Multi-state phase change memory device with vertical cross-point structure

An apparatus, comprising:

• a three-dimensional array of non-volatile memory cells formed over a substrate, comprising:
• a plurality of layers of word lines, each of the layers of word lines running horizontally over the substrate, the layers separated in a vertical direction by dielectric layers;
• a plurality of bit lines running vertically with respect to the substrate;
• and
• a plurality of memory cells each connected between a corresponding one of the word lines and a corresponding one of the bit lines, each of the memory cells comprising:
• a phase change memory material configured to provide a first current path between the corresponding word line and the corresponding bit line for the memory cell, the phase change memory material having a first resistivity in a first phase and a second resistivity in a second phase, the first resistivity being higher than the second resistivity;
• and
• an intermediate resistance material adjacent to the phase change memory material and configured to provide second current path in parallel with the first current path between the memory cell's corresponding word line and bit line, the intermediate resistance material having a resistivity between the first and second resistivities;
• and
• one or more control circuits connected to the three-dimensional array of non-volatile memory cells, the control circuits configured to program multi-state data into the memory cells and read multi-state data from the memory cells.