JP4836509B2 - Dielectric porcelain - Google Patents

Description

The present invention relates to a dielectric porcelain suitably used for 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, the crystal grains constituting the dielectric layer Miniaturization has been performed.

  For example, in Patent Document 1 below, which focuses on glass particles, the dielectric material 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 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 multilayer ceramic capacitors, in order to improve the sinterability of dielectric ceramics, for example, as described in Patent Document 1, glass powder having a high silicon component content is used together with fine barium titanate powder. When such glass powder is used, local grain growth of the dielectric powder is induced, and the added glass component is easily dissolved in the dielectric powder. As a result, the relative dielectric constant of crystal grains that originally exhibit a high dielectric constant is lowered, and therefore, in a multilayer ceramic capacitor having such crystal grains, the capacitance is lowered and the temperature characteristics of the capacitance are increased. There was a problem.

Accordingly, the present invention aims at providing a very thin can be applied to the dielectric layer, a dielectric porcelain having a high dielectric constant stable temperature characteristics.

The dielectric ceramic of the present invention, crystal grains mainly composed of titanium barium is coupled via a configured grain boundary phase by auxiliary component containing silicon, containing magnesium, a rare earth element and manganese dielectric In the body porcelain, the average particle size of the crystal particles is 0.00. 05-0 . 19 Ri Ah in mu m, 0 when the BaTiO ₃ barium titanate, relative to the BaTiO ₃ 100 parts by weight of silicon in terms of SiO _2. 07 parts by mass , magnesium from 0.04 to 0.14 parts by mass in terms of MgO, rare earth elements from 0.1 to 1.5 parts by mass in terms of RE ₂ O ₃ , and manganese from 0.02 to 0.3 in terms of MnO The total amount of silicon, magnesium, rare earth elements and manganese in terms of oxides is 2 parts by mass or less, and the crystal grains have a core-shell structure having the silicon on the surface side. It is characterized by having.

In the above dielectric ceramic, the concentration of silicon in the grain boundary phase center portion between front Symbol crystal grains CGB, the concentration of silicon when the CGR at the position of distance 3nm from the interface of the crystal grains, CGB / CGR It is desirable to satisfy the relationship of ≧ 10 . Further, in the dielectric ceramic, pre-Symbol barium A mole of barium titanate constituting the crystal grains, when the titanium B mole, the molar ratio A / B is 1.003 or more der Rukoto is desirable. Further, in the above dielectric ceramic, the lattice constant ratio c / a of the crystal grains is desired is 1.005 der Rukoto.

According to the onset bright, dielectric ceramic having a temperature profile of an average even grain size is not more 0.2μm or less, high have dielectric constant and stable dielectric constant of the crystal grains mainly composed of barium titanate Ru can be obtained.

FIG. 1 is a schematic diagram showing the internal structure of a dielectric ceramic according to the present invention. The dielectric porcelain of the present invention has a crystal grain 1 ( hereinafter sometimes referred to as BT crystal grain) containing barium titanate as a main component through a grain boundary phase 3 composed of subcomponents containing silicon. The dielectric ceramic is bonded and contains magnesium, rare earth element and manganese, and the average grain size of the crystal grains 1 is 0.00. 05-0 . Oh Ru in 19 μ m. The maximum grain size of crystal grains 1 that put the present invention is is preferably 0.3μm or less when expressed in D90. D90 is a 90% cumulative cumulative value by mass in the particle size distribution. In the present invention, the average particle diameter is D50 (50% cumulative cumulative value).

Further, the dielectric ceramic of the present invention, when the BaTiO ₃ of titanium barium, and pair to the BaTiO ₃ 100 parts by weight, 0 to silicon in terms of SiO _2. Ru 07 parts by weight of Der. Thus, by reducing the content of silicon ( SiO ₂ ) (hereinafter, silicon may be expressed as Si) contained in the dielectric ceramic, the solid solution amount of Si in the crystal particles 1 is reduced. In addition, it is possible to suppress a decrease in the dielectric constant of the crystal particle 1. In particular, as in the present invention, the dielectric ceramic has an average particle size of 0. 19 [mu] m or less, when the D90 is constituted by the following pole Umate fine crystal grains 1 0.3 [mu] m, reduction of the Si component has good in terms of improving the dielectric constant.

In the dielectric ceramic of the present invention, silicon, magnesium, the total amount of rare earth elements and manganese were converted respectively oxide Ru der than 2 parts by weight when the B ATiO ₃ 100 parts by mass. By reducing the subcomponent amount to be added in this manner to BaTiO _3, it can be reduced amount of solid solution S i other than components of the crystal grains 1, thereby making it possible to high dielectric constant of the dielectric ceramic it can.

Further, the dielectric ceramic of the present invention, the concentration of silicon in the central portion of the grain boundary phase 3 between the crystal grains 1 CGB, the concentration of silicon in the position of the distance 3nm from the interface of the crystal grains 9 when the CGR It is desirable to satisfy the relationship of CGB / CGR ≧ 10. If the silicon concentration gradient is in such a condition, the X5R standard can be satisfied in terms of improvement of the dielectric constant and its temperature characteristics. The concentration gradient of silicon can be measured by an analyzer attached to the transmission electron microscope.

The dielectric ceramic of the present invention contains magnesium ( Mg ) , rare earth element (RE), and manganese ( Mn ) . In this case, the content of Mg, rare earth element and Mn contained in the BT crystal particles is 0.04 to 0.14 parts by mass in terms of Mg ₂ O , and RE ₂ O _{3 in} terms of 100 parts by mass of the BT crystal particles. 0.1 to 1.5 parts by mass , 0.02 to 0.3 parts by mass in terms of Mn 2 O.

These Mg, a rare earth element and Mn from Do Rukoto to sintering aid, these elements are a solid solution portion in one crystal grain, a lot existing in the grain boundary phase 3.

In the dielectric ceramic of the present invention, Mg and rare earth elements are components having a crystal shell core-shell structure, while Mn is a component that compensates for oxygen defects in the BT crystal particles generated by firing in a reducing atmosphere , and is insulated. And high temperature load life can be improved.

In the dielectric ceramic according to the present invention , similarly to the Si component, the grain boundary phase 3 where the rare earth element is the particle surface has the highest concentration, and there is a concentration gradient from the surface of the crystal particle 1 to the inside of the particle.
And it is, its concentration gradient to be 0.05 atomic% / nm or more preferably, made thereby to be satisfactory dielectric constant and X 5R standards as a capacity-temperature characteristics with improved high-temperature load life. Here, the rare earth element in the present invention is preferably at least one of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Y, Er, Tm, Yb, Lu, and Sc.

As described above, crystal grains 1 for composing the dielectric ceramic of the present invention, have a core-shell structure which is eccentrically distributed is S i on the particle surface than the particle center, for this, a high dielectric constant and high insulating properties Doo ing. In this case, the dielectric constant of the dielectric ceramic is preferably 1400 or more, particularly 2000 or more.

Further, the crystal grain 1 constituting this dielectric ceramic has a lattice constant ratio c 1 / a of 1.005.
It is desirable that the above be achieved, whereby a high dielectric constant can be obtained. That is, the crystal grains 1 composed mainly of barium titanate lattice constant ratio c / a to c / a ≧ 1.005 Thus, the proportion of tetragonal crystal grains 1 Ri heightened, cubic opposite Since the ratio is reduced, the dielectric constant of the crystal particle 1 itself can be increased. In addition the present invention is, in barium titanate constituting the crystal grains 1, barium A mol, and the molar ratio A / B is 1.003 or more der Rukoto is desirable when the titanium and B moles, such Further, by defining the A / B ratio as described above, the grain growth of the crystal grains 1 can be suppressed, and the temperature characteristics of the relative dielectric constant can be stabilized.

Thus, by using the dielectric ceramic of the present invention having fine particles and a high dielectric constant , a small and high capacity multilayer ceramic capacitor can be obtained.

  FIG. 2 is a schematic cross-sectional view showing a multilayer ceramic capacitor. In the multilayer ceramic capacitor formed using the dielectric ceramic of the present invention, external electrodes 13 are formed at both ends of the capacitor body 11. The external electrode 13 is formed, for example, by baking Cu or an alloy paste of Cu and Ni. The capacitor body 11 is configured by alternately laminating dielectric layers 15 and internal electrode layers 17. The dielectric layer 15 is composed of the dielectric ceramic of the present invention.

  The thickness is preferably 2 μm or less, particularly 1 μm or less in order to reduce the size and capacity of the multilayer ceramic capacitor. Furthermore, in the present invention, it is more desirable that the thickness variation of the dielectric layer 15 is within 10% in order to stabilize the capacitance variation and capacitance temperature characteristics.

  The internal electrode layer 17 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 17 is highly laminated, and in particular, simultaneous firing with the dielectric layer 15 according to the present invention is possible. Nickel (Ni) is more preferable in that it can be achieved.

To the next, it will be described in detail preparation of dielectrics porcelain. Preparation of dielectrics porcelain is also the you fired by molding the mixed powder to a Jo Tokoro of the shape of the composite oxide powder of titanic acid Barium Powder and a plurality of metal oxides.

Ruchi Tan barium powder used in this method (hereinafter sometimes to BT powder) is a raw material powder represented by BaTiO _3. 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 the BT powder Among obtained, BT powder obtained by hydrothermal synthesis because of high crystallinity is preferable.

The average particle size of the powder dielectric powder mainly composed of titanium acid Barium is area by der of 0.05 to 0.15 .mu.m. When the average particle diameter of the BT powder is smaller than 0.05 μm, the relative dielectric constant is originally low or the grains grow easily and it becomes difficult to control the particle diameter during firing. When the thickness is larger than 0.15 μm, the insulating property is lowered when the dielectric layer is thinned, and the surface of the dielectric layer 5 cannot be flattened. The composite oxide preferably has the same particle size as the barium titanate powder from the viewpoint of dispersibility and sintering speed. Incidentally, barium powder titanium acid, by performing the calcination of a plurality of times in the synthesis time, Ru can be fine powders increase the proportion of tetragonal. In this case, c / a is preferably at 1.003 or more.

Also, as the composite oxide used, but a melting point Ru with more than 1000 ° C., in this case,
It is desirable to use two or more complex oxides having different melting points. In particular, it is preferable that one of the two complex oxides has a melting point of 1000 ° C. or higher. When the composite oxide is a mixture of two or more of different melting points, the composite oxide having a melting point of 1000 ° C. or higher suppresses the solid solution of the additive component in the barium titanate powder, and each composite oxide has a melting point. Since it acts as a sintering aid from the vicinity, it becomes possible to sinter the porcelain in a wide temperature range.

  On the other hand, when the melting point of the composite oxide is lower than 1000 ° C., when the average particle diameter of the dielectric powder such as barium titanate is extremely small, the additive component to the dielectric powder is likely to be solid-dissolved during firing. For this reason, grain growth of the dielectric powder occurs, and there arises a problem that the insulating layer as a thin dielectric layer and the temperature characteristics of the relative dielectric constant cannot be satisfied.

Further, if added melting point of one or more purposes solid solution suppresses the double if more oxide 1000 ° C., by mixing the different composite oxide melting point, in a wide temperature range, it is possible to obtain a high ceramic density it can. For example, by adding a composite oxide having a low melting point, the firing temperature range can be widened to the low temperature side. On the contrary, if a complex oxide having a high melting point is added, the firing temperature range can be widened to the high temperature side. That is, by using two or more composite oxides having different melting points, the firing temperature range can be made wider than when added alone, and the change in the sintered density due to the firing temperature can be reduced. At the same time, the rate of change due to the firing temperature can be reduced for the relative dielectric constant and its temperature characteristics.

Usually, the particle size of the barium titanate powder is 0.05～0.15Myu m, because higher sintering of barium titanate itself, in the case of adding a low melting point sintering aids, the sintering property is promoted is, the grain boundaries of growth and core-shell structure of the powder particles is disrupted intends want.

In contrast, when the melting point is added a composite oxide of more than 1000 ° C. is barium titanate
Since it is possible to suppress the sintering of the beam powder itself, it is possible to suppress the destruction of growth and core-shell structure between the barium titanate powder. Thereby, since a core-shell structure can be formed with a small amount of additive, a dielectric ceramic having a high relative dielectric constant can be provided.

The dielectric ceramic according to the present invention thus obtained has a high dielectric constant. For example, when barium titanate having an average particle diameter of 0.1 μm is used, the relative dielectric constant ε (20 ° C.) at 20 ° C. is 1900 or more, and the temperature change rate TCC can be within ± 15%. .

As the composite oxide having a melting point of 1000 ° C. or higher, for example, Ba 2 O = 40 to 70% by mass, CaO = 20 to 40% by mass, and SiO ₂ = 5 to 30% by mass are suitable. As a high-melting-point composite oxide, the melting point can be changed by appropriately adjusting the above composition and the mixing ratio of two or more kinds of composite oxides. It is preferable in that it has a melting point and hardly forms a liquid phase.

Further, in this dielectric ceramic manufacturing method , it is desirable to add terbium oxide together with the composite oxide to the barium titanate powder. Terbium (Te) having a relatively large ionic radius is easily dissolved in barium titanate, so that the amount of terbium (Te) can be reduced. Thereby, the shell layer having a relatively low dielectric constant, which is a reaction layer with barium titanate, can be thinned, and the relative dielectric constant of the dielectric ceramic can be improved. At the same time, since it is possible to suppress the sintering property by melting point be added a composite oxide of more than 1000 ° C., it becomes possible to suppress the destruction of growth and core-shell structure between the barium titanate powder. As a result, a core-shell structure can be more easily formed even when terbium that is relatively easily dissolved is used, and a dielectric ceramic having a high relative dielectric constant can be provided. In this case, terbium element is added in pressurized our basic Te ₂ O _3.

Further, in the method of the dielectric ceramic state, and are able is preferable from the viewpoint of improving characteristics such as grain growth inhibition and insulating adding Mg to the barium titanate powder, oxides of rare earth elements and Mn, rare earth elements Is preferably a combination of Y and Tb. In this case, Y has the effect of increasing the relative dielectric constant of the dielectric ceramic.

The amount of the component added to the BT powder is 0.04 to 0.14 parts by mass of Mg 2 O and 0.1 to 1.5 parts by mass of the rare earth element oxide with respect to 100 parts by mass of the BT powder. It is preferable that the oxide of Mn is 0.04 to 0.3 parts by mass .

The addition amount of the composite oxide, with respect to barium titanate Powder 1 00 parts by weight, preferably from 0.3 to 2 parts by weight, thereby it is possible to increase the sinterability and dielectric constant of the porcelain It becomes .

Titanium barium powder, barium A mole of barium titanate, when a titanium B moles, but is preferably is 1.003 or more molar ratio A / B, such barium titanate powder , obtained by fixing the carbon dioxide barium powder on the surface of the barium titanate powder, thereby Ru can suppress grain growth.

Then, the mixed powder obtained by mixing additives such as a composite oxide with respect to titanium barium powder was molded into a predetermined shape, the molded body under a predetermined atmosphere, the dielectric ceramic was fired at a temperature Is formed.

The firing temperature is in the range of 1100 to 1300 ° C., the holding time at the maximum temperature is 2 to 3 hours, and the atmosphere is hydrogen in that a base metal can be used as an internal electrode layer when making a multilayer ceramic capacitor. -Nitrogen is preferred. Heat treatment after firing (reoxidation treatment)
It is preferable that the maximum temperature is 900 to 1100 ° C. and the atmosphere is nitrogen.

Crystal grains 1 which is based on titanium barium powder is generally prone to grain growth by atomic diffusion during sintering, in which difficult to obtain a dense sintered body of fine particle size. 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, the sintered body of crystal particles 1 having a microparticle size smaller than 0.15 μm must be introduced between the particles so as to easily cause solid solution or grain growth and suppress 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 the microcrystalline raw material, an additive component whose melting point is closer to the sintering temperature, or an additive component whose melting point is close to the sintering temperature and having a different melting point, and further adjusting the firing conditions, A fine particle sintered body reflecting the size of the raw crystal particles can be obtained. In addition, when the element ratio on the A site side is increased in barium titanate, the presence of a large amount of barium on the particle surface promotes sintering by diffusing the barium to the particle surface to form a liquid phase, Grain growth is suppressed by suppressing the movement of additive component atoms such as Ba, Ti, Mg, Mn, and rare earth elements in the vicinity of the grain boundary and between crystal grains that are the parent phase existing in the grain boundary.

  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 side of the crystal particles 1. 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 1 with a transmission electron microscope.

By using a mixed powder containing a titanium barium and composite oxides to form a green sheet, the internal electrode pattern is formed on the main surface of the green sheet, the green sheet forming the internal electrode pattern were stacked, laminated It goes without saying that a multilayer ceramic capacitor having the dielectric ceramic according to the present invention as a dielectric layer can be formed by forming a body and firing at the above temperature conditions.

FIG. 4 is a schematic diagram showing the internal structure of another dielectric ceramic. This dielectric ceramic is composed of crystal particles 1 (BT crystal particles) mainly composed of barium titanate, and barium titanate crystal particles (BCT crystal particles) 11 containing calcium between the barium titanate crystal particles. Thus, a dielectric ceramic having excellent dielectric characteristics can be formed even with such composite crystal particles. In this case, the amount of silicon in the dielectric ceramic is obtained by calculating the total amount of BT crystal particles and BCT crystal particles with respect to 100 parts by mass in terms of SiO ₂ .

That is, the part containing calcium crystal grains mainly composed of titanium barium, when expressed barium titanate containing calcium in formula _{Ba 1-x Ca x TiO 3} , X = 0. It is desirable that it is 02-0.1.

When X is 0.02 or more, is an advantage that crystal grains mainly composed of barium titanate-dependent increases by AC bias dielectric constant by solid solution of Ca, the order can increase the specific dielectric constant is there.

If X is 0.1 or less, it is less than the solid solubility limit of Ca in barium titanate, and it is difficult to form different crystal phases. Therefore, the ratio of the crystal phase effective for the high dielectric constant of the dielectric ceramic increases. For this reason, there exists an advantage that a dielectric constant can be improved.

Further, the dielectric ceramic of this, highly crystalline particles of Ca component concentration in the other case that exist between low BT crystal grains of Ca component concentration, high crystal grains of this Ca component concentrations as compared to the BT crystal grain In the case of extremely fine particles, it is desirable to form a grain boundary phase between crystal grains having a low Ca component concentration. Ca component concentration high crystal grains has the advantage of improving the sinterability of the C a component concentration of less crystal grains due to the low melting point than the original Ca component concentration of less crystal grains. In such a dielectric ceramic, the average concentration of Ca contained in main crystal particles with respect to Ba is 1 mol% or more at a position of a distance of 3 nm from the interface of the crystal particles.

Also in the dielectric ceramic made of crystal particles containing calcium, as in the case of dielectric ceramics composed of crystal grains containing no calcium, the crystal reasons of insulation gains associated with thinning of the dielectric layer the average particle diameter of the particles is 0.11 to 0.2 [mu] m, it is desirable that D90 is 0.3μm or less. Here, D90 means the value of the particle size at 90% accumulation from the small particle size in the particle size distribution measurement. For the dielectric ceramic, the average particle diameter and D90 are obtained from image of the crystal structure obtained by observation with an electron microscope, and an arbitrary number of crystal particles existing in the unit area are obtained by image analysis.

In this dielectric ceramic, the Si concentration in the grain boundary phase is preferably below the detection limit. Thus, when the Si concentration in the grain boundary phase is low, the relative permittivity of the grain boundary phase itself is increased, and therefore the dielectric The relative dielectric constant of the body porcelain can be naturally increased.

Also in the dielectric ceramic having crystal grains of a barium titanate containing calcium, like the above-described BT crystal grains, Mg in the crystal grains, it is possible to include a rare earth element and Mn, the If, it is desirable that the same amount as the BT crystal grains, the effect is also Ru can be obtained the same effect as the BT crystal grains.

Also in the dielectric ceramic having a B CT crystal grains 11, as in the case of BT crystal grains 1, B CT crystal grains 11 form a core-shell structure in which S i is unevenly distributed in the grain surface side than the particle centers and As a result, it has a high dielectric constant and high insulating properties. The dielectric constant of the dielectric ceramic is preferably 1500 or more, particularly 2000 or more.

Furthermore, it is desirable for the dielectric ceramic having the BCT crystal particles 11 described above to have a lattice constant ratio c / a of 1.005 or more, whereby a high dielectric constant can be obtained. In addition, in the barium titanate constituting the BCT crystal grains 11, A mole of barium, and titanium when the B mole, the molar ratio A / B is not to desirable at 1.003 or more. By defining the molar ratio A / B as described above, the grain growth of the BCT crystal particles 11 can be suppressed, and the temperature characteristics of the relative dielectric constant can be stabilized. In this case, it is desirable that the barium titanate BT crystal particles 1 not containing calcium also have a relationship of A / B ≧ 1.003 in terms of suppression of grain growth.

The dielectric ceramic having a B CT crystal grains 11, the powder (BT powder) composed mainly of barium titanate, barium calcium titanate was replaced with calcium part of barium in barium titanate (BCT powder) When the barium titanate containing calcium is represented by the chemical formula Ba _1-x Ca _x TiO ₃ , X = 0.02 to 0.15. It is preferable.

In this case, it is desirable that the average particle diameter of the BCT powder is smaller than the average particle diameter of the BT powder. For example, when the average particle diameter of the BT powder is 0.05 to 0.15 μm, the average particle diameter of the BCT powder is Is 0.05 μm or less, the BCT powder can also be used as a sintering aid in the sintering of the BT powder.

  In the present invention, first, in order to confirm the melting point of the composite oxide to be used, various composite oxides are formed into a tablet shape having a diameter of 12 mm and a thickness of 1 mm, and this is fired and evaluated using a differential thermal analysis (DTA) apparatus. did. The composition and melting point results are shown in Table 1.

In addition, Table 2 shows the average particle diameter of the barium titanate powder used, the sintering aid and its addition amount, the firing temperature, and the characteristics of the dielectric ceramic. Barium titanate powder used per 100 parts by mass of the barium titanate powder was Mg _O, it is contained by adding _{Y 2} O 3, Mn O respectively 0.3,0.7,0.2 parts by . In the sample shown in Table 6, instead of Y, Tb was added in an amount shown in Table 6. The BT powder used here had a molar ratio A / B of 1.003 and c / a = 1.005.

The above mixed powder was wet mixed using a zirconia ball having a diameter of 5 mm and a mixed solvent of toluene and alcohol as a solvent. Next, a mixed solvent of polyvinyl butyral resin and toluene / alcohol is added to the wet-mixed powder, and wet-mixed using a zirconia ball having the same diameter of 5 mm to form a tablet with a diameter of 16 mm and a thickness of 1 mm. A sample was prepared by firing in the air. The electrodes were formed by applying In—Ga electrodes on the upper and lower surfaces of the tablet.

  Next, the average particle diameter of the crystal particles constituting the dielectric ceramic 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.

Next, the dielectric ceramic was polished to a thickness of 400 μm, and In—Ga was applied to the upper and lower surfaces of the sample to form electrodes. For the electrical characteristics, the relative dielectric constant was calculated by measuring the capacitance under the conditions of AC: 1 V and measurement frequency: 1 kHz in the temperature range of −25 ° C. to 85 ° C. using an LCR meter. The temperature change rate TCC of the relative dielectric constant was determined from the following formula: TCC (%) = {ε (T) −ε (20 ° C.)} × 100 / ε (20 ° C.). The reference temperature is 20 ° C. The concentration of silicon at the center of the grain boundary phase between crystal grains and the position at a distance of 3 nm from the interface of the crystal grains was determined by an analyzer attached to a transmission electron microscope (FIG. 3 shows (a) conventional, (b) It is a graph which shows the density | concentration distribution of the silicon | silicone in dielectric ceramic of invention. The results are shown in Tables 1-6. Sample numbers 22 to 25, 26, 27, and 29 to 31 in Table 4, Table 5, and Table 6 are reference examples.

Table 1 As is apparent from the results of 6, specimen of the present invention No. In 7-10, the rate of change of the dielectric constant was also all within ± 15% will -7.1～-11.7% at 85 ° C. and 125 ° C.. In addition, the sample (No. 7) of the present invention has CGB as the silicon concentration at the center of the grain boundary phase between crystal grains, and CGR as the silicon concentration at a distance of 3 nm from the interface of the crystal grains. CGB / CGR = 17, and the diffusion of the Si component was suppressed as compared with the sample (No. 13) using the composite oxide having a melting point of 900 ° C.

  Further, as is apparent from the results of Tables 4 and 5, the dielectric according to the present invention obtained by adding a predetermined amount of complex oxides having different melting points to barium titanate powder having an average particle size of 0.1 μm. In the porcelain (sample No. 22.24), the temperature range in which the firing density is 5.75 g / cm 3 or more can be widened, the relative dielectric constant is 1440 to 1700, and the temperature characteristic of the relative dielectric constant is the highest at 85 ° C. It was within -14.8% even at -9.4% and 125 ° C.

  Further, as apparent from the results in Table 6, in the dielectric ceramic in which 0.4 parts by mass of terbium oxide is added instead of yttrium oxide together with the composite oxide having a melting point of 1220 ° C., the average particle diameter of the barium titanate powder Is 0.05 to 0.15 μm, the crystal grain size is 0.17 μm or less, the sintered density of the dielectric ceramic is 5.7 or more, and the relative dielectric constant is high (1450 or more when the average particle size is 0.1 μm). ), The change rate of the dielectric constant was −7.5% at 85 ° C. and −14.3% at 125 ° C., both of which were within ± 15%.

On the other hand, the sample outside the range of the present invention had a temperature change rate of the relative dielectric constant of ± 15% or did not satisfy the crystal grain size defined in the present invention.

If the melting point using a composite oxide of less than 1000 ° C., either an average grain size of crystal grains is greater than 0.2 [mu] m, or the dielectric constant is large but the temperature change rate of the relative dielectric constant ± 15 % Was off.

It is a schematic diagram which shows the internal structure of the dielectric material ceramic of this invention. It is a longitudinal cross-sectional view of a multilayer ceramic capacitor. It is a graph which shows the density | concentration distribution of the silicon in a dielectric ceramic of (a) conventional manufacturing methods and (b) this invention. It is a schematic diagram which shows the internal structure of another dielectric ceramic.

1 Crystal grain 3 Grain boundary phase 11 BCT crystal grain

Claims (4)

In the dielectric ceramic containing magnesium, rare earth element and manganese, crystal grains mainly composed of barium titanate are bonded through a grain boundary phase constituted by silicon-containing subcomponents.
The average grain size of the crystal grains is 0. 05-0 . Ri Oh in 19 μ m,
When the barium titanate is BaTiO ₃ , the silicon is converted to SiO _{2 in} terms of SiO ₂ with respect to 100 parts by mass of the BaTiO ₃ . 07 parts by mass , magnesium from 0.04 to 0.14 parts by mass in terms of MgO, rare earth elements from 0.1 to 1.5 parts by mass in terms of RE ₂ O ₃ , and manganese from 0.02 to 0.3 in terms of MnO The total amount of the silicon, magnesium, rare earth element and manganese in terms of oxides is 2 parts by mass or less while being contained in a proportion by mass.
The dielectric ceramic according to claim 1, wherein the crystal particles have a core-shell structure having the silicon on the surface side . The concentration of silicon in the grain boundary phase center portion between the crystal grains CGB, the concentration of silicon when the CGR at the position of distance 3nm from the interface of the crystal grains, to satisfy the relationship of CGB / CGR ≧ 10 The dielectric ceramic according to claim 1 . 3. The dielectric according to claim 1, wherein the molar ratio A 2 / B is 1.003 or more , where barium of barium titanate constituting the crystal particles is A mol and titanium is B mol. Body porcelain. The dielectric ceramic according to any one of claims 1 to 3 , wherein a lattice constant ratio c 1 / a of the crystal grains is 1.005 or more .

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