Feb 5, 2009
Embedded ferroelectric nanostructure arrays
Tuning of the device properties thus requires quantitative data from individual memory cells. But how can this be achieved with only about 1000 electrons of displacement charge on a nanoscale capacitor? Qualitatively, the inversion of the polarization is associated with an inversion of the piezoelectric tensor that can be monitored as a phase-shift of π in piezoresponse force microscopy but this method is prone to an undefined point contact that prevents reproducible data. Quantitatively there is just not enough charge to e.g. display a P-E loop.
We thus suggested investigating a larger number of lead titanate ferroelectric nanoislands in parallel in order to obtain sufficient displacement charges to overcome the detection noise. Our previous experiments of template-mediated growth by electron-beam lithography paved the way for large numbers of ferroelectric nanoislands with long-range ordering and a narrow size distribution. These results were complemented by our recent experiments on the embedding of unregistered ferroelectric nanoislands into a low-k dielectric matrix of a spin-on glass that was polished down to deposit macroscopic top electrodes without electrical shorts between the nanoislands.
In this contribution we now open the door to a study of thousands of well-registered and almost identical ferroelectric nanoislands in parallel as we embed those ordered structures into a low-k dielectric matrix and show qualitative ferroelectric functionality on individual nanostructures by means of piezoresponse force microscopy. The chemical mechanical polishing helps tuning the overall thickness and yields a planarized surface that eliminates topography effects in piezoresponse force microscopy.
In what is to come, the deposition of macroscopic top electrodes will allow for averaging the electronic properties of ferroelectric nanocapacitors far below 100 nm to explore coercivity, permittivity and polarization as a function of lateral dimensions. About the authors
About the author
The study was performed in close collaboration between the Institute of Materials in Electrical Engineering and Information Technology 2 (IWE II), RWTH Aachen University (Germany), and the Institute of Electronic Materials (IEM), Department IFF & JARA - Fundamentals of Future Information Technology, Research Center Jülich (Germany). Sven Clemens and Serge Röhrig performed this work during their Ph.D. studies at the IWE II, and the IEM respectively. Andreas Rüdiger is now Professor for Nanoelectronics at the Université du Québec, INRS-EMT, Canada. Theodor Schneller, Ph.D., is a senior scientist and head of the chemical solution deposition group at the IWE II. Rainer Waser is Professor and head of both institutes, IWE II and IEM.