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Nanoscale Properties of SrBi2Ta2O9 Thin Films A. Gruverman1 , C. Isobe* and M. Tanaka* Sony Corporation, Yokohama Research Center, Hodogaya-ku, Yokohama 240-0005, Japan *Sony Corporation, Core Technology Development Center, Atsugi 243-0014, Japan

ABSTRACT Piezoresponse scanning force microscopy (PFM) was applied to study the nanoscale mechanism of retention loss in SrBi2Ta2O9 (SBT) thin films. Experiments were conducted by performing local polarization reversal within an individual grain with subsequent imaging of a resulting domain structure at different time intervals. The retention behavior of the films was studied as a function of switching conditions and electrode material. SFM was also used for nanoscale mapping of leakage current sites and investigation of electrical conduction mechanism at these sites. For the first time, the development of dielectric breakdown in SBT films was directly observed at nanoscale. INTRODUCTION The ability of ferroelectric films to maintain their polarization in the absence of external voltage provides the unique nonvolatility of ferroelectric memories [1]. However, commercial application of ferroelectric films is hindered by the degradation effects which limit the lifetime and reliability of ferroelectric-based devices. Numerous efforts have been undertaken to better understand the physical mechanism of the retention failure which manifests itself in the spontaneous reversal of polarization leading to a progressive loss of stored data. It has been proposed that retention failure in thin ferroelectric films is largely determined by the depolarizing fields resulting from incomplete compensation of the polarization charges at the film-electrode interface [2,3]. However, so far most of the studies of this effect focused on controlling macroscopic integral parameters of ferroelectric capacitors and could not provide information on the exact nature of polarization decay. In this respect, application of high resolution techniques such as scanning force microscopy (SFM) in conjunction with conventional electrical measurements may provide an opportunity to achieve a unique insight into the real physical processes which occur in ferroelectric thin films. Recently, it was shown that SFM operating in the piezoresponse mode, or piezoresponse scanning force microscopy (PFM), is a well-suited technique both for nanoscale imaging and control of ferroelectric domains and for investigation of the basic mechanism of degradation processes in ferroelectric thin films by direct observation of their domain structures [4-12]. The aim of this paper is to investigate the nanoscale retention behavior of ferroelectric SrBi2Ta2O9 (SBT) thin films. One of the advantages of these films compared to films of the PZT family is their fatigue-free behavior [13]. However, their retention properties, which are closely related to the performance of memory devices, have been less studied [14-16]. In this article, we report on PFM studies of the mechanism of polarization retention loss in SBT films via the direct obser