JP2008239402A - Dielectric ceramic and stacked ceramic capacitor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dielectric ceramic having a high dielectric constant, excellent in stability of temperature characteristic of specific dielectric constant, and having a small voltage dependence of insulation resistance, and to provide stacked ceramic capacitor equipped with such dielectric ceramic as a dielectric layer, and excellent in life characteristic tested under high temperature load. <P>SOLUTION: The dielectric ceramic has: crystalline particles with a core shell structure where barium titanate is a major component and calcium, vanadium, magnesium, manganese, and at least one kind of rare earth element selected from yttrium, dysprosium, holmium, erbium and terbium are solid solubilized; and an intergranular phase present between the crystal grains. By incorporating specific ratio of vanadium, magnesium and rare earth element and manganese to set Curie temperature in the range of 95-105°C, the dielectric ceramic having a high dielectric constant, a small temperature changing rate of the specific dielectric constant a small voltage dependency of the insulation resistance can be obtained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a dielectric ceramic composed of crystal particles mainly composed of barium titanate and a multilayer ceramic capacitor using the dielectric ceramic as a dielectric layer.

  In recent years, with the widespread use of mobile devices such as mobile phones and the high speed and high frequency of semiconductor devices, which are the main components of personal computers and the like, multilayer ceramic capacitors mounted on such electronic devices are required to be smaller and have higher capacities. The dielectric layer constituting the multilayer ceramic capacitor is required to be thin and highly multilayered.

  By the way, as a dielectric ceramic for a dielectric layer constituting a multilayer ceramic capacitor, a dielectric constant material mainly composed of barium titanate (hereinafter referred to as barium calcium titanate) in which calcium is dissolved is used. It has been. Recently, oxide powders of magnesium and rare earth elements have been added to this barium calcium titanate powder, and magnesium and rare earth elements are further dissolved in the vicinity of the surface of crystal particles mainly composed of barium calcium titanate. In addition, dielectric ceramics composed of so-called core-shell structured crystal particles have been developed and put to practical use as multilayer ceramic capacitors (see, for example, Patent Document 1).

Here, the core-shell structure of the crystal particle means a structure in which the core part which is the center part of the crystal particle and the shell part which is the outer shell part form physically and chemically different phases, and barium titanate. As for crystal grains mainly composed of barium calcium titanate, the core part is occupied by barium titanate or barium calcium titanate having a tetragonal crystal structure, and the shell part has a cubic crystal structure. The state occupied by barium titanate or barium calcium titanate.
JP 2000-58377 A JP 2004-79686 A

  However, dielectric ceramics composed of core-shell structured crystal particles as described above are excellent in relative permittivity and stability of temperature characteristics of relative permittivity, but are applied with a DC voltage to the dielectric ceramic. When the DC voltage is increased, the insulation resistance is lowered (hereinafter referred to as voltage dependency of the insulation resistance).

  As described above, a multilayer ceramic capacitor including a dielectric ceramic composed of core-shell structured crystal particles as a dielectric layer has a high temperature due to the voltage dependence of the insulation resistance as described above in the dielectric ceramic. It has been difficult to improve the life characteristics in the load test.

  Accordingly, the present invention is provided with a dielectric ceramic having a high dielectric constant and excellent stability of the temperature characteristic of a relative dielectric constant and having a small voltage dependency of insulation resistance, and such a dielectric ceramic as a dielectric layer, An object of the present invention is to provide a multilayer ceramic capacitor having excellent life characteristics in a test.

  The dielectric ceramic of the present invention is mainly composed of barium titanate, and calcium, vanadium, magnesium, manganese, and at least one rare earth element selected from yttrium, dysprosium, holmium, erbium and terbium are solid. A dielectric ceramic having melted core-shell structure crystal grains and a grain boundary phase existing between the crystal grains, wherein the crystal grains have a calcium concentration of 0.4 atomic% or more, and the barium titanate Is 0.1 to 0.2 mol in terms of oxide, magnesium is 0.55 to 0.75 mol in terms of oxide, yttrium, displo At least one rare earth element selected from oxides of sium, holmium, erbium and terbium .55～0.75 mol, and manganese were 0.25 to 0.6 moles contained in terms of the oxide, the Curie temperature is characterized by a 95 to 105 ° C..

  The dielectric ceramic preferably contains 0.25 to 0.35 mol of the manganese in terms of oxide.

  In the dielectric ceramic, it is preferable that an average particle diameter of the crystal particles is 0.25 to 0.35 μm.

  Next, the multilayer ceramic capacitor of the present invention is characterized in that it is composed of a laminate of a dielectric layer made of the above dielectric ceramic and an internal electrode layer.

  According to the dielectric ceramic of the present invention, calcium, vanadium, magnesium, rare earth element and manganese are contained in a predetermined ratio with respect to barium titanate, respectively, and the dielectric ceramic crystal particles have a core-shell structure with a Curie temperature. Is within the range of 95 to 105 ° C., the temperature change rate of the dielectric constant and the dielectric constant can be reduced, and the decrease in insulation resistance when a voltage is applied is small (the voltage dependence of the insulation resistance is small). ) A dielectric ceramic can be obtained.

  Moreover, when 0.25 to 0.35 mol of manganese in terms of oxide is contained in the dielectric ceramic of the present invention, a dielectric ceramic having almost no voltage dependency of insulation resistance can be obtained.

  In addition, when the average particle size of the crystal grains mainly composed of barium titanate is 0.25 to 0.35 μm, the dielectric ceramic according to the present invention has an insulating property within a predetermined range of applied DC voltage. It is possible to obtain a dielectric ceramic showing a tendency to increase.

  Also, according to the multilayer ceramic capacitor of the present invention, by applying the above dielectric ceramic as the dielectric layer, high insulation can be secured even if the dielectric layer is thinned. In addition, it is possible to obtain a multilayer ceramic capacitor having excellent life characteristics.

  The dielectric porcelain of the present invention has a substantially core-shell structure, is mainly composed of barium titanate, and is composed of calcium, vanadium, magnesium, manganese, yttrium, dysprosium, holmium, erbium and terbium. It has crystal grains in which at least one kind of rare earth element is dissolved, and a grain boundary phase existing between the crystal grains, and vanadium is converted to oxide in terms of oxide with respect to 100 mol of the total amount of barium and calcium. 1 to 0.2 mol, magnesium 0.55 to 0.75 mol in terms of oxide, and at least one rare earth element among yttrium, dysprosium, holmium, erbium and terbium 0.55 in terms of oxide It contains 0.75 mol and 0.25 to 0.6 mol of manganese in terms of oxide.

  In the dielectric ceramic according to the present invention, it is important that the Curie temperature is 95 to 105 ° C. In the present invention, the Curie temperature is a temperature at which the relative dielectric constant becomes maximum in the range (−60 to 150 ° C.) in which the temperature characteristic of the relative dielectric constant is measured.

In the above composition and Curie temperature range, the relative dielectric constant at room temperature (25 ° C.) can be 3300 or more, and the temperature characteristic of the relative dielectric constant is X5R (with respect to 25 ° C. in the temperature range of −55 to 85 ° C.). The rate of change of the dielectric constant is within ± 15%), and further, the insulation resistance can be increased to 10 ¹⁰ Ω or more when the value of the DC voltage applied per unit thickness (1 μm) is 12.5 V There is.

  FIG. 1A is a schematic cross-sectional view of a crystal particle mainly composed of barium titanate having a core-shell structure constituting the dielectric ceramic of the present invention. FIG. 1B is a cross-sectional view of FIG. It is the schematic diagram which showed the density | concentration change of rare earth elements and magnesium.

  As can be seen in FIGS. 1A and 1B, the crystal particles constituting the dielectric ceramic of the present invention were formed around the core portion 1 mainly composed of barium titanate and around the core portion 1. It is comprised from the shell part 3 which has barium titanate as a main component.

  In the crystal particles, calcium, vanadium, magnesium, rare earth elements and manganese are solid-dissolved. In particular, when the solid solution state of magnesium and rare earth elements is seen, the shell portion 3 is more magnesium or rare earth elements than the core portion 1. The concentration gradient is high.

  As shown in FIG. 1B, the concentration change of rare earth elements and magnesium from the outermost surface SS of the crystal particles toward the core portion 1 side is directed from the surface S of the core portion 1 toward the center portion C of the core portion 1. It is larger than the concentration change of rare earth elements and magnesium.

  In the crystal particle having the core-shell structure constituting the dielectric ceramic of the present invention, the concentration change of the rare earth element and magnesium in the shell part 3 is 0.05% from the outermost surface SS to the inside, with the outermost surface SS of the crystal particle being the highest concentration. On the other hand, the core portion 1 has a concentration change of at least atomic% / nm, while the core portion 1 has a concentration change of rare earth elements and magnesium smaller than that of the shell portion 3. This measurement is performed using a transmission electron microscope apparatus provided with elemental analysis equipment. In this case, the concentration change of the rare earth element or magnesium can be determined by performing elemental analysis using an energy dispersive analyzer (EDS) at a predetermined interval from the surface side of the crystal particle to the center portion C.

  In the dielectric ceramic according to the present invention, part or all of at least one rare earth element selected from calcium, vanadium, magnesium, manganese, and yttrium, dysprosium, holmium, erbium, and terbium with respect to barium titanate. In addition, the Curie temperature of the dielectric ceramic formed by crystal grains mainly composed of barium titanate in which these components are dissolved is 95 to 105 ° C., and the Curie temperature is shifted to the room temperature side.

  This makes it possible to increase the dielectric constant of conventional dielectric ceramics having crystal grains mainly composed of barium titanate having a core-shell structure with a Curie temperature around 140 ° C., and having a core-shell structure. In comparison with the prior art, the ratio of the core portion 1 is decreased and the volume ratio of the shell portion 3 is increased. As a result, a dielectric ceramic having a high insulation resistance can be obtained.

  This is because the barium titanate forming the core portion 1 has a small amount of solid solution of magnesium and rare earth elements, so that the crystal grains contain many defects such as oxygen vacancies. For this reason, when a DC voltage is applied, oxygen vacancies or the like are likely to be carriers that carry electric charges in the crystal grains constituting the dielectric ceramic, which causes a decrease in the insulation of the dielectric ceramic.

  On the other hand, the dielectric ceramic according to the present invention reduces the carrier density such as oxygen vacancies derived from barium titanate forming the core part 1 by reducing the ratio of the core part 1 in the crystal grains. It is considered that a high insulating property can be obtained because the ratio of the shell portion 3 containing a large amount of rare earth elements and magnesium and having few oxygen vacancies can be increased.

However, when the content of vanadium with respect to 100 mol of the total amount of barium and calcium is less than 0.1 mol or more than 0.2 mol in terms of V ₂ O ₅ , the total amount of barium and calcium is 100 Yttrium, dysprosium, holmium, erbium, and yttrium, dysprosium, holmium, erbium and the total amount of barium and calcium of 100 mol when the magnesium content is less than 0.55 mol or more than 0.75 mol in terms of MgO When the content of at least one rare earth element in terbium is less than 0.55 mol or more than 0.75 mol in terms of RE ₂ O ₃ , manganese in addition to 100 mol of the total amount of barium and calcium When the content of is less than 0.25 mol, DC voltage insulation resistance is lower than 10 ¹⁰ Omega in 12.5 V, when the more the manganese content relative to the total amount 100 mol of barium and calcium is more than 0.6 moles relative dielectric constant per unit thickness descend.

Therefore, 0.1 to 0.2 mol of vanadium in terms of V ₂ O ₅ and 0.55 to 0.75 mol in terms of MgO, yttrium and dysprosium with respect to 100 mol of the total amount of barium and calcium. It is important that at least one rare earth element among holmium, erbium and terbium is contained in an amount of 0.55 to 0.75 mol in terms of RE ₂ O ₃ and manganese is contained in an amount of 0.25 to 0.6 mol in terms of MnO. is there.

As a preferred composition, 0.1 to 0.2 mol of vanadium in terms of V ₂ O ₅ , 0.55 to 0.75 mol in terms of MgO, yttrium, with respect to 100 mol of the total amount of barium and calcium, Containing at least one rare earth element among dysprosium, holmium, erbium and terbium in an amount of 0.55 to 0.75 mol in terms of RE ₂ O ₃ and manganese in an amount of 0.25 to 0.35 mol in terms of MnO A dielectric ceramic in this range is a dielectric ceramic with almost no decrease in insulation resistance when the insulation resistance is evaluated by setting the values of the DC voltage applied per unit thickness to 3.15 V and 12.5 V. be able to. As the rare earth element, yttrium is particularly preferable in that a higher relative dielectric constant is obtained and an insulation resistance is high.

In the dielectric ceramic according to the present invention, it is important that the Curie temperature is 95 to 105 ° C. That is, when the content of manganese increases and the Curie temperature is lower than 95 ° C., the relative dielectric constant decreases. On the other hand, when the Curie temperature is higher than 105 ° C., the unit thickness of the dielectric ceramic (in both cases) This is because the insulation resistance becomes lower than 10 ¹⁰ Ω when the DC voltage applied per 1 μm) is 3.15 V and 12.5 V. And, as described above, in the present invention, the ratio of the core part 1 in the crystal particles can be reduced and the ratio of the shell part 3 can be increased, whereby the Curie temperature can be set to 95 to 105 ° C. The dielectric constant is high and the insulation resistance is high.

  It is important that the Ca concentration in the crystal grains is 0.4 atomic% or more. When the Ca concentration in the crystal particles is lower than 0.4 atomic%, the Curie temperature is lower than 95 ° C., and the relative dielectric constant may be lowered.

  In the dielectric ceramic of the present invention, the size of the crystal particles may be large in terms of enabling a high dielectric constant, but 0.5 μm or less is preferable in terms of reducing variation in capacitance, Furthermore, it is desirable that the average particle size of the crystal particles is 0.25 to 0.35 μm. When the average grain size of the crystal grains is 0.25 to 0.35 μm, the insulation resistance increases between 3.15 V and 12.5 V per unit thickness (1 μm) of the dielectric ceramic when the applied DC voltage is There is an advantage that a highly insulating dielectric ceramic exhibiting a tendency (positive change) can be obtained.

Next, a method for manufacturing the dielectric ceramic according to the present invention will be described. First, as raw material powder, barium calcium titanate powder (purity 99% or more) in which calcium is solid-dissolved in barium titanate, as additives, V ₂ O ₅ powder and MgO powder, and further Y ₂ O ₃ powder , _Dy 2 _{O 3} powder, _Ho 2 _{O 3} powder, adding an oxide powder and MnCO ₃ powder of at least one rare earth element selected from _Er 2 _{O 3} powder and _Te 2 _{O 3} powder, and mixed.

The barium calcium titanate powder is a perovskite-type barium titanate in which part of the Ba site of barium titanate is substituted with Ca, and is represented by the chemical formula (Ba _1-x Ca _x ) TiO ₃ . In the present invention, the amount of Ca substitution in the Ba site is preferably X = 0.01 to 0.2. This is because if the Ca substitution amount is within this range, excellent temperature characteristics and DC bias characteristics can be secured in the temperature range used as the capacitor.

  Further, the Ca contained in the barium calcium titanate powder is preferably dissolved in a uniformly dispersed state in the barium calcium titanate, and the Ca concentration as an analytical value is 0.4 atomic% or more. Use things. Causes that the Ca concentration in the crystal particles is lower than 0.4 atomic%, the Curie temperature is lower than 95 ° C., and the relative dielectric constant is lowered when the amount of substitution of Ca contained in the barium calcium titanate powder is reduced. It becomes.

  The average particle size of the barium calcium titanate powder is preferably 0.05 to 0.15 μm. When the average particle size of the barium calcium titanate powder is 0.05 μm or more, the core-shell structure can be easily formed in the crystal particles, and the ratio of the core portion 1 can be increased, so that the relative dielectric constant can be improved. There is.

  On the other hand, when the average particle size of the barium calcium titanate powder is 0.15 μm or less, it becomes easy to dissolve the additive into the crystal particles, and the titanium before and after firing as described later. There is an advantage that the ratio of grain growth from barium calcium acid powder to crystal grains can be increased.

Also, an oxide powder of at least one rare earth element among Y ₂ O ₃ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder, Er ₂ O ₃ powder and Te ₂ O ₃ powder as additives, V ₂ Regarding the O ₅ powder, MgO powder and MnCO ₃ powder, it is preferable to use those having an average particle diameter equivalent to or less than that of the barium calcium titanate powder.

Next, these raw material powders are 0.1 to 0.2 mol of V ₂ O ₅ powder and 0.55 to 0.55 MgO powder with respect to 100 mol of barium and calcium constituting the barium calcium titanate powder. 0.75 mol, 0.55 to 0.75 mol of rare earth oxide powder, and 0.25 to 0.6 mol of MnCO ₃ powder as MnO are blended, and glass powder as a sintering aid The organic vehicle is added thereto, mixed using a ball mill, molded into a predetermined shape, and the molded body is degreased and fired in a reducing atmosphere.

  The firing temperature is preferably 1100 to 1150 ° C. because the solid solution of the additive in the barium calcium titanate powder and the grain growth of the crystal particles are controlled in the present invention.

  In the present invention, in order to obtain such a dielectric ceramic, a fine amount of barium calcium titanate powder is used, a predetermined amount of the above-mentioned additive is added thereto, and the various additives are included by firing at the above-mentioned temperature. The barium calcium titanate powder is fired so that the average particle size is twice or more before and after firing. By firing so that the average particle size of the crystal particles after firing is at least twice the average particle size of the barium calcium titanate powder containing vanadium and other additives, the crystal particles are dissolved in the additive components. As a result, the ratio of the core part 1 decreases and the volume ratio of the shell part 3 increases.

  Moreover, in this invention, after baking, it heat-processes in a weak reduction atmosphere again. This heat treatment is performed to re-oxidize the reduced dielectric ceramics during firing in a reducing atmosphere, and to recover the reduced insulation resistance that was reduced during firing. 900-1100 degreeC is preferable from the reason of raising the amount of reoxidation, suppressing it. Thus, the volume ratio of the highly insulating shell portion 3 in the crystal particles is increased, and a dielectric ceramic exhibiting a Curie temperature of 95 to 105 ° C. can be formed.

  FIG. 2 is a schematic cross-sectional view showing an example of the multilayer ceramic capacitor of the present invention. The multilayer ceramic capacitor of the present invention is one in which external electrodes 3 are provided at both ends of a capacitor body 10, and the capacitor body 10 is a multilayer body in which dielectric layers 5 and internal electrode layers 7 are alternately stacked. 10A. It is important that the dielectric layer 5 is formed by the above-described dielectric ceramic of the present invention.

  According to the multilayer ceramic capacitor of the present invention, by applying the above dielectric ceramic as the dielectric layer 5, high insulation can be secured even if the dielectric layer 5 is thinned, and a high temperature load test is performed. A multilayer ceramic capacitor having excellent lifetime characteristics can be obtained.

  Here, the thickness of the dielectric layer 5 is preferably 3 μm or less, and particularly preferably 2.5 μm or less, in order to reduce the size and capacity of the multilayer ceramic capacitor. For stabilization, the thickness of the dielectric layer 5 is more preferably 1 μm or more.

  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, and in particular, simultaneous firing with the dielectric layer 1 in the present invention can be achieved. In this respect, nickel (Ni) is more desirable.

  The external electrode 3 is formed by baking, for example, Cu or an alloy paste of Cu and Ni.

  Next, a method for manufacturing a multilayer ceramic capacitor will be described. A ceramic slurry is prepared by adding a dedicated organic vehicle to the raw material powder, and then a ceramic green sheet is formed from the ceramic slurry using a sheet forming method such as a doctor blade method or a die coater method. In this case, the thickness of the ceramic green sheet is preferably 1 to 4 μm from the viewpoint of thinning the dielectric layer for increasing the capacity and maintaining high insulation.

  Next, a rectangular internal electrode pattern is printed and formed on the main surface of the obtained ceramic green sheet. Ni, Cu, or an alloy powder thereof is suitable for the conductor paste that forms the internal electrode pattern.

  Next, stack the desired number of ceramic green sheets with internal electrode patterns, and stack multiple ceramic green sheets without internal electrode patterns on the top and bottom so that the upper and lower layers are the same number. Form the body. In this case, the internal electrode pattern in the sheet laminate is shifted by a half pattern in the longitudinal direction.

  Next, the sheet laminate is cut into a lattice shape to form a capacitor body molded body so that the end of the internal electrode pattern is exposed. By such a laminating method, the internal electrode pattern can be formed so as to be alternately exposed on the end surface of the cut capacitor body molded body.

  Next, after the capacitor body molded body is degreased, the capacitor body is manufactured by performing heat treatment under the same firing conditions and weak reducing atmosphere as the above-described dielectric ceramic.

  Next, an external electrode paste is applied to the opposite ends of the capacitor body and baked to form external electrodes. Further, a plating film may be formed on the surface of the external electrode in order to improve mountability.

First, as raw material powders, two types of barium calcium titanate powder (hereinafter referred to as BCT powder, composition: Ba _0.95 Ca _0.05 TiO ₃ or Ba _0.98 Ca _0.02 TiO ₃ ), MgO powder, Y ₂ O ₃ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder, Er ₂ O ₃ powder, Tb ₂ O ₃ powder, MnCO ₃ powder and V ₂ O ₅ powder were prepared. It mixed in the ratio shown. These raw material powders having a purity of 99.9% were used. The average particle size of the BCT powder is shown in Table 1. MgO powder, Y ₂ O ₃ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder, Er ₂ O ₃ powder, Tb ₂ O ₃ powder, MnCO ₃ powder and V ₂ O ₅ powder have an average particle size of 0.1 μm. The thing of was used. The Ba / Ti ratio of the BCT powder was 1.005. As the sintering aid, glass powder having a composition of SiO ₂ = 55, BaO = 20, CaO = 15, and Li ₂ O = 10 (mol%) was used. The addition amount of the glass powder was 1 part by mass with respect to 100 parts by mass of the BCT powder.

  Next, these raw material powders were 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 polyvinyl butyral resin and a mixed solvent of toluene and alcohol are added to the wet-mixed powder, and wet-mixed using a zirconia ball having a diameter of 5 mm to prepare a ceramic slurry, and a ceramic having a thickness of 2.5 μm is obtained by a doctor blade method. A green sheet was produced.

  Next, a plurality of rectangular internal electrode patterns mainly composed of Ni were formed on the upper surface of the ceramic green sheet. The conductor paste used for the internal electrode pattern was Ni powder having an average particle size of 0.3 μm, and 30 parts by mass of BT powder used for a green sheet as a co-material with respect to 100 parts by mass of Ni powder.

Next, 360 ceramic green sheets on which internal electrode patterns were printed were laminated, and 20 ceramic green sheets on which the internal electrode patterns were not printed were laminated on the upper and lower surfaces, respectively. The layers were laminated together under the conditions of 10 ⁷ Pa and time 10 minutes, and cut into predetermined dimensions.

Next, the laminated molded body was subjected to binder removal treatment at 300 ° C./h in the atmosphere at a heating rate of 10 ° C./h, and the temperature rising rate from 500 ° C. was 300 ° C./h. -A capacitor body was fabricated by firing at 1100 to 1145 ° C for 2 hours in nitrogen. The sample was then cooled to 1000 ° C. at a rate of 300 ° C./h, reoxidized at 1000 ° C. for 4 hours in a nitrogen atmosphere, and cooled at a rate of 300 ° C./h to produce a capacitor body. did. The size of this capacitor body was 0.95 × 0.48 × 0.48 mm ³ , the thickness of the dielectric layer was 2 μm, and the area of one internal electrode layer was 0.3 mm ² .

  Next, the fired capacitor body was barrel-polished, and then an external electrode paste containing Cu powder and glass was applied to both ends of the capacitor 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.

  Next, the following evaluation was performed on these multilayer ceramic capacitors. In the following evaluations, the number of samples was 10 and the average value was obtained. The relative dielectric constant was determined from the thickness of the dielectric layer and the total area of the internal electrode layer by measuring the capacitance under the measurement conditions of a temperature of 25 ° C., a frequency of 1.0 kHz, and a measurement voltage of 1 Vrms. Moreover, the temperature characteristic of the relative dielectric constant was measured by measuring the capacitance in the range of temperature -55 to 85 ° C. The Curie temperature was determined as the temperature at which the relative dielectric constant was maximum in the range in which the temperature characteristic of the relative dielectric constant was measured. The insulation resistance was evaluated at DC voltages of 6.3V and 25V.

  The high temperature load test was performed at a temperature of 85 ° C. under the conditions of applied voltages of 9.45 V and 12.6 V, and the product with no defects was regarded as non-defective product up to 1000 hours. The number of samples in the high temperature load test was 20 samples.

  Moreover, the average particle diameter of the crystal grains constituting the dielectric layer was determined by a scanning electron microscope (SEM). The polished surface is etched, 20 crystal particles in the electron micrograph are arbitrarily selected, the maximum diameter of each crystal particle is obtained by the intercept method, the average value thereof is obtained, and the grain growth from the dielectric powder is determined. The percentage was evaluated.

  As for the Ca concentration, the crystal particles existing in the polished dielectric ceramic are analyzed at an arbitrary location near the center of the crystal particles using a transmission electron microscope and an energy dispersion analyzer (EDS). Asked. At this time, the content of Ba, Ti, Ca, V, Mg, rare earth elements and Mn detected from the crystal particles was taken as 100%, and the content was determined. The crystal grains evaluated were 100 points for each sample, and the average value was obtained.

In addition, the composition analysis of the obtained sintered body sample was performed by ICP analysis or atomic absorption analysis. In this case, the obtained dielectric porcelain mixed with boric acid and sodium carbonate and dissolved in hydrochloric acid is first subjected to qualitative analysis of the elements contained in the dielectric porcelain by atomic absorption spectrometry, and then specified. The diluted standard solution for each element was used as a standard sample and quantified by ICP emission spectroscopic analysis. Further, the amount of oxygen was determined using the valence of each element as the valence shown in the periodic table. The composition and firing temperature are shown in Table 1, the composition of each element in the sintered body is shown in Table 2, and the characteristics results are shown in Table 3.

As is apparent from the results of Tables 1 to 3, a predetermined amount of at least one rare earth element and manganese of vanadium, magnesium, yttrium, dysprosium, holmium, erbium and terbium is contained in the porcelain, and the Curie temperature is set. Sample No. 90 having a dielectric layer made of dielectric ceramic at 90 to 105 ° C. In 2 to 4, 8 to 10, 16 to 18, 24 to 28, 30 to 34, and 38 to 43, the decrease in insulation resistance with respect to the increase in DC voltage when the applied voltage is 6.3 V and 25 V is small. The insulation resistance at a voltage of 25 V was 10 ¹⁰ Ω or more, and the relative dielectric constant was 3300 or more. All of these samples had a grain growth rate before and after firing, which is a change rate of the average grain size of the BT powder before firing and the average grain size of the crystal particles after firing, of 225% or more. Moreover, when the high temperature load test was conducted on the multilayer ceramic capacitor having the dielectric ceramic according to the present invention as a dielectric layer under the conditions of a temperature of 85 ° C. and an applied voltage of 9.45 V, all had zero defects after 1000 hours. there were.

  In addition, Sample No. 2 having a manganese content of 0.25 to 0.35 mol was used. In 2-4, 8-10, 16-18, 24-25, 30-34, and 38-43, there is no decrease in insulation resistance with respect to an increase in DC voltage, and these samples are applied at a temperature of 85 ° C. The voltage satisfied a high temperature load test of 12.6 V and 1000 hours.

  Furthermore, Sample No. in which the average particle diameter of the crystal particles is 0.25 to 0.35 μm. 2 to 3, 9 to 10, 24 to 25, 31 to 32, and 38 to 41, all show a tendency for the change in insulation resistance to increase with increasing DC voltage, and a dielectric ceramic having excellent insulation characteristics is obtained. It was.

On the other hand, sample no. 1, 5-7, 11-15, and 19-23 show a tendency for the insulation resistance to decrease with increasing DC voltage when the applied voltage is 6.3 V and 25 V, and the insulation resistance at DC voltage 25 V is 10 ^It was lower than ¹⁰ Ω.

  Sample No. 8 containing 0.8 mol of manganese was used. In No. 29, the Curie temperature was 76 ° C., and the capacitance was 3100, which was lower than that of the dielectric ceramic of the present invention.

  Further, the grain growth rate before and after firing, which is the rate of change of the average particle size of the BCT powder before firing and the average particle size of the crystal particles after firing, is 105% to 120%, and the Curie temperature is 115 ° C to 140 ° C. Some sample No. In 35 to 37, the relative dielectric constant was 2400 to 2700.

In addition, Sample No. 2 produced using a barium titanate powder in which the amount of substitution of Ca was X = 0.02. No. 44 had a Ca concentration of 0.2 atomic% in the crystal grains, a Curie temperature of 85 ° C., and a dielectric constant as low as 3100. These sample Nos. About 35-37, the insulation resistance showed the tendency to fall with respect to the increase in DC voltage, and the insulation resistance in DC voltage 25V was lower than ¹⁰ < ¹⁰ > (omega | ohm). Moreover, in the sample out of the range of the present invention, the life of the high temperature load test under the conditions of the temperature of 85 ° C. and the applied voltage of 9.45 V did not satisfy 1000 hours.

It is a cross-sectional schematic diagram of the crystal particle which has as a main component the barium calcium titanate which has the core shell structure which comprises the dielectric material ceramic of this invention, (b) is a density | concentration change of the rare earth elements and magnesium in the cross section of (a). It is the shown schematic diagram. It is a longitudinal cross-sectional view which shows the example of the multilayer ceramic capacitor of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core part 3 Shell part 10A Laminated body 5 Dielectric layer 7 Internal electrode layer 10A Laminated body

Claims (4)

Core-shell crystal grains mainly composed of barium titanate, in which calcium, vanadium, magnesium, manganese, and at least one rare earth element of yttrium, dysprosium, holmium, erbium, and terbium are dissolved. A dielectric ceramic having a grain boundary phase existing between the crystal grains, wherein the crystal grains have a calcium concentration of 0.4 atomic% or more, and the barium titanate and the calcium For a total amount of 100 mol, vanadium is 0.1 to 0.2 mol in terms of oxide, magnesium is 0.55 to 0.75 mol in terms of oxide, yttrium, dysprosium, holmium, erbium and terbium. Of these, at least one rare earth element is converted to 0.55-0.75 mol in terms of oxide. And manganese containing 0.25 to 0.6 mol of the oxide equivalent, the dielectric ceramic Curie temperature, characterized in that a 95 to 105 ° C.. The dielectric ceramic according to claim 1, wherein the manganese is contained in an amount of 0.25 to 0.35 mol in terms of oxide. 3. The dielectric ceramic according to claim 1, wherein the crystal grains have an average grain size of 0.25 to 0.35 μm. A multilayer ceramic capacitor comprising a laminate of a dielectric layer made of the dielectric ceramic according to any one of claims 1 to 3 and an internal electrode layer.

Images