Yukie Nakano

Reliability of multilayer ceramic capacitors with nickel electrodes

Abstract The reliability of multilayer ceramic capacitors (MLCCs) with Ni internal electrodes has been studied trom the viewpoint of partial oxygen pressure (PO2) during firing. It is shown that the load-life time of the insulation resistance (1R) was prolonged by firing under low Po2 annealing after firing, and the addition of dopants. It is also shown that the generation of oxygen vacancies led to the degradation of IR. Annealing treatment for the oxidation of the dielectric body accelerates the dielectric aging of MLCCs. It is found that the appropriate control of the PO2 during firing can improve the reliability of MLCCs with Ni electrodes to a level as high as that of MLCCs with precious metal electrodes. Thus, we have developed an MLCC with Ni electrodes that features high reliability and a large capacitance of 10 μF for the Y5V characteristic and 4.7 μF for the X7R characteristic, both in the case of the C3216 (3.2 mm × 1.6 mm × 1.4 mm) form.

Mechanism of improvement of resistance degradation in Y-doped BaTiO3 based MLCCs with Ni electrodes under highly accelerated life testing

Abstract The mechanism of improvement of resistance degradation in Y-doped BaTiO3 based multilayer ceramic capacitors (MLCCs) with Ni electrodes has been studied using electrical measurement techniques, minor phase identification and the measurement of oxygen vacancy concentration. Admittance spectroscopy and thermally stimulated current measurements show the relaxation due to barium vacancy states caused by Y doping. The minor phase identification by XRD indicated those Y3+ substitutes for perovskite A-site. Oxygen vacancy concentration measurement indicated that Y decreases the oxygen ion vacancy concentration in BaTiO3. These results suggest that Y3+ acts as a donor and creates barium vacancies, which compensate for the oxygen vacancies and thereby improve the resistance degradation.

Residual stress of multilayer ceramic capacitors with Ni-electrodes (Ni-MLCCs)

The residual stress of multilayer ceramic capacitors (MLCCs) has been studied. The capacitance decreased significantly under external compressive stress applied to MLCCs in the thickness direction, on the other hand, the capacitance increased under external stress in the width direction. These capacitance changes depended on the number of dielectric layers in MLCCs. The compressive residual stress at the surface of MLCCs has been shown by X-ray diffraction (XRD) analysis. The stress increased with the number of dielectric layers in MLCCs. Moreover the tensile stress was confirmed in the thickness direction of MLCCs by XRD analysis also. Therefore the dependence of electrical characteristics dependence on the number of dielectric layers, i.e., apparent dielectric constant, temperature dependence of capacitance, and aging deterioration can be explained by the residual stress.

Effect of Y-Doping on Resistance Degradation of Multilayer Ceramic Capacitors with Ni Electrodes under the Highly Accelerated Life Test

The effect of Y-doping on the degradation behavior of insulation resistance for multilayer ceramic capacitors with Ni electrodes has been studied using electrical measurement techniques such as admittance spectroscopy, thermally stimulated current (TSC), and electrical conductivity measurements. TSC measurements show that a strong internal bias field remained after applying an electrical field at a high temperature, like during highly accelerated life testing. This internal bias field originated from the migration of positive carriers. Admittance spectroscopy indicated three types of relaxation, with activation energies of 0.4, 0.8, and 0.8–1.0 eV. The intensity of the 0.4 eV relaxation peak increased with Y3+ doping and disappeared at low oxygen partial pressure ( PO2) annealing. The existence of holes was also observed from the temperature dependence of insulation resistance. The 0.4 eV relaxation is considered to be due to the transition of electrons from the valence band to barium vacancy states. These results suggest that Y3+ acts as a donor and creates barium vacancies, which compensate for the oxygen vacancies and thereby improve the resistance to degradation.

Aging Behavior of Ni-Electrode Multilayer Ceramic Capacitors with X7R Characteristics

Capacitance aging under dc field has been studied on BaTiO3-based dielectrics with X7R characteristics for multilayer ceramic capacitors with Ni internal electrodes. Capacitance change strongly depends on additives and firing conditions as well as microstructure. Aging behavior under no dc field is well explained by Richters relaxation curve. On the other hand, aging under dc field cannot be fitted by Richters curve. Therefore, a new model which assumes two factors that affect relaxation is proposed. According to the new model, capacitance changes in two stages, short-term and long-term relaxations. Capacitance change in short-term relaxation strongly depends on applied dc field. On the contrary, that of long-term relaxation does not depend on dc field.

Number of Dielectric Layers Dependence of Dielectric Properties and Residual Stress of Multilayer Ceramic Capacitors with Ni Electrodes

The relationship between the residual stress and dielectric properties of multilayer ceramic capacitors with Ni electrodes (Ni-MLCCs) has been studied. Residual stress measurement by X-ray diffraction revealed that tensile stress inside MLCCs in the thickness direction increased with increasing number of dielectric layers. The increase in the ratio of the c-axis to the a-axis of BaTiO3 in the thickness direction of MLCCs was expected from the results of X-ray diffraction with increasing number of dielectric layers. The increase in dielectric constant and its temperature dependence with increasing number of dielectric layers were expectedly related to crystal structures.

Multilayer ceramic capacitors-recent trends

Recently, reduction of production costs with maintaining high reliability is required for wider applications of capacitors. Ni-electrode multilayer ceramic capacitors (MLCCs) of BaTiO/sub 3/-based dielectrics and AgPd-electrode MLCCs of relaxor materials were developed to meet the requirements. Thinner dielectric layers, miniaturization, and high capacitance are also major requirements for MLCCs. In these circumstances, much effort has been paid in order to achieve higher reliability. Ni-electrode MLCCs are promising way to satisfy the requirements of high capacitance, low cost, and high reliability. Major problems about the reliability were mechanical fracture, degradation of insulation resistance, and capacitance aging. These phenomena are strongly affected by both chemical composition and producing process.

Residual Stress of Multilayer Ceramic Capacitors (MLCCs)

The residual stress of MLCCs has been studied. The compressive res idual stress at the surface of MLCCs was shown by X-ray diffraction. The stress increased wi th the number of dielectric layers in MLCCs. The dielectric constant at room temperature increased with the number of layers in MLCCs. Moreover, the external compressive stress showed a delete rious ffect on the dielectric constant. Therefore, it is supposed that the residual stress caused t he increase of the dielectric constant with the number of layers in MLCCs.

Electrical properties and distortion characteristics of MLCCs with composite dielectric material

The electrical properties and distortion characteristics of multilayer ceramic capacitors (MLCCs) with composite dielectric material, which consisted of ferroelectric and paraelectric phases were studied. In composite dielectrics, BaTiO3 (BTO) was used for the ferroelectric phase, while SrTiO3 (STO) and CaTiO3 CTO were used for the paraelectric phases. The dielectric ceramics with composite structure of MLCC were prepared with these perovskite grains and additives. The temperature dependence of dielectric constant of the MLCC could be controlled by the volume ratio of ferroelectric and paraelectric phases. The distortion characteristic of MLCC with composite structure was smaller than that of BTO.