Regular Article

Ultrascalability and electron transport properties of ultra-thin film phase change material Ge₂Sb₂Te₅

¹ Department of Physics, Kharazmi University, 15719-14911 Tehran, Iran
² Department of Physics, Payame Noor University (PNU), 19395-3697 Tehran, Iran
³ Department of Physics, Iran University of Science and Technology, Narmak 16345, Tehran, Iran

^a e-mail: aashokri@nano.ipm.ac.ir

Received: 11 July 2019
Received in final form: 10 September 2019
Published online: 25 December 2019

Abstract

In the present work, we have used ab initio molecular dynamics (AIMD) and non-equilibrium Green’s function (NEGF) formalism to investigate the scaling behavior of electron transport in ultra-thin films of Ge₂Sb₂Te₅ (GST). The relation between the thickness of GST and its electron transport properties are studied in both crystalline (c-GST) and amorphous (a-GST) phases. For thin films with lower than 36 Å thickness, we have observed a dramatic increase in the conductivity of the amorphous phase and an associated reduction in the conductance contrast between the two phases. Metal-induced gap states (MIGS) near the electrodes are observed in the density of states and the transmission coefficient of a-GST. The disappearance of the bandgap of a-GST due to the overlap of MIGS is responsible for the sharp reduction of crystalline to amorphous conductance ratio (ON/OFF). The ON/OFF ratio of the devices is about one order of magnitude upon downscaling the ultra-thin film of the active bit to 36 Å. This estimation is the ultimate scalability for the simulated PCM device. When the thickness of GST further scales down, the reliable read operation is not possible. Our results show very good agreement with experimental work and it seems promising to engineers and designers of ultra-thin PCM devices.