KR20020028279A - Fabrication method of SrTiO3 SMD-type varistor-capacitor multifunctional device - Google Patents

Abstract

PURPOSE: A method for manufacturing a varistor-capacitor multifunctional device is provided to simultaneously obtain varistor characteristic and capacitor characteristic of a dielectric index larger than 10000 and dielectric loss less than 5%. CONSTITUTION: A SrTiO3 SMD varistor-capacitor multifunctional device is manufactured by using Sr0.9Ca0.1TiO3 as basic material powder. The basic material powder is subjected to wet milling after Nb2O5 of 0.4-0.6 mol% is added and SiO2 of 0.1-0.3 mol% and MnO of 0.1-0.3 mol% are added. Organic vehicle is added to the basic material powder after wet milling to form slurry. The slurry is molded by a tape caster to form a ceramic sheet. After cutting the ceramic sheet, internal electrodes are printed on the ceramic sheet by Ag/Pd or Ni electrodes. Three to five ceramic sheets are deposited on and on and subjected to pre-sintering at 1100°C for 1 hour. The sintered ceramic is re-oxidized in a furnace with the air at 900-1100°C.

Description

Fabrication method of SRTTiO3-based SMD varistor-capacitor composite functional device {Fabrication method of SrTiO3 SMD-type varistor-capacitor multifunctional device}

The invention SrTiO ₃ based SMD (Surface Mountable Device) type varistor-capacitor composite function as devices on the manufacturing technology, more particularly to a grain boundary (grain boundary through an after heat-treatment the semiconductor screen of halitosis (grain) in a reducing atmosphere during sintering Insulation) and to reduce the sintering temperature to 1200 ℃ in order to use the Ag / Pd or Ni electrode as an internal electrode.

Conventional varistors use zinc oxide (ZnO) as a basic raw material, add a small amount of elements such as bismuth oxide (Bi ₂ O ₃ ), cobalt oxide (CoO), and manganese oxide (CrO ₃ ), and then dry, assemble and It is generally manufactured by sintering through a molding process. Such varistors are widely used as devices for protecting devices and circuits from sudden overvoltage or noise that may be introduced from the outside.

Recently, a technology for manufacturing such devices using SrTiO ₃ has been developed. Since SrTiO ₃ varistors have a dielectric constant of about 100 to 1000 times larger than conventional ZnO based varistors, they can be applied as capacitors and can be rapidly introduced into noise. The efficiency of absorbing overvoltage is superior.

SrTiO ₃ -based varistors are generally manufactured by improving grain conductivity and insulating grain boundaries. Recently, due to the miniaturization and integration of circuits, development of SMD type stacked chips has been in progress.

In the case of such a stacked chip, since the oxide diffusion, which is a conventional method of forming the grain boundary layer, cannot be used, the resistance of the grain boundary must be controlled through oxidation after reduction sintering.

The most important part in the development of SrTiO ₃ varistor-capacitor composite functional devices is the reoxidation process. In general, grains must be semiconductorized and grain boundaries must be insulated for SrTiO ₃ -based varistors to be characterized. In the state in which the ceramic is completely reduced after reduction sintering, not only the resistance difference between the grains and grain boundaries is small, but also the resistance of each is low so that the capacitor characteristics cannot exist. In addition, varistor characteristics cannot be expected.

Accordingly, an object of the present invention in view of the foregoing is to zinc oxide by insulating grain boundaries through heat treatment after semiconductorizing grains with a reducing atmosphere during sintering in order to exhibit the characteristics of SrTiO ₃ -based varistors. The present invention provides a method for manufacturing a varistor-capacitor composite functional device which simultaneously exhibits varistor and capacitor characteristics having a dielectric constant of 10000 or more and a dielectric loss of less than 5% compared to a (ZnO) varistor.

Another object of the present invention is to use a Ag / Pd or Ni electrode as an internal electrode in order to lower the production cost, to provide a varistor-capacitor composite functional device manufacturing technology for this purpose to lower the sintering temperature from the existing 1440 ℃ to 1200 ℃ have.

1 is a view showing the shape of the device to which the present invention is applied.

2 is a flow chart showing a manufacturing process of the present invention.

Figure 3 is a graph showing the dielectric properties according to the temperature of the specimen according to the present invention.

4 is a graph showing the current-voltage characteristics of the specimen according to the present invention.

The manufacturing technology of the present invention for achieving the above object is to manufacture a device having a capacitor characteristics and varistor characteristics through the reduction atmosphere sintering and reoxidation process using SrTiO ₃ as a basic composition and Ag / Pd or Ni electrode as an internal electrode It is.

The manufacturing technology for manufacturing a composite device having the characteristics of the varistor and the capacitor at the same time, a step of preparing a slurry by mixing the raw powder and the organic medium, casting the prepared slurry to prepare a ceramic sheet, titrating the ceramic sheet Printing the internal electrode by cutting to size, laminating ceramic sheets printed with the internal electrode, sintering the laminated ceramic laminate in a reducing atmosphere, reoxidizing the sintered body by sintering, and reoxidized sintered body Forming an external electrode on the substrate.

Hereinafter, the manufacturing technology of the present invention will be described in detail with reference to the illustrated drawings.

Figure 1 shows the shape of the device manufactured by the present invention, is manufactured according to the manufacturing process of FIG.

In the embodiment of the present invention, the basic composition of the raw material powder for slurry production was fixed to Sr _0.9 Ca _0.1 TiO ₃ . In this case, the semiconductor storage Nb ₂ O ₅ is added to a mixture of raw material powder was added by 0.4 ~ 0.6 mol%. Calcination was carried out at 1100 ° C. for 2 hours to synthesize, and 0.1 to 0.3 mol% and 0.1 to 0.3 mol% of SiO ₂ and MnO were added for low temperature sintering, and then wet milling for 48 hours. After the milled powder was sufficiently dried, a slurry was prepared by adding an appropriate organic vehicle for sheet molding and mixing for 48 hours. The slurry was prepared by an oxide mixing method, but the batch amount was fixed at about 600 g, and the weighing was adjusted in the range of about 10 ^-3 g.

At this time, the ratio between the solid amount of the organic medium and the raw material powder was prepared by fixing at a ratio of 40:60. The slurry thus prepared was molded to a thickness of about 80 μm by a tape caster device using a doctor blade method, and then dried sufficiently for about 12 hours after preparing ceramic specimens. At this time, by adjusting the viscosity and specific gravity of the slurry and the tape casting speed and the like to adjust the overall characteristics of the ceramic sheet.

The internal electrode is printed after cutting a sufficiently dried ceramic sheet to an appropriate size. This internal electrode uses Ag / Pd or Ni electrode, and after printing the internal electrode on the green sheet, it is 3 to 5 layers. Stacked and stacked. After the laminate was cut to 3216 size, the binder burnout was sufficiently performed at a constant temperature for 24 hours. The ceramic specimens after binder burnout were pre-sintered at 1100 ° C. for 1 hour. The sintering atmosphere is carried out by fixing the mixing ratio of N ₂ and H ₂ to 10: 1. The sintering atmosphere was controlled using an automated mass flow controller (MFC), and the tube was made of high purity aluminum. Next, the ceramic sintered body was reoxidized, and this reoxidation process was used as an atmosphere furnace and reoxidized with air. At this time, the reoxidation temperature was adjusted to 900 ~ 1100 ℃.

External electrode formation proceeds differently according to the type of internal electrode, and the process using Ag / Pd or Ni internal electrodes will be described later in detail.

First, in the case of using an Ag / Pd internal electrode, the Ag / Pd electrode formed an internal electrode using a composition having a mixing ratio of 30:70, respectively. Ag / Pd internal electrode is a noble metal electrode that has no effect of internal electrode oxidation during reoxidation, so it is sintered for 1 hour at 1175 ℃ under reduced atmosphere with N ₂ and H ₂ ratio of 90: 10 It was done.

Reoxidation process was carried out varying from 900 ℃ to 1100 ℃, was also manufactured with a change in holding time.

The dielectric properties and varistor characteristics of the reoxidation temperature and the retention time are shown in Table 1.

Temperature (℃) Holding time (unit: minute) 60 180 300 900 K 170000 11000 3000 tan δ (%) 150 3.5 15 α 6 10 4 1000 K 4000 2500 500 tan δ (%) 31 15 2.2 α 4 3 - 1100 K 1000 400 400 tan δ (%) 2 0.7 2.8 α - - -

(K: dielectric constant, tan δ: dielectric loss, α: nonlinear coefficient from 0.1㎃ to 1㎃)

The ceramic specimens finished up to the reoxidation process were polished to expose the internal electrodes and then coated with Ag electrodes to form external electrodes.

Next, in the case of using the Ni internal electrode, since the Ni internal electrode is a non-metal electrode, there is a risk that the internal electrode is oxidized during the reoxidation process and loses its function as an electrode. Therefore, in the present invention, the pre-sintered specimen was polished prior to reduction sintering to expose the internal electrode, and then the Ni electrode was applied to form the external electrode.

Sintering was carried out at 1200 ° C. for 1 hour under a reducing atmosphere of N ₂ : H ₂ ratio of 10: 1, and reoxidation proceeded from 900 ° C. to 1100 ° C. in the same manner as the Ag / Pd electrode specimens.

The dielectric properties and varistor characteristics of the reoxidation temperature and the retention time are shown in Table 2.

Temperature (℃) Holding time (unit: minute) 60 180 300 900 K 210000 16000 3000 tan δ (%) 230 5 19 α 5 10 4 1000 K 4000 2500 500 tan δ (%) 2 3.5 3.2 α 6 7 4 1100 K 300 350 350 tan δ (%) One 0.3 0.2 α - - -

(K: dielectric constant, tan δ: dielectric loss, α: nonlinear coefficient from 0.1㎃ to 1㎃)

After the reoxidation process, the ceramic specimens were polished to expose the external electrode from which the oxidized NiO layer was removed during the reoxidation process.

The temperature-dependent characteristics and the current-voltage characteristics for each prepared specimen are shown in FIGS. 3 and 4, respectively.

When all processes are completed by the above-described process, the finally manufactured device is tested.

The device according to the present invention exhibits a capacitor characteristic with an average dielectric constant of 10000 or more, a dielectric loss of less than 5%, and a varistor characteristic of a nonlinear coefficient of 10 or more, regardless of the type of the internal electrodes described above. In particular, as shown in Figure 3 it can be seen that the characteristics of the X7R composition of the capacitance change rate less than 15% in the temperature range of -25 ℃ to 85 ℃.

In the SrTiO ₃ of the present invention as a basic composition, the varistor-capacitor composite functional device in the form of a laminated chip can lower the sintering temperature to 1200 ° C. by adding an appropriate low temperature sintering agent to produce a laminated chip. In addition, there is an effect of reducing the production cost by using Ag / Pd and Ni internal electrodes as the internal electrode. In particular, according to the present invention, the dielectric constant and the nonlinear coefficient of the X7R composition with the dielectric loss less than 5% and the capacitance change rate less than 15% in the temperature range of -25 ° C to 85 ° C are realized. By exhibiting varistor characteristics of 10 or more, a composite function device can be manufactured. This multifunctional device can replace the existing varistor and capacitor devices to improve the electrical properties as well as the protection of the device.

Claims (10)

In the manufacturing technology for manufacturing a composite device having the characteristics of the varistor and the capacitor at the same time, (1) preparing a slurry by mixing the raw powder and the organic medium; (2) casting the prepared slurry to produce a ceramic sheet; (3) cutting the ceramic sheet to an appropriate size and printing an internal electrode; (4) stacking the ceramic sheets printed with the internal electrodes; (5) sintering the laminated ceramic laminate in a reducing atmosphere; (6) reoxidizing the sintered body by the sintering; And (7) A multilayer varistor-capacitor composite functional device manufacturing technique comprising the steps of forming an external electrode on the reclaimed sintered body. The method of claim 1, wherein the basic composition of the raw material powder for slurry production in step (1) is Sr _0.9 Ca _0.1 TiO ₃ characterized in that the laminated varistor-capacitor composite functional device manufacturing technology. The method of claim 1, wherein in step (1), the raw material powder is added with 0.4 to 0.6 mol% of Nb ₂ O _{5, which} is a semiconducting material, and 0.1 to 0.3 mol% and 0.1 to 0.3 mol% of SiO ₂ and MnO, respectively, which are low temperature sintering additives Multi-layer varistor-capacitor composite functional device manufacturing technology characterized in that the addition of 0.3 mol%. The method of manufacturing a multilayer varistor-capacitor composite functional device according to claim 1, wherein the internal electrodes are manufactured using Ag / Pd electrodes in step (3). The method of manufacturing a multilayer varistor-capacitor composite functional device according to claim 1, wherein the internal electrode is manufactured using a Ni electrode in the step (3). _2. The technique of claim 1, wherein the reducing atmosphere sintering in step (5) is performed by fixing a mixing ratio of N ₂ and H ₂ to 10: 1. 2. The manufacturing technique of the stacked varistor-capacitor composite functional element according to claim 1, wherein the reoxidation in step (6) uses air. The method of claim 4, wherein the mixing ratio of Ag / Pd used in the internal electrode manufacturing is 30:70. 5. The multilayer varistor-capacitor composite functional device manufacturing method according to claim 4, wherein the internalization of the internal electrode is performed for 1 hour at 1175 DEG C under a reducing atmosphere in which the ratio of N ₂ and H ₂ is 90:10. The method of manufacturing a multilayer varistor-capacitor composite functional device according to claim 5, wherein the sintering is performed at 1200 DEG C for 1 hour in a reducing atmosphere having a ratio of N ₂ and H ₂ of 10: 1.