Toward the ultimate limit of phase change in Ge₂Sb ₂Te₅

The limit to which the phase change memory material Ge₂Sb ₂Te₅ can be scaled toward the smallest possible memory cell is investigated using structural and optical methodologies. The encapsulation material surrounding the Ge₂Sb₂Te ₅ has an increasingly dominant effect on the material's ability to change phase, and a profound increase in the crystallization temperature is observed when the Ge₂Sb₂Te₅ layer is less than 6 nm thick. We have found that the Increased crystallization temperature originates from compressive stress exerted from the encapsulation material. By minimizing the stress, we have maintained the bulk crystallization temperature in Ge₂Sb₂Te₅ films just 2 nm thick,