Study of Ge_2Sb_2Te_5 Film for Nonvolatile Memory Medium

摘要

The amorphous Ge_2Sb_2Te_5 film with stoichiometric compositions was deposited by co-sputtering of separate Ge, Sb, and Te targets on SiO_2/Si (100) wafer in ultrahigh vacuum magnetron sputtering apparatus. The crystallization behavior of amorphous Ge_2Sb_2Te_5film was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). With an increase of annealing temperature, the amorphous Ge_2Sb_2Te_5 film undergoes a two-step crystallization process that it first crystallizes in face-centered-cubic (fee) crystal structure and finally fee structure changes to hexagonal (hex) structure. Activation energy values of 3.636+ -0.137 and 1.579+ -0.005 eV correspond to the crystallization and structural transformation processes, respectively. From annealing temperature dependence of the film resistivity, it is determined that the first steep decrease of the resistivity corresponds to crystallization while the second one is primarily caused by structural transformation from "fee" to "hex" and growth of the crystal grains. Current-voltage (I-V) characteristics of the device with 40 nm-thick Ge_2Sb_2Te_5 film show that the Ge_2Sb_2Te_5film with nanometer order thickness is still applicable for memory medium of nonvolatile phase change memory.