Ab Initio Molecular-Dynamics Simulations of Doped Phase-Change Materials

Ab Initio Molecular-Dynamics Simulations of Doped Phase-Change Materials 

Claverton Down, Bath BA2 7AY, UK e-mail j.m.skelton bath.ac.uk 

Current PCRAM cells have dimensions of the order of a few 10 s of nanometers (although further down-size scaling seems to bepossible, since PC switching between c- and a-states, and vice versa, has been demonstrated down to dimensions of 2 nm [5]), with transformation times of the order of nanoseconds. It is extremely challenging to perform experimental smdies of PC transformations in situ in actual memory cells, at such very small dimensions and very short times, although synchrotron experiments are now approaching this capability. Thus, computer simulations can play an 

All the AIMD simulations that we have performed have been carried out using the Vienna Ab Initio Simulation Package (VASP) [12], which is a plane-wave electronic-structure code using the projector-augmented wave (PAW) method [3], together with the PBE exchange-correlation functional [15]. 

Two types of dopants in (GST) PCRAM materials have been investigated experimentally and computationally. The first class of dopants includes light non-metallic elements, such as C, N, O etc., which are incorporated primarily to improve the crystallization, as well as electrical, properties of PC materials. The second class of dopants includes metallic elements, e.g. transition metals, which can introduce magnetic functionality into the PC process. 

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