总剂量和重离子协同作用下浮栅单元错误的退火特性研究

Annealing behavior study on floating gate errors induced by γ followed by heavy ion irradiation

针对25 nm商用Flash存储器,利用中国科学院新疆理化技术研究所的60Coγ射线源和兰州重离子加速器先后进行了总剂量效应和单粒子效应实验。实验中器件先辐照30 krad(Si)的γ射线,然后再辐照不同线性能量转移(Linear Energy Transfer,LET)的重离子,得到了不同条件下Flash存储器浮栅单元错误的退火特性。实验结果表明与只进行重离子辐照相比,总剂量和重离子协同作用下器件浮栅单元错误消失的比例会发生变化,且在不同LET离子的辐照下表现出相异的趋势。分析认为辐照总剂量会引起浮栅单元电荷丢失和电荷俘获,影响浮栅单元的错误退火特性。

[Background]Flash memories have been widely used in many space systems because of their high density and non-volatility.The single event effect(SEE)and total ionizing dose(TID)of Flash memories are attracting more and more attentions.[Purpose]This study aims at the impact of total ionizing dose on annealing of floating gate errors induced by heavy ion irradiation.[Methods]The commercial single level cell(SLC)25 nm NAND flash devices manufactured by Micron technology Inc.were selected for experimental study.TID irradiations were performed with 60Coγ-rays at Xinjiang Technical Institute of Physics and Chemistry,Chinese Academy of Sciences.Then heavy ion irradiations were conducted at the heavy ion research facility in Lanzhou(HIRFL)using three ion sources.[Results]The percentage of annealing error of samples previously irradiated with TID is very different from that of unirradiated samples.[Conclusions]The charge loss of floating gate(FG)and charge trapping in the tunnel oxide induced byγ-rays have great influence on the percentage of annealing error of FG cells.