Kenkou Tanaka

Scanning Nonlinear Dielectric Microscopy Nano-Science and Technology for Next Generation High Density Ferroelectric Data Storage

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.

Realization of 10Tbit∕in.2 memory density and subnanosecond domain switching time in ferroelectric data storage

Nanosized inverted domain dots in ferroelectric materials have potential application in ultrahigh-density rewritable data storage systems. Herein, a data storage system is presented based on scanning nonlinear dielectric microscopy and a thin film of ferroelectric single-crystal lithium tantalite. Through domain engineering, nanosized inverted domain dots have been successfully formed at a data density above 10.1Tbit∕in.2 and subnanosecond (500ps) domain switching speed has been achieved. Moreover, actual information storage is demonstrated at a density of 1Tbit∕in.2

Actual information storage with a recording density of 4 Tbit/in.2 in a ferroelectric recording medium

A new method to achieve real information recording with a density above 1 Tbit∕in.(2) in ferroelectric data storage systems is proposed. In this system, data bits were written in the form of the polarization direction, and the data were read by scanning nonlinear dielectric microscopy technique. The domain-switching characteristics of the virgin and inversely prepolarized media were compared, and the conditions of the pulse voltage for writing were optimized. As a result, actual data containing 64×64 bits were recorded at an areal density of 4 Tbit∕in.(2). The bit error rate was evaluated to be 1.2×10(-2).

Novel HDD-type SNDM ferroelectric data storage system aimed at high-speed data transfer with single probe operation

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.

Nanodomain manipulation for reduction of bit error rate in Terabit/inch2-class ferroelectric data storage

Actual information data storage was studied using a data storage system based on scanning nonlinear dielectric microscopy. The bit error rates of the data recorded on a LiTaO3 single-crystal medium were evaluated. The data were written at the density of 403 Gbit/in.2 using a conductive-diamond-coated cantilever as a read/write probe. The tendencies of the bit errors were affected by the arrangement of the surrounding data bits. A writing method using bipolar pulses was discussed in order to decrease the bit error rate. The data with the highest recording density, 0.98 Tbit/in.2, were recorded by using a sharp cantilever. The bit error rate was decreased by a factor of four by adjusting the pulse amplitudes according to the bit arrangements.

Real Information Storage using Ferroelectrics with a Density of 1 TBIT/INCH2

Real information data bits were written onto a ferroelectric medium in the form of the polarization direction of nano-domains. Local domain switching was carried out by applying a voltage pulse. Pulse voltage value was varied based on the polarization directions in the immediate environment to keep the bit size constant. As a result, writing and storing of real information data was demonstrated at a density of 1 Tbit/inch2 and a bit error rate as low as 1.8 × 10− 2.

Ferroelectric Ultra High-Density Data Storage Based on Scanning Nonlinear Dielectric Microscopy

Nano-sized inverted domain dots in ferroelectric materials have potential application in ultrahigh-density rewritable data storage systems. Herein, a data storage system is presented based on scanning non-linear dielectric microscopy and a thin film of ferroelectric single-crystal lithium tantalite. Through domain engineering, we succeeded to form an smallest artificial nano-domain single dot of 5.1 nm in diameter and artificial nano-domain dot-array with a memory density of 10.1 Tbit/inch2 and a bit spacing of 8.0 nm, representing the highest memory density for rewritable data storage reported to date. Sub-nanosecond (500 psec) domain switching speed also has been achieved. Next, long term retention characteristic of data with inverted domain dots is investigated by conducting heat treatment test. Obtained life time of inverted dot with the radius of 50 nm was 16.9 years at 80degC. Finally, actual information storage with low bit error and high memory density was performed. A bit error ratio of less than 1times 10-4 was achieved at an areal density of 258 Gbit/inch2. Moreover, actual information storage is demonstrated at a density of 1 Tbit/inch2.

Ferroelectric Data Recording Using Servo-Controlled Tracking Technique

A new method of achieving real information recording with a density above 1 Tbit/in.2 using servo tracking control in ferroelectric data storage systems is proposed. In this system, position control of the read/write head was realized by the scanning nonlinear dielectric microscopy technique. The data bits can be read by only one-line scanning on a one-line data track using high-precision head position control. The tracking accuracy of this system was evaluated to be about 2 nmpp. As a result, actual data composed of 64×64 bits were recorded at an areal density of 1 Tbit/in.2 and the bit error rate was evaluated to be 1.7×10-3.

Development of Ferroelectric Data Storage Test System for High-Density and High-speed Read/Write

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 LiTaO 3 recording medium. The diameter of the written dot was as small as 7 nm. Epitaxial-thin-film LiTaO 3 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.

Terabit Per Square Inch Information Data Storage on Ferroelectrics with Low Bit Error Rate

The bit error rate was evaluated in ultrahigh-density ferroelectric data storage based on scanning nonlinear dielectric microscopy. Data bits were written on ferroelectric media in the form of the polarization direction of nanodomains. Information data were recorded on a LiTaO 3 single-crystal at the density of 260 Gbit/inch2 using the probe with the tip radius of 50 nm. There were no bit errors out of ten-thousand bits under the optimized conditions, thus bit error rate was less than 1 × 10−4. Sharp probes with the tip radius of 25 nm enabled recording at the density of 982 Gbit/inch2 with a few bit errors.