Evolution of the conductive filament with cycling in TaOx-based resistive switching devices

Physical changes occurring in TiN/TaO2.0 +/- 0.2/TiN resistive random-access memory devices after prolonged cycling have been analyzed by two scanning transmission electron microscopy modalities: high angle annular dark field and x-ray energy dispersive spectroscopy. In just formed devices, filaments had a shape of a 10nm diameter Ta-enriched column with the O-rich gap next to electrodes, which was positively biased during electroformation. Devices that failed by stuck-in-high resistance state mode exhibited Ta depletion and oxygen interdiffusion at interfaces with both electrodes akin to effects observed in complementary switching devices. Initially narrow Ta-rich filaments broadened into similar to 50nm diameter columns showing speckled contrast due to phase separation. In devices that failed by stuck-in-low resistance state mode, we have observed a strong Ta-enriched sub-filament bridging the gap. The amount of oxygen in the TiN anode in the vicinity of the filament has not changed significantly between as-formed and failed devices, thus indicating that oxygen is not lost during switching. All devices at the end of endurance exhibited interdiffusion of O into TiN and Ti and N into TaOx.