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.

The dependence of thermal properties of Ag 8 In 14 Sb 55 Te 23 phase-change memory materials in crystalline and amorphous states on temperature was measured and analyzed. The results show that in the crystalline state, the thermal properties monotonically decrease with the temperature and present obvious crystalline semiconductor characteristics. The heat capacity, thermal diffusivity, and thermal conductivity decrease from 0.35 J/g K, 1.85 mm 2 /s, and 4.0 W/m K at 300 K to 0.025 J/g K, 1.475 mm 2 /s, and 0.25 W/m K at 600 K, respectively. In the amorphous state, while the dependence of thermal properties on temperature does not present significant changes, the materials retain the glass-like thermal characteristics. Within the temperature range from 320 K to 440 K, the heat capacity fluctuates between 0.27 J/g K and 0.075 J/g K, the thermal diffusivity basically maintains at 0.525 mm 2 /s, and the thermal conductivity decreases from 1.02 W/m K at 320 K to 0.

In this work, we propose nonlinear absorption and melt-ablation threshold characteristics induced subwavelength direct laser writing. The writing materials need to have two features: one is strong nonlinear absorption, and the other is melt-ablation threshold characteristics. According to the strong nonlinear absorption and melt-ablation threshold characteristics of AgInSbTe thin films, the effective energy absorption spot is calculated. The results indicate that the full width at half maximum of the effective energy absorption spot is about 2/5 the original spot. If only the energy intensity above 80% maximum can induce the melt-ablation, the direct laser writing mark size or linewidth can be reduced to 0.14λ/NA (NA denotes numerical aperture), which is only about 0.115 times the original spot size. The calculated results are verified, where the mark size is reduced to about 1/8 the real spot.