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Silicon thick films deposited by thermal plasma spray are of interest as inexpensive electronic materials for conformal meso-scale electronics applications. In addition they also serve as a model system for the investigation of electrical properties of coatings with layered anisotropy. In this study impedance spectroscopy was used to measure the complex resistivity of free-standing 64 μm-thick polycrystalline silicon films deposited by thermal plasma spraying in an atmospheric ambient. Impedance spectroscopy measurements were taken in the through-thickness (across-splat) and edge-to-edge (in-splat) directions and revealed a resistivity difference of approximately 7.5±0.23 between the two directions. The complex resistivity results are explained on the basis of a brick-layer type model, associated with the layered splat microstructure obtained from cross-sectional transmission electron microscope imaging of the films. In addition a circuit-based model made up of parallel, resistor-capacitor elements in series, and Cole–Cole and Davidson–Cole impedance functions were used to fit the impedance data to extract material parameters and contributions from the grains and splat boundaries. Furthermore, thermal processing and phosphorus doping is shown to lead to higher and lower resistivity, respectively, in the films. [ABSTRACT FROM AUTHOR]

MnZn ferrite/Permalloy composites have potential in high frequency magnetic applications and can be made into thick-film devices by air plasma spray. The as-sprayed composites have lower saturation magnetization than the starting powder. After annealing below 600 °C, the magnetic properties and electrical resistivity improve significantly. The changes in magnetic and electrical properties were correlated to structural changes and studied by x-ray-diffraction analysis, vibrating-sample magnetometer measurements, and microstructural analysis. [ABSTRACT FROM AUTHOR]

A thermal spray process has been developed for the deposition of ferrites and highly anisotropic composites of magnetic alloys and ferrites. The critical volume fraction for conduction is at 5 to 10 volumetric percent (vol.%) metal in these thick films as compared to 33 vol.% in isotropic mixtures of spheroidal particles. The low percolation threshold and highly anisotropic transport properties are associated with the unusual microstructure of thermal spray coatings which are composed of lamellar splats stacked one upon the other. By varying the volume fraction of metal in these composites it is possible to drastically change the electrical, magnetic and mechanical properties of these coatings. In the sintered mixture the conductivity increases rapidly when the metal volume fraction reaches about 33 vol.% whereas in the thermal spray coating the conductivity increase occurs at metal fractions of about 2–6 vol.%. The magnetoresistance was measured in the parallel, perpendicular and transverse geometry in each case in fields up to 2 kilogauss. There is a clear and sharp transition from giant magnetoresistance (GMR) (negative \mit\DeltaR/R) to anisotropic magnetoresistance (AMR) at the percolation threshold in both cases. These results show that the GMR comes from the scattering of weakly exchange coupled spins in the polycrystalline ferrite which can be aligned in high fields decreasing the resistance. The AMR is in the conductive metallic phase and its field dependence is mainly controlled by the shape anisotropy of the disk shaped splats as expected. [ABSTRACT FROM PUBLISHER]

Plasma-Sprayed MnZn ferrite thick films are built up by splats, which consist of columnar grains with diameter ∼200 nm and height ∼1 μm. The existence of the conductive wustite FeO in the as-sprayed films greatly reduces the dc resistivity. However, a useful structure can be developed in these ferrite films with fine equal-axis ferrite grains insulated by the high-resistivity hematite Fe2 O3 because of the polygonization of the columnar grains and the oxidation of the wustite during an annealing process. The dc resistivity increases significantly after the annealing process, an effect ascribed to the growth of hematite Fe2 O3 on the basis of impedance analysis. The magnetic properties of these ferrite films improve concurrently. The high-frequency response of the annealed plasma-sprayed MnZn ferrites shows a permeability of ∼ 700 stabilized to above 10 MHz. The maximum Q factor at about 10 MHz increases from 5 to 20 as a result of the increase of the dc resistivity. [ABSTRACT FROM AUTHOR]

Ni80 Fe20 and Ni80 Co20 alloys anisotropic magneto- resistive sensor films were deposited by plasma spray. The resistivity (ρ) of the films is determined to be 40-70, μΩcm in the as-sprayed state. The oxygen impurity dissolved in the metal acts as a strong scattering center and results in higher resistivity. The ρ of sensor film improves significantly with thermal annealing up to 500 °C and it remains constant for further increase in temperature. The dissolved oxygen precipitates out as oxide phase during heat treatment and that reduces the scattering. The ρ values are 19 and 22 μΩ·cm for permalloy and NiCo alloy turns, respectively, which are close to bulk values. The anisotropic magnetoresistance (AMR) effect is found to be increased by a factor of 2 in both the permalloy and the NiCo sensors. The Δ R/R values are increased from 2.0% to 4.0% and 2.6% to 5.8%, respectively, for permalloy and NiCo sensors. [ABSTRACT FROM AUTHOR]