High Speed Overwritable Phase Change Optical Disk Material

Abstract

It was found that GeTe-Sb2Te3 pseud-binary amorphous alloy films showed remarkably fast switching properties to laser irradiation. By the static laser irradiation test, the film whose composition corresponded to stoichiometric compound of GeSb2Te4 were crystallized within 50ns of pulse duration at power of 8mW, whilst they could be amorphized with the same pulse duration at power of 20mW. Direct overwriting cycle test was performed on the revolving disk system for 105 times using single laser beam. CNR of more than 50dB and erasability of -22dB were obtained for linear velocity of 22m/s and overwriting frequencies of 5 and 7 MHz. The laser powers were 22 mW for recording and 10 mW for erasing. These materials will be applicable to high data rate direct overwritable disk media.

Origin, secret, and application of the ideal phase‐change material GeSbTe

“…From the XRD analyses, the initial phase is identified as NaCl-like structure as depicted in the left hand figure in Fig. 2 [2]. In the metastable NaCl-type cubic phase, 4a sites are occupied exclusively by Te atoms and 4b sites are randomly occupied by Ge atoms, Sb atoms, and many vacancies [9].…”

“…As seen in the upper figure, the variation of the refractive index, Dn, is very large in the infrared range (telecom range) and increasingly small around the visible-light range (BD/DVD range). On the other hand, the variation of the extinction coefficient, Dk, is sufficiently large around the BD/DVD Figure 3 Experimental results of the crystallization properties of the GeSbTe amorphous films (100 nm for each) formed by electron beam evaporation [2]. Figure 4 Repetitious overwriting test results using a 4.7-GB capacity DVD-RAM optical disc [16].…”

“…The development speed at the early stage were not so high during the 1970s and 1980s, and the activities sometimes stagnated. Nevertheless, the discovery of the GeSbTe phase-change materials by the Yamada et al [2] drastically turned the tide.…”

Electron diffraction and high-resolution transmission electron microscopy of the high temperature crystal structures of GexSb2Te3+x (x=1,2,3) phase change material

“…Crystallization is considered the rate-limiting process, because amorphization is inherently a much faster process. 5,6 It has been argued that a possible disadvantage of the use of Ge 2 Sb 2 Te 5 is that the crystalline state used in phase change optical recording applications is metastable, 10,11 whereupon after an increased heat input ͑to higher temperatures͒ a stable structure develops. On the other hand, the demanded high crystallization rate of Ge 2 Sb 2 Te 5 is possibly a direct consequence of the metastability of the phase, which allows for a much easier crystallization process due to fewer constraints on the short range diffusion and ordering of the different atomic species.…”

Determination of Optical Constants and Optical Band Gap in Ge40te60-XSBX Thin Films

“…Modern chalcogenide compounds like GeSb-Te, widely used in rewritable optical disks and PRAM devices, are fragile glassformers; therefore they are able to crystallize in about 100 ns [4][5][6][7][8][9][10][11] . Therefore these alloys are used for data recording based on the rapid and reversible amorphous-to-crystalline phase transformation 12,13 that is accompanied by increase in the optical reflectivity and the electrical conductivity.…”