Heshan Yu1,Changming Wu2,Huairuo Zhang3,Asir Intisar Khan4,Albert Davydov3,Apurva Mehta5,Eric Pop4,Mo Li2,Ichiro Takeuchi1
University of Maryland1,University of Washington2,National Institute of Standards and Technology3,Stanford University4,Stanford Synchrotron Radiation Lightsource5
Heshan Yu1,Changming Wu2,Huairuo Zhang3,Asir Intisar Khan4,Albert Davydov3,Apurva Mehta5,Eric Pop4,Mo Li2,Ichiro Takeuchi1
University of Maryland1,University of Washington2,National Institute of Standards and Technology3,Stanford University4,Stanford Synchrotron Radiation Lightsource5
As one of the most promising candidates for developing neuromorphic architectures for non-von Neumann computing and information storage, phase-change memory materials in both photonic and electronic devices show non-volatile, fast, and multi-level switching between the amorphous and metastable states. With the assistance of machine learning methodology, in particular, a closed-loop autonomous system and a clustering method, we systematically perform combinatorial exploration on a broad composition range of M-Sb-Te ternary systems, where M is a transition metal. The composition spreads are fabricated by the co-sputtering method, and their composition ranges are measured by wavelength dispersive spectroscopy across the Si spread wafers. To identify optimized compositions out of these spreads, X-ray diffraction measurements (synchrotron radiation), Raman spectroscopy, resistance and optical mapping are carried out in order to determine the evolution of structure and other properties. One composition we identified is Ti<sub>0.3</sub>SbTe<sub>2</sub>, which shows a higher phase-change temperature and a lower melting point compared to the widely-used Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub> (GST225). It also has the largest bandgap contrast between the amorphous and crystalline phases within the Ti-Sb-Te (TST) spread. Scanning transmission electron microscope (STEM) measurements indicate that Ti<sub>0.3</sub>SbTe<sub>2</sub> is an epitaxial nanocomposite where TiTe<sub>2</sub> nanograins have grown homogenously inside the TST matrix. We believe TiTe<sub>2</sub> nanoprecipitates can play the role of a precursor in phase transformation. Both photonic and electrical devices fabricated using this nanocomposite phase-change memory material show clear multi-level symmetric switching with low resistance drift and low quenching energy. These results suggest that this composition can be promising for neuromorphic devices. This work is funded by an ONR MURI (Award No. N00014-17-1-2661) and nCORE (Task 2966.010).