Guenther Schindler

High-resolution x-ray reflectivity study of thin layered Pt-electrodes for integrated ferroelectric devices

The structural interface properties of layered Pt/Ti/SiO2/Si electrodes have been investigated using high-resolution specular and diffuse x-ray reflectivity under grazing angles. Currently this multilayer system represents a technological standard as bottom electrodes for ferroelectric thin-film applications. For the electronic and ferroelectric properties of integrated devices, the film-electrode interface is of crucial importance. We focused on Pt 1000 A/Ti 100 A/SiO2/Si electrodes prepared under annealing conditions as employed in industrial processing, prior to the deposition of ferroelectric films. The comparison between annealed and non-annealed electrodes clearly revealed strong interfacial effects due to interdiffusion and oxidation of Ti, especially at the Pt-Ti interface. Migration of Ti into the Pt layer results in a shift of the critical angle due to the enclosure of TiO2-x within the Pt layer. The heterogeneous distribution of TiO2-x suggests a diffusion mechanism mainly along the Pt grain boundaries. At the SiO2 interface a relatively weakly oxidized Ti layer of 20 A remained, which is most probably correlated with the remaining adhesion to the substrate.

Domain structure of (100) strontium bismuth tantalate (SBT) SrBi2Ta2O9 films

Abstract (100) Strontium bismuth tantalate (SBT) SrBi2Ta2O9 films (∼114–234 nm thickness) on (111) Pt deposited by chemical solution deposition (CSD) and chemical vapor deposition (CVD) were investigated with tapping mode scanning force microscopy (TMSFM). The domain structure was found to be strongly influenced by film composition and defect density. Ideal samples showed an a-axis-oriented material with in-plane 180° domains of ∼22 nm width (film thickness 180–225 nm). The domains were visible by a surface corrugation of 0.5–2 nm downwards at the site of domain walls, which followed 〈001〉 planes. In samples with slightly higher defect density in-plane 180° domains, normal-to-plane 180° domains (∼10 nm difference in corrugation between differently poled domains) and 90° domains (∼5 nm difference in corrugation between differently poled domains) occurred. Finally, for (100) SBT samples, which deviated from the ideal composition by several percent, this very high defect density precluded the ordered formation of domain walls. Instead, as-grown a1 and a2-axis oriented SBT films showed random orientation of whole crystallites poled either in or normal to the surface. The observed surface corrugation between two differently poled crystallites was >10 nm. Single crystallites as well as single domains could be activated and their polarization state was switched mechanically with an electron beam deposited (EBD) or a plasma-sharpened silicon supertip (SSS) by a force of ∼5 nN.