Rewritable Optical Storage Research Articles

Ultrafast Defect Manipulation with Optical Anisotropy in Fused Silica

AbstractWe report the evidence that the oxygen defects induced by focusing an intense infrared femtosecond laser pulse in fused silica can be self-organized by the interference pattern between photon and electron plasma wave. Self-organized nanostructure with a sub-wavelength modulation in refractive index exhibits form birefringence which is rewritable and directionally-controllable. Intriguingly, such optical anisotropy, which indicates a remarkable non-reciprocity, has initially evolved from residual birefringence originated from internal stress distribution due to local heating followed by structural change, regardless of interpulse time. This anisotropic light-matter interaction could be interpreted in terms of an asymmetric relation between light polarization and pulse front tilt. Apart from fundamental understanding of self-organization mechanism, the direction of encoded birefringence can introduce an entirely new concept for rewritable optical storage beyond the diffraction limit of light.

Re-Writability and its Mechanism in DVD: Phase-Change Mechanism Chalcogenide Alloy between Amorphous and Crystal

In optical phase-change materials, especially, Ge2Sb2Te5 has widely been used as a heat of rewritable optical storage media. The chalcogenide material shows a good performance in write-erase cyclability and optical contrast: refractive index change between amorphous and crystal state. However, the high-speed switching mechanism has long been not well understood because of the difficulty of the amorphous analysis. In 2004, we gave one solution for the issue. Since then, a number of discussions and critics have raised up on the new model because the amorphous state in the model is not amorphous like. In this review, we want to give a clear solution to understand what is amorphous in chalcogenides and how different is the amorphous from normal glass amorphous.

Phase-change materials for rewriteable data storage

Phase-change materials are some of the most promising materials for data-storage applications. They are already used in rewriteable optical data storage and offer great potential as an emerging non-volatile electronic memory. This review looks at the unique property combination that characterizes phase-change materials. The crystalline state often shows an octahedral-like atomic arrangement, frequently accompanied by pronounced lattice distortions and huge vacancy concentrations. This can be attributed to the chemical bonding in phase-change alloys, which is promoted by p-orbitals. From this insight, phase-change alloys with desired properties can be designed. This is demonstrated for the optical properties of phase-change alloys, in particular the contrast between the amorphous and crystalline states. The origin of the fast crystallization kinetics is also discussed.

Unique Melting Behavior in Phase-Change Materials for Rewritable Data Storage

Ge2Sb2Te5 (GST) is a technologically very important phase-change material for rewritable optical and electrical storage because it can be switched rapidly back and forth between amorphous and crystalline states for millions of cycles by appropriate pulsed heating. However, an understanding of this complicated phenomenon has not yet been achieved. Here, by ab initio molecular dynamics, we unravel the reversible phase transition process of GST. The melting of rocksalt-structured GST is unique in that it forms two-dimensional linear or tangled clusters while keeping order in the perpendicular direction. It is this specific character that results in the fast and reversible phase transition between amorphous and crystalline and hence rewritable data storage.

On the Physical Parameters and Relaxation Processes in Nematic Azobenzene Polymers for Optical Nanowriting

AbstractThe possibility of achieving devices for rewritable optical storage is provided by liquid‐crystalline polymers with azobenzene side groups, because they undergo photochemically induced trans‐cis reversible isomerization. In this work we overview our investigations into a nematic azobenzene‐polymethacrylate (PMA4) as a suitable material for optical nanowriting. Relaxation processes over different time‐length scales are discussed with particular reference to understanding the interplay between homogeneity at the molecular level, bit stability and working temperature range.

Influence of Hot Carrier Diffusion on the Density Limitation of Optical Data Storage

Hot carrier diffusion (HCD) in Ge-Sb-Te phase change materials for re-writable optical data storage applications may limit the resolution of blue laser recording and cause additional cross-talk. As simulation studies show, the high optical excitation energy and small optical focus size characteristic of blue laser data storage formats lead to significant hot carrier diffusion prior to the energy transfer to the crystal lattice. As a consequence, the optical energy is deposited in an area larger than the laser spot size, leading to enhanced intertrack cross-talk and thermal cross-erase that reduces the quality of high-density optical storage. Therefore, the fundamental limit of resolution for re-writable optical storage systems is no longer determined by the laser focus size alone, but also by additional nonequilibrium HCD effects.

Chalcogenide memory arrays: characterization and radiation effects

The chalcogenide material used for phase-change applications in rewritable optical storage (Ge/sub 2/Sb/sub 2/Te/sub 5/) has been integrated with a 0.5-/spl mu/m radiation-hardened CMOS process to produce 64-Kbit memory arrays. On selected arrays, electrical testing demonstrated up to 100% memory cell yield, 100-ns programming and read speeds, and write currents as low as 1 mA/bit. Devices functioned normally from -55/spl deg/C to 125/spl deg/C. Write/read endurance has been demonstrated to 1/spl times/10/sup 8/ before first bit failure. Total ionizing dose (TID) testing to 2 Mrad(Si) showed no degradation of chalcogenide memory element, but it identified a write current generator circuit degradation specific to the test chip, which can be easily corrected in the next generation of array and product. Static single-event effects (SEE) testing showed no effect to an effective linear energy transfer (LET/sub EFF/) of 98 MeV/mg/cm/sup 2/. Dynamic SEE testing showed no latchup or single-event gate rupture (SEGR) to an LET/sub EFF/ of 123 MeV/mg/cm/sup 2/. Two sensitive circuits, neither containing chalcogenide elements, and both with small error cross sections, were identified. The sense amp appears sensitive to transients when reading the high-resistance state. The write driver circuit may be falsely activated during a read cycle, resulting in a reprogrammed bit. Radiation results show no degradation to the hardened CMOS or effects that can be attributed to the phase-change material.

Green-Light Static Rewritable Optical Storage Properties of aNovel CuTCNQ Derivative Thin Film

A novel charge-transfer complex film: copper-(n-propyl ester 7,7,8,8-tetracyanoquinodimethane-2,5-ylene-(3-propionic acid))(Cu-TCNQ(C2H4COOC3H7)2) was preparedby spin-coating. Absorption spectra, green-light (514.5 nm) staticrewritable optical recording properties and rewritable mechanism ofthis film were studied. The results show that there are two strongabsorption peaks at 388 nm and 675 nm, which can be assigned toelectronic transitions in anion radicalTCNQ(C2H4COOC3H7)2−.Green-light optical storage experimental results of this filmwere as follows: write-in power was 9 mW, pulse duration was 80 ns;erasing power was 4 mW, pulse duration was 500 ns; the reflectivitycontrast C⩾15%; number of write–erase cycles N⩾100. Itis found that the realization of rewritable optical storage of theCu-TCNQ(C2H4COOC3H7)2 film isrelated to the reversible changes of the optical properties, which iscaused by the reversible charge transfer between copper and n-propylester 7,7,8,8- tetracyanoquinodimethane-2,5-ylene-(3-propionic acid) inthe complex through inducement of laser irradiation.

Laser-addressing rewritable optical information storage of (liquid crystalline side chain copolymer/liquid crystals/photo-responsive molecule) ternary composite systems

A laser-addressing rewritable optical information storage for (liquid crystalline side chain copolymer: LCcoP/low molecular weight nematic liquid crystals: nematic LCs/photo-responsive molecule: PM) ternary composite systems in a smectic state was investigated on the basis of a reversible and bistable electro-optical switching driven by ac electric fields with two different frequencies. In order to improve the response speed for the electro-optical switching for the ternary composite system, a LCcoP with the mesogenic side chain fraction of 52.5mol% was synthesized. The ternary composite system with the LCcoP fraction of 36wt% showed a smectic state over a wide range near room temperature. High speed reversible and bistable electro-optical switching (∼100ms) under an appropriate electric field, and a stable memory effect (∼y) were demonstrated upon irradiation of UV light of 355nm by using a YAG laser for the ternary composite systems in a smectic phase at room temperature.

A Novel Organic Complex Thin Film for Rewritable Optical Storage

Erasable optical storage on an organic complex thin film m-nitrobenzal malononitrile and diamine benzene (m-NBMN/DAB) has been demonstrated. High contrast pattern can be produced by 780 nm laser pulses and can be erased by heating. The static optical recording characteristics were studied by the homemade static characterizer, and the structural properties of the thin films were investigated by the high resolution scanning electron microscope (HRSEM) and transmission electron microscope (TEM).

Rewritable Optical Storage Effect of (Liquid Crystalline Polymer)/(Low Molecular Weight Liquid Crystal)/(Photoresponsive Molecule) Ternary Composite System

Abstract A rewritable optical storage effect induced by photoirradiation to a (liquid crystalline polymer)/(low molecular weight liquid crystal)/(photoresponsive molecule) ternary composite system was investigated. Turbid and transparent states were reversibly switched upon photoirradiation with ultraviolet and visible light, respectively, under the application of an a. c. electric field. A light-addressed optical storage of the composite film was demonstrated.