11include a plurality of crystal grains in the thickness direction, the peak A and the peak B remarkably appear. It is therefore preferable that the dielectric layers11include a plurality of crystal grains in the thickness direction. For example, it is preferable that an average number of the crystal grains per one of the dielectric layers11is 3 to 8. It is possible to calculate the average number of the crystal grains per one of the dielectric layers11, by observing the cut cross section of the dielectric layer11in parallel with the stacking direction by an electronic microscopy, counting the number of the crystal grains crossing an arbitral straight line in parallel with the stacking direction in one of the dielectric layers11, repeating the counting in 20 dielectric layers11which are selected optionally, and calculating an average value.

For example, an average thickness of the dielectric layers11is 1 μm or more and 3.5 μm or less. This is because it is preferable that the dielectric layer11includes a plurality of crystal grains in the thickness direction. When a cut section in parallel with the stacking direction of the dielectric layers11is observed by an electron microscopy, it is possible to calculate the average thickness by calculating an average value of thicknesses of 20 points which are optionally selected.

The values themselves of IA, IBand (IA+IB) fluctuate in accordance with the size, the electrode structure, the thickness of the dielectric layers, the polarization condition, or other conditions of the multilayer ceramic capacitor100. It is therefore difficult to control the lifetime of the multilayer ceramic capacitor100, only with use of the values themselves. From the viewpoint, the embodiment focuses on the ratio of IAand IB.

Next, a description will be given of a manufacturing method of the multilayer ceramic capacitor100.FIG.4illustrates a manufacturing method of the multilayer ceramic capacitor100.

(Making process of raw material powder) A dielectric material for forming the dielectric layer11is prepared. Generally, an A site element and a B site element are included in the dielectric layer11in a sintered phase of grains of ABO3. For example, BaTiO3is tetragonal compound having a perovskite structure and has a high dielectric constant. Generally, BaTiO3is obtained by reacting a titanium material such as titanium dioxide with a barium material such as barium carbonate and synthesizing barium titanate. Various methods can be used as a synthesizing method of the ceramic structuring the dielectric layer11. For example, a solid-phase method, a sol-gel method, a hydrothermal method or the like can be used. The embodiment may use any of these methods.

An additive compound may be added to resulting ceramic powders, in accordance with purposes. The additive compound may be an oxide of Mg (magnesium), Mn (manganese), V (vanadium), Cr (chromium) or a rare earth element (Y (yttrium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium) and Yb (ytterbium)), or an oxide of Co (cobalt), Ni, Li (lithium), B (boron), Na (sodium), K (potassium) and Si, or glass.

For example, the resulting ceramic raw material powder is wet-blended with additives and is dried and crushed. Thus, a ceramic material is obtained. For example, the grain diameter may be adjusted by crushing the resulting ceramic material as needed. Alternatively, the grain diameter of the resulting ceramic power may be adjusted by combining the crushing and classifying. With the processes, the ceramic material acting as a main component of the dielectric layers is obtained.

(Stacking process) Next, a binder such as polyvinyl butyral (PVB) resin, an organic solvent such as ethanol or toluene, and a plasticizer are added to the resulting dielectric material and wet-blended. With use of the resulting slurry, a base material is coated with a stripe-shaped dielectric green sheet with a thickness of 1 μm or more, for example, a die coater method or a doctor blade method, and then dried.

Then, a pattern of the internal electrode layer12is provided on the surface of the dielectric green sheet by printing metal conductive paste for forming an internal electrode with use of screen printing or gravure printing. The conductive paste includes an organic binder. A plurality of patterns are alternatively exposed to the pair of external electrodes. The metal conductive paste includes ceramic particles as a co-material. A main component of the ceramic particles is not limited. However, it is preferable that the main component of the ceramic particles is the same as that of the dielectric layer11. For example, BaTiO3having an average grain diameter of 50 nm or less may be evenly dispersed.

Then, the dielectric green sheet on which the internal electrode layer pattern is printed is stamped into a predetermined size, and a predetermined number (for example, 100 to 1000) of stamped dielectric green sheets are stacked while the base material is peeled so that the internal electrode layers12and the dielectric layers11are alternated with each other and the end edges of the internal electrode layers12are alternately exposed to both end faces in the length direction of the dielectric layer11so as to be alternately led out to a pair of the external electrodes20aand20bof different polarizations. A cover sheet to be the cover layer13is clamped to an upper face of the stacked dielectric green sheets, and another cover sheet to be the cover layer13is clamped to a lower face of the stacked dielectric green sheets. The resulting stacked structure is stamped into a predetermined size (for example, 1.0 mm×0.5 mm).

After that, the binder is removed from the ceramic multilayer structure in N2atmosphere. After that, metal conductive paste for the external electrodes20aand20bis provided from the both end faces to the side faces of the ceramic multilayer structure and is dried. The metal conductive paste includes a metal filer, a co-material, a binder, a solvent and so on. The metal conductive paste is to be ground layers of the external electrodes20aand20b.

(Firing process) The binder is removed in N2atmosphere in a temperature range of 250 degrees C. to 500 degrees C. After that, the resulting compact is fired for 10 minutes to 2 hours in a reductive atmosphere having an oxygen partial pressure of 10−8to 10−13atm in a temperature range of 1100 degrees C. to 1300 degrees C. Thus, each compound is sintered. In this manner, the ceramic multilayer structure is obtained.

(Re-oxidation process) After that, the re-oxidation process is performed in N2gas atmosphere in a temperature range of 600 degrees C. to 1000 degrees C. For example, the re-oxidation process is performed for 1 hour at 950 degrees C. After that, in a cooling process, the ceramic multilayer structure is cooled in the N2gas atmosphere, and the temperature of the ceramic multilayer structure is reduced to 500 degrees C. At 500 degrees C., the atmosphere is switched from the N2gas atmosphere to ambient air. And the ceramic multilayer structure is kept for 24 hours at 500 degrees C. And the ceramic multilayer structure is cooled to a room temperature. With the processes, it is possible to enlarge the oxygen concentration of the crystal grain boundary16of the dielectric layers11. Thus, it is possible to largely reduced the peak current value of the TSDC. And it is possible to suppress the movement of the oxygen vacancy14crossing over the crystal grain boundary16or along the crystal grain boundary16. Accordingly, it is possible to relatively reduce IBwith respect to IA. By the long-time keeping at 500 degrees C., multilayer ceramic capacitors having a large size and 1000 number of dielectric layers or more such as 4532 size (length is 4.5 mm, width is 3.2 mm, and height is 2.5 nn) can be sufficiently re-oxidized.

(Plating process) After that, with a plating process, ground layers of the external electrodes20aand20bare coated with a metal such as Cu, Ni, and Sn. With the processes, the multilayer ceramic capacitor100is manufactured.

In the manufacturing method of the embodiment, IA/IBof at least one of the dielectric layers11is more than 0.30. And IBis 100 pA/mm2or less. Therefore, long lifetime can be achieved and reliability can be improved even if a relatively high electric field is applied.

(Second embodiment) A description will be given of a second embodiment. The TSCD condition is changed in the multilayer ceramic capacitor100described based onFIG.1.

The present inventors have found that a long lifetime is achieved when decreasing with respect to increasing of the polarizing temperature is not observed in a peak current on the lowest side (near 150 degrees C.) in peak currents when increasing a temperature to 350 degrees C., in the TSDC of the dielectric layer11in which the polarizing time is 60 min, the polarizing electric field is 10 V/μm, the polarizing is achieved by changing the polarizing temperature within a temperature range of 150 degrees C. to 210 degrees C., and an increasing speed of temperature after cooling to 130 degrees C. is 10° C./min.

It is thought that the peak on the lowest side (around 150 degrees C.) is caused by dipole of vacancy (cluster of oxygen vacancy, cation vacancy, metal vacancy or the like). When the peak does not decrease with respect to increasing of the polarizing temperature, the cluster is not dissociated and the oxygen vacancy is hardly migrated. It is therefore thought that the increasing of the peak on the higher temperature side having a large influence on the reliability of the multilayer ceramic capacitor is suppressed.

In concrete, a peak current value of a TSDC peak around 150 degrees C. in a case of polarization at a polarizing temperature of 150 degrees C. is referred to as J150. A peak current value of a TSDC peak around 150 degrees C. in a case of polarization at a polarizing temperature of 170 degrees C. is referred to as J170. When a relationship of “×J=(J170−J150)/J150≥0” is satisfied, a long lifetime is achieved. In a normal TSDC, a temperature is increased to 350 degrees C. or more. However, in the embodiment, the temperature is increased to 350 degrees C. or so. It is therefore possible to simply evaluate the reliability of the multilayer ceramic capacitor100.

FIG.5illustrates J170 and J150. InFIG.5, a solid line indicates the TSDC in the case of the polarization at 170 degrees C. A dotted line indicates the TSDC in the case of the polarization at 150 degrees C. As illustrated inFIG.5, in both J170 and 150, a peak is observed around 150 degrees C. J170 is larger than J150. A temperature of a peak in J170 and J150 is observed within 130 degrees C. to 150 degrees C.

In the multilayer ceramic capacitor100of the embodiment, at least one of the dielectric layers11has a structure satisfying the relationship of “AJ=(J170−J150)/J150≥0”. It is preferable that all of the dielectric layers11have the structure satisfying the relationship of “ΔJ=(J170−J150)/J150≥0”.

The relationship of “ΔJ=(J170−J150)/J150≥0” can be achieved by adjusting parameters such as the composition, the crystal grain diameter or the firing condition of the dielectric layers11. In a viewpoint of improving the reliability, it is preferable that the relationship of “ΔJ=(J170−J150)/J150≥0.5” is satisfied. It is more preferable that the relationship of “ΔJ=(J170−J150)/J150≥1.0” is satisfied.

It is possible to enlarge ΔJ=(J170−J150)/J150 by increasing the number of crystal grain boundary crossing over electric field or thickening the crystal grain boundary. However, when ΔJ=(J170−J150)/J150 is excessively large, the electrostatic capacity of the product may be degraded. It is therefore preferable that ΔJ=(J170−J150)/J150 has an upper limit from a viewpoint of securing capacity and achieving high reliability. For example, it is preferable that ΔJ=(J170−J150)/J150 is 2.0 or less. It is more preferable that ΔJ=(J170−J150)/J150 is 1.5 or less. It is still more preferable that ΔJ=(J170−J150)/J150 is 1.25 or less.

With respect to the above-mentioned TSDC, it is preferable that decreasing with respect to increasing of the polarizing temperature is not observed in a peak current on the lowest side (near 150 degrees C.) in peak currents when increasing a temperature to 350 degrees C., in the TSDC in which an increasing speed of temperature after cooling to 130 degrees C. is 10° C./min, even if both of the polarizing temperature from 150 degrees C. to 210 degrees C. are notified.

The multilayer ceramic capacitor100of the embodiment can be manufactured by the same manufacturing method as the first embodiment. In the manufacturing method, at least one of the dielectric layers11satisfies the relationship of “A J=(J170−J150)/J150”. In this case, even if the multilayer ceramic capacitor100is used under a relatively high temperature environment, the multilayer ceramic capacitor100achieves a long lifetime and has high reliability.

In the embodiments, the multilayer ceramic capacitor is described as an example of ceramic electronic devices. However, the embodiments are not limited to the multilayer ceramic capacitor. For example, the embodiments may be applied to another electronic device such as varistor or thermistor.

EXAMPLES

The multilayer ceramic capacitors of the above-mentioned embodiments were made. And characteristic was measured.

Barium titanate powder was prepared as a dielectric material. Additive compound was added to the barium titanate powder. The barium titanate powder and the additive compound were wet-blended with each other in a ball mill and were crushed. Thus, a dielectric material was obtained. An organic binder and a solvent were added to the dielectric material. A dielectric green sheet was made by a doctor blade method. As the organic binder, a butyral-based material was added to the dielectric material. As the solvent, toluene and ethyl alcohol were added to the dielectric material. In addition, a plasticizer and so on were added to the dielectric material.

Next, metal conductive paste for forming internal electrode layers was made with use of planetary ball mill. The metal conductive paste included the main component of the internal electrode layers12, the co-material, the binder (ethyl cellulose), the solvent and necessary additive.

The metal conductive paste for forming internal electrode layers was printed on the resulting dielectric green sheet. 301 numbers of the dielectric green sheets on which the metal conductive paste was printed were stacked. A cover sheet was stacked on an upper face and a lower face of the stacked dielectric green sheets and was thermally clamped. The resulting multilayer structure was cut into a predetermined size.

The binders were removed in N2atmosphere. After that, as the ground layer, metal conductive paste including a metal filler of which a main component was Ni, a co-material, a binder, a solvent or the like was painted from both edge faces to each side face of the multilayer structure. The metal conductive paste was dried. The resulting multilayer structure was fired in a reductive atmosphere for 10 minutes to 2 hours at a temperature of 110 degrees C. to 1300 degrees C. Thus a sintered structure was formed. The sintered structure had a length of 3.2 mm, a width of 1.6 mm and a height of 1.6 mm.

After that, the re-oxidation process was performed. The sintered structure was kept at 950 degrees C. in N2gas atmosphere for 1 hour. After that, the temperature of the sintered structure was reduced to 500 degrees C. in the N2gas atmosphere. The atmosphere was switched to normal air. The sintered structure was kept at 500 degrees C. for 24 hours. After that, the temperature of the sintered structure was reduced to the room temperature. After that, a Cu-plated layer, a Ni-plated layer and a Sn-plated layer were formed on a surface of the base layer by the plating method. Thus, the multilayer ceramic capacitor100was obtained. The thickness of the dielectric green sheet was adjusted so that the average thickness of the dielectric layer11observed in a cross section was 1.2 μm.

In an example 2, the temperature of the sintered structure was kept at 500 degrees C. for 20 hours after switching the atmosphere to the normal air. Other conditions were the same as those of the example 1.

In an example 3, the temperature of the sintered structure was kept at 500 degrees C. for 30 hours after switching the atmosphere to the normal air. Other conditions were the same as those of the example 1.

In an example 4, the number of the dielectric layers11was 1100. The average thickness of each of the dielectric layers11observed in the cross section was 0.7 μm. Other conditions were the same as those of the example 1.

In an example 5, the number of the dielectric layers11was 100. The average thickness of each of the dielectric layers observed in the cross section was 3.6 nm. Other conditions were the same as those of the example 1.

Comparative Example 1

In a comparative example 1, the sintered structure was kept at 950 degrees C. in the N2gas atmosphere for 1 hour, in the re-oxidation process. After that, the temperature of the sintered structure was reduced to 500 degrees C. in the N2gas atmosphere. After that, the atmosphere was switched to the normal air, and the temperature of the sintered structure was reduced to the room temperature. That is, the keeping at 500 degrees C. was not performed. Other conditions were the same as those of the example 1.

Comparative Example 2

In a comparative example 2, the sintered structure was kept at 950 degrees C. in the N2gas atmosphere for 1 hour, in the re-oxidation process. After that, the temperature of the sintered structure was reduced to 500 degrees C. in the N2gas atmosphere. After that, the atmosphere was switched to the normal air. The sintered structure was kept at 500 degrees C. for 5 hours. After that, the temperature of the sintered structure was reduced to the room temperature. That is, the time for the keeping at 500 degrees C. was shorter than that of the example 1. Other conditions were the same as those of the example 1.

Comparative Example 3

In a comparative example 3, the sintered structure was kept at 950 degrees C. in the N2gas atmosphere for 1 hour, in the re-oxidation process. After that, the temperature of the sintered structure was reduced to 500 degrees C. in the N2gas atmosphere. After that, the atmosphere was switched to the normal air. The sintered structure was kept at 500 degrees C. for 15 hours. After that, the temperature of the sintered structure was reduced to the room temperature. That is, the time for the keeping at 500 degrees C. was shorter than that of the example 1. Other conditions were the same as those of the example 1.

(Analysis 1) With respect to each of the examples 1 to 5 and the comparative examples 1 to 3, IA/IBwas measured in the TSDC in which the polarizing temperature was 150 degrees C., the polarizing time was 60 min, the polarizing electric field was 20 V/μm, the increasing speed of temperature was 10 degrees C./min. Each of the examples 1 to 5 and the comparative examples 1 to 3 was subjected to HALT (Highly Accelerated limit Test) at a high temperature of 150 degrees C. and at a high electric field of 40 V/μm. Table 1 shows the results. MTTF (Mean Time To Failure) was measured with respect to each 20 samples of the examples 1 to 5 and the comparative examples 1 to 3. A lifetime until electric conduction was measured. An average of the lifetime was calculated as the MTTF.

In the examples 1 to 5 and the comparative examples 1 to 3, the average number of the crystal grains in the dielectric layers in the thickness direction was 3 to 10.

The MTTF of the examples 1 to 5 was more than 2000 min. Therefore, long lifetime was achieved. It is thought that this was because the relationship of “IA/IB>0.30” was satisfied, and the peak current IBat the maximum temperature was 100 pA/mm2or less. In contrast, the MTTF of the comparative example 1 was a short time of 100 min. It is thought that this was because IA/IBwas a low value of 0.15, and the IBwas not sufficiently small. The MTTF of the comparative example 2 was a short time of 500 min. It is thought that this was because although IA/IBwas a high value of 0.35, IBwas a high value of 250 pA/mm2and the IBwas not sufficiently small. The MTTF of the comparative example 3 was a short time of 2000 min. It is thought that this was because although IA/IBwas a high value of 1.50, the IBwas a high value of 105 pA/mm2and the IBwas not sufficiently small.

In an example 6, the manufacturing method and the conditions were the same as those of the example 1.

In an example 7, the manufacturing method and the conditions were the same as those of the example 2.

In an example 8, the manufacturing method and the conditions were the same as those of the example 3.

In an example 9, the manufacturing method and the conditions were the same as those of the example 4.

(Example 10) In an example 10, the manufacturing method and the conditions were the same as those of the example 5.

Comparative Example 4

In a comparative example 4, the sintered structure was kept at 950 degrees C. in the N2gas atmosphere for 1 hour, in the re-oxidation process. After that, the temperature of the sintered structure was reduced to 500 degrees C. in the N2gas atmosphere. After that, the atmosphere was switched to the normal air, and the temperature of the sintered structure was reduced to the room temperature. That is, the keeping at 500 degrees C. was not performed. Other conditions were the same as those of the example 1.

Comparative Example 5

In a comparative example 5, the sintered structure was kept at 950 degrees C. in the N2gas atmosphere for 1 hour, in the re-oxidation process. After that, the temperature of the sintered structure was reduced to 500 degrees C. in the N2gas atmosphere. After that, the atmosphere was switched to the normal air. The sintered structure was kept at 500 degrees C. for 10 hours. After that, the temperature of the sintered structure was reduced to the room temperature. That is, the time for the keeping at 500 degrees C. was shorter than that of the example 1. Other conditions were the same as those of the example 1.

(Analysis 2) With respect to each of the examples 6 to 10 and the comparative examples 4 and 5, ΔJ=(J170−J150)/J150 was measured by measuring J 150 and J170 in the TSDC in which the polarizing time was 60 min, the polarizing electric field was 10 V/μm, the polarization was achieved by changing the temperature within 150 degrees C. to 210 degrees C., and the increasing speed of temperature was 10 degrees C./min after cooling to the 130 degrees C. Each of the examples 6 to 10 and the comparative examples 4 and 5 was subjected to HALT (Highly Accelerated limit Test) at a high temperature of 150 degrees C. and at a high electric field of 40 V/μm. Table 1 shows the results. MTTF (Mean Time To Failure) was measured with respect to each 20 samples of the examples 6 to 10 and the comparative examples 4 and 5. A lifetime until electric conduction was measured. An average of the lifetime was calculated as the MTTF.

In the examples 6 to 10 and the comparative examples 4 and 5, the average number of the crystal grains in the dielectric layers in the thickness direction was 3 to 10.

As illustrated inFIG.6, in the example 6, the MTTF was 15000 min, and AJ was 0.07. In the example 7, the MTTF was 12500 min, and AJ was 0.04. In the example 8, the MTTF was 23000 min, and AJ was 0.18. In the example 9, the MTTF was 12000 min, and AJ was 0.02. In the example 10, the MTTF was 30000 min, and AJ was 0.3. In the comparative example 4, the MTTF was 100 min, and AJ was −0.2. In the comparative example 5, the MTTF was 1200 min, and ΔJ was −0.05.

In the examples 6 to 10, the MTTF was more than 2000 min. And a long lifetime was achieved. It is thought that this was because AJ was 0 or more. On the other hand, in the comparative examples 4 and 5, the MTTF was less than 2000 min. It is thought that this was because AJ was less than 0.