Charging effects on ferroelectric SBT thin films imaged by noncontact electrostatic force microscopy

SBT (SrBi2Ta2O9) thin films are ferroelectric high-k materials with layered perovskite structure being developed for integration into high-density CMOS technology as non-volatile memories. Research is mainly focused on their polarization properties which are also studied by different Scanning Force Microscopy (SFM) methods, one of which is non-contact Electrostatic Force Microscopy (nc-EFM). After scanning in contact with a voltage applied between tip and a bottom electrode the resulting polarization of the SBT surface can be imaged by this method. Artefact formation was observed in such SFM experiments and studied by different soft treatments of SBT layers after the polarization step. Heating, immersion in isopropanol, grounding, scanning with opposite polarization voltage and time dependent investigation of retention loss were used to identify the origin of,the main intensity of the detected electrostatic field. This was a weak surface charge and is unlikely to be attributed to permanent polarization properties which are supposed to have a more stable character.