10 Tbit/inch 2 Ferroelectric Data Storage with Offset Voltage Application Method
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10 Tbit/inch2 Ferroelectric Data Storage with Offset Voltage Application Method Sunao HASHIMOTO and Yasuo CHO Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan ABSTRACT Ferroelectrics are expected to become one of the next generation ultra-high density data storage media. The requirements for pulse amplitude and the duration to switch the domain were both markedly decreased by using a new domain stabilizing method; offset voltage application method. Additionally, with this method it became possible to invert a smaller domain with a diameter of less than 10 nm. Finally, significant progress was made regarding the memory density for ferroelectric data storage, and an area density of 10.1 Tera-bit/inch2 was successfully achieved. This represents the highest memory density for rewritable data storage reported to date. INTRODUCTION Recently, average amounts of electronic data generally used for storage have increased markedly. Therefore, there is a pressing need to develop information storage devices that have sufficient capacity to store large amounts of information in less physical space. It was hoped that this requirement would be temporarily satisfied by the development of perpendicular magnetic recording. However, for mobile applications, there is an increasing demand for storage capacity. The importance of developing next-generation storage devices remains and ferroelectrics are expected to be one type of storage media playing a main role for next-generation ultra-high density recording devices. The thickness of a ferroelectric domain wall is considered to be in the order of only a few lattice places [1]. Therefore, ferroelectrics can store information bits within these small inverted ferroelectric domains. Ferroelectric storage media has been studied by some research groups, given the background information regarding the ferroelectric domain wall [2]. As a candidate for application as storage media, focus was made on congruent LiTaO3 (CLT), which is a ferroelectric single crystal. High density recording; that is, a density of 1.5 Tbit/inch2, has already been achieved with a close packed domain inversion pattern on a CLT thin film using a Scanning Nonlinear Dielectric Microscopy (SNDM) domain engineering system [3]. The SNDM is used to analyze the ferroelectric domain with sub nanometer resolution [4][5]. Inversion of the ferroelectric domain was performed by applying a pulse voltage between the conductive probe of the SNDM and the bottom electrode of the specimen. However, the area density was insufficient when compared with the theoretical potential. The pulse duration time to switch the domain is 10 times longer than our best results achieved, which was 4 ns [6]. This means that there is sufficient room to improve the area density and the durational time. However, with inversion of the ferroelectric
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domain in order to achieve higher density, reproducibility of the small domain was insufficient. With a shorter pulse
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