Stroboscopic X-Ray Diffraction Measurements of sub-ns Domain Dynamics in Ferroelectric Films
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Stroboscopic X-Ray Diffraction Measurements of sub-ns Domain Dynamics in Ferroelectric Films E. Zolotoyabko, J. P. Quintana1, D. J. Towner2, and B. W. Wessels2 Department of Materials Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel. 1 Northwestern University, DND-CAT, APS/ANL Sector 5, Building 432A, 9700 South Cass Ave, Argonne, IL 60439-4857, U.S.A. 2 Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, U.S.A.
ABSTRACT We used the Advanced Photon Source (APS) at Argonne National Laboratory to perform fast (ps range) time-resolved diffraction measurements of the dynamic characteristics in BaTiO3 films subjected to strong high-frequency electric fields. The timedependent lattice response measured at frequencies between 6.5 MHz and 1.3 GHz revealed damped domain movements with attenuation time rapidly increasing with electric field frequency, ν. We found that at frequencies higher than ν ≈ 600 MHz the domain motions in BaTiO3 films become heavily damped, information that may be important to future device operation. A minimum attenuation time, τ ≈ 330 ps, measured at ν = 1.3 GHz was limited by the time constant of the electrical circuit.
INTRODUCTION Ferroelectric thin films have great potential for applications as memory elements, piezoelectric and electro-optic devices (see Refs. [1-4] and references therein). Domain dynamics in the ns to ps time scale is the major factor, which determines the speed of future ferroelectric random access memory (FERAM) devices. However, despite extensive study, this issue is far from being completely understood. For example, the fundamental question “how fast can domain wall move?” raised by Merz in 1954 [5] is still open. The studies of the relaxation processes revealed contradictory results especially concerning a very wide spectrum of measured relaxation times. In fact, domain dynamics in ferroelectric films are derived from electrical [1], dielectric (see e.g. Ref. [6]) or optical (see e.g. Ref. [7]) measurements. However, the measured characteristics, as a rule, are not directly related to microscopic parameters, and thorough theoretical models are needed to extract the latter. In this paper, we continue to explore the capabilities of fast time-resolved x-ray diffraction at synchrotron beam lines to probe domain dynamics via dynamic response of lattice parameters, in situ, under high-frequency electric field application. In ferroelectric films, the largest contribution to measured lattice parameter variations is due to the flip of 90o-domains. Hence, time-resolved x-ray diffraction, in principle, is able to probe domain dynamics. Experimental technique and first results of dynamic measurements in ferroelectric films by stroboscopic x-ray diffraction technique at APS are described in earlier papers [8, 9]. Here we are focused on establishment of the correct procedure for data analysis, taking into account the temporal characteristics of the electrical circuit.
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DATA ANALYSIS IN STROBOSCOPIC MEAS
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