Vijaya Puri

Refractive index and adhesion of Al2O3 thin films obtained from different processes — a comparative study

Abstract Al 2 O 3 thin films ranging from 50 to 200 nm in thickness are deposited by four different methods viz, electron beam evaporation of Al 2 O 3 with and without chopping, and the oxidation of aluminium films by hot water and by steam. The prepared films are also subjected to heat at 120°C for 3 h and moisture for 3 h. The pre ambient and post ambient refractive index and adhesion are compared for the four types of films. The chopped electron beam evaporated Al 2 O 3 films give the highest refractive index and adhesion. The adhesion of steam oxidised aluminium films compare well with electron beam deposited Al 2 O 3 films. The post ambient refractive index changes are thickness dependent especially for both the types of oxidised aluminium films. The post ambient changes do not seem to be only porosity dependent but some composite oxide formation seems to be taking place.

A study on sintering and microstructure development of fritless silver thick film conductors

Thick film materials have proved to possess economic processing and functional advantages over other technologies in high-volume production of miniaturized circuits. The development of a low-cost fritless silver paste with different binder composition is described in the present work. The effect of composition and firing temperature (700–900 °C) on the microstructure is also reported. The sheet resistivity and surface morphology of all the indigenously formulated Ag thick film pastes are compared with the imported (ESL) paste. The results suggest that the thick films can be fired at 700 °C instead of the conventional 900 °C firing temperature.

Structural, dielectric and magnetic properties of nickel substituted cobalt ferrite nanoparticles: Effect of nickel concentration

Nickel substituted cobalt ferrite nanoparticles with composition Co1−xNixFe2O4 (0.0 ≤ x ≤ 1.0) was synthesized using simple, low temperature auto combustion method. The X-ray diffraction patterns reveal the formation of cubic phase spinel structure. The crystallite size varies from 30-44 nm with the nickel content. Porous and agglomerated morphology of the bulk sample was displayed in the scanning electron microscopy. Micro Raman spectroscopy reveals continuous shift of Eg and Eg(2) stokes line up to 0.8 Ni substitution. The dispersion behavior of the dielectric constant with frequency and the semicircle nature of the impedance spectra show the cobalt nickel ferrite to have high resistance. The ferromagnetic nature is observed in all the samples, however, the maximum saturation magnetization was achieved by the 0.4 Ni substituted cobalt ferrite, which is up to the 92.87 emu/gm at 30K.

Thin film, thick film microstrip band pass filter: a comparison and effect of bulk overlay

Abstract This paper reports the comparison of two fabrication techniques (viz. thin and thick film) for microstrip broadband filter in the X-band. The effect of bulk Al2O3 overlay (in pellet form and at different positions) on the characteristics of the broadband filter is also reported in this paper. The characteristics vary with the overlay position and thin film circuits seem to be more affected than thick film circuits.

Comparison of adhesion and intrinsic stress of chopped and non-chopped ZnS thin films

Abstract The adhesion and intrinsic stress of chopped and non-chopped ZnS thin films in the thickness range 50 to 200 nm and the changes occurring due to exposure to moisture, heat (120 °C) and air (30 days) are reported in this paper. The preambient adhesion is higher and the intrinsic stress substantially lower for chopped ZnS films. The post-ambient changes in adhesion and intrinsic stress are less for the chopped films. Chopping seems to increase preferential orientation and to assist in the grain growth, so that structural inhomogeneities are reduced. Reduction of voids and defects also occur as a result of chopping thereby improving the mechanical properties.

Adhesion Enhancement of Thin Film Deposits by Chopping

The chopping technique has been successfully used to enhance the adhesion of MgF2, ZnS and copper films. Chopping does not appreciably alter the adhesion of aluminium and chromium films. Chopping seems to increase the surface mobility of adatoms and prevent growth of large crystallites whereby producing more defect-free thin films because of higher relaxation leading to higher adhesion. The adhesion of chopped MgF2 and ZnS films compare well with those deposited on heated substrate and after glow discharge cleaning. The enhanced adhesion of copper films is being explained in terms of enhanced oxygen affinity at interface similar to that observed for aluminium and chromium. Chopping technique might provide a simple and cost effective process of depositing good adherent thin film coatings.

Structural and mechanical properties of Sr+2-doped bismuth manganite thick films

Bismuth strontium manganites Bi1 − xSrxMnO3 (0.20 ≤ x ≤ 0.50) belonging to the orthorhombic structural family were prepared in furnace using a solid-state reaction technique. Thick films of Bi(1 − x)SrxMnO3 were prepared by simple screen printing route. X-ray diffraction data suggest that the synthesized materials have an orthorhombic structure. For synthesized materials, texture coefficient (TC), dislocation density (ρD), density of crystallites per unit area (ψ), and mechanical properties are reported along with the influence of x on the structure and mechanical properties of BiMnO3 thick films.

MICROWAVE ABSORPTION, CONDUCTIVITY AND COMPLEX PEMITTIVITY OF FRITLESS Ni(1-x)CuxMn2O4 (0â¤xâ¤1) CERAMIC THICK FILM:EFFECT OF COPPER

The effect of copper on the microwave absorption, conductivity and complex permittivity of fritless Ni(1−x)CuxMn2O4 (x = 0, 0.4, 0.8, 1) thick film on alumina have been investigated in the 8–18GHz frequency range. The structural changes have been identified by scanning electron microscope (SEM), FTIR and RAMAN scattering spectroscopy. The microwave conductivity and permittivity increase as copper content increases. The fritless Ni(1−x)CuxMn2O4 (0 ≤ x ≤ 1) thick film with x = 0.4 shows best absorption properties, though all the other compositions also show good absorption in a large frequency range. The microwave conductivity increases from 1S/cm to 951 S/cm due to copper and the dielectric constant (έ) increases from 7 to 19.5.

Dielectric spectroscopy and microwave conductivity of bismuth strontium manganites at high frequencies

Bismuth strontium manganites (BSM) with variation in strontium content have been synthesized by simple solid state reaction method. X-ray diffraction data show that the samples have orthorhombic structure with crystallite size ∼40 to 60 nm. SEM studies reveal morphology of micro-rods and micro-flakes. The dielectric constant (ɛ′) and the dielectric loss (tan δ) decreases with the strontium content and the applied frequency which has been attributed to Maxwell-Wagner polarization. The microwave conductivity of samples decreases from 8.9 S/cm to 2.29 S/cm at 8.2 GHz as strontium increases. The penetration depth has also been reported at microwave frequencies from 8–18 GHz.

Effect of Ca on microwave properties of strontium manganite synthesized by microwave processing

Nanostructured Sr1−xCaxMnO3 was prepared by oxalic precursor method and sintered using microwave process. The pervoskite structure was confirmed by x-ray diffraction. The complex permittivity and permeability with calcium concentration were measured by VSWR in the frequency range 8–12 GHz. We present the frequency dependence of microwave absorbing properties of Sr1−xCaxMnO3 (0 ≤ x ≤ 0.4) powders at room temperature which is correlated to the value of its complex permittivity and permeability. The composition dependent microwave absorption was observed and it increased with Ca concentration from 47% to 68% at 9.7 GHz. The excellent microwave absorption properties were attributed to a better electromagnetic impedance match and a higher electric resistivity.