Kenjiro Fujimoto

Tbit/inch2 ferroelectric data storage based on scanning nonlinear dielectric microscopy

Nanosized inverted domain dots in ferroelectric materials have potential applications in ultrahigh-density rewritable data storage systems. Here, a data storage system based on scanning nonlinear dielectric microscopy and thin films of ferroelectric single-crystal lithium tantalite is presented. Through domain engineering, nanosized inverted domain dots have been successfully formed at a data density of 1.50 Tbit/in.2.

High-speed switching of nanoscale ferroelectric domains in congruent single-crystal LiTaO3

The nanodomain reversal characteristics of congruent LiTaO3 (CLT) single crystal are investigated. It is found that fast nanosecond domain switching can be achieved by reducing the sample thickness, even for CLT, which contains many Li vacancy defects that pin domain-wall movement. As an example, the authors obtain a polarization inverted domain dot with a radius of 7.9 nm by application of a 4 ns 10 V pulse. These results demonstrate that the speed of polarization reversal is closely related to the thickness of the medium.

Ultrahigh-Density Ferroelectric Data Storage Using Scanning Nonlinear Dielectric Microscopy

Ferroelectrics have generated considerable interest as promising storage media. In this paper, an investigation of ultrahigh-density ferroelectric data storage based on scanning nonlinear dielectric microscopy (SNDM) was carried out. For the purpose of obtaining fundamental knowledge of high-density ferroelectric data storage, several experiments on nanodomain formation in lithium tantalate (LiTaO3) single crystal were conducted. As a result, a very small inverted domain with a radius of 6 nm was successfully formed in stoichiometric LiTaO3 (SLT), and in addition, a domain dot array with an areal density of 1.5 Tbit/inch2 was written on congruent LiTaO3 (CLT). Additionally, the first prototype high-density ferroelectric data storage system was developed. Using this system, reading and writing data transfer rates were evaluated.

Nanosecond Switching of Nanoscale Ferroelectric Domains in Congruent Single-Crystal LiTaO3 Using Scanning Nonlinear Dielectric Microscopy

The domain switching characteristics of a congruent LiTaO3 (CLT) single crystal are investigated mainly with respect to switching speed. It is found that fast nanosecond domain switching can be achieved by reducing the sample thickness, even for CLT, which has been thought to be unsuitable for high-speed switching. As an example, the authors successfully obtain a polarization inverted domain dot with a radius of 7.9 nm in a 60-nm-thick CLT plate by application of a 4 ns, 10 V pulse. These results demonstrate that the speed of polarization reversal is closely related to the thickness of the medium.

Very High-Density Ferroelectric Digital Data Storage Using Tracking and Error Correction Technique

Ferroelectric digital data recording and reproducing experiment was successfully demonstrated by using both tracking and error correction techniques. The relationship between off-track amounts of scanning probe and signal detection tolerances were evaluated. Tracking accuracy demanded for achieving Tbit/in.2 class high-density recording was estimated to be sub-nanometer range by using a ferroelectric recording/reproducing system with nanometer order position controller. Based on these results, a high-density of 258 Gbit/in.2 ferroelectric recording and reproducing of digital image file was performed by using one reproducing scan for one recorded track method.

Fundamental Study on Ferroelectric Data Storage with the Density Above 1 Tbit/inch2 Using Congruent Lithium Tantalate

Ferroelectrics have created considerable interest as promising storage media. In this paper, an investigation for ultra high-density ferroelectric data storage based on scanning nonlinear dielectric microscopy (SNDM) was carried out. For the purpose of obtaining the fundamental knowledge of high-density ferroelectric data storage, several experiments of nano-domain formation in lithium tantalate (LiTaO3 ) single crystal were conducted. As a result, domain dot array with areal density of 1.5 Tbit/inch2 was written in congruent LiTaO3 (CLT). We also found that quite fast nano second domain switching was possible by reducing a sample thickness even in CLT with a lot of Li vacancy defects which played a role of pinning sites against domain wall movement.

Tbit/Inch 2 Data Storage Using Scanning Nonlinear Dielectric Microscopy

Nano-sized inverted domain dots in ferroelectric materials is a technology with potential applications in ultrahigh-density rewritable data storage systems. Up to now, we have studied domain inversion characteristics of stoichiometric and congruent LiTaO 3 single crystals in nanoscopic area using scanning nonlinear dielectric microscopy (SNDM), which is the technique for observing ferroelectric polarization distribution with sub-nanometer resolution. In this study, we have revealed nano-sized inverted domain remained stably for a long time, and successfully formed inverted domain dots at a data density of 1.50 Tbit/inch 2, representing the highest memory density for rewritable electric data storage reported to date.

1 Tbit/in.2 Very-High-Density Recording in Mass-Productive Polycrystalline Ferroelectric Thin Film Media

We demonstrate very-high-density ferroelectric recording experiments of 1 Tbit/in.2 in polycrystalline Pb(Zr,Ti)O3 (PZT) thin film for the first time. A high-quality polycrystalline PZT thin film was successfully deposited on a silicon substrate with a SrRuO3 (SRO) electrode by metal–organic chemical vapor deposition (MOCVD). The roughness of the PZT film was reduced to less than 1 nm by chemical mechanical polishing (CMP). The PZT film has very high controllability for domain inversion. Our fabrication process also enables high productivity. Therefore, our PZT film has potential to be a mass-productive ferroelectric recording medium for high-density storage systems.