Alexandre Zirpoli Simões

Retention characteristics in Bi3.25La0.75Ti3O12 thin films prepared by the polymeric precursor method

Ferroelectric Bi3.25La0.75Ti3O12 (BLT) thin films were deposited on Pt∕Ti∕SiO2∕Si substrates by the polymeric precursor method. The films present c-axis preferred orientation after annealing at 700°C for 2h in conventional furnace. All the capacitors showed good polarization fatigue characteristics at least up to 1×1010 bipolar pulse cycles and excellent retention properties up to 1×104s. We found that the polarization loss is insignificant with five write∕read voltages at a waiting time of 10u2009000 S. Independently of the applied electric field the retained switchable polarization approached a nearly steady-state value after a retention time of 10s.

Evidence of magnetoelectric coupling on calcium doped bismuth ferrite thin films grown by chemical solution deposition

Magnetoelectric coupling was observed at room temperature in calcium modified bismuth ferrite BiFeO3 (BFO) thin films deposited on Pt/TiO2/SiO2/Si (100) substrates by the chemical solution deposition. Undoped and Ca-doped BiFeO3 films were coherently grown at a temperature of 500u2009°C for 2 h. The highest doped BFO film has a tetragonal structure with P4mm space group, while BFO has a rhombohedral structure with space group R3c, which can be treated as a special triclinic structure. Room temperature magnetic coercive field indicates that the undoped film is magnetically soft with maximum magnetoelectric coefficient in the longitudinal direction was about 12u2009V/cm. Adding Ca2+ ions to BFO in high concentration decreases the remnant polarization and stabilizes the charged domain walls which interact with oxygen vacancies reducing coercive field.

Dielectric properties of Ca(Zr0.05Ti0.95)O-3 thin films prepared by chemical solution deposition

Ca(Zr0.05Ti0.95)O3 (CZT) thin films were grown on Pt(1 1 1)/Ti/SiO2/Si(1 0 0) substrates by the soft chemical method. The films were deposited from spin-coating technique and annealed at 928 K for 4 h under oxygen atmosphere. CZT films present orthorhombic structure with a crack free and granular microstructure. Atomic force microscopy and field-emission scanning electron microscopy showed that CZT present grains with about 47 nm and thickness about 450 nm. Dielectric constant and dielectric loss of the films was approximately 210 at 100 kHz and 0.032 at 1 MHz. The Au/CZT/Pt capacitor shows a hysteresis loop with remnant polarization of 2:5mC=cm 2 , and coercive field of 18 kV/cm, at an applied voltage of 6 V. The leakage current density was about 4:6 � 10 � 8 A=cm 2 at 3 V. Dielectric constant–voltage curve is located at zero bias field suggesting the absence of internal electric fields.

Influence of oxygen atmosphere on LiNbO/sub 3/ thin films prepared by Pechini process

Thin films of lithium niobate were deposited on the Pt/Ti/SiO/sub 2/ (111) substrates by the polymeric precursor method (Pechini process). Annealing in static air and oxygen atmosphere was performed at 500/spl deg/C for 3 hours. The films obtained were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The dielectric constant, dissipation factor and resistance were measured in frequency region from 10 Hz to 10 MHz. Electrical characterizations of the films pointed to ferroelectricity via hysteresis loop. The influence of oxygen atmosphere on crystallization and properties of LiNbO/sub 3/ thin films is discussed.