First Prototype of High-Density Ferroelectric Data Storage System
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First Prototype of High-Density Ferroelectric Data Storage System Yoshiomi Hiranaga, Yasuo Cho and Yasuo Wagatsuma Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan ABSTRACT The first prototype of high-density ferroelectric data storage system based on scanning nonlinear dielectric microscopy was developed in order to establish basic elemental technologies for actual read/write functions aiming for practical application. Using this system, a data transfer rate was evaluated. 9 kbps reading and 50 kbps writing were demonstrated with respect to 440 kbit/inch bit data array written on a lithium tantalate single crystal thin plate. Additionally, we considered future prospects for developing the data storage system with further fast data transfer rate. INTRODUCTION Recently, recording density of high-capacity storage media has increased at a rate of approximately 100% per year, and is expected to exceed 1 Tbit/inch2 in the near future. However, magnetic storage, which plays a main role in this field, has a serious problem that data retention is degraded in accordance with miniaturization of bit size due to thermal fluctuation, and therefore, an alternative high-density data storage method is required. With these backgrounds, we have proposed an high-density ferroelectric data storage system using scanning nonlinear dielectric microscopy (SNDM) as a pickup device. SNDM is a method of detecting the local crystal anisotropy of dielectric materials in a purely electrical way, and now, its resolution has become the sub-nanometer order, which is much higher than that of other scanning probe microscopy techniques employed for the same purpose [1,2]. In ferroelectric data storage, polarization directions act as data bits of “1” and “0”. Up to now, we have reported that nanodomain dot array with an areal density of 1.5 Tbit/inch2 was successfully written on a lithium tantalate (LiTaO3) single crystal thin plate [3]. Although traditional SNDM domain engineering system, which is remodeled from commercial atomic force microscope (AFM) unit, is useful for studies on domain inversion characteristics in nanoscopic region, this system is inadequate to establish basic elemental technologies of high-density ferroelectric data storage, and a system equipped with all components necessary for actual read/write functions is required for further studies aiming at
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practical application. Therefore, in this study, we developed the first prototype of high-density ferroelectric data storage system. EXPERIMENT Figure 1 shows the schematic diagram of the data storage system developed in this study. The probe is composed of a metal-coated conductive cantilever (typical tip radius is 25 nm), an oscillator and a grounded metal ring. The contact load of the tip is kept constant using AFM technique in order to ensure stable actions of the system and minimize tip damage. Polarity distinction is performed by detecting the small variation in resonance frequency caused by
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