Laser pulse induced bumps in chalcogenide phase change films

Abstract

Formation of bumps in chalcogenide phase change thin films during the laser writing process is theoretically and experimentally investigated. The process involves basically fast heating and quenching stages. Circular bumps are formed after cooling, and the shape and size of the bumps depend on various parameters such as temperatures, laser power, beam size, laser pulse duration, etc. In extreme cases, holes are formed at the apex of the bumps. To understand the bumps and their formation is of great interest for data storage. In the present work, a theoretical model is established for the formation process, and the geometric characters of the formed bumps can be analytically and quantitatively evaluated from various parameters involved in the formation. Simulations based on the analytic solution are carried out taking Ag8In14Sb55Te23 as an example. The results are verified with experimental observations of the bumps.

Temperature dependence of thermal properties of Ag8In14Sb55Te23 phase-change memory materials

“…When the laser beam is switched off, the melted marks quench into an amorphous state due to the high thermal conductivity of the substrate underneath the phase-change materials. Conversely, the recorded marks are erased when the materials are heated above the glass transition temperature but yet below the melting threshold so that the materials return to the crystalline state [7][8][9][10][11][12][13][14][15][16][17]. For the nonvolatile electrical storage, applying a higher voltage pulse (reset pulse) to the crystalline state with low resistivity leads to the local melting and consequently the formation of an amorphous information bit with high resistivity due to the rapid quenching.…”

“…Chalcongenide phase-change materials are extensively used as the optical and nonvolatile electrical data storage media due to the apparent difference in optical reflectivity and electrical resistivity between the crystalline and amorphous state [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. For optical data storage, the recording is achieved by forming amorphous marks on a crystalline base with a focused laser beam.…”

Focused ion beam milled pattern structures induced by laser pulse on AgInSbTe phase change films

“…The convection flow is almost symmetric, which is in correspondence to the annular distribution of laser energy. The linear thermal expansion coefficient of liquid is about ten times that of the solid [12]. Thus, the molten material has no room to expand because of the closed system.…”

“…These gradients produce radial surface tension gradients, which in turn generate radial convective liquid flows. The C film has a higher melting point than that of AIST [12]. At the beginning of the process, the surface AIST material is heated to melt.…”

“…The structures in above mentioned are tapered or dome shaped, or even jet shaped, due to volume expansion of the material under laser irradiation. Recently, chalcogenide phase change materials, usually used as optical and electronic data storage media because of the differences in electrical conducting between the crystalline and amorphous states [11], were also found to exhibit similar tapered morphologies upon laser irradiation [12]. Different models have been proposed to explain the formation mechanism of the structures, such as Marangoni convection flow of the melted material [13], material evaporation of the thin film [14], thermoplastic deformation of the film [15], and photomechanical spallation of the upper film [16].…”