Yoshiomi Hiranaga

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.

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

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.

Evaluation of Bit Error Rate for Ferroelectric Data Storage

Bit data was recorded on a LiTaO3 single-crystal medium using a data storage system which was based on scanning nonlinear dielectric microscopy, and bit error rate was evaluated. The recording medium with a highly homogeneous thickness of 119 nm was prepared employing both polarization controlled wet etching and dry etching techniques. A 256×256 data bit array was recorded at an areal density of 258 Gbit/inch2. The bit error rate was determined to be 1.2×10-3 by visual inspection. An automated analysis method was subsequently discussed in detail.

Nanodomain Formation on Ferroelectrics and Development of Hard-Disk-Drive-Type Ferroelectric Data Storage Devices

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 LiTaO3 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 LiTaO3 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.

Ultrahigh-Density Ferroelectric Data Storage with Low Bit Error Rate

Actual information data were recorded on a LiTaO3 single-crystal medium using a data storage system based on scanning nonlinear dielectric microscopy. For increasing recording density and reducing bit error rate, conductive-diamond-coated probes with a sharp tip and thin recording media were prepared. The domain-switching characteristics of virgin and prepolarized recording media were compared. The conditions of pulse voltage for writing were optimized. As a result, actual information data containing 128 ×128 bits were recorded at an areal density of 258 Gbit/inch2 without bit errors; thus, the bit error rate was calculated to be less than 1 ×10-4.

Lateral resolution improvement in scanning nonlinear dielectric microscopy by measuring super-higher-order nonlinear dielectric constants

Scanning nonlinear dielectric microscopy (SNDM) can be used to visualize polarization distributions in ferroelectric materials and dopant profiles in semiconductor devices. Without using a special sharp tip, we achieved an improved lateral resolution in SNDM through the measurement of super-higher-order nonlinearity up to the fourth order. We observed a multidomain single crystal congruent LiTaO3 (CLT) sample, and a cross section of a metal-oxide-semiconductor (MOS) field-effect-transistor (FET). The imaged domain boundaries of the CLT were narrower in the super-higher-order images than in the conventional image. Compared to the conventional method, the super-higher-order method resolved the more detailed structure of the MOSFET.

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.

Ferroelectric Single Crystal Recording Media Fabricated by Polarization Controlled Wet Etching Process

Ferroelectric single crystal thin plates are promising materials for ultrahigh-density storage devices. In order to fabricate recording media with large area and high homogeneity, a polarization controlled wet etching process was developed in this paper. Differential etch rates of ferroelectrics are useful in controlling the thickness during the wet etching process. By applying DC voltage to a substrate, the etching process can be stopped when the thickness reaches the desired value. A 455-nm-thick LiTaO3 thin plate with a diameter of 3 mm was prepared using this method. Nanodomains were artificially formed by applying voltage pulses to the substrate using a metal-coated cantilever top electrode.