Direct observation of amorphous to crystalline phase transitions in nanoparticle arrays of phase change materials

Abstract

We have used time-resolved x-ray diffraction to study the amorphous-crystalline phase transition in 20–80nm particles of the phase change materials Ge2Sb2Te5, nitrogen-doped Ge2Sb2Te5, Ge15Sb85, Sb2Te, and Sb2Te doped with Ag and In. We find that all samples undergo the phase transition with crystallization temperatures close to those of similarly prepared blanket films of the same materials with the exception of Sb2Te that shows the transition at a temperature that is about 40°C higher than that of blanket films. Some of the nanoparticles show a difference in crystallographic texture compared to thick films. Large area arrays of these nanoparticles were fabricated using electron-beam lithography, keeping the sample temperatures well below the crystallization temperatures so as to produce particles that were entirely in the amorphous phase. The observation that particles with diameters as small as 20nm can still undergo this phase transition indicates that phase change solid-state memory technology should scale to these dimensions.

Liquid-Phase Synthesis of Uniform Cube-Shaped GeTe Microcrystals

“…9 Widespread use of phase change technologies that operate via differential resistivity, however, still relies critically on optimizing material parameters that govern the speed, cyclability, and power consumption of devices. 7,10, 11 Many technologically relevant phase-change materials are located on the ternary Ge-Sb-Te phase diagram, including alloys along the pseudobinary GeTe-Sb 2 Te 3 tie line, Ge 15 Te 85 , and doped Sb 2 Te. 11 Recent synthetic routes to these materials have largely focused on sputter deposition and lithographical patterning of phase-change films.…”

GeTe-filled Carbon Nanotubes for Data Storage Applications

“…The dimensionality of these systems ranges from thin films [9] to nanowires [13] and to nanoparticles [14]. Diameters of phase change nanowires previously synthesized range between 200 nm to 20 nm and depend on the size of the catalyst particle.…”

Electrical switching dynamics in circular and rectangular Ge2Sb2Te5 nanopillar phase change memory devices

“…Following the original work of Ovshinsky 1 , the reversible switching phenomena observed in disordered semiconductors has attracted substantial theoretical 2,3,4,5,6,7 and experimental 8,9,10,11,12,13 efforts targeted at gaining a deep understanding of the physical principles that govern the switching dynamics, and also learning how to control and optimize the power requirements coupled with characteristic switching timescales. Dramatic and ultra-fast (nanosecond scale) changes in the physical properties such as electrical resistivity and optical reflectivity upon amorphization or crystallization makes chalcogenides ideal potential candidates for a universal non-volatile memory device, especially if, the device switching characteristics are highly scalable to nanometer dimensions.…”