Detailed Analysis of the Role of Thin-${\rm HfO}_{2}$ Interfacial Layer in ${\rm Ge}_{2}{\rm Sb}_{2}{\rm Te}_{5}$-Based PCM

In this paper, we show that performances of Ge
₂
Sb
₂
Te
₅
-based phase-change memory (PCM) cells can be improved by the insertion of a thin HfO
₂
interfacial layer between the phase-change material and the tungsten plug. Significant reduction of the RESET and SET currents and of the energy required to switch the PCM cells are demonstrated. In addition, compared with pure GST reference cells, the presence of the HfO
₂
layer leads to an enhanced endurance (>10
⁸
cycles) and an improved data-retention (ten years at 172°C). Using cross-sectional TEM-Energy Dispersive X-Ray (EDX) analyses and technology computer-aided design simulations, the decreases of the programming currents and energy are explained through the reduction of the PCM cell active area, due to the creation of conductive paths in the HfO
₂
layer during the initial forming procedure. Electrical measurements and modeling of the forming procedure indicate that the size of the conductive paths is controlled by the maximum current flowing through the PCM cells during the current overshoot of the forming procedure.