Modification of Ge₂Sb₂Te₅ by the Addition of SiO_x for improved operation of phase change random access memory

Conventional Ge₂Sb₂Te₅ (GST) was modified by adding up a small amount of SiO_x, using co-sputtering technique from multiple targets. The SiO_x content was gradually increased by increasing the power applied to SiO_x target, up to 8 volume percent. The sheet resistance of SiO_x-containing GST exponentially increased, when the room-temperature-deposited samples were annealed at 300°C. Transmission electron microscopy images revealed that no SiO_x particulates were formed, which was confirmed by Gattan image filtering. It was indicated by x-ray diffraction patterns that the grain size of SiO _x-containing GST is smaller than normal GST with lattice locally distorted at its crystalline state, suggesting that molecular SiO_x is homogeneously distributed throughout the GST matrix. We observed that the crystallization temperature of SiO_x-containing GST is gradually elevated by increasing the SiO_x content, while the melting point decreased. These observations led to the reset current reduction, which is a critical requirement for the high density PRAM.