Physical properties of the intermediate states of multilevel phase change memories for neuromorphic devices – INTERSTATE

We want to demonstrate the possibility of programming phase change memories (PCMs) based on a nitrogen-doped germanium-rich GeSbTe alloy (NG-GST) in several states, with an electrical resistance intermediate between those of the extrem SET and RESET states of the device (intermedate resistance states, IRS) and with a low resistance drift over time. This would allow to propel into the neuromorphic era an already existing advanced digital platform fabricated by our partner STMicroelectronics. A deep understanding of the physical properties (from the atomic to the device scales) of the IRS is required to successfully control the formation of several distinguishable IRS with a good stability in time. We aim at understanding: 1-which kinds of conduction paths must be opened in the NG-GST layer for each of the targeted IRS, 2-which precise micro/nanostructure of this layer must be reached to open these specific conduction paths and 3-which sequence of electric current pulses must be applied to get this microstructure. This understanding can only be achieved by combining the complementary set of techniques and scientific skills offered in the INTERSTATE project: measurement of the atomic and chemical structure down to the nanoscale, measurement of the static and dynamic transport properties, multiscale simulation of the physical properties. The results that we will obtain from our investigations at the border between materials science and physical properties will pave the way towards futur developments on brain-inspired electronic devices working at high temperature and are a prerequisite before future investigations on the programming strategies adapted to specific neuromorphic or AI application.