We developed TiNHfO2TiN RRAM devices by using hydrogen-based plasma enhanced atomic layer deposition (PEALD) for the top-electrode TiN processing, demonstrating attractive bipolar switching properties (by positive RESET voltage to the PEALD TiN). Better endurance performance was gained as compared with cells having no hydrogen plasma treatment. The improved switching property is related to partial reduction in the stoichiometry ALD HfO2 film, as indicated by electron recoil detection analysis. On the other hand, pure H2 and NH3 thermal annealing treatments were also utilized with the same purpose. However, neither of these treatments resulted in as good switching performances, which underlines the need of a plasma-based process to generate reactive H-based species able to controllably and partially reduce the HfO2 layer.