Study On The Single Event Effect Of SRAM Cell In Extremely Low Temperature Environment

Based on the application of storage equipment in extreme low temperature environment and irradiation environment,this paper adopts the method of combining TCAD software simulation and experiment to study the mechanism of changes in the electrical characteristics of MOS devices under low temperature environment,the mechanism of transient current generated by particle incident and the mechanism of changes in single event effect under low temperature condition.Furthermore,the LET threshold,which leads to the potential reversal of the storage node,is studied in the low temperature environment of SRAM cell.Firstly,through low temperature test and simulation of 65nm MOS device,the changes of electrical characteristics in the range of 300K-77K are studied.The experimental results of NMOS device show that the threshold voltage of the device increases with the decrease of temperature,which is related to the decrease of intrinsic carrier concentration and the increase of band gap width in low temperature environment.The change of drain current is related to the increase of carrier mobility at low temperature.The variation trend of threshold voltage and drain current of PMOS device is consistent with that of NMOS device.Using the experimental data to build the cryogenic device model for the subsequent simulation.Secondly,the influence of different LET values on the single event effect of NMOS devices is studied by using the normal temperature model.The results show that with the increase of LET value,the peak value and duration of the transient current caused by the single event effect increases,and the amount of charge accumulated on the particle track also increases.According to the established low temperature model of NMOS,the single event effect is simulated.The simulation results show that the peak value of the transient current increases and the duration of the transient current decreases with the decrease of temperature.The variation range also increases with the increase of LET value.This indicates that the increase of LET value will intensify the influence of temperature on the single event effect of NMOS devices.Finally,PMOS and NMOS devices were used to build SRAM cell to simulate the LET value that caused the potential reversal of storage nodes.The simulation results show that when the temperature drops from 300K to 77K,the LET threshold drops from0.49MeV·cm~2/mg to 0.33MeV·cm~2/mg.That's down 32.7 percent.This indicates that the single event flipping effect intensifies with the decrease of temperature.