JP4782552B2 - Dielectric porcelain - Google Patents

Description

  The present invention relates to a dielectric ceramic, and more particularly to a dielectric ceramic having a high dielectric constant even in a low AC electric field region and having a small AC voltage dependency.

  In recent years, a small-sized, high-capacity monolithic ceramic capacitor uses a base metal such as nickel for the internal electrode layer. Therefore, a dielectric layer is often made of a barium titanate-based dielectric material (for example, Patent Document 1). This barium titanate-based dielectric material is prepared by previously synthesizing barium titanate and then adding a predetermined amount of additives such as rare earth elements, magnesium oxide and manganese oxide to the main component powder. Even after sintering, the additive is present in the vicinity or at the grain boundaries of the crystal grains of barium titanate and barium calcium titanate, and the crystal structure is assumed to have a core-shell structure.

Here, the core-shell structure is a basic crystal structure of a tetragonal crystal in which the core portion exhibits ferroelectricity when the inside of the crystal grain is a core and the periphery thereof is a shell, while the shell portion is always a regular crystal structure. It has a double structure mainly composed of cubic crystals showing dielectric properties.
JP-A-11-322414

  In recent years, loads such as ICs tend to be low voltage / large current, and therefore decoupling capacitors arranged in the vicinity of ICs are required to have high capacity and low operating voltage.

  As described above, the barium titanate-based dielectric material is a dielectric material useful for high dielectric constant applications. However, this material has a large relative dielectric constant AC voltage dependency, and has a low operating voltage. Due to the large decrease in the relative dielectric constant sometimes obtained, even if a multilayer ceramic capacitor is formed using such a dielectric material, a desired capacitance cannot be obtained. Alternatively, there is a problem that it is difficult to obtain a stable capacitance output with respect to an AC voltage that varies according to the IC operation.

  Therefore, an object of the present invention is to provide a dielectric porcelain having a small dielectric constant AC voltage dependency.

The dielectric ceramic of the present invention has a perovskite-type crystal structure containing barium titanate as a main component and rare earth elements, magnesium and manganese as subcomponents, and has a composition formula (Ba _1-y RE _y ) (Ti _{1- a 0 -b Mg a0 Mn b)} O 3 (RE: when the table with a rare earth element), each of the range _{0.06 ≦ y ≦ 0.09,0.03 ≦ a 0} ≦ 0.045,0.012 ≦ b ≦ 0.018, and the lattice constant ratio c / a in the perovskite crystal structure is 1.001 to 1.004 .

In the above dielectric ceramic, (2) key Jury temperature is preferably in the range of -50 ℃ ~ + 50 ℃.

  According to the present invention, a large amount of rare earth elements, magnesium and manganese are dissolved in the main component, barium titanate, and the lattice constant ratio c / a is in the range of 0.001 to 1.004. Thus, by increasing the cubic crystallinity and setting the Curie point in the range of −50 ° C. to 50 ° C., it is possible to obtain a dielectric ceramic having a low AC voltage dependency with respect to the relative dielectric constant.

  The dielectric ceramic according to the present invention will be described in detail. The dielectric ceramic of the present invention is composed of barium titanate as the main component and rare earth elements, magnesium and manganese as solid components.

As the main component of the barium titanate-based dielectric material, BaTiO ₃ which is pure in terms of high dielectric constant and low dielectric loss is suitable, and besides this, BaTiO ₃ such as Sr, Ca, etc. A solid solution barium calcium titanate represented by Ba _1-x M _x TiO ₃ (M: Sr, Ca x = 0.001 to 0.05) in which an alkaline earth solution is dissolved can also be used.

Next, the content of various additives to be dissolved in the main component, barium titanate, is as follows: composition formula (Ba _1-y RE _y ) (Ti _{1-a 0 -b} Mg _a0 Mn _b ) O ₃ (RE: Each range is 0.06 ≦ y ≦ 0.09, 0.03 ≦ a ₀ ≦ 0.045, 0.012 ≦ b ≦ 0.018. .

The composition of various additives and the effects thereof will be described. In the above composition formula, it is important that the composition range of the rare earth element is 0.06 ≦ y ≦ 0.09. Within this composition range, the AC voltage dependency of the relative dielectric constant of the barium titanate-based dielectric material can be reduced, and reduction resistance and high reliability can be obtained.

  On the other hand, when the solid solution amount of the rare earth element is out of the composition range, the AC voltage dependency of the relative dielectric constant becomes large. In particular, when y is less than 0.06, the reduction resistance decreases, , More than 0.09, rare earth elements are precipitated and the relative dielectric constant is lowered.

As the rare earth element, at least one oxide selected from Y ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , V ₂ O _{5 and the} like is preferable, but Y is improved in terms of improvement in relative dielectric constant and high insulation. ₂ O ₃ is particularly desirable.

Next, in the above composition formula, it is important that the composition range of magnesium (Mg) is 0.03 ≦ a ₀ ≦ 0.045. In this composition range, as in the case of the rare earth element, the AC voltage dependency of the relative dielectric constant of the barium titanate dielectric material can be reduced, and the Curie point of the dielectric ceramic can be lowered. There is.

In contrast, with the set configuration of magnesium AC voltage dependency increases the dielectric constant when outside the above composition range, depending of high AC voltage is Curie point when the a ₀ is less than 0.03 Increase. On the other hand, when it exceeds 0.045, the ferroelectricity is impaired and the dielectric constant is lowered.

  Next, in the above composition formula, it is important that the composition range of manganese (Mn) is 0.012 ≦ b ≦ 0.018. Within this composition range, the reduction resistance of the dielectric ceramic can be increased and high reliability can be obtained.

In contrast, with the set configuration of manganese (Mn) is AC voltage dependency increases the dielectric constant when outside the above composition range, if the b is less than 0.012, reduction resistance is lowered . When b is more than 0.018, the relative dielectric constant decreases.

Subcomponent of the dielectric ceramic of the present invention, although expressed as a solid solution in one of the sites of Ba site and the Ti site in the barium titanate as the above composition formula, in fact, these alkaline earth metal Each component of the element (M), rare earth element (RE), magnesium (Mg), and manganese (Mn) is contained in the dielectric porcelain and achieves the desired object of the present application if it is dissolved in barium titanate. Therefore, it is not necessary to selectively dissolve at each site of Ba and Ti as represented by the above composition formula.

Then, the dielectric ceramic of the present invention having the composition described above, the lattice constant ratio c / a is area by der of 1.001 to 1.004. Since the dielectric constant of the present invention has a lattice constant ratio c / a close to a cubic crystal as described above, the crystal grain structure does not clearly take a core-shell structure.

  Therefore, the Curie temperature of the dielectric ceramic according to the present invention is in the range of −50 to + 50 ° C., the ferroelectricity near room temperature is weakened, and thus the AC dependence of the relative permittivity can be reduced.

Further detailed description will be given based on the result of verification of the dielectric ceramic of the present invention. When preparing the dielectric ceramic of the present invention, the starting materials are BaCO ₃ with a purity of 99.9%, TiO ₂ , Y ₂ O ₃ as the rare earth element, and MgO and MnCO ₃ are prepared. A dielectric material mainly composed of BaTiO ₃ was prepared.

  Next, the above metal oxide and carbonic acid compound were mixed at a predetermined ratio in a ball mill using water as a solvent and dried. Next, the mixed powder was calcined at a temperature of 900 to 1050 ° C. for about 2 hours. Next, the calcined powder was pulverized in a ball mill to obtain a calcined barium titanate-based dielectric powder adjusted to a predetermined particle size. Next, the calcined barium titanate-based dielectric powder is formed into pellets having a diameter of 16.5 mm and a thickness of 1 mm, and fired at a temperature of 1300 to 1500 ° C. for 2 hours in an air atmosphere. Went.

In addition to the samples outside the scope of the present invention shown in Table 1, as a sample for the comparative example, a conventional barium titanate-based powder having a core / shell structure was prepared and subjected to the same conditions as the sample according to the present invention. Thus, a sintered body sample was prepared (sample 5 shown in FIG. 3B). A conventional barium titanate powder having a core / shell structure was prepared by adding Y ₂ O ₃ , MgO and MnCO ₃ to a barium titanate powder synthesized in advance. The composition was BaTiO ₃ = 98.5 mol, Y ₂ O ₃ = 0.75 mol, MgO = 0.75 mol, and MnO = 0.30 mol.

  Next, the following characteristics evaluation was performed about the obtained sample. The crystal structure was measured using a Cukα X-ray diffractometer in a diffraction angle range of 20 to 60 °.

  The relative dielectric constant was measured by applying In-Ga to both principal surfaces of the obtained pellet-like sample, and using a Toyo Technica ferroelectric evaluation device, with a frequency of 100 Hz and AC voltage dependence in the range of 50 to 2000 Vrms. did.

The temperature characteristics of the relative permittivity were measured using HP 4291A impedance analyzer in the range of frequency 1 kHz, AC voltage 1 Vrms, temperature −55 to 150 ° C. Table 1 shows the AC change rate of the composition and relative permittivity, the lattice constant ratio c / a, and the Curie temperature.

  In Samples 2 and 3 prepared in the composition range of the present invention, the AC voltage dependence of the dielectric constant is −4.82% to 1.6%, and the lattice constant ratio c / a is 1.001 to 1.0029, The Curie temperature was −25 to 25 ° C.

  On the other hand, in samples 1 and 4 which are samples outside the scope of the present invention, the AC voltage dependence of the dielectric constant is 370% to 695%, and the lattice constant c / a ratio is 1.0055 and 1. 0073 is larger than the sample of the present invention, and the Curie temperatures are also as high as 65 ° C. and 87 ° C.

  FIG. 1 shows temperature characteristics of a dielectric ceramic according to the present invention and a dielectric ceramic having a composition outside the range of the present invention. In the dielectric ceramic of the present invention (samples 2 and 3 in FIG. 1), the Curie point is 70 ° C. or less. FIG. 2 is a graph showing the AC voltage dependence of the relative permittivity, and FIG. 3 is a graph showing the rate of change (the following calculation formula) with respect to the AC voltage normalized by the permittivity at an AC voltage of 0.1 V / μm. is there.

Rate of change = (ε (AC1V / μm) −ε (0.1V / μm)) / ε (0.1V / μm)
As is apparent from the results of Table 1 and FIGS. 1, 2, and 3, in the dielectric ceramic according to the present invention (samples 2 and 3 in Table 1), c / a = 1. The crystal structure is 001 to 1.0029 and the tetragonal crystallinity is suppressed. Thereby, the relative dielectric constant (AC voltage 0.1 V / μm) in the low AC voltage region was 2000 or more, and the rate of change of the relative dielectric constant with respect to the AC voltage was 20% or less. Sample 5 is a case of a dielectric ceramic having a core / shell structure outside the scope of the present invention.

  FIG. 3A is an X-ray diffraction diagram at a diffraction angle of 20 to 60 ° of the sample 3 which is a dielectric ceramic according to the present invention. As long as the dielectric ceramic of the present invention is seen in an X-ray diffraction diagram at a diffraction angle of 20 to 60 °, the crystal structure has a crystal structure with small peak separation and suppressed tetragonality.

  On the other hand, when various additive elements defined in the present invention are added to the barium titanate powder synthesized in advance (sample 5), as can be seen from FIG. Peak separation was observed at the 46 ° peak, the crystal structure was highly tetragonal due to barium titanate in the core, and the AC voltage dependency was 350%.

  In addition, in the samples (samples 1 and 4) in which the amount of additive solid solution such as rare earth elements, magnesium and manganese is outside the range of the present invention, the tetragonality is high and the AC voltage dependency is large, or a paraelectric material is used. The dielectric constant was low.

It is a graph which shows the temperature characteristic about the dielectric material ceramic which has the composition outside the range of the dielectric material ceramic of this invention, and this invention. It is a graph which shows the temperature characteristic of the dielectric constant of the samples 1-4 about the dielectric material ceramic of this invention, and the dielectric material ceramic which has a composition outside the range of this invention. (A) X-ray diffraction pattern of Sample 3 within the scope of the present invention up to 20 to 60 °, (b) Sample 5 having a core-shell structure corresponding to outside the scope of the present invention, and the core portion being barium titanate It is an X-ray diffraction diagram of 20 to 60 degrees.

Claims (2)

It has a perovskite-type crystal structure containing barium titanate as a main component and rare earth elements, magnesium and manganese as subcomponents, and has a composition formula (Ba _1-y RE _y ) (Ti _{1-a
0 -b Mg a0 Mn b) O} 3 (RE: when the table with a rare earth element), each of the ranges 0.06
≦ y ≦ 0.09, 0.03 ≦ a ₀ ≦ 0.045, 0.012 ≦ b ≦ 0.018, and the lattice constant ratio c / a in the perovskite crystal structure is 1.001 to 1 A dielectric porcelain characterized by .004 . The dielectric ceramic of claim 1 Symbol placement Curie temperature is in the range of -50 ℃ ~ + 50 ℃.

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