Carbon doping in InSbTe alloys for thermal stable phase transformations

Carbon doping in InSbTe alloys for thermal stable phase transformations
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We have doped carbon atoms in the InSbTe (IST) alloys and investigated phase change mechanism and electrical performance of multi level cell (MLC) phase change random access memory (PRAM). Among Te based chalcogenide materials, the IST has been already reported as a promising candidate for MLC-PRAM. However, during the phase transformation process migrations of vacancies and atom generate voids and volume change in the IST, which may result in failure of retention and resistance drift. Increasing the C concentration from 0 to 8.4, and 12.5 at.% glass transition temperature increases from 300 to 370, and 440℃, respectively. The activation energy is also increased from 5.138, to 5.278 and 5.398 eV. High resolution transmission electron microscopy shows that the C atoms form C graphite planes, which interrupts inter-diffusion between the the InSb and the InTe planes to form the InSbTe phase since the C atoms prevent the atomic migrations via the vacancy sites while changing the crystal structure from amorphous to metastable FCC structure. Therefore, it is plausible that the phase transformation needs more energy as increasing the C concentration, and volume change of the C doped IST is reduced by about 30 % comparing the undoped IST. In addition, the resistance drift is completely prevented by the C doping, and switching speed of the C doped IST-PRAM is also not sensitive to the C doping. The reason is ascribed to the micro spherical InSb grains distributed along the bottom to the top phase change volume because switching takes place through these 7-15nm size InSb crystalline grains. In this work, we will discuss the atomic lattice image in detail and electrical performance of MLC-PRAM.
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