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Ferrites have been used for various high frequency applications as bulk
materials. These applications, however, are limited to large dimension devices. In
this thesis, thin film ferrites were deposited from a low temperature solution-based
deposition process that is suitable for micro-scale high frequency applications. The
low temperature nature of this deposition technique makes it an excellent back end
process. In this work, a high rate deposition process for zinc ferrite thin films was
established. A deposition rate of 0.2 μm/min was determined by the surface
profiler. The deposited films have a plate-like morphology with fibrous texture.
Zinc was uniformly incorporated into the ferrite film confirmed by the local
chemical analysis by Energy Dispersive X-ray spectroscopy. The deposited films
are polycrystalline with a typical cubic ferrite structure. The overall composition of the films was determined by Auger electron spectroscopy as Zn[subscript x]Fe[subscript y]O[subscript 4], x ranges
from 0.25 to 0.55, and y ranges from 2.2 to 2.7.
A model consisting of resistors, capacitors and inductors was constructed
and used for the analysis of impedance spectroscopy. The dielectric properties of
zinc ferrite thin films were obtained by fitting the data to the model. The results
show that the dielectric constants are around 15 regardless of Zn/Fe ratio. This
value is consistent with most of the reported values for bulk ferrite materials. The
resistivity changes from 0.6 x 10[superscript 6] ohm.meter to 1.3 x 10[superscript 6] ohm.meter when Zn/Fe
ratio varies from 0.06 to 0.14.
A grounded coplanar waveguide structure was developed for microwave
characterization of the thin film material to obtain the complex relative
permittivity and the complex relative permeability. The method is based on
conformal mapping and determination of filling factors for the coplanar waveguide
configuration and is applicable to a wide range of dielectric as well as magnetic
materials. The proposed approach was validated by determining the scattering
parameters of a number of test structures using the 3D full-wave electromagnetic
simulation. In all examples, the extracted parameters from the proposed technique
resulted in values that are within 2% error. |
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