Three-dimensional Thermal Simulation And Structure Design Of Phase Change Access Random Memory

Phase change random access memory (PCRAM) has a lot of advantages which makes PCRAM to be one of the most promising candidate for the next generation non-volatile memory.PCRAM writes/erases data by thermal energy generated from an electrical pulse, which induces phase transition between conductive crystalline and resistive amorphous states of phase change material. Therefore, it is essential to have a good understand of the thermal properties. Especially, the thermal influence is very critical when the feature size is scaling down.Based on the finite element method, this thesis built the finite element model of PCRAM cell by using the commercial software ANSYS and had a series of simulations under different conditions. The thermal properties of PCRAM cell on material parameters(including thermal conductivity of phase change material, electrode material and insulator material; electrical resistivity of phase change material) of T-type PCRAM cell with fixed feature size were simulated and the results were analyzed. The relation between the feature size and the maximum temperature of the phase change cell was obtained. Then the thermal distribution of T-type cell on the geometrical parameters (including thickness of phase change layer, and insulator layer) were simulated when the cell feature size of cell changes from 45nm to 10nm.High reset current is a critical issue which limits the progress of PCRAM. This thesis proposed a novel asymmetric structure which was confirmed to be effective in decreasing reset current based on the 3D electric-thermal simulation . Then a series of simulations on asymmetric structure with the feature size from 45nm to 10nm were conducted to study the thermal performance of the asymmetric PCRAM cell on the geometrical variations. At last, a comparison between cells with an asymmetric and T-type structure was conducted to try to find out why the cell with asymmetric structure has better electric-thermal performance than that with T-type structure. Besides, the simulation results show that the?smaller feature size, the more remarkable improvement in asymmetric PCRAM cell.