JPS6051208B2 - High dielectric constant porcelain composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is particularly applicable to barium titanate (BaTiO0), which is used as a thin film dielectric material such as multilayer ceramic capacitors.
The present invention relates to a high-permittivity ceramic composition having a high dielectric constant and a dense ceramic structure mainly consisting of:

Conventional Structures and Their Problems Many ceramic capacitor compositions based on barium titanate have been known in the past.

As is well known, barium titanate is a unique substance with ferroelectric properties, and at high temperatures it has a cubic perovskite structure.At temperatures below 120°C, the C-axis slightly stretches and becomes a tetragonal structure, and furthermore, at temperatures below 120°C, it becomes a tetragonal structure. It changes to orthorhombic crystals near the vicinity, and to rhombohedral crystals near -80°C. The above-mentioned phase transition point near 120° C. is called the Curie point, and beyond this Curie point, it exhibits paraelectricity at higher temperatures and exhibits ferroelectricity at lower temperatures. At this cue point, the dielectric constant exhibits an extremely high value of 10,000. Here, barium titanate alone cannot provide a high dielectric constant at room temperature. Many attempts have been made to commercialize small capacitors with appropriate capacitance near room temperature by moving the high dielectric constant of barium titanate near its Curie point to a lower temperature side. The additive that shifts the temperature at which the peak value of the dielectric constant occurs is called a shifter.
,PbSnO3,cusno3,ZnSnOa,,Cd
stannate such as SnO3, BaZrO3, ca2roa,
, zirconates such as sr2ro3 and SrTiOa)
Titanate salts of PbTiOa are generally known and have the strongest effect as a shifter in the order listed above. Barium titanate ceramic capacitors using these shifters have been used as single-plate lead wire type capacitors. However, with recent advances in stacked chip technology,
So-called multilayer ceramic chip capacitors, in which many layers of this thin film are laminated with electrodes sandwiched between them, have been used in various electronics industries, and conventional dielectric ceramic compositions are increasingly being used as thin film dielectrics for such lamination. However, in conventional single-plate ceramic capacitors, the dielectric thickness is as thick as 100 μm to 10,000 μm, whereas in multilayer ceramic capacitors, the thickness is 10 μm to 20 μm.
Since it is as thin as 5 m, it is subjected to an electric field strength of 5 to 1 pm or more. Therefore, there is a need for a composition that has less voltage dependence than conventional single-plate capacitors. In addition, as the dielectric layer becomes thinner, structural defects in the ceramic become more likely to appear in the characteristics, so it is required that the crystal grains be uniform and fine, and that the pores be small and small. . Purpose of the Invention In view of the above, an object of the present invention is to provide a high dielectric constant ceramic composition that has a high dielectric constant, has few ceramic structural defects, has low voltage dependence, has few ceramic structural defects, and has a high withstand voltage. It is something.

Structure of the Invention The present invention uses barium titanate (BaTiO3), gadolinium oxide (Gd2O3) and titanium oxide (TiO2).
It is a high dielectric constant ceramic composition consisting of.

Description of examples Examples of the present invention will be described in detail below.

*
* First, barium titanate (BaTiO3) was synthesized as follows. That is, barium carbonate (BaCO3)
and titanium oxide (TiO2) [? ]/[TO ratio is 1.0
00+. Mix with an accuracy of 0.005, 1100-115
The product was calcined at 0°C and then ground.

Add Gd2O3 and TiO2 to this BaTiO3 [Gd
]/[Ti] at a ratio of 10, and after mixing,
Add a binder and granulate it, form it into a square plate shape and make 1250
It was fired in the range of ~1350°C. After this, a silver electrode was formed. Table 1 below shows the characteristics of each composition at each firing temperature.

As is clear from Table 1 above, composition NO. It can be seen that 2, 3, and 4 can be used as EIA standard Y5V characteristics.

That is, as shown in Figure 1, the capacitance change rate is +22% to -82% in the temperature range of -30'C to +85°C.
It sufficiently satisfies the rate of change within the standard (20° C. standard), and also shows a dielectric constant equivalent to that of a commercially available Y5V ceramic capacitor with a dielectric constant of 1000011i]. At the end of Table 1, a Y5V characteristic composition containing a zirconate salt is shown as a conventional example. The grain size (particle size) of the ceramic is 1 to 3 μm in the composition of the present invention, and the maximum bore size is around 3 μm. *In the conventional example, the grain size is as large as 10 to 20 μm, and the bore size is 20 μm at maximum. Before and after. Composition NO. 3
We prototyped a multilayer ceramic capacitor as shown in Figure 2.

The results of a comparison between this capacitor and a zirconate-based multilayer ceramic capacitor are shown in Table 2 below. In FIG. 2, 1 is a dielectric, the thickness between the electrodes is 35 μM, 2 is a palladium electrode, and 3 is a terminal electrode. As is clear from Table 2 above, it was found to have twice the bending strength and three times the breakdown voltage of the conventional products.

Effects of the Invention As described above, the composition of the present invention is suitable for use in ceramic capacitors, which has fine grains, a dense ceramic with a small bore, has a high dielectric constant, and whose temperature change in dielectric constant satisfies the EIA standard Y5V characteristic. In particular, it can be used as a multilayer ceramic capacitor.

In addition, since it has a breakdown voltage value that is approximately three times that of conventional ceramic capacitors, it is possible to reduce the dielectric thickness of multilayer ceramic capacitors to about 1B compared to conventional capacitors, and expand the capacitance acquisition range to three times that of conventional capacitors. It has extremely high industrial value, as it has the characteristics of being able to Although barium titanate was synthesized in the above example, commercially available barium titanate may also be used.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the range of temperature change rate of capacitance for the composition of the present invention, and FIG. 2 is a sectional view of a multilayer ceramic capacitor to which the composition of the present invention is applied.

Claims (1)

[Claims] 1 100 mol parts of barium titanate (BaTiO_3), 1/3 (7±1) of gadolinium oxide (Gd_2O_3)
) and 7±1 molar parts of titanium oxide (TiO_2).