Memory device, memory system having the same, and write method thereof

A memory device includes: a first wafer including a first substrate, a plurality of first electrode layers and a plurality of first interlayer dielectric layers alternately stacked along first vertical channels projecting in a vertical direction on a top surface of the first substrate, and a dielectric stack comprising a plurality of dielectric layers and the plurality of first interlayer dielectric layers alternately stacked on the top surface of the first substrate; and a second wafer disposed on the first wafer, and including a second substrate, and a plurality of second electrode layers that are alternately stacked with a plurality of second interlayer dielectric layers along second vertical channels projecting in the vertical direction on a bottom surface of the second substrate and have pad parts overlapping with the dielectric stack in the vertical direction.