Redesigning Multilayer Ceramic Capacitors by Preservation of Electrode Conductivity and Localized Doping

Both Li₂CO₃-coated nickel particles and fast firing technique were utilized in the manufacturing of MLCCs. They preserved the conductivity of Ni electrodes and provided the possibility of sintering the devices in oxidizing atmospheres. By using our method, the partial pressure of oxygen increased from 10^–10 atm in conventional methods to 10^–4 atm. The oxidizing atmosphere reduced the oxygen vacancy concentration as illustrated by the color change of the samples, and the results of EELS (electron energy loss spectroscopy). A systematic test with variable parameters, Li₂CO₃ coating, the sintering schedule, and the oxygen flow during sintering were executed, and the dissipation factor and the capacitance of the MLCCs were documented. Three type of MLCCs were studied: Conventional (fired with the conventional technique), Uncoated (fast fired with uncoated Ni particles), and Coated (fast fired with the coated Ni particles). The maximum oxygen activity during sintering (i.e., pO₂ = 1.2 × 10^–4 atm) was obtained for coated samples, and due to the minimum <i>V</i>_O^•• concentration, their dissipation factor decreased up to 60% relative to the Conventional ones. In addition, the impedance spectroscopy, together with the map of Li ion distribution, suggested that Li ions accumulated around the electrode–dielectric interface and amplified the activation energy at these interfaces. This eventually caused the coated MLCCs to show higher capacitance than their uncoated counterparts. As a conclusion, it is shown that the manufacturing process described in this paper can provide a better MLCC with higher capacitance, and lower dissipation factor and leakage current

Hydrothermal-Assisted Cold Sintering Process: A New Guidance for Low-Temperature Ceramic Sintering

Sintering is a thermal treatment process that is generally applied to achieve dense bulk solids from particulate materials below the melting temperature. Conventional sintering of polycrystalline ceramics is prevalently performed at quite high temperatures, normally up to 1000 to 1200 °C for most ceramic materials, typically 50% to 75% of the melting temperatures. Here we present a new sintering route to achieve dense ceramics at extraordinarily low temperatures. This method is basically modified from the cold sintering process (CSP) we developed very recently by specifically incorporating the hydrothermal precursor solutions into the particles. BaTiO₃ nano polycrystalline ceramics are exemplified for demonstration due to their technological importance and normally high processing temperature under conventional sintering routes. The presented technique could also be extended to a much broader range of material systems than previously demonstrated via a hydrothermal synthesis using water or volatile solutions. Such a methodology is of significant importance, because it provides a chemical roadmap for cost-effective inorganic processing that can enable broad practical applications

Protocol for Ultralow-Temperature Ceramic Sintering: An Integration of Nanotechnology and the Cold Sintering Process

The sintering process is an essential step in taking particulate materials into dense ceramic materials. Although a number of sintering techniques have emerged over the past few years, the sintering process is still performed at high temperatures. Here we establish a protocol to achieve dense ceramic solids at extremely low temperatures (<200 °C) <i>via</i> integrating the particle nanotechnology into the recently developed cold sintering process (CSP). The sintering path has been appropriately tailored <i>via</i> effectively utilizing the large surface-to-volume ratio of nanoparticles. BaTiO₃ ceramics have been used for the illustration, given its importance in extensive electronic device applications, as well as its scientific interest, being a model material for many of the ferroelectric materials. Together with detailed experimental studies, the trends are also analyzed with a fundamental thermodynamic consideration. Such an impactful technique could have widespread application prospects in a wide variety of materials and would also provide a clear roadmap to guide future studies on ultralow-temperature ceramic sintering, ceramic materials related integration, and sustainable manufacturing practices

Cold Sintering Na₂Mo₂O₇ Ceramic with Poly(ether imide) (PEI) Polymer to Realize High-Performance Composites and Integrated Multilayer Circuits

The cold-sintering process is utilized to fabricate ceramic–polymer (Na₂Mo₂O₇-poly­(ether imide), PEI) composites and integrated multilayer circuits. The Na₂Mo₂O₇-PEI bulk composites cold-sintered at 120 °C show high densities (>90% theoretical). The permittivity at microwave frequencies decreases with increasing PEI content, following the classical logarithmic mixing law, and <i>Qf</i> values show no deterioration with the addition of PEI. Furthermore, the characteristic dielectric breakdown strength of the ceramic–polymer composite obtained from a Weibull plot increases dramatically from 55.1 to 107.5 MV/m with 10–20 vol % PEI additions. In the case of high PEI content where there is more segregation of the polymer within the ceramic matrix, there is a gradual decrease in the dielectric breakdown strength. Na₂Mo₂O₇-PEI-Ag bulk ring resonators can be obtained by post screen printing, and the mixing laws are used to calculate the permittivity of the ring resonators. As a prototype of integrated multilayer circuits, Na₂Mo₂O₇-PEI-Ag multilayer ring resonators with good microwave dielectric properties can be successfully densified by cold-sintered cofired ceramic-composite technology at 120 °C without delamination or warping, demonstrating the feasibility of cold sintering in the ceramic–polymer composite integrated multilayer circuits