Lateral SbTeN based multi-layer phase change memory for multi-state storage

X-ray diffraction patterns and resistivity measurement indicate that as-deposited N-doped Sb"2Te"3 (STN) films become amorphous while the as-deposited Sb"2Te"3 film is crystalline. A lateral as-deposited STN-based multi-layer phase change memory was proposed for multi-state storage. The active region of the device consists of a top 30-nm TiN/180-nm STN/20-nm TiN/bottom 120-nm STN stacked multi-layer. Static switching properties of the device with STN initially starting from the amorphous state exhibit two apparent S-shaped switchings, which correspond to two marked device resistance drops by a factor of 2-5. The first and second threshold voltages are around 2.8-3.2 and 4.3-5.4V, respectively. Finite element analysis of the device shows that the two switchings could sequentially occur at the electrode steps from the bottom 120-nm STN layer to the top thick 180-nm STN layer.