Layers In Multilayer Ceramic Capacitors Research Articles

Degradation monitoring of multilayer ceramic capacitors during high accelerated lifetime testing using ultrasound

Multilayer ceramic capacitors (MLCCs) are vital circuitry components where long-term stability at high temperature and fields is critical to device operation. High accelerated lifetime testing (HALT) statistically investigates reliability and lifetime of MLCCs through exposure to temperatures and voltages exceeding normal operating conditions. The long-term reliability of the dielectric layers in MLCCs strongly depends on potential variability in the dielectric microstructure, such as cracking, which can be challenging to detect. Nondestructive ultrasonic evaluation is sensitive to microstructural changes through measurements of wave scattering. This work uses high frequency (100 MHz) focused ultrasonic scattering methods to nondestructively monitor structural and microstructural changes in MLCCs from the pristine to the failed state during HALT to understand structural origins of electrical failure. Printed circuit board mounted MLCCs were electrically and ultrasonically characterized in a pristine state and during various degraded states before and after electrical failure under HALT. Evidence of damage pre-HALT was ultrasonically indicated by high attenuation regions on the ultrasonic maps suggesting that the mounting process may induce damage. The high attenuation regions in the pristine samples evolved throughout HALT indicating that the damage in the pristine state might be the spatial origin of part failure, which underscores the impact and importance of detection of structural defects on the reliability of MLCCs.

Ultra-thin barium titanate nanocrystal monolayer capacitor with graphene electrode

Ultra-thin capacitor structures of barium titanate (BaTiO3, BTO) nanocube monolayers are fabricated using graphene as an electrode without high-temperature sintering. The capacitor consists of a self-assembled BTO nanocube monolayer (approximately 20 nm in thickness) and an eight-layer graphene electrode (≤3 nm in thickness) that are sandwiched metal electrodes. The graphene electrode functions as a barrier layer preventing the occurrence of short circuits caused by the penetration of metal species into the dielectric layer during the deposition process of the metal electrode, dramatically reducing the leakage current of the capacitor in comparison with the case without the graphene electrode. Furthermore, this approach is applicable to the fabrication of the graphene/BTO-nanocube-monolayer multi-stacked structures, demonstrating the potential to reduce the thickness of individual electrode/dielectric layers in multilayer ceramic capacitors down to less than 25 nm. This opens up possibilities for energy-efficient production of high-performance ceramic capacitors.

Simultaneous enhancement of dielectric properties and temperature stability in BaTiO3‐based ceramics enabling X8R multilayer ceramic capacitor

AbstractModified BaTiO3 ceramics that possess high dielectric permittivity and acceptable temperature stability have been widely utilized as multilayer ceramic capacitors (MLCCs) for high‐frequency bypass and power filtering in automotive applications. However, since the increasing demand for high‐capacity and small‐size, high‐permittivity materials that can serve as dielectric layers in MLCCs are urgently required. In this work, we design and fabricate a special BaTiO3‐0.03Mg‐0.02Y‐0.02CaZrO3 ceramic with a high dielectric permittivity of 3000 and the dielectric variation below ±13% in the temperature range of ‐55–150°C, fulfilling the requirements of X8R capacitors. To achieve these results, we employed grain size engineering and cation doping, using BaTiO3 precursors with a particle size of 240 nm to prepare the BaTiO3‐based ceramics with fine grains, while Mg and Y co‐doping was used for improving the temperature stability due to dielectric dispersion. Utilizing these high‐permittivity BaTiO3‐based materials, we fabricated MLCCs that satisfy the X8R criterion, possessing a high dielectric constant of 2950 and a high breakdown field (410 kV/cm).

Change in Electric Field Distribution in Non-Reducing BaTiO<sub>3</sub> Based-Dielectric Layer Loaded at High Temperature

The electric field distributions in loaded dielectric layers of multilayer ceramic capacitors were investigated at several stages of insulation degradation for the load, using Kelvin probe force microscopy. The electric field distribution was found to be different at each stage of loaded time. Initially, the electric field was concentrated near the cathode, indicating that the insulation resistance near the anode decreased. Then, following the homogeneous distribution shown for an intermediate stage, the electric field eventually concentrated near the anode. This change indicates how insulation degradation occurs locally; this change can plausibly be explained by a hole density increase.

Numerical analysis of dielectric ceramic and void containing Ni electrode layers of multilayer ceramic capacitors

In this article, we performed a numerical analysis of dielectric ceramic and Ni electrode layers with voids in a multilayer ceramic capacitor using the finite element method. To numerically analyze a multilayer ceramic capacitor composed of several hundred ceramic and Ni layers, we defined a unit cell, and equivalent material properties from the ceramic and Ni layers were calculated by the homogenization method. We predicted the deformation of the overall multilayer ceramic capacitor from that of a unit cell with equivalent material properties. Voids in the Ni layer, produced during the manufacturing process, were taken into consideration. Because both ceramic and Ni layers are viscoelastic and are in contact with each other, viscoelastic and contact analyses were carried out using the commercial software ANSYS. Dynamic mechanical analysis was used to determine the viscoelastic material properties of the ceramic and Ni layers. We compared the elastic results with the viscoelastic results to determine the viscoelastic characteristics of a multilayer ceramic capacitor. The surface roughness of a multilayer ceramic capacitor was measured by confocal microscopy to verify the reliability of the numerical analysis. The experimental results showed reasonable agreement with the model-based results.

The Kelvin Probe Force Microscopy Measurement of Degraded Multilayer Ceramic Capacitors with Ni Inner Electrode

Electric potential mapping of degraded dielectric layers of multilayer ceramic capacitors (MLCCs) was carried out using Kelvin probe force microscopy in order to clarify their degradation mechanism under conditions of an accelerated lifetime test condition. In the cross sections of the degraded and as-prepared dielectric layers, a significant electric field concentration was found in the vicinity of the anode of the degraded dielectric layer, in contrast to a homogeneous concentration found throughout layers of the samples before the accelerated lifetime test.

Electric field concentration in the vicinity of the interface between anode and degraded BaTiO3-based ceramics in multilayer ceramic capacitor

The electric field distribution of degraded dielectric layers in multilayer ceramic capacitors (MLCCs) was investigated by Kelvin probe force microscopy (KFM) to clarify the insulation degradation mechanism in MLCCs. For the degraded dielectric layers, the electric field was found to be concentrated near the anodes. This concentration easily moved to the opposite side with a reversal of the applied voltage of 5 V (13 kV/cm) during KFM measurement at room temperature. On the other hand, electric field concentrations and electric field distributions did not change in fresh MLCCs, indicating that the electric field concentrations easily transfer near higher-potential interfaces between electrodes and ceramics only in degraded MLCCs. These facts suggest that Schottky barriers would be formed in degraded MLCCs. The KFM technique discussed in this work is a very useful tool for measuring the surface potential and helps clarify the local electric field concentration near the electrodes.

Electrocoloration and oxygen vacancy mobility of BaTiO3

The electrical-insulation degradation of BaTiO3 is now of growing interest as the BaTiO3-based dielectric layers of multilayer ceramic capacitors are getting thinner to submicron thicknesses. The degradation is understood to be due to the electrotransport of oxygen vacancies and may be monitored by the colors emanating from the cathode and/or anode. In the case of single crystal BaTiO3, a brown color emanates from the anode and a blue color from the cathode. We will experimentally review the generation of the colors in BaTiO3 in electric fields, and discuss their origins and kinetics of color front migration. From the latter the oxygen vacancy mobility against temperature in the range of 150–500°C is subsequently determined and compared with all the literature data that have normally been estimated by other means at elevated temperatures.

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.

Role of PbO and Ag on Insulation Resistance Degradation in Relaxor‐Based MLCs

The relationship between the grain boundary phase and insulation resistance of dielectric layers in multilayer ceramic capacitors (MLCs) was clarified, leading to a proposal for the mechanism of insulation resistance degradation. A Pb‐rich secondary phase was present at grain boundaries, and a small amount of Ag was detected from the secondary phase, while no secondary phase existed in dielectric layers with normal insulation resistance. These results suggest that diffusion from an internal electrode into the secondary phase in dielectric layers is responsible for the extremely low insulation resistance: oxygen vacancies, formed as a result of substitution of Ag for Pb, may play a role in lowering insulation resistance.

Effects of Silver Doping on the Reliability of (Pb0.875 Ba0.125)[(Mg1/3 Nb2/3) 0. 5(Zn1/3 Nb2/3)0.3 Ti0.2] O3 Relaxor Dielectric Ceramics

The reliability of the silver‐doped dielectric ceramic (Pb0.875Ba0.25)0.995[(Mg1/3Nb2/3)0.5(Zn1/3Nb2/3)0.3Ti0.2]O3 was investigated to speculate on the effects of silver diffusion from internal electrodes into dielectric layers on the reliability of multilayer ceramic capacitors (MLCs). The addition of silver into the dielectric ceramic degraded the insulation resistance under humid loading conditions. Scanning transmission electron microscopy (STEM) revealed that a Pb‐rich grain boundary phase exists at triple points of Ag‐doped specimens. The Pb‐rich phase appeared to be PbO by X‐ray photoelectron spectroscopy (XPS). Degradation of insulation resistance was interpreted as a result of silver migration from the anode to the cathode through a grain boundary phase dissolved in water. Although silver diffusion from internal electrode layers in MLCs into dielectric layers was confirmed by STEM, a secondary phase was not observed. Intensive study is needed to clarify the effect of silver diffusion on degradation of insulation resistance of MLCs under humid loading conditions.