Intrinsic Switching Behavior in HfO2 RRAM by Fast Electrical Measurements on Novel 2R Test Structures

In this work, we present a detailed electrical characterization of TiNHfO2HfTiN RRAM elements, and show for the first time the intrinsic switching characteristics in the low current operation regime (100uA till few uA´s) of small scaled cells (20nm) under DC and fast ramps (up to 1MV/s) condition, using a newly proposed 2R test structure. The main characteristic parameters of the SET and RESET switching are defined and their speed dependence is characterized. Resistance decrease during SET is observed to occur at a constant voltage V_trans, while symmetrically RESET process starts at -V_trans. With reducing operation current, mean values of the symmetric SET and RESET transition voltages remain unchanged but their spread strongly increases. The actual I-V characteristics show discrete current jumps and non-linear quantum-mechanical conduction is evidenced and more pronounced at smaller currents. Increasing the ramp rate increases the SET and RESET transition voltage logarithmically with a concomitant reduction of the HRS resistance. These measurements allow for a better insight and understanding of the dynamic switching properties in low-current, ultra-scaled RRAM cells.