Suppressed resistance drift from short range order of amorphous GeTe ultrathin films

Abstract

The nanosize confined effect is believed to contribute to improving the resistance drift in nanophase change devices. However, the smaller dimension of device designs is limited by plane lithography techniques. Phase change memory with a confined thickness of ultrathin GeTe layers is fabricated to overcome the limit of current plane lithography. Those memory cells composed of two-dimensional materials present a suppressed resistance drift in their amorphous phase. The drift exponent ν is reduced to 0.05 for 3 nm GeTe layers. Combined with Raman spectroscopy and ab initio molecular dynamics simulations, the structural relaxation process is described as the decay of tetrahedral-bonded sites. Tetrahedrons in ultrathin films are more stable than those in bulk materials. The local motifs of amorphous GeTe ultrathin films are covalently bonded and highly ordered in a short range. The majority of highly ordered tetrahedral clusters prevents spontaneous structural relaxation and leads to high stability in amorphous states, which helps to stop intrinsic fluctuations in physical properties of SET and RESET states, without an extra processing cost.