Base-metal Electrode Multilayer Ceramic Capacitors Research Articles

Quality assessment and lifetime prediction of base metal electrode multilayer ceramic capacitors: Challenges and opportunities

Base metal electrode (BME) multilayer ceramic capacitors (MLCCs) are widely used in aerospace, medical, military, and communication applications, emphasizing the need for high reliability. The ongoing advancements in BaTiO3-based MLCC technology have facilitated further miniaturization and improved capacitive volumetric density for both low and high voltage devices. However, concerns persist regarding infant mortality failures and long-term reliability under higher fields and temperatures. To address these concerns, a comprehensive understanding of the mechanisms underlying insulation resistance degradation is crucial. Furthermore, there is a need to develop effective screening procedures during MLCC production and improve the accuracy of mean time to failure (MTTF) predictions. This article reviews our findings on the effect of the burn-in test, a common quality control process, on the dynamics of oxygen vacancies within BME MLCCs. These findings reveal the burn-in test has a negative impact on the lifetime and reliability of BME MLCCS. Moreover, the limitations of existing lifetime prediction models for BME MLCCs are discussed, emphasizing the need for improved MTTF predictions by employing a physics-based machine learning model to overcome the existing models’ limitations. The article also discusses the new physical-based machine learning model that has been developed. While data limitations remain a challenge, the physics-based machine learning approach offers promising results for MTTF prediction in MLCCs, contributing to improved lifetime predictions. Furthermore, the article acknowledges the limitations of relying solely on MTTF to predict MLCCs’ lifetime and emphasizes the importance of developing comprehensive prediction models that predict the entire distribution of failures.

Dielectric properties of BaTiO3 and Ba0.95Ca0.05TiO3 sintered in a reducing atmosphere

The dielectric materials utilized in high-performance barium titanate-based base-metal electrode multilayer ceramic capacitors (BME MLCCs) must satisfy stringent criteria such as high dielectric constant, low dielectric loss, high insulation resistivity, and reliability. In this investigation, the effects of raw materials, BaTiO3 (BT), and Ba0.95Ca0.05TiO3 (BCT) on densification, microstructure, and dielectric behavior were explored by introducing acceptor and rare earth elements. The findings revealed that BCT could attain densification at a lower sintering temperature of 1275 °C than BT. Moreover, BCT samples displayed relatively smaller grain sizes, resulting in a greater number of grain boundaries, which in turn increased the insulation resistivity. BCT had a lower oxygen vacancy concentration, thus resulting in lower leakage currents at high temperatures than BT. Substituting BCT for BT resulted in higher activation energies for conductivity in the core, shell, and grain boundary. This investigation demonstrates that BCT can enhance the dielectric properties, insulation resistance, and reliability of the BME MLCCs.

Coating of Crystalline BaTiO3 Layer on Ni Nanoparticles for Multilayer Ceramic Capacitor Electrode

The base‐metal electrode (BME) is widely applied in multilayer ceramic capacitors (MLCCs) to replace the Pd/Ag electrode, whereas the oxidation and low shrinkage temperature during sintering is difficult to be resolved in nanosized electrode powders. Herein, a facile two‐step route for the fabrication of the crystalline BaTiO3 (BT) layer on Ni nanoparticles is developed. The amorphous BT layer is first coated on Ni nanoparticles by a normal precipitation method. Then, the as‐prepared Ni@BT powders are hydrothermally treated at alkaline conditions to facilitate the crystallization of the coating layer. Due to the dense and uniform crystalline BT layer, the Ni@BT powders show significantly enhanced sintering and antioxidation performance, which provides a high‐performance electrode for BME MLCC.

Anti-reductive characteristics and dielectric loss mechanisms of Ba2ZnSi2O7 microwave dielectric ceramic

Abstract Ba2ZnSi2O7 ceramic was prepared by conventional solid-state method and sintering under four different atmospheres (air, O2, N2, and N2–1 vol% H2). The Ba2ZnSi2O7 ceramic exhibited a single phase under air, O2, and, N2, whereas two phases (including BaSiO3 impurity) were observed under the N2–1 vol% H2 atmosphere due to Zn2+ evaporation. Dielectric loss was proportional to oxygen partial pressure due to the conduction mechanism of dominant holes. The Ba2ZnSi2O7 ceramic exhibited good microwave dielectric properties (er = 8.3, Q × f = 27200 GHz, τf = −41.5 ppm/°C) under the N2–1 vol% H2 atmosphere, making it a novel candidate with good anti-reductive characteristics for base metal electrode–multilayer ceramic capacitor applications.

Effects of addition of Sc2O3 on microstructure and dielectric properties of BaTiO3-based X8R MLCCs

This study investigated the changes in dielectric properties of the disc capacitor and base metal electrode (BME) multilayer ceramic capacitor (MLCC) fabricated from the host material (BaTiO3 + 1.0 mol% MgO + 0.05 mol% MnCO3 + 1.37 mol% BaSiO3) with different amounts of Sc2O3 addition. The results of transmission electron microscope (TEM) analysis verified that the addition of 0.6 mol% Sc2O3 led to the formation of a grain core–shell structure. The formation of the grain core–shell structure can improve the temperature stability of the dielectric properties. The presence of Sc2O3 can increase the room-temperature insulation resistance and reduce dielectric loss (tanδ); however, an excessive addition of Sc2O3 resulted in the decline of the insulating property of MLCCs at a high temperature. This study revealed that the temperature coefficient of the capacitance (TCC) curves can be flattened by adding 0.3–0.6 mol% Sc2O3 into the host material so that the developed BME MLCCs can comply with the requirements of the Electronic Industries Alliance (EIA) X8R specification. In particular, the MLCC with 0.3 mol% Sc2O3 addition had satisfactory TCC stability and insulating properties; the dielectric constant was 2084, tanδ was 1.23%, the TCC at −55 °C and 150 °C was −2.8% and −5.8%, respectively, and the insulation resistance at −55 °C and 150 °C was 3.6 × 1010 Ω and 2.6 × 107 Ω, respectively.

Cu<sub>3</sub>TeO<sub>6 </sub>Dielectric Thick Films: Processing by Electrophoretic Deposition and Electrical Characterization

Te-based compounds are promising dielectric candidates for Base-Metal Electrode Multilayer Ceramic Capacitors (BME-MLCCs) and Low-Temperature Co-fired Ceramics (LTCCs) applications due to their low sintering temperature and good dielectric properties. In spite of the possible compatibility with Cu electrodes for microelectronics, data on compounds of the CuO-TeO2 system are scarce. Recently, we have reported the phase formation process of Cu3TeO6 and the first dielectric data for Cu3TeO6 ceramics. Due to the interest for some applications in thick films, in this work Cu3TeO6 thick films were fabricated by electrophoretic deposition (EPD) on platinized silicon substrates under different processing conditions. The relation between processing and film’s quality was established. ~ 50 μm Cu3TeO6 thick films sintered at 860 oC for 5 h exhibit a permittivity of ~2 and dielectric loss of 0.01 at room temperature and the temperature coefficient of the dielectric permittivity is 9.5×103 ppm°C-1 at 1 MHz from 40 °C to 120 °C. It is expected that this dielectric performance, when compared with the one of Cu3TeO6 ceramic counterparts, improves if the density of the films is increased.

New Cu3TeO6 Ceramics: Phase Formation and Dielectric Properties

Targeting low temperature cofired ceramics (LTCC) applications and base-metal electrode multilayer ceramic capacitors (BME-MLCCs), ceramics of a new composition, tricopper tellurate (Cu3TeO6), are reported here. The crystal structure of Cu3TeO6 was determined to be cubic, Ia3, with the unit cell parameter a = 9.538 Å. The sequence of phase formation is proposed with the oxidation of tetravalent tellurium (Te(4+)) into hexavalent tellurium (Te(6+)) as a key step for the formation of Cu3TeO6. Ceramics sintered at 865 °C with densities of 94% exhibit two dielectric anomalies in the temperature dependence of the dielectric response, around -150 °C and +50 °C, respectively, accompanied by obvious frequency dispersion of the relative permittivity (ε(r)) and dielectric losses (tan δ), with an Arrhenius like behavior. A temperature stable dielectric region (near room temperature) formed between the two anomalies with ε(r) ∼ 12 and tan δ ∼ 0.01, and a very low positive temperature coefficient of the relative permittivity (TCε(r)), 2.07 × 10(-4) °C(-1), was obtained in the same region. The low temperature dielectric anomaly is associated with the possible mixed Cu(+)/Cu(2+) valence in Cu3TeO6 ceramics, while the high temperature anomaly is attributed to point defect ordering, including VO, CuCu2+(+)', which might be formed during sintering. Therefore, Cu3TeO6 ceramics are of interest in view of not only the possible applications in BME-MLCCs, LTCC, and related technologies, but also for their possible compatibility with low cost abundant Cu electrodes.

Polar Nanoregions and Dielectric Properties of BaTiO3‐Based Y5V Multilayer Ceramic Capacitors

Commercial EIA‐Y5V base‐metal‐electrode multilayer ceramic capacitors (BME‐MLCCs) made of (CaO+ZrO2)‐doped BaTiO3 are analyzed for the microstructure and investigated for its relation to dielectric properties. The characteristic diffuse scattering (DS) intensities observed in BaTiO3 ceramics and the featureless “solid‐solution” grains in Y5V capacitor chips are originated from multiple Ti sites in the dynamic BaTiO3 structure. The pseudo‐cubic (PC)‐grains retaining the overall cubic (C‐) symmetry metastably at room temperature are embedded with polar nanoregions (PNRs) in the ferroelectric (FE) tetragonal (T‐), and rhombohedral (R‐) phases, as revealed by high‐resolution transmission electron microscopy (HRTEM). The presence of PNRs contributes effectively to large relative permittivity εr ≈ 13 200 at 25°C. The FE T‐domains grow from within PC‐grains at the expense of embedded PNRs after prolonged annealing by extending “oxidizing firing” at 950°C in pO2 = 10−7 atm. These domains contain less Zr with otherwise homogeneously distributed solutes in PNR‐dispersed PC‐grains. Although preserving the relaxors characteristics, εr is reduced to ~11 000 after 12 h, and then to ~9000 after 24 h annealing. The reduction in εr is attributed to the annealing‐induced FE T‐domains grown at the expense of PNRs in PC‐grains. The Vögel–Fulcher analysis indicates that Y5V ceramics are in the relaxor FE category, containing PNRs derived from polarization frustration.

Effect of Rare Earth Oxide Content on Nanograined Base Metal Electrode Multilayer Ceramic Capacitor Powder Prepared by Aqueous Chemical Coating Method

The aqueous chemical coating route is highly effective in preparing BaTiO3 nanoparticles uniformly coated with additives. Such nanoparticles can be used to produce nano-grained temperature stable BaTiO3 ceramics with core–shell structure, fulfilling the need of next-generation ultrathin layer base metal electrode (BME) multilayer ceramic capacitors (MLCCs). Rare earth oxides are an important class of additives owing to their ability to fulfill both donor and acceptor roles. In this paper, the effects of Y2O3 and Ho2O3 co-dopant content on dielectric and microstructural properties were investigated. By applying chemical coating, BaTiO3-based high performance temperature stabilized ceramics with the average grain size of about 130 nm, which met the requirement of next generation BME MLCCs, were obtained.

High Performance BaTiO3‐Based BME‐MLCC Nanopowder Prepared by Aqueous Chemical Coating Method

Dispersion plays an important role in aqueous chemical coating process for the preparation of BaTiO3‐based powder for base‐metal‐electrode multilayer ceramic capacitors (BME‐MLCCs) in our previous research. In this article, a powerful sand mill (SC‐milling) machine is utilized instead of traditional ball milling to produce BaTiO3 MLCC nanopowder, in which small ZrO2 beads help to achieve high centrifugal accelerations and avoid BaTiO3 agglomerates. As much as 1 kg BaTiO3 nanopowder has been effectively dispersed very well in one time, then a uniform coating of additives on BT nanoparticles has been achieved by aqueous chemical coating method. High performance X7R BaTiO3 nanoceramics with the average grain size of about 96 nm are obtained. The experimental result indicates that this technology can be feasible to the industry for manufacturing next generation BME‐MLCCs.

Preparation of BME MLCC Powders by Aqueous Chemical Coating Method

High and large capacitance base–metal–electrode multilayer ceramic capacitors (BME MLCCs) for future application require much thinner dielectric layers (<l μm) than ever before, which means that grain size uniformity of BME MLCC powder should be effectively controlled. In this paper, high‐performance nanosized BME MLCC powder was developed by a novel and convenient aqueous chemical coating method. Various kinds of dispersants were used to disperse BaTiO3 particles in aqueous solutions. Poly(acrylic acid–comaleic acid) was found to be the best for dispersing. BaTiO3 particles were well coated by adding the doping elements into the uniform BaTiO3 slurry in the form of inorganic solutions and organic solutions under an appropriate pH value. Thermogravimetric analysis, transmission electron microscopy, and energy‐dispersive spectroscopy were utilized in the study of calcining, microstructures, and element analysis. The dielectric constants of the ceramics at room temperature could reach 2100, with low dielectric loss <1.0% and high insulation resistivity ∼1012 Ω·cm. The average grain size is as low as about 130 nm.

Microstructure Evolution and Dielectric Properties of Ultrafine Grained BaTiO3-Based Ceramics by Two-Step Sintering

The base-metal electrode multilayer ceramic capacitors for future application require much thinner dielectric layers ( < 1 μm). Therefore, the grain size and uniformity of dielectric ceramics should be effectively controlled. In this paper, a two-step sintering (TSS) method has been utilized to prepare the ultrafine-grained X7R BaTiO 3 ceramics in reducing atmosphere with the average grain size below 200 nm. And the influence of TSS schedule on the microstructure (such as bulk density, grain size) and dielectric properties is discussed in detail. Furthermore, the development of core-shell structure and corresponding temperature coefficient of capacitance characteristics during the intermediate stage of TSS process has been systematically investigated.

Degradation behaviors and failure analysis of Ni–BaTiO 3 base-metal electrode multilayer ceramic capacitors under highly accelerated life test

The degradation in insulation resistance under highly accelerated test conditions was investigated in terms of micro-structural and micro-chemical changes in dielectric layer of multilayer ceramic capacitor. The ceramic capacitors were prepared by using BaTiO 3 powder with different size of 0.52 μm, 0.55 μm, and 0.58 μm. As the particle size of BaTiO 3 powder was increased, the capacitance and the dissipation factor were decreased. According to the result of highly accelerated test conducted at 150 °C, 75 V, and 20 h, failure in insulation resistance was increased with the particle size and the calculated FITs (failure in term) were 1.10 at 0.52 μm, 2.11 at 0.55 μm, and 6.69 at 0.58 μm, respectively. The failure was examined by X-ray photoelectron spectroscopy and transmission electron microscopy, which was attributed to the oxidation of Ni inner electrode that could create oxygen vacancies and increase electric conduction of the ceramic capacitors.

Preparation of micron-sized flake copper powder for base-metal-electrode multi-layer ceramic capacitor

The preparation of flake micron-sized copper powders with the chemical–mechanical method was investigated. Reaction of [Cu(NH 3) 4] 2+ complex with hydrazine hydrate at 85 °C produced monodispersed fine spherical copper powders, which were used as precursor to synthesize flake copper powders by the ball milling process. The flake copper powders having an excellent dispersibility and a uniform size of 9 ± 2 μm could be achieved. Thermogravimetry (TG), differential thermogravimetry (DTG) and differential thermal analysis (DTA) of the flake copper were investigated with thermal analyzer. The results showed that the oxidizing temperature increased with a decreasing specific area. The flake copper powder particles were employed as functional conductive materials in copper thick film paste for base-metal-electrode multi-layer ceramic capacitors (BME-MLCCs). Excellent connection between internal and terminal electrode and even distribution of glass in copper thick film can be observed by polarized light photograph. The dense thick films were also found by scanning electron microscopy (SEM) analysis, and the high densification of the fired films could be attributed to the “framework” effects.

Microstructures and Dielectric Characteristics of Ultrafine-Grained Barium Titanate-Based Ceramics for Base-Metal-Electrode Multilayer Ceramic Capacitors Applications

Ultrafine-grained ceramics based on barium titanate for base-metal-electrode multilayer ceramic capacitors (BME-MLCCs) applications have been prepared. X-ray diffraction analysis was used to identify the phase compositions of the ceramics. The microstructures were characterized by scanning electron microscopy and transmission electron microscopy. The effects of different dopant contents on the crystal structures, grain growth, microstructures, and dielectric characteristics of the ceramics were investigated. Desired core–shell structures have been observed and the relationships of composition, crystal structure, grain growth, and microstructure have been discussed. The present ceramics show an average grain size of 180 nm and homogeneous microstructures, as well as a high dielectric constant, a low degree of dielectric loss and good X7R temperature characteristics, which would be promising candidates for next-generation BME-MLCC applications.

Preparation of Fine Copper Powder With Chemical Reduction Method and Its Application in MLCC

In this paper, the preparation of fine copper powder with chemical reduction method was investigated. Polyhedron nonagglomerated monodispersed copper powders by the reaction of CuSO4ldr5H2O and ascorbic acid were synthesized at pH 6~7 and reaction temperature of 60degC~70degC. It was also found by X-ray diffraction (XRD) analysis that a mixture of copper and cuprous oxide could be obtained when [Cu(NH3)4]2+ was reduced by ascorbic acid. Reaction temperature and pH have great effects on efficiency and particle size of copper powders. Copper powders were applied as terminal electrode materials of base metal electrode-multilayer ceramic capacitor (BME-MLCC), and the microstructures, including cross section and interface, of copper thick film were discussed with scanning electron microscopy. The results indicated that copper thick film has a loose, porous cross section and a rough interface. The adhesion strength of copper electrode is high due to rough microstructure caused by interfacial reaction.

Termination of BME–MLCC Using Copper–Nickel Bimetallic Powder as Electrode Material

Microstructure of termination of a base metal electrode multilayer ceramic capacitor (BME-MLCC) using copper-nickel bimetallic powder as electrode material was investigated. Thick film paste containing nonagglomerated monodispersed copper-nickel bimetallic powder was applied in preparing the termination electrode of a BME-MLCC. Influence of an inorganic binder on the microstructure of the termination of BME-MLCC was studied. The distribution of metallic copper on the surface of glass bubbles in termination was investigated by energy dispersive X-ray. A scanning electron microscope and a polarized light microscope were applied to discuss the microstructure of thick film. The results show that suitable binder and firing temperature result in the excellent connection between internal and termination electrode, as well as one between termination electrode and green chip. The BME-MLCCs with a dense surface of end termination, high adhesion, and qualified electrical behavior were obtained. The rough interface from interfacial reaction between glass and chip gives high adhesion

Preparation of ultra fine nickel–copper bimetallic powder for BME-MLCC

The preparation of ultra fine nickel–copper bimetallic powder with two-stage chemical reduction method was investigated. Reductive sugar and hydrazine hydrate were employed as reducing agent in different reductive stage, respectively. Reaction of CuSO4·5H2O with reductive sugar at 70°C gives cuprous oxide and copper particles, then as-prepared mixture and nickelous hydroxide were reduced by hydrazine hydrate, and nickel–copper powder having excellent dispersibility was prepared. Influences of nickel added on composition and dispersibility of powder were studied. TG/DTG/DTA of nickel–copper powder, which is stable in room temperature, were discussed with thermal analyzer. Relation of nickel content to oxidation temperature was investigated. Ni–Cu bimetallic powder particles have a fully coated structure when nickel content is up to 30%. As-prepared nickel–copper powder was applied in base metal electrode-multilayer ceramic capacitor (BME-MLCC). The end termination has high adhesion force, fairly good densification, low resistivity, excellent solderibility behavior and resistance behavior to soldering.

Synthesis and Characterization of Ba(Zr0.15Ti0.85)O3 Nano Powders by Oxalate Precipitation Method

Barium zirconate titanate (BZT) is considered to be an important dielectric material for the fabrication of multilayer ceramic capacitors (MLCCs). The synthesis of nanocrystalline powders of high purity is the key to improving the performance of BZT-based ceramics. In this study, we developed Ba(Zr0.15Ti0.85)O3 nano powders with a perovskite structure and a homogeneous granularity through the oxalate precipitation method. The average particle size of the powders can be controlled from 30 to 100 nm at different calcining temperatures. The sintering property of the powders is superior to that of powders prepared by the conventional solid-state method, such that the more compact ceramics with a smaller grain size can be obtained at a sintering temperature of 1250 °C. The dielectric property of the ferroelectric-powder-based ceramics was so excellent for the development of dielectric materials for base-metal electrode multilayer ceramic capacitors (BME MLCCs) with a large capacitance.

An Investigation Demonstrating the Feasibility of Microwave Sintering of Base-Metal-Electrode Multilayer Capacitors

A microwave sintering technique has been developed for base-metal electrode (BME) multilayer ceramic capacitors (MLCCs). Commercial green chips of size 0603 MLC with nickel electrodes were sintered in a microwave field. With a specially designed susceptor/insulation package to optimize coupling and uniformity of heating, a number of sintering experiments were conducted in the temperature range of 1200 to 1250∘C in a multimode microwave cavity operating at 2.45 GHz under a partially reducing atmosphere. Microstructure of the microwave processed MLCCs was investigated with both SEM and TEM techniques. The dielectric properties of the microwave sintered MLCCs were measured and compared with those sintered using conventional process at 1320∘C and lower pO2’s ≈ 10− 9 atms. The results demonstrate that nickel electrodes remain metallic after microwave sintering even though the pO2’s were relatively high and would thermodynamically favor NiO. The microwave sintered samples showed a dense, fine and uniform microstructure. The properties of the microwave-sintered samples were comparable to the conventionally sintered samples. The microwave processing was found to have enhanced sintering kinetics of the BME MLCCs, lowering sintering temperature by about 100∘C and also the processing time by about 90%.