2, Japan Synchrotron Radiation Research Institute (JASRI), SPring-8, Mikazuki, Hyogo, Japan
In a world of increasing demand for energy-efficient and portable devices, the need for fast, non-volatile memory continues to grow. The advent of interfacial phase change memory based upon van der Waals (vdW)-bonded GeTe/Sb2Te3 superlattices (SL) has yielded order of magnitude faster switching rates and lower energy consumption compared with comparable alloy-based devices and now constitutes a major new research area in phase-change memory (PCM). Unlike conventional alloy-based PCM where the SET and RESET states correspond to the crystalline and amorphous phases, in SLs both the SET and RESET states remain crystalline. While in earlier work the superior performance of SLs was attributed with the reduction of entropic loses associated with the quasi one-dimension motion of Ge atoms across GeTe/Sb2Te3 interfaces, recent experimental transmission electron microscopy studies have revealed that the GeTe and Sb2Te3 blocks intermix during the growth of the GeTe phase challenging the initial conclusion and raising new fundamental issues. In the current work, we suggest that the switching process is associated with the reconfiguration of vdW gaps along with concomitant deviations in the local stoichiometry from the GeTe/Sb2Te3 quasibinary alloys. The proposed model resolves the existing controversies and at the same time explains why the large conductivity contrast between the SET and RESET states is unaffected by Ge/Sb intermixing while providing a new perspective for the development of SL-based PCM. The proposed concept of vdW gap reconfiguration bay also be applicable to designing a wide range of engineered two-dimensional solids.