Phase Transition Phenomena in Ultra-Thin Ge₂Sb₂Te₅ Film

We observe reversible phase transition phenomena in proto-type chalcogenide random access memory (C-RAM) devices adopting ultra-thin (12nm) Ge₂Sb₂Te₅ thin film. In this kind of proto-type device, the ultra-thin amorphous Ge₂Sb₂Te₅ thin film undergoes a crystallization process when a voltage is applied. The polycrystalline Ge₂Sb₂Te₅ remain unchanged when the voltage is below 0.6V. A higher power is needed if the transition from polycrystalline to amorphous is expected. The re-amorphization process can be realized by applying a voltage higher than 0.7V. The threshold voltage V_th and threshold electric field E_th of the transition from the polycrystalline state to the amorphous state in this proto-type device are ～0.7V and ～5×10⁵V/cm, respectively. The programming voltage is significantly reduced compared to the values of C-RAM devices adopting a 200-nm-thick
Ge₂Sb₂Te₅ inset.