JP5832255B2 - Capacitor - Google Patents

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JP5832255B2
JP5832255B2 JP2011260286A JP2011260286A JP5832255B2 JP 5832255 B2 JP5832255 B2 JP 5832255B2 JP 2011260286 A JP2011260286 A JP 2011260286A JP 2011260286 A JP2011260286 A JP 2011260286A JP 5832255 B2 JP5832255 B2 JP 5832255B2
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capacitor
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松原 聖
聖 松原
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京セラ株式会社
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  The present invention relates to a capacitor using a dielectric ceramic composed of crystal particles mainly composed of barium titanate as a dielectric layer.
  In recent years, with the development of high-luminance blue light-emitting diodes (LEDs), the development of lighting equipment that uses LEDs as light sources has rapidly progressed along with full-color LED display devices that can achieve high visibility. It's getting on.
  In such an electronic device using an LED, a method of generating a DC voltage for driving the LED from a commercial power source using an AC-DC converter is adopted. However, the AC-DC converter uses a commercial power source (100V). ) Is a circuit that drives a LED by generating a desired DC output voltage from the AC voltage, and a rectifier circuit used in such a circuit is equipped with a capacitor together with a field effect transistor (MOSFET) as a control circuit element (For example, refer to Patent Document 1).
  However, in an electronic device using such an LED, since the applied voltage is high and the temperature change due to heat generation during light emission is large, the capacitor has a high capacitance and is static even in a high temperature load state. There is a demand for a capacitor having stable temperature characteristics.
JP 2011-35112 A
  The present invention has been made in view of the above problems, and an object of the present invention is to provide a capacitor having a high capacitance and a low relative dielectric constant temperature change rate even in a high temperature load state.
A capacitor according to the present invention includes a dielectric ceramic comprising barium titanate crystal particles and containing magnesium, manganese, and one kind of rare earth element (RE) selected from yttrium, dysprosium, holmium, and erbium. A capacitor having a layer, wherein the dielectric ceramic is based on 100 mol of titanium constituting the barium titanate, 0.3 to 1.5 mol of magnesium in terms of MgO, and manganese in terms of MnO. 0.05 to 0.3 mol, containing 0.3 to 0.6 mol of the rare earth element (RE) selected from yttrium, dysprosium, holmium and erbium in terms of RE 2 O 3 , gradient of the magnesium in the range of the grain boundaries of 20nm depth of 0.05 atomic% / nm or more 0.20 A first crystal group is child% / nm or less, the second crystal concentration gradient of the magnesium in the range of the grain boundaries of 20nm depth is less than 0.005 atomic% / nm or more 0.03 atomic% / nm And the average particle size of the crystal grains constituting the first crystal group and the crystal grains constituting the second crystal group is 0.15 to 0.40 μm, and the dielectric B / (a + b) is 0 when the area of the crystal grains constituting the first crystal group seen on the polished surface of the porcelain is a and the area of the crystal grains constituting the second crystal group is b. .4~0.7 Ru der.
According to the present invention, it is possible to obtain a capacitor having a high capacitance and a low relative dielectric constant temperature change rate even in a high temperature load state.
(A) is a schematic sectional drawing which shows an example of the capacitor | condenser of this invention, (b) is an enlarged view of the dielectric material layer which comprises the capacitor | condenser of FIG. 1, and is the schematic diagram which shows a crystal grain and a grain boundary phase It is. (A) is a schematic diagram showing the concentration gradient of the crystal grains constituting the first crystal group and the magnesium inside thereof, and (b) is the crystal grains constituting the second crystal group and the magnesium inside thereof. It is a schematic diagram showing the concentration gradient. It is a graph which shows concentration distribution of two types of magnesium of the crystal grain which comprises a dielectric material layer (sample No. 1 of Table 1 of an Example).
  The capacitor of this embodiment will be described in detail based on the schematic cross-sectional view of FIG. FIG. 1A is a schematic cross-sectional view showing an example of the capacitor of the present invention, and FIG. 1B is an enlarged view of a dielectric layer constituting the capacitor of FIG. 1, showing crystal grains and grain boundary phases. It is a schematic diagram. FIG. 2 (a) is a schematic diagram showing a concentration gradient of crystal grains constituting the first crystal group and magnesium therein, and FIG. 2 (b) is a diagram showing crystal grains constituting the second crystal group and the inside thereof. It is a schematic diagram showing the concentration gradient of magnesium.
  In the capacitor of this embodiment, external electrodes 3 are formed at both ends of the capacitor body 1. The external electrode 3 is formed, for example, by baking Cu or an alloy paste of Cu and Ni.
  The capacitor body 1 is configured by alternately laminating dielectric layers 5 made of dielectric ceramics and internal electrode layers 7. In FIG. 1, the laminated state of the dielectric layer 5 and the internal electrode layer 7 is shown in a simplified manner. However, the capacitor of the present invention includes a laminated body having several hundreds of dielectric layers 5 and internal electrode layers 7. It has become.
  The dielectric layer 5 made of a dielectric ceramic is composed of crystal grains 9 and a grain boundary phase 11, and the average thickness is preferably 5 μm or less, particularly 3 μm or less. Can be realized. The average thickness of the dielectric layer 5 is preferably 1 μm or more from the viewpoint of reducing variation in capacitance, stabilizing capacitance-temperature characteristics, and improving high-temperature load life.
  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 when the number of layers is increased, and in particular, the dielectric layer 5 constituting the capacitor of the present embodiment Of these, nickel (Ni) is more desirable in that it can be fired simultaneously.
  The dielectric ceramic constituting the dielectric layer 5 in the capacitor according to the present embodiment includes crystal particles 9 of barium titanate, and one kind of rare earth element selected from magnesium, manganese, yttrium, dysprosium, holmium and erbium ( RE).
Further, this dielectric porcelain is composed of 0.3 to 1.5 moles of magnesium in terms of MgO and 0.05 to 0.3 moles of manganese in terms of MnO, based on 100 moles of titanium constituting barium titanate. , Dysprosium, holmium and erbium, one kind of rare earth element (RE) is contained in an amount of 0.3 to 0.6 mol in terms of RE 2 O 3 .
The crystal grains 9 include a first crystal group crystal grain 9a having a magnesium concentration gradient of 0.05 atomic% / nm or more in a depth range of 20 nm from the grain boundary, and a depth of 20 nm from the grain boundary. And a crystal grain 9b of the second crystal group in which the concentration gradient of magnesium in the range is 0.03 atomic% / nm or less.
  The average particle diameter of the crystal grains 9a constituting the first crystal group and the crystal grains constituting the second crystal group is 0.15 to 0.40 μm.
  Further, when the area of the crystal grains 9a constituting the first crystal group seen on the polished surface of the dielectric ceramic is a and the area of the crystal grains 9b constituting the second crystal group is b, b / ( a + b) is 0.4 to 0.7.
  As a result, it is possible to obtain a capacitor having a high capacitance and a low rate of change in the temperature of the capacitance even in a high temperature load state. For example, the relative permittivity at room temperature (25 ° C.) is 4400 or more, and at 85 ° C., the rate of change of the relative permittivity when a DC voltage of 2 V is applied is at room temperature (25 ° C.) in an unloaded state. It has a dielectric characteristic of -40% or less (direction approaching NPO (± 0%)) with respect to the relative dielectric constant.
    When barium titanate is dissolved in magnesium, the Curie temperature of barium titanate can be changed from 125 ° C. to the low temperature side due to the difference in the amount of the solid solution, thereby the temperature of the relative dielectric constant of barium titanate. It becomes possible to change the rate of change.
  The dielectric ceramic according to the present embodiment contains the above-mentioned amounts of magnesium together with the rare earth element (RE) and manganese, and is particularly composed of two types of crystal particles 9a and 9b having different magnesium concentration gradients.
  As shown in FIG. 2 (a), in the crystal particle 9 mainly composed of barium titanate, the concentration gradient of magnesium in the depth range of 20 nm from the grain boundary is 0.05 atomic% / nm or more. When the concentration gradient of magnesium in the vicinity of the surface of 9 is large, most of the magnesium in the crystal particles 1 a remains in a very thin region near the surface of the crystal particles 1 and is in a solid solution state. For this reason, since magnesium hardly dissolves in the central portion of the crystal particle 1a, and the central portion is dominated by a tetragonal crystal phase, a dielectric ceramic having a high relative dielectric constant is obtained. Can do. Here, in the crystal particle 9a, a region in which magnesium is dissolved is formed in the vicinity of the surface of the crystal particle 9a, the temperature change rate of the relative permittivity can be reduced, and the insulating property can be increased. The concentration gradient of magnesium in the depth range is preferably 0.20 atomic% / nm or less.
  On the other hand, the dielectric ceramic contains a predetermined amount of magnesium, and as shown in FIG. 2B, the concentration gradient of magnesium in the depth range of 20 nm from the grain boundary is 0.03 atomic% / nm or less. When the concentration gradient of the element (in this case, magnesium) near the surface of 1 is low, magnesium is in a solid solution state near the surface of the crystal grain 9b. For this reason, a cubic system is dominant in the crystal phase near the surface of the crystal grain 9b. Here, in the crystal grain 9b, the concentration gradient of magnesium in the range of 20 nm depth from the grain boundary is 0 because the tetragonal crystal phase is left in the central part of the crystal grain 9b to increase the dielectric constant. It is desirable that it is 0.005 atomic% / nm or more.
  As a result, although the relative permittivity of the crystal particle 9b is lower than that of the crystal particle 9a, the cubic crystal phase is dominant, so that the voltage dependency of the relative permittivity can be reduced. Become.
The crystal particle 9a alone cannot reduce the temperature change rate of the relative dielectric constant when a DC voltage is applied. However, if the crystal particle 9b coexists with the crystal particle 9a, the crystal particle 9b originally has a relative dielectric constant. Due to the fact that the voltage dependency of the rate can be reduced, the temperature change rate of the relative permittivity when a DC voltage is applied becomes small, and the high dielectric constant which is a property of the crystal grain 9a It is possible to increase the rate at the same time.
  As a result, the capacitor of this embodiment has a relative dielectric constant of 4400 or more at room temperature (25 ° C.), for example, a ratio measured at room temperature (25 ° C.) without applying a DC voltage (no load state). The rate of change of the relative dielectric constant at 85 ° C. and 2 V applied to the dielectric constant can be made within −40%. Hereinafter, the change rate of the relative permittivity at 85 ° C. and 2 V applied to the relative permittivity measured at room temperature (25 ° C.) without applying a DC voltage (the no-load state) is the relative permittivity in the high temperature load state. It is called rate of change.
  In addition, as a composition of the dielectric ceramic, when the content of magnesium is less than 0.3 mol in terms of MgO with respect to 100 mol of titanium constituting barium titanate, the temperature characteristic of the relative dielectric constant becomes large on the + side. The X5R condition that is the temperature characteristic of the capacitance is not satisfied, and the temperature change rate of the relative permittivity in a high temperature load state is increased. On the other hand, when the magnesium content is more than 1.5 mol, the relative dielectric constant at room temperature (25 ° C.) becomes lower than 4500.
  If the content of manganese is less than 0.05 mol in terms of MnO with respect to 100 mol of titanium constituting barium titanate, the condition of X5R, which is the temperature characteristic of capacitance, is not satisfied, and high temperature load The temperature change rate of the relative dielectric constant in the state also increases. On the other hand, when the amount of barium titanate is large, the relative dielectric constant at room temperature (25 ° C.) becomes lower than 4400.
When the content of one rare earth element (RE) selected from yttrium, dysprosium, holmium and erbium is less than 0.3 mol in terms of RE 2 O 3 with respect to 100 mol of titanium constituting barium titanate, The X5R condition, which is the temperature characteristic of the capacitance, is not satisfied, and the temperature change rate of the relative permittivity in a high temperature load state is larger than −40%, while the content of the rare earth element is RE 2 O 3. When the amount is more than 0.6 mol in terms of conversion, the relative dielectric constant at room temperature (25 ° C.) becomes lower than 4400.
  FIG. 3 is a graph showing the concentration distribution of magnesium contained in crystal grains in the dielectric layer constituting the capacitor of this embodiment. This example is a sample No. in Examples described later. 1 was evaluated.
Here, regarding the concentration distribution of magnesium in the crystal particles 9, after the cross section of the dielectric ceramic is polished, a circle containing about 30 crystal particles is drawn on the image displayed on the monitor attached to the transmission electron microscope. Then, the crystal particles in the circle and the circumference are selected, and elemental analysis is performed using a transmission electron microscope equipped with an elemental analysis instrument. The crystal particles 9 to be selected at this time are obtained by calculating the area of each particle by image processing from the contour, and calculating the diameter when replaced with a circle having the same area. The crystal grains 9 are in the range of ± 60%. The spot size of the electron beam at the time of analysis is 0.5 to 2 nm, and the location to be analyzed is in the range from the vicinity of the grain boundary of the crystal grain 9 to the center position of the central portion, on a straight line drawn toward the center. substantially equal intervals and a point located, the vicinity of the grain boundary is obtained from the values was analyzed in a depth of approximately 20nm from the grain boundary (referred to as d G in FIG. 2 (a) (b)) of. In this case, a value obtained by subtracting the magnesium concentration at a depth of 19 to 21 nm (magnesium concentration) from the magnesium concentration at the grain boundary (0 to 1 nm) of the crystal grain 9 is the analyzed range (for example, 20 nm-0 nm = Divide by a distance of 20 nm) to obtain a concentration gradient.
In addition, as described above, the capacitor according to the present embodiment includes the crystal grains 9a constituting the first crystal group and the crystal grains 9b constituting the second crystal group as the crystal grains 9.
The ratio is such that b / (a + b) is 0.4 to 0.4, where a is the area of the crystal grains 9a constituting the first crystal group and b is the area of the crystal grains 9b constituting the second crystal group. 0.7.
  That is, when b / (a + b), which is the ratio of the area of the crystal grains 9a constituting the first crystal group and the area of the crystal grains 9b constituting the second crystal group, is smaller than 0.4, The X5R condition that is the temperature characteristic of the capacitance is not satisfied, and the temperature change rate of the relative permittivity in a high temperature load state is also increased. On the other hand, when b / (a + b) is larger than 0.7, the relative dielectric constant is lower than 4400.
  In the multilayer ceramic capacitor of this embodiment, the average particle diameters of the crystal grains 9a constituting the first crystal group and the crystal grains 9b constituting the second crystal group are 0.15 to 0.40 μm.
  That is, the relative dielectric constant is lower than 4400 when the average particle size of the crystal particles 9 composed of the crystal particles 9a of the first crystal group and the crystal particles 9b of the second crystal group is smaller than 0.15 μm. When the average particle size of the crystal particles 1 composed of the crystal particles 9a of the first crystal group and the crystal particles 9b of the second crystal group is larger than 0.40 μm, the relative permittivity increases, but the high temperature load test The life of the is shortened.
  Here, the average particle size of the crystal particles 9 composed of the crystal particles 9a constituting the first crystal group and the crystal particles 9b constituting the second crystal group is polished by polishing (ion milling) the cross section of the dielectric ceramic. For the surface, capture the image projected by the transmission electron microscope into the computer, draw a diagonal line on the screen, image processing the outline of the crystal particles present on the diagonal line, find the area of each particle, The diameter when replaced with a circle having the same area is calculated and obtained from an average value of about 50 calculated crystal grains.
  The area ratio of the crystal grains 9b constituting the second crystal group to the total area of the crystal grains 9a constituting the first crystal group constituting the dielectric ceramic and the crystal grains 9b constituting the second crystal group is: It calculates using the data of the area used when calculating | requiring the said average particle diameter.
  In the capacitor of this embodiment, it is desirable that the dielectric ceramic contains 0.05 to 0.20 mol of vanadium with respect to 100 mol of titanium constituting barium titanate. By setting it as the said composition, since the insulation resistance of a dielectric ceramic increases, it becomes possible to extend the lifetime in a high temperature load test.
  When yttrium, dysprosium, holmium, and erbium are included among the rare earth elements, a heterogeneous phase is hardly generated when dissolved in barium titanate, and high insulation can be obtained. Yttrium is more preferable because the lifetime in the high temperature load test can be increased.
  Further, in the multilayer ceramic capacitor of the present embodiment, other components may be included in addition to the above-described components as long as desired dielectric characteristics can be maintained. For example, as an auxiliary agent for improving sinterability. A glass component and other additive components can be contained in the dielectric ceramic in a proportion of 0.5 to 2% by mass.
Next, a method for manufacturing the capacitor of the present embodiment will be described. However, the manufacturing method described below is an example, and the method is not limited to this method. First, as raw material powder, a barium titanate powder (hereinafter referred to as BT powder) having a purity of 99% by mass or more, MnCO 3 powder, Y 2 O 3 powder, Dy 2 O 3 powder, Ho 2 O 3 powder and An oxide powder of one kind of rare earth element selected from Er 2 O 3 powder is prepared. If necessary, prepare the V 2 O 5 powder.
Here, the average particle size of the BT powder is preferably 0.20 to 0.35 μm, and particularly preferably 0.25 to 0.30 μm. MgO powder as an additive, or one rare earth oxide powder selected from Y 2 O 3 powder, Dy 2 O 3 powder, Ho 2 O 3 powder and Er 2 O 3 powder, MnCO 3 powder and V As for the 2 O 5 powder, it is preferable to use one having an average particle diameter equal to or less than that of the BT powder.
Next, these raw material powders are 0.3 to 1.5 mol of MgO powder, 0.05 to 0.3 mol of MnCO 3 powder, and Y 2 O 3 powder with respect to 100 mol of titanium constituting the BT powder. A rare earth element (RE) selected from Dy 2 O 3 powder, Ho 2 O 3 powder and Er 2 O 3 powder is blended at a ratio of 0.3 to 0.6 mol in terms of RE 2 O 3 . Optionally, the V 2 O 5 powder, relative to the titanium 100 mole constituting the BT powder, is added at a ratio of 0.05 to 0.20 mol.
  Here, when the capacitor of the present embodiment is manufactured, the crystal particles 1b of the second crystal group formed in the dielectric ceramic are dielectric powder (hereinafter, referred to as BT powder) coated with MgO powder in advance. It may be referred to as BMT powder). Of the BT powder, the amount of BT powder to be the crystal particles 1b and the corresponding MgO powder are weighed and heated at a temperature of about 700 ° C. to prepare a BT powder coated with a magnesium component. Next, a mixed powder of the BT powder coated with the magnesium component and the BT powder uncoated with the magnesium component is prepared by mixing the BT powder not coated with the MgO powder and the remaining MgO powder. . The added amount of the post-added MgO powder is a ratio excluding the MgO powder that was previously coated with BT powder and dissolved therein.
  Next, a ceramic slurry is prepared by adding a special organic vehicle to the dielectric powder prepared as described above, and then a ceramic green sheet is formed using a sheet forming method such as a doctor blade method or a die coater method. To do. In this case, the thickness of the ceramic green sheet is preferably 1 to 6 μm from the viewpoint of reducing the thickness of the dielectric layer 5 to increase 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, the capacitor body molded body is degreased and fired. The firing temperature is preferably 1100 to 1200 ° C. because the solid solution of the additive in the BT powder and the BMT powder and the grain growth of crystal grains in the present embodiment are suppressed.
Moreover, after baking, it heat-processes in a weak reducing atmosphere again. This heat treatment is performed to reoxidize the dielectric ceramic reduced in firing in a reducing atmosphere and recover the insulation resistance reduced and reduced during firing. The temperature is preferably 900 to 1100 ° C. for the purpose of increasing the amount of reoxidation while suppressing the grain growth of the crystal grains 9. In this way, a dielectric ceramic having a small relative dielectric constant temperature change rate can be obtained even in a high temperature load state.
  Next, an external electrode paste is applied to the opposing ends of the capacitor body 1 and baked to form the external electrodes 3. Further, a plating film may be formed on the surface of the external electrode 3 in order to improve mountability.
  Hereinafter, although an example is given and a capacitor of the present invention is explained in detail, the present invention is not limited to the following examples.
First, BT powder, MgO powder, Y 2 O 3 powder, Dy 2 O 3 powder, Ho 2 O 3 powder, Er 2 O 3 powder, MnCO 3 powder and V 2 O 5 powder are prepared as raw material powders, Were mixed in the proportions shown in Table 1. These raw material powders having a purity of 99.9% by mass were used. As the BT powder, one having an average particle diameter of 0.1 to 0.50 μm was used. MgO powder, Y 2 O 3 powder, Dy 2 O 3 powder, Ho 2 O 3 powder, Er 2 O 3 powder, Tb 4 O 7 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 set to 1. In this case, a dielectric powder coated with MgO powder was prepared according to the ratio of the crystal grains of the second crystal group formed in the dielectric ceramic, and the remaining BT powder and MgO powder were added thereto. Dielectric powder (BMT powder) coated with MgO powder was prepared by adding a predetermined amount of MgO powder to BT powder and then heating at 700 ° C.
  The mixing ratio of the BT powder and the BMT powder was such that the molar ratio b / (a + b) was a ratio shown in Table 1 when the BT powder was a mole and the BMT powder was b mole.
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. A polyvinyl butyral resin and a mixed solvent of toluene and alcohol were added to the wet-mixed powder, and wet-mixed using a zirconia ball having a diameter of 5 mm to prepare a ceramic slurry. A ceramic green sheet having a thickness of 2 μm was prepared by a doctor blade method. .
  A plurality of rectangular internal electrode patterns mainly containing 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, 350 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 Lamination was performed under the conditions of 10 7 Pa and time 10 minutes, and cut into predetermined dimensions to form a laminated molded body.
The obtained laminated molded body was subjected to binder removal treatment at 300 ° C. in the atmosphere at a temperature rising rate of 10 ° C./h, heated at the same temperature rising rate, and then heated from 500 ° C. to 300 ° C./h. Then, after baking at 1150 ° C. for 2 hours in hydrogen-nitrogen, and then cooling to 1000 ° C. at a temperature drop rate of 300 ° C./h, heat treatment (reoxidation treatment) is performed at 1000 ° C. for 4 hours in a nitrogen atmosphere. 300
The capacitor body was manufactured by cooling at a temperature drop rate of ° C / h. The size of the capacitor body is a size of a monolithic ceramic capacitor that is compatible with the 1608 type. The average thickness of the dielectric layer was 1.2 μm, and the effective area of one internal electrode layer was 0.92 mm 2 . Here, the effective area is an area where internal electrode layers formed so as to be exposed at end faces in different directions of the capacitor body overlap.
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.
<Evaluation>
The obtained multilayer ceramic capacitor was evaluated as follows. Here, the evaluation of the temperature characteristics of the relative permittivity, dielectric loss, and capacitance was all 10 samples, and the average value was obtained.
(1) Relative permittivity The capacitance is measured under the measurement conditions of a temperature of 25 ° C., a frequency of 1.0 kHz, and a measurement voltage of 1 Vrms. From the obtained capacitance, the thickness of the dielectric layer, the total area of the internal electrode layer, and vacuum It was calculated based on the dielectric constant of
(2) Dielectric loss It measured on the same conditions as an electrostatic capacitance.
(3) Temperature characteristics of capacitance The capacitance was measured at a temperature of 85 ° C., and the rate of change relative to the capacitance at 25 ° C. was determined. In addition, by applying a DC voltage of 2 V, the capacitance at 85 ° C. was measured, and the rate of change with respect to the capacitance at 25 ° C. without load (DC = 0 V) was obtained (hereinafter referred to as high temperature load). This is called the temperature change rate of the relative permittivity in the state.)
(4) High-temperature load test The test was performed at a temperature of 140 ° C. under an applied voltage of 9.45V. The number of samples in the high-temperature load test was 30 samples, and the average failure time, which was the time when the failure probability reached 50%, was examined.
(5) Average particle diameter of crystal particles comprising crystal grains constituting the first crystal group and crystal grains constituting the second crystal group Polishing to a state where the cross section of the dielectric ceramic can be observed with a transmission electron microscope For the polished surface (ion milling), an image displayed by a transmission electron microscope is taken into a computer, a diagonal line is drawn on the screen, and the contours of crystal particles existing on the diagonal line are image-processed. The diameter when the area was replaced with a circle having the same area was calculated, and the average value of about 50 calculated crystal grains was determined. As a result of the measurement, the average particle diameter of the crystal particles of the prepared samples was a value corresponding to the average particle diameter of the barium titanate powder used.
(6) Measurement of magnesium concentration gradient and crystal particle ratio (b / (a + b)) in crystal particles Regarding the magnesium concentration distribution in crystal particles, the cross section of the dielectric ceramic was polished and then transferred to a transmission electron microscope. Draw a circle containing about 30 crystal particles on the image displayed on the attached monitor, select the crystal particles that fall within and around the circle, and use a transmission electron microscope with an elemental analyzer to perform elemental analysis Went. The crystal particles to be selected at this time are obtained by calculating the area of each particle by image processing from the contour, and calculating the diameter when replaced with a circle having the same area, and the calculated crystal particle diameter is ± 60 of the average particle diameter. Crystal grains in the range of%. The spot size of the electron beam at the time of analysis is about 1 nm, and the location to be analyzed is in the range from the vicinity of the grain boundary of the crystal grain to the center position of the central part, and approximately equal intervals on a straight line drawn toward the center. It was determined from the values analyzed in the vicinity of the grain boundary and at a depth of about 20 nm from the grain boundary. In this case, a value obtained by subtracting the magnesium concentration at a depth of 19 to 21 nm (magnesium concentration) from the magnesium concentration at the grain boundary (0 to 1 nm) of the crystal grains is analyzed (for example, 20 nm-0 nm = 20 nm). ) To obtain a concentration gradient. This analysis was performed at five locations for each sample to determine the average value.
In such an analysis, a crystal particle having a magnesium concentration gradient of 0.05 to 0.20 atomic% / nm is referred to as a “crystal particle constituting the first crystal group”, and the magnesium concentration gradient is 0.005. The crystal grains showing ˜0.03 atomic% / nm were defined as “crystal grains constituting the second crystal group”.
In the dielectric ceramic, the area ratio of the crystal grains constituting the second crystal group to the total area of the crystal grains constituting the first crystal group and the crystal grains constituting the second crystal group, b / (a + b) (Where a represents the area of the crystal grains 1a constituting the first crystal group, and b represents the area of the crystal grains 1b constituting the second crystal group), the crystal grains 1a, The average particle size of 1b was calculated from the area data obtained. The b / (a + b) ratio of the prepared sample was equivalent to the mixing ratio of BT powder and BMT powder.
(7) Composition analysis of sample The composition analysis of the sample which is the obtained sintered compact was performed by ICP analysis and 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. Manganese was determined in terms of MnO. As a result of the analysis, the composition of the dielectric layer was consistent with the prepared composition for all the samples. The results of the composition and properties are shown in Table 1.
  As is clear from the results in Table 1, sample No. 1 to 3, 7, 8, 10, 11, 13, 14, 16 to 21, 23 to 26, 28 and 29, the dielectric ceramic has a relative dielectric constant of 4400 or more at room temperature (25 ° C.) and a high temperature. The temperature change rate of the relative permittivity in the loaded state was within -40%.
The dielectric ceramic further contains vanadium, and the content of vanadium is 0.05 to 0.20 mol in terms of V 2 O 5 with respect to 100 mol of titanium constituting the barium titanate. 1 to 3, 7, 8, 11, 13, 14, 16 to 21, 23 to 26, 28 and 29, the dielectric ceramic has a relative dielectric constant of 4400 or more at room temperature (25 ° C.) and a high temperature load state. The temperature change rate of the dielectric constant at -40% was within -40%, and the high temperature load life was 8 hours or more.
  In contrast, sample no. For 4-6, 9, 12, 15, 22, 27, and 30-34, the relative dielectric constant is lower than 4400, or applied at 85 ° C. and 2 V against the relative dielectric constant measured at no load and at room temperature (25 ° C.). The rate of change in relative permittivity at ˜ was greater than −40%.
DESCRIPTION OF SYMBOLS 1 ...... Capacitor body 3 ... External electrode 5 ... Dielectric layer 7 ... Internal electrode layer 11 ... Grain boundary phase 9 ... Crystal grain 9a ... 1st The crystal particles 9b constituting the crystal group of the crystal grains constituting the second crystal group

Claims (2)

  1. A capacitor comprising a dielectric layer made of a dielectric ceramic containing crystal grains of barium titanate and containing magnesium, manganese, and one kind of rare earth element (RE) selected from yttrium, dysprosium, holmium and erbium And the dielectric ceramic is based on 100 moles of titanium constituting the barium titanate.
    0.3 to 1.5 mol of the magnesium in terms of MgO,
    0.05 to 0.3 mol of the manganese in terms of MnO,
    Containing 0.3 to 0.6 mol of one of the rare earth elements (RE) selected from yttrium, dysprosium, holmium and erbium in terms of RE 2 O 3 ;
    The crystal grains include a first crystal group having a magnesium concentration gradient of 0.05 atomic% / nm or more and 0.20 atomic% / nm or less in a depth range of 20 nm from the grain boundary, and 20 nm from the grain boundary. A second crystal group in which the concentration gradient of magnesium in the depth range is 0.005 atomic% / nm or more and 0.03 atomic% / nm or less;
    The average particle diameter of the crystal grains constituting the first crystal group and the crystal grains constituting the second crystal group is 0.15 to 0.40 μm,
    B / (a + b) where a is the area of the crystal grains constituting the first crystal group and b is the area of the crystal grains constituting the second crystal group as seen on the polished surface of the dielectric ceramic. ) Is 0.4 to 0.7.
  2. 2. The dielectric ceramic according to claim 1, wherein the dielectric ceramic further contains 0.05 to 0.20 mol of vanadium in terms of V 2 O 5 with respect to 100 mol of titanium constituting the barium titanate. Capacitor.
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