Abstract
Femtosecond laser-induced crystallization and ablation of Ge2Sb2Te5 (GST) phase change film is investigated by reflectivity pump-probing technology. Below the ablation threshold, the face-centered cubic structure (FCC) state in the central area can be formed, and cylindrical rims are formed in the peripheral dewetting zone due to the solidification of transported matter. The time of surface temperature dropping to the crystallization point needs about 30 ps for 5.86 mJ/cm2 and 82 ps for 7.04 mJ/cm2, respectively. At higher laser fluence, crystallization GST island structures appear in the central ablation region due to the extremely short heating time (100 ps). Furthermore, crystallization rate is faster than the ablation rate of the GST film, which is caused by different reflectivity.
Highlights
The quest for non-volatile random-access memories for information storage has led to the exploration of various solutions based on different physical effects
We investigated the evolution of the surface morphology of the phase change film material induced by the femtosecond laser
We used the 220 nm thick Ge2 Sb2 Te5 (GST) film as the sample for the study, it has been fabricated on a SiO2 substrate by magnetron sputtering system, using a GST alloy target and a mixture of argon and nitrogen as the sputtering gas
Summary
The quest for non-volatile random-access memories for information storage has led to the exploration of various solutions based on different physical effects. In phase-change memories, each bit of information is stored in a small portion of a phase-change material, which can exist in two different solid states: crystalline and amorphous. Ge–Sb–Te alloys are widely used for data recording based on a fast and reversible amorphous-to-crystalline phase transition [1], which can be achieved by local heating/cooling (either with laser or electrical pulses) at high rates. A femtosecond laser pulse can induce such an ultrafast phase change due to the fast displacement of energy on the phase film [7,8] Since it is intercalation with the material in a short time, it can effectively suppress the thermal and flow mechanical effects of the ablation process [7]. The high temperature can make the material vaporize instantaneously, but the residual heat could still be transferred inside the material, causing
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