Microstructural Control of BaTiO3 Thick Film Fabricated by Utilizing Slide-Off Transfer Printing

Effects of fabrication conditions on the microstructure of thick BaTiO₃ films have been investigated by employing slide-off transfer printing technique. Formation of dense films with good adhesive properties was difficult when screen-printing was employed in preparing the slide-off transfer sheets (BaTiO₃ green films), irrespective of the kind of solvents used for the slurries. On the other hand, relatively dense films could be fabricated from the slide-off transfer sheet prepared by spin-coating of the slurries consisting of fine BaTiO₃ powder (particle size: ca. 0.1 m), printing oil, and 2-propanol, though cracks formed obviously. Co-addition of large BaTiO₃ particles (particle size: ca. 0.5 m) was very effective for reducing the formation of cracks, and homogenous and dense films could be fabricated by controlling the additive amount of the large particles.     

Synthesis of fine Ca-doped BaTiO3 powders by solid-state reaction method—Part I: Mechanical activation of starting materials

Fine (Ba_0.98Ca_0.02)_1.002TiO₃ powders for high capacitance multilayer ceramic capacitors (MLCCs) application were synthesized by solid state reaction method. The effects of mechanochemical activation using high energy milling and the starting materials properties on the reaction temperature and on the final powder properties were investigated. Previous heavy milling of BaCO₃ and the adoption of fine, anatase-rich TiO₂ phase were effective in decreasing the reaction temperature and in increasing the tetragonality (=c/a). BaCaTiO₃ powders with a tetragonality of 1.0097, an average particle size of 213 ± 43 nm and a specific surface area of 6.30 m²/g were acquired after heat treatment at 985 °C for 2 h. MLCCs utilizing this developed powder showed superior dielectric and temperature characteristics to those with conventional, Ca-free BaTiO₃ powder.     

Microstructural evolution of BaTiO3/ultrahigh-molecular-weight poly(ethylene) (UHMWPE) cast body: influence of free organic additive in a nonaqueous medium

The consolidation behavior of ultrahigh-molecular-weight polyethylene (UHMWPE) in BaTiO₃/ UHMWPE suspension was investigated by the control of the non-adsorbed organic additives. The suspensions were characterized by adsorption isotherm, rheology, sedimentation behavior, and microstructural observation. The co-dispersion stability of the BaTiO₃/UHMWPE particulates was correlated with the uniformity of the green microstructure. These studies can be helpful for the successful fabrication of ultra thin dielectric layer of MLCC using newly improved extrusion method.     

PREPARATION OF BaTiO3 FILMS FOR MLCCS BY DIRECT VAPOR DEPOSITION

ABSTRACT

BaTiO₃ films were deposited by the direct vapor deposition (DVD) technique to prepare thin dielectric layers for multilayer ceramic chip capacitors (MLCCs). The BaTiO₃ films were successfully prepared by co-evaporation of the BaTiO₃ ceramic and Ti metal source. The films deposited at room temperature and 600°C were amorphous and crystalline phases, respectively. The intensity of (110) and (111) peaks increased as Ba/Ti ratios were close to stoichiometric composition. BaTiO₃ films deposited with e-beam power of 700 W showed the deposition rate of 33 nm/min. The dielectric constant and dissipation factor of BaTiO₃ films measured at 1 kHz were 150～ 180 and 2～ 5%, respectively. The capacitance decreased with increasing the temperature and varied only between 787pF and 752pF in the temperature range 15～ 125°C.     

Dielectric Degradation and Microstructures of Heterogeneous Interfaces in Cofired Multilayer Ceramic Capacitors

The compatibility of electrodes and dielectrics in cofired MLCCs with both Ni and Ag/Pd electrodes was characterized by transmission electron microscopy (TEM) using tripod polished samples. Tripod polishing procedures can reduce entire devices to a thickness of less than 1 m. After low angle ion milling for a short time, many regions across several dielectric and electrode layers are electron transparent, which makes it possible to characterize the cofired interfacial microstructures. When analyzed by convergent beam electron diffraction (CBED) and energy dispersive X-ray spectrometry (EDS), NiO lamellae and P-rich intermediate layers were found in highly accelerated life tested (HALT) MLCCs with Ni electrodes. CBED confirmed that the P-rich layers had a Ba₄Ti₁₃O₃₀ (B₄T₁₃) structures. Oxidized Ni layers containing Mn were also found in the HALT samples. It is believed that Mn ions were reduced by the Ni electrodes, as P-rich and Mn-rich segregated layers were observed in the virginal non-life tested MLCCs. Grains with stacking faults, containing dopants such as Mn, Si, and Mg, had the BaTi₄O₉ (BT₄) structure. No silver diffusion was found in either the BaTiO₃ based perovskite lattices or the flux phases in air-fired X7R type MLCCs.     

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%.     

Moldless micropatterning of BaTiO<Subscript>3</Subscript> nanoparticles via electrophoretic deposition: A simple and feasible method

In this work, a simple, reproducible, and inexpensive fabrication route for moldless micropatterning of a colloidal assembly on a conducting substrate surface is actualized by means of electrophoretic deposition (EPD) technique. A synergetic combination of photolithography and EPD is employed for fabricating micropatterns of barium titanate (BaTiO₃) nanoparticles on an indium-tin-oxide (ITO) coated glass slide or a Pt/ITO substrate. At first, high quality resist molds with various micropatterns are fabricated on ITO glass slide by photolithography technique, which is used for providing a controlled local electric field during the EPD process. Then, BaTiO₃ nanoparticles suspension is prepared in KCl aqueous solution and is demonstrated the BaTiO₃ nanoparticles are negative charged in the suspension. At last, EPD of various BaTiO₃ micropatterns is accomplished successfully on the anodic ITO glass slide or Pt/ITO substrate using the micropatterned ITO glass slide as the cathode, indicating that it is a simple and potential route for micropatterning of colloidal assembly on a non-modified conducting substrate by virtue of EPD process.     

Fabrication and characterization of micropatterned barium titanate ceramics

A new patterning method combining electron beam (EB) lithography and electrophoretic deposition (EPD) for fabricating micropatterned barium titanate (BaTiO₃) thin films was investigated. At first, resist molds with high resolution were prepared using EB lithography on Pt/Ti/Si substrates. Then BaTiO₃ nanoparticles were deposited on the substrates by EPD from a transparent suspension of monodispersed BaTiO₃ nanoparticles; a mixed solvent of 2-methoxyethonal and acetylacetone with a 9:1 volumetric ratio was used as a dispersion medium. The nanoparticles with an average size of about 10 nm were synthesized at a low temperature of 90 °C by a high concentration sol-gel process. EPD layers superfluously deposited on the resist molds were mechanically polished away, followed by chemically removing the molds in a resist remover to leave micropatterns of BaTiO₃ nanoparticles on the substrates, which were finally sintered to yield micropatterned BaTiO₃ ceramic thin films. The method developed may be used to fabricate other micropatterned electroceramic thin films.     

Surface modification of BaTiO3 with yttrium, and dissolution and adsorption/precipitation behaviors of BaTiO3

An attempt was made to retard the dissolution of Ba ions from BaTiO₃ by coating Y compounds on the BaTiO₃ particle surface. A hysteresis in the electrokinetic behavior of as-received BaTiO₃ occurred during sequential acid and base titrations, while there was no hysteresis in the Y-coated BaTiO₃. In the bare BaTiO₃, dissolved Ba ions are adsorbed and/or precipitated onto the surface during sequent base titration to yield a more positively charged Ba-rich phase on top of the Ba-depleted lattice. On the contrary, the dynamic mobility of Y-coated BaTiO₃ during base titration closely followed the corresponding acid titration, providing that the starting surface of Y-coated BaTiO₃ and the surface after acid-base treatment was the same. It is suggested that Y compounds on the BaTiO₃ particles retard the dissolution of Ba ions from BaTiO₃.     

Crack formation in MLCCs depending on position with and without post-heat treatment

The crack formation behavior and mechanical properties, hardness (H), modulus (E), and fracture toughness (K _IC), at each plane of BaTiO₃ based multilayer ceramic capacitors (MLCCs) have been investigated and estimated using a nanoindentation technique, including effects of the post-heat treatment and the external electrode on the crack formation and mechanical properties. The crack length in each plane, length (x plane) and width (y plane) planes, has been measured for MLCCs with and without the post-heat treatment, as a function of the distance from the internal electrode. H and E values are 11.5–12.0 GPa and 175–190 GPa, respectively, independent of the plane and the post-heat treatment. The crack length in the x plane is smaller than that in the y plane, which is gradually increased as the indentation position is far away from the internal electrode. The external electrode affects the crack formation in regions near to the internal electrode, showing small crack length till 20 μm from the internal electrode. K _IC values in the x plane are larger than those in the y plane. The external electrode affects only the K _IC values in the x plane within the error range, without effect of the post-heat treatment.     

Solubility of silver in non-stoichiometric barium titanate

Barium titanate (BaTiO₃) can form solid solution with many oxides. The present study demonstrates that BaTiO₃ can also dissolve a small amount of Ag during co-firing, and its solubility depends strongly on the Ba/Ti ratio. A solid-state reaction was employed in the present study to prepare the BaTiO₃ powders with Ba/Ti ratio varied from 0.991 to 1.010. Fine Ag particles were then mixed intimately with the non-stoichiometric BaTiO₃ powders. The solubility of Ag in the non-stoichiometric BaTiO₃ at 1,350 and 1,390 °C was then determined by using a modified electron-probe micro-analysis (EPMA) technique. The solubility of Ag in Ti-rich BaTiO₃ is nearly double that in Ba-rich BaTiO₃. The diffusion distance of Ag in the non-stoichiometric BaTiO₃ is longer than 5 μm.     

Effect of BaTiO3 size on dielectric property of BaTiO3/PVDF composites

The BaTiO₃/polyvinylidene fluoride (BaTiO₃/PVDF) polymer-based composites with different size and concentration of BaTiO₃ particles were fabricated via a simple physical mixing and subsequently hot-press processing. Effect of the filler size and frequency on the dielectric properties of the BaTiO₃/PVDF binary composites was discussed. The result shows that the BaTiO₃ size has an effect on the morphology of the BaTiO₃/PVDF composites. The composites with 0.2 and 0.3 μm BaTiO₃ exhibit high dielectric permittivity than those with 0.4 and 0.5 μm BaTiO₃. The composite with 0.4 μm BaTiO₃ has a minimum dielectric permittivity except one with 0.1 μm BaTiO₃. Dielectric loss of the BaTiO₃/PVDF binary composites changes slightly with the BaTiO₃ sizes. The ternary BaTiO₃/PVDF composites with 0.1 and 0.7 μm BaTiO₃ in coexistence exhibit good dielectric properties. As a result, the BaTiO₃/PVDF ternary composites in this study may have a promising application as dielectric material in embedded capacitor.     

Lead-free (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)<Subscript>0.95</Subscript>(LiSb)<Subscript>0.05</Subscript>Nb<Subscript>0.95</Subscript>O<Subscript>3</Subscript>-BaTiO<Subscript>3</Subscript> piezoceramics

Lead-free (1-x)(K_0.5Na_0.5)_0.95(LiSb)_0.05Nb_0.95O₃-xBaTiO₃ (abbreviated as (1-x)KNNLS-xBT) piezoceramics were synthesized by conventional solid state sintering and the effect of BaTiO₃ on the microstructure, dielectric and piezoelectric properties was investigated. It was found that both orthorhombic-tetragonal (T _O-T) and tetragonal-cubic (T _C) phase transition temperatures decreased obviously with increasing BaTiO₃ content. Although proper amount of BaTiO₃ facilitated the sintering of (1-x)KNNLS-xBT ceramics, the addition of BaTiO₃ affected the relaxor behavior slightly and it was not beneficial to improve piezoelectric strain coefficient d ₃₃, remnant polarization P _r and piezoelectric coupling constant k _p.     

Mechanism of capacitance aging under DC-bias field in X7R-MLCCs

Capacitance aging under DC electric fields has been studied on multilayer ceramic capacitors (MLCCs) with the X7R characteristics. The capacitance change with time was divided into two stages, the first- and the second-stage. The first-stage was due to the nonlinear permittivity of dielectrics and it should not be involved in the aging phenomenon. The second-stage depended on the MnO content, grain size and firing condition of dielectrics. From the behavior of the second-stage, it was concluded that the capacitance aging was caused by the 90-degree domain switching in BaTiO₃ in the core. The first-stage was due to the nonlinear permittivity but the domain switching was also included in the first-stage if the domain walls moved by the first application of DC field. The change in the aging behavior with the intensity of DC field could be explained by separating capacitance change into the nonlinear permittivity and the domain switching according to the mechanism proposed in this study.     

Carbon nanotube-ceramic composites

The effective utilization of CNTs in composite application depends strongly on the ability to disperse CNTs homogeneously throughout the matrix and the interfacial combination is necessary for improving the CNT-based composite properties. In our work, we used surfactant and acid treatment to modify the CNTs surface and then incorporated the functionalized CNTs into various ceramic matrices including oxide and nitride ceramics. The fabrication of ceramic nanoparticle-immobilized CNTs not only improves the homogeneous distribution of CNTs in the ceramic matrices, but also makes the combination between two phases more tight. Mechanical property measurements clealy reveal obvious enhancement confirming the fabrication of true CNT-based composite materials with improved toughness properties. The addition of 0.1 wt% CNTs in the alumina increased the fracture toughness by about 1.6 times from 3.7 to 4.9 MPa.m^1/2. For 1 wt% CNTs/BaTiO₃composite, the toughness value (1.65 MPa.m^1/2) is about 2.4 times than that of pure BaTiO₃(0.68 MPa.m^1/2). For 5 wt% CNTs/TiN composite, the fracture toughness is 3.81 MPa.m^1/2, which is about 1.6 times than that of pure TiN ceramic whose toughness is 2.45 MPa . m^1/2.     

The variation of Curie temperature and dielectric relaxor behaviour in the nominal (1-x)BaTiO3-xBiAlO3 system

BiAlO₃ is a perovskite ferroelectric with a high Curie temperature above 520°C. However, it is difficult to prepare pure perovskite phase by the conventional method. In this experiment, BaTiO₃ has been selected as host to incorporate BiAlO₃, and the nominal binary system of (1-x)BaTiO₃-xBiAlO₃ has been investigated with regard to its Curie temperature (T _c) and dielectric relax behaviors. It was found that the pure perovskite phase can be retained below x?=?0.08. However, the value of T _c in the system doesn’t follow the normal Vegard’s law, on the contrary, shows the decreasing trend with the increase of x. According to the compared experiments about Bi³⁺ and Al³⁺ doping in BaTiO₃, it can be safely concluded that the combined substitution of Bi³⁺ and Al³⁺ played the dominant role to decrease the T _c and increase the relaxor behavior in (1-x)BaTiO₃-xBiAlO₃ system.     

Microstructural Analysis of X7R-Type BaTiO<Subscript>3</Subscript> Multilayer Ceramic Capacitors (MLCCs)

The microstructures of typical commercial X7R MLCCs were characterized by transmission electron microscopy (TEM), using tripod polished specimens and ion milled samples. Core-shell structures were clearly observed in the TEM specimens, and glass phases located at the grain boundaries and triple points were frequently observed. Their chemical composition was analyzed using energy dispersive X-ray spectrometry (EDS), which showed bismuth ions diffused into the shell regions, while the cores were pure BaTiO₃. X-ray diffraction (XRD) suggested that the predominant phase in the microstructure had pseudocubic global symmetry, while ferroelectric domains were observed in TEM bright field (BF) images. The internal electrodes in the devices were an alloy of Ag/Pd, and these regions were found to have twinned crystal structures. The stress states in the interfaces between the electrodes and the dielectric layers were revealed, and no silver migration in the flux at the electrode-dielectric interfaces was observed.     

Investigation of ferroelectric domains and structural twins in barium titanate crystal

Abstract

The Ferroelectric domain patterns and the {111} twin boundaries are frequently observed in the BaTiO₃ ceramics. The ferroelectric domain structures in BaTiO₃ single crystal were investigated by a conventional and a synchrotron white beam X-ray topographies. The domain structure of {111} twinned crystal sample was also observed under a polarizing microscope and under a TEM. The relation between the {111} twin and the ferroelectric domain structure was verified by insitu observation of the behaviors of 90° domains during the phase transitions. It is observed that the 90° ferroelectric domain boundaries around the {111} twin boundary which was produced during the crystal growth obey the symmetry relation of the {111} twinning and that they meet each other coherently at the same position of the {111} twin boundary.     

Effect of Cr additions on the microstructural stability of Ni electrodes in ultra-thin BaTiO3 multilayer capacitors

Microstructural control in thin-layer multilayer ceramic capacitors (MLCC) is one of the present day challenges to maintain an increase in capacitive volumetric efficiency. This present paper opens a series of investigations aimed to engineer the stability of ultra-thin Ni electrodes in BaTiO₃-based multilayer capacitors using refractory metal additions to Ni. Here, pure Ni and Ni–1 wt.% Cr alloy powders are used to produce 0805-type BME MLCCs with 300 active layers and with dielectric and electrode layer thickness around 1 μm. To investigate the continuity of Ni electrodes, both MLCC chips with pure and doped electrodes were sintered at different temperatures for 5 h. It is found that the continuity of Ni electrodes is improved most likely due to the effect of Cr on the low-melting point (Ni,Ba,Ti) interfacial alloy layer formation. The interfacial alloy layer is not observed when Cr is segregated at Ni-BaTiO₃ interface in the Cr-doped samples, while it is found in all undoped samples. The interfacial alloy layer is believed to increase mass-transfer along the Ni-BaTiO₃ interfaces facilitating an acceleration of Ni electrodes discontinuities.     

Modeling of the core-shell microstructure of temperature-stable BaTiO3 based dielectrics for multilayer ceramic capacitors

A simplified model was proposed for the core-shell microstructure, which existed in the temperature-stable BaTiO₃ (BT) based dielectrics for multilayer ceramic capacitors (MLCCs) and was regarded as the reason resulting in the temperature-stable characteristics. In this model the capacitance of a core-shell grain can be regarded as the parallel combination of the capacitance of the grain core and the grain shell. To verify the validity of the model, core material, shell material and core-shell material were prepared. Based on our previous work, BT with a grain size of 400 nm was chosen as the core material; X7R material milled for 1 hour was chosen as the core-shell material; doped BT milled for 36 h was chosen as the shell material. The calculated results showed good agreement with the measured experimental results of the core-shell material, which proved the validity of the model.