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|Title: ||Research on a high performance multilayer ZnO varistor and its fabrication with water based tape casting|
|Other Titles: ||Gao xing neng duo ceng yang hua xin ya min dian zu qi ji qi shui ji liu yan gong yi de yan jiu|
|Authors: ||Wang, Lanyi (王蘭義)|
|Department: ||Department of Physics and Materials Science|
|Degree: ||Doctor of Philosophy|
|Issue Date: ||2010|
|Publisher: ||City University of Hong Kong|
Zinc oxide -- Electric properties.
|Notes: ||CityU Call Number: TK7871.99.V3 W36 2010|
x, 120 leaves : ill. ; 30 cm.
Thesis (Ph.D.)--City University of Hong Kong, 2010.
Includes bibliographical references (leaves 102-117)
|Abstract: ||With the rapid development of small size, low working voltage and high reliability
of electronic products, the demands for multilayer chip varistors (MLV) which are
designed for surge protection and electrostatic discharge (ESD) protection in circuits are
increasing rapidly and the requirements for the MLV’s properties become stricter. In
order to meet the demands of "green" production methods in an environmental
protection modern world, it is important to study environmentally friendly water-based
(aqueous) tape casting and the replacement of solvent-based (non-aqueous) tape casting
with aqueous tape casting. In this study, using chemically synthesized doped zinc oxide
(CS powder) as the starting powder, high performance multilayer ZnO varistors were
prepared with water-based tape casting.
For the first time, high performance multilayer ZnO varistors were successfully
fabricated using both water-based tape casting and a chemically synthesized compound
powder. The MLVs made by water-based tape casting exhibit better electrical properties
than those made using the solvent-based tape casting. Water-based tape casting reduces
MLV’s production costs and reaches the goal of environmentally friendly green
production, resulting in great social and economic benefits.
The electrical properties of MLVs made by CS powder were compared with those
made by metal oxide powder (MO powder). The effect of sintering temperature on the
electrical properties of MLVs was studied. With the help of microstructure analysis and
electrical property measurement of the MLVs, the MLVs made by CS powder display
superior electrical properties as a result of their uniform microstructure throughout. The
optimal sintering temperature range for our MLVs is 950℃~1050℃.
Water-based tape casting process was studied. The influence of a water-soluble
binder and dispersant on the tape casting slurry was analyzed. The aqueous slurry with
shear thinning rheological behavior which was desirable for tape casting was
successfully developed by the optimization study of slurry composition. The aqueous
slurry could be stabilised electrosterically by the dispersant. The MLV green sheets
were successfully made with water-based tape casting.
Water-based tape casting process was compared with solvent-based tape casting.
The microstructure and electrical properties of the MLVs made by water-based tape
casting were also compared with those made by solvent-based tape casting. The
aqueous green tape is denser than the non-aqueous one. The multilayer ZnO varistors
prepared by aqueous tape casting display better electrical properties than those prepared
using non-aqueous tape casting. We believe that these superior electrical properties are
a direct result of the well dispersed and stable slurry with a shear thinning rheological
behavior, which makes dopants distribute more uniformly throughout the MLVs. We
conclude that water-based tape casting can replace solvent-based tape casting for the
manufacture of high performance multilayer ZnO varistors considering MLV
production costs and protection of the environment.|
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b3947501|
|Appears in Collections:||AP - Doctor of Philosophy |
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