Improvement of reliability and speed of phase change memory devices with N_7.9(Ge_46.9Bi_7.2Te_45.9) films

In this study, we propose a nitrogen-incorporated GeBiTe ternary phase of N_7.9(Ge_46.9Bi_7.2Te_45.9) as a phase change material for reliable PCM (Phase Change Memory) with high speed operation. We found that the N_7.9(Ge_46.9Bi_7.2Te_45.9) film shows the resistance value of 40 kΩ after annealing at 440^oC for 10 minutes, which is much higher than the value of 3.4 kΩ in the case of conventional N_7.0(Ge_22.0Sb_22.0Te_56.0) films. A set operation time of 14 nsec was achieved in the devices due to the increased probability of the nucleation by the addition of the elemental Bi. The long data retention time of 10 years at 85^oC on the base of 1% failure was obtained as the result of higher activation energy of 2.52 eV for the crystallization compared to the case of N_7.0(Ge_22.0Sb_22.0Te_56.0) film, in which the activation energy is 2.1 eV. In addition, a reset current reduction of 27% and longer cycles of endurance as much as 2 order of magnitude compared to the case of N_7.0(Ge_22.0Sb_22.0Te_56.0) were observed at a set operation time of 14 nsec. Our results show that N_7.9(Ge_46.9Bi_7.2Te_45.9) is highly promising for use as a phase change material in reliable PCMs with high performance and also in forthcoming storage class memory applications, too.