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Abstract-A forming-free 3-nm-thick HfOx, resistive memory device is demonstrated. The percolation threshold of insulatingto-conductive transition in the ultrathin HfOx, can be lowered by using the Ti capping layer with an adequate post metal annealing. By the reaction between Ti and HfOx,, oxygen ions are depleted from the oxide, and conductive percolative paths, which consist of charged oxygen vacancies, are formed. Without any forming step, the memory can operate with stable bipolar resistance switching by initial positive or negative voltage sweep. Possible scenarios of switching mechanism for the initial state of the device with different sweep directions are proposed. This forming-free device also exhibits an on/off ratio of about ten and excellent memory performances, including high speed (~10 ns), low operation voltages (<; 1.2 V), robust endurance (> 106 cycles), good nonvolatile property (500 min at 85 °C), and 2-b switching per cell.