Cross-Sectional Observation of Nano-Domain Dots Formed in Congruent Single-Crystal LiTaO3
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0966-T09-03
Cross-Sectional Observation of Nano-Domain Dots Formed in Congruent Single-Crystal LiTaO3 Yasuo Cho1 and Yasuhiro Daimon2 1 Research Institute of Electrical Communication, Tohoku University, 2-1-1, Katahira Aoba-ku, Sendai, 980-8577, Japan 2 Research Institute of Electrical Communication, Tohoku University, Sendai, 980-8577, Japan
ABSTRACT Cross-sectional shapes of reversal nano-domain dots formed in a congruent LiTaO3 single-crystal recording medium were studied by scanning nonlinear dielectric microscopy (SNDM). Images obtained by SNDM measurements confirm that reversal nano-domain dots penetrate through the entire sample. The domain wall thickness was evaluated by the crosssectional measurement results. The variation of the domain wall thickness as a function of sample thickness and of depth position was evaluated. It was found that thinner samples have a tendency to have thinner domain walls, and it was confirmed that the domain wall thickness at the bottom of the sample was thinner than at the front surface of the sample. A discussion of the measured result is also provided.
INTRODUCTION The volume of information has been expanding as a result of the advances in information technologies. Thus, the memory density of magnetic data storage, which plays a major role in data storage methods, will soon reach a theoretical limit. This necessitates the development of an alternative next-generation ultrahigh-density recording system. Therefore, we have been studying ferroelectric ultrahigh-density data storage. Ferroelectrics can preserve bit information as 1 and 0, which correspond to upward and downward polarization directions, respectively. Characteristics include the advantage for highdensity data recording; for example, the domain wall is very thin and the domain sizes are smaller. The present authors have developed a scanning nonlinear dielectric microscope (SNDM) for the observation of ferroelectric polarization distributions with sub-nanometer order resolution.[1][2] The polarization of the medium immediately under the probe tip is reversed by applying a pulse voltage across the probe and the metal stage of the SNDM. Therefore, SNDM can be applied as a recording reproduction method, and this has attracted considerable interest. We have previously reported the successful formation of nanosized inverted domain dot arrays at a data density of 10.1 Tbit/in2 in a congruent LiTaO3 (CLT) single-crystal thin plate.[3] In addition, we have achieved real data recording at an area density of 1 Tbit/in2 with a bit error rate of only 1.8×10-2.[3] However, there are many points to be studied, for example, concerning the mechanism of polarization reversal, the cross-sectional shapes of nano-domain dots formed just below the probe tip and the effects of stress in the domain boundary vicinity. It is very important to
elucidate these points experimentally. However, we have been able to obtain information on the sample surface only by conventional SNDM due to the high concentration of the electric field just below
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