JP5137429B2 - Dielectric porcelain and capacitor - Google Patents

Description

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

  At present, the spread of digital electronic devices such as mobile computers and mobile phones is remarkable, and in the near future digital terrestrial broadcasting is going to be deployed nationwide. There are liquid crystal displays, plasma displays, and the like as digital electronic devices that are receivers for digital terrestrial broadcasting, and many LSIs are used for these digital electronic devices.

Therefore, many bypass capacitors are mounted on the power supply circuits that make up these digital electronic devices such as liquid crystal displays and plasma displays, but the capacitors used here require high capacitance. In some cases, a high dielectric constant monolithic ceramic capacitor (see, for example, Patent Document 1) is adopted. On the other hand, when temperature characteristics are important even with a low capacitance, a temperature compensation type monolithic ceramic capacitor (eg, a small capacitance change rate) , See Patent Document 2).
JP 2001-89231 A JP 2001-294482 A

  However, since the multilayer ceramic capacitor having a high dielectric constant disclosed in Patent Document 1 is composed of crystal grains of dielectric ceramic having ferroelectricity, the temperature change rate of relative permittivity is large and exhibits dielectric polarization. There was a problem of large hysteresis.

  In addition, a capacitor formed by using a ferroelectric dielectric ceramic disclosed in Patent Document 1 tends to generate a “sounding” phenomenon due to an electrically induced strain on a power supply circuit. It was an obstacle when using it.

  On the other hand, temperature compensated monolithic ceramic capacitors have the advantage that the dielectric porcelain constituting them is paraelectric, so that the hysteresis in the electric field-dielectric polarization characteristics is small, and the electrical induced strain peculiar to ferroelectricity does not occur However, since the dielectric ceramic has a low relative dielectric constant, there is a problem in that the storage capacity is low and the performance as a bypass capacitor is not satisfied.

  Accordingly, an object of the present invention is to provide a dielectric ceramic exhibiting a temperature characteristic of a high dielectric constant and a stable relative dielectric constant, and a capacitor using the dielectric ceramic.

The dielectric ceramic of the present invention is mainly composed of barium titanate, a cubic crystalline particles mainly composed of a dielectric ceramic consisting of a grain boundary phase and formed between the crystal grains, Ba Magnesium in an amount of 0.01 to 0.06 mol in terms of MgO, yttrium in a proportion of 0.0015 to 0.03 mol in terms of Y ₂ O ₃ , and manganese in terms of MnO with respect to 1 mol of lithium. .0002 to 0.03 mol in proportion to 100 parts by mass of barium titanate and 4.2 to 33.3 parts by mass of niobium in terms of Nb ₂ O ₅ , and The average particle size is 0.05 to 0.2 μm.

  The 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 a conductor layer.

  According to the dielectric ceramic of the present invention, it has crystal grains mainly composed of barium titanate, contains magnesium, yttrium, manganese and niobium in the above-mentioned ratio in terms of oxides, and the average grain of the crystal grains By making the diameter 0.05 to 0.2 μm, the temperature change rate of the relative permittivity is smaller than that of a conventional dielectric ceramic having ferroelectricity, and compared with a conventional dielectric ceramic having paraelectricity. Thus, a dielectric ceramic having a high dielectric constant and a stable relative dielectric constant temperature characteristic and a small spontaneous polarization can be obtained.

  Further, according to the capacitor of the present invention, the dielectric layer exhibits temperature characteristics of a high dielectric constant and a stable relative dielectric constant, and the dielectric ceramic having a small spontaneous polarization is applied, so that the dielectric layer is higher than the conventional capacitor. Capacitors with stable capacitance and temperature characteristics can be formed. For this reason, when this capacitor is used in a power supply circuit, it is possible to suppress the occurrence of a “sounding” phenomenon caused by electrically induced distortion.

The dielectric porcelain of the present invention contains barium titanate as a main component and contains magnesium, yttrium, manganese and niobium. The content of magnesium is 0.000 in terms of MgO with respect to 1 mol of barium. While containing yttrium in a proportion of 0.0015 to 0.03 mol in terms of Y ₂ O ₃ and manganese in a proportion of 0.0002 to 0.03 mol in terms of MnO, in a proportion of 01 to 0.06 mol, Niobium is contained in an amount of 4.2 to 33.3 parts by mass in terms of Nb ₂ O ₅ with respect to 100 parts by mass of the barium titanate.

  In the dielectric ceramic according to the present invention, it is important that the average grain size of crystal grains constituting the dielectric ceramic is 0.05 to 0.2 μm.

When the composition and particle size are within the above ranges, the relative permittivity at room temperature is 250 or more, the relative permittivity at 125 ° C. is 230 or more, and the temperature coefficient of relative permittivity between 25 ° C. and 125 ° C. ((ε _t −ε ₂₅ ) / Ε ₂₅ (T-25)) can be made to be 1000 × 10 ⁻⁶ / ° C. or less in absolute value, and there is an advantage that a dielectric ceramic having a small hysteresis in electric field-dielectric polarization characteristics can be formed.

  Such a dielectric porcelain of the present invention is a solid solution of barium titanate with magnesium, yttrium, manganese and niobium, and barium titanate having a tetragonal crystal structure and exhibiting ferroelectricity, magnesium, yttrium, In addition to solid solution of manganese and niobium, by making the average particle size of the crystal particles mainly composed of barium titanate in which these components are dissolved into a specific range, the crystal structure of the crystal particles is cubic. It can be the subject. As a result, the ferroelectricity due to the tetragonal crystal structure is lowered, the paraelectricity can be increased, and the spontaneous polarization can be reduced by increasing the paraelectricity.

  Further, by making the crystal structure of the crystal grains mainly composed of barium titanate into a crystal structure mainly composed of a cubic system, a curve indicating a change rate of relative permittivity is in a temperature range of −55 ° C. to 125 ° C. In both cases, the hysteresis in the electric field-dielectric polarization characteristics is reduced. Therefore, even when the relative dielectric constant is 250 or more, a dielectric ceramic having a small relative dielectric constant temperature coefficient can be obtained.

That is, when a predetermined amount of magnesium, yttrium and manganese is contained in barium titanate within the above-mentioned range, a dielectric having a Curie temperature of room temperature (25 ° C.) or higher and a positive temperature coefficient of relative dielectric constant is shown. However, when Nb ₂ O ₅ is further added to the dielectric ceramic exhibiting such dielectric characteristics, the effect of the present invention appears greatly, and the temperature coefficient of the relative permittivity is reduced. Temperature characteristics can be flattened. In this case, the curve indicating the change rate of the relative dielectric constant has two peaks centering on room temperature in the temperature range of −55 ° C. to 125 ° C.

Here, niobium has a function of suppressing coarsening of crystal grains mainly composed of barium titanate, and niobium is converted to 4.2 to 33.3 in terms of Nb ₂ O ₅ with respect to 100 parts by mass of barium titanate. It is important to contain part by mass.

That is, when the content of Nb ₂ O ₅ with respect to 100 parts by mass of barium titanate is less than 4.2 parts by mass, although the dielectric constant of the dielectric ceramic is high, the temperature coefficient of the dielectric constant is large, When the content of Nb ₂ O ₅ with respect to 100 parts by mass of barium titanate is more than 33.3 parts by mass, the relative dielectric constant at 25 ° C. is lower than 250, and the relative dielectric constant at 125 ° C. is less than 230. It is because it becomes.

The contents of magnesium, yttrium, and manganese are 0.01 to 0.06 mol in terms of MgO and 0.0015 to 0.005 in terms of Y ₂ O ₃ with respect to 1 mol of barium. It is important that manganese is contained in a proportion of 0.0002 to 0.03 mol in terms of MnO in a proportion of 03 mol.

That is, when the content of magnesium with respect to 1 mol of barium is less than 0.01 mol or more than 0.06 mol in terms of MgO, the temperature coefficient of the dielectric constant of the dielectric ceramic increases, and When the content of yttrium with respect to 1 mol of barium is less than 0.0015 mol in terms of Y ₂ O ₃ or more than 0.03 mol, the dielectric constant of the dielectric ceramic is high, but the relative permittivity When the content of manganese with respect to 1 mol of barium is less than 0.0002 mol or more than 0.03 mol in terms of MnO, the relative permittivity of the dielectric ceramic is increased. This is because the temperature coefficient increases.

  Furthermore, in the dielectric ceramic according to the present invention, it is important that the average particle diameter of crystal grains mainly composed of barium titanate is 0.05 to 0.2 μm.

  That is, by setting the average particle size of the crystal particles mainly composed of barium titanate to 0.05 to 0.2 μm, the crystal particles mainly composed of cubic system of the crystal particles mainly composed of barium titanate. When the average particle size of the crystal grains mainly composed of barium titanate is smaller than 0.05 μm, the hysteresis in the electric field-dielectric polarization characteristics is small and the characteristics are close to paraelectric properties. The relative permittivity of the dielectric porcelain is reduced because the contribution of the above is lost. On the other hand, when the average grain size of the crystal grains is larger than 0.2 μm, a tetragonal crystal phase is observed in the measurement by X-ray diffraction. This is because the temperature coefficient of the dielectric constant of the dielectric ceramic increases. Note that the crystal structure mainly composed of a cubic system means a state in which the intensity of the diffraction peak of the (110) plane, which is the strongest peak of cubic barium titanate, is larger than the intensity of the diffraction peak of a different phase.

In the present invention, the average grain size of the crystal grains is more preferably 0.14 to 0.18 μm in that the polarization charge at 0 V can be ²⁰ nC / cm ² or less in the electric field-dielectric polarization characteristics.

Further, preferable niobium, magnesium, yttrium and manganese contents are as follows: magnesium is 0.017 to 0.06 mol in terms of MgO with respect to 1 mol of barium, and yttrium is 0.005 to 0.01 mol in terms of Y ₂ O _3. , Manganese is contained in a ratio of 0.01 to 0.03 mol in terms of MnO, and niobium is contained in a range of 6.3 to 15.6 parts by mass in terms of Nb ₂ O _{5 with} respect to 100 parts by mass of barium titanate. In addition, the titanium ratio with respect to 1 mole of barium is preferably 0.97 to 0.98, and the dielectric ceramic in this range has a relative dielectric constant of 400 or more at 25 ° C. and a relative dielectric constant of 125 or more at 125 ° C. Thus, the temperature coefficient of the relative permittivity can be made to be 400 × 10 ⁻⁶ / ° C. or less in absolute value.

Next, a method for manufacturing the dielectric ceramic according to the present invention will be described. First, BaCO ₃ powder, TiO ₂ powder, MgO powder, Y ₂ O ₃ powder, and manganese carbonate powder each having a purity of 99% or more are used as the raw material powder. These raw material powders are composed of 0.01 to 0.06 mol of MgO and 0.0015 to 0.03 mol of Y ₂ O ₃ with respect to 1 mol of barium constituting barium titanate. , Manganese carbonate is blended at a ratio of 0.0002 to 0.03 mol.

  Next, the above mixture of raw material powders is wet-mixed and dried, and then calcined at a temperature of 900 to 1100 ° C. and pulverized. At this time, a dielectric ceramic having a high dielectric constant maintaining a temperature characteristic of a dielectric constant close to paraelectricity is obtained by growing grains so that the crystal structure of the calcined powder is mainly composed of a cubic system. Is possible.

Next, Nb ₂ O ₅ powder is mixed at a ratio of 4.0 to 32 parts by mass with respect to 100 parts by mass of the calcined powder. Then, the dielectric ceramic of this invention can be obtained by shape | molding mixed powder in the shape of a pellet and baking in the temperature range of 1150 degreeC-1250 degreeC in air | atmosphere. Here, when the firing temperature is lower than 1150 ° C., the grain growth and densification of the crystal grains are suppressed, so that the density is low. On the other hand, when the firing temperature is higher than 1250 ° C., the crystal grains grow. There is a risk of doing too much.

  Next, FIG. 1 is a schematic sectional view showing an example of the capacitor of the present invention. The following capacitor can be formed using the dielectric ceramic of the present invention.

  The capacitor of the present invention has an external electrode 12 provided at the end of the capacitor body 10, and the capacitor body 10 is a laminate in which dielectric layers 13 and conductor layers 14 as internal electrode layers are alternately laminated. It is composed of a body 1. It is important that the dielectric layer 13 is formed by the above-described dielectric ceramic of the present invention. In this case, a base metal such as Ni or Cu is desirable in that the manufacturing cost can be suppressed even if the conductor layer 14 is highly laminated, and particularly, simultaneous firing with the dielectric layer 13 constituting the capacitor of the present invention is intended. Ni is more desirable. The conductor layer 14 preferably has an average thickness of 1 μm or less.

  In the case of producing such a capacitor, the above-mentioned mixed powder is formed into a green sheet, a conductor paste to be a conductor layer 14 is prepared, printed on the surface of the green sheet, laminated and fired. The laminated body 1 is formed. Thereafter, a conductor paste is further printed on the end face of the laminate 1 and fired to form the external electrode 2, whereby a capacitor can be obtained.

The dielectric ceramic according to the present invention was produced as follows. First, BaCO ₃ powder, TiO ₂ powder, MgO powder, Y ₂ O ₃ powder, and manganese carbonate powder each having a purity of 99.9% were prepared and mixed at a ratio shown in Table 1 to prepare a mixed powder. The amounts of Mg, Y and Mn shown in Table 1 are amounts corresponding to MgO, Y ₂ O ₃ and MnO, respectively. Ti is a molar ratio relative to 1 mol of Ba.

Next, the mixed powder was calcined at a temperature of 1000 ° C. to prepare a calcined powder, and the obtained calcined powder was pulverized. Thereafter, Nb ₂ O ₅ powder having a purity of 99.9% was mixed at a ratio shown in Table 1 with respect to 100 parts by mass of the calcined powder. Thereafter, the mixed powder was granulated and formed into pellets having a diameter of 16.5 mm and a thickness of 1 mm.

  Next, 10 pellets of each composition were fired at a temperature shown in Table 1 in the air. The average grain size of the dielectric ceramic is obtained by polishing the fracture surface of the dielectric ceramic, taking a picture of the internal structure using a scanning electron microscope, and then processing the contours of the crystal grains shown in the photograph. Each particle was regarded as a circle, and the diameter was obtained and averaged. The magnification of the photograph was about 30000 times, the number of observation points was 3 for each sample, and the average value was obtained.

  An indium gallium conductor layer was printed on the surface of the fired sample. These samples, which are dielectric ceramics, were measured for capacitance using an LCR meter 4284A at a frequency of 1.0 kHz and an input signal level of 1.0 V, and the relative dielectric constant was determined from the diameter and thickness of the sample and the area of the conductor layer. The rate was calculated. Moreover, the temperature coefficient of the dielectric constant was measured in the range of 25 to 125 ° C. In these measurements, the number of samples was 10 and the average value was obtained.

  Moreover, the magnitude | size of the electrically induced distortion was calculated | required by the measurement of dielectric polarization about the obtained dielectric ceramic. In this case, the evaluation was based on the value of the charge amount (residual polarization) at 0 V when the voltage was changed in the range of ± 1250 V. The composition analysis of the 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, the average particle size of the calcined powder, and the firing temperature, and Table 2 shows the results of the average particle size and characteristics of the crystal particles after firing.

Here, the addition amount of Nb ₂ O ₅ in Table 1 is a ratio with respect to 100 parts by mass of the calcined powder. On the other hand, the content of Nb ₂ O ₅ in Table 2 is a ratio with respect to 100 parts by mass of barium titanate in the dielectric ceramic. The amounts of Mg, Y and Mn shown in Table 2 are oxide equivalent amounts. In Table 2, samples without a circle in the column of the relative dielectric constant temperature change curve indicate samples in which two peaks are not observed, and samples without a circle in the polarization charge column indicate polarization. It is meant to indicate a sample whose charge is not less than 20 nC / cm ² .

As is clear from the results in Table 2, the sample No. In 2-7, 10-13, 16-19, 21-25, 27, 28, 30, 33, and 34, the relative dielectric constant at 25 ° C. is 250 or more, the relative dielectric constant at 125 ° C. is 230 or more, and 25 The temperature coefficient of the relative dielectric constant at ˜125 ° C. was 1000 × 10 ⁻⁶ / ° C. or less in absolute value.

In particular, 0.017 to 0.06 mol of MgO, 0.005 to 0.01 mol of Y ₂ O ₃ , 0.01 to 0.03 mol of MnO, and Nb relative to 100 parts by mass of barium titanate as the main component. Sample No. ₂ having a content of ₂ O ₅ of 6.3 to 15.6 parts by mass and a titanium ratio with respect to 1 mol of barium of 0.97 to 0.98. 3 to 5, 11, 12, 17 to 19, 24, 25, 27, 33 and 34, the relative dielectric constant at 25 ° C. is 400 or more, the relative dielectric constant at 125 ° C. is 380 or more, and the temperature coefficient of the relative dielectric constant is In the measurement of the electric field-dielectric polarization characteristics, the absolute value is 400 × 10 ⁻⁶ / ° C. or less, the curve indicating the change rate of the relative dielectric constant has two peaks in the temperature range of −55 ° C. to 125 ° C. There was no significant hysteresis. The sample in which no hysteresis was observed had a polarization charge of 20 nC / cm ² or less at 0V.

  Sample No. selected from these samples. FIG. 2 shows an X-ray diffraction diagram of the dielectric ceramic No. 4, FIG. 3 shows a graph showing a change in relative permittivity of the sample, and FIG. 4 shows an electric field-dielectric polarization characteristic of the sample. Sample No. As shown in FIGS. 2 to 4, the dielectric ceramic of No. 4 has a cubic crystal structure as a main component, and the temperature characteristics of the relative permittivity have two peaks centering on 25 ° C. In addition, the change rate of the relative dielectric constant was small, and the hysteresis of the electric field-dielectric polarization characteristics was small. The other samples also have a crystal structure mainly composed of a cubic system, and the change rate of the relative permittivity is small.

On the other hand, in a sample outside the scope of the present invention, the relative dielectric constant at 25 ° C. is less than 200, or there is hysteresis in dielectric polarization, and the temperature coefficient of relative dielectric constant is 1000 × 10 ^{−6 in} absolute value. It was larger than / ° C.

It is a cross-sectional schematic diagram which shows the example of the capacitor | condenser of this invention. It is a typical example of the X-ray diffraction pattern of the dielectric ceramic of the present invention (Sample No. 4). It is a graph which shows the change rate of the dielectric constant about the dielectric material ceramic of this invention (sample No. 4, sample No. 33, and sample No. 34). It is a typical example of the dielectric polarization (VQ) characteristic calculated | required about the dielectric material ceramic of this invention (sample No. 4).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laminated body 10 Capacitor main body 13 Dielectric layer 14 Conductor layer

Claims (2)

Barium titanate as a main component, and crystal grains mainly composed of cubic, a dielectric ceramic consisting of a grain boundary phase and formed between the crystal grains, with respect to bar helium 1 mole of magnesium Of MgO in a proportion of 0.01 to 0.06 mol, yttrium in a proportion of 0.0015 to 0.03 mol in terms of Y ₂ O ₃ and manganese in a proportion of 0.0002 to 0.03 mol in terms of MnO. While contained in a ratio, with respect to 100 parts by mass of the barium titanate, niobium is contained in an amount of 4.2 to 33.3 parts by mass in terms of Nb ₂ O ₅ , and the average grain size of the crystal grains is 0.05 to A dielectric ceramic characterized by being 0.2 μm.   A capacitor comprising a laminate of a dielectric layer made of the dielectric ceramic according to claim 1 and a conductor layer.

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