TWI447750B - Chip varistor containing rare-earth oxide sintered at lower temperature and method of making the same - Google Patents

Description

Rare earth group component varistor made by low temperature sintering and preparation method thereof

The invention relates to a wafer type surge absorber made by low temperature sintering and a preparation method thereof, in particular to a rare earth group-containing wafer type surge absorber made by low temperature sintering.

The electronics industry is booming, and a large number of semiconductor components are used, but ESD statics are inevitable on the line. Because semiconductor components are quite sensitive to static electricity, they lose their original function due to static electricity. Therefore, an electrostatic protection component must be added to absorb static electricity to protect the product from static electricity. In particular, a large number of hand-held devices have been widely used in recent years, and electrostatic protection has become an important issue.

There are two types of electrostatic protection components currently in commercial use, one is a germanium-based diode made by a semiconductor process, and the other is a wafer-type surge absorber mainly composed of zinc oxide (ZnO). Among them, the latter is widely used in handheld related devices such as mobile phones, digital cameras and notebook computers because of its low price and unsatisfactory performance.

A common wafer type zinc oxide surge absorber (hereinafter referred to as a varistor) is mainly made of zinc oxide, and is added with bismuth (Bi), bismuth (Sb), bismuth (Si), cobalt (Co), manganese (Mn), An oxide such as chromium (Cr) is sintered at a high temperature to form a varistor containing a bismuth component. However, the melting point of cerium oxide is low, and the pressure of cerium vapor is high during sintering, which may cause defects in the varistor finished product to be easily formed by holes, and affect the quality of the varistor. In addition, the grain boundary phase of the varistor has a higher insulation resistance value, so the damper's Clamping voltage is relatively high. This factor is not a problem for the application of varistor, but with the low voltage of semiconductor products, the demand for varistor with low suppression voltage is particularly strong. Therefore, varistor containing bismuth (Bi) component is not suitable for use in the field of low voltage semiconductor products.

Another commercially available varistor containing a rare earth component is also mainly composed of zinc oxide, and a rare earth oxide such as Pr ₆ O ₁₁ , Nd ₂ O ₃ , Dy ₂ O ₃ or the like is added as a surge absorber forming agent. However, the melting point of the rare earth oxide is high, and the varistor containing the rare earth component during sintering needs to be sintered at a temperature of 1300 ° C or higher to obtain good electrical characteristics. Therefore, the rare earth-containing varistor requires expensive palladium or platinum as the internal electrode, so the production cost is relatively high.

In view of this, the main object to be solved by the present invention is to develop a rare earth-containing composition varistor which is formed by low-temperature sintering, and a relatively inexpensive silver-palladium alloy can be used as a material for the internal electrode during the sintering process. The varistor thus produced also has excellent antistatic properties, and in particular, the manufacturing cost is relatively inexpensive.

Therefore, the main object of the present invention is to disclose a rare earth element-containing varistor made by low-temperature sintering, which has a rare earth group oxide as a characteristic forming agent and has a low Clamping voltage; and, in a rare earth-containing group In the formulation component of the ceramic body of the composition varistor, a titanium oxide (TiO2) component which lowers the sintering temperature is added, and the sintering temperature can be lowered to 1080 °C.

The rare earth-containing component varistor of the invention can be cooled down to 1080 ° C and sintered at a low temperature. The internal electrode can be used without the use of expensive pure palladium or platinum, and can be directly used for the conventional fabrication of laminated wafer surge absorbers. Ag/Pd (70/30 by weight) is an internal electrode material, and the varistor obtained can reduce the manufacturing cost in addition to excellent antistatic properties.

The rare earth-containing composition varistor of the present invention comprises a ceramic body, a pair of upper and lower (including a pair) of internal electrodes staggered in the interior of the ceramic body, and a pair of electrodes disposed at both ends of the ceramic body and An external electrode contacting the electrode; wherein the composition of the ceramic body comprises 90~97.5 mol% of the main raw material of zinc oxide and the total addition amount is at most 2.5-10 mol% of the auxiliary material, wherein the auxiliary material comprises six additives, the first additive 0.02~2.5mol% TiO ₂ ; the second additive is 0.05~5mol% rare earth oxide selected from one of Pr ₆ O ₁₁ , Nd ₂ O ₃ , CeO ₂ , Sm ₂ O ₃ or Dy ₂ O ₃ or One or more kinds of mixing; the third additive is 0.2-3.0 mol% of Co oxide or Cr oxide; the fourth additive is 0.1-0.5 mol% of an alkaline earth compound selected from CaO, SrO, BaO or CaCO ₃ , SrCO ₃ or BaCO ₃ One or more of the mixture; the fifth additive is 0.001 to 0.02 mol% of the boron (B) compound, selected from B ₂ O ₃ or H ₃ BO ₃ ; the sixth additive is 0.001 to 0.05 mol % of the aluminum (Al) compound, It is selected from Al ₂ O ₃ or Al(NO ₃ ) ₃ .

The breakdown voltage value of the rare earth-containing component varistor of the present invention can be controlled by the thickness of the green body of the ceramic body, the sintering temperature, and the addition amount of the additive, wherein titanium oxide (TiO ₂ ), rare earth oxide, and calcium oxide (CaO) The amount of addition has a large influence on the characteristics of the varistor.

As shown in Fig. 1, the rare earth-containing composition varistor 10 of the present invention is characterized by being produced by a multilayer technology and sintered at a low temperature. The varistor 10 includes a ceramic body 11 , a pair of inner electrodes 12 disposed on the left and right sides of the ceramic body, and a pair of external electrodes 13 disposed at both ends of the ceramic body 11 and in contact with the internal electrodes 12 .

The formulation of the ceramic body 11 of the present invention comprises 90 to 97.5 mol% of the main raw material of zinc oxide and the total addition amount is at most 2.5 to 10 mol% of the auxiliary material. The auxiliary material comprises six additives; the first additive is 0.02-2.5 mol% TiO ₂ ; the second additive is 0.05-5 mol% rare earth oxide, including Pr ₆ O ₁₁ , Nd ₂ O ₃ , CeO ₂ , Sm ₂ O ₃ , Dy ₂ O _{3 ,} etc.; third additive 0.2-3.0 mol% Co oxide or Cr oxide; fourth additive 0.1-0.5 mol% alkaline earth compound such as CaO, SrO, BaO, CaCO ₃ , SrCO ₃ or BaCO _3, etc.; fifth additive 0.001 to 0.02 mol% of boron (B) compound, such as B ₂ O ₃ , H ₃ BO _{3 ,} etc.; sixth additive 0.001 to 0.05 mol% of aluminum (Al) compound, such as Al ₂ O ₃ , Al (NO ₃ ) ₃ .

It is known that the sintering temperature of the rare earth-containing component varistor reaches 1300 ° C or higher. In the rare earth-containing composition varistor 10 of the present invention, the crystal growth aid TiO _{2 is} added to the formulation of the ceramic main body 11. When sintered, ZnO-TiO _{2 is} generated in a liquid phase, and the sintering is promoted by liquid phase sintering to reduce sintering. The varistor has a sintering temperature of 1080 ° C and is characterized by low temperature sintering.

Since the sintering temperature can be lowered to 1080 ° C, another characteristic of the rare earth-containing composition varistor of the present invention is that the internal electrode 12 can be used without a Pd or Pt material having a high sintering temperature, and a commonly used Ag/Pd (weight ratio) can be selected. 70/30) As a material for fabricating the internal electrode 12, it has the advantage of reducing manufacturing cost.

The method for preparing the rare earth-containing component varistor 10 of the present invention comprises the following steps:

(1) First, weighed 90 ~ 97.5mol% ZnO, addition of _{0.02 ~ 2.5mol% TiO 2, 0.05} ~ 5mol% of rare earth oxide comprises _{Pr 6 O 11, Nd 2 O} 3, CeO 2, Sm 2 O 3, One or more of Dy ₂ O ₃ and the like, followed by addition of 0.2-3.0 mol% CoO, 0.1-0.5 mol% Cr ₂ O ₃ , 0.001-0.02 mol% B ₂ O ₃ and 0.001-0.05 mol% Al ₂ O ₃ Or Al(NO ₃ ) ₃ ‧9H ₂ O. All of the above powders were ball milled, dried, and calcined at 700 to 900 ° C for 2 hr. The calcined powder is then ground to a particle size of less than 1 μm by water milling.

(2) The composite powder prepared above is added with a binder, a dispersing agent, an organic solvent, etc., and is slurried into a green thin strip having a thickness of about 10 to 50 μm according to a conventional layering technique.

(3) A plurality of outer layers of raw embryonic strips are firstly stacked, and then uniformly pressed into a lower cover of about 200 μm. The inner electrode is printed on the lower cover, and after drying, a 30 μm inner layer of raw embryonic strip is placed, and the inner electrode is printed. As shown in Fig. 1, the inner electrode 12 of the inner layer of the raw layer and the inner electrode 12 of the lower cover are produced in a staggered manner, and are printed to the ends of the inner layer of the raw embryonic strip and the lower cover, respectively. The inner electrode 12 may be selected from a metal such as platinum (Pt), palladium (Pd), gold (Au), silver (Ag), or nickel (Ni), or an alloy of any two of the above metals.

A plurality of outer layers of raw embryonic strips were first stacked and pressed into an upper cover of about 200 μm. Then, the upper cover is placed on the upper layer of the inner layer of raw embryos and stacked together, and after being pressure-pressed, it is cut into green embryo grains. The green embryo grains are then sintered in a sintering furnace at a sintering temperature of about 1050 to 1200 ° C, preferably 1080 to 1130 ° C, and most preferably 1080 ° C. After the sintering, the crystal grains are sintered into the ceramic body 11, and the outer electrodes 13 are applied to the left and right ends thereof, and sintered at 600 to 900 ° C to form a varistor 10 containing a rare earth-containing composition capable of suppressing surge or static electricity.

The following examples illustrate the process of the present invention, and the resulting rare earth-containing composition varistor 10 has a low breakdown voltage, high electrostatic protection capability, and excellent surge suppression capability.

Example 1: Ceramic body powder formula

Take commercial zinc oxide powder with particle size in the range of 0.2~0.5μm. According to the formula of Table 1, weigh other related powders, add 40wt% water and dispersant, then ball mill for 24hr, and pour out the slurry. After drying, it was calcined at 750 ° C for 2 hr. Next, the calcined powder is further ground by a planet to a particle size of less than 1 μm or less for use.

To expedite the verification of the sinterability of these formulations, an appropriate amount of the preceding process powder was added, and after adding about 0.5% by weight of the binder, about 0.2 g of the powder was weighed and placed in a mold to apply a pressure molding of about 1000 kg/cm ² . The formed embryo bodies were sintered at 1130 ° C and 1080 ° C for 2 hr, respectively. Then, on the two parallel faces of the sintered ceramic body, silver electrodes were applied and heat-treated at 825 ° C for about 10 minutes.

Next, the basic electrical test of the ceramic body finished products made at different sintering temperatures, including V _1mA , nonlinear index (α), leakage current and capacitance value. The results are shown in Table 2.

From the results of Table 2, it was shown that the addition of TiO ₂ can lower the sintering temperature of the finished ceramic body, wherein the finished ceramic body has the lowest V _{1 mA} value with 0.05 mol% added. However, as the amount of TiO ₂ added increases, the V _{1mA of the} finished ceramic body increases, and this phenomenon is more pronounced at 1080 ° C.

When the amount of TiO ₂ added is 0.05 mol% and 0.15 mol%, the dispersion value of the capacitance of the ceramic body is quite large, but the change of V _1mA is not large. This phenomenon may be accompanied by a small amount of TiO ₂ added and the sintering temperature is low. Due to the problem of TiO ₂ dispersion, there is a phenomenon that abnormal grain growth occurs. Further, according to the results of Table 2, it was also shown that the amount of addition of Pr was increased, and the finished ceramic body had a higher V _{1 mA} . In addition, the amount of Cr ₂ O ₃ added increases, and the non-linear index of the finished ceramic body is low.

Example 2: Low temperature sintering to produce a varistor containing rare earth elements

Take the pre-formed ceramic body powder formula of Example 1, add solvent (toluene and n-butanol), binder (polyvinyl butyral), dispersant, and then put together in a ball mill barrel to obtain a slurry, and then The doctor blade was scraped into a green thin strip having a thickness of 30 μm.

A number of outer layers of raw embryonic strips were firstly folded and then pressed into a lower cover of about 200 μm. On the lower cover, the inner electrode is printed, and after drying, a 30 μm inner layer of the raw embryonic strip is placed, and the inner electrode is printed. As shown in Fig. 1, the inner electrode and the inner inner electrode of the inner layer of the raw layer of the raw layer are produced in a staggered manner, and the end portions of the inner layer of the raw embryo and the lower cover are respectively connected. Ag/Pd (weight ratio 70/30) was selected as the internal electrode material.

Then, several sheets of raw embryonic thin strips were firstly stacked, and they were uniformly pressed into an upper cover of about 200 μm. Then, the upper cover is placed on the upper layer of the inner layer of raw embryos and stacked together, and after equalizing and pressing, the green embryo grains having a width and height of 1.2 mm*0.6 mm*0.6 mm are cut. The raw embryo grains are then sintered in a sintering furnace, and the sintering temperature is about 1080 to 1130 °C. After sintering, the length and width of the crystal grains are 1.0 mm * 0.5 mm * 0.5 mm. The ends of the crystal grains are covered with an external electrode, and after firing at 600-900 ° C, the finished product of the rare earth-containing composition varistor 10 is obtained.

The breakdown voltage of each of the rare earth-containing varistor 10 products and the component breakdown voltage and capacitance after the 20KV static test were measured. The results are shown in Table 3.

According to the results of Table 3, the rare earth-containing composition varistor 10 of the present invention has the effects of reducing the breakdown voltage and leakage current and increasing the nonlinearity index, and has no influence on the ESD static electricity protection capability, and can withstand 20KV static electricity, that is, appropriate addition. TiO ₂ can lower the sintering temperature of the varistor 10 containing the rare earth component, and can improve the non-recurring index of the varistor 10 containing the rare earth component and reduce the leakage current, and has little effect on the electrostatic protection capability of the varistor 10 containing the rare earth component.

10. . . Rheological component containing rare earth elements

11. . . Ceramic body

12. . . Internal electrode

13. . . External electrode

1 is a schematic view of a varistor containing a rare earth element composition of the present invention.

11. . . Ceramic body

12. . . Internal electrode

13. . . External electrode

Claims (6)

A rare earth-containing composition varistor made by low-temperature sintering, comprising a ceramic body, a pair of inner electrodes, a left-right staggered inner portion of the ceramic body, and a pair of external electrodes disposed at two ends of the ceramic body, wherein The composition of the ceramic body comprises 90~97.5mol% of zinc oxide main raw material and the total addition amount is at most 2.5~10mol% of auxiliary materials, and the auxiliary material comprises six additives, wherein the first additive is 0.02~2.5mol% TiO ₂ ; the second additive is 0.05 to 5 mol% of the rare earth oxide selected from one or more of the group consisting of Pr ₆ O ₁₁ , Nd ₂ O ₃ , CeO ₂ , Sm ₂ O ₃ or Dy ₂ O ₃ ; Is 0.2 to 3.0 mol% of Co oxide or Cr oxide; the fourth additive is 0.1 to 0.5 mol% of an alkaline earth compound selected from one or more of CaO, SrO, BaO, CaCO ₃ , SrCO ₃ or BaCO ₃ ; The fifth additive is 0.001 to 0.02 mol% of the B compound selected from B ₂ O ₃ or H ₃ BO ₃ ; and the sixth additive is 0.001 to 0.05 mol % of the Al compound selected from Al ₂ O ₃ or Al(NO ₃ ) ₃ . A rare earth-containing composition varistor produced by low-temperature sintering according to claim 1, wherein the inner electrode of the ceramic body is an Ag/Pd inner electrode having a weight ratio of 70/30. A method for producing a rare earth-containing composition varistor produced by low-temperature sintering according to claim 1, wherein the ceramic body of the varistor has a sintering temperature of 1050 to 1200 °C. A method for producing a rare earth-containing composition varistor produced by low-temperature sintering according to claim 1, wherein the ceramic body of the varistor has a sintering temperature of 1080 to 1130 °C. A method for producing a rare earth-containing composition varistor produced by low-temperature sintering according to claim 1, wherein the ceramic body of the varistor has a sintering temperature of 1080 °C. The method for producing a rare earth-containing composition varistor formed by low-temperature sintering according to any one of claims 3 to 5, wherein the rupture voltage of the varistor is a green body thickness of the ceramic body And the sintering temperature to adjust.