Investigations of Mesoscopic Ferroelectric Structures Prepared by Imprint Lithography
- PDF / 372,867 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 28 Downloads / 205 Views
U4.2.1
Investigations of Mesoscopic Ferroelectric Structures Prepared by Imprint Lithography C. Harnagea, M. Alexe, J. Schilling, R.B. Wehrspohn, D. Hesse, and U. Gösele Max-Planck-Institut für Mikrostrukturphysik, D-06120 Halle (Saale), Germany ABSTRACT Arrays of mesoscopic ferroelectric PZT structures with lateral sizes from several micrometers down to below 300 nm were prepared applying nanoimprint lithography. The ferroelectric properties of the mesoscopic structures were investigated by scanning force microscopy in piezoresponse mode. The best chemical route to obtain ferroelectric structures was found to be the sol-gel method. Using Nb-doped SrTiO3 single crystals as bottom electrodes, the crystallization into the ferroelectric phase was uniform with grain sizes in the 35 nm range. The best ferroelectric properties of individual 300 nm structures were obtained if an intermediate, continuous ferroelectric layer was present on the bottom electrode.
INTRODUCTION Mesoscopic ferroelectric structures with lateral sizes less than 100 nm made from PZT and SBT by electron-beam direct writing has been shown to be functional, viz. polarizable and switchable without crosstalk [1]. For the development of non-volatile ferroelectric random access memories (NV-FRAMs) of Gigabit memory density the preparation of mesoscopic ferroelectric structures will, however, be necessary using more economic means than the slow and expensive electron-beam direct writing. Nanoimprint lithography has emerged as a rapid, low-cost technique for the preparation of polymer structures well below the limit of the other lithography techniques used for patterning of large areas down to 20 nm feature size [2-4]. Similar to imprint into polymer films, we propose the use of nanoimprint lithography (NIL) to obtain large arrays of ferroelectric structures. Using a variant of this technique, we succeeded in preparing ferroelectric cells with lateral sizes down to 300 nm, and we proved the ferroelectric nature of these structures using piezoresponse scanning force microscopy (PFM).
EXPERIMENT Applying NIL to ferroelectrics Briefly, the standard NIL technique implies the use of a thermoplastic resist which becomes a viscous liquid above its glass transition temperature and which thus can flow above this temperature. Therefore, it can be deformed easily. NIL is usually performed in two steps. In the first step (the imprint step) a mold with the negative of the desired pattern on its surface is pressed into a thin resist cast on a substrate, followed by removal of the mold. This step transfers the pattern of the mold into the resist film, or, in other words, it creates a thickness contrast pattern in the resist. The second step is the pattern transfer in which an anisotropic etching process, such
U4.2.2
as reactive ion etching (RIE), is used to remove the residual resist in the compressed area. This step transfers the thickness contrast pattern into the entire resist. Preparing ferroelectric films using chemical solution deposition (CSD) techniques impli
Data Loading...
