No abstract

The failure mechanisms of multilayer ceramic capacitors (MLCCs) with Ni internal electrodes under high temperature and high voltage conditions have been investigated through highly accelerated life tests (HALTs) in recent years. Generally, insulation resistance degradation during HALTs is presumed to be because of the electromigration of oxygen vacancies. Reliability in high-temperature, high-humidity, and rated-voltage environments is important for MLCCs. However, only a few studies have investigated the causes of insulation resistance degradation in MLCCs in these environments. We investigated the failure mechanisms of MLCCs through a highly accelerated temperature and humidity stress test. On the basis of presence of a degraded area on the anode side, we presumed that hydrogen ions were produced by H 2 O electrolysis at the interface between the ceramics and internal electrodes on the anode side, and that these hydrogen ions caused insulation resistance degradation.

Although it has been suggested that infiltration of water vapor into multi-layer ceramic capacitors (MLCCs) can increase leakage current, few studies have reported how this increase is directly linked to the infiltration. In this work we performed accelerated temperature and humidity stress tests with heavy water as a tracer and investigated, using secondary ion mass spectrometry, whether traces of water vapor could be detected in MLCCs. In particular, deuterium was found in areas where an augmented leakage current was detected. It is clear that infiltration of water vapor into MLCCs increased the leakage current. This finding could lead to further improvements in MLCCs.

High-capacitance multilayer ceramic capacitors (MLCCs) are mostly electronic ceramic components in which Ni inner electrodes and BaTiO3-based dielectrics are laminated alternately. Owing to their usefulness in portable electronic devices such as smartphones, there is an ongoing demand to attain an MLCC with smaller dimensions and improved capacity. We investigated the effect of alloying Ni inner electrodes with various elements on the leakage current degradation of MLCCs. Fe, Cu, Zn, and Sn were chosen and added to Ni and co-fired with BaTiO3, from which Cu and Sn were alloyed with Ni. The leakage current degradation time of MLCCs using the Ni–Cu and Ni–Sn inner electrodes was longer than that of MLCCs using the Ni internal electrodes. In particular, the leakage current degradation of the MLCCs using Ni–Sn inner electrodes was significantly suppressed. This suppression effect increased as the thickness of the BaTiO3-based dielectrics decreased. This method of optimization of the Ni inner-electrode composition could lead to further miniaturization and increased capacity of MLCCs.

Dielectrics composed of BaTiO3-rare earth oxide-MgO have been studied to design a non-reducible low-loss dielectric material. Curie temperatures of dielectrics composed of BaTiO3–Gd2O3–MgO were lowered by Gd2O3, which provided the dielectrics with low power loss. It was found that the addition of BaZrO3 to BaTiO3–Gd2O3–MgO decreased the capacitance change with temperature. Gd2O3 diffused easily into BaTiO3, but, it could not easily diffuse into BaTiO3 to which BaZrO3 had been added. It was considered that BaZrO3 prevented the Gd2O3 diffusion into BaTiO3, resulting the remains of ferroelectricity and reduced capacitance change. Thus non-reducible and low power loss X7R dielectric ceramics were developed.