Magnetic and structural properties of ion beam sputtered Fe-Zr-Nb-B-Cu thin films

Magnetic and structural properties of Fe-Zr-Nb-B-Cu thin films, prepared by ion beam sputtering on silicon substrates by using a target made up of amorphous ribbons of nominal composition Fe₈₄Zr_3.5Nb_3.5B₈Cu₁, are reported. As-deposited thin film samples exhibit an in-plane uniaxial anisotropy, which can be ascribed to the preparation technique and the coupling of quenched-in internal stresses. Structural measurements indicate no significant variation of the grain size with thickness and with the annealing temperature. Increase in surface irregularities with annealing temperature and oxidation results in aggregates that would act as pinning centers, affecting the magnetic properties leading to magnetic hardening of the specimens. The role of the magnetic anisotropy is thoroughly discussed with the help of magnetic and ferromagnetic resonance measurements.     

Electrical and optical investigations on Pb1 − 3x/2LaxZr0.2Ti0.8O3 thin films obtained by radiofrequency assisted pulsed laser deposition

Thin films of ferroelectric relaxor Pb_1 − 3x/2La_xZr_0.2Ti_0.8O₃, x = 0.22 have been integrated in an oxidic heterostructure for electro-optical investigations. The quadratic electro-optic behavior and optical properties have been studied by means of variable angle spectroscopic ellipsometry method in reflection mode. Birefringence values up to δΔ = 0.17° have been obtained for quadratic compositions at λ = 540 nm and 65° angle of incidence. Structural, chemical and morphologic properties of Pb_1-3x/2La_xZr_0.2Ti_0.8O₃ (x = 0.22) thin films have been investigated by x-ray diffraction and atomic force microscopy techniques. The dielectric and ferroelectric behavior has been investigated using dielectric spectroscopy and a ferroelectric test system.     

Optical and electric properties of strontium bismuth tantalate thin films

High quality SrBi₂Ta₂O₉ ferroelectric thin films were fabricated on platinized silicon using pulsed laser deposition. The optical properties of the thin films were studied by spectroscopic ellipsometry from the ultraviolet to the infrared region. Optical constants, n ∼ 0.25 in the infrared region and n ∼ 2.18 in the visible spectral region, were determined through multilayer analyses on their respective pseudodielectric functions. The band-gap energy is estimated to be 4.14 eV. It was found that the leakage current mechanism of the film was from bulk limited Poole-Frenkle emission to interface-controlled Schottky emission with applied field increasing, and that the breakdown field of the film had a negative linear variation with the logarithm of the electrode area.     

Application of the X-ray combined analysis to the study of lead titanate based ferroelectric thin films

Lead titanate based ferroelectric thin films are well known for their excellent piezo and pyroelectric properties. In order to obtain a complete characterisation of the structural, micro structural and texture parameters of these films, a recently developed combined analysis of the X-ray diffraction data is carried out. The advantages of this approach reside in the fact that we obtain simultaneously quantitative and more reliable information of these parameters than with more conventional methods. Results obtained for ferroelectric thin films are analysed and compared with those obtained with other methods of analysis. The conclusions show that the texture of the films obtained with the combined method is able to separate the contributions of close texture components, like 〈100〉 and 〈001〉, or to study components with low contribution to the texture of the film.     

Gold embedding influence on the magnetic behaviour of iron in Fe/Si3N4 multilayers prepared by sputtering

Au/Fe/Au/Si₃N₄ multilayers have been prepared in order to improve ferromagnetism in Fe/Si₃N₄ system. A huge enhancement of magnetization is observed when the iron layers are embedded into gold ones, showing saturation magnetization values near the bulk ones. In this paper, a careful microstructural study has been carried out to explain the observed magnetic behaviour of this ferromagnetic system prepared in the transparent silicon nitride matrix.     

Magnetization and crystal structure of RF-sputtered nanocrystalline CuFe2O4 thin films

Cu-ferrite films were deposited on glass substrates by RF-magnetron sputtering in pure Ar and mixture of (Ar + O₂) environment. The XRD studies of the as-deposited films indicate nanocrystalline cubic spinel structure. The observed increase in the intensity of (400) line at the expense of (220) line with increase in O₂ content is ascribed to the change in distribution of Cu and Fe-ions among tetrahedral A-site and octahedral B-sites. The highest saturation magnetization (M_S) of 264 emu/cm³ (in-plane) and 188 emu/cm³ (out of-plane) was obtained for the as-deposited films in pure Ar. The high deposition rate in reducing atmosphere leads to the formation of Cu⁺ ions which prefer occupation of the A-site in the spinel structure displacing Fe³⁺ cations to occupy the B-sites giving rise to the change in cation distribution among A and B-sites and consequently leading to high value of M_S. The decrease in M_S value with increase in oxygen content is ascribed to the decrease in film growth rate and Cu⁺ concentration which allow the cations to take up their preferable sites. The observed change in the film properties with environment is due to the presence of multivalent copper and iron ions with differing site preferences.     

Thin film Ba0.25Sr0.75TiO3 voltage tunable capacitors on fused silica substrates for applications in microwave microelectronics

Thin film Au/Pt/Ba_0.25Sr_0.75TiO₃/Pt/Au/Ti capacitor structures were fabricated on fused silica substrates using pulsed laser deposition of ferroelectric films. Low-field dielectric measurements were performed as a function of frequency in the range 1-25 GHz at different external dc fields up to 360 kV/cm. Resonant microwave power absorption observed at frequencies less than 10 GHz under dc field is due to electrostriction and field induced piezoelectric effects. The effects are simulated using an electroacoustic model of the multilayer capacitor structure. A circuit model is applied to investigate the influence of series resistance and inductance of interconnect/lead strips on capacitor performance. Analysis shows that the measured loss tangent of the capacitor is mainly due to series resistance and frequency dispersion of capacitance is caused by series inductance. The de-embedded value of the loss tangent is 0.005 at 10 GHz. The measured loss tangent is less than 0.02 and tunability is up to 40% in the whole frequency range. These parameters indicate high potential of Ba_0.25Sr_0.75TiO₃ capacitors for applications in voltage controlled devices of microwave microelectronics.     

Multiferroic Bi0.7Dy0.3FeO3 thin films directly integrated on Si for integrated circuit compatible devices

Magnetoelectric multiferroic Bi_0.7Dy_0.3FeO₃ (BDFO) thin films deposited on p-type Si (100) substrate using pulsed laser deposition technique demonstrated a saturated ferroelectric and ferromagnetic hysteresis loop at room temperature. More interestingly, the observed change in electric polarization with applied magnetic field in these films indicated the presence of room temperature magnetoelectric coupling behavior. Using high-frequency capacitance-voltage measurements, the fixed oxide charge density, interface trap density and dielectric constant were estimated on Au/BDFO/Si capacitors. These results suggest the integrated circuit compatible application potential of BDFO films in the field of micro-electro-mechanical systems and non-volatile memories.     

Modeling of ferroelectric domains in thin films and superlattices

We have developed the set of numerical (finite-element) and analytical tools that are based on the self-consistent solution of the electrostatic equations coupled with material Ginzburg–Landau equations with an objective to model the profile of domain textures in the entire temperature region. We calculated the evolution of principal parameters of domain texture: modulation vector, distribution of polarization, renormalization of critical temperature etc. In contrast to the Kittel approximation we conclude that the profile of polarization across domains in nanometric ferroelectric thin films is highly nonuniform.