A 2-bit/cell, Maskless, Self-Aligned Resistance Memory with High Thermal Stability

We report the first demonstration of a multilevel cell (MLC) resistance device using a self-aligned WO
_x
film prepared by plasma oxidation. The 2-bit/cell operation is achieved by applying a series of 1.5 V programming pulses. The device shows high thermal stability and good data retention. The resistance change can be attributed to variable-range hopping and Ohmic transport mechanisms. This device has the potential for future low-voltage, 3-dimensional nonvolatile memory with multiple bits per layer. In addition, no additional mask is needed to form the self-aligned device.