Study On The Sb-Se Based Nanomaterials For Low-power Phase Change Random Access Memory

Phase-change random access memory(PCRAM)has attracted growing attention due to its fast reading speed,good miniaturization and nonvolatile properities.At the same time,relative poor data retention and higher power consumption limit its application.As one of the phase change storage medium,Sb-Se materials with its low thermal conductivity and low melting point can effectively reducing power consumption.In this paper,the microstructures of Sb-Se-based nanofilms and nanowires are studied in order to optimize the phase change materials and improve the density of the devices.This article mainly includes two parts: First of all,a series of Sb-Te-Se films were prepared using Sb2Se3 and Sb2 Te targets by magnetron co-sputtering method.The electrical properties and microstructures of Sb-Te-Se films were systematically studied.Here are the results:(1)With increasing Se content,Tc raises from 150 ? for Sb60Te31Se9 to 180 ? for Sb55Te22Se23.Both amorphous and crystalline resistivities increase with Se content,which is favorable for low power consumption.The temperatures for 10-year data retention of Sb60Te31Se9,Sb57Te26Se17,Sb56Te24Se20 and Sb55Te22Se23 films are 75.4,84.1,93.1 and 102.6?,respectively.The composition of Sb60Te31Se9 is unsuitable for PCM device due to relatively poor thermal stability.Other compositions in this study have a better thermal stability than Ge2Sb2Te5(82?C).It indicates that the increasement of Se content can significantly improve the archival life of the amorphous Sb-Te-Se films.(2)The characteristic peak of Sb is observed only for Sb60Te31Se9 and Sb60Te31Se9 films at 300 ?.For Sb56Te24Se20 and Sb55Te22Se23 films,with increasing annealing temperature to 300 ?,rhombohedra Sb2 Se Te2 and hexagonal Sb phase can be found.The black particles which are crystallized after annealing with a size of several tens of nanometers are uniformly distributed in the film.(3)Se atoms in Sb Se3/2 enter into Sb-Te and form chemical bonds with Te.Thus,rhombohedra Sb2 Se Te2 and hexagonal Sb phase can be found in XRD patterns.The bond recombination accounts for the enhancing crystallization temperature for Sb-Te-Se films with higher Se concentration.Meanwhile,Ge-Sb-Se nanowires were prepared by hot-vapor deposition(VLS)in a double-temperature horizontal tube furnace.The effects of carrier gas flow rate,growth temperature and growth distance on the nanowire morphology were systematically studied.The results are as follows:(1)The result indicates that the most suitable position for the growth of nanowires is 7cm away from the evaporation source at 100 Torr,400? and 100 SCCM of carrier gas.(2)The morphology of Ge-Sb-Se nanowires does not change when growing between 400 ? and 450 ?,and the diameter increases with the temperature increasing.With the increasement of temperature,the diffraction peaks of nanowires were Ge Sb2 and Sb2Se3,indicating that the growth temperature had effect on the diameter of Ge-Sb-Se nanowires.(3)As the carrier gas rate increases,the growth of the nanowires becomes more dense.Because the larger gas flow rate can bring more gaseous raw materials to the growth area,and the excess reactants are integrated into the substrate to the Au droplets of the catalyst and deposited.That makes more rapid of the growth of nanowires.