Simulation On Thermal Stress Distribution Of Phase Change Memory Element

As semiconductor processes evolve to the nanometer scale,a variety of new types of non-volatile memories emerge as the times require,and phase-change memory,as a new type of memory,is one of the most powerful contenders for the next generation of nonvolatile memory,but at the same time phase change device faces failure problems after repeatedly read and write cycles,fatigue has become an important factor restricting the commercialization of phase change memory.The existence of thermal stress is one of the main reasons for the failure of the phase change unit,simulating the thermal stress distribution in the phase change unit,we can get the stress level at every position of the cell,and analyze the failure possibility of the unit in different locations,and provide a basis for the design of the working pulse.The finite element method is used in the simulation.The whole three-dimensional simulation program is written on MATLAB,and the electrical and thermal properties,as well as the stress and strain fields of the phase change element are simulated.First,the simulation model of displacement field is established,and the displacement field is used to solve the stress and strain field of the element.At the same time,the traditional Fourier equation is modified during thermal simulation,and the bidirectional coupling relationship between strain field and temperature field is theoretically proved.Based on the first strength theory and the fourth strength theory,the first principal stress and the von Mises stress are respectively considered,and the possible brittle failure and fatigue failure in the unit are analyzed.The simulation results show that the stress concentration mainly occurs inside the GST,between the GST and the heating pole and inside the heating pole when the first principal stress is considered.In the cooling stage,the magnitude of the first principal stress is positive and the unit is in the three-way tensile stress state,the unit may appear brittle failure only during the cooling phase.The magnitude of the absolute value of the first principal stress is related to both the rate of change of temperature and the crystallization rate of GST.Considering Mises stress,the stress concentration is mainly distributed in the internal heating electrode,Mises stress compared to the size of the first principal stress issmaller.The Mises stress previous working pulse produced will generate a “cumulative effect” to the Mises stress subsequent working pulse produced,and the shorter cooling time is,the cumulative effect is more obvious.