Tungsten Added Sb$_{80}$Te$_{20}$ for Phase-Change RAM

Sb
₈₀
Te
₂₀
has the merit of high crystallization speed yet with low crystallization temperature (T
_x
~132degC), and hence, not suitable for use as a medium of phase change random access memory (PCRAM). We proposed to add refractory metals to solve this problem. It was found that W-added Sb
₈₀
Te
₂₀
show increased T
_x
up to 233degC with increasing W. More important, the melting temperature of W-Sb-Te materials, 536-539degC irrespective of W content, is more than 80degC lower than that of Ge
₂
Sb
₂
Te
₅
. They show a two to four orders of magnitude lowering in resistance during phase change from an amorphous to a crystalline state. With these promising properties, the composition Sb
₈₀
Te
₁₇
W
₃
is recommended as a potential candidate for PCRAM