Cross bar arrays and a method for forming cross-bar arrays are provided. The cross bar array device includes first conductive lines spaced apart and extending in a first direction in a first plane, the first conductive lines including a bottom electrode layer. Second conductive lines are spaced apart and arranged transversely to the first conductive lines in a second plane, the second conductive lines including a top electrode layer. An oxide layer formed on the bottom electrode layer of the first conductive lines and in contact with the top electrode layer of the second conductive lines such that a resistive element is formed through the oxide layer at intersection points between the first conductive lines and the second conductive lines. A multivalent oxide spacer that switches between at least two oxidative states on at least one sidewall of the oxide layer between the first plane and the second plane.