Enhanced Memory Behavior in Phase-Change Nonvolatile-Memory Devices Using Multilayered Structure of Compositionally Modified Ge–Sb–Te Films

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A unique and novel phase-change memory device employing multilayered chalcogenide films was proposed and fabricated. In this structure, Ge18Sb39Te43, which corresponds to a 22 at. % Sb-excessive phase of typical stoichiometric Ge2Sb2Te5 (GST), was located in the middle and acted as the main operating region to exploit its superior properties, thus ensuring reliable memory operations. Thinner GST layers were inserted to above and below the middle layer. The introduction of a bottom GST layer promotes the temperature rise and the thermal insulation within the device operating volume owing to its lower thermal conductivity. The top GST layer effectively suppresses the undesirable interdiffusion between the top electrode of W and the Sb added to excess. Moreover, the upper and lower GST supplementary layers promote the initial crystallization stage during set operations owing to their higher crystallization rate compared with that of the Sb-rich phase of GST. As a result, the required current for reset, the required time for set, and the number of rewritable cycles of the proposed device with an active pore size of $0.5 \times 0.5$ μm2 were 6.1 mA, 80 ns, and $6.4 \times 10^{6}$, respectively, which are superior values compared with those for the device using a single layer of Ge18Sb39Te43. We can conclude that the proposed multilayered structure of compositionally modified GST films provides a very promising approach to enhancing all types of the memory behaviors required for the phase-change memory devices.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2009-04-25

Enhanced Memory Behavior in Phase-Change Nonvolatile-Memory Devices Using Multilayered Structure of Compositionally Modified Ge–Sb–Te Films

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