Song Zhitang

PINNING EFFECT OF LEAD LANTHANUM TITANATE THIN FILMS DEPOSITED ON DIFFERENT SUBSTRATES

Pinning effect of lead lanthanum titanate (PLT) ferroelectric thin films with excess PbO of 20 mol% has been studied for deposition on different substrates. Silicon, sapphire and quartz were used as substrates on which Pt/Ti or LaNiO3 thin films were deposited as bottom electrodes. Electron probe analysis results showed that there was still a certain amount of excess Pb in PLT films after annealing at 550 ?C for 1 h, and the amount of it was dependent on the substrate used. The distribution of excess Pb in the films was investigated by Auger electron spectroscopy depth profile. It was shown that the substrates and the bottom electrodes had significant effects on the content and distribution of excess Pb in PLT films. The excess Pb and its accumulation at the interface between the film and bottom electrode may act as pinning centers and have a pinning effect on domains, which can be observed by abnormal P-E hysteresis loops and abnormal C-V curves. The excess Pb content in the films and the accumulation of Pb at the interface were high in PLT films deposited on Pt/Ti/Si, and considerable pinning effect was observed. As LaNiO3 would absorb most part of the excess Pb in PLT films, the content of excess Pb in the films deposited on LaNiO3/Si was very low and the pinning effect was hardly observed.

Effect of bottom electrodes on structures and electric properties of PLT ferroelectric thin films

Lead lanthanum titanate (PLT) thin film with 10 at.% of La and 15 at.% of excess Pb were deposited on Pt/Ti electrodes with different thickness of Ti layer by metallo-organic decomposition (MOD) process. X-ray diffraction (XRD) and scanning electron microscopy (SEM) have been applied to investigate the micro structure and morphology of the PLT thin films. The grain sizes of PLT thin films are between 0.9/spl sim/1.5 /spl mu/m. The thickness of the Ti layer has a dominant effect on the dielectric and ferroelectric properties of the PLT films. The dielectric constants of the thin films annealed at 550/spl deg/C for 1 hr are between 510/spl sim/580, the dielectric loss tangent is less than 2%. The remanent polarization is between 6.3/spl sim/7.6 /spl mu/m/cm/sup 2/ and the coercive field is about 68.9/spl sim/83.7 kV/cm at 1 kHz.