BaTiO3-based Multilayer Ceramic Capacitors Research Articles

Investigation of coherent interface on relaxation behavior and reliability of Mg-doped BaTiO3 dielectric ceramics: Experiments and first-principle calculations

The addition of Mg generally enhances the high-temperature stability and reliability of BaTiO3-based multilayer ceramic capacitors (MLCCs). Herein, a series of Mg-doped BaTiO3-based ceramics and ultra-thin MLCCs were successfully fabricated, and the coherent and semi-coherent interface has been observed in samples. Based on the density functional theory (DFT) calculations, the improvement in temperature stability is due to changes in the coherent interface and electronic structure that promote the formation of polar nano-regions (PNRs) and induce relaxation behavior. Based on the atomic displacement, it is found that the excess substitution released the coherent stresses in the form of defects and formed semi-coherent interfaces. The reliability degradation of MLCCs is mainly due to the evolution of the semi-coherent interfaces. This work points out an avenue to obtain high-temperature stability and high reliability in BaTiO3-based MLCCs.

An anomalous low dose phenomenon in gamma irradiated BaTiO3-based commercial multilayer ceramic capacitors

Owing to its miniaturization and high dielectric permittivity, BaTiO3-based multilayer ceramic capacitors (MLCCs) have attracted more and more attention in recent years, and are widely used in gamma-ray environments, such as nuclear and space application. Compared to the extensively studied thermal or electrical reliability issues, the potential risks caused by irradiation have not been well understood, let alone the dielectric structure changes. Unlike the common monotonic dose-dependent trend, we found non-monotonic results in MLCCs with low dose, named as the anomalous low dose (ALD) phenomenon. That is the capacitance decreases at low gamma-ray doses, and then abnormally recovers to the initial value at high doses. Similar cases have been found in almost all the physical properties of MLCCs. Intensive characterizations help to confirm that it is the dose-dependent consistent lattice and electronic structure changes that are most likely to cause this anomalous phenomenon. In detail, the gamma irradiation induces charged defects and consequently lattice distortion, which reduces the number of domains with low-field inversion and eventually causes the capacitance decrease. This work provides a new cognition about the gamma irradiation effect of BaTiO3-based (BTO) dielectrics and commercial MLCCs based on BTO.

High DC-Bias Stability and Reliability in BaTiO3-Based Multilayer Ceramic Capacitors: The Role of the Core-Shell Structure and the Electrode.

With the miniaturization of multilayer ceramic capacitors (MLCCs) and the increase of the electric field on a single dielectric layer, dielectric constant DC-bias stability and reliability have gradually aroused attention in the advanced electronics industry. In this study, MLCCs with outstanding DC-bias stability and reliability were prepared by using dielectric ceramic optimization and electrode optimization strategies. The effect of the Dy-Y doping concentration on the microstructure, dielectric properties, and reliability of BaTiO3-based ceramics was investigated. The shell ratio and effective shell doping concentration of the core-shell structure in ceramic grains play important roles in defects and electrical performances. The ceramic with appropriate doping contents shows a dielectric constant of 1800 and a dielectric constant change rate of -17% under a DC field of 4 kV/mm, which was fabricated into prototype MLCCs with different Ni electrodes. MLCCs exhibit outstanding DC-bias stability with a -28% degradation in the dielectric constant under a DC field of 4 kV/mm while possessing a dielectric constant of 2300 and satisfying the EIA X7S specification. Additionally, it was discovered that MLCCs prepared by using fine-size Ni particle electrodes have low electrode roughness and high interfacial Schottky barriers, resulting in better reliability. This study provides promising candidate materials and theoretical references for high-end and high DC-bias stability MLCCs.

Utilizing time domain electrical methods to monitor MLCCs' degradation

The continued development of BaTiO3-based multilayer ceramic capacitors has contributed to further miniaturization by reducing the thickness of each dielectric layer for different voltage range components. MLCC designs that achieve higher volumetric capacitive efficiency must be balanced with stable properties over long operational times at higher fields and temperatures, raising concerns about their reliability. To improve the reliability and slow transient mechanisms of oxygen vacancy electromigration that drive the degradation of insulation resistance of MLCCs, we need to develop new models and improved metrologies to enhance the performance of MLCCs. This paper demonstrates how electrical characterization techniques, such as thermally stimulated depolarization current and highly accelerated life test, can be used to better understand MLCCs' degradation and assess their reliability. Also, the limitations of existing lifetime prediction models and their shortcomings of using mean time to failure in predicting the lifetime of MLCCs are discussed along with future perspectives on evaluating the reliability of MLCCs.

Study of polarization behavior in BaTiO<sub>3</sub>-based multilayer ceramic capacitors using AC- and Uni-poling treatment ∼ Part 1: Effects of microstructural changes

To obtain guidelines for the microstructure design of BaTiO3-based multilayer ceramic capacitors from the viewpoint of polarization behavior, the effects of AC- and Uni-poling treatments were examined using intentionally grain-growth samples. For purposes of comparison, the DC-aging characteristics of each sample were also examined. From the results of the polarization behavior induced by AC- and Uni-poling treatments, it was confirmed that changes in the core–shell structure, grain size, and oxygen vacancy concentration of the dielectrics strongly affected the domain wall pinning. In comparison with DC-aging characteristics, AC- and Uni-poling treatments are also expected to be effective tools for clarifying the relationships among more detailed microstructure and polarization behaviors of dielectrics.

Importance of uniformity of grain size to reduce dc degradation and improve reliability of ultra-thin BaTiO3-based MLCCs

Excellent direct current (dc)-bias and reliability have become increasingly important for ultra-thin BaTiO3-based multilayer ceramic capacitors (MLCCs). Herein, X5R-MLCCs with a thickness of ∼1 μm are fabricated using BaTiO3 with varied grain size. It is shown that the uniformity of the grain size plays an important impact on the direct current (dc)-bias and the reliability of ultra-thin MLCCs. Uniform grain size, which is indicative of good distribution of doping element contributes to improved temperature stability. By contrast, abnormal large grains induce reinforced space charge polarization. Chips with non-uniform grains exhibit dramatic dielectric constant change under dc-bias due to the high tetragonality and irreversible domain-wall motion. Weibull distribution and highly accelerated life test (HALT) reveal that non-uniform grains contain more oxygen vacancies supported by impedance spectra analysis at 300–450 °C. This study provides a feasible strategy to improve the dc-bias and the reliability of the ultra-thin MLCCs.

Suppressive effect of Ni–Sn internal electrode at the anode on the leakage current degradation of BaTiO3-based multilayer ceramic capacitors

As the BaTiO3 dielectric layer of multi-layer ceramic capacitors (MLCCs) becomes thinner, the problem of leakage current degradation arises. In this study, the leakage current degradation was investigated for the cases when the Ni–Sn internal electrode was placed at either the anode or the cathode. The MLCCs with the Ni–Sn internal electrode at the anode suppressed the leakage current degradation with time significantly better than that at the cathode. The leakage current types for the degraded MLCCs were tunnel and Schottky or Poole–Frenkel for the Ni and Ni–Sn internal electrodes, respectively. High-resolution scanning transmission electron microscopy revealed an interface layer with a high Sn concentration at the interface between the Ni–Sn internal electrode and BaTiO3. Therefore, the interface of the electrode at the anode plays an important role in the leakage current degradation of MLCCs with time.

High-energy storage performance in BaTiO3-based lead-free multilayer ceramic capacitors

Abstract

Effect of alloying Ni inner electrodes on the leakage current degradation of BaTiO3-based multilayer ceramic capacitors

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.

Correlation between tetragonality (c/a) and direct current (dc) bias characteristics of BaTiO3-based multi-layer ceramic capacitors (MLCC)

The influence of tetragonality (c/a) of the dielectrics of BaTiO3-based multi-layer ceramic capacitors (MLCC) on the direct current (dc) bias characteristics was investigated.

Influence of temperature on the dielectric nonlinearity of BaTiO3-based multi-layer ceramic capacitors

Temperature dependence of the dielectric nonlinearity was investigated for the BaTiO3 multilayer ceramic capacitor. The decrease in temperature caused a significant increase in the degree of dielectric nonlinearity. The Preisach analysis shows that such effect corresponds to a decrease in reversible and a significant increase in irreversible domain wall contribution to polarization. The magnitude of spontaneous polarization (PS) was increased with decreasing temperature. It can be associated with phase transition from pseudo-cubic to monoclinic and its resultant change in the polar direction, which was observed through transmission electron microscopy. These results demonstrate that the increase in PS with the decrease in temperature inhibits domain wall motion in low driving field as it is anticipated to increase the degree of intergranular constraints during domain wall motion. But it results in a more steep increase in the dielectric constants beyond the threshold field where domain wall motion can occur.

Highly accelerated resistance degradation and thermally stimulated relaxation in BaTiO3-based multilayer ceramic capacitors with Y5V specification

Correlation between resistance degradation and thermally stimulated relaxation in commercial BaTiO3-based multilayer ceramic capacitors (MLCCs) with Y5V specification were analyzed. The temperature dependence of dielectric behavior shows that the polarization response is activated by increasing AC electric field, especially the dielectric permittivity peak value. Highly accelerated degradation test and thermally stimulated depolarization current (TSDC) measurements were performed. It has been found that the reliability of capacitors greatly depends on temperature and electric field. TSDC of capacitor dielectrics before and after degradation were also investigated for a fundamental understanding of the resistance degradation mechanism. Two TSDC relaxation peaks were detected, and were correspondingly assigned to in-grain and across-grain boundary migration of oxygen vacancies. Contrary to our predictions, the degraded sample shows an evident decrease in TSDC density and activation energy of the across-grain boundary relaxation compared with the ceramic capacitor without degradation. It is demonstrated that the insulation resistance degradation is associated with the migration of oxygen vacancy defects. The strong degradation indicates that more oxygen vacancies may jump out of potential well and probably form defect clusters. Such clusters will not have the mobility to relax back, subsequently causing the decrease in the measured relaxation current.

Grain-growth effect on dielectric nonlinearity of BaTiO3-based multi-layer ceramic capacitors

A significant difference in dielectric nonlinearity was contrasted between fine- and coarse-grained BaTiO3-based multilayer ceramic capacitors. Grain growth resulted in a decrease in dielectric constant in low field but a steep increase with increase in alternating current field, which can be associated with a decrease in reversible and a significant increase in irreversible domain wall contribution from Preisach analysis. Fine-grained specimens showed almost cubic structure despite ferroelectric domain contrasts, which is anticipated to significantly reduce strain incompatibility during domain wall motion, and clean domain boundaries with no lattice defects. However, coarse-grained specimens with high aspect ratio of the tetragonal lattice should accompany lattice distortion with increased intergranular constraints during domain wall motion, and many lattice defects were observed near domain boundaries. These results demonstrate experimentally the presence of weak pinning centers in coarse-grained specimens, which inhibit domain wall motion in low alternating current fields. Long-range motion occurs beyond the threshold field and results in an abrupt increase in dielectric constant.

Synergistic effect of rare-earth elements on the dielectric properties and reliability of BaTiO3-based ceramics for multilayer ceramic capacitors

Fine-grain BaTiO3-based ceramics co-doped with different amounts of Ho and Dy were prepared by a chemical coating method, giving good dielectric properties and gentle temperature stability. The co-doping effect on the dielectric properties and microstructure evolution of BaTiO3-based ceramics was investigated. The highly accelerated lifetime test was conducted to study the failure of the insulation resistance under high electric field and elevated temperature. Results showed that ceramic samples with Ho and Dy co-doping exhibit better insulation degradation behavior than those with Ho or Dy doped separately. Impedance analysis proved that different co-doped amounts of Ho and Dy show almost no effect on the resistance and the activation energy of grain boundary in BaTiO3-based ceramics. However, there was an obvious difference on the resistance and the activation energy for grain bulk. The synergistic effect of Dy and Ho is helpful to improve the reliability of BaTiO3-based multilayer ceramic capacitors.

Electrical Properties of BaTiO3-Based Multilayer Ceramic Capacitors Sintered with Plasma-Treated Glass Powder

The influence of glass power morphology on the electrical and microstructural properties of BaTiO3-based multilayer ceramic capacitors (MLCCs) was investigated to enhance the reliability of MLCCs. For a sintering additive, glass particles of different sizes and shapes were prepared by jet-milling and RF plasma treatment. Plasma treatment decreased the glass particle size and transformed the irregular shape of glass particles into homogeneous spherical shapes. It was found that MLCCs sintered with plasma-treated glass powder have a more homogeneous microstructure, a clear core–shell structure, a more stable capacitance against voltage and temperature changes, and a higher degradation resistance. It is inferred that nanosized spherical glass powder prepared by plasma treatment helps so-called magic dopants such as rare-earth elements to be distributed homogeneously around the BaTiO3 particles.

Effect of Vanadium Addition on Reliability and Microstructure of BaTiO3-Based Multilayer Ceramic Capacitors

The vanadium distribution in multilayer ceramic capacitors (MLCCs), sintered under a reducing atmosphere, was investigated using scanning transmission electron microscopy–electron energy loss spectroscopy (STEM–EELS), and insulation resistance degradation was analyzed using impedance spectroscopy in highly accelerated lifetime tests to clarify the effects of vanadium on both the electrical properties and microstructure of MLCCs. Vanadium mitigated insulation resistance degradation and increased the reliability of MLCCs. Moreover, vanadium content increased and insulation resistance at the ceramic/electrode interface decreased slowly. This change in dynamics directly resulted in an improved lifetime of MLCCs. The results of STEM–EELS analysis showed that vanadium distributed along the grain boundary and grain boundary junction, but substituted into BaTiO3 at the ceramic/electrode interface. Therefore, it is considered that vanadium substitution at the ceramic/electrode interface improves the reliability of MLCCs.

Field-induced domain switching in BaTiO3-based multilayer ceramic capacitors observed by polarized Raman spectroscopy

Polarized Raman spectroscopy was employed to observe field-induced domain switching in BaTiO3-based multilayer ceramic capacitors (MLCCs). Un-polarized Raman intensities of vibration modes A1(TO2,TO3) are decreased with increasing the external field from 0 MV/m to 5 MV/m, which is caused by the decrease of c-domain volumes. This phenomenon can be visualized from the simulated image gained from the mapping results in cross polarization. It shows that the c-domains are switched to the direction of electric field (3.75 MV/m). We also found that the load to imprint Vickers indentation on the polished MLCCs surface can drive the domains out of the plane parallel to internal electrodes into in-plane textures. Meanwhile, the in-plane domains in the investigated area are switched to form a uniform orientation by the local introduced compressive stress. Due to the existence of cracks, the domains near cracks will re-orient and align with the direction of the relative tensile stress, resulting in a different orientation.

Theoretical Study on Interactions between Oxygen Vacancy and Doped Rare-Earth Elements in Barium Titanate

We performed first-principles theoretical calculations to examine the interactions between oxygen vacancy (VO) and rare-earth (RE) elements in barium titanate (BaTiO3), in order to clarify the mechanism of VO trapping by RE dopants, which affects the insulating reliability of BaTiO3-based multilayer ceramic capacitors (MLCC). It was found that VO is stabilized at the first and second nearest O sites of RE at Ba site (REBa), and at the second nearest O site of RE at Ti site (RETi). The structural relaxations on bond lengths of REBa–O and RETi–O in BaTiO3, which are brought about by the existence of VO at the above sites, decrease the total energy, and thus VO is stabilized. Furthermore, we revealed that the stability of VO increases with decreasing solution stability of RE dopants in BaTiO3. Accordingly, we concluded that RE dopants with higher solution energy in BaTiO3 efficiently trap VO, and thus the insulation reliability of MLCC is improved.

Phase Mixture and Reliability of BaTiO3-Based X7R Multilayer Ceramic Capacitors: X-Ray Diffractometry and Raman Spectroscopy

BaTiO3-based multilayer ceramic capacitors (MLCCs) using Ni base-metal electrodes (BME) exhibiting EIA-X7R dielectric behavior are represented by the characteristic microstructure of core–shell grains. In the present study, the crystalline phase contents in the mixture were determined quantitatively for two groups of experimental BME-MLCCs, one with CaO doping and the other with (CaO+MgO) codoping by Rietveld refinement using the software package TOPAS®. X-ray diffractometry was used for the identification of crystalline phases whose quantities were determined for cubic (C), tetragonal (T), and rhombohedral (R)–BaTiO3. Phase identification was corroborated by Raman spectroscopy where the characteristic phonon vibration modes corresponding to the C-, T-, and R-phase were assigned. It is suggested that the C-phase content, corresponding to the shell grains containing intragranular voids and the shell region of the core–shell grains, and the R-phase content, corresponding to the modulated core region, not only determine the diffusiveness of the temperature coefficient of capacitance curve but also serve as measuring indices for evaluating the resistance of MLCC formulations against dc degradation.

Electric Field-Dependent Properties of BaTiO3-Based Multilayer Ceramic Capacitors

The DC electric field-dependent properties of BaTiO3-based multilayer ceramic capacitors (MLCCs) with X7R specification were studied. The dependence of dielectric-temperature behavior on electric field showed that a field-induced phase transition took place under high DC field, which was characterized by the enhanced Curie temperature and the decreased dielectric constant. The ferroelectric measurements showed the field-dependent hysteresis behavior, which was considered to be originated from the field induced transition and the injected charge effects. The current-voltage measurement for MLCCs revealed that a transition from an Ohmic linear dependence to a nonlinear behavior, corresponding to the space charge limited conduction mechanism.