JP4594049B2 - Multilayer ceramic capacitor - Google Patents

Description

The present invention is related to a multilayer ceramic capacitor of small type and high capacity.

  In recent years, with the miniaturization and high performance of electronic devices, there has been an increasing demand for miniaturization and large capacity of multilayer ceramic capacitors. In order to meet such demands, in multilayer ceramic capacitors (MLC), the dielectric layer is made thinner to increase the capacitance, and by increasing the number of layers, the size and capacity can be reduced. It has been. In addition, in order to form a flat dielectric layer corresponding to the thinning and to suppress a decrease in reliability due to an increase in electric field applied to the multilayer ceramic capacitor due to the thinning, particles are miniaturized. Yes.

For example, in the following Patent Document 1 focusing on glass particles, the dielectric layer satisfies the relationship of D / t ≦ 0.5, where t is the thickness of the dielectric layer and D is the maximum diameter of the glass particles. It is described that by forming a layer, it has high insulation and can improve reliability in a high-temperature load test.

Further, in Patent Document 2 below, the average particle size of the barium titanate crystal particles constituting the dielectric layer is controlled in order to suppress a decrease in the relative dielectric constant that occurs when a DC bias is applied along with the thinning of the dielectric layer. Describes using barium titanate powders of less than 0.4 μm.
JP 2003-309036 A JP 2003-40671 A Ferroelectrics, 1998, Vols. 206-207, pp 337-353. H. FREY, Z. XU, P.M. HAN and D.H. A. PAYNE

  By the way, barium titanate mainly used for the dielectric material of the multilayer ceramic capacitor described above has, for example, a perovskite crystal structure according to Non-Patent Document 1, but has a relative dielectric constant of about 4800. It is known that the dielectric constant is extremely high.

  However, in the production of a multilayer ceramic capacitor, for example, when a fine barium titanate powder as described in Patent Document 1 is used for thinning a dielectric layer, firing is usually performed under atmospheric pressure. Then, it is accompanied by abnormal grain growth. For this reason, the crystal particles constituting the dielectric layer do not have a uniform particle size, and there are large crystal particles that are partially grown. Therefore, in a multilayer ceramic capacitor having such crystal particles, the relative dielectric constant is low. There has been a problem that the temperature characteristics are increased, the insulating property is lowered, and the reliability is lowered particularly in a high temperature load test.

Accordingly, the present invention aims to have temperature characteristics and insulating stable and high dielectric constant even when extremely thin thickness of the dielectric layer, and obtain a multilayer ceramic con den Sa reliable.

Multilayer ceramic capacitor of the present invention, there a laminated ceramic capacitor comprising crystal grains of several and a dielectric layer which is sintered through the grain boundary layer, a capacitor body formed by alternately stacking internal electrode layers (A) the average particle size of the crystal particles constituting the dielectric layer is 0.2 μm or less, (b) the main component of the pre-crystal particles is barium titanate, and (c) the X-rays of the dielectric layer It is obtained from the volume V _bulk per unit cell represented by the product of the lattice constants (a, b, c) obtained from the diffraction pattern, and the X-ray diffraction pattern of the crystal particles obtained by grinding the dielectric layer. lattice constant (a, b, c) is the ratio of the volume _{V powder} per unit cell represented by a product of, and satisfies the relationship of _V bulk _{/ V powder} ≧ 1.005.

In the laminated ceramic capacitor, the barium A mole of barium titanate constituting the crystal grains, when the titanium B mol, the molar ratio of the barium and titanium satisfy the relationship of A / B ≧ 1 Is desirable.
In the multilayer ceramic capacitor, it is preferable that a lattice constant ratio obtained from an X-ray diffraction pattern of the dielectric layer satisfies a relationship of c / a ≧ 1.005 .
Further, in the laminated ceramic capacitor, a multilayer ceramic capacitor, the temperature higher than the Curie temperature indicated crystal grains mainly composed of the barium titanate constituting the dielectric layer, and the rated voltage of the multilayer ceramic capacitor When exposed to a high temperature load atmosphere at a voltage of 1/3 or higher, the resistance reduction rate of the grain boundary layer in the dielectric layer in the AC impedance measurement before and after that is 0.5% / min. The following is desirable.

According to the multilayer ceramic capacitor of the present invention has a temperature characteristic and insulating property and excellent very thin to be high relative dielectric constant and the thickness of the dielectrics layer, and a highly reliable multilayer ceramic capacitor and its manufacturing method Obtainable.

(Construction)
The multilayer ceramic capacitor of the present invention will be described in detail based on the schematic sectional view of FIG.

  FIG. 1 is a schematic cross-sectional view showing a multilayer ceramic capacitor of the present invention.

  The enlarged drawing of the drawer is a schematic view showing the crystal grains and the grain boundary layer constituting the dielectric layer.

  In the multilayer ceramic capacitor of the present invention, external electrodes 3 are formed at both ends of the capacitor body 1. The external electrode 3 is formed, for example, by baking Cu or an alloy paste of Cu and Ni. The capacitor body 1 is configured by alternately laminating dielectric layers 5 and internal electrode layers 7. The dielectric layer 5 includes crystal grains 9 and a grain boundary layer 11.

  The thickness is preferably 1.6 μm or less from the viewpoint of reducing the size and capacity of the multilayer ceramic capacitor. When the thickness of the dielectric layer 5 is thus thin, the structure comprising the dielectric crystal particles according to the present invention. The effectiveness of this is increased.

  Furthermore, in the present invention, the thickness variation of the dielectric layer 5 is more preferably within 10% in order to stabilize the capacitance variation and capacitance temperature characteristics.

  The internal electrode layer 7 is preferably a base metal such as nickel (Ni) or copper (Cu) in that the manufacturing cost can be suppressed even if the internal electrode layer 7 is highly laminated. In particular, simultaneous firing with the dielectric layer 5 according to the present invention is possible. Nickel (Ni) is more preferable because it can be achieved.

In the multilayer ceramic capacitor of the present invention, the crystal grains 9 constituting the dielectric layer 5 is mainly ing of crystal grains of the barium titanate perovskite. That is, in the multilayer ceramic capacitor of the present invention, since the crystal grains 9 that make up the dielectric layer 5 is composed mainly of barium titanate, as described above, and indicates a high dielectric constant. In the multilayer ceramic capacitor of the present invention, the crystal grains 9 constituting the dielectric layer 5 have an average particle size of 0.1 because the dielectric layer 5 has high insulation and high temperature load reliability. It is important that it is 2 μm or less. When the average particle size is larger than 0.2 μm, high insulating properties and high temperature load reliability cannot be obtained. In addition, an average particle diameter is represented by D50, and D50 is an integrated cumulative value in volume in the particle size distribution.

  On the other hand, the lower limit of the grain size of the crystal grains 9 is preferably 0.05 μm or more because the dielectric constant of the dielectric layer 5 is increased and the temperature dependence of the dielectric constant is suppressed.

  The crystal particles 9 desirably contain Mg, rare earth elements and Mn, and the contents of Mg, rare earth elements and Mn contained in the crystal particles 9 are based on 100 parts by mass of the barium titanate component. Mg = 0.04 to 0.3 parts by mass, rare earth elements = 0.5 to 2 parts by mass, and Mn = 0.04 to 0.3 parts by mass are preferable. Since these Mg, rare earth element and Mn are derived from the sintering aid, these elements partially dissolve in the crystal grains 9, but many exist in the grain boundary layer 11.

That is, in the dielectric layer 5 that make up the multilayer ceramic capacitor of the present invention, Mg, a rare earth element is a component of the crystal grains 9 core-shell structure, whereas the crystal grains Mn is produced by firing in a reducing atmosphere 9 It can compensate for oxygen deficiency in the inside, and improve insulation and high temperature load life.

Further, the dielectric layer 5 that make up the multilayer ceramic capacitor of the present invention, together with a rare earth element has a concentration gradient of crystal grains 9 surface grain boundary layer 11 is a particle surface as the highest concentration toward inside of the grain, 0.05 It is desirable to be at least atomic% / nm. In other words, if the concentration gradient of the rare earth element is such a condition, the X5R standard can be satisfied in terms of the capacitance temperature characteristics as well as the improvement of the relative permittivity and the high temperature load life. Here, the rare earth element in the present invention is preferably at least one selected from La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Y, Er, Tm, Yb, Lu, and Sc. In particular, Y is preferable from the standpoint of increasing the dielectric constant and insulating properties.

Further, the dielectric layer 5 that make up the multilayer ceramic capacitor of the present invention, because it can maintain a high dielectric constant of the dielectric layer 5, and increase the resistance in the accelerated test, the alumina contained in the porcelain impurities The amount is desirably 1% by mass or less.

As described above, in the multilayer ceramic capacitor of the present invention , the crystal particles 9 constituting the dielectric layer 5 are derived from the sintering aid on the particle surface side from the particle center, in particular, the core shell in which Mg and rare earth elements are unevenly distributed. A mold structure is formed, resulting in a high dielectric constant and high insulating properties. In the present invention , the dielectric layer 5 preferably has a relative dielectric constant of 2000 or more, particularly 2500 or more.

The dielectric layer 5 that make up the multilayer ceramic capacitor of the present invention, the volume Vbulk per unit cell represented by the product of the lattice constant determined from X-ray diffraction pattern (a, b, c), the dielectric body layer X-ray lattice constant determined from the diffraction pattern of the crystalline particles obtained by pulverizing (a, b, c) is the ratio of the volume Vpowder per unit cell is represented by the product of, Vbulk / Vpowder ≧ 1 .005 relationship is satisfied. This relationship is due to the residual stress that the crystal grains 9 in the porcelain receive from the grain boundary layer 11, and the relative dielectric constant increases when the difference in thermal expansion coefficient between the crystal grains 9 and the grain boundary layer 11 is large. That is, the smaller the thermal expansion coefficient of the glass powder as the additive component, the more effective. On the other hand, when Vbulk / Vpowder is smaller than 1.005, improvement of the dielectric constant is suppressed. When obtaining the above Vbulk / Vpowder relationship, both the exponents (h k l) of the X-ray diffraction patterns are 1 to 1.
The peak was in the range of 4. For example, h: (1 0 0), (2 0 0), (4 0 0). The same applies to the other k and l.

  Furthermore, in the crystal grains 9 constituting the dielectric layer 5 described above, when the lattice constant ratio satisfies the relationship of c / a ≧ 1, a higher relative dielectric constant can be obtained. The lattice constant ratio c / a is particularly preferably equal to or greater than 1.003 because the dielectric constant of the dielectric layer 5 is increased.

In addition, the present invention, barium A mole of barium titanate constituting the crystal grain 9, and titanium when the B mole, the molar ratio of the barium and titanium, A / B ≧ 1, in particular, the grain growth It is desirable to satisfy the relationship of A / B ≧ 1.003 for the reason of suppression. By thus defining the A / B ratio as described above, the grain growth of the crystal grains 9 can be suppressed, and the relative dielectric constant can be suppressed. The temperature characteristics of the rate can be stabilized.

Figure 2 is a schematic diagram showing the evaluation method of the resistance of the grain boundary layer of the dielectric layer using the ac impedance measurements. In FIG. 2, 20a is a thermostatic chamber for controlling the temperature by mounting a multilayer ceramic capacitor as a sample, 20b is a HALT measuring device for applying a DC voltage to the sample, and 20c is an impedance measuring device having an AC power source. Figure 3 is a representation of the resistance evaluation results of the grain boundary layer of the dielectric layer using the ac impedance measurements.

In the present invention, a multilayer ceramic capacitor, a temperature higher than the Curie temperature of the crystal grains 9 shows that the main component Ruchi Tan barium make up the dielectric layer 5, and, in the rated voltage of the multilayer ceramic capacitor 1 / Leave in a high-temperature load atmosphere at a voltage of 3 or higher. Then, the resistance reduction rate of the grain boundary layer 11 in the dielectric layer 5 is measured under the same conditions before and after being left in the high temperature load atmosphere under the above conditions. 3, the core (center) of crystal grains 9, the shell (outer peripheral portion) is a graph of the impedance change at the interface between the internal electrode 7 and the dielectric layer 5 and the grain boundary layer (Cole-Cole plot). In this evaluation, the dielectric layer 5 is divided into four components, ie, the core (center portion), the shell (outer peripheral portion), the grain boundary layer 11 and the interface between the internal electrode layer 7 and the dielectric layer 5 as shown in the equivalent circuit of FIG. Distinguish. The horizontal axis of the graph indicates the real part of the impedance signal, and the vertical axis indicates the imaginary part. The graph showing the change in impedance is the difference between before and after the accelerated life test (HALT) and the fitting by simulation. In the present invention, attention is particularly paid to the resistance change in the grain boundary layer 11, and the change rate of the real part (change rate per load time) is 0.5% / min. The following is desirable. This evaluation can be obtained, for example, by dividing the Cole-Cole plot of FIG. 3 before and after the accelerated life test (HALT) into the above four components by using dedicated software. Here, the temperature is reduced to the Curie temperature in that the diffusion of ions in the dielectric layer 5 and the movement of electrons in the dielectric layer 5 before and after the high temperature load treatment are increased, and the resistance reduction rate of the grain boundary layer 11 can be seen remarkably. The voltage is preferably 1.5 times or more than 2/5 V of the rated voltage.

(Manufacturing method)
It will now be described in detail preparation of the product layer ceramic capacitor. Figure 4 is a process diagram showing a process of a product layer ceramic capacitor.

To obtain a product layer ceramic capacitors, and green sheets containing a powder mix of the dielectric powder and a glass powder mainly composed of barium titanate, the capacitor body molded constructed by alternately laminating the internal electrode pattern Bake the body . In this case, the dielectric powder has an average particle size of 0.2 μm or less, a glass powder has a softening point of 650 ° C. or more, and a thermal expansion coefficient of 9.5 × 10 ⁻⁶ / ° C. or less.

Further, in the production method of the laminated ceramic capacitor, the dielectric powder is Mg, it is obtained by coating an oxide of a rare earth element and Mn, when the barium site in titanate Barium Powder A, and B to titanium site in a molar ratio, satisfying the relation of a / B ≧ 1, and this average particle diameter of the glass powder is 0.3μm or less.

Figure 4 is a process diagram showing a process of a product layer ceramic capacitor.

Step (a): In this method, firstly, a ceramic slurry was prepared raw material powder shown below and an organic resin such as polyvinyl butyral resins, and mixed by using a ball mill with a solvent such as toluene and alcohol, and then, The ceramic green sheet 21 is formed on the ceramic slurry by using a sheet forming method such as a doctor blade method or a die coater method. The thickness of the ceramic green sheet 21 is preferably 1 to 2 μm from the viewpoint of reducing the thickness of the dielectric layer 5 to increase the capacity and maintaining high insulation.

Use Irare Ruchi Tan barium powder (BT powder) is a raw material powder represented by BaTiO _3. The BT powder has a barium / titanium molar ratio of A / B ≧ 1 , where A mol is the barium in the A site (barium) and B site (titanium) and titanium is B mol . It is desirable that A / B is 1.003 or more from the viewpoint of suppressing the grain growth during firing. This BT powder is obtained by a synthesis method selected from a solid phase method, a liquid phase method (including a method of producing via oxalate), a hydrothermal synthesis method, and the like. Narrow particle size distribution of these obtained dielectric powder, flour powder obtained by hydrothermal synthesis because of high crystallinity is preferable.

Particle size distribution of the B T Powder may not less 0.2μm or less in terms of facilitating thinning of the dielectric layer 5, in particular, increasing the dielectric constant to increase the c / a ratio, and It is desirable that the thickness is 0.05 to 0.2 μm from the viewpoint of increasing the insulating property.

Further, the crystallinity of its is, when evaluated using X-ray diffraction, for example, a peak indicating the tetragonal is be greater than the peak indicating the cubic lattice constant ratio c With such a powder / A can be increased. Components of coating added to the BT powder, with respect to BT powder 100 parts by weight, respectively, Mg = 0.04-3 parts by weight, the rare earth element = 0.5 to 2 parts by weight, Mn = from .04 to 0 .3 parts by mass is preferable.

The glass powder added to the dielectric powder is good that the softening point of 650 ° C. or higher. When the softening point is lower than 650 ° C., the softening flow of the glass occurs for a long time during firing, and the grain growth of barium titanate tends to occur. In particular, 690 ° C. or higher is preferable in terms of suppressing aggregation due to softening of the glass component itself and enhancing dispersibility in the porcelain.

Furthermore, glass powder in thermal expansion coefficient from room temperature to 300 ° C., is the better than 9.5 × ^{10 -6} / ℃ or less. Glass thermal expansion coefficient of the powder shows an effect at 9.5 × 10 -6 ^/ ℃ less, is remarkable dielectric constant improvement in the case of a 9 × 10 -6 ^/ ℃ or less. Furthermore, when the glass powder has a high softening point of, for example, 700 ° C. or higher, more preferably 800 ° C. or higher, a larger stress is applied between the crystal grains 9 and the grain boundary layer 11 during the cooling process. It is effective for controlling dielectric characteristics.

On the other hand, if the thermal expansion coefficient is larger than 9.5 × 10 ⁻⁶ / ° C. (temperature range from room temperature to 300 ° C.), the difference from the thermal expansion coefficient of the dielectric powder (12.5 × 10 ⁻⁶ / ° C.) As a result, the stress on the crystal grains 9 of the dielectric is reduced and the relative permittivity is lowered.

The glass powder preferably has an average particle size of 0.3 μm or less from the viewpoint of reducing the particle size difference from the barium titanate powder and improving dispersibility.

As a _component, is preferable to SiO 2, BaO, CaO, and _B 2 _{O 3} as a main component, the composition _is, SiO 2 = 40 to 70 mol%, BaO = 5 to 40 mol%, CaO = 5 to 40 mol%, and _B 2 _O 3 = is preferably from 1 to 30 mol%, Li component in terms of maintaining high softening point is preferably one which does not contain.

Further, as the glass powder, in addition to the above-mentioned components, as the glass powder satisfying the above softening point and thermal expansion coefficient, does not contain a Si component, BaO = 10 to 40 mol%, CaO = 10 to 40 mol%, and B A glass having ₂ O ₃ = 30 to 60 mol% can also be suitably used. The addition amount of the glass powder for BT Powder 1 00 parts by weight, preferably in that it is 0.7 to 2 parts by weight improve the sinterability of the porcelain.

As described above, the BT powder preferably has a barium / titanium molar ratio ( A / B ratio ) of 1 or more, particularly preferably 1.003 or more. However, such a powder has carbon dioxide on the surface of the BT powder. It is formed by fixing powder such as barium. The amount is preferably 0.1 to 1 part by mass with respect to 100 parts by mass of the BT powder for the reason of suppressing grain growth.

  (B) Step: Next, a rectangular internal electrode pattern 23 is printed and formed on the main surface of the ceramic green sheet 21 obtained above. The conductor paste used as the internal electrode pattern 23 is prepared by using Ni, Cu, or an alloy powder thereof as a main component metal, and adding an organic binder, a solvent, and a dispersing agent thereto. As the metal powder, Ni is preferable because it enables simultaneous firing with the dielectric powder and is low in cost. The thickness of the internal electrode pattern 23 is preferably 1 μm or less because the multilayer ceramic capacitor is miniaturized and the steps due to the internal electrode pattern 23 are reduced.

In order to eliminate steps by the internal electrode pattern 23 on the cell la Mick Green sheet 21, it is preferable to form a ceramic pattern 25 around the inner electrode pattern with the internal electrode pattern 23 substantially the same thickness. As the ceramic component constituting the ceramic pattern 25, it is preferable to use the dielectric powder in terms of making the firing shrinkage in the simultaneous firing the same.

  Step (c): Next, a desired number of ceramic green sheets 21 on which the internal electrode patterns 23 are formed are stacked, a plurality of ceramic green sheets 21 on which the internal electrode patterns 23 are not formed are the same, and the upper and lower layers are the same. The temporary laminated body is formed by overlapping the number of sheets. The internal electrode pattern in the temporary laminate is shifted by a half pattern in the longitudinal direction. By such a laminating method, the internal electrode patterns 23 can be alternately exposed on the end faces of the cut laminate.

As noted above, in addition to the method of laminating in advance form the internal electrode pattern 23 on the main surface of the ceramic green sheet 21, after it has once brought into close contact with the lower side gear ceramic green sheet 21, the internal After the electrode pattern 23 is printed and dried, the ceramic green sheet 21 on which the internal electrode pattern 23 is not printed is superimposed on the printed and dried internal electrode pattern 23 and temporarily adhered thereto. It can also be formed by a method of sequentially performing the adhesion of the sheet 21 and the printing of the internal electrode pattern 23.

  Next, the temporary laminated body is pressed under conditions of higher temperature and higher pressure than the temperature pressure during the temporary lamination to form a laminated body 29 in which the ceramic green sheet 21 and the internal electrode pattern 23 are firmly adhered.

Next, the laminated body 29 is cut along the cutting line h, that is, approximately at the center of the ceramic pattern 25 formed in the laminated body 29 in a direction perpendicular to the longitudinal direction of the internal electrode pattern 23 (see FIG. 4). (
In (c1) and (c2) of FIG. 4, the capacitor body molded body is formed so as to be cut parallel to the longitudinal direction of the internal electrode pattern 23 so that the end portion of the internal electrode pattern is exposed. On the other hand, in the widest portion of the internal electrode pattern 23, the internal electrode pattern is formed in an unexposed state on the side margin portion side.

Next, this capacitor body molded body is fired under a predetermined atmosphere at a temperature condition to form a capacitor body. In some cases, the ridge line portion of the capacitor body 1 is chamfered and the capacitor body 1 faces the capacitor body 1 . Barrel polishing may be performed to expose the internal electrode layer 7 exposed from the end face. Degreasing is in the temperature range up to 500 ° C, the heating rate is 5 to 20 ° C / h, the firing temperature is in the range of 1150 to 1300 ° C, and the heating rate from degreasing to the maximum temperature is 200 to 500 ° C / h. h, Holding time at the maximum temperature is 0.5 to 4 hours, the rate of temperature decrease from the maximum temperature to 1000 ° C is 200 to 500 ° C / h, the atmosphere is hydrogen-nitrogen, and the heat treatment (reoxidation treatment) after firing is the highest It is preferable that the temperature is 900 to 1100 ° C. and the atmosphere is nitrogen.

  Next, an external electrode paste is applied to the opposite ends of the capacitor body 1 and baked to form the external electrodes 3. A plating film is formed on the surface of the external electrode 5 in order to improve mountability.

In the multilayer ceramic capacitor of the present invention described above, the crystal grains 9 that make up the dielectric layer 5 are generally prone to grain growth by atomic diffusion during sintering, difficult to obtain a dense sintered body of fine particle size Is. In particular, when the raw material particle size to be used is smaller than submicron, the surface area occupies a large proportion with respect to the particle volume, and the surface energy is large, resulting in an energetically unstable state. For this reason, during firing, grain growth is caused by atomic diffusion, the surface area is reduced, and stabilization is caused by a reduction in surface energy. Therefore, grain growth is likely to occur, and it is difficult to obtain a dense sintered body made of fine particles.

Specifically, a sintered body of crystal particles 9 having a fine particle size smaller than 0.2 μm must be introduced between the particles, which easily causes solid solution and grain growth and suppresses the movement of atoms between the particles. For example, a sintered body having a large particle size exceeding 1 μm is formed, and it is difficult to obtain a dense sintered body having a fine particle size of submicron or less. However, in the present invention, together with microcrystalline material, close to the softening point is more sintering temperature, by thermal expansion coefficient selecting a smaller additional components than barium titanate, adjusting the calcination conditions, the raw material grains A fine particle sintered body reflecting the size can be obtained. In addition, when the element ratio on the A site side in barium titanate is increased, a large amount of barium is present on the particle surface, so that these barium diffuses on the particle surface and forms a liquid phase, thereby promoting sintering. In addition, the movement of additive component atoms such as Ba, Ti, Mg, Mn, and rare earth elements between BT crystal grains 9 that are present in the vicinity of and at the grain boundary is suppressed, and grain growth is suppressed.

  As a result, a crystal phase in which Mg and rare earth elements are diffused and dissolved in addition to barium is formed on the surface of the crystal particle 9. That is, a core-shell structure in which Mg and rare earth elements are unevenly distributed on the particle surface is formed. The formation of such a core-shell structure can be confirmed by observing these crystal particles 9 with a transmission electron microscope.

In the present invention, first, in order to confirm the effects of the softening point and the thermal expansion coefficient of the glass, the dielectric powder was formed into a tablet shape having a diameter of 12 mm and a thickness of 1 mm, and this was baked for evaluation. The results are shown in Table 1 as porcelain. Table 1 shows the average particle diameter of the barium titanate powder (BT powder) used, the molar ratio of barium to titanium ( A / B ratio ) , c / a ratio, addition amount, firing temperature, and glass composition. The dielectric powder used is Mg, based on 100 parts by mass of barium titanate powder.
Y and Mn were used by covering and containing 0.1, 1, and 0.2 parts by mass in terms of oxides. The amount of the glass component was 1 part by mass with respect to 100 parts by mass of the barium titanate powder. The molar ratio of barium to titanium in the BT powder used here (A / B ratio) was used 1.003 and 1.001.

  The softening point of the glass powder was measured by molding the glass powder into a tablet shape and using TG-DTA. The thermal expansion coefficient was measured in the range of room temperature to 300 ° C. using a thermal expansion coefficient measuring apparatus after forming glass powder into a tablet shape.

The dielectric powder was wet mixed by adding a mixed solvent of toluene and alcohol as a solvent using zirconia balls. Next, a mixed solvent of polyvinyl butyral resin and toluene / alcohol was added to the wet-mixed powder, and the mixture was wet-mixed using the same zirconia balls and compared to form a compact.

Then, the product layer ceramic capacitor was prepared as follows. The barium titanate powder and glass powder used were prepared from the above porcelain.

  This mixed powder was wet mixed by adding a mixed solvent of toluene and alcohol as a solvent using zirconia balls having a diameter of 5 mm. Next, a mixed solvent of polyvinyl butyral resin and toluene / alcohol was added to the wet-mixed powder, and wet-mixed using the same zirconia balls to prepare a ceramic slurry, and a ceramic green sheet having a thickness of 2 μm was prepared by a doctor blade method. . Next, a plurality of rectangular internal electrode patterns mainly composed of Ni were formed on the upper surface of the ceramic green sheet.

  Next, 100 ceramic green sheets on which the internal electrode patterns were printed were stacked, and 20 ceramic green sheets each having a thickness of 5 μm on which the internal electrode patterns were not printed were stacked on the upper and lower surfaces. The layers were laminated at a temperature of 10 ° C., a pressure of 107 Pa, and a time of 10 minutes, and cut into predetermined dimensions.

Next, the molded body and the laminated molded body formed from the powder are subjected to binder removal treatment at 300 ° C./h in the air at a temperature rising rate of 10 ° C./h, and the temperature rising rate from 500 ° C. is 300 ° C./h. calcination at 1140 to 1300 ° C. in hydrogen-nitrogen for 2 hours at a temperature increase rate of h, followed by cooling to 1000 ° C. at a temperature decrease rate of 300 ° C./h and reoxidation treatment at 1000 ° C. for 4 hours in a nitrogen atmosphere. Then, it was cooled at a temperature decreasing rate of 300 ° C./h to produce a capacitor body. The size of the capacitor body was 2 × 1 × 1 mm ³ and the thickness of the dielectric layer was 1.5 μm.

  Next, after the sintered electronic component body was barrel-polished, an external electrode paste containing Cu powder and glass was applied to both ends of the electronic component body, and baked at 850 ° C. to form external electrodes. Thereafter, using an electrolytic barrel machine, Ni plating and Sn plating were sequentially performed on the surface of the external electrode to produce a multilayer ceramic capacitor. The thickness of the dielectric layer of this multilayer ceramic capacitor was 1.5 μm.

Next, the following evaluation was performed on these multilayer ceramic capacitors. Rare earth elements in crystal grains that make up the dielectric layer of the present invention (Y) is the concentration gradient of 0.7 atomic% from the crystal grain surface a grain boundary layer is a particle surface as the highest concentration toward inside of the grain / nm That was all.

The unit cell volume ratio was measured using an X-ray diffractometer by collecting 30 capacitor bodies prepared, dividing all samples into two, collecting and setting them on a sample stage. Next, the capacitor body was pulverized so that the average particle size of the pulverized dielectric layer was 1 μm or less, and measured in the same manner.

  The temperature characteristics of the capacitance, relative permittivity, and relative permittivity were measured under the measurement conditions of a frequency of 1.0 kHz and a measurement voltage of 0.5 Vrms. The relative dielectric constant was calculated from the capacitance, the effective area of the internal electrode layer, and the thickness of the dielectric layer. The average particle size of the crystal particles constituting the dielectric layer was determined by a scanning electron microscope (SEM). The polished surface was etched, 20 crystal particles in the electron micrograph were arbitrarily selected, the maximum diameter of each crystal particle was determined by the intercept method, and the average value (D50) was determined.

As the evaluation of the grain boundary layer , it was separately measured using the AC impedance method. As high temperature load conditions in this case, the temperature was 250 ° C., and the voltage applied to the external electrode of the multilayer ceramic capacitor was 3V. The voltage during measurement was 0.1 V, the frequency was 10 mHz to 10 kHz, and the AC impedance before and after the treatment was evaluated for 30 samples.

As a comparative example, a glass powder having a softening point lower than 650 ° C. and a thermal expansion coefficient larger than 9.5 × 10 ⁻⁶ / ° C. was used to produce the same. The results are shown in Tables 1-4.

As is apparent from the results of Tables 1 to 4, in the sample of the present invention, the unit cell volume ratio is 1.0059 or more, the relative dielectric constant is 2010 or more, and the change rate of the relative dielectric constant is −19.8 to +14. It was 5%. Even when the same glass powder was used, the temperature characteristic of the dielectric constant decreased when the A / B ratio of the BT powder was large, and the relative dielectric constant was improved when c / a was large.

In contrast, in the case of a glass powder that is out of range with respect to the glass powder used to prepare the sample of the present invention, the unit cell volume ratio is 1.0039 or less and the relative dielectric constant is lower than 2000. Or the temperature characteristic of the relative permittivity was as large as −21% or more on the low temperature side.

In the multilayer ceramic capacitor as the sample of the present invention, the unit cell volume ratio is 1.0056 or more, the relative dielectric constant is 3030 or more, the temperature characteristic is −55 ° C. within −12.4%, and 85 ° C. It was within 6.7%, the temperature characteristics were good, and the rate of change in AC impedance was -0.43 % or less.

In contrast, in a multilayer ceramic capacitor having a dielectric layer formed using a glass powder having a softening point lower than 650 ° C. and a thermal expansion coefficient larger than 9.5 × 10 −6 / ° C., the unit The lattice volume ratio was 1.0048 or less, and the relative dielectric constant was lower than that of the multilayer ceramic capacitor as the sample of the present invention, and the temperature characteristics of the relative dielectric constant were large.

It is a longitudinal cross-sectional view of the multilayer ceramic capacitor of this invention. It is a schematic diagram showing the evaluation method of the grain boundaries of the resistance of the dielectric layer using the ac impedance measurements. It is representative of the resistance evaluation results of the grain boundary layer of the dielectric layer using the ac impedance measurements. It is a process diagram showing a process of a product layer ceramic capacitor.

DESCRIPTION OF SYMBOLS 1 Capacitor body 3 External electrode 5 Dielectric layer 7 Internal electrode layer 9 Crystal particle 21 Ceramic green sheet 23 Internal electrode pattern 25 Ceramic pattern 29 Laminate

Claims (4)

A multilayer ceramic capacitor comprising a capacitor body in which a plurality of crystal grains are sintered via a grain boundary layer and internal electrode layers are alternately laminated, and (a) the dielectric layer (B) a main component of the crystal particles is barium titanate, and (c) a lattice constant (a) determined from an X-ray diffraction pattern of the dielectric layer (a) , B, c) and a lattice constant (a, b, c) obtained from the volume V _bulk of the unit cell represented by the product of the above and the X-ray diffraction pattern of the crystal particles obtained by pulverizing the dielectric layer. multilayer ceramic capacitor of the ratio of the volume _{V powder} per unit cell is represented by the product, characterized by satisfying the relation of _V bulk _{/ V powder} ≧ 1.005. Claim wherein the barium A mole of barium titanate, when a titanium B mol, the molar ratio of barium and titanium, and satisfies the A / B ≧ 1 of relationships that make up the crystal grains 1. The multilayer ceramic capacitor according to 1. The multilayer ceramic capacitor according to claim 1 or 2 lattice constant ratio determined from X-ray diffraction pattern of the dielectric layer is characterized by satisfying the relation of c / a ≧ 1.005. The multilayer ceramic capacitor, the temperature higher than the Curie temperature indicated crystal grains mainly composed of the barium titanate constituting the dielectric layers, and, more than 1/3 of the rated voltage of the multilayer ceramic capacitor, the When exposed to a high temperature load atmosphere, the resistance reduction rate of the grain boundary layer in the dielectric layer was 0.5% / min. Multilayer ceramic capacitor according to any one of claims 1 to 3, wherein the or less.

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