Rewritable Digital Versatile Discs Research Articles

A Magnetoresistance Induced by a Nonzero Berry Phase in GeTe/Sb2Te3 Chalcogenide Superlattices

AbstractThe chalcogenide alloy Ge–Sb–Te (GST) has not only been used in rewritable digital versatile discs, but also in nonvolatile electrical phase change memory as a key recording material. Although GST has been believed for a long time not to show magnetic properties unless doped with magnetic impurities, it has recently been reported that superlattices (SLs) with the structure [(GeTe)L(Sb2Te3)M]N (where L, M, and N are usually integers) have a large magnetoresistance at room temperature for particular combinations of L and M. Here it is reported that when [(GeTe)L(Sb2Te3)M]N chalcogenide SL films are thermally annealed at 470 K and cooled down to room temperature under an external magnetic field accompanied by current pulse injections, a large magnetoresistance change (>2500 Ω) is induced. This study shows that the phenomenon has a strong correlation with the GeTe thickness and the periodic structure of the SL films, and that it is induced by the structural phase transition between electrically nonpolar and polar phases in the GeTe layers in the SLs. This study proposes that the relationship between the polar (ferroelectric) phase and the Berry curvature in the SLs is responsible for the magnetoresistance change.

Voltammetric behaviour of hydrogen peroxide at a silver electrode fabricated from a rewritable digital versatile disc (DVD) and its determination in water samples

In this study we investigated the possibility of applying Ag electrodes manufactured from recordable rewritable digital versatile discs (DVD-RW) for the voltammetric determination of hydrogen peroxide. The calibration plot was linear from 0.087 mM to 3.41 mM hydrogen peroxide with a sensitivity of 58.7 μA mM−1 over this range. A corresponding detection limit of 78.35 μM, based on a signal-to-noise-ratio of 3 was recorded. No interferences were observed by 500 mg L−1 chloride, 50 mg L−1 nitrate, 700 mg L−1 sulphate or 700 mg L−1 carbonate which are found in swimming pool water at these concentrations. Using the multiple standard addition method a percentage recovery of 90.67% with a coefficient of variation of 4.69% (n = 5) was found for a representative swimming pool water concentration of 1.2 mM hydrogen peroxide. Therefore, the performance data suggests that the method is reliable at the concentrations examined in this study and that a rapid, simple, economical and precise method of monitoring hydrogen peroxide in swimming pool and aquaculture applications is possible.

Thermodynamic assessment of the Ag–Te binary system

Pure silver and its alloys are very important materials for various technological applications. Tellurium is one of the unwanted admixture in silver and is removed during metallurgical processes; however Ag–Te alloy is necessary for production of rewritable digital versatile discs. The knowledge of phase diagram of Ag–Te is essential for applications and refining process. The critical assessment of binary system Ag–Te has been done using literature information. Good agreement between experimental data reported in literature and calculated values has been found.

Correlations between Electrical Parameters of Rewritable Digital Versatile Disc and Optical and Thermal Properties of Phase Change Alloy: Effect of Sputter Power

The correlations between the electrical parameters of digital versatile rewritable disc with optical and thermal properties of phase change alloy films, as a function of sputter power, are discussed in this paper. Non-isothermal studies carried out on differential scanning calorimeter revealed insignificant changes in crystallization temperature, decrease in melting point and solidification temperatures with increasing sputtering power. The energy required for melting increased with an increase in sputtering power whereas that liberated during crystallization and solidification was found to be highest in films sputtered at 400 W. Spectrophotometric studies in the spectral range of 400–1000 nm revealed an increase in refractive index and a decrease in the extinction coefficient around 650 nm wavelength, with an increase in sputter power. Although the spectral variation of ξ2 showed a maximum in all films at approximately 650 nm but that of optical conductivity occurred at lower wavelengths. Electrical measurements revealed a decrease in Jitter, an increase in optimum recording power and operating power window with an increase in sputtering power.

Large Optical Transitions in Rewritable Digital Versatile Discs: An Interlayer Atomic Zipper in a SbTe Alloy

ABSTRACTChalcogenides, in particular germanium-antimony-tellurium (GeSbTe) and antimony-rich tellurium (R-SbTe) based alloys, are the most technologically significant alloys currently being applied to recordable optical storage as typified by rewritable digital versatile discs (DVD-RW), DVD random access memory, (DVD-RAM). The same alloys are also being applied to nonvolatile random access memory electrical memory in the form of phase change random access memory (PCRAM). In 2004, the phase transition mechanism of GeSbTe was first revealed, demonstrating that the amorphous state is not a random configurational network but is locally well-ordered with the crystalline to amorphous switching process being based upon Ge atoms moving between octahedral and tetrahedral symmetry positions. The kinetic barrier between these two states gives rise to the non-volatile nature of GeSbTe as a storage medium. In contrast, no theoretical analysis has been proposed for SbTe alloys because a Ge-free system. In this paper, the Sb2Te structure has been investigated using the local density approximation (LDA) using a plane-wave basis and compared with experimental results. The effect of external stress on the structure was also investigated. It was found that Sb2Te undergoes two phase-transitions at around 18 GPa (compressive) and −3 GPa (tensile). In the case of negative stress, the c-axis was found to expanded more than the other axes, giving rise a large refractive index change. We report on coherent (uniaxial) melting induced by the breaking a sigma bond between Sb2Te3 and Sb superlattices. We believe this to be the origin of the phase transition that induces a large change in physical properties.

Detection of Recording Marks on Digital Versatile Discs and Blu-ray Discs using Conductive Atomic Force Microscopy

Recording bits on recordable phase-change discs are studied using conductive atomic force microscopy (C-AFM) at high contrast. The grain size and boundary analysis of different phase-change recording materials can be performed at nanoscale spatial resolution. This study shows that C-AFM is not only suited to image the amorphous marks written on phase-change-based rewritable digital versatile discs (DVD) or Blu-ray discs (BD), but is also capable of revealing the appearance of bits in CuSi-based write-once BD discs.

Archival-overwrite performance of GeSnSb-based phase-change discs

High-speed rewritable digital versatile discs based on GeSnSb phase-change materials may show poor archival-overwrite performance. We have related this to a decrease in the crystalline reflectivity. Transmission electron microscopy images indicate that this is connected to morphology changes of the material. Materials optimization by addition of dopants such as Se or Te can stabilize the crystalline reflectivity and, as a result, improve the archival-overwrite performance to within the specifications for optical recording.

Adaptive write strategy selection mechanism for optical recording systems

This paper discusses a smart algorithm for setting the write strategy in an optical recording device like consumer DVD (digital versatile disc) recorders. The proposed algorithm improves the quality of recorded optical media, being particularly efficient for recordable and rewritable DVDs. One of the biggest challenges faced by optical recorder manufacturers is the increasing availability of low-cost optical media that obey marginally the standardized specifications causing poor recordability and corrupt discs. As the mass market embraces optical recorders in their homes, this problem aggravates resulting in consumer dissatisfaction. This paper presents a novel, yet not very complex method to improve the compatibility of conventional DVD recorders with widely available media.

High Speed Rewritable Digital Versatile Disc Recording

High speed rewritable digital versatile discs (DVD+RW) can be written well in a speed range from 3.3× to 8×. Special attention points for recording this type of discs are in the area of byte error rate (BER) and archival-overwrite. Archival-overwrite means that the disc is written with data, archived for some time and subsequently overwritten once. The cause of the high BER is unwanted nucleation near the trailing edge of the amorphous marks. This nucleation can be avoided by choosing proper cooling gap lengths in the write strategy. The raised jitter after archival-overwrite is caused by changes of the crystalline phase during aging. These changes might also endanger the reliability of the results of the optimum power control (OPC), which is performed prior to recording. By applying measures from both the drive side and the media side, a good archival-overwrite and a robust OPC-result is ensured.

Multilevel-Enabled Double-Density Writable and Rewritable Digital Versatile Disc System

Multilevel (ML) recording technology doubles the speed and capacity of standard digital versatile disc (DVD) writable and rewritable systems. Implemented with the addition of single chip or core to the standard drive architecture, ML technology doubles performance with no change to the optical mechanical unit. While custom media has been optimized for high speed ML recording, ML recording works well with standard writable and rewritable media.

A New Partial-Read Only Memory (ROM) System for a High-Density Digital Video Disc Recorder

In recent years, the use of optical disc memory such as compact disc (CD) and digital versatile disc (DVD) has become increasingly common; most personal computers and audio/visual (A/V) peripherals are now expected to be equipped with optical disc memory. In particular, the advent of the rewritable DVD is believed to facilitate the future trend of replacing the videotape media. On the other hand, the reality remains that there are no new applications available, only very limited uses for this technology. Thus, in this paper, the high-density digital video disc recorder equipped with a partial-read only memory (ROM) system is proposed as a new application for optical disc memory.

Structural Analysis of Ag–In–Sb–Te Phase-Change Material

The Ag–In–Sb–Te system is widely used for phase-change discs such as compact disc rewritable (CD-RW) and rewritable digital versatile disc (DVD+RW). To clarify the effect of Ag and In in the Ag–In–Sb–Te system, we studied the local structure of Ag–In–Sb–Te phase-change material by extended X-ray absorption fine structure (EXAFS). The results suggest that the existence of Ag contributes to the thermal stability of amorphous marks and existence of In contributes to high-speed phase-change.

Wobble Addressing Method for Land and Groove Structured Optical Storage

In this paper, two wobble addressing methods for land and groove structured optical discs are proposed. These methods use only modulated wobble signals for addressing, while excluding the need for an embossed prepit. As a consequence, the overhead associated with the proposed methods is less than that of the conventional addressing method for rewritable digital versatile discs. In addition, the proposed methods enable the use of a one-beam mastering machine for making discs. This is possible because a signal from a land track is optically added to two signals from adjacent groove tracks, which are produced by a single laser beam for each signal, while maintaining its phase relationship for signal decoding. The advantages of the proposed methods have been demonstrated through computer simulation as well as through evaluation of test discs.

A Feasibility Study of Writing Compensation for Tangential Tilt

For achieving a higher density than that of current digital versatile discs(DVD), a high numerical aperture(NA) and blue wavelength light source is tested to increase the areal density. In contrast to this positive effect, the coma aberration is doubled with a NA of 0.65 and wavelength of 400 nm compared to that of the current rewritable DVD at the same disc tilt. Additionally, the effective power density for recording is much smaller than that in the case of a DVD with a tilt. In this paper an efficient compensation method for disc tilt will be presented.

Antimony Aperture Properties on Super-Resolution Near-Field Structure using Different Protection Layers

Modifying a rewritable digital versatile disc (DVD) structure by Sb and SiN thin films, near-field super-resolution was performed beyond the optical diffraction limit only using a current DVD optical pickup. Using the wavelength (λ) of 635 nm and the lens numerical aperture (NA) of 0.6, a mark size of 60 nm was recorded and detected at the double rotation speed of Compact Disc. The super-resolution properties of Sb thin films sandwiched by different dielectric layers of SiO2 and ZnS–SiO2 instead of SiN were also investigated. Super-resolution did not occur and the resolution was close to 200 nm, when using the ZnS–SiO2 layers.