Seminars Archive

Interfaces in ferroelectric-based structures

Abstract
Epitaxial ferroelectric (multi)layers, super-lattices and ferroelectric-based heterostructures are studied nowadays both for basic understandings of the size effects and physical phenomena related to the presence of ferroelectricity, as well for developing and optimizing applications such as non-volatile memories, tunable capacitors, sensors, actuators, etc. In all cases the interfaces play a major role, either it the electrode one or it is about interfaces between different phases of the multilayer heterostructure. The basic question arising is how the presence of bound polarization charges is influencing the construction of the interface and its electronic properties. Recent results obtained on some epitaxial ferroelectric-based structures will be presented. These are: Lead Zirconate Titanate (PZT) and BaTiO3 (BTO) films grown on single crystal SrTiO3 (STO) substrates with bottom SrRuO3 (SRO) electrode and different metals as top contacts; PZT-ZnO heterostructures; PZT-PbZrO3 (PZO) multilayers; BiFeO3 (BFO) grown on single crystal STO substrate with bottom SRO electrode and top Pt contact; Gd doped BFO grown on Nb-doped SrTiO3 (STON) substrate with Pt to contact. The samples were investigated using various techniques such as XRD, AFM/PFM, (HR)TEM, XPS, and the electric properties were studied by performing hysteresis, I-V and C-V measurements in different temperature and bias conditions. In all studied samples it was found that the interface(s) has a major impact on the macroscopic electrical properties. It affects the capacitance, with effect on the estimated dielectric constant, affects the polarization switching, reflected in the shape of the hysteresis loop, and has a tremendous impact on the leakage current, observed in the magnitude and the shape of the I-V characteristic. The experimental data hints that the interface properties are related to three main factors: structural quality; chemical composition; polarization charges. Optimization of the electrical properties requests clean interfaces, with controlled terminations and able to provide the compensation charges in real time.