4 research outputs found
Redesigning Multilayer Ceramic Capacitors by Preservation of Electrode Conductivity and Localized Doping
Both Li<sub>2</sub>CO<sub>3</sub>-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<sup>–10</sup> atm in conventional
methods to 10<sup>–4</sup> 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, Li<sub>2</sub>CO<sub>3</sub> 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., pO<sub>2</sub> = 1.2 × 10<sup>–4</sup> atm) was obtained for
coated samples, and due to the minimum <i>V</i><sub>O</sub><sup>••</sup> 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. BaTiO<sub>3</sub> 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. BaTiO<sub>3</sub> 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 Na<sub>2</sub>Mo<sub>2</sub>O<sub>7</sub> 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
(Na<sub>2</sub>Mo<sub>2</sub>O<sub>7</sub>-polyÂ(ether imide), PEI)
composites and integrated multilayer circuits. The Na<sub>2</sub>Mo<sub>2</sub>O<sub>7</sub>-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.
Na<sub>2</sub>Mo<sub>2</sub>O<sub>7</sub>-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, Na<sub>2</sub>Mo<sub>2</sub>O<sub>7</sub>-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