Measurement of Three Dimensional Polarization Direction in Ferroelectric Thin Films Using Scanning Nonlinear Dielectric
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Measurement of Three Dimensional Polarization Direction in Ferroelectric Thin Films Using Scanning Nonlinear Dielectric Microscopy with Rotating Electric Field Hiroyuki Odagawa and Yasuo Cho Research Institute of Electrical Communication, Tohoku University, Sendai, 980-8577, Japan ABSTRACT A scanning nonlinear dielectric microscope (SNDM) probe, called the ε 311 -type probe, and a system to measure the ferroelectric polarization component parallel to the surface using rotating electric field have been developed. This is achieved by measuring the ferroelectric material’s nonlinear dielectric constant ε 311 instead of ε 333 , which is measured in conventional SNDM. Experimental result shows that we can successfully determine polarization component parallel to the surface. The SNDM system can measure polarization at any angle from the surface normal which is often of interest.
INTRODUCTION Recently, several researchers have studied and reported various techniques for determining ferroelectric polarization direction and observing domain structure with high spatial resolution using scanning probe microscopy [1-12]. These techniques are very useful in studying physical properties arising from the behavior of small ferroelectric domains, and the development of such measurement systems is an important subject of research. One of the useful methods for observing polarization distributions is the piezoelectric response imaging technique (piezo-imaging) using scanning force microscopy [1-4]. This technique measures the displacement of the surface of ferroelectric materials caused by the piezoelectric response by applying an electric field at the top of a cantilever or a probe needle. To date, this technique can measure a three-dimensional polarization direction with a resolution of 40 nm [2]. We have previously proposed and developed a technique for imaging the state of ferroelectric polarization and local crystal anisotropy of dielectric materials. The technique involves the measurement of the point-to-point variation of the nonlinear dielectric constant of a sample, and is termed "scanning nonlinear dielectric microscopy" (SNDM) [7-9]. This is a purely electrical method for observing the ferroelectric polarization distribution, without the influence of the free charge shielding effect. To date, the spatial resolution for the distribution of the polarization has been improved down to 0.5 nm [10-11], exceeding piezo-imaging in resolution [12]. However, conventional SNDM measures only the polarization component perpendicular to the surface. If SNDM could simultaneously measure the polarization component parallel to the surface with high resolution, it could be applied to the evaluation of the point-to-point variation of the three-dimensional polarization vector. SNDM could then be used for observing ferroelectric materials having polarization orientated in every direction with respect to the sample surface, such as PZT thin film having a-c domains and complex domain structures near MPB. In this paper we describe a sys
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