Quantification of Properties for Ferroelectric Thin Films Using Piezo-response Force Microscopy
M.G. Cain, M.J. Lowe, A. Cuenat, M. Stewart and J. Blackburn
National Physical Laboratory, UK
piezo porce microscopy, ferroelectric thin films, FE-RAM memory devices
Ferroelectric thin films are used within FE-RAM Memory devices, thermal imaging cameras and for new and emerging micro-integrated applications. Piezo Force Microscopy (PFM) is a method that can be used to probe (using a modified AFM) the functional properties of ferroelectric thin films at spatial length scales of better than 10nm. The influence of surface layers and surface states, as well as any contamination present on the film, can result in PFM yielding erroneous values for material properties such as d33 and d31. In this work, piezoresponse force microscopy (PFM) has been used to reliably determine the d33 values from various ferroelectric thin films. d33 values have been calibrated with the use of quartz and results have been compared with those obtained using a double-interferometric method. Through appropriate choices of AFM tip type, pressure and frequency, values for quartz may be reliably obtained, leading to accurate determination of the d33 values for each sample. In addition, modelling of the AFM tip-sample interaction has been performed using finite difference methods. A variety of tip-sample conditions have been studied, including surface layers resulting from oxidation and contamination, and a thin air layer between the tip and sample. Incorporating such layers leads to large variations in the electric field across the ferroelectric film. The use of such models provides a better understanding of the tip-sample interactions, allowing for more robust measurements of piezoelectric properties of thin films using PFM.
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Nanotech 2005 Conference Program Abstract