Effects of carbon doping on thermal stability of InSbTe phase change memory

Effects of carbon doping on thermal stability of InSbTe phase change memory
Issue Date
The 14th Non-Volatile Memory Technology Symposium(NVMTS 2014)
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). Although the IST has been already reported as a promising candidate for MLC-PRAM [1], during the phase transformation process migrations of vacancies and atoms generate voids and volume change in the IST, which may result in device failure [2]. Increasing the C concentration from 0 to 8.4, and 12.5 at.% glass transition temperature from high resistive amorphous to low resistive crystalline state increases from 300 to 370, and 440℃, respectively as shown in Fig. 1. The activation energy is also increased from 5.138, to 5.278 and 5.398 eV. High resolution transmission electron microscopy (Fig.2) shows that voids are not appeared in the C doped IST cell device after multiple set/reset operations since the C atoms prevent the atomic migrations via the vacancy sites while changing the crystal structure from amorphous to metastable FCC structure. Since the bonding energy of In-Sb (151.9±10.5KJ/mol) is smaller than that of In-Te (218.0±17KJ/mol) [3], the InSb seems to be formed at first and the InTe is crystallized late. When the InSb reacted with the InTe, forming the IST, the C atoms prevent the migration of Sb atoms and formation of voids [4]. Increasing the C concentration, the phase transformation needs more energy 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 (7~15nm) distributed in the phase changing volume because current pass through these InSb micro grains. In this work, we will discuss the atomic lattice image in detail and electrical performance of MLC-PRAM.
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