Ti–Sb–Te Alloy: A Candidate for Fast and Long-Life Phase-Change Memory

Phase-change memory (PCM) has great potential for numerous attractive applications on the premise of its high-device performances, which still need to be improved by employing a material with good overall phase-change properties. In respect to fast speed and high endurance, the Ti–Sb–Te alloy seems to be a promising candidate. Here, Ti-doped Sb<sub>2</sub>Te<sub>3</sub> (TST) materials with different Ti concentrations have been systematically studied with the goal of finding the most suitable composition for PCM applications. The thermal stability of TST is improved dramatically with increasing Ti content. The small density change of T<sub>0.32</sub>Sb<sub>2</sub>Te<sub>3</sub> (2.24%), further reduced to 1.37% for T<sub>0.56</sub>Sb<sub>2</sub>Te<sub>3</sub>, would greatly avoid the voids generated at phase-change layer/electrode interface in a PCM device. Meanwhile, the exponentially diminished grain size (from ∼200 nm to ∼12 nm), resulting from doping more and more Ti, enhances the adhesion between phase-change film and substrate. Tests of TST-based PCM cells have demonstrated a fast switching rate of ∼10 ns. Furthermore, because of the lower thermal conductivities of TST materials, compared with Sb<sub>2</sub>Te<sub>3</sub>-based PCM cells, T<sub>0.32</sub>Sb<sub>2</sub>Te<sub>3</sub>-based ones exhibit lower required pulse voltages for Reset operation, which largely decreases by ∼50% for T<sub>0.43</sub>Sb<sub>2</sub>Te<sub>3</sub>-based ones. Nevertheless, the operation voltages for T<sub>0.56</sub>Sb<sub>2</sub>Te<sub>3</sub>-based cells dramatically increase, which may be due to the phase separation after doping excessive Ti. Finally, considering the decreased resistance ratio, Ti<sub><i>x</i></sub>Sb<sub>2</sub>Te<sub>3</sub> alloy with <i>x</i> around 0.43 is proved to be a highly promising candidate for fast and long-life PCM applications.