본 연구에서는 BaTiO₃의 나노 분말(grain size 150nm)을 이용하였으며, 첨가제 원소 MnCO₃, Y₂O₃을 첨가하여 적층 세라믹 커패시터 유전체로서의 적용하기 위하여 유전특성 및 온도특성을 향상 시키고자 하였다. 실험방법은 순수 BaTiO₃ 분말에 MnCO₃, Y₂O₃을 0.02~0.1 wt% 첨가하였으며, 균일한 혼합 및 분쇄를 위해 IPA(Isopropyl Alcohol)에서 Ф3 mm ZrO2 볼을 이용하여 42시간 ...
본 연구에서는 BaTiO₃의 나노 분말(grain size 150nm)을 이용하였으며, 첨가제 원소 MnCO₃, Y₂O₃을 첨가하여 적층 세라믹 커패시터 유전체로서의 적용하기 위하여 유전특성 및 온도특성을 향상 시키고자 하였다. 실험방법은 순수 BaTiO₃ 분말에 MnCO₃, Y₂O₃을 0.02~0.1 wt% 첨가하였으며, 균일한 혼합 및 분쇄를 위해 IPA(Isopropyl Alcohol)에서 Ф3 mm ZrO2 볼을 이용하여 42시간 볼밀 하였다. 이렇게 혼합된 분말은 80℃에서 건조 후 120 메시(mesh) 이하에서 채 가름하여 Ф15 mm 디스크 형태로 CIP (cold isostatic pressing, 1300 kgf/㎠)를 이용하여 성형하였다. 그 다음 최적의 소결 온도를 확인하기 위해서 1200~1280℃ 까지 다양한 온도로 소결을 진행하였다. 소결된 시편은 XRD 분석을 통하여 상을 확인하였고, SEM을 이용하여 미세조직을 관찰하였다. 또한 유전 및 전기적 특성을 측정하기 위하여 임피던스 분석기 (HP4194 Impedance/ Gain Phase Analyzer)를 이용하였다. 소결 후 모든 BaTiO₃ 시편에서 이차상이 없는 순수한 페로브스카이트 구조를 확인 할 수 있었다. 또한 Y₂O₃ 첨가량에 따라 소결 밀도는 불순물의 양이 증가하면서 함께 증가되는 것을 확인하였다. 비유전율과 유전손실은 Y₂O₃ 0.05 wt%까지 첨가할 때까지는 거의 비슷한 값을 나타났지만 0.05 wt% 이상에는 큰 누설전류로 인해 강유전성이 상쇄됨을 나타내었다. 이러한 결과는 Y₂O₃을 소량 첨가하면 도너 역할을 하여 산소 공공의 농도를 감소시키고, 그에 따라 BaTiO₃ 커패시터의 신뢰성을 향상시킬 수 있을 것으로 판단되었다. MnCO₃ 첨가의 경우, 비유전율과 유전손실은 MnCO₃ 첨가량의 따라 감소되어지는 것을 확인하였다. 이러한 결과는 Mn^(2+) 이온이 Ti^(4+) 자리에 치환됨으로써 BaTiO₃ 세라믹스에 억셉터 첨가제로 작용하는 것을 알 수 있다. 따라서 MnCO₃ 첨가 시, BaTiO₃ 세라믹스의 전자 농도를 줄일 수 있었고, 유전손실의 향상이 나타났다. 본 실험 결과들로부터, 향후에는 Y₂O₃와 MnCO₃을 동시 첨가함으로써 BaTiO₃ 커패시터의 유전체 특성을 더욱 향상시킬 수 있을 것으로 유추되었다.
본 연구에서는 BaTiO₃의 나노 분말(grain size 150nm)을 이용하였으며, 첨가제 원소 MnCO₃, Y₂O₃을 첨가하여 적층 세라믹 커패시터 유전체로서의 적용하기 위하여 유전특성 및 온도특성을 향상 시키고자 하였다. 실험방법은 순수 BaTiO₃ 분말에 MnCO₃, Y₂O₃을 0.02~0.1 wt% 첨가하였으며, 균일한 혼합 및 분쇄를 위해 IPA(Isopropyl Alcohol)에서 Ф3 mm ZrO2 볼을 이용하여 42시간 볼밀 하였다. 이렇게 혼합된 분말은 80℃에서 건조 후 120 메시(mesh) 이하에서 채 가름하여 Ф15 mm 디스크 형태로 CIP (cold isostatic pressing, 1300 kgf/㎠)를 이용하여 성형하였다. 그 다음 최적의 소결 온도를 확인하기 위해서 1200~1280℃ 까지 다양한 온도로 소결을 진행하였다. 소결된 시편은 XRD 분석을 통하여 상을 확인하였고, SEM을 이용하여 미세조직을 관찰하였다. 또한 유전 및 전기적 특성을 측정하기 위하여 임피던스 분석기 (HP4194 Impedance/ Gain Phase Analyzer)를 이용하였다. 소결 후 모든 BaTiO₃ 시편에서 이차상이 없는 순수한 페로브스카이트 구조를 확인 할 수 있었다. 또한 Y₂O₃ 첨가량에 따라 소결 밀도는 불순물의 양이 증가하면서 함께 증가되는 것을 확인하였다. 비유전율과 유전손실은 Y₂O₃ 0.05 wt%까지 첨가할 때까지는 거의 비슷한 값을 나타났지만 0.05 wt% 이상에는 큰 누설전류로 인해 강유전성이 상쇄됨을 나타내었다. 이러한 결과는 Y₂O₃을 소량 첨가하면 도너 역할을 하여 산소 공공의 농도를 감소시키고, 그에 따라 BaTiO₃ 커패시터의 신뢰성을 향상시킬 수 있을 것으로 판단되었다. MnCO₃ 첨가의 경우, 비유전율과 유전손실은 MnCO₃ 첨가량의 따라 감소되어지는 것을 확인하였다. 이러한 결과는 Mn^(2+) 이온이 Ti^(4+) 자리에 치환됨으로써 BaTiO₃ 세라믹스에 억셉터 첨가제로 작용하는 것을 알 수 있다. 따라서 MnCO₃ 첨가 시, BaTiO₃ 세라믹스의 전자 농도를 줄일 수 있었고, 유전손실의 향상이 나타났다. 본 실험 결과들로부터, 향후에는 Y₂O₃와 MnCO₃을 동시 첨가함으로써 BaTiO₃ 커패시터의 유전체 특성을 더욱 향상시킬 수 있을 것으로 유추되었다.
Ferroelectric BaTiO₃ (BT) fine particles have been used as raw materials for electronic devices such as MLCC(Multi Layer Ceramic Capacitor). Recently, with the miniaturization of electronic devices, the down-sizing of MLCC has been developed and accelerated. As a result, it is expected that the thic...
Ferroelectric BaTiO₃ (BT) fine particles have been used as raw materials for electronic devices such as MLCC(Multi Layer Ceramic Capacitor). Recently, with the miniaturization of electronic devices, the down-sizing of MLCC has been developed and accelerated. As a result, it is expected that the thickness of dielectric layers in the MLCC will become less than 1μm. Consequently, the particle size of the required BT raw materials will decrease to about one hundred nm. In addition to grain sizes, the crystal structures of BT are also affect the dielectric properties. Among all phases, the tetragonal structure is desired for optimizing dielectric properties. Traditionally, MLCCs were made of successive layers of precious metal (Pt, Pd, Pd-Ag alloy) and BT dielectric. However, in order to reduce the manufacturing cost, the noble metal electrodes are recently replaced by the base metal electrodes (BME) such as Ni and Cu. The BME are readily oxidized during the sintering process performed under the oxygen ambient conditions. It is therefore necessary to fire the BME-BT layers in reduction conditions, that is, in low oxygen partial pressure. This creates other problems, such as high dielectric losses and dielectric degradation. Because the BT layers contain large content of oxygen vacancies and electrons caused by firing at low oxygen partial pressure. The electron concentration can be easily reduced by addition of acceptor impurities such as Mn and Ca at the Ti site. This suppresses the conductivity and contributes to improving the dielectric loss. By the way, the concentration of the oxygen vacancy is increased by the addition of the acceptor dopants. The redistribution of oxygen vacancies under dc bias is responsible for failure mechanism of the capacitors. Extensive previous researches have shown that the addition of some trivalent dopants to the BT layer can improve the lifetime. Specifically, Y, Ho, Dy can improve the lifetime under certain compositions and heat treatment conditions. Therefore this work studied both the sintering behaviors and electrical properties of nanometer-scale BT powders having some amount of MnCO₃ and Y₂O₃ dopants. For these purpose, the sintered density at different temperatures, microstructure changes and dielectric properties were measured and discussed. The particle size of the BT raw powder used in this study was about 150 nm. And 0.02 ~ 0.1 wt% of MnCO₃ and Y₂O₃ dopants were added to the pure BT raw powder. The prepared powder was mixed by using a ball mill for 42 hours and the mixed powder was dried at 80℃. The powder was sieved with 120-mesh and formed to the disk shape of 15mm in diameter by using a CIP (cold isostatic pressing, 1300 kgf/㎠) method. The specimens were sintered at the temperature range of 1200 ~ 1280℃. The crystal structure after sintering process was analyzed by using the XRD method and the microstructure was observed by using SEM. In order to measure the electrical properties, the sintered specimens were lapped down to 1mm in thickness and were electroded with Ag paste. HP4194 Impedance/Game Phase Analyzer was used for measuring the dielectric properties. All the BT ceramics after sintering process had the tetragonal perovskite structure without secondary phases. In the case of doping the Y₂O₃, the sintering density was increased with increasing the dopant content. The relative dielectric constant and the dielectric loss was nearly same up to the dopant amount of 0.05 wt%. But the dielectric loss and leakage current were increased with adding the Y₂O₃ over 0.05 wt%. These results implies that the Y₂O₃ dopant acts as donors and it will improve the reliability of the BT capacitor by reducing the concentration of oxygen vacancies. In the case of doping the MnCO₃, the relative dielectric constant and dielectric loss were decreased with increasing the doping content. From these results, we could know that the Mn^(2+) ion in the BT ceramics acts as acceptor. The acceptor can reduce the electron concentration in the BT ceramics, which improves the dielectric loss. Further studies on the BT materials having the co-dopants of Y₂O₃ and MnCO₃ will be performed for improving the dielectric properties of the capacitor.
Ferroelectric BaTiO₃ (BT) fine particles have been used as raw materials for electronic devices such as MLCC(Multi Layer Ceramic Capacitor). Recently, with the miniaturization of electronic devices, the down-sizing of MLCC has been developed and accelerated. As a result, it is expected that the thickness of dielectric layers in the MLCC will become less than 1μm. Consequently, the particle size of the required BT raw materials will decrease to about one hundred nm. In addition to grain sizes, the crystal structures of BT are also affect the dielectric properties. Among all phases, the tetragonal structure is desired for optimizing dielectric properties. Traditionally, MLCCs were made of successive layers of precious metal (Pt, Pd, Pd-Ag alloy) and BT dielectric. However, in order to reduce the manufacturing cost, the noble metal electrodes are recently replaced by the base metal electrodes (BME) such as Ni and Cu. The BME are readily oxidized during the sintering process performed under the oxygen ambient conditions. It is therefore necessary to fire the BME-BT layers in reduction conditions, that is, in low oxygen partial pressure. This creates other problems, such as high dielectric losses and dielectric degradation. Because the BT layers contain large content of oxygen vacancies and electrons caused by firing at low oxygen partial pressure. The electron concentration can be easily reduced by addition of acceptor impurities such as Mn and Ca at the Ti site. This suppresses the conductivity and contributes to improving the dielectric loss. By the way, the concentration of the oxygen vacancy is increased by the addition of the acceptor dopants. The redistribution of oxygen vacancies under dc bias is responsible for failure mechanism of the capacitors. Extensive previous researches have shown that the addition of some trivalent dopants to the BT layer can improve the lifetime. Specifically, Y, Ho, Dy can improve the lifetime under certain compositions and heat treatment conditions. Therefore this work studied both the sintering behaviors and electrical properties of nanometer-scale BT powders having some amount of MnCO₃ and Y₂O₃ dopants. For these purpose, the sintered density at different temperatures, microstructure changes and dielectric properties were measured and discussed. The particle size of the BT raw powder used in this study was about 150 nm. And 0.02 ~ 0.1 wt% of MnCO₃ and Y₂O₃ dopants were added to the pure BT raw powder. The prepared powder was mixed by using a ball mill for 42 hours and the mixed powder was dried at 80℃. The powder was sieved with 120-mesh and formed to the disk shape of 15mm in diameter by using a CIP (cold isostatic pressing, 1300 kgf/㎠) method. The specimens were sintered at the temperature range of 1200 ~ 1280℃. The crystal structure after sintering process was analyzed by using the XRD method and the microstructure was observed by using SEM. In order to measure the electrical properties, the sintered specimens were lapped down to 1mm in thickness and were electroded with Ag paste. HP4194 Impedance/Game Phase Analyzer was used for measuring the dielectric properties. All the BT ceramics after sintering process had the tetragonal perovskite structure without secondary phases. In the case of doping the Y₂O₃, the sintering density was increased with increasing the dopant content. The relative dielectric constant and the dielectric loss was nearly same up to the dopant amount of 0.05 wt%. But the dielectric loss and leakage current were increased with adding the Y₂O₃ over 0.05 wt%. These results implies that the Y₂O₃ dopant acts as donors and it will improve the reliability of the BT capacitor by reducing the concentration of oxygen vacancies. In the case of doping the MnCO₃, the relative dielectric constant and dielectric loss were decreased with increasing the doping content. From these results, we could know that the Mn^(2+) ion in the BT ceramics acts as acceptor. The acceptor can reduce the electron concentration in the BT ceramics, which improves the dielectric loss. Further studies on the BT materials having the co-dopants of Y₂O₃ and MnCO₃ will be performed for improving the dielectric properties of the capacitor.
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