JPH0435883B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of 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 SrTiO ₃ -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. are doing. These conventionally used porcelains are made of SrTiO ₃
It is made by sintering a mixture of ceramic materials with trace amounts of metal oxides such as Bi ₂ O ₃ , Cu ₂ O, PbO, and ZnO 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] However, the varistor having the above capacitance,
Disadvantages include large dielectric loss (tan δ), vulnerability to thermal shock, and the tendency for cracks 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 SrTiO ₃ ceramic crystal grains made into a semiconductor by adding a trace amount of metal oxide. At least either K ions or Ag ions are diffused near the field. Further, the method for manufacturing the dielectric ceramic according to the second invention includes SrTiO ₃ to which a trace amount of metal oxide is added.
A K or Ag compound is applied to the surface of a sintered body obtained by sintering ceramic materials, and then heat treated. [Example] Next, a specific example of the present invention will be described. (Sr _1-X M _X ) (Ti _1-Y M′ _Y ) O ₃ (M=Ca,
SrCO ₃ , TiO ₂ with a purity of 99.0% or more and the above M,
The carbonate, oxalate, nitrate, or oxide of M' was weighed and blended. This was then stirred in a ball mill for 15 hours, 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. For 100 mole parts (constant) of this first component, Nb ₂ O ₅ , Ta ₂ O ₅ , Nd ₂ O ₃ , Dy ₂ O ₃ , with a purity of 99.0% or more,
Powder of one or more metal oxides (second component) selected from Y ₂ O ₃ , La ₂ O ₃ , CeO ₃ and SiO ₂ , Al ₂ O ₃ , MnO ₂ with a purity of 99.0% or more and powder of one or more metal oxides (fourth component) were weighed so as to have the ratios shown in Table 1. Next, these powders were stirred and mixed using a ball mill for 20 hours. Further, 10 to 15% by weight of polyvinyl alcohol was mixed into the above mixture as an organic binder, and after granulation, the mixture was pressure-molded into a disk with a diameter of 13 mm and a thickness of 1.2 mm at a pressure of approximately 1000 Kg/ ^cm2. . These discs were heated with _N2 gas (95% by volume) and _H2 gas (5% by volume).
1400℃ in a reducing atmosphere consisting of
Semiconductor porcelain with a diameter of 10 mm and a thickness of 0.8 mm was obtained by firing at a temperature of 3 hours. Next, a fluoride or oxide of K or Ag is applied to the surface of this porcelain at a rate of 1.0 mg/cm ² .
Heat treatment was performed in the air at a temperature of 800 to 1250°C for 30 minutes to diffuse Ag or K ions into the semiconductor ceramic. Next, in order to investigate the characteristics of the above-mentioned porcelain, as shown in Fig. 1, a known silver paste was applied to both main surfaces of the porcelain 1 and baked at a temperature of 800°C, and a silver electrode 2 with a diameter of about 7 mm was applied. , 2 were formed to constitute a varistor. Then, for this varistor, the varistor voltage V ₁ , the nonlinear coefficient α, the temperature change rate ΔV ₁ of the varistor voltage V 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. The varistor voltage V ₁ was measured using the circuit shown in FIG. In other words, a varistor is connected to the DC constant current power source E.
Connect VR, and also connect DC constant current power supply E and varistor.
An ammeter A was connected between VR and a voltmeter V was connected in parallel to the varistor VR. And the barista
Only the VR was stored in a thermostatic chamber C maintained at a temperature of 20°C, a current I1 of ₁ mA was passed through the varistor VR, and the voltage at that time was measured and defined as the varistor voltage _V1 . To calculate the nonlinear coefficient α, use the device shown in Figure 2 above, and in addition to the varistor voltage V _1, apply a current of 10 mA to the varistor VR.
The applied voltage V ₁₀ when I ₁₀ was applied was measured and calculated using the following formula. α=log(I ₀ /I ₁ )/log(V ₁₀ /V ₁ )=1/log(V ₁₀
/V ₁ ) The temperature change rate ΔV ₁ is determined by changing the temperature in the constant temperature chamber C in the range of -40℃ to +125℃ in the apparatus shown in Fig. 2.
The varistor voltage V _T was measured when a current of 1 mA was passed through the varistor VR at each temperature T (°C), and the extent to which this changed from V ₁ at 20°C was calculated using the following equation. Note that each table shows the maximum value of ΔV ₁ in the above temperature range. ΔV ₁ V1T-V1/V1×100/1-20 (%/℃) For the solder heat resistance test, the above varistor was preheated at 80℃ for 2 minutes, and then immersed in eutectic solder at 270℃ for 3 seconds. This was done by visually inspecting for the presence of cracks. In addition, in Tables 1 and 2, sample number 55
The following are comparative examples for this example. As shown in each column of Table 1, in these comparative examples, Bi ₂ O ₃ , CuO,
PbO etc. were used.

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[Table] As shown by the above results, the varistors according to the embodiments of the present invention shown as samples No. 1 to 54 in the above tables have a varistor voltage V equal to or lower than that of the comparative examples after sample No. 55. ₁ was obtained, and remarkable improvements in characteristics were observed in the temperature change rate ΔV ₁ of the varistor voltage V ₁ , capacitance C, 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 V _{1 that is equal to or lower than that of the conventional varistor, while the temperature change rate of the varistor voltage V 1 is} lower than that of the conventional varistor. More excellent characteristics can be obtained in terms of ΔV ₁ , capacitance C, 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 used to test the electrical characteristics of the varistor.

Claims (1)

[Claims] 1 Made into a semiconductor by adding a trace amount of metal oxide
In a dielectric ceramic having varistor characteristics made of a SrTiO ₃ -based sintered body, the dielectric material having varistor characteristics is characterized in that at least either K ions or Ag ions are diffused near the grain boundaries of the ceramic crystal. Body porcelain. 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. In a method for manufacturing semiconductor porcelain having varistor characteristics by sintering SrTiO ₃ ceramic material which has been made into a semiconductor by adding a trace amount of metal oxide, a compound of K or Ag is added to the surface of the sintered body. A method for manufacturing dielectric porcelain having varistor properties, which comprises coating and heat-treating. 4. The method for producing dielectric ceramics according to claim 3, wherein the compound of 4 K or Ag is a fluoride thereof. 5. The method for producing dielectric ceramic according to claim 3 or 4, wherein the heat treatment temperature after applying the 5 K or Ag compound is 800 to 1200°C.