Three Programming States in Bilayer Ga-Sb Phase Change Memory With AlO_xDiffusion Barrier

Tellurium-free antimony-based phase change memory (PCM) alloys have attracted much attention due to their superior attributes such as fast switching speed, wide resistance window, and low drift. However, programming reproducible intermediate states in such PCM materials has been challenging. In this study, bilayer PCM cells comprised of Ga-Sb films with two different compositions separated by a 1-nm-thick AlOx diffusion barrier layer were fabricated on Si foundry templates with a O120-nm TiN heater and TaN top contact. The current-voltage measurements of the cells exhibit two threshold voltages, separating three stable resistance regions. These cells can be controllably switched among three resistance states, that is, the SET (∼ 103Ω), intermediate (∼ 104 Ω), and RESET states ( ∼ 5× 105Ω). The phase transitions during switching among three resistance states are discussed and correlated with the device resistance profiles. The stability of the AlOx barrier layer is investigated with transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS).