Scanning probe microscopy studies and dynamic behaviour of ferroelectric domains in PbZr0.53Ti0.47O3 thin films

Abstract

Ferroelectric domains play an essential role in all ferroelectric materials applications, for example, microelectromechanical sensors systems (MEMS) and integrated optical systems. The prime interest in recent years is, however, in non-volatile random accesses memories (FRAM) based on ferroelectric thin film. This requires substantial improvement in the understanding of the basic proprieties at the nanometer length scale. Especially the domain nucleation and growth processes in ferroelectric is of key importance. As the optical methods are limited by diffraction, novel high resolution techniques are required. The scanning force methods introduced during this thesis offer the required high resolution together with high sensitivity. In this thesis experimental and theoretical evidence for the origin of the force acting on the tip, the cantilever deflection and the image contrast mechanisms is given for various SFM (Scanning Force Microscopy) operation modes. For imaging ferroelectric domains the best suited SPM technique is the piezoresponse SFM that is performed with the tip in contact with the sample. The spontaneous growth of the domains 1 nucleating in lead zirconate titanate sample is investigated in detail using the EFM (Electrostatic Force Microscopy) technique. Even more interesting is the case where the domains are intentionally created switching the spontaneous polarization by means of an electric field between the EFM tip and an electrode below the sample. This allows to create any desired pattern of domains. The ability to use the same tip for domain switching and imaging is another advantage of the EFM. The domain formed in this way varies in size from few nanometers to few micrometers. Using EFM technique we demonstrate ferroelectrostatic switching in Lead Zircanate Titanate (PZT) thin film. This has important technological implication because the ferroelectric switching must be used in ferroelectric devices.