Effects of High-Pressure Hydrogen Annealing (HPHA) on Reliability Characteristics of RRAM

Reliability characteristics (retention and endurance) of RRAM are critical for its practical realization and need to be improved. In this work, we confirmed the trade-off between retention and endurance by using various top electrode thickness conditions. The trade-off between retention and endurance characteristics was mainly due to the different amount of oxygen in scavenging layer (Ta) and the amount of oxygen vacancy in switching layer (HfO2). The amount of the oxygen in scavenging layer (Ta) and the amount of the oxygen vacancy in switching layer (HfO2) will be increased with the increase of Ta thickness. Therefore, the thicker Ta cells have worse retention because the large amount of oxygen in scavenging layer (Ta) can diffuse back into switching layer (HfO2) and recombine with oxygen vacancies in the filament. However, it has longer endurance because the large amount of oxygen vacancy in switching layer (HfO2) can be a source of the filament. Hence, there exists a trade-off relation between retention and endurance under the various Ta thickness conditions. To improve both retention and endurance characteristics, we proposed a new method by using high-pressure hydrogen annealing (HPHA). The thin Ta cells have longer retention and worse endurance because it has small amount of both oxygen in scavenging layer (Ta) and oxygen vacancy in switching layer (HfO2). Therefore, to generate more oxygen vacancies in switching layer (HfO2) maintaining small amount of oxygen in scavenging layer (Ta), we treated the samples by HPHA before Ta deposition. Finally, we obtained both improved retention and endurance characteristics in HfO2 based RRAM devices after high-pressure hydrogen annealing treatment.