Materials engineering for Phase Change Random Access Memory

Crystallization properties of the phase change materials GeSb_xTe and Ge_xSb₂Te were studied. For GeSb_xTe we found that for large x = 6 the crystallization was very fast but crystallization temperature was low while for small x = 1 crystallization was slow but crystallization temperature was high. An alloy with a good compromise between crystallization time and temperature can be found at x = 4.6, with still very fast crystallization (about 50 ns) and high crystallization temperature of 200 ^oC. Time resolved x-ray ray diffraction shows that these alloys crystallize in a single rhombohedral phase similar to Sb. For Ge_xSb₂Te we found that alloys richer in Ge have higher crystallization temperatures. Ge-rich alloys also have higher resistances in the amorphous phase and a larger electrical contrast. They crystallize in the hexagonal Sb₂Te phase. For both materials system alloys with the highest Ge content show the appearance of the Ge(111) diffraction peak indicative of elemental segregation.