Ultrafast switching in nanoscale phase-change random access memory with superlattice-like structures

Abstract

Phase-change random access memory cells with superlattice-like (SLL) GeTe/Sb(2)Te(3) were demonstrated to have excellent scaling performance in terms of switching speed and operating voltage. In this study, the correlations between the cell size, switching speed and operating voltage of the SLL cells were identified and investigated. We found that small SLL cells can achieve faster switching speed and lower operating voltage compared to the large SLL cells. Fast amorphization and crystallization of 300 ps and 1 ns were achieved in the 40 nm SLL cells, respectively, both significantly faster than those observed in the Ge(2)Sb(2)Te(5) (GST) cells of the same cell size. 40 nm SLL cells were found to switch with low amorphization voltage of 0.9 V when pulse-widths of 5 ns were employed, which is much lower than the 1.6 V required by the GST cells of the same cell size. These effects can be attributed to the fast heterogeneous crystallization, low thermal conductivity and high resistivity of the SLL structures. Nanoscale PCRAM with SLL structure promises applications in high speed and low power memory devices.

Nano Superlattice-like Materials as Thermal Insulators for Phase-Change Random Access Memory

“…This indicates an overall good thermal confinement in both the in-and cross-plane directions, with a slight dominance of the interface scattering mechanism in the cross-plane direction. The PT difference (between the in-and cross-plane directions at low thermal conductivity) of the SLL dielectric is also observed to be smaller than that of the GeTe/Sb 2 Te 3 SLL material that we have reported earlier [12]. A smaller PT difference would indicate a better control of the heat flow within the cell structure.…”

Photo-induced oxidation and amorphization of trigonal tellurium: A means to engineer hybrid nanostructures and explore glass structure under spatial confinement

“…Recent trends in Ge-Sb-Te materials to be used as phase-change memories are directed towards miniaturizing the memory cell size down to few tens of nm's, i.e., less than 40 nm. 41 Therefore, laser-assisted fabrication of low-dimensional chalcogenide structures might prove essential for obtaining materials with significantly improved phase-change characteristics desirable for power-efficient memories.…”

Phase change memory (PCM) materials and devices

“…Materials that show very fast switching in laser testing experiments include the Ge:Sb:Te = 1 × 1 alloys with large x, such as Ge:Sb:Te = 1:6:1 (Cheng et al 2010b). Fortunately, the scaling behavior for PCM cells is in favor of fast switching and smaller PCM cells have shorter crystallization times, which can be on the 1 ns timescale (Bruns et al 2009;Loke et al 2011;Wang et al 2009). Ultrafast switching in 500 ps for both set and reset operation was recently demonstrated using a special programming scheme (Loke et al 2012).…”