Materials for phase-change memory with elevated temperature stability

Thermal stability is one of the key issues in phase-change memory. We try to tackle it by developing new compositions based on Ga-Te-Sb system. Thermal stability is exemplified using Ga 18 Te 12 Sb 70 which shows crystallization-temperature (T x ) 248°C and activation energy of non-isothermal crystallization 5.9 eV. Films were isothermally soaked at 5 ∼ 30°C below T x to estimate the failure-time when electrical resistance dropped to a half of the original. Arrhenius plot attained using logarithm failure-time versus reciprocal temperature were extrapolated to the temperature corresponding to 10-year failure (T 10y ) as 183°C. Pre-crystallization structure upon heating to 2∼5°C below T x reflects stable amorphous phase of the alloy up to at least 240°C. Memory-cells made of Ga 18 Te 12 Sb 70 can be set-reset at 20 ∼ 500 ns with electrical currents around 66% those of our Ge 2 Sb 2 Te 5 cells. We suggest that compositions Ga 18-25 Te 8-12 Sb 67-70 are optimal to ensure T x > 240°C, T 10y > 180°C and with low operation-currents.