Phase-change materials are key components in rewritable optical disks and are promising for non-volatile electronic memories. The very different structure and ultrafast recrystallization dynamics of another class of phase-change materials, Sb–Te-based alloys, now suggests their use in future memory applications.

From local structure to nanosecond recrystallization dynamics in AgInSbTe phase-change materials

Isothermal crystallization of doped SbxTe fast-growth phase-change films, with and without capping layers, was investigated using transmission electron microscopy, which provided direct and quantitative information on nucleation and growth processes separately. Two types of amorphous dielectric layers, ZnS–SiO2 and GeCrN, were used for sandwiching the SbxTe films to form typical trilayer stacks, which are the active part in applications. The nucleation and growth parameters of SbxTe films were found to be influenced by the dielectric capping layers. The crystal growth rate is temperature dependent and it reduces when the film is sandwiched between the dielectric layers. The reduction in growth rate differs with the capping layer type. The capping layer influence on the growth rate is pronounced at lower temperatures ∼160°C, but tends to vanish at higher temperatures ∼200°C. The activation energy for crystal growth is 2.4±0.3eV for an uncapped film and it increases ∼40% when the capping layers, GeCrN or Zn...

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Influence of capping layers on the crystallization of doped SbxTe fast-growth phase-change films

A series of superlatticelike (SLL) structure incorporated with two phase-change materials GeTe and Sb7Te3 was applied in lateral phase change memory. Power consumption and lifetime were used as two criteria to optimize the SLL structure. It was found that with the thickness ratio of GeTe to Sb7Te3 at 1.6, the RESET current could be as low as 1.5 mA and the endurance could reach as high as 5.3×106 cycles. By varying the thickness ratio of GeTe to Sb7Te3, the crystallization temperature of SLL structures and the performance of lateral phase change memory with these SLL structures can be controlled.

GeTe/Sb7Te3 superlatticelike structure for lateral phase change memory

As-sputtered and melt-quenched amorphous structures together with the laser-induced crystallized structure of Ge-Sb-Te thin films were investigated using high-resolution electron microscopy (HREM) and nanobeam electron diffraction (NBED). Each of the Ge-Sb-Te thin films was embedded in a four-layered stack, which is the same as the layered structure of phase-change optical disks. Cross-sectional HREM revealed crystalline atomic clusters in the melt-quenched amorphous layer at a greater frequency than in the as-sputtered amorphous layer. Autocorrelation function analysis of the HREM images revealed similarity between the structures of atomic ordered regions in the amorphous phase and that of crystalline Sb. Atomic pair-distribution functions derived from halo NBED intensity analysis indicated that the atomic neighbor correlations developed more in the melt-quenched amorphous phase than in the as-sputtered phase. The development of locally ordered regions is considered to be closely related to the differenc...

Local structure analysis of Ge-Sb-Te phase change materials using high-resolution electron microscopy and nanobeam diffraction

Antimony alloys for phase-change memory with high thermal stability

Adding specific foreign elements into the eutectic Sb70Te30 fast-growth material is expected to be an effective way to increase its thermal stability for blue laser recording. We have studied the effects of Ag and In addition on the optical properties and crystallization kinetics of the eutectic Sb70Te30 recording film. The results showed that the addition of Ag and In increased the refractive index and decreased the extinction coefficient of amorphous Sb70Te30 film and decreased both the refractive index and extinction coefficient of crystalline Sb70Te30 film. The archival stability of the eutectic SbTe alloy could be effectively improved by adding Ag and In elements, however, the addition of Ag and In also made the initialization of the as-deposited eutectic SbTe film more difficult. During the isothermal crystallization process, the incubation time was extended, crystallization speed was reduced, and the crystallization process became more grain-growth dominated as Ag and In were added. All these effec...

http://web.nchu.edu.tw/pweb/users/ycho22081/research/5058.pdf

Effects of ag and in addition on the optical properties and crystallization kinetics of eutectic Sb70Te30 phase-change recording film

Eutectic Sb70Te30 fast-growth material is one of the promising candidates for high data transfer rate recording. However, it also shows the disadvantage of poor thermal stability. Germanium, with a high value of glass transition temperature, is expected to play the role of thermal stabilizer. It was found that the effect of Ge doping on reflectivity difference between as-deposited and annealed states is not significant. However, the addition of Ge element into Sb70Te30 can reduce the initialization or erasure power, and increase the stability of the phase change recording media at room temperature at the same time. Unfortunately, doping Ge element would also slow down the crystallization speed of eutectic Sb70Te30 recording film.

http://web.nchu.edu.tw/pweb/users/ycho22081/research/5057.pdf

Optical Properties and Crystallization Characteristics of Ge-Doped Sb70Te30 Phase Change Recording Film.

As the thickness of eutectic Sb 70 Te 30 phase change recording film was reduced, the crystallization temperature and activation energy for crystallization would increase, while the melting temperature and activation energy for melting would decrease. Accordingly, the archival stability and recording sensitivity can be improved. However, the recording speed for direct over write will be slowed down. Based upon the Johnson–Mehl–Avrami equation, it was found that the increase of film thickness would increase the nucleation rate of eutectic Sb 70 Te 30 recording film and make the crystallization process become more nucleation-dominated.

Thickness dependence of crystallization and melting kinetics of eutectic Sb70Te30 phase change recording film

Doping Ag into the fast-growth Sb70Te30 recording film can increase the crystallization temperature and activation energy for crystallization so that the archival stability can be improved, however, the initialization will become more difficult. The activation energy for melting of the Ag-doped Sb70Te30 recording films will decrease with Ag concentration so that the recording sensitivity can also be improved. New compounds such as Ag5Te3 and AgSbTe2 will form due to the addition of Ag. When the concentration of Ag was increased, the crystallization mechanisms of the Ag-doped Sb70Te30 recording films will gradually transfer from polyhedral growth to linear growth. Under pulsed laser irradiation, the melt-quenched amorphous zone for the annealed Ag-doped Sb70Te30 recording films will enlarge as the Ag content was increased, representing that the recording sensitivity will increase. However, once the concentration of Ag was increased to 10.8 at. %, the as-deposited Ag-doped Sb70Te30 recording film will become difficult to be initialized.

Thermal-and laser-induced order-disorder switching of Ag-doped fast-growth Sb70Te30 phase-change recording films

Adding In into Sb70Te30 recording film can improve the archival stability. However, initializing ability and recording sensitivity will be scarified, and ablation effect will be enhanced. Recording bits could only be smoothly switched between the amorphous and crystalline states with an adequate value of reduced activation energy

http://web.nchu.edu.tw/pweb/users/ycho22081/research/6680.pdf

Yung-Sung Hsu

Papers

Effects of ag and in addition on the optical properties and crystallization kinetics of eutectic Sb70Te30 phase-change recording film

Optical Properties and Crystallization Characteristics of Ge-Doped Sb70Te30 Phase Change Recording Film.

Thickness dependence of crystallization and melting kinetics of eutectic Sb70Te30 phase change recording film

Thermal-and laser-induced order-disorder switching of Ag-doped fast-growth Sb70Te30 phase-change recording films

Thermal- and Laser-Induced Order–Disorder Switching of In-Doped Fast-Growth Sb $_{70}$ Te $_{30}$ Phase-Change Recording Films