The effect of carbon nanotube electrodes on electron transport properties of nanowire phase change material Ge[formula omitted]Sb[formula omitted]Te[formula omitted]

Abstract

The present work studied the scalability of phase change material (PCM) down to a single-digit nm with single wall metallic carbon nanotubes (SWCNT) electrodes. For this purpose, the low bias electron transport properties of Ge2Sb2Te5 (GST) are investigated using a DFT–NEGF formalism. The amorphous Ge2Sb2Te5 (a-GST) is obtained using DFT-based molecular dynamic simulation. It has been seen that while 6 nm crystalline Ge2Sb2Te5 (c-GST) has a large transmission near the Fermi level, a-GST exhibits a clear band-gap, and by further reduction of its length to 12 Å, the band-gap disappears. The electrical conductance of nanowire a-GST is predominantly due to coherent electron transport via acceptor-like and donor-like traps. The c-GST/a-GST conductance (Gc/Ga) ratio as a function of the device length is calculated, which shows good agreement compared with experimental works. We show that the ultimate limit for downscaling the nanowire GST sandwiched between SWCNT electrodes is about 24 Å . This can be attributed to the overlapping metal-induced gap states from electrodes that lead to the disappearance of the band-gap of the amorphous phase and a sharp decrease in the Gc/Ga ratio in shorter channel length. The On/Off ratio of 12 Å GST sharply drops below 10, and the reliable read procedure is not possible on this size scale. We have also investigated the effect of interfacial stress between the electrode and GST and show that it reduces the Gc/Ga ratio and hurts the switch-ability of the device.