Nozomi Odagawa

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

The influence of 180° ferroelectric domain wall width on the threshold field for wall motion

Unlike ideal 180° ferroelectric walls that are a unit cell wide (∼0.5 nm), real walls in ferroelectrics have been reported to be many nanometers wide (1–10 nm). Using scanning nonlinear dielectric microscopy of lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) ferroelectrics, we show that the wall width at surfaces can vary considerably and even reach ∼100 nm in places where polar defects adjoin a wall. The consequence of such variable wall widths is investigated on the specific property of threshold field required for wall motion. Using microscopic phase-field modeling, we show that the threshold field for moving an antiparallel ferroelectric domain wall dramatically drops by two to three orders of magnitude if the wall was diffuse by only ∼1–2 nm, which agrees with experimental wall widths and threshold fields for these materials. Modeling also shows that wall broadening due to its intersection with a surface will influence the threshold field for wall motion only for very thin films (1–10 nm) whe...

Wall behavior of nanodomains as a function of their initial state

A method for visualizing ferroelectric domain walls based on higher order nonlinear dielectric detection is proposed. This technique enables the authors to obtain information to visualize the domain wall clearly. Using this method, nanodomain variations with high temperature treatments are observed. The results indicate that the manner of domain variation depends on the state of the domain walls at the time of writing. This result can be explained from the point of view of wall energy transition.

Study of Long-Term-Retention Characteristics and Wall Behavior of Nano-Inverted Domains on Congruent Single-Crystal LiTaO3 Based on Wall Energy

To investigate the long-term retention characteristics of a ferroelectric-data-storage system, 80-nm-thick congruent LiTaO3 plates with inverted-domain dot arrays composed of 100-nm-Phi dots were baked at 220, 250, 280 and 300degC. After heat treatment over a range of different time intervals, the dots shrank. From the change in the dot radius data, the activation energy (Ea) and frequency factor ( alpha ), parameters of the Arrhenius equation, were determined to be Ea = 0.76 eV, alpha = 2.21 times105. From these parameter we can predict competitive retention characteristics compared with general memory devices. The phenomenon of dot shrinking can be explained from the energy transition of the system based on wall energy.

Long-term-retention characteristics of small inverted dots formed on congruent single-crystal LiTaO3

To investigate the long-term retention characteristics of a ferroelectric-data-storage system, 80-nm-thick congruent LiTaO3 plates with inverted-domain dot arrays composed of 100-nm-φdots were baked at 220, 250, 280, and 300°C. After heat treatment over a range of different time intervals, the dots shrank. From the change in the dot area density, the activation energy and frequency factor, parameters of the Arrhenius equation, were determined to be Ea=0.76eV and α=2.21×105, respectively. Using these parameters, lifetime length at 80°C was estimated to be more than 16yr and is sufficiently long compared with that of general memory devices.

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.

Dependence of long term stability on the initial radius of small inverted domains formed on congruent single-crystal LiTaO3

The dependence of the initial radius on the long term stability of small inverted domain dots was investigated by heat treatment of an 80-nm-thick congruent LiTaO3 plate with inverted domain dots with radii of 20–200 nm at 250 °C for 20 h. A linear relationship between the dot area after heat treatment and the initial dot area was determined, and the initial radius dependency on the long term stability of small inverted domains was formulated.

Study of Long-Term-Retention Characteristics and Wall Behavior of Nano-Inverted domains on Congruent Single-Crystal LiTaO 3 Based on Wall Energy

To investigate the long-term retention characteristics of a ferroelectric-data-storage system, 80-nm-thick congruent LiTaO3 plates with inverted-domain dot arrays composed of 100-nm-Phi dots were baked at 220, 250, 280 and 300degC. After heat treatment over a range of different time intervals, the dots shrank. From the change in the dot radius data, the activation energy (Ea) and frequency factor ( alpha ), parameters of the Arrhenius equation, were determined to be Ea = 0.76 eV, alpha = 2.21 times105. From these parameter we can predict competitive retention characteristics compared with general memory devices. The phenomenon of dot shrinking can be explained from the energy transition of the system based on wall energy.

Non-Contact Probe Control and High-Speed Writing for Rotated-Disk-Type Ferroelectric Data Storage Devices

In this study, several read/write tests were conducted using novel type of ferroelectric data storage system, which was equipped with spindle motor, under the conditions relatively close to the actual operations. Firstly, high-speed data transfer was demonstrated regarding both reading and writing. Subsequently, the novel non-contact probe-height control technique was discussed.