Chengtao Yang

The Study of Ferroelectric La-Doped PbTiO3 Thin Films Prepared by RF Magnetron Sputtering

Ferroelectric La-modified lead titanate (PLT) thin film were grown on Pt/Ti/SiO2/Si by sputtering the Pb0.93La0.07TiO3 targets containing an amounts of excess 8% PbO. The effects of sputtering and annealing conditions on the crystalline structures and the surface morphologies of the PLT thin films have been investigated. The remanent polarization (Pr) and the coercive field of the PLT film through rapid thermal annealing (RTA) was 10.2 μC/cm2 and 45 kV/cm respectively. The maximum pyroelectric coefficient reached 19 nC/cm2.K at 20°C.

Investigation of the crystal structure and electrical properties of La3+-doped SrBi2Ta2O9 ceramics

The layered-perovskite ferroelectric ceramics of La3+-doped SrBi2Ta2O2 (SBT), with the chemical formula of SrBi(2 - x)LaxTa2O9 (SBLT), have been prepared by the conventional mixed-oxide method. The effect of substitution of La3+ for Bi3+ in the crystal structure and electrical properties of SBT ceramics was explored with the aid of X-ray diffraction, ε(T) curve and ferroelectric hysteresis loop measurements. The electrical properties such as dielectric constant (ε) and remanent polarization (Pr) showed a dependence on the crystal structure, and both reached maxima of 243 and 25 μC cm−2, respectively, with 6 at % La3+ substitution, accompanying the greatest structure change. Theoretical considerations were presented to suggest that the atomic displacements and the crystal deformation implied by the crystal structure change are responsible for the improvement of electrical properties. On the other hand, degradation of fatigue resistance was observed in SBLT ceramics, which is believed to be caused by the chemical environment change of the perovskite layers arising from La3+ substitution on Bi3+ sites.

Structure and electrical properties of AlN films prepared on PZT films by the DC reactive magnetron sputtering

Aluminum nitride (AlN) films were deposited by DC reactive magnetron sputtering on the (111)-orientated Lead zirconate titanate (PZT) films. The heterostructures was characterized by x-ray diffraction and atomic force microscopy. The results showed that the AlN films reasonably textured in (002) orientation and revealed good interface quality with root-mean-square values of about 7.9 nm. The scanning electron microscopy images showed that the AlN films grown on PZT layer revealed an obvious and quite uniform columnar structure, and there was a clear interface between AlN and PZT films. MIF (Metal-Insulator-Ferroelectric) structures were fabricated and electrically evaluated by C-V (capacitance-voltage) and I-V (current-voltage) measurements at high frequency (1 MHz). The results obtained from C-V curves indicated that the MIF capacitor was consistent with the traditional Al-SiO2-Si capacitor. The current-voltage curves of AlN/PZT heterostructure showed a good insulating characteristic.

Ferroelectric Property Dependence on the Texture of SrBi2Ta2O9 Thin Films

ABSTRACT SrBi2Ta2O9 (SBT) thin films with different textures were fabricated by pulsed laser deposition under different deposition conditions. The influence of the deposition condition on the texture of the SBT films can be explained by the interactions between the plume and the substrate. With the aid of x-ray diffractometry, piezoreponse scanning probe microscopy, and ferroelectric-property measurements, a correlation between the film texture, as well as the domain structure, and the ferroelectric properties was established. It was found that the ferroelectrics properties, such as the polarization and the coercive field, had a strong dependence on the texture of the SBT films. Whats more, 90° domains were observed in the (115)-textured SBT films. These results are of interest for the fabrication of ferroelectric memories with fatigue free SBT thin films.

Fabrication of Ferroelectric Thin Films With Alternate Deposition of Multilayers

Pb(Zr0.52Ti0.48)O3 (PZT) and SrBi2Ta2O9 (SBT) films have been fabricated onto Pt/Ti/SiO2/Si substrates with a new chemical solution deposition (CSD) technique, in which PbZrO3(PZ)/PbTiO3(PT) and SrTa2O6(ST)/Bi2O3(B) precursors were spin-coated and heated individually. Polycrystalline PZT and SBT films were formed through the reactions between the multilayers at relative low temperatures, without post-annealing. With the aid of AFM, an island-column hybrid growth mode and a nucleus growth mode were suggested for the PZT and SBT film growths, respectively. However, it was found that the deposition orders affected substantially the microstructure of SBT films. This study suggests that the processing temperatures for the ferroelectric film fabrications can be reduced with alternate deposition of multilayers.