| The developments of digital information age rely on the storage of data,and the rapid growth of data itself makes data storage extremely important,especially in the big data era.The rapid improvement of memory performance provides a good opportunity for the storage of massive data.Charge-trap 3D NAND flash memory(CT 3D NAND)has become the mainstream of nonvolatile memory due to its high storage density and low cost,in which the charge-trap layer is shared by memory cells in the same bit line,so the lateral charge diffusion between adjacent cells becomes a key problem affecting reliability.Previous study has shown that the lateral charge diffusion is related to the shallow-trap centers in the charge-trap layer(Si3N4).Defects of 3D NAND charge-trap layer have been widely studied,but the regulation scheme for shallow energy level defects is still lack of systematic research.As a result,the breakthrough of shallow energy level defect regulation technology may become the key point to improve the reliability of 3D NANDThis work systematically studies the defects in charge-trap layer of 3D NAND by first-principle calculation and simulation.The metallic doping in Si3N4 reduces shallow-trap centers and increases electronic storage density,resulting in high reliability memory.And the stability of metallic doping defects during data retention is also explored.To make full sense of the inevitable transition layer under size scaling,we discuss the effects of transition layer intrinsic defects and metallic doping defects on memory reliability.Then,aiming at reducing lateral charge diffusion caused by shallow-trap centers,we propose that working mode optimization could be effective.Finally,to reduce the reliability problems arising from frequent data search,we propose hardware data search mechanism based on 3D NAND,which could realize data search through single read operation.First,considering that the storage density of 3D NAND flash memory is improved with future device size scaling,but higher requirements for the reliability also arise.Lateral charge diffusion caused by shallow-trap centers is an important problem of reliability in 3D NAND flash memory,so it is necessary to effectively modulate shallow-trap centers.All defects are systematically studied in this work.Hydrogen and oxygen atoms at interface impact the metallc doping defects,which are also considered.The results show that metallic doping can effectively regulate the defect levels and reduce shallow-trap centers.It is found that Ti and Hf could be the appropriate dopping atoms,since they can provide suitable defect energy levels(Tisi,Et?1.43 eV;Hfi,Et?1.32 eV)and high electron storage density.More importantly,Ti and Hf doping can also effectively inhibit the generation of shallow traps at the SiOx/Si3N4 interface.Therefore,metallic doping can effectively modulate the defect levels for high reliability.Secondly,transition layer(Si2N2O)between the stacked layers(SiO2/Si3N4/SiO2)in 3D NAND becomes an inevitable problem,so we study the charge loss resulting from intrinsic and metallic doping defects in transition layer.Our work indicates that shallow-trap centers,such as nitrogen vacancy defects(VN)and Ti doping defects(Tii),could effectively capture charges,which could lead to serious charge lateral diffusion problems.On the other hand,if the defect levels in the Si2N2O can resonate with the electron defects level in the Si3N4,which leads to the rapid charge transfer aggravating the reliability problem of 3D NAND.Therefore,the process optimization and hydrogen passivation of the interface have practical significance in charge loss of 3D NAND.Thirdly,lateral charge diffusion caused by shallow-trap centers is an important factor affecting reliability of 3D NAND flash memory,which should be attached more importance.In this work,how to recover the lateral charge diffusion is explored in detail.It is found that lateral charge diffusion caused by shallow-trap centers is recovered by read operation.Based on the simulation and chip characterization of TLC 3D NAND,we found that the read operation could recover the lateral charge diffusion.This is beneficial to verify the effectiveness of our proposed method.Read operation can effectively recover the charge diffusion caused by shallow-trap centers and improve the reliability of memory.Finally,3D NAND is a large capacity data storage center,so the frequent read cycles of big data blocks is inevitable in data search,which could induce reliability issues.Thus,we propose a 3D NAND all-hardware data search strategy for the first time,which is achieved through one read operation to avoid the reliability problems caused by multiple read operations.We expound the principle in detail and study the impacts of the variation memory cell on the efficiency of data search.The results show that the parameter optimization of V R,con is the key factor to increase the current ratio and improve the search speed.The variation of Vth will greatly affect the accuracy which should be controlled.In short,this strategy enables data search through single read operation,which is significant to improve memory reliability. |
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