JP2014189464A - Ceramic composition and ceramic electronic part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel ceramic composition which has a high relative dielectric constant and can suppress lowering of the relative dielectric constant even when a high DC voltage is applied and a ceramic electronic part which uses the ceramic composition and keeps a high capacity even when a DC voltage is applied.SOLUTION: A ceramic composition has a general formula of (BiSr)(FeTi)O, where 0.2≤x≤0.7 and 0.2≤y≤0.7, and its sintered body has an average particle size of 1.0 μm or smaller.

Description

  The present invention relates to a porcelain composition and a ceramic electronic component using the porcelain composition.

  In recent years, miniaturization and high performance of electrical equipment and electronic equipment have rapidly progressed, and ceramic electronic components used in such equipment are also required to be small and to have a larger capacity (smaller and larger capacity). .

In a ceramic capacitor which is one of ceramic electronic components, a BaTiO ₃ based material having a high relative dielectric constant is used as a porcelain composition in order to reduce the size and capacity. However, the relative dielectric constant of the BaTiO ₃ -based porcelain composition is lowered by the voltage applied with the DC voltage. For this reason, when used in an environment where a DC voltage is applied, an increase in the DC voltage to be applied decreases the relative dielectric constant, resulting in a decrease in capacity as an electronic component. For this reason, in order to use such an electronic component in an electronic circuit, it is necessary to take into account a decrease in capacity due to application of a DC voltage.

  For this reason, it has been required to suppress a decrease in the relative dielectric constant of the porcelain composition and the capacity of the electronic component by the applied DC voltage. In particular, in recent years, the DC voltage applied voltage applied to electronic components tends to increase, and the demand has become stronger.

On the other hand, Patent Document 1 and Patent Document 2 are BaTiO ₃ based materials having a high relative dielectric constant as a porcelain composition, and have an effect of reducing a decrease in relative dielectric constant due to application of a DC voltage. A composition is disclosed.

JP 2000-058377 A JP 2000-058378 A

  However, the porcelain compositions disclosed in Patent Document 1 and Patent Document 2 are not sufficient to suppress the change in capacitance when the DC voltage applied to the electronic component is increased. In particular, when a DC voltage having a high electric field strength of 5 V / μm or more is applied to the porcelain composition, the rate of change of the relative dielectric constant is reduced by 30% or more compared to when no DC voltage is applied. It was.

  The present invention has been made in view of the above problems, and provides a novel ceramic composition having a high relative dielectric constant capable of suppressing a decrease in relative dielectric constant even when a high DC voltage is applied. With the goal. Another object of the present invention is to provide a ceramic electronic component that can maintain a high capacity even when a DC voltage is applied using the porcelain composition.

The porcelain composition of the present invention has a general formula represented by (Bi _1-x Sr _x ) (Fe _1-y Ti _y ) O ₃ , and 0.2 ≦ x ≦ 0.7 and 0.2 ≦ y ≦ The average particle size of the sintered body is 1.0 μm or less.

  Accordingly, it is possible to provide a novel porcelain composition having a high relative dielectric constant that can suppress a decrease in relative dielectric constant even when a high DC voltage is applied.

  In the porcelain composition of the present invention, the ratio of x and y in the general formula is preferably in the range of 0.9 ≦ x / y ≦ 1.1.

  The ceramic electronic component of the present invention is characterized by having the above-mentioned porcelain composition.

  The present invention can provide a novel porcelain composition having a high dielectric constant capable of suppressing a decrease in relative dielectric constant even when a high DC voltage is applied. In addition, a ceramic electronic component that can maintain a high capacity even when a DC voltage is applied can be obtained using the porcelain composition.

1 is a cross-sectional view of a multilayer ceramic capacitor according to an embodiment of the present invention.

  Hereinafter, the present invention will be described based on embodiments shown in the drawings.

The porcelain composition of the present embodiment is represented by the general formula (Bi _1-x Sr _x ) (Fe _1-y Ti _y ) O ₃ , and 0.2 ≦ x ≦ 0.7 and 0.2 ≦ y ≦ 0. The average particle size of the sintered body is 1.0 μm or less.

It is represented by the general formula _{(Bi 1-x Sr x)} (Fe 1-y Ti y) O 3, if 0.2 ≦ x ≦ 0.7 and a 0.2 ≦ y ≦ 0.7, the relative dielectric constant The relative dielectric constant can be kept high even when a high DC voltage is applied. Further, x is more preferably not less than 0.3 and not more than 0.65 from the viewpoint that the relative permittivity can be kept high even when the relative permittivity and a high DC voltage are applied. And y is more preferably 0.5 or more and 0.65 or less from the viewpoint of relative dielectric constant.

Further, the ratio of x and y in the general formula is more preferably 0.9 ≦ x / y ≦ 1.1. Within this range, in the general formula (Bi _1-x Sr _x ) (Fe _1-y Ti _y ) O ₃ , the ratio of (Bi, Sr) and (Fe, Ti) is close to the stoichiometric composition. The inventors believe that since the crystals in the sintered body are stable, the relative permittivity of the porcelain composition is higher, and the decrease in the relative permittivity can be suppressed even when the applied DC voltage is high. .

  The sintered body average particle diameter of the ceramic composition in the present embodiment is an average particle diameter constituting the sintered body structure. The measurement method is not particularly limited, but the sample is cut on an arbitrary surface, the cut surface is polished, and the polished surface is subjected to chemical etching or the like so that the particles and grain boundaries in the sintered body can be confirmed. Then, the particle diameter of the image obtained by observing the surface with a scanning electron microscope (SEM) is measured by a code method. The particle diameter can be the average particle diameter of the sintered body particles.

In this coding method, an arbitrary straight line is drawn with a length L on the observed image plane, and the intersection N with the grain boundary intersecting with the straight line is measured. As shown in the equation (1), the straight line length L Is divided by N to obtain the average length between the grain boundaries. Then, assuming that the crystal grains are isometric spheres, 1.5 can be multiplied to obtain the average particle diameter, that is, the sintered body average particle diameter D.
D = 1.5 × (L / N) (1)

  The sintered compact average particle diameter D of this embodiment is 1.0 micrometer or less. Spontaneous polarization resulting from dielectric properties as a porcelain composition is controlled by grain boundaries in the sintered body, but the critical sintered body average particle diameter D for obtaining the control effect is 1.0 μm or less. The ferroelectricity as a porcelain composition is suppressed depending on the size. For this reason, the inventors speculate that it is possible to obtain an effect of reducing a decrease in relative permittivity due to application of a DC voltage. Furthermore, from the viewpoint of obtaining a higher relative dielectric constant, the sintered body average particle diameter D is preferably 0.1 μm or more.

As a method for producing ceramic composition of the present embodiment, the general formula _{(Bi 1-x Sr x)} (Fe 1-y Ti y) O 3 is prepared raw material to a desired ratio, mixed, 1000 A sintered body can be obtained by performing a heat treatment (firing) at a temperature of 0 ° C. or higher.

  For controlling the average particle size of the sintered body, it is effective to adjust the particle size when powder is used as a raw material. Furthermore, the raw material powder is mixed by a ball mill using a dispersant, whereby the dispersion of the raw material powder can be improved and the average particle size of the sintered body can be controlled more. Furthermore, a structure having a uniform composition can be obtained as the sintered body.

  In the heat treatment at 1000 ° C. or higher, in particular, the average particle size of the sintered body can be controlled by the temperature rising / falling process, the heat treatment temperature, and the heat treatment holding time. In order to make the particle size uniform, the temperature increase / decrease process is more preferably a rapid temperature increase / decrease of 30 ° C./min or more. Moreover, it is more preferable from the viewpoint of making the particle size uniform that the temperature of the heat treatment is set to 1000 ° C. or higher and the holding time thereof is within 1 minute.

As the raw material, an oxide mainly composed of Bi, Sr, Fe, and Ti or a mixture thereof can be used as the raw material powder. Furthermore, various compounds that become the above-described oxides and composite oxides by firing, for example, carbonates, oxalates, nitrates, hydroxides, organometallic compounds, and the like can be appropriately selected and mixed for use. Specifically, SrO may be used as a raw material for Sr, or SrCO ₃ may be used.

  In the ceramic composition according to the present embodiment, it is more preferable that the sintered body has a uniform particle diameter (sintered body average particle diameter D) from the viewpoint of reducing a decrease in relative permittivity due to application of a DC voltage. . As a method of uniformly controlling the sintered body average particle diameter D, it is possible to use a raw material powder having a uniform particle diameter, or to control by the firing conditions. The average sintered body average particle diameter D means that the average sintered body average particle diameter D is 1.0 μm, the maximum value of the sintered body particles is 1.2 μm, It shows that the particle size distribution is smaller. Specifically, when the standard deviation σ of the sintered body average particle diameter D is σ <3, it is more preferable from the viewpoint of reducing a decrease in relative dielectric constant due to application of a DC voltage.

Further, the ceramic composition according to the present embodiment has a uniform composition of the sintered body, that is, a structure (uniform structure) in which the elements constituting the composition are distributed without being biased by applying a DC voltage. This is more preferable from the viewpoint of reducing the decrease in relative permittivity. A method for determining whether or not the obtained porcelain composition has a uniform structure is to form a perovskite structure represented by ABO ₃ from an X-ray diffraction pattern by X-ray diffraction measurement using CuKα as a radiation source. It can be judged by whether or not.

  Examples of the ceramic electronic component having the porcelain composition according to the present embodiment include, but are not limited to, a multilayer ceramic capacitor, a piezoelectric element, a chip inductor, a chip varistor, a chip thermistor, a chip resistor, and other surfaces. A mounting (SMD) chip type electronic component is exemplified.

  A multilayer ceramic capacitor will be exemplified and described. FIG. 1 shows a multilayer ceramic capacitor according to an embodiment of the present invention. The multilayer ceramic capacitor 1 has a capacitor element body 10 having a configuration in which dielectric layers 2 and internal electrode layers 3 are alternately stacked. At both ends of the capacitor element body 10, a pair of external electrodes 4 are formed which are electrically connected to the internal electrode layers 3 arranged alternately in the element body 10. The shape of the capacitor element body 10 is not particularly limited, but is usually a rectangular parallelepiped shape. Moreover, there is no restriction | limiting in particular also in the dimension, What is necessary is just to set it as a suitable dimension according to a use.

  In order to increase the capacitance of the multilayer ceramic capacitor 1, it is effective to reduce the thickness of the dielectric layer 2 sandwiched between the internal electrode layers 3. In this case, when the thickness of the dielectric layer 2 is reduced to several μm or less, the sintered body average particle diameter D is 1.0 μm or less, which is effective for suppressing short circuit failure and breakdown voltage failure. Is obtained. This is presumed to be because there are more sintered particles in the direction of the internal electrode layer facing the dielectric layer. And from a viewpoint of preventing a short circuit defect and a pressure | voltage resistant defect more, the sintered compact average particle diameter D is 1.0 micrometer or less, and the particle diameter of the largest sintered compact among these is 1.2 micrometer or less.

  The thickness of the dielectric layer 2 is not particularly limited, and may be appropriately determined according to the use of the multilayer ceramic capacitor 1.

  The conductive material contained in the internal electrode layer 3 is not particularly limited, but Pd, Ag, Pd—Ag alloy, Cu or Cu-based alloy is preferable. The Pd, Ag, Pd—Ag alloy, Cu, or Cu-based alloy may contain various trace components such as P or the like in an amount of about 0.1% by weight or less. The internal electrode layer 3 may be formed using a commercially available electrode paste. What is necessary is just to determine the thickness of the internal electrode layer 3 suitably according to a use etc.

  As mentioned above, although embodiment of this invention has been described, this invention is not limited to the embodiment mentioned above at all, and can be variously modified within the range which does not deviate from the summary of this invention.

  EXAMPLES Hereinafter, although the specific Example of this invention is given and this invention is demonstrated further in detail, this invention is not limited to these Examples.

As raw materials, Bi ₂ O ₃ , SrCO ₃ , Fe ₂ O ₃ , and TiO ₂ powders were prepared.

  These were weighed so that the composition was as shown in Table 1, wet-mixed with a ball mill, and then dried to obtain each mixed powder. And these mixed powder was calcined at 900 degreeC, and the calcined powder was obtained.

  The obtained calcined powder: 100 parts by weight, polyvinyl butyral resin: 10 parts by weight, dibutyl phthalate (DOP) as a plasticizer: 5 parts by weight, and alcohol as a solvent: 100 parts by weight were mixed by a ball mill. Thus, a dielectric layer paste was prepared.

  In addition to the above, Pd particles: 44.6 parts by weight, terpineol: 52 parts by weight, ethyl cellulose: 3 parts by weight, and benzotriazole: 0.4 parts by weight are kneaded by three rolls to form a slurry. To prepare an internal electrode layer paste.

  And the green sheet was formed on the PET film so that the thickness after drying might be set to 7 micrometers using the produced dielectric layer paste. Next, the internal electrode layer was printed in a predetermined pattern using the internal electrode layer paste thereon, and then the sheet was peeled from the PET film to produce a green sheet having the internal electrode layer. Next, a plurality of green sheets having internal electrode layers were laminated and pressure-bonded to form a green laminate, and the green laminate was cut into a predetermined size to obtain a green chip.

  Next, the obtained green chip was subjected to binder removal treatment (temperature rising rate: 25 ° C./hour, holding temperature: 260 ° C., temperature holding time: 8 hours, atmosphere: in air), and fired (temperature rising rate: 200). C./hour, holding temperature: temperature shown in Table 1, temperature holding time: 2 hours, cooling rate: 200.degree. C./hour, atmosphere: in air) to obtain a multilayer ceramic fired body.

  Next, after polishing the end face of the obtained multilayer ceramic fired body with sand blasting, In-Ga eutectic alloy was applied as an external electrode, and Examples 1 to 17 having the same shape as the multilayer ceramic capacitor shown in FIG. In Examples 1 to 3, multilayer ceramic capacitors were obtained. The size of the obtained multilayer ceramic capacitor is 3.2 mm × 1.6 mm × 1.2 mm. The thickness of the dielectric layer is 1.0 μm, the thickness of the internal electrode layer is 1.5 μm, and is sandwiched between the internal electrode layers. The number of dielectric layers was 10.

For the obtained multilayer ceramic capacitors of Examples 1 to 17 and Comparative Examples 1 to 3, the relative dielectric constant (ε _s ) and the change in relative dielectric constant (DC bias characteristics) due to the application of a DC voltage were measured by the following methods. did.

Dielectric constant (ε _s )
A signal having a frequency of 1 kHz and an input signal level (measurement voltage) of 1 Vrms was input to the multilayer ceramic capacitor with a digital LCR meter (4284A manufactured by YHP) at 25 ° C., and the capacitance C was measured. Then, the relative dielectric constant ε _s (no unit) was calculated based on the thickness of the dielectric layer, the effective electrode area, and the capacitance C obtained as a result of the measurement. The results are shown in Table 1. A higher relative dielectric constant is preferable, and a value of 300 or more was judged to be good.

DC bias characteristics A multilayer ceramic capacitor is maintained in an electric field application state of a DC voltage of 5 V / μm at 25 ° C., and a digital LCR meter (4284A manufactured by YHP) has a frequency of 1 kHz and an input signal level (measurement voltage) of 1 Vrms. A signal was input and the capacitance C was measured. The DC bias characteristic was calculated based on equation (2) as the rate of change with respect to the capacitance under an electric field of 0 V / μm.
DC bias characteristic = (capacitance under electric field of 5 V / μm−capacitance under electric field of 0 V / μm) / capacitance under electric field of 0 V / μm × 100 (2)
In this example, it was judged that the DC bias characteristic was within ± 5%, and that the relative dielectric constant decreased due to the application of the current voltage was very good.

Sintered body average particle diameter The multilayer ceramic capacitors of Examples 1 to 17 and Comparative Examples 1 to 3 were obtained by obtaining an arbitrary cross section perpendicular to the stacking direction of the internal electrode layers, and polishing the cross section for chemicals on the surface. Etched. Then, 10 photographs of the sample cross section were obtained from any part of the cross section at a magnification of 10000 using a scanning electron microscope (SEM). The average particle size of the sintered body was calculated by the code method. At this time, 10 straight lines of 5 μm are drawn per photograph, the intersection N with the grain boundary intersecting with the straight line is measured, and the length L of the straight line is divided by N as shown in the equation (1). The average length between the grain boundaries was determined, and the crystal grains were assumed to be isometric spheres, and multiplied by 1.5 to obtain an average particle diameter, that is, a sintered body average particle diameter D. The results are also shown in Table 1.
D = 1.5 × (L / N) (1)

  As shown in Table 1, by comparing Examples 1 to 8 and Comparative Examples 2 to 3, when the Sr and Ti content of the porcelain composition is 0.2 or more and 0.7 or less, the relative dielectric is It can be seen that the rate is high and the DC bias characteristics are better. In Comparative Example 2, since the Sr content was 0.1 and the Ti content was 0.1, the relative dielectric constant was low and the DC bias characteristics were poor. In Comparative Example 3, since the Sr content was 0.9 and the Ti content was 0.9, the relative dielectric constant was low, and the DC bias characteristics were not preferable.

  Further, by comparing Examples 5 and 17 with Comparative Example 1, it can be seen that the DC bias characteristics are good when the sintered body average particle diameter is 1.0 μm or less. In Comparative Example 1, since the average particle size of the sintered body was 1.21 μm, the DC bias characteristics were not preferable.

  Further, Examples 9 to 16 show that when the ratio of x and y is in the range of 0.9 ≦ x / y ≦ 1.1, the relative dielectric constant is high and the DC bias characteristics are good.

  Furthermore, in the photograph which evaluated the sintered compact average particle diameter, the particle size was computed from the area of the area | region enclosed by a grain boundary, and the largest particle size was confirmed. In any of the multilayer ceramic capacitors of Examples 1 to 17, the maximum particle size was 1.2 μm or less, and no short circuit failure or breakdown voltage failure was observed, which was good.

From these results, it was confirmed that a high relative dielectric constant (ε _s ) and good DC bias characteristics can be obtained by setting the dielectric ceramic composition and particle size within the predetermined range of the present invention.

  As described above, the porcelain composition according to the present invention has industrial applicability as a dielectric device and a piezoelectric device.

DESCRIPTION OF SYMBOLS 1 Multilayer ceramic capacitor 2 Dielectric layer 3 Internal electrode layer 4 External electrode 10 Capacitor element body

Claims (3)

The general formula is represented by (Bi _1-x Sr _x ) (Fe _1-y Ti _y ) O ₃ , 0.2 ≦ x ≦ 0.7 and 0.2 ≦ y ≦ 0.7, and sintering A porcelain composition having a body average particle size of 1.0 μm or less.   The porcelain composition according to claim 1, wherein a ratio of x and y in the general formula is 0.9 ≦ x / y ≦ 1.1. A ceramic electronic component comprising the porcelain composition according to claim 1.

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