Crystallization properties of ultrathin phase change films

The crystallization behavior of ultrathin phase change films was studied using time-resolved x-ray diffraction (XRD). Thin films of variable thickness between 1 and 50 nm of the phase change materials Ge2Sb2Te5 (GST), N-doped GST, Ge15Sb85, Sb2Te, and Ag- and In-doped Sb2Te were heated in a He atmosphere, and the intensity of the diffracted x-ray peaks was recorded. It was found for all materials that the crystallization temperature increases as the film thickness is reduced below 10 nm. The increase depends on the material and can be as high as 200 degrees C for the thinnest films. The thinnest films that show XRD peaks are 2 nm for GST and N-GST, 1.5 nm for Sb2Te and AgIn-Sb2Te, and 1.3 nm for GeSb. This scaling behavior is very promising for the application of phase change materials to solid-state memory technology. (C) 2008 American Institute of Physics.