Electrical characterization of HfO2 films obtained by UV assisted injection MOCVD

HfO₂ films were deposited at low temperature (400 °C) by UV assisted injection metal-organic chemical vapor deposition (UVI-MOCVD). A three-step process was used for this study, consisting of (A) Pre-deposition anneal for nitridation; (B) Deposition step; (C) Post-deposition annealing in oxygen. Special attention was paid to the effect of UV exposure during these steps. Films were characterized by physical, optical and electrical techniques. Thickness was determined by different methods (X-ray Reflectrometry (XRR), spectroscopic ellipsometry and transmission electron microscopy) and a good agreement was found for all samples. The HfO₂ permittivity, equivalent oxide thickness (E_OT), flat-band voltage (V_fb) and total charge (Q_t) were extracted from the CV response at high frequency taking into account the HfO₂ and SiO₂ thicknesses obtained by XRR. The calculated permittivity values were in the range 7–13, i.e. lower than theoretical values for the monoclinic phase. Explanations are suggested in the context of the other characterizations. JE_eff characteristics were constructed taking into account the E_OT values (E_eff = V/E_OT). Effective breakdown fields range between 8.7 and 16.9 MV/cm. No dependence of E_eff with UV exposure was found.     

Application of pulsed liquid-injection MOCVD to the growth of ultrathin epitaxial oxides for magnetic heterostructures

We illustrate the capabilities of pulsed-liquid injection metal–organic chemical vapor deposition in the nano-engineering of complex oxides with results obtained on (La_0.7Sr_0.3MnO₃/SrTiO₃)₁₅ (LSMO/STO) superlattices. Superlattices with ultrathin films of a few monolayers have been successfully prepared, as shown by synchrotron radiation diffraction experiments. Laue oscillations were observed between the satellite peaks, indicating a smooth upper surface. Sets of superlattices with varying LSMO or STO thickness were synthesized on different substrates (LaAlO₃, SrTiO₃, MgO). By varying the relative thickness of each compound and changing the substrate, the strain in the stackings could be changed.     

Etude par spectrometrie mössbauer de ZnMn3 et de la transition antiferro-ferromagnetique de GaMn3 C dopes au fer 57

Mössbauer measurements have been performed on ⁵⁷Fe-doped GaMn₃C and ZnMn₃C. A strong variation of hyperfine field parameters at the antiferro-ferromagnetic transition of GaMn₃C is related to the variation of the transferred fields and to the electronic anisotropy. The direction of spins is [111] for ferro and antiferromagnetic GaMn₃C and [001] for ferromagnetic ZnMn₃C.     

Magnetoresistivity of CeSi1.86

We present measurements of the magnetoresistance up to 20 teslas from 2 K to room temperature on a CeSi_1.86 single crystal. This alloy behaves as an anisotropic Kondo lattice where strong ferromagnetic correlations are dominant. We observe a clear relationship between the magnetotransport and the magnetic susceptibility of this compound.     

Characterization of crystalline MOCVD SrTiO3 films on SiO2/Si(100)

SrTiO₃ thin films (STO), were deposited on Si(100) covered by 2 nm of SiO₂, at different temperatures from 450 °C to 850 °C using liquid injection MOCVD, the bimetallic precursor being Sr₂Ti₂(OiPr)₈(tmhd)₄. The STO films were analysed by XRD, FTIR, SIMS and TEM. An amorphous layer was observed between STO and SiO₂/Si. The nature and thickness of the interlayer were determined, as well as the most favourable conditions for a good quality crystalline STO film, and a reduced interlayer.     

Investigations of the interface stability in HfO2–metal electrodes

As the sharpness of the metal–oxide interface is of major importance to develop efficient structures, we have studied the thermal stability of interfaces in a series of thin film samples where the metallic component was either Pt, Al, Pd, Ni, Nb or Ti deposited on a thin HfO₂ film. Thermodynamic considerations have been carried out to determine the possible products of metal–oxide reaction at a temperature of 500 °C. The evolution of the as-deposited thin film structures as a function of annealing temperature has been analysed by combining various techniques and specifically using X-ray reflectometry. This particular technique allows one to detect very thin embedded interfaces, distinguish small density variations and determine accurately the thickness, the normal roughness and the density of each layer. In addition, reflectometry results have been correlated with atomic force microscopy and transmission electron microscopy observations of selected samples. Our results indicate that platinum, palladium and nickel are stable up to 500 °C on hafnium oxide. Annealed aluminium, an interfacial layer forms, whereas niobium and titanium present a diffuse interface.     

Angular Dependence of the Activation Energy in YBCO/PBCO Multilayers

The activation energy in several (YBCO) _m /(PBCO) _n superconducting multilayers was deduced from resistivity measurements in magnetic fields up to 16 T, as a function of the angle between the magnetic field and the ab planes. The activation energy U ₀ (B,) scales with a reduced field B _red =B(sin ² +cos ² / ² ) ^1/2 , with an angle dependent anisotropy parameter . A crossover from U ₀ log B _red , at low B _red , to U ₀ (B _red ) at high B _red , is also observed. The implications of these results on vortex dynamics and on the coupling between the superconducting layers will be discussed.     

Epitaxial and polycrystalline BaFe12O19 thin films grown by chemical vapour deposition

Epitaxial and polycrystalline barium hexaferrite BaFe₁₂O₁₉ thin films were prepared by metalorganic chemical vapour deposition (MOCVD). Films were grown by a liquid MOCVD technique which aim is to control precisely the precursor vapour pressures. Two kinds of substrates were used: sapphire (001) and silicon thermally oxidized. On Si/SiO₂ films are polycrystalline and the magnetization is isotropic. On Al₂O₃ (001), structural studies reveal the films to be predominantly single phase, well crystallized without annealing procedure and with the c-axis perpendicular to the film plane; epitaxial relationships between the film and the substrate were determined. The magnetic parameters, deduced from vibrating sample magnetometer measurements, show a high dependence of the magnetization with the orientation of the field with respect to the surface of the film.