Tungsten added Sb80Te20 for phase-change RAM

Sb-80 Te-20 has the merit of high crystallization speed yet with low crystallization temperature (T-infinity similar to 132 degrees C), 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 Sb80Te20 show increased T-infinity up to 233 degrees C with increasing W. More important, the melting temperature of W-Sb-Te materials, 536-539 degrees C irrespective of W content, is more than 80 degrees C lower than that of Ge2Sb2Te5. 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.