KR100310035B1 - Microwave dielectric ceramic composition for low temperature firing - Google Patents

Abstract

A dielectric ceramic composition is provided that is capable of low temperature firing and has excellent microwave properties. The composition of the present invention is capable of low temperature sintering by using B ₂ O ₃ and MnO ₂ as additives in (Mg _0.93 Ca _0.07 ) TiO ₃ , while having good microwave characteristics. In the region in which the appropriate amount of B ₂ O ₃ was added at 1200 ° C., the quality coefficient value was higher than that of pure (Mg _0.93 Ca _0.07 ) TiO ₃ sintered at 1350 ° C.

Description

Microwave dielectric ceramic composition for low temperature firing {MICROWAVE DIELECTRIC CERAMIC COMPOSITION FOR LOW TEMPERATURE FIRING}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to microwave dielectric ceramic compositions for use in consumer and industrial electronic devices, and more particularly to dielectric ceramic compositions having excellent microwave properties while being capable of low temperature firing.

There are many kinds of microwave dielectric ceramic compositions, but (Ma, Ca) TiO ₃ (hereinafter MCT) microwave ceramics have lower cost, easier sintering and reproducible microwave dielectric properties than Ba or Pb series microwave dielectrics. Because of the advantage that can be obtained, it is widely used in the manufacture of actual microwave devices.

In general, MCT-based microwave ceramics are fired at a high temperature of 1350 ° C. Due to the high firing temperature, a large amount of energy is consumed for the heat treatment of the firing in mass production. In addition, due to such a high firing temperature, there is a problem in that it is difficult to apply to a multilayer microwave ceramic device that requires simultaneous firing with electrodes.

Accordingly, an object of the present invention is to provide a microwave ceramic composition for low temperature sintering that is well baked at a low temperature of about 1200 ° C. and has excellent microwave characteristics by adding an appropriate plastic additive in the manufacture of MCT-based microwave dielectric ceramics.

The present inventors have intensively studied to solve the above-mentioned problems of the prior art and found that when B ₂ O ₃ and MnO ₂ are added to the MCT system, the composition can be obtained while lowering the sintering temperature and at the same time obtaining good microwave characteristics. The invention has been completed. Hereinafter, the present invention will be described in detail with reference to the following Examples.

Example

MgO, CaCO ₃ and TiO ₂ were used as starting materials for the preparation of MCT. When preliminary experiments confirmed that 7 mol% of CaTiO ₃ was added, the temperature coefficient of the resonant frequency had a value close to zero. Thus, the raw material was weighed to have a final composition of (Mg _0.93 Ca _0.07 ) TiO ₃ . The mixture was mixed with deionized water and zirconia balls for 24 hours, and dried and calcined in air at 1200 ° C. for 2 hours at a temperature rising rate of 5 ° C./min. Thereafter, B ₂ O ₃ and MnO ₂ selected as sintering additives were added to the calcined powder in the range of 0 to 2.0 wt%, and then mixed and ground for 24 hours using a ball mill. After crushing, uniaxial pressure molding was performed on a 10 mm diameter immersion at a pressure of 1000 Kg / cm ² to make a specimen for measuring dielectric properties. This specimen was heated for 2 hours at a temperature of 1100 to 1350 ℃ at a heating rate of 5 ℃ / min. After sintering and then cooled. In order to measure the microwave dielectric properties of the sintered body, the quality factor (Qxf, Q: no load quality factor, f: measurement frequency) and the temperature coefficient of the resonance frequency were measured by a network analyzer using a measuring tool and a metal resonator.

The physical and microwave properties of the ceramic specimens prepared by the above method are shown in Tables 1 and 2 below.

Microwave Dielectric Properties According to Firing Temperature and B ₂ O _{3 Addition} in MCT Production Example Firing temperature (℃) B ₂ O ₃ (wt%) Player Ratio (%) Quality Factor (Qxf) Temperature coefficient of resonant frequency (ppm / ℃) One 1350 0.00 15.4 63000 +2.0 2 0.20 15.4 61500 +1.5 3 0.15 15.5 61000 0.0 4 0.20 15.5 61000 -0.7 5 0.30 15.4 59000 -0.7 6 0.40 15.6 58000 +0.2 7 0.50 15.7 56000 +0.4 8 1.00 15.8 54000 +0.2 9 1200 0.00 12.2 23000 -12.0 10 0.10 13.5 51000 +0.8 11 0.15 14.1 63000 -0.5 12 0.20 14.5 66000 -0.5 13 0.30 15.1 69000 -0.8 14 0.40 15.3 64000 -0.9 15 0.50 15.5 61000 -2.3 16 1.00 15.5 56000 -2.5 17 1150 0.00 8.5 13000 18 0.10 10.3 14000 19 0.15 11.5 15000 20 0.20 12.3 17000 21 0.30 14.0 22000 22 0.40 14.1 24000 23 0.50 14.2 25000 24 1.00 14.2 29000

Microwave Dielectric Properties with MnO _{2 Addition} in MCT Preparation Example Firing temperature (℃) MnO ₂ (wt%) Player Ratio (%) Quality Factor (Qxf) Temperature coefficient of resonant frequency (ppm / ℃) 25 1350 0.0 15.3 64800 +3.45 26 0.4 15.5 66600 +2.98 27 0.8 15.7 68800 +1.05 28 1.2 15.9 71000 +2.54 29 1.6 16.1 65400 +1.12 30 2.0 16.3 65200 +1.18

As can be seen from Table 1, when the amount of B ₂ O ₃ added was 0.2 wt% or more, the shrinkage at the sintering temperature of 1200 ° C. was nearly 15%. The change in the quality coefficient according to the amount of B ₂ O ₃ addition shows that the quality coefficient gradually decreases as the amount of sintering additives sintered at 1350 ° C increases and the sintering temperature is 1200 ° C. The quality factor rapidly increased until the quantity reached the appropriate range, and the value of the quality factor decreased when it was over-added to more than 0.3 wt%. In the region in which the appropriate amount of B ₂ O ₃ was added at 1200 ° C., the quality coefficient value was higher than that of pure (Mg _0.93 Ca _0.07 ) TiO ₃ sintered at 1350 ° C.

Both the sintering temperature of 1200 ℃ and 1350 ℃ showed a value close to 0ppm / ℃, and at 1200 ℃ showed a stable temperature coefficient even if a small amount of sintering additive is added. In other words, B ₂ O ₃ added to (Mg _0.93 Ca _0.07 ) TiO ₃ was found to be a sintering additive that did not affect the temperature coefficient and dielectric constant of the resonant frequency.

From these results, it was found that the optimum amount of the amount of B ₂ O ₃ added was 0.2 to 0.4. Therefore, the addition amount of B ₂ O ₃ is fixed to 0.3 wt% and MnO ₂ is further added to the plastic test at 1200 ℃ and the results are shown in Table 3 below.

Microwave Dielectric Properties when the Addition of B ₂ O ₃ was Fixed at 0.3 wt% and the Addition of MnO ₂ was Changed Example Firing temperature (℃) B ₂ O ₃ (wt%) MnO ₂ (wt%) Player Ratio (%) Quality Factor (Qxf) Temperature coefficient of resonance frequency (ppm / ℃) 31 1200 0.3 0.0 15.4 68400 +3.91 32 0.3 0.4 15.6 69400 +4.28 33 0.3 0.8 15.7 70500 +4.46 34 0.3 1.2 15.8 67000 +4.55 35 0.3 1.6 15.9 66400 +5.03 36 0.3 2.0 16.1 66200 +4.95

From Table 3, when the amount of B ₂ O ₃ is fixed to 0.3 wt%, it can be seen that the quality factor increases when the amount of MnO ₂ is 0.4 to 1.2 wt%.

By using B ₂ O ₃ and MnO ₂ as sintering additives in the (Mg _0.93 Ca _0.07 ) TiO ₃ -based microwave dielectric ceramic composition, not only the baking at a relatively low temperature of 1200 ° C. can be maintained but also the microwave dielectric properties are excellent.

Claims (4)

A low temperature sinterable microwave dielectric ceramic composition comprising (Mg _0.93 Ca _0.07 ) TiO ₃ -based composition, wherein B ₂ O ₃ and MnO ₂ are added as a sintering additive. The low-temperature sinterable microwave dielectric ceramic composition according to claim 1, wherein the amount of B ₂ O ₃ added is 0.2 to 0.4 wt% and the amount of MnO ₂ is 0.4 to 1.2 wt%. The low temperature sinterable microwave dielectric ceramic composition according to claim 2, wherein the amount of B ₂ O ₃ added is 0.3 wt%. 4. The low temperature sinterable microwave dielectric ceramic composition according to claim 1, which is sinterable at 1200 ° C. 5.