The　authors　report　the　fabrication　and　characterization　of　resistive　random　access　memory　(RRAM)　with　Ni/ZnO/HfO2/Ni　structure　at　room　temperature.　It　was　found　that　the　proposed　device　exhibited　bipolar　switching　behavior　with　multilevel　characteristics　in　a　reset　process.　It　was　found　that　the　device　exhibited　two-step　reset　stage　under　high　reset　bias.　By　applying　a　2nd　reset　stage　after　the　transformation　of　the　1st　reset　stage,　it　was　found　that　the　RRAM　could　return　to　the　initial　state.　From　I-V　curves　measured　in　these　two　reset　stages,　it　was　found　that　the　current　conduction　was　dominated　by　Schottky　emission　due　to　the　migration　of　oxygen　ions　and　recombination　with　oxygen　vacancies.　This　reaction　could　break　the　conducting　filament　so　as　to　transform　carrier　transport　mechanism　to　Schottky　emission.　This　also　results　in　the　simultaneous　transformation　from　low　resistance　state　(LRS)　to　high　resistance　state　(HRS).　(C)　2015　Elsevier　Ltd.　All　rights　reserved.