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基于60Co-γ射线和10 keV X射线辐射源, 系统地研究了55 nm硅-氧化硅-氮化硅-氧化硅-硅闪存单元的电离总剂量效应, 并特别关注其电学特性退化的规律与物理机制. 总剂量辐照引起闪存单元I- V特性曲线漂移、存储窗口变小和静态电流增大等电学特性的退化现象, 并对其数据保持能力产生影响. 编程态闪存单元的Id- Vg曲线在辐照后显著负向漂移, 而擦除态负向漂移幅度较小. 对比两种射线辐照, 擦除态的Id- Vg曲线漂移方向不同. 相比于擦除态, 富含存储电子的编程态对总剂量辐照更为敏感; 且相比于60Co-γ射线, 本文观测到了显著的X射线剂量增强效应. 利用TCAD和Geant 4工具, 从能带理论详细讨论了55 nm硅-氧化硅-氮化硅-氧化硅-硅闪存单元电离总剂量效应和损伤的物理机制, 并模拟和深入分析了X射线的剂量增强效应.The total ionizing dose (TID) effects on 55 nm SONOS flash cell, caused by 60Co-γ ray and 10 keV X-ray radiation source, are systematically investigated in this paper. The degradation of electrical characteristics is discussed while the underlying physical mechanism is analyzed. The drift of I-V characteristic curve, the degradation of memory window, and the increase of stand-by current are observed after TID irradiation separately by the two radiation sources. The data retention capability is also affected by the TID irradiation. The I-Vg curve of the programmed single flash cell significantly drifts towards the negative direction after TID irradiation, while the negative drift of erased state is much slower. Referring to the erased state, the drift directions of Id-Vg curves for γ- and X-ray radiation source are obviously different. The physical mechanism of irradiation damage in a 55 nm SONOS single flash cell is discussed in detail by the energy band theory and TCAD simulations. The storage charge loss in silicon nitride layer, the charge accumulation, and the generation of interface states all together lead to the degradation of threshold voltage and stand-by current after TID irradiation. Another cause for the increase of stand-by current is the positive trapped charges in the isolated oxide induced by irradiation, which leads to the generation of leakage paths. Significant dose enhancement effect of X-ray irradiation is observed in this paper. Device model of memory transistor c is established while the dose enhancement effect of X-rays is investigated by Geant 4 tool. The high-Z materials above the poly-silicon gate lead to the dose enhancement effect of X-rays’ irradiation, which results in the higher degradation. The density of electron-hole pairs produced by irradiation in W layer is much higher than in Cu layer. In particular, W layer is a critical factor regardless of the thickness, which can be obviously observed in the simulation.
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Keywords:
- flash /
- charge-trapping /
- total ionizing dose /
- dose enhancement
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图 1 (a) SONOS结构示意图; (b) 2 × 2位的闪存单元微阵列及其TEM横截面
Fig. 1. (a) Diagram of SONOS structure; (b) 2 × 2 bit flash cells mini-array and the TEM cross-section.
图 2 60Co-γ射线总剂量辐照后, 编程态和擦除态的SONOS闪存单元的I-V特性变化规律
Fig. 2. I-V characteristics of the programmed and erased single SONOS flash cell after total ionizing dose irradiation by 60Co-γ rays.
图 3 编程态和擦除态闪存单元的(a)阈值电压和归一化的存储窗口, 以及(b)静态电流随60Co-γ射线总剂量辐照的变化规律
Fig. 3. (a) Threshold voltage and normalized memory window, and (b) stand-by current of the programmed and erased single flash cell after total ionizing dose irradiation by 60Co-γ rays.
图 4 辐射源为10 keV X射线下编程态和擦除态闪存单元的I-V特性变化规律
Fig. 4. I-V characteristics of the programmed and erased single flash cell after total ionizing dose irradiation by 10 keV X-rays.
图 5 编程态和擦除态闪存单元的(a)阈值电压和归一化的存储窗口, 以及(b)静态电流随10 keV X射线总剂量辐照的变化规律
Fig. 5. (a) Threshold voltage and normalized memory window, and (b) stand-by current of the programmed and erased single flash cell after total ionizing dose irradiation by 10 keV X-rays.
图 8 辐射源为10 keV X射线下编程态和擦除态闪存单元的亚阈值斜率变化规律
Fig. 8. Sub-threshold slopes of the programmed and erased single flash cell after total ionizing dose irradiation by 10 keV X-rays.
图 9 (a)闪存单元中MT的布局简图和沟道边缘的漏电路径; (b)沿虚线A—A', MT可等效成一个主晶体管与两个寄生晶体管的并联, MT靠近隔离氧化物处反型层的形成导致寄生电流产生
Fig. 9. (a) MT top view with the leakage paths at the channel edges; (b) cross-section of MT along line A–A' indicates that MT can be considered as a main transistor in parallel with two parasitic transistors. The formation of the inverse layer along the isolated oxide leads to the generation of parasitic currents.
图 11 Geant 4工具模拟高Z材料与X射线剂量增强效应的关系
Fig. 11. Dose enhancement effect of X-rays on high-Z materials, simulated by Geant 4 tool.
表 1 SONOS闪存单元的操作条件
Table 1. Operation conditions of the SONOS single flash cell.
操作 VWLS/Vg/V VWL/V VBL/Vd/V VSL/V 脉冲宽度/ms PGM 9.5 0 0 0 1.5 ERS −9.5 0 0 0 2.5 READ −3—3 2.5 0.6 0 — 
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[1] Lu C Y, Hsieh K Y, Liu R 2009 Microelectron. Eng. 86 283
Google Scholar
[2] Houdt J V 2011 Curr. Appl. Phys. 11 e21
Google Scholar
[3] Li M, Bi J S, Xu Y N, Li B, Xi K, Wang H B, Liu J, Li J, Ji L L, Liu M 2018 Chin. Phys. Lett. 35 078502
Google Scholar
[4] Takeuchi H, King T J 2003 IEEE Electr. Device Lett. 24 309
Google Scholar
[5] Cellere G, Paccagnella A, Lora S, Pozza A, Tao G 2004 IEEE Trans. Nucl. Sci. 51 2912
Google Scholar
[6] Cellere G, Paccagnella A, Visconti A, Bonanomi M, Candelori A 2006 IEEE Trans. Nucl. Sci. 52 2372
Google Scholar
[7] Oldham T R, Mclean F B 2003 IEEE Trans. Nucl. Sci. 50 483
Google Scholar
[8] Bi J S, Han Z S, Zhang E X, Mccurdy M W, Reed R A, Schrimpf R D, Fleetwood D M, Alles M L, Weller R A, Linten D, Jurczak M, Fantini A 2013 IEEE Trans. Nucl. Sci. 60 4540
Google Scholar
[9] Fleetwood D M 2013 IEEE Trans. Nucl. Sci. 60 1706
Google Scholar
[10] Wang Z, Liu C, Ma Y, Wu Z, Wang Y 2015 IEEE Trans. Nucl. Sci. 62 527
Google Scholar
[11] Bi J S, Xi K, Li B, Wang H B, Ji L L 2018 Chin. Phys. B 27 098501
Google Scholar
[12] Oldham T R, Chen D, Friendlich M, Carts M A, Seidleck C M, LaBel K A 2011 IEEE Trans. Nucl. Sci. 58 2904
Google Scholar
[13] Petrov A, Vasil’ev A, Ulanova A, Chumakov A, Nikiforov A 2014 Central Eur. J. Phys. 12 725
Google Scholar
[14] Duncan A R, Gadlage M J, Roach A H, Kay M J 2016 IEEE Trans. Nucl. Sci. 63 1276
Google Scholar
[15] Bagatin M, Gerardin S, Paccagnella A, Visconti A, Bonanomi M 2015 IEEE Trans. Nucl. Sci. 62 2815
Google Scholar
[16] Snyder E S, McWhorter P J, Dellin T A, Sweetman J D 1989 IEEE Trans. Nucl. Sci. 36 2131
Google Scholar
[17] Puchner H, Ruths P, Prabhakar V, Kouznetsov I, Geha S 2014 IEEE Trans. Nucl. Sci. 61 3005
Google Scholar
[18] Adams D A, Mavisz D, Murray J R, White M H 2002 IEEE Aerospace Conference Proceedings (Cat. No.01TH8542) Big Sky, MT, USA, March 10−17, 2001 p2295
[19] Adams D A, Smith J T, Murray J R, White M H, Wrazien S 2005 2004 Proceedings IEEE Computational Systems Bioinformatics Conference Stanford, CA, USA, November 17, 2004 p36
[20] Qiao F, Yu X, Pan L, Ma H, Wu D, Xu J 2012 19th IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits Singapore, July 2−6, 2012 p1
[21] Bassi S, Pattanaik M 2014 18th International Symposium on VLSI Design and Test Coimbatore, India, July 16−18, 2014 p1
[22] Qiao F, Pan L, Blomme P, Arreghini A, Liu L 2014 IEEE Trans. Nucl. Sci. 61 955
Google Scholar
[23] 谯凤英 2013 博士学位论文 (北京: 清华大学)
Qiao F Y 2013 Ph. D. Dissertation (Beijing: Tsinghua University) (in Chinese)
[24] Yoshii I, Hama K, Maeguchi K 1989 IEEE Trans. Nucl. Sci. 36 2124
Google Scholar
[25] 李蕾蕾, 于宗光, 肖志强, 周昕杰 2011 60 098502
Google Scholar
Li L L, Yu Z G, Xiao Z Q, Zhou X J 2011 Acta Phys. Sin. 60 098502
Google Scholar
[26] Hu Z Y, Liu Z L, Shao H, Zhang Z X, Ning B X 2011 Microelectron. Reliab. 51 1295
Google Scholar
[27] Ning B X, Zhang Z X, Liu Z L, Hu Z Y, Chen M 2012 Microelectron. Reliab. 52 130
Google Scholar
[28] 刘张李, 胡志远, 张正选, 邵华, 宁冰旭 2011 60 116103
Google Scholar
Liu Z L, Hu Z Y, Zhang Z X, Shao H, Ning B X 2011 Acta Phys. Sin. 60 116103
Google Scholar
[29] Pei Y P, Huang R, An X, Liu W, Tian J Q 2012 J. Appl. Phys. 51 1295
[30] Barnaby H J 2006 IEEE Trans. Nucl. Sci. 53 3103
Google Scholar
[31] 陈盘训, 周开明 1997 物理 12 725
Google Scholar
Chen P X, Zhou K M 1997 Physics 12 725
Google Scholar
[32] 吴正新, 何承发, 陆妩, 郭旗, 艾尔肯·阿不列木 2013 核技术 36 060201
Wu Z X, He C F, Lu W, Guo Q, Aierken A 2013 Nucl. Technol. 36 060201
[33] 郭红霞, 韩福斌, 陈雨生, 周辉, 贺朝会 2002 核技术 25 811
Google Scholar
Guo H X, Han F B, Chen Y S, Zhou H, He C H 2002 Nucl. Technol. 25 811
Google Scholar
[34] 卓俊, 黄流兴, 牛胜利, 朱金辉 2015 现代应用物理 6 168
Google Scholar
Zhuo J, Huang L X, Niu S L, Zhu J H 2015 Mod. Appl. Phys. 6 168
Google Scholar
[35] Allison J, Amako K, Apostolakis J, Arce P, Asai M 2016 Nucl. Instrum. Meth. A 835 186
Google Scholar
[36] Allison J, Amako K, Apostolakis J, Araujo H, Dubois P A 2006 IEEE Trans. Nucl. Sci. 53 270
Google Scholar
[37] Agostinelli S, Allison J, Amako K, Apostolakis J, Araujo H 2003 Nucl. Instrum. Meth. A 506 250
Google Scholar
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