Mechanical properties of phase-change recording media: GeSbTe films

Mechanical properties of as-deposited GeSbTe media on SiO2/Si(100) with different compositions and film thicknesses were successfully investigated by using the microcantilever method and nanoindentation. All the studied films show a compressive residual stress state, which increases proportionally to the elastic constant. Because of the accumulating effects during film deposition, the mechanical properties of these GeSbTe films can be greatly affected. As the film thicknesses were 20 and 25 nm, compared with the Ge4SbTe5 and Ge4Sb0.5Te5Bi0.5 films, the Ge2Sb2Te5 film has the highest residual stress value ranging from 3 MPa to 15 MPa. When the film thickness was 30 nm, the composition-induced stress relaxation occurred. Bi addition, which leads to lattice expansion in Ge4SbTe5 films, resulted in a decrease of stress. Compared with the Ge4SbTe5 and Ge4Sb0.5Te5Bi0.5 films, the Ge2Sb2Te5 film also has the lowest coefficient of thermal expansion (CTE) value ranging from 2 x 10(-6) to 7 x 10(-6)/degreesC, and a lower CTE was obtained when the film thickness was increased. By nanoindentation, the Ge4SbTe5 film shows higher hardness and elastic constant than those of the Ge2Sb2Te5 film. The measured hardnesses for Ge2Sb2Te5 and Ge4SbTe5 films are 12 GPa and 18 GPa; and the reduced elastic modului are 120 GPa and 140 GPa, respectively.