Reversible Phase Change Optical Recording Research Articles

Bi–Ge–Sb–Sn–Te films for reversible phase-change optical recording

Bi–Ge–Sb–Sn–Te phase-change recording films (Films A–D) were prepared by the co-sputtering of Bi 30Ge 10Te 60, Ge 20Sb 80, Sb and Sn targets. The composition of the recording films was controlled by the dc power. The film composition, surface roughness and reflectivity were also closely related. Dynamic tests revealed that disks with Film C exhibited a low jitter value and a high modulation value after direct overwriting. Therefore, the composition of the recording film dominated the reversible recording properties of the phase-change optical disk.

Doped Ge–Sb–Te phase-change materials for reversible phase-change optical recording

Differently doped Ge–Sb–Te phase-change recording films were prepared by the individual dc magnetron sputtering of Sn 5Ge 3Sb 72Te 20, In 5Ge 3Sb 72Te 20, Ga 5Ge 3Sb 72Te 20 and Bi 5Ge 3Sb 72Te 20 targets. A close relationship was observed between surface roughness and reflectivity. The Ge–Sb–Te films doped with Bi showed the highest surface roughness and reflectivity. The phase-change optical disks with Bi-doped Ge–Sb–Te recording films showed the best overwriting characteristics. Therefore, the reversible recording properties of the phase-change optical disk were dominated by the composition of the recording film.

The effect of thickness on the Bi–Ge–Sb–Te films for reversible phase-change optical recording

The Bi–Ge–Sb–Te phase-change recording films were prepared by the dc magnetron sputtering of a Bi 5Ge 9Sb 68Te 18 target in an atmosphere of Ar. The surface of the Bi–Ge–Sb–Te films grew in the form of needles as the film thickness increased. There was the close relation among the film thickness, surface roughness, and optical properties. The Bi–Ge–Sb–Te film with a thickness of 16 nm had the lowest jitter value and the highest modulation value. As the results, the film thickness affected the Bi–Ge–Sb–Te film for phase-change optical recording significantly.

Suitability of Ge-As-Te system for optical data storage

We report the study of crystallization kinetics and time-temperature-transformation in alloys of Ge7.5AsxTe92.5-x (x=20, 40, 45, 47.5, 50, 52.5, 55) and Ge10AsxTe90-x (x=15, 20, 22.5, 35, 40, 45, 50), in order to examine the suitability of these alloys for reversible phase change optical recording (RPCOR) films, which is one of the leading optical storage devices. Using the values of viscosity and kinetics of crystal nucleation and growth process, the time-temperature-transformation curves were obtained. The variation of critical parameters such as minimum erasure time and thermal stability has been calculated as a function of composition. It has been observed that for our samples, the critical cooling rate is high (2.1*105-4.3*104 K/min) for Ge10AsxTe90-x (x=15, 20, 22.5, 35, 40, 45, 50) and 1.51*105-2.91*104 K/min for Ge7.5AsxTe92.5-x (x=15, 20, 22.5, 35, 40, 45, 50) ensuring fast erasure speed ( approximately=1 mu s) which is an essential requirement for high quality RPCOR films. It is suggested that the material with lower concentration of Germanium (<10 at.%), Arsenide and Tellurium concentration between (35-55 at.%) are better contenders for the above application.

相変化を利用した新規な４元系Ａｇ‐Ｉｎ‐Ｓｂ‐Ｔｅ光記録材料

Reversible phase change optical recording material with a new quarternary system of Ag-In-Sb-Te has been studied. The starting material for the Ag-In-Sb-Te system is a combination of AgInTe2 with the chalcopyrite structure and Sb. In this work, we report the basic properties of the Ag-In-Sb-Te films investigated by means of DSC, XRD, ED, and HR-TEM. We also discuss the phase change process of the Ag-In-Sb-Te system.

Study of Se–Te–Sb System for Application to Reversible Optical Data Storage

In the present work variation of the two main parameters–viscosity and critical cooling rate, required for the recent upcoming optical data storage devices, have been analysed for different compositions of Se80-xSbxTe20 (0≤x≤9) system. Temperature dependence of viscosity has been determined using the activation energy for glass transition and for crystallization obtained from heating rate dependence of glass transition temperature and peak crystallization temperature from DSC measurements. Vicsocity has been estimated with the help of Vogel-Tamman-Fulcher equation. It has been found that for samples containing Sb≤4 at.%, the viscosity increases with the increase in Sb content. Further increase in Sb concentration causes a decrease in the viscosity. These results are consistent with the structural changes taking place in the Se–Te system with increase in Sb content. Using these values of viscosity and kinetics of crystal nucleation and growth process, the time-temperature-transformation curves were obtained. The critical cooling rate Rc is found to increase for Sb>4 at.%. For good reversible phase change optical recording, the critical cooling rate of the material should be high enough so as to get an erasure time of less than 1 µs. From the analysis of the data the suitability of the SeTeSb system for optical recording has been discussed.

Discussion on the Mechanism of Reversible Phase Change Optical Recording

In stoichiometric GeTe-Sb2Te3 films, reversible phase change optical recording materials, Sb addition is used widely in order to improve the crystallization speed, the data retention time and the stability of cyclic operation, but its mechanism is not clear. V-VI compounds (GeTe, SnTe) are well known as compounds in which the ferroelectric structural phase transition occurs. The dielectric constant ε0 changes largely due to a change in the short-range order of weakly bound nearest neighbors in the crystal to more strongly bound nearest neighbors in the amorphous phase. Therefore, it is necessary to discuss the effect of Sb addition in the stoichiometric GeTe-Sb2Te3 composition upon the thermal stabilities, the dynamic properties of crystallization and the dielectric constant change Δε0 based on the amorphous-to-crystalline phase transition.

The Effect of Doping on the Erasure Speed and Stability of Reversible Phase-Change Optical Recording Films

The crystallization kinetics of chalcogenide films, to which small concentrations of foreign elements such as Cu, Co, Pb, Ag and Sb are added, were investigated theoretically. It is found that the critical cooling rate can be taken as the criterion for evaluating the roles of various elements on the erasure speed. Since the elements having lower Tg/Tm possess higher critical cooling rates, they are favorable for enhancing the erasure speed of the above films. On the other hand, the Tg of the elements having lower Tg/Tm is found to be the main factor in determining the stability of corresponding films at room temperature because these elements possess higher crystallization speed in the temperature range between Tg and Tm. Therefore, the elements having lower Tg/Tm and higher Tg can be used to improve both the erasure speed and the stability of the reversible phase-change optical recording films.

Sn–Te–Se Films for Reversible Phase-Change Optical Recording

Characteristics of optical recording films that consist of Sn–Te–Se and have an amorphous crystalline phase change recording mechanism are analyzed. High crystallization temperatures and high crystallization activation energies, which certify the long life of the recorded dots, can be obtained for compositions whose ratio of Sn concentration to Se concentration is about 1 to 2. Among these compositions, high speed erasing, long life of the recorded dots, and high recording sensitivity are achieved in compositions whose Te concentration is 10 to 20 at%. When the Te concentration is 50 to 60 at% and the Se concentration is 17 to 25 at%, the crystallization temperature of the recorded dots is much lower than that of the as-deposited amorphous state.

In–Se–Pb–Based High Speed Reversible Phase Change Optical Recording Films

A new high speed reversible phase change optical recording material In–Se–Pb–Cu film is reported. The roles of Pb and Cu elements on erasing speed and stability of In–Se–based films are discussed.