JPS63268202A - 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 Na on the surface of a baked body and heat treating the same for diffusing Na 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 weighed appropriately and these powders are mixed and stirred. Polyvinyl alcohol is incorporated in the mixture for granulating the same and the granules are pressure shaped into a disk, which is baked in a reducing atmosphere. A fluoride or oxide of Na 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 the atmospheric air in order to diffuse Na 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 a 5rTiOa-based sintered body is a typical ceramic for electronic materials that utilizes grain boundaries, and has an apparent high dielectric constant as well as voltage nonlinear characteristics, so-called varistor characteristics. ing.

These porcelains conventionally used include 5rT103-based porcelain materials with Bi20a, Cu2O, and 'PbO.

It is made by sintering a mixture to which a trace amount of metal oxide such as ZnO is added. 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] 2) The varistor having the above-mentioned capacitance has a large dielectric loss (tan δ) and is weak against thermal shock.
The drawback is that cracks may form on the crystal plate during soldering. This is thought to be caused by the fact that 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 high capacitance according to the first invention is made of a 5rTiCh ceramic crystal made into a semiconductor by adding a trace amount of metal oxide. Near the grain boundaries,
It is made by diffusing Na ions.

In addition, the method for manufacturing dielectric ceramic according to the second invention (B) includes the surface of a sintered body obtained by sintering a 5rTiOq-based ceramic material to which a trace amount of metal oxide is added; is applied and heat treated.

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

(S r+-×1Vh) (T j, I-YM'Y
) 03' (However, M=, Ca, Mg, Pb, Ba,
The purity is 99.0% or more so that M' = Sn, Z's X and Y are respectively the values in each column of the first component in Table 1.
SrCO3, TiO2, and carbonates, oxalates, nitrates, or oxides of the above M, , M' were weighed and blended, respectively. Then, this was stirred for 20 hours using a ball mill, dried, and then ground. Furthermore, the powder after pulverization was calcined at 1200° C. for 3 hours and pulverized again. This yields the first component.

Purity 99% for 100 mole parts (constant) of this first component
．． 0% or more Nbp○5, T a205, N d203
, Dyp03, Y20q, La2O3, and Ce0q 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 the following.

Next, these powders were stirred for 20 hours using a ball mill.
Mixed. Further, 10 to 15% by weight of polyvinyl alcohol is mixed into the above mixture as an organic binder, and after granulation, about 10% by weight is added. Diameter 1 at a pressure of OO, kg/cm2
It was press-molded into a disk with a diameter of 3 mm and a thickness of 1.2...1 nm. These discs were fired in a reducing atmosphere consisting of N2 gas (95% by volume) and H2 gas (5% by volume) at a temperature of about 1400°C for 3 hours to give a diameter of 10 mm, thickness Q, and 8 mm. of semiconductor porcelain was obtained.

Next, Na fluoride or oxide was applied to the surface of this porcelain at a rate of 1.0 m and g/cm2, and heat treated in the air at a temperature of 800 to 1250°C for 30 minutes.
Na ions were diffused into the semiconductor porcelain.

Next, in order to investigate the characteristics of the above porcelain, as shown in Fig. 1, a known silver base coat was applied to both main surfaces of the porcelain 1, and this was baked at a temperature of 800 degrees Celsius, and silver electrodes with a diameter of about 7 cm were applied. 2.
2 to form a varistor. Then, for this varistor, the varistor voltage V1, the nonlinear coefficient α, the temperature change rate v1 of the varistor voltage 1, the capacitance C, and the dielectric loss tan δ were measured, and a solder heat resistance test was conducted. The results are shown in Table 2.

Varistor voltage (1) 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 batten VR, and a voltmeter V was connected in parallel to the varistor voltage.

Then, store the varistor VR+ in a thermostatic chamber C maintained at a temperature of 20°C, and apply an electric current to 1m to the varistor VR+. The voltage at that time was measured and defined as the varistor voltage V1.

The nonlinear coefficient α was determined by using the apparatus shown in FIG. 2, and by measuring the applied voltage V+p when a current 1+n of 10 mA was applied to the varistor VR in addition to the varistor voltage V1, and using the following equation.

log (l[]/11) 1m degree change rate 8 ■ 1 is the temperature in the thermostatic chamber C in the apparatus shown in Figure 2 at -40
We measured the varistor voltage VT when a current of 1 m was passed through the varistor VR at each temperature T (°C) by changing it in the range of °C to +125 °C, and how much did this change from V1ζ at 20 °C? was calculated using the following formula. In addition, the maximum value of V1 above in the above temperature range is shown on the 6th side.

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 Tables 1 and 2, sample numbers 28 and later are comparative examples with respect to the present example. As shown in each column of Table 1, in these comparative examples, Bi2O3, CuO5P I) O, etc. were used in place of NaF used in the above examples.

Back 1 Back 2 As the above results show, sample N00
The varistors according to the embodiments of the present invention shown in 1 to 27 can obtain varistor voltages V1 that are equal to or lower than those of the comparative examples after Samples No. Remarkable improvements in characteristics are observed in the capacitance C5 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 reducing the temperature change rate ΔV1 of the varistor voltage V1. , better characteristics can be obtained in terms of capacitance C5 dielectric loss tan δ and solder heat resistance.

[Brief explanation of drawings]

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
A dielectric porcelain having varistor characteristics made of a TiO_3-based sintered body and having Na ions diffused near the grain boundaries of the ceramic crystal. (2) The dielectric ceramic according to claim 1, wherein Na 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 dielectric porcelain having varistor characteristics, which is a method of manufacturing semiconductor porcelain having varistor characteristics by sintering rTiO_3-based porcelain material, which comprises applying a Na compound to the surface of the sintered body and heat-treating it. manufacturing method. (4) The method for manufacturing dielectric ceramics according to claim 3, wherein the Na compound is a fluoride of these. (5) The heat treatment temperature after applying the Na compound is 800℃.
The method for manufacturing dielectric ceramic according to claim 3 or 4, wherein the temperature is 1200°C.