Three-dimensional Finite Element Analysis of Phase Change Memory Cell with Thin TiO_2 Stop Layer used for Forming Deep Sub-micro Electrode

摘要

Thin TiO_2 layer inserted in phase change memory (PCM) cell to form Deep sub-micro Bottom Electrode (DBE) was interposed and its electrical-thermal characteristics were investigated with finite element analysis. Compare with other dielectric material, TiO_2 with good heat stability and low heat conductivity is suitable for preventing heat diffusion from phase change region. Besides, TiO_2 layer as stop layer during Chemical Mechanical Planarization (CMP) can effectively control the height of deep sub-micro electrode. Additionally, there exits the appropriate height of DBE (200nm) to contribute more heat during RESET operation. Compared with the conventional cell (SiN layer), the RESET threshold current of the DBE cell is reduced from 1.8mA to 1.2mA. It is illustrated in simulation results that the ratio of amorphous resistance and crystalline resistance will be larger in RESET operation when TiO_2 film is 10nm approximately. Therefore, not only TiO_2 film is stop layer during sub-micro electrode fabrication, but also is it benefiting for writing current reduction.