1. A method of changing a state of a memristor having a first intermediate layer, a second intermediate layer, and a third intermediate layer positioned between a first electrode and a second electrode, said method comprising: applying a first pulse having a first bias voltage across the memristor, wherein the first pulse causes mobile species to flow in a first direction within the memristor and collect in the first intermediate layer thereby causing the memristor to enter into an intermediate state; and applying a second pulse having a second bias voltage across the memristor, wherein the second pulse causes the mobile species from the first intermediate layer to flow in a second direction within the memristor and collect in the third intermediate layer, wherein the flow of the mobile species in the second direction causes the memristor to change from the intermediate state to a fully changed state.