Bertrand Vilquin

Orientation control of textured PZT thin films sputtered on silicon substrate with TiOx seeding

Abstract In situ deposition of Pb(Zr 0.25 Ti 0.75 )O 3 thin films by RF magnetron sputtering has been performed at 500°C on Pt/Ti/SiO 2 /Si substrates without any postannealing treatment. The growth of PZT is ensured, provided that a thin TiO x layer is sputtered prior to PZT. Moreover, we find that sputtering Ti in a 100% argon atmosphere leads to highly (100) oriented films, while adding oxygen during sputtering of Ti leads to purely (111) oriented films. Electrical measurements performed on these films show remanent polarization P r , coercive field E c , and dielectric constant consistent with their Zr/Ti ratio.

Molecular beam epitaxy of SrTiO3 on Si (001): Early stages of the growth and strain relaxation

The molecular beam epitaxy of SrTiO3 (STO) layers on Si (001) is studied, focusing on the early stages of the growth and on the strain relaxation process. Evidence is given that even for optimized growth conditions, STO grows initially amorphous on silicon and recrystallizes, leading to the formation of an atomically abrupt heterointerface with silicon. Just after recrystallization, STO is partially strained. Further increase in its thickness leads to the onset of a progressive plastic relaxation mechanism. STO recovers its bulk lattice parameter for thicknesses of the order of 30 ML.

Asymmetrical leakage currents as a possible origin of the polarization offsets observed in compositionally graded ferroelectric films

Offsets of hysteresis loops along the polarization axis have been observed on a step graded Pb(Zr,Ti)O3 (PZT) thin film using a Sawyer–Tower (ST) circuit. However, the same effect may be artificially reproduced by adding adequate resistors and diodes in parallel with a nongraded PZT thin film. The hypothesis that the offsets were mainly due to the asymmetrical charging up of the standard capacitor used in the ST circuit, allows us to establish that the graded ferroelectric sample behaves as a kind of rectifying device. It is concluded that the presence of asymmetrical leakage currents in compositionally graded devices may allow the elucidation of the origin of the offsets often observed in these structures. Correlatively, it is demonstrated that such offsets do not represent an abnormal static polarization but a dc voltage. The Em4 power law dependence of the offsets (where Em is the amplitude of the electric field) was found to be attributable to the nonlinear increase of the net leakage current.

Graded ferroelectric thin films: Possible origin of the shift along the polarization axis

Hysteresis measurements performed on graded Pt/lead zirconate titanate (PZT)/Pt structures with well oxygenated PZT films do not display any shift along the polarization axis (Voffset) as previously reported. On the other hand, when the PZT graded films were grown under low oxygen pressure, an offset voltage was measured. This shift was systematically enhanced after cycling the film as for fatigue measurements. It was also observed that the Voffset is independent of the value of the reference capacitor used in the Sawyer–Tower circuit. We propose an asymmetry in the leakage current of the structure to be at the origin of the shift along the polarization axis.

Screening of ferroelectric domains on BaTiO3(001) surface by ultraviolet photo-induced charge and dissociative water adsorption

The surface potential contrast between oppositely polarized ferroelectric domains of a BaTiO3(001) single crystal under ultraviolet (UV) illumination before and after the dissociative adsorption of water is measured using the transition from mirror electron microscopy to low-energy electron microscopy. Both photo-generated free charge carriers and dissociative adsorption of water are effective screening mechanisms of the surface polarization charge. The screening rate is dominated by drift, whereas the relaxation in the absence of UV light is driven by thermal diffusion. Surface chemistry plays an important role in the surface charge dynamics.

Epitaxial PZT thin films on TiOx covered Pt/MgO substrate by RF magnetron sputtering

Abstract C-axis epitaxial ferroelectric Pb(Zr0.25Ti0.75)O3 (PZT) thin films with high crystalline quality structure have been prepared at a temperature of 500 °C on MgO(200) single crystal covered with epitaxial Pt(200) thin film. PZT and Pt depositions were performed by RF magnetron sputtering and PZT growth was ensured provided that an ultra thin 0.3–3 nm TiOx upper layer was sputtered on Pt electrode prior to PZT deposition. Moreover it was found that in situ crystallization of a perovskite phase with epitaxial c-axis microstructure required to control precisely the O2/(Ar+O2) ratio in the plasma gas during both PZT and TiOx upper layer depositions. Otherwise, depositions led to crystallization of PZT with high c-axis orientation but simply textured microstructure. Growth of perovskite with either (101) or (111) preferred orientation has also been demonstrated at the same temperature. Additionally strong hysteresis loop deformations, likely rising from oxygen vacancies, are reported for the less oxidized samples.

Interface electronic structure in a metal/ferroelectric heterostructure under applied bias

The effective barrier height between an electrode and a ferroelectric (FE) depends on both macroscopic electrical properties and microscopic chemical and electronic structure. The behavior of a prototypical electrode/FE/electrode structure, Pt/BaTiO

Oxides heterostructures for nanoelectronics

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Full field electron spectromicroscopy applied to ferroelectric materials

/Nb-doped SrTiO

Electromechanical response of amorphous LaAlO3 thin film probed by scanning probe microscopies

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