Electrical Characterization of Nonvolatile Phase-Change Memory Devices Using Sb-Rich Ge–Sb–Te Alloy Films

概要

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We modified the composition of Ge–Sb–Te alloys for phase-change-type nonvolatile memory devices to realize more reliable memory operations. It is expected that the stability of the low-resistance crystalline phase of the Ge–Sb–Te alloy can be improved when an appropriate amount of excess Sb is added to conventional stoichiometric Ge2Sb2Te5 (GST), because a phase transition directly occurs from the amorphous phase to the more conductive hcp phase without the formation of the less conductive metastable fcc phase. Phase-change memory devices using Sb-rich Ge–Sb–Te alloys were fabricated, where the Sb atomic ratio was controlled to be from 31 to 47%. The effect of Sb addition to GST on the phase-change switching characteristics was investigated in terms of the electrical behaviors of the fabricated memory devices. For the set operations, the threshold voltage ($V_{\text{th}}$) for electronic switching and the required current for set were observed to decrease with increasing Sb composition. The data endurance of memory devices under repetitive operations was measured to be in the range from $1\times 10^{5}$ to $2\times 10^{6}$ cycles. From the investigations using energy dispersive X-ray spectroscopy (EDS), it was clearly shown that there was no phase separation and/or marked compositional change of the device experiencing $2\times 10^{6}$ successive operations, when the Sb atomic ratio in the Ge–Sb–Te alloy was 39%.
2007-11-15