A non-volatile memory device includes a plurality of word lines, a plurality of bit lines, and an array of variable resistance memory cells each electrically connected between a respective word line and a respective bit line. Each of the memory cells includes first and second resistance variable patterns electrically connected in series between first and second electrodes. A material composition of the first resistance variable pattern is different than a material composition of the second resistance variable pattern. Multi-bit data states of each memory cell are defined by a contiguous increase in size of a programmable high-resistance volume within the first and second resistance variable patterns.