Improved phase change properties in layered ScxIn2−xSe3 for multilevel information storage

Abstract

Phase change random access memory stores information by utilizing large resistance differences between crystalline and amorphous states of phase change materials (PCM). It would be highly advantageous to realize multilevel devices with single PCM system in nanoscale to improve memory capacity and reduce power consumption. Experimental results verify the possibility of multilevel phase change in two dimensional In2Se3 thin layers with two stable single crystal phases (α and β). Here, we report, the phase change properties of layered In2Se3 can be greatly improved by substitutional doping with Sc atoms based on first-principle calculations together with semiclassical Boltzmann transport theory. The lattice thermal conductivity of both α- and β-ScxIn2−xSe3 are lower than that of the undoped models in the temperature range from 300 K to 700 K. Particularly, of β-Sc0.167In1.833Se3 at 300 K is 0.53 W m−1 K−1, which is reduced by 60% compared to β-In2Se3. The out-of-plane electrical conductivities also show a significant decrease after Sc doping. These results indicate better performance of Sc-doped In2Se3 PCM with minimized thermal crosstalk and lower RESET current. Moreover, we found the resistance difference between α and β phase can become 1–2 orders of magnitude larger in Sc0.167In1.833Se3, which is beneficial for the multilevel programming. The phase change process from α-In2Se3 to its β phase with different Sc doping sites are calculated by ab-initio molecular dynamics simulations. It is found that with the introduction of Sc atoms in tetrahedral sites, phase change speed can be significantly increased. Our studies shed light on the modification of phase change properties of layered In2Se3 with rare earth doping.