Deposition and dielectric properties of CaCu3Ti4O12 thin films on Pt/Ti/SiO2/Si substrates using pulsed-laser deposition

CaCu₃Ti₄O₁₂ (CCTO) thin films were successfully deposited on Pt/Ti/SiO₂/Si(1 0 0) substrates using pulsed-laser deposition technique. The crystalline structure and the surface morphology of the CCTO thin films were greatly affected by the substrate temperature and oxygen pressure. Thin films with a (2 2 0) preferential orientation were obtained at the substrate temperature above 700 °C and oxygen pressure above 13.3 Pa. The 480-nm thin films deposited under 720 °C and 26.6 Pa have a fairly high dielectric constant of near 2000 at 10 kHz and room temperature. The values of the dielectric constant and loss and their temperature-dependence under different frequency are comparable with those obtained in the epitaxial CCTO films grown on oxide substrates.     

Large area Ba1 − xSrxTiO3 thin films for microwave applications deposited by pulsed laser ablation

Large area Ba_1 − xSr_xTiO₃ (BST) thin films with x = 0.4 or x = 0.5 were deposited on 75 mm diameter Si wafers in a pulsed laser deposition (PLD) chamber enabling full-wafer device fabrication using standard lithography. The deposition conditions were re-optimized for large PLD chambers to obtain uniform film thickness, grain size, crystal structure, orientation, and dielectric properties of BST films. X-ray diffraction and microstructural analyses on the BST films grown on Pt/Au/Ti electrodes deposited on SiO₂/Si wafers revealed films with (110) preferred orientation with a grain size < 100 nm. An area map of the thickness and crystal orientation of a BST film deposited on SiO₂/Si wafer also showed (110) preferred orientation with a film thickness variation < 6%. Large area BST films were found to have a high dielectric tunability of 76% at an electric field of 400 kV/cm and dielectric loss tangent below 0.03 at microwave frequencies up to 20 GHz and a commutation quality factor of ~ 4200.     

Measurement of epitaxial misorientations and related effects in thin films of YBa2Cu3O7-δ grown on nominally (001)MgO substrates by pulsed laser deposition

Heteroepitaxial YBa₂Cu₃O_7-δ thin films have been deposited onto nominal (001)MgO substrates by pulsed laser deposition. For some of these films, Rutherford backscattering spectrometry analysis revealed anomalous variations in the backscattered yield at the substrate level during [001] YBa₂Cu₃O_7-δ axial channelling. A novel angular-dependent ion channelling technique has been developed to investigate these effects. It has been shown that the anomalies arise from an epitaxial misorientation between the lattices of the substrate and deposit. Strong correlations were found between the magnitudes of the misorientations, the densities of spiral features on the deposit surface and the critical current densities exhibited by the deposits. It is proposed that the misorientation arises due to vicinal offcut of the substrate surface, which leads to a lower density of threading dislocations and hence less flux pinning.     

CCT diagrams of tricalcium silicate: Part II: Influence of the Al2O3 content

This work studies the effect of the aluminum oxide content on the kinetics of thermal decomposition of tricalcium silicate, or C₃S, the main component of Portland cement. The experimental results allowed the construction of novel continuous cooling transformation (CCT) diagrams, showing the effect of the Al content on the C₃S stability, under continuous cooling.