Understanding the switching mechanism of interfacial phase change memory

Abstract

Phase Change Memory (PCM) is a leading candidate for next generation data storage, but it typically suffers from high switching (RESET) current density (20–30 MA/cm2). Interfacial Phase Change Memory (IPCM) is a type of PCM using multilayers of Sb2Te3/GeTe, with up to 100× lower reported RESET current compared to the standard Ge2Sb2Te5-based PCM. Several hypotheses involving fundamentally new switching mechanisms have been proposed to explain the low switching current densities, but consensus is lacking. Here, we investigate IPCM switching by analyzing its thermal, electrical, and fabrication dependencies. First, we measure the effective thermal conductivity (∼0.4 W m−1 K−1) and thermal boundary resistance (∼3.4 m2 K GW−1) of Sb2Te3/GeTe multilayers. Simulations show that IPCM thermal properties account only for an ∼13% reduction of current vs standard PCM and cannot explain previously reported results. Interestingly, electrical measurements reveal that our IPCM RESET indeed occurs by a melt-quench process, similar to PCM. Finally, we find that high deposition temperature causes defects including surface roughness and voids within the multilayer films. Thus, the substantial RESET current reduction of IPCM appears to be caused by voids within the multilayers, which migrate to the bottom electrode interface by thermophoresis, reducing the effective contact area. These results shed light on the IPCM switching mechanism, suggesting that an improved control of layer deposition is necessary to obtain reliable switching.