Ion-Induced Phase Changes in 2D MoTe₂ Films for Neuromorphic Synaptic Device Applications

Two-dimensional molybdenum ditelluride (2D MoTe₂) is an interesting material for artificial synapses due to its unique electronic properties and phase tunability in different polymorphs 2H/1T′. However, the growth of stable and large-scale 2D MoTe₂ on a CMOS-compatible Si/SiO₂ substrate remains challenging because of the high growth temperature and impurity-involved transfer process. We developed a large-scale MoTe₂ film on a Si/SiO₂ wafer by simple sputtering followed by lithium-ion intercalation and applied it to artificial synaptic devices. The Al₂O₃ passivation layer allows us to develop a stable 1T′-MoTe₂ phase by preventing Te segregation caused by the weak bonding between Mo and Te atoms during lithiation. The lithiated MoTe₂ film exhibits excellent synaptic behavior such as long-term potentiation/depression, a high I_on/I_off ratio (≈10³) at lower sweep voltage, and long-term retention. The in situ Raman analysis along with a systematic microstructural analysis reveals that the intercalated Li ion can provide an efficient pathway for conducting filament formation.