Simulation And Analysis On Thermoelectric Effects Of Phase Change Nanometer Memory Element

The semiconductor storage technology increasingly update, phase change random access memory(PCRAM) is considered to be one of the most hopeful to become a mainstream for the next generation of the new type of nonvolatile solid-state storage technology. When the size of the storage element is further reduced to the nanometer order of magnitude, phase change storage element can be called as phase change nanometer element(PCNE). The influence of thermoelectric effects to the electricity and thermal performance of PCNE can not be ignored. Hence, the thermoelectric effects study of PCNE has very important significance.In this paper, a physical simulation model was developed to simulate the RESET process based on storage principle of PCNE, the finite element method and thermoelectric effects which mainly includes seebeck effect, thomson effect and peltier effect. Expounded the electricity and thermal performance simulation principle of PCNE.For the need of electricity-heat-induced phase transition process simulation, a multi-grid system including hexahedral grids and tetrahedral was proposed and the relative application technology is presented too. Finite element discrete formules for electricity and heat conduction partial differential equations were derivated. In order to simulate the electrical and thermal performance of PCNE, designed the simulation process and algorithm and wrote three-dimensional simulation program.With only considering the joule heat, according to whether the material parameters change with temperature, under the action of multiple sets of voltage pulses with different amplitude, pulse width, and polarity, three-dimensional electricity and thermal performance simulation were done on the RESET process of bottom-up PCNE. Simulation results show that the RESET operation voltage reduced 33% and the heating rate increases by 25% when the physical parameters change with temperature of phase change materials, compared with the physical parameters of phase change materials is constant. At the same time, the pulse polarity has no effect on the temperature distribution of PCNE. So research on the electricity and thermal performance for PCNE, must consider the influence of temperature on the storage medium material parameters.On the basis of joule heat simulation results, research the thermoelectric effect influence on the temperature distribution of PCNE, three-dimensional electricity and thermal performance simulation were done on the RESET process of bottom-up PCNE again. Simulation results show that under the action of thermoelectric effect, not only the RESET operation voltage reduced 10%, but also increases the heating efficiency and write "0" speed, which is compared with considering only the joule heat. When considering the thermoelectric effect, the pulse polarity has significant effect on the temperature distribution of PCNE. Negative polarity pulses require more current to produce the same size molten volume within the GST, making positive polarity pulses more energy efficient.