1. A memory device having a crossbar array, the memory device comprising: a first array of first electrodes extending along a first direction; a second array of second electrodes extending along a second direction; a non-crystalline silicon structure provided between the first electrode and the second electrode at an intersection defined by the first array and the second array, the non-crystalline silicon structure having a first layer having a first defect density and a second layer having a second defect density different from the first defect density, wherein each intersection of the first array and the second array defines a two-terminal resistive memory cell.