In order to significantly accelerate the memory technology, many NAND flashes were stacked vertically on top of each other in order to achieve shorter connections between the memory cells, which reduces the runtimes between the individual NAND flashes. This led to the three-dimensional 3D NAND memory.
Another technique was developed by Intel and Micron. This technology, called 3D XPoint, can be used to build non-volatile 3D memory that is thousands of times faster than NAND flashes. Unlike NAND flash technology, which can store multiple voltage levels in one memory cell with Multi Level Cells( MLC), 3D XPoint works on the principle of phase change memory, based on resistance changes. Storage is at the bit level. The memory cells, which are arranged in three dimensions, are located at the intersections of the vertical lines. They are activated by the current flowing through the vertically and horizontally arranged lines. The memory states show up in the high or low resistance level. They are non-volatile and can hold resistance levels for a long time.
Like 3D NAND memory, 3D XPoint's memory cells are stacked in multiple layers. The memory cell density is many times higher than that of NAND flashes.