Study On The Physical Mechanism Of Data Upsetting In Flash Memory Induced By Proton Irradiation

NAND Flash memory is an ideal choice for space electronic storage systems due to its advantages of large capacity,non-volatile and high reliability.In the space radiation environment,the protons with the largest proportion will cause various radiation effects in Flash memory,and change the data in the memory.With the shrinking of the process node,the radiation effect caused by protons has a more and more serious impact on the memory,and the physical mechanism of the bit flip in the Flash memory needs to be further studied.In this dissertation,the NAND Flash memory with nanoscale feature size is targeted,the physical mechanism of bit flip and the performance degradation of floating gate cell under the proton irradiation is studied.The main innovations and research contents of the dissertation are as follows:（1）The traditional single-event-upset（SEU）cross-section simulation method only considers the secondary particles generated by protons in the floating gate,while ignoring the influence of the secondary particles in the upper material of the floating gate,obtaining a smaller SEU cross-section than the reality via this method.Using numerical simulation software,this dissertation proposes a new method to obtain high-energy proton SEU cross-section by counting the distribution of effective linear energy transfer(₀1)1)))values of secondary particles.The method replaces the linear energy transfer（）value with the₀1)1))value of the secondary particle,which can more accurately estimate the real proton SEU cross section of the floating gate cell.（2）Combined with proton irradiation experiments and simulation studies,the effects of proton energy and fluence on the SEU cross section of the floating gate cell are analyzed.Proton irradiation experiment with different energies shows that the SEU cross section of the floating gate cell increases with the increase of proton energy.Simulation studies show that there are differences in the nuclear reaction cross sections of high-energy recoil nuclei generated by protons with different energies,resulting in the energy dependence of the proton SEU cross section.Proton irradiation experiment with different fluences shows that the SEU cross section decreases with increasing proton fluence,which is due to the difference in the single-event-effect（SEE）sensitivity of the floating gate cells.Compared with the early irradiation stage,the threshold voltage of the floating gate cell without SEU is higher in the late irradiation stage,and it is more difficult that the floating gate cell has a SEU effect.（3）Aiming at the effect of non-ionization damage caused by protons on the performance of Flash memory,the error annealing characteristics of floating gate cells were studied,and the effect of proton irradiation on the data retention capability of floating gate cells was analyzed.The proton-induced non-ionizing damage can form partially permanent defect damage in the tunnel oxide layer,creating the multi-Trap-Assisted Tunneling that can leak floating gate electrons,resulting in the increase of floating gate cell errors and the degradation of data retention ability.The effect of increasing the number of errors over time is more obvious when low-energy protons are incident,because the non-ionizing damage of low-energy protons in the tunneling oxide layer is more serious.（4）In view of the effect of displacement damage on SEE in Flash memory,the proton SEE sensitivity of floating gate cell after neutron pre-irradiation is studied.The experiments show for the first time that neutron pre-irradiation enhances the proton SEE sensitivity of floating gate cells.The displacement damage induced by neutrons leads to the generation of the multi-Trap-Assisted Tunneling,and makes it easier for floating gate electrons to escape after irradiation,which is the intrinsic reason for the enhanced SEE sensitivity of floating gate cells.