JP5354867B2 - Dielectric porcelain and multilayer ceramic capacitor - Google Patents

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 porcelain serving as a dielectric layer constituting a multilayer ceramic capacitor, a dielectric constant material mainly composed of barium titanate has been conventionally used. However, in recent years, barium titanate powder and titanic acid have been used. A composite dielectric material in which these dielectric materials coexist is developed by mixing powder in which calcium is dissolved in barium, and applied to a multilayer ceramic capacitor (see, for example, Patent Document 1). ).

  In addition, in the dielectric ceramic produced using the above-mentioned barium titanate powder or powder obtained by dissolving calcium in barium titanate, magnesium, rare earth elements and manganese oxides are used as additives, and firing. Sometimes, these additives are dissolved in the vicinity of the surface of barium titanate powder or powder of calcium in barium titanate to form crystal particles having a so-called core-shell structure. The temperature characteristics of the rate are improved.

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. In any of the crystal grains mainly composed of, the core portion is occupied by a tetragonal crystal phase, while the shell portion is occupied by a cubic crystal phase.
JP 2001-156450 A

  However, the dielectric ceramic composed of the core-shell structured crystal particles as described above has an increase in the relative permittivity and, as a temperature characteristic of the relative permittivity, X5R (change in temperature of the relative permittivity with respect to 25 ° C. X6R which is a temperature characteristic of relative permittivity up to a temperature higher than X5R (relative to 25 ° C as a reference). It was difficult to satisfy a rate of ± 15% at −55 to 105 ° C.).

  In addition, when a DC voltage is applied to the dielectric ceramic and the DC voltage is increased, there has been a problem that the decrease in insulation resistance becomes large.

  In addition, the multilayer ceramic capacitor provided with the dielectric ceramic composed of the core-shell structured crystal particles as the dielectric layer as described above cannot satisfy X6R as the temperature characteristic of the relative dielectric constant in the dielectric ceramic. Due to the decrease in insulation resistance, it has been difficult to improve the life characteristics in the high temperature load test.

  Accordingly, the present invention provides a dielectric ceramic with excellent stability of temperature characteristics of high dielectric constant and relative dielectric constant, and low voltage dependency of insulation resistance when the voltage is increased, and such a dielectric ceramic. An object of the present invention is to provide a multilayer ceramic capacitor that is provided as a dielectric layer and has excellent life characteristics in a high-temperature load test.

The dielectric ceramic of the present invention contains barium titanate as a main component, and includes calcium, vanadium, magnesium, manganese, and at least one rare earth element selected from yttrium, dysprosium, holmium, erbium, and terbium. A dielectric ceramic having crystal particles, wherein the crystal particles include a first crystal particle having a calcium concentration of less than 0.3 atomic% in the crystal particle, and a calcium concentration in the crystal particle of not less than 0.3 atomic%. The vanadium is 0.1 to 0.2 mol in terms of V ₂ O ₅ and the magnesium is 0.1 in terms of MgO with respect to 100 mol of titanium constituting the barium titanate. 55-0.75 mol, at least one of yttrium, dysprosium, holmium, erbium and terbium 0.55 to 0.75 mole rare earth element and (RE) in terms _of RE ₂ O _3, and manganese containing 0.25 to 0.6 mole in terms of MnO, the first seen in the polished surface of the dielectric ceramic C2 / (C1 + C2) is 0.5 to 0.8 and the Curie temperature is 85 to 95 ° C. where C1 is the area of the crystal grains and C2 is the area of the second crystal grains. It is characterized by.

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

  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 elements and manganese are contained in barium titanate at a predetermined ratio, and the dielectric ceramic crystal particles are divided into two types having different calcium concentrations. And having a Curie temperature in the range of 85 to 95 ° C., the temperature change rate of the dielectric constant and the dielectric constant can be reduced, and the insulation resistance when a voltage is applied can be reduced. A dielectric ceramic having a small drop (insulation resistance having a small voltage dependency) can be obtained.

  In addition, 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.

  Furthermore, when the average particle diameter of the crystal grains mainly composed of barium titanate is 0.25 to 0.35 μm for the dielectric ceramic of the present invention, the insulation resistance is within a predetermined range of the applied DC voltage. An excellent dielectric ceramic exhibiting a tendency to increase can be obtained.

  Also, according to the multilayer ceramic capacitor of the present invention, by applying the above dielectric ceramic as the dielectric layer, the temperature characteristics of the relative dielectric constant are stable, and high insulation is achieved even if the dielectric layer is thinned. Therefore, it is possible to obtain a multilayer ceramic capacitor having excellent life characteristics even in a high temperature load test.

  FIG. 1 is a schematic cross-sectional view showing the microstructure of a dielectric ceramic according to the present invention.

  The dielectric ceramic of the present invention is mainly composed of barium titanate, and a part or all of at least one rare earth element selected from calcium, vanadium, magnesium, manganese, and yttrium, dysprosium, holmium, erbium, and terbium. The crystal particles include a first crystal particle 1a having a low calcium concentration, a second crystal particle 1b having a higher calcium concentration than the first crystal particle 1a, and the first crystal particles 1a. The crystal grain 1a and the grain boundary phase 2 existing between the second crystal grains 1b.

  The first crystal particle 1a is a crystal particle mainly composed of barium titanate having a Ca concentration lower than 0.3 atomic%, and the second crystal particle 1b is a crystal particle having a Ca concentration of 0.3 atomic% or more. It is. The first crystal particles 1a include those having a Ca concentration of zero.

  The Ca concentration in the crystal particles is measured using a transmission electron microscope apparatus provided with an energy dispersive analyzer (EDS). In this case, with respect to the crystal particles projected on the cross section of the polished dielectric ceramic, the EDS is used to analyze an arbitrary location near the center of the crystal particles, and the main components and additives detected from the crystal particles Assuming that the total amount of each element is 100%, the content of Ca contained therein is obtained, and crystal grains having a Ca concentration lower than 0.3 atomic% and crystal grains having a Ca concentration of 0.3 atomic% or more are classified. To do. The ratio of the crystal particles having a Ca concentration lower than 0.3 atomic% and the crystal particles having a Ca concentration of 0.3 atomic% or more is determined from the area ratio of the cross section of the crystal particles displayed in the transmission electron micrograph. Further, the vicinity of the center portion of the crystal grain is a region deeper than 1/3 of the diameter from the grain boundary of the crystal grain appearing on the surface of the sample whose dielectric ceramic has been subjected to cross-section polishing in the depth direction.

  Next, the internal structure of the first crystal particle 1a and the second crystal particle 1b constituting the dielectric ceramic of the present invention will be described. Since the first crystal particle 1a and the second crystal particle 1b have the same internal structure, the first crystal particle 1a will be described as an example here.

  FIG. 2 (a) is a schematic cross-sectional view of crystal grains constituting the dielectric ceramic of the present invention, and FIG. 2 (b) is a schematic view showing a change in the concentration of rare earth elements or magnesium in (a). .

  As shown in FIGS. 2 (a) and 2 (b), the crystal particles include a core portion 1 mainly composed of barium titanate and a shell portion mainly composed of barium titanate formed around the core portion 1. 3. In addition, calcium, vanadium, magnesium, rare earth elements, and manganese are dissolved in the crystal particles. In particular, when the solid solution state of magnesium and rare earth elements is seen, the shell portion 3 has a higher magnesium content than the core portion 1. The concentration gradient of rare earth elements is increasing. That is, as shown in FIG. 2B, the concentration gradient of the rare earth element or magnesium in the shell portion 3 is larger than the concentration gradient of the rare earth element or magnesium in the core portion 1, and the rare earth element in the shell portion 3 Alternatively, the magnesium concentration is higher than the rare earth element or magnesium concentration in the core portion 1.

  This measurement can be performed using a transmission electron microscope apparatus equipped with an energy dispersive analyzer (EDS), and by performing elemental analysis with EDS at a predetermined interval from the surface side to the center of the crystal particles, the rare earth Changes in the concentration of elements and magnesium can be obtained.

  In the crystal particles constituting the dielectric ceramic of the present invention, the concentration gradient of the rare earth element or magnesium in the shell portion 3 makes the outermost surface SS of the crystal particles the highest concentration, and 0.1 to 2 atomic% / from the outermost surface SS to the inside. It is desirable that it is nm, and when the concentration gradient of the rare earth element or magnesium is 0.1 to 2 atomic% / nm, there is an advantage that life characteristics such as a high temperature load test can be improved.

  For the crystal particles having a core-shell structure, the boundary between the core part 1 and the shell part 3 follows the plot of the change in the concentration of rare earth elements in the crystal particles determined by EDS, from the outermost surface SS of the crystal particles, and It is calculated | required from the intersection of the mutually drawn straight line toward the outermost surface SS from the center part of a crystal grain.

  In this case, the concentration gradient of the rare earth element or magnesium in the shell portion 3 is larger than 0.1 atomic% / nm, the concentration gradient of the rare earth element or magnesium in the core portion 1 and the concentration gradient of the rare earth element or magnesium in the shell portion 3. If it is 0.1 atomic% / nm or more, the core portion 1 and the shell portion 3 can be determined.

  The composition of the dielectric ceramic of the present invention is such that vanadium is 0.1 to 0.2 mol in terms of oxide and magnesium is 0.55 to 0.005 in terms of oxide with respect to 100 mol of titanium constituting barium titanate. 75 mol, at least one rare earth element of yttrium, dysprosium, holmium, erbium and terbium in an oxide equivalent of 0.55 to 0.75 mol, and manganese in an oxide equivalent of 0.25 to 0.6 It is characterized by containing a mole.

  In the dielectric ceramic of the present invention, C2 / (C1 + C2) is 0.5 to 0.8 when the area of the first crystal particle 1a is C1 and the area of the second crystal particle 1b is C2. In addition, it is important that the Curie temperature is 85 to 95 ° 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.

When the dielectric ceramic composition, Curie temperature, and the ratio of crystal grains are within the above ranges, the relative dielectric constant at room temperature (25 ° C.) can be 3800 or more, and the temperature characteristic of the relative dielectric constant is X6R (−55 to 105). Insulation resistance when the rate of change of the relative dielectric constant with respect to 25 ° C is within ± 15% in the temperature range of ℃, and the value of DC voltage applied per unit thickness (1µm) is 12.5V There is an advantage that can be made 10 ¹⁰ Ω or more.

  That is, in the dielectric ceramic according to the present invention, a part 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 or The first crystal particles 1a and the second crystal particles 1b constituting the dielectric porcelain are all made into a solid solution, and the C2 / (C1 + C2) ratio is 0.5 to 0.8. The temperature is 85 to 95 ° C., and the Curie temperature is shifted to the room temperature side.

  As a result, even when calcium is solid-solved in barium titanate and has a core-shell structure, a high dielectric constant can be achieved with respect to a conventional dielectric ceramic having crystal particles having a Curie temperature near 125 ° C. The temperature characteristics of the relative permittivity can be stabilized up to a high temperature.

  Moreover, since the ratio of the core part 1 decreases and the ratio of the shell part 3 increases in the crystal particles having the core-shell structure, a dielectric ceramic having a high insulation resistance can be obtained.

  That is, when the solid solution amount of magnesium and rare earth elements in the crystal particles is small, the ratio of the core part 1 containing many defects such as oxygen vacancies increases, so that when a DC voltage is applied, the dielectric ceramic It is considered that oxygen vacancies or the like are likely to be carriers that carry electric charges inside the crystal particles constituting the material, and the insulating property of the dielectric ceramic is lowered. However, the dielectric ceramic according to the present invention is added to the crystal particles by adding vanadium. By increasing the solid solution of components such as magnesium, rare earth elements and manganese in the crystal grains and reducing the ratio of the core portion 1 in the crystal grains, the carrier density such as oxygen vacancies in the crystal grains is reduced. It is considered that a high insulating property can be obtained because the ratio of the shell part 3 containing a large amount of oxygen and few oxygen vacancies can be increased.

However, when the content of vanadium with respect to 100 mol of titanium constituting barium titanate is less than 0.1 mol or more than 0.2 mol in terms of V ₂ O ₅ , it also constitutes barium titanate. When the content of magnesium with respect to 100 mol of titanium is less than 0.55 mol or more than 0.75 mol in terms of MgO, yttrium, dysprosium and holmium with respect to 100 mol of titanium constituting barium titanate When the content of at least one rare earth element of erbium and terbium is less than 0.55 mol or more than 0.75 mol in terms of RE ₂ O ₃ , titanium constituting barium titanate When the content of manganese is less than 0.25 mol per 100 mol, Is because the insulation resistance in the DC voltage 12.5V per unit thickness is lower than 10 ¹⁰ Omega, further, when the content of manganese to titanium 100 moles constituting the barium titanate is larger than 0.6 mol The dielectric constant decreases, and the life characteristics in the high temperature load test decrease.

Therefore, with respect to 100 mol of titanium constituting barium titanate, vanadium is 0.1 to 0.2 mol in terms of V ₂ O ₅ , magnesium is 0.55 to 0.75 mol in terms of MgO, yttrium, It is important to contain at least one rare-earth element of 0.55 to 0.75 mol in terms of RE ₂ O ₃ and manganese in an amount of 0.25 to 0.6 mol in terms of MnO among sium, holmium, erbium and terbium. It is.

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

  Further, when the area ratio C2 / (C1 + C2) of the first crystal particles 1a and the second crystal particles 1b in the dielectric ceramic is smaller than 0.5, the dielectric constant is high and high insulation resistance can be obtained. If the area ratio C2 / (C1 + C2) ratio is greater than 0.8, high insulation resistance can be obtained, and the temperature characteristics of the dielectric constant Although X6R can be satisfied, the relative permittivity may be lowered.

In addition, when the Curie temperature is lower than 85 ° C., the relative dielectric constant decreases, and when the Curie temperature is higher than 95 ° C., the DC voltage applied per unit thickness (1 μm) of the dielectric layer is applied. The insulation resistance at 3.15 V and 12.5 V is lower than 10 ¹⁰ Ω. Therefore, in the dielectric ceramic according to the present invention, the area ratio C2 / (C1 + C2) is set to 0.5 to 0.8, and the Curie temperature is set to 85 to 95 ° C. The temperature characteristics are stable up to high temperatures and have high insulation resistance.

  Further, in the dielectric ceramic according to the present invention, the size of the crystal particles may be 0.1 μm or more in terms of enabling a high dielectric constant, but 0.5 μm if the variation in capacitance is reduced. The average particle size of the crystal particles constituting the first crystal particle 1a and the second crystal particle 1b is preferably 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 layer applied to the DC voltage. There is an advantage that a highly insulating dielectric ceramic exhibiting a tendency (positive change) can be obtained.

  In the dielectric ceramic according to the present invention, a glass component may be included as an auxiliary for enhancing the sinterability as long as desired dielectric characteristics can be maintained.

Next, a method for manufacturing the dielectric ceramic according to the present invention will be described. First, as raw material powder, a barium titanate powder (hereinafter referred to as BT powder) having a purity of 99% or more and a powder in which calcium is solid-solved in barium titanate (hereinafter referred to as BCT powder) are mixed with V ₂ O ₅ powder. And MgO powder, and also Y ₂ O ₃ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder, Er ₂ O ₃ powder and Tb ₂ O ₃ powder at least one rare earth element oxide powder and MnCO ₃ Add powder and mix. The BCT powder is a solid solution mainly composed of barium titanate in which a part of the A site is substituted with Ca, and is represented by (Ba _1-x Ca _x ) TiO _3. The amount is preferably X = 0.01-0.2. If the amount of Ca substitution is within this range, a crystal structure in which grain growth is suppressed can be formed by the coexistence structure with the first crystal grains 1a. Thus, when used as a capacitor, excellent temperature characteristics can be obtained in the operating temperature range. Note that Ca contained in the second crystal particles 1b is solid-dissolved in a state of being dispersed in the second crystal particles 1b.

  The average particle size of the BT powder and BCT powder used is preferably 0.05 to 0.15 μm. When the average particle size of the BT powder and the BCT powder is 0.05 μm or more, it is easy to form a core-shell structure in the first crystal particle 1a and the second crystal particle 1b, and the volume ratio of the core portion 1 is increased. Therefore, there is an advantage that the relative permittivity can be improved.

  On the other hand, when the average particle size of the BT powder and the BCT powder is 0.15 μm or less, additives such as magnesium, rare earth elements and manganese are dissolved in the first crystal particles 1a and the second crystal particles 1b. Further, as described later, there is an advantage that the ratio of grain growth from the BT powder and the BCT powder to the first crystal particles 1a and the second crystal particles 1b can be increased before and after firing, as will be described later. is there.

Y ₂ O ₃ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder, Er ₂ O ₃ powder and Tb ₂ O ₃ powder which are additives, oxide powder of at least one rare earth element, V ₂ O ₅ Regarding the powder, MgO powder, and MnCO ₃ powder, it is preferable to use those having an average particle diameter equal to or less than that of the dielectric powder.

Next, these raw material powders are 0.1 to 0.2 mol of V ₂ O ₅ powder, 0.55 to 0.75 mol of MgO powder with respect to 100 mol of titanium constituting BT powder and BCT powder, After blending 0.55 to 0.75 mol of rare earth element oxide powder and 0.25 to 0.6 mol of MnCO ₃ powder as MnO and degreasing the molded body, Bake.

  In the production of the dielectric ceramic of the present invention, glass powder may be added as a sintering aid so long as the desired dielectric properties can be maintained, and the addition amount is the main raw material powder. 0.5-2 mass parts is good when the total amount of BT powder and BCT powder is 100 mass parts.

  The firing temperature is preferably 1100 to 1150 ° C. because the solid solution of the additive in the BT powder and BCT 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, fine BT powder and BCT powder are used, a predetermined amount of the above-mentioned additive is added thereto, and the mixture is baked at the above temperature to include various additives. The BT powder and the BCT powder are fired so that the average particle size becomes 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 titanate powder containing vanadium and other additives, the first crystal particles 1a and the second crystal particles In the crystal particles 1b, the solid solution of the additive increases, and 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 reoxidize the dielectric ceramic reduced in firing in a reducing atmosphere and recover the reduced insulation resistance reduced during firing, the temperature of which is the first crystal particles 1a and 900-1100 degreeC is preferable from the reason of raising the amount of reoxidation, suppressing the further grain growth of the 2nd crystal grain 1b. Thus, the volume ratio of the highly insulating shell portion 3 in the first crystal particle 1a and the second crystal particle 1b is increased, and a dielectric ceramic exhibiting a Curie temperature of 85 to 95 ° C. can be formed.

  FIG. 3 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. In FIG. 3, the laminated state of the dielectric layer 5 and the internal electrode layer 7 is shown in a simplified manner, but the multilayer ceramic capacitor of the present invention has several hundreds of dielectric layers 5 and internal electrode layers 7. A laminated body extending to the layers is formed.

  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 4 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 degreasing the capacitor body molded body, the capacitor body is fabricated by performing heat treatment under the same firing conditions and weak reducing atmosphere as the above dielectric ceramic.

  Next, an external electrode paste is applied to the opposite ends of the capacitor body and baked to form the external electrodes 4. Further, a plating film may be formed on the surface of the external electrode 4 in order to improve mountability.

First, as the raw material powder, BT powder, BCT powder (composition _{(Ba 1-x Ca x)} TiO 3, X = 0.05), 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, to prepare a MnCO ₃ powder and _V 2 _{O 5} powder, mixing these various powders in proportions shown in Table 1. These raw material powders having a purity of 99.9% were used. The average particle sizes of the BT powder and BCT powder are 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 BT 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 BT 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, using a press machine at a temperature of 60 ° C. and pressure 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 all cases, 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 surface of the dielectric layer obtained by polishing the cross section in the stacking direction of the multilayer ceramic capacitor is observed at about 30000 times, and elemental analysis is performed on about 100 crystal particles present on the screen. An arbitrary location near the center of the crystal particle was analyzed using a transmission electron microscope equipped with an instrument. 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 evaluated crystal grains were 100 points for each sample, and the average value was obtained. In the area of the photographed transmission electron microscope, the area ratio of each of the first crystal grains 1a and the second crystal grains 1b (C2 / (C1 + C2) ) The vicinity of the center of the crystal grain is a region deeper than 1/3 of the diameter in the depth direction from the grain boundary of the crystal grain appearing on the surface of the sample obtained by polishing the dielectric ceramic.

  The concentration gradient of the rare earth elements was also measured using a transmission electron microscope equipped with an elemental analysis instrument. In this case, the concentration of the rare earth element is determined by polishing the cross section in the stacking direction of the multilayer ceramic capacitor and performing elemental analysis using an energy dispersive analyzer at intervals of 5 nm from the outermost surface side to the center of the crystal particles of each sample. Sought change. Then, 5 particles were arbitrarily extracted from the measurable crystal particles within a predetermined area of the dielectric ceramic photographed at 30000 times, and the average value was also obtained. In this case, in a sample having an Mn amount of 0.5 mol or less with respect to 100 mol of titanium, the concentration gradient of the rare earth element in the shell portion near the surface of the crystal particles was 0.1 to 1 atom% / nm or more. However, in the sample in which Mn was 0.6 mol or more with respect to 100 mol of titanium, the concentration gradient of the rare earth element in the shell portion near the surface of the crystal particles was 0.04 atomic% / nm.

  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.

Table 1 shows the preparation composition and the firing temperature, Table 2 shows the composition of each element in the sintered body in terms of oxide, and Table 3 shows the results of the characteristics.

As is apparent from the results of Tables 1 to 3, calcium, vanadium, magnesium, rare earth elements and manganese are contained at a predetermined ratio with respect to barium titanate, and the dielectric ceramic crystal particles have different calcium concentrations. It is composed of two types of crystal particles, and the area ratio of the second crystal particles to the total area of the first crystal particles and the second crystal particles (C2 / (C1 + C2)) is 0.5 to 0.8, and Sample No. with Curie temperature in the range of 85-95 ° C. In 2 to 4, 8 to 10, 16 to 18, 24 to 28, 31 to 33, 35, 36, and 39 to 44, the insulation resistance decreases with increasing DC voltage when the applied voltage is 6.3 V and 25 V. The insulation resistance at an applied voltage of 25 V was 10 ¹⁰ Ω or higher, the relative dielectric constant was 3800 or higher, and the temperature characteristics of the relative dielectric constant satisfied X6R. All of these samples had a grain growth rate of 215% or more before and after firing, which is the rate of change of the average particle size of BT powder and BCT powder before firing and the average particle size of crystal particles after firing. 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, 31-33, 35, 36 and 39-44, there is no decrease in insulation resistance with respect to an increase in DC voltage. The high-temperature load test of 85 ° C., applied voltage of 12.6 V, and 1000 hours was satisfied.

  Furthermore, Sample No. in which the average particle diameter of the crystal particles is 0.25 to 0.35 μm. 2, 3, 9, 10, 24, 25, 32, 33, 36, and 39 to 42 all show a tendency that the insulation resistance increases as the DC voltage increases, and the dielectric ceramic is excellent in insulation characteristics. was gotten.

On the other hand, sample no. 1, 5-7, 11-15, and 19-23, 37, and 38 show a tendency for the insulation resistance to decrease when the applied voltage is 6.3 V and 25 V, and the DC voltage is 25 V. The insulation resistance was lower than 10 ¹⁰ Ω.

  Sample No. 8 containing 0.8 mol of manganese was used. In No. 29, the Curie temperature was 82 ° C., and the relative dielectric constant was 3600, which was lower than that of the dielectric ceramic of the present invention.

  The grain growth rate before and after firing, which is the rate of change between the average particle diameter of the dielectric powder before firing and the average grain diameter of the crystal particles after firing, is 105% to 120%, and the Curie temperature is 100 ° C. to 125 ° C. Sample No. In 37 and 38, the relative dielectric constant was 3000 to 3200.

  In addition, the sample No. 1 in which the area ratio (C2 / (C1 + C2)) of the second crystal particles to the total area of the first crystal particles and the second crystal particles is 0.4. 34, the temperature characteristics of the relative dielectric constant could not satisfy X6R. In addition, sample No. C2 / (C1 + C2) ratio is 0.9. 30, the dielectric constant was 3500, which was lower than that of the dielectric ceramic according to the present invention.

It is a cross-sectional schematic diagram which shows the microstructure of the dielectric material ceramic of this invention. (A) is a schematic cross-sectional view of crystal grains constituting the dielectric ceramic according to the present invention, and FIG. 2 (b) is a schematic diagram showing concentration changes of rare earth elements and magnesium in the cross-section of (a). . 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 1a 1st crystal particle 1b 2nd crystal particle 2 Grain boundary phase 5 Dielectric layer 7 Internal electrode layer 10A Laminate

Claims (4)

A dielectric porcelain having crystal grains mainly composed of barium titanate and containing calcium, vanadium, magnesium, manganese, and at least one rare earth element selected from yttrium, dysprosium, holmium, erbium and terbium. The crystal particles include a first crystal particle having a calcium concentration in the crystal particle of less than 0.3 atomic%, and a second crystal particle having a calcium concentration in the crystal particle of 0.3 atomic% or more. Vanadium is 0.1 to 0.2 mol in terms of V ₂ O ₅ and magnesium is 0.55 to 0.75 mol in terms of MgO with respect to 100 mol of titanium constituting the barium titanate, and yttrium. , dysprosium, holmium, at least one rare earth element selected from erbium and terbium (RE) E ₂ O ₃ in terms of in 0.55 to 0.75 mol, and manganese were 0.25 to 0.6 molar content in terms of MnO, the area of the first crystal grains observed on the polished surface of the dielectric ceramic C1, a dielectric having C2 / (C1 + C2) of 0.5 to 0.8 and a Curie temperature of 85 to 95 ° C. when the area of the second crystal grain is C2. porcelain. 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 MnO .   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.

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