(color online) (a) The structure of Pt/HfO_x/graphene/Ti/TiN RRAM. (b) The I–V curves of RRAMs with and without graphene, showing that the GRRAM owns lower SET voltage and RESET current. (c) The relation between the contact resistance between graphene and the top electrode and the graphene length, indicating low contact resistance with the top electrode. (d) The relation between the cumulative probability and the RESET current of RRAMs with and without graphene respectively. The RESET current of RRAM with graphene has a 22 reduction compared to that without graphene. (e) Retention time of GRRAM under HRS and LRS, repectively. The figure is reproduced from Ref. [51].