An investigation of ultrahigh-density ferroelectric data storage based on scanning nonlinear dielectric microscopy (SNDM) is described. To obtain fundamental knowledge of high-density ferroelectric data storage, several studies of nanodomain formation in a congruent lithium tantalate single crystal were conducted. This paper is a summary report consisting of the most recent experimental data from investigations of ferroelectric high density data storage.
In this study, several read/write (R/W) tests were conducted using a hard-disk-drive-type ferroelectric data storage test system based on scanning nonlinear dielectric microscopy (SNDM). A periodically inverted signal, which corresponded to artificial domain stripes formed on LiTaO 3 single crystal, could be read correctly with a bit rate of 2 Mbps using this test system. Bit writing on a 50-nm-thick epitaxial LiTaO 3 film at 20 Mbps was also demonstrated. In addition, a noncontact probe-height control technique was adapted to solve the problem of tip abrasion. The gap distance between a probe and a medium surface was successfully controlled on the nanometer order using a noncontact SNDM technique with sharp-pointed tungsten needle probes prepared by electrolytic polishing. Bit writing under a noncontact state was also studied. Artificial domain dots with diameters of less than 100 nm could be formed under the noncontact state.
In this study, several read/write tests were conducted using a novel ferroelectric data storage test system equipped with a spindle motor, targeted at high-speed data transfer using a single probe head. A periodically inverted signal can be read out correctly with a bit rate of 100 kbps using this test system, and 10 Mbps data transfer is also possible during writing operations. The effect of a dc-offset voltage applied to the writing waveform with high-speed probe scanning is discussed. In addition, a novel noncontact probe height control technique was adopted to solve the problem of tip abrasion.
In this study, we have developed ferroelectric data storage test systems based on scanning nonlinear dielectric microscopy (SNDM) to conduct various experiments concerning read/write capability. Nanodomain formation on ferroelectric recording media was studied using the data storage test system. A nanodomain dot array was successfully written on a single-crystal LiTaO3 recording medium. The diameter of the written dot was as small as 7 nm. Epitaxial-thin-film LiTaO3 recording media were also developed. Nanodomain dots with the diameter of 25 nm were written on the thin-film recording medium. In addition, a non-contact probe-height control technique was adopted to solve the problem of tip abrasion using higher-order nonlinear dielectric response detection method. Finally, a hard-disk-drive (HDD)-type ferroelectric data storage test system was developed for conducting read/write tests under conditions close to those of actual operation. Capabilities of reading at the bit rate of 2 Mbps and writing at the bit rate of 20 Mbps were confirmed using the HDD-type data storage test system.
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