JPS63268201A - Dielectric porcelain having varistor characteristic and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide dielectric porcelain having improved characteristics, e.g. less variation in varistor voltage due to change of temperature, improved electrostatic capacity, less dielectric loss and improved thermal resistance in a soldering process, by applying a compound of K or Ag on the surface of a baked body and heat treating the same for diffusing either K or Ag ions into a region near the grain boundary of SrTiO3 porcelain crystals converted into a semiconductor. CONSTITUTION:Appropriate amounts of SrCO3, TiO2 and salts or oxides of M and M' are mixed to provide (Sr1-XMX)(Ti1-YM'Y). The mixture was baked and crushed to produce a first component. Powder of a material selected from Nb2O5 and others as second component and powder of one or more metal oxides selected from SiO2 and others are weighted appropriately and these powders are mixed and stirred. Polyvinyl alcohol is incorporated in the mixture for granulating the same and the granules are pressure molded into a disk, which is baked within reducing atmosphere. A fluoride or oxide of K or Ag is applied on the surface of the disk at 1.0 mg/cm<2>. The applied layer is heat treated at 800-1250 deg.C for 30 minutes in atmospheric air in order to diffuse K or Ag ions into semiconductor porcelain.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a porcelain having characteristics as a dielectric and voltage nonlinear characteristics as a varistor, and a method for manufacturing the same.

[Prior Art] Porcelain made of sintered 5rTiOq is a typical ceramic for electronic materials that utilizes grain boundaries, and has an extremely high dielectric constant as well as voltage nonlinear characteristics, so-called varistor characteristics. have.

, these porcelains conventionally used are SrTiO3-based porcelain materials, Bi2O3, CL120, pb-o, Zn
It is made by sintering a mixture with the addition of a trace amount of metal oxide such as O. This porcelain has the structure of N-type semiconductor porcelain, with the metal oxide precipitated at the grain boundaries.

[Problems to be solved by the invention] However, the varistor having the above-mentioned capacitance has a large dielectric loss (tan8) and is weak against thermal shock.
A drawback is that cracks are likely to occur in the crystal plate during soldering. This is considered to be because the metals or their oxides diffused into the grain boundaries form a second layer that is different from the metal oxide layer.

It is an object of the present invention to solve the above-mentioned conventional problems and to provide a porcelain that is resistant to thermal shock while providing a large capacitance and a low varistor voltage, and a method for manufacturing the same.

[Means for solving the problem] That is, the dielectric ceramic having varistor characteristics with capacitance according to the first invention is made of a 5rTi○3 ceramic crystal made into a semiconductor by adding a trace amount of metal oxide. Near the grain boundaries, K
At least either ions or Ag ions are diffused therein.

Further, the method for manufacturing the dielectric ceramic according to the second invention includes:
K or Ag is added to the surface of the sintered body obtained by sintering the S "T103 series porcelain material to which a trace amount of metal oxide has been added.
The compound is applied and heat treated.

[Example] Next, specific examples of the present invention will be described.

(Sr+-xMx) (Tit-yM'y) 03(
However, M=Ca, Mg, Pb, Ba, M'=Sn,
SrCO3 with a purity of 99.0% or more, so that X and Y of Zr) are each in the first column of the first component in Table 1
TiO2 and the above IV1. ．． The carbonate, oxalate, nitrate, or oxide of M' was weighed and blended. Then, this was stirred in a ball mill for 15 hours, dried, and then ground. Furthermore, the powder after crushing was heated to 1200°.
The mixture was calcined at C for 3 hours and ground again. This yields the first component.

Purity 99% for 100 mole parts (constant) of this first component
．． 0% or more Nb2O5, Ta205. Nd203
, Dy20q, Y2O3, La20a, and Ce0a powder of one or more metal oxides (second component);
S i 02, A l 203. with a purity of 99.0% or more.
Powder of one or more metal oxides (fourth component) selected from MnO2 were weighed so as to have the ratios shown in Table 1.

Next, these powders were stirred for 20 hours using a ball mill.
Mixed. 10 to 15% by weight of polyvinyl alcohol is mixed with the above mixture as an organic binder, and the mixture is granulated.
It was press-molded into a disk with a thickness of 1.2 mm and a thickness of 1.2 mm. These disks were heated with N2 gas (95% by volume) and H2 gas (5% by volume).
3 at a temperature of about 1400℃ in a reducing atmosphere consisting of
After firing for several hours, semiconductor porcelain with a diameter of 10 mm and a thickness of 0.8 mm was obtained.

Next, K or Ag fluoride or oxide is applied to the surface of this porcelain at a rate of 1.0 mg/cm2, and heat treated in the air at a temperature of 800 to 1250°C for 30 minutes to remove Ag or K ions. It was diffused into semiconductor porcelain.

Next, in order to investigate the characteristics of the above porcelain, as shown in Fig. 1, a known silver paste was applied to the bidirectional surfaces of the porcelain 1, and this was baked at a temperature of 800°C, and a silver electrode 2 with a diameter of about 7 mm was
．． 2 to form a varistor. Then, for this varistor, we measured the varistor voltage (1), the nonlinear coefficient α, the temperature change rate of the varistor voltage (1), the capacitance C, and the dielectric loss tan δ, and conducted a rough solder heat resistance test. did. The results are shown in Table 2.

Varistor voltage V1 was measured using the circuit shown in FIG. That is, a varistor VR was connected to a DC constant current power source E, an ammeter A was connected between the DC constant current power source E and the varistor VR, and a voltmeter (2) was connected in parallel to the varistor VR. Then, only the varistor VR is stored in a thermostatic chamber C maintained at a temperature of 20°C, and a 1 mA voltage is applied to the varistor VR. M I 1
of? W, measure the voltage at that time and find the varistor voltage V1
And so.

The nonlinear coefficient α was determined by the following equation using the apparatus shown in FIG. 2 and measuring the applied voltage VI9 when a current 10 mA +z was applied to the varistor VR in addition to the varistor voltage V1.

The temperature change rate V1 is determined by changing the temperature in the thermostatic chamber C in the range of -40°C to +125°C in the apparatus shown in Figure 2, and passing a current of 1 mA through the varistor VR at each temperature T (°C). The varistor voltage VT at that time was measured, and the extent to which this changed with respect to Vl at 20°C was calculated using the following equation.

In addition, each table shows the maximum value of (1) above in the above temperature range.

In the solder heat resistance test, the above varistor was tested at a temperature of 80°C.
After preheating for a minute, it was immersed in eutectic solder at 270° C. for 3 seconds and visually inspected for the presence of cracks.

In addition, in the first page and the second table, sample numbers 55 and after are comparative examples with respect to the present example. As shown in each column of Table 1, in these comparative examples, KF and A
B12Q3, CuO, Pb0, etc. were used in place of gF.

Table 1 =8- As the above results show, in each of the above tables, sample N00
The varistors according to the embodiments of the present invention shown in Nos. 1 to 54 have a varistor voltage V1 equal to or lower than that of the comparative examples after Sample No. 55, and have a change in the temperature change rate of the varistor voltage V1, V1, and capacitance. Remarkable improvements in characteristics were observed in C1 dielectric loss tan δ and solder heat resistance.

[Effects of the Invention] From the above, the varistor constructed using the porcelain according to the present invention can obtain a varistor voltage V1 equal to or lower than that of the conventional one, while achieving a temperature change rate ΔVI of the varistor voltage ■1. , capacitance C1, dielectric loss tan δ, and solder heat resistance.

[Brief explanation of the drawing]

FIG. 1 is a half-sectional perspective view showing the structure of a varistor tested in an embodiment of the present invention, and FIG. 2 is a circuit diagram of an apparatus in which the electrical characteristics of the varistor were tested.

Claims (5)

[Claims] (1) Sr made into a semiconductor by adding a small amount of metal oxide
In dielectric ceramics with varistor properties made of TiO_3-based sintered bodies, K ions or A are present near the grain boundaries of the ceramic crystals.
A dielectric ceramic having varistor characteristics characterized by diffusing at least one of g-ions. (2) The dielectric ceramic according to claim 1, wherein K ions or Ag ions are diffused in a layer with a thickness of about 100 Å near the grain boundaries of crystal grains. (3) S made into a semiconductor by adding a trace amount of metal oxide
A method for producing semiconductor porcelain having varistor characteristics by sintering rTiO_3-based porcelain material, which comprises applying a compound of K or Ag to the surface of the sintered body and heat-treating the dielectric material having varistor characteristics. Method of manufacturing body porcelain. (4) The method for producing dielectric ceramics according to claim 3, wherein the compound of K or Ag is a fluoride thereof. (5) The method for manufacturing dielectric ceramics according to claim 3 or 4, wherein the heat treatment temperature after applying the K or Ag compound is 800 to 1200°C.