Thermal Simulation And Structural Optimization Of High Storage Density Phase Change Memory

As a non-volatile memory,phase change memory(PCM)is expected to replace flash memory as one of the next generation of mainstream storage technologies.In order to improve storage density and cost competitiveness,the current three-dimensional phase change memory(3D PCM)using three-dimensional stacking has received general attention from the industry,but the existing 3D PCM mainly adopts a three-dimensional horizontal stacking method based on cross-point structure,due to process constraints There is an inevitable limit of the number of stacked layers,and the outstanding thermal crosstalk problem of PCM also limits the further improvement of storage density.To this end,this paper first establishes a finite element simulation model containing a new two-terminal site selection device,the OTS strobe tube,solves the problem of lack of OTS switch regulation in the previous planar PCM thermal simulation,and deeply discusses the influence of thermal crosstalk on the specific numerical value of the phase transition fraction of the array unit,makes up for the lack of quantitative research on thermal crosstalk in the previous work,and provides a basis for studying the thermal and electrical characteristics of 3D PCM and designing 3D PCM structure;on this basis,a new vertical three-dimensional integrated structure is proposed,and explores its multi-value storage characteristics,which have the potential for higher storage density.The main efforts and results are as follows:In this paper,the model establishment and simulation study of phase change storage single-layer devices with OTS were first carried out based on finite element simulation software,and the SET and RESET operations were well reproduced,and the influence of OTS threshold switching parameters(threshold electric field and holding electric field,open conductivity and off-state conductivity)on the set operation process was studied,and the device optimization was guided according to the conclusions,and the multi-value storage of RESET operation was studied.It was found that the emergence of the Current-path in the RESET process will have a certain impact on the multi-block state of the device unit.Then,a three-dimensional phase change storage simulation model is established,and the "±1/2 voltage" operation method is used for SET and RESET simulation research.By comparing with the results of single-layer integrated structure,the effect of thermal crosstalk on 3D storage structure under different operating modes is studied.The effect of thermal crosstalk is reduced by the reduction of the cell diameter under SET operation,and the influence of thermal crosstalk is reduced by the reduction of PCM cell thickness under RESET operation.A preliminary study of multi-value storage in a three-dimensional integrated state was also carried out by adjusting the voltage amplitude,and the difference between the three-dimensional structure and the single-layer structure was summarized.Further,a new vertical electrode three-dimensional stacked structure model is proposed,and the simulation results show that this structure can effectively suppress the influence of thermal crosstalk,and realize the multi-value erase operation of three resistive states,which has the potential to achieve higher storage density.Finally,the experimental preparation of vertical electrode three-dimensional stacked 3D PCM array was tested and verified for this novel structure.