Improved thermal and electrical properties of Al-doped Ge ₂Sb ₂Te ₅ films for phase-change random access memory

Al _x(Ge ₂Sb ₂Te ₅) _100-x materials with different Al contents are systemically studied for applications in phase-change random access memory (PRAM) devices. Al-doped Ge ₂Sb ₂Te ₅ (GST) films show better thermal stability than GST because they do not have phase transformation from face-centred cubic (fcc) to hexagonal at high annealing temperatures. As the Al content increases, the resistance in both amorphous and crystalline phases improves and there is four to five orders of magnitude difference in the resistance between the amorphous and crystalline phases, all of which are helpful in achieving a higher On/OFF ratio for PRAM. In addition, the introduction of Al into the GST films can increase the optical band gap that is favourable to decrease the threshold current of PRAM devices. Raman spectra show that a significant change in the local bonding arrangement around Sb atoms has occurred due to the phase transformation from fcc to hexagonal in the GST film but this can be suppressed by Al addition during the crystallization process. All these results confirm that Al-doped GST films are suitable for use in PRAM.