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The effect of substrate temperature on the crystallographic texture and surface morphology of Ba0.5Sr0.5TiO3 deposited by rf magnetron sputtering on (111) oriented Pt (150 nm)/Ti (10 nm)/SiO2 (300 nm)/Si (100) substrates is reported. The onset of crystallinity is observed above 500 °C, beyond which all films are oriented along the (111) plane up to a temperature of 800 °C. Over this temperature range, the misfit strain and root mean square roughness (rmsroughness) peak at 600 °C, decreasing beyond this peak value. The tunability of the dielectric constant at 100 kHz is highest (60% for a field strength of 300 kV/cm) at the lowest values of rmsroughness and misfit strain and decreases as these values increase. It is also shown that the morphology of the Pt underlayers is strongly affected by the processing conditions. This in turn influences the tunable behavior of the BST films as much as the substrate temperature during growth and the consequent microstructural variations. [ABSTRACT FROM AUTHOR]

Thin Films of (Ba0.5, Sr0.5) TiO3 have been deposited on quartz substrates by RF magnetron sputtering. The percentage of oxygen in sputtering atmosphere was varied between 25 to 100%. The as-deposited films were x-ray amorphous and crystallized on post deposition annealing at 900°C for 1 min. Microstructure as determined by Atomic Force Microscope (AFM) showed a strong dependence on oxygen mixing percentage (OMP) in the sputtering gas. The microwave dielectric properties of these thin films are determined up to 20 GHz using a calibration comparison technique with patterned coplanar waveguide (CPW) transmission lines deposited on the surface of the film. Two CPW test structures of 100-micron gap and 200 micron width are deposited simultaneously one on the test film and the other on the bare substrate by directly sputtering silver through a shadow mask. The scattering parameters of these two CPW transmission lines were measured using a Vector Network Analyzer and a probe station mounted with the GSG probes of 250-micron pitch. The dielectric constant of the BST films crystallized on quartz vary between 150-220 and the loss tangent is found to be varying from 0.018 to 0.021 depending upon the processing conditions. The relaxation currents present in the films due to the structural defects associated with the processing conditions may be responsible for the observed dielectric loss as well as the frequency dependent permittivity. [ABSTRACT FROM AUTHOR]

Large picosecond nonlinearities in Ba0.5Sr0.5TiO3 thin films, grown at different temperatures in situ on (100) MgO substrates using rf magnetron sputtering technique, were studied using the Z-scan technique. The nonlinear absorption mechanism, studied near 800 nm using ∼2 and 25 ps pulses, switched from reverse saturable absorption type in the films deposited at temperature<600 °C to three-photon absorption (3PA) in the films deposited at temperature>600 °C. The magnitude of the 3PA coefficient was estimated to be ∼10-21 cm3/W2. Two-photon absorption (2PA) was the dominant mechanism recorded with ∼6 ns pulses. The observed behavior is correlated with morphological and crystallographic texture of the films. The linear refractive index and optical band gap of the films have also been calculated and these show a strong dependence on the substrate temperature. [ABSTRACT FROM AUTHOR]