JPH037621B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is mainly made of barium titanate (BaTiO ₃ ), which has a high dielectric constant and good temperature characteristics of capacitance.
The present invention also relates to a high dielectric constant ceramic composition having a dense ceramic structure. Many ceramic capacitor compositions based on barium titanate have been known. As is well known, barium titanate is a unique substance with ferroelectric properties.At high temperatures, it has a cubic perovskite structure.At temperatures below 120°C, the C-axis slightly stretches to become a tetragonal structure, and further below 120°C, it becomes a tetragonal structure. It changes to orthorhombic crystal at around -80℃ and to rhombohedral crystal at around -80℃. the above
The phase transition point around 12°C is called the Curie point, and beyond this point it exhibits paraelectricity at higher temperatures and ferroelectricity at lower temperatures. At this Curie point, the dielectric constant exhibits an extremely high value of 6000 to 7000. Here, barium titanate alone cannot provide a high dielectric constant at room temperature. Conventionally, many attempts have been made to commercialize capacitors that have an appropriate capacitance near room temperature by moving the high dielectric constant of barium titanate near the Curie point to a lower temperature side. The dielectric agent that shifts the temperature at which the peak value of the dielectric constant appears is called a shifter, and BaSnO ₃ , CaZrO ₃ , BaZrO ₃ , and CaSnO ₃ are commonly known. Capacitors have been used as single-plate type with lead wires. However, with the recent advances in laminated chip technology, dielectric sheets of about 30 to 100 μm can be easily obtained, and so-called laminated ceramic chip capacitors, which are made by laminating many layers with these thin films sandwiched between them, have entered various electronics industries. Increasingly, conventional dielectric ceramic compositions are being used as such laminated thin film dielectrics. However, in conventional single-plate capacitors, the dielectric thickness is as thick as 100 to 10,000 μm, while in multilayer ceramic chip capacitors, the thickness is 20 to 10,000 μm.
Because it is thin at ~50 μm, it receives an electric field strength of 5 to 10 times more. Therefore, there is a need for a composite that has less voltage dependence than conventional single-plate capacitors. Additionally, as the dielectric layer becomes thinner, structural defects in the ceramic become more likely to appear in the characteristics.
It is required that the crystal grains be uniform and fine, and that the pores be small and small. As a result of repeated various experiments to achieve this objective, the present invention has developed a combination of BaZrO ₃ , CeO ₂ , BaZrO ₃ and BaTiO 3 .
The present invention has led to the provision of a high dielectric constant ceramic composition to which TiO ₂ is added. Furthermore, in a preferred embodiment, at least one of oxides of Mn, Cr, Fe, Ni, and Co is added in an amount of 0.01 to 0.5 wt based on the main component.
% of the high dielectric constant ceramic composition. The present invention will be explained below along with examples. Example For 100 molar parts of BaTiO ₃ (purity 98%),
Various additives (however, CeO ₂ and TiO ₂ [Ce]/
Add [Ti] (2/3 ratio), mix thoroughly in a ball mill, and pass through a 30-mesh sieve to granulate. This granulated powder is placed in a mold with an inner diameter of 13 mm at a pressure of 1 ton/
Multiply cm ² to produce a molded body with a diameter of 13 mm and a thickness of 0.5 mm. These molded bodies are heated at 1250 to 1400℃ for 1~
Bake for 2 hours. After this, silver electrodes are provided on both sides of the sintered body of the disk. Tables 1 and 2 below show the properties of the sintered bodies obtained for various additive compositions. In the table, G is the grain size, P is the pore size, ε ₂₅ is the dielectric constant determined from the capacitance measured at 25° C., 1 KHz, and AC 1 V, and tan δ is the dielectric loss at this time. In addition, 1R is the volume resistivity when measured at DC50V, BDV is the boost breakdown voltage, and TC is the rate of change in capacitance at 10°C and 85°C with 25°C as the reference. AC-T is 1KHz under AC voltage per 30V/mm
The value of tanδ measured in is shown.

【table】

【table】

[Table] As is clear from the above table, the high dielectric constant ceramic composition of the present invention has the EIA standard Z5U characteristics (+1℃~+85℃
It can be seen that it can be used as a capacitance change within the standard of +22% to -56% in the temperature range of °C. In addition, it has a large dielectric constant and has an AC voltage characteristic of 30V/mm or less.
It is observed that tan δ is small and the fine structure of the ceramic is small and uniform. Conventional _BaTiO3
A ceramic porcelain assembly with better physical and electrical properties than ceramic compositions such as -BaSnO ₃ -CaTiO ₃ -MnO ₃ was obtained. However, as shown in Table 1,
When x is 6 or more for 100 mol parts of BaTiO ₃ ,
As in Sample No. 1 and Sample No. 2, the temperature change rate of Tc, that is, the capacitance, becomes too large, making it impossible to satisfy the Z5U characteristics of the EIA standard mentioned above, and when x is less than 3, the Curie point is near room temperature. However, as in Sample No. 12 and Sample No. 13, the dielectric constant (ε ₂₅ ) at room temperature is small and tan δ becomes large.
Furthermore, even if BaZrO ₃ is less than 1 mole part, the shift of the Curie point is insufficient, resulting in a small dielectric constant (ε ₂₅ ) and a large tan δ at room temperature (Sample No. 8, Sample No. 11). If the amount exceeds 4 mole parts, the sinterability of the fired body will deteriorate (Sample No. 5, Sample No.
9). Furthermore, from Table 2, Mn, Cr, Fe, Ni, Co
at least one of the oxides of
By adding a trace amount of 0.01wt% or more, the AC voltage at 1KHz per 30V/mm was lower than that of sample No. 14 without addition.
It can be seen that there is an effect of improving the AC voltage characteristic (AC-T) indicating the tan δ value at
%, the dielectric constant (ε ₂₅ ) at room temperature will decrease significantly (Sample No. 17, Sample No. 29), and the grain size G and pore size P will become too large (Sample No. 20, Sample No. .23), the temperature change rate TC of capacitance becomes large (Sample No. 26), making it unsuitable as a capacitor. Therefore, from the above, for 100 mol parts of BaTiO ₃ , CeO ₂ and TiO ₂ are respectively 2/3x mol parts and x mol parts (3≦x<6),
It is appropriate to set BaZrO ₃ to 4 to 1 mole part,
More preferably, at least one of the oxides of Mn, Cr, Fe, Ni, and Co is added to the main component by 0.01 to
By adding a trace amount of 0.5 wt%, a high dielectric constant ceramic composition with good physical and electrical properties can be obtained. A multilayer ceramic capacitor as shown in the figure was prototyped using the composition of sample No. 6 in Table 1, and the characteristics were investigated. The results are shown in Table 3 below. Table 3 is
11 parts by weight of CaZrO ₃ for 100 parts by weight of BaTiO ₃ ;
It also shows the characteristics of a capacitor prototyped using a typical conventional composition containing 6 parts by weight of BaSnO ₃ , 8 parts by weight of CaTiO ₃ , and 0.2 parts by weight of MnO ₂ . The element shape in this case is 3.07 x 1.56 x 0.56 mm. In the figure, 1 is a ceramic dielectric made of the composition of sample No. 6, 2 is a palladium electrode, and 3 is a terminal electrode (Ag electrode). Also, in Table 3, C and
tanδ is a value measured at 1KHz and AC1V. IRe is
The insulation resistance value is measured at DC50V, and BDVe is the boost breakdown voltage value. The resistance force is the pressure just before the element breaks when the element is supported with a span of 2.5 mm and the center of the element is pressed with a 0.5 mm wide knife.

[Table] As is clear from Table 3 above, the samples of the present invention
It was found that the prototype capacitor No. 6 had much better tan δ, breakdown voltage, and transverse rupture strength than the conventional capacitor. From the above, the braid of the present invention has fine grains, few pores, small, dense ceramics, high dielectric constant, and temperature characteristics of capacitance.
It can be used as a ceramic capacitor that satisfies EIA standard Z5U characteristics, especially as a multilayer ceramic capacitor. And about 2
Because it has twice the breakdown voltage value, the dielectric thickness of multilayer ceramic capacitors can be reduced to about 1/3 of that of conventional capacitors, expanding the range of capacitance acquisition to three times that of conventional capacitors. It has extremely high industrial value as it has the characteristics of being able to

[Brief explanation of the drawing]

The figure is a partially sectional front view showing a multilayer ceramic capacitor prototyped using the composition of the present invention. 1...Porcelain dielectric, 2...Palladium electrode, 3
...Terminal electrode.

Claims (1)

[Claims] 1 100 mol parts of barium titanate (BaTiO ₃ ),
High dielectric constant consisting of 2/3x molar parts and x molar parts (3≦x<6) of cerium oxide (CeO ₂ ) and titanium oxide (TiO ₂ ), respectively, and 1 to 4 molar parts of barium zirconate (BaZrO ₃ ). Porcelain composition. 2. The high dielectric constant ceramic composition according to claim 1, which contains at least one of oxides of Mn, Cr, Fe, Ni, and Co in an amount of 0.01 to 0.5 wt% based on the main component.