Interfacial phase-change memory

Abstract

Phase-change memory technology relies on the electrical and optical properties of certain materials changing substantially when the atomic structure of the material is altered by heating or some other excitation process. For example, switching the composite Ge(2)Sb(2)Te(5) (GST) alloy from its covalently bonded amorphous phase to its resonantly bonded metastable cubic crystalline phase decreases the resistivity by three orders of magnitude, and also increases reflectivity across the visible spectrum. Moreover, phase-change memory based on GST is scalable, and is therefore a candidate to replace Flash memory for non-volatile data storage applications. The energy needed to switch between the two phases depends on the intrinsic properties of the phase-change material and the device architecture; this energy is usually supplied by laser or electrical pulses. The switching energy for GST can be reduced by limiting the movement of the atoms to a single dimension, thus substantially reducing the entropic losses associated with the phase-change process. In particular, aligning the c-axis of a hexagonal Sb(2)Te(3) layer and the 〈111〉 direction of a cubic GeTe layer in a superlattice structure creates a material in which Ge atoms can switch between octahedral sites and lower-coordination sites at the interface of the superlattice layers. Here we demonstrate GeTe/Sb(2)Te(3) interfacial phase-change memory (IPCM) data storage devices with reduced switching energies, improved write-erase cycle lifetimes and faster switching speeds.

Improved structural and electrical properties in native Sb2Te3/GexSb2Te3+x van der Waals superlattices due to intermixing mitigation

“…An impressive achievement has been accomplished when it was realized that PCM memory cells based on superlattices (SLs), structures made of alternating GeTe and Sb 2 Te 3 layers, showed dramatically improved performance in terms of reduced switching energies with ultra-low energy consumption, enhanced write-erase cycle lifetimes, and faster switching speeds. [5][6][7] However, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) investigations carried out on molecular beam epitaxy (MBE) grown Sb 2 Te 3 /GeTe SLs 8 have shown that the constituting materials intermix at the interfaces, forming alternating layers of Sb 2 Te 3 and natural Ge x Sb 2 Te 3+x (GST) 9 blocks with 7-to 15-atomic layers randomly distributed along the growth direction. Such phenomenon, explained in terms of the different bonding dimensionality of GeTe and Sb 2 Te 3 , is thermodynamically driven and therefore it cannot be easily controlled during the growth.…”

Optical switching at 1.55 μm in silicon racetrack resonators using phase change materials

“…A thin film of the phasechange material 10 (PCM) Ge 2 Sb 2 Te 5 (GST), which is commonly encountered in optical and electrical data storage applications [11][12][13][14] , is used to switch the resonant frequency and Q-factor of the microring resonator. GST shows high optical contrast between its amorphous, covalently bonded, and crystalline, resonantly bonded, structural phases [15][16][17][18] (n cryst − n amorph = 2.5 ; k cryst − k amorph = 1 at 1.55 µm) 19 .…”

“…If one considers the out-of-equilibrium nature of the sputter deposition process, then small differences between the optical properties of the as-deposited amorphous state and the laser reamorphized state are to be expected. Indeed it is normally necessary to cycle GST data storage devices more than 100 times before the electrical properties of the amorphous state converge to a stable value 14 . Table II also shows a clear effect of the amorphous to crystalline phase transition on the transmission.…”

Interband characterization and electronic transport control of nanoscaledGeTe/Sb2Te3superlattices

“…[12]. Following this trend, phase-change heterostructures had been produced, showing to function with improved performances [13]. Here we focus on chalcogenide superlattice (CSL) films made by high temperature deposition of alternating nm-size layers of GeTe and Sb 2 Te 3 [14].…”