纳米静态随机存储器质子单粒子多位翻转角度相关性研究

器件特征尺寸的减小带来单粒子多位翻转的急剧增加, 对现有加固技术带来了极大挑战. 针对90 nm SRAM(static random access memory, 静态随机存储器)开展了中高能质子入射角度对单粒子多位翻转影响的试验研究, 结果表明随着质子能量的增加, 单粒子多位翻转百分比和多样性增加, 质子单粒子多位翻转角度效应与质子能量相关. 采用一种快速计算质子核反应引起单粒子多位翻转的截面积分算法, 以Geant4中Binary Cascade模型作为中高能质子核反应事件发生器, 从次级粒子的能量和角度分布出发, 揭示了质子与材料核反应产生的次级粒子中, LET(linear energy transfer)最大, 射程最长的粒子优先前向发射是引起单粒子多位翻转角度相关性的根本原因. 质子能量、临界电荷的大小是影响纳米SRAM器件质子多位翻转角度相关性的关键因素. 质子能量越小, 多位翻转截面角度增强效应越大; 临界电荷的增加将增强质子多位翻转角度效应.     

基于重离子试验数据预测纳米加固静态随机存储器质子单粒子效应敏感性

为实现对纳米DICE (dual interlocked cell)加固器件抗质子单粒子能力的准确评估,通过对65 nm双DICE加固静态随机存储器(static random access memory, SRAM)重离子单粒子翻转试验数据的分析,获取了其在重离子垂直和倾角入射时的单粒子翻转(single event upset, SEU)阈值以及离子入射最劣方位角,并结合蒙卡仿真获取不同能量质子与器件多层金属布线层发生核反应产生的次级粒子LET(linear energy transfer)值最大值以及角度分布特性,对器件在不同能量下的质子单粒子效应敏感性进行了预测,质子单粒子效应实验结果验证了预测方法的有效性以及预测结果的准确性,并提出针对DICE加固类器件在重离子和质子单粒子效应试验评估中均应开展离子最劣方位角下的倾角入射试验.     

深亚微米SRAM质子单粒子翻转实验研究

宇航半导体器件运行在一个复杂的空间辐射环境中,质子是空间辐射环境中粒子的重要组成部分,因而质子在半导体器件中导致的辐射效应一直受到国内外的关注。利用兰州重离子加速器(Heavy Ion Research Facility In Lanzhou) 加速出的H2 分子打靶产生能量为10 MeV 的质子,研究了特征尺寸为0.5/0.35/0.15 μm体硅和绝缘体上硅(SOI) 工艺静态随机存储器(SRAM) 的质子单粒子翻转敏感性,这也是首次在该装置上开展的质子单粒子翻转实验研究。实验结果表明特征尺寸为亚微米的SOI 工艺SRAM器件对质子单粒子翻转不敏感,但随着器件特征尺寸的减小和工作电压的降低,SOI 工艺SRAM器件对质子单粒子翻转越来越敏感;特征尺寸为深亚微米的体硅工艺SRAM器件单粒子翻转截面随入射质子能量变化明显,存在发生翻转的质子能量阈值,CREME-MC模拟结果表明质子在深亚微米的体硅工艺SRAM器件中通过质子核反应导致单粒子翻转。Microelectronic devices are used in a harsh radiation environment for space missions. Among all the reliability issues concerned, proton induced single event upset (SEU) is becoming more and more noticeable for semiconductor components exposed on space. In this work, an experimental research of SEU induced by 10 MeV proton for static random access memory (SRAM) of 0.5, 0.35 and 0.15 m feature size is carried out on HeavyIon Research Facility in Lanzhou for the rst time. The experimental results show that proton induced SEUs in submicron and deep-submicron (SRAMs) are dominated by secondary ions generated by proton nuclear reaction events. The silicon-on-insulator SRAMs characters natural radiation-hardened SEU by proton. For the deep-submicron bulk-silicon technology SRAM, the proton SEU cross section is closely related to the proton energy and there is a threshold energy for the SEU occurrence by proton indirect ionization. CREME-MC simulation indicates that the SEU events in deep-submicron SRAM are induced by the proton nuclear reaction.     

重离子核反应对单粒子翻转的影响（英文）

LET作为一个传统的工程参量,并不能完全满足单粒子翻转数据表征的需要,而且也不能直接地反映核反应的一些特性(包括核反应概率与次级粒子),因此研究了重离子与器件作用过程中核反应对单粒子翻转的影响。基于蒙特卡罗模拟与深入的分析,本研究对比了在直接电离与考虑核反应两种模式下的模拟结果。在模拟中,利用不同的重离子表征了核反应在单粒子翻转发生中所起的作用。结果显示,核反应对单粒子翻转截面的贡献依赖于离子的能量,并呈现非单调的变化关系。基于模拟的结果,建议用重离子核反应引起单粒子翻转的最恶劣情况来预估空间单粒子翻转率。     

纳米静态随机存储器低能质子单粒子翻转敏感性研究

针对65, 90, 250 nm三种不同特征尺寸的静态随机存储器基于国内和国外质子加速器试验平台, 获取了从低能到高能完整的质子单粒子翻转截面曲线. 试验结果表明, 对于纳米器件1 MeV以下低能质子所引起的单粒子翻转截面比高能质子单粒子翻转饱和截面最高可达3个数量级. 采用基于试验数据和器件信息相结合的方法, 构建了较为精确的复合灵敏体积几何结构模型, 在此基础上采用蒙特卡罗方法揭示了低能质子穿过多层金属布线层, 由于能量岐离使展宽能谱处于布拉格峰值的附近, 通过直接电离方式将能量集中沉积在灵敏体积内, 是导致单粒子翻转截面峰值的根本原因. 并针对某一轨道环境预估了低能质子对空间质子单粒子翻转率的贡献.     

质子在碳化硅中不同深度的非电离能量损失

利用蒙特卡罗方法,应用Geant4程序,模拟计算了1—500 MeV质子在碳化硅材料中的非电离能量损失,并研究了不同种类的初级反冲原子对非电离能量损失的贡献.模拟结果表明:在相同质子辐照下,碳化硅材料中的非电离能量损失要比硅、镓等半导体材料更小,说明碳化硅器件的稳定性更好,抗位移损伤能力更强;当靶材料足够厚时,在不同能量质子辐照下,材料损伤最严重的区域会随着质子入射能量的增加从质子射程末端逐渐前移到材料表面;不同种类的初级反冲原子对非电离能量损失的贡献表明,在低能质子辐照下,28Si和~(12)C是位移损伤的主要原因,而随着质子能量的增加,通过核反应等过程产生的次级离子迅速增多,并对材料浅层造成严重的位移损伤.     

空间高能离子在纳米级SOI SRAM中引起的单粒子翻转特性及物理机理研究

基于蒙特卡罗方法研究空间高能离子在65—32 nm绝缘体上硅静态随机存取存储器(SOI SRAM)中产生的灵敏区沉积能量谱、单粒子翻转截面和空间错误率特性及内在的物理机理.结果表明:单核能为200 MeV/n的空间离子在60—40 nm厚的灵敏区中产生的能损歧离导致纳米级SOI SRAM在亚线性能量转移阈值区域出现单粒子翻转;宽的二次电子分布导致灵敏区仅能部分收集单个高能离子径迹中的电子-空穴对,致使灵敏区最大和平均沉积能量各下降25%和33.3%,进而引起单粒子翻转概率降低,以及在轨错误率下降约80%.发现俘获带质子直接电离作用导致65 nm SOI SRAM的在轨错误率增大一到两个数量级.     

Geant4模拟δ电子对单粒子翻转的影响

利用Geant4蒙特卡洛程序包, 基于RPP (Rectangular ParallelePiped Volume)模型构建SRAM器件单元的灵敏体积, 编写了重离子在器件材料中的输运程序和单粒子翻转截面计算方法, 得到了简化器件结构的单粒子翻转截面σ与线性能量转移LET的关系曲线, 计算得到的翻转LET阈值和饱和截面与实验结果基本一致。模拟获得了LET值为99.69 MeV/(cm-2·mg)的Bi离子及LET值为69 MeV/(cm-2·mg)的Bi离子和Xe离子在器件材料中产生的δ电子分布图像,讨论了δ电子分布对翻转截面的影响。 计算了灵敏体积中能量沉积与δ电子分布的关系,认为δ电子分布对单粒子效应的影响随着器件的特征尺寸减小将更加严重。In this paper, the sensitive volume of SRAMs was constructed based on RPP(Rectangular ParallelePiped Volume) model using the Monte-Carlo code Geant4. The interactions of heavy ion with materials and the SEU(Single Event Upset) cross section calculation method were presented in the program. The SEU cross section curves with the linear energy deposition ware obtained. The SEU threshold value and saturation cross section were consistent with the testing data with heavy ions beam. The δ electrons distribution were different in the device material, which were generated by Bi ion with LETs of 99.67 MeV/(cm2·mg) and Bi ion, Xe ion with LETs of 69 MeV/(cm-2·mg). These results indicate δ electrons distribution impacts on the SEU cross section. According to the relation of energy deposition in the sensitive volume, the δ electrons distribution have more and more important effect on the Single Event Effect with reducing the feature size of semiconductor devices.     

铁电存储器中高能质子引发的单粒子功能中断效应实验研究

利用中国原子能科学研究院的中高能质子实验平台,针对两款商用铁电存储器开展了中高能质子单粒子效应实验研究,发现其中一款器件在质子辐照下发生了单粒子翻转和单粒子功能中断.本文主要针对单粒子功能中断效应展开了后续实验研究.首先通过改变质子能量对器件进行辐照,发现单粒子功能中断截面随质子能量的提高而增加.为进一步研究器件发生单粒子功能中断的机理,利用激光微束平台开展了辅助实验,对铁电存储器的单粒子功能中断效应的敏感区域进行了定位,最后发现铁电存储器单粒子功能中断是由器件外围电路发生的微锁定导致的.     

重离子在14-nm FinFET SRAM器件引起的单粒子翻转

通过重离子实验研究了14-nm FinFET工艺静态随机存取存储器(SRAM)的单粒子翻转(SEU)特性。通过使用Weibull函数拟合SEU截面获得该器件的线性能量转移(LET)阈值:0.1 MeV/(mg/cm2)。对多位翻转(MBU)贡献的统计结果表明,当LET等于40.3 MeV/(mg/cm2)时,MBU的占比超过95%。此外,FinFET SRAM的SEU截面呈现出与Fin相关的入射角度的各向异性。该研究对基于FinFET工艺的抗辐射CMOS集成电路(IC)的设计具有一定的指导作用。     

Dosimetry and microdosimetry of 10–220 MeV proton beams with CR-39 and their verifications by calculation of reaction cross sections using ALICE,TALYS and GEANT4 codes

High- and intermediate-energy protons are not able to directly form a track in a CR-39 etch detector (TED). Such detectors, however, can be used for the detection and dosimetry of the beams of these particles through the registration of secondary charged particles with sufficiently high values of linear energy transfer (LET). High-energy protons (72–220 MeV) and Intermediate-energy protons (10–30 MeV) with low LET values ranging from 1.1 down to 0.4 keV/μm and 5.87 down to 2.40 keV/μm, respectively are considered in this study. It seems to be sufficient to create secondary particles, although the LET values are low. This phenomenon can modify the characteristics of the energy transfer process due to these particles, which should be taken into account when such particles are used for radiobiology studies or for radiotherapy. The importance of these secondary particles was investigated experimentally by means of an LET spectrometer based on a chemically etched track detector in which the tracks of the primary protons are not revealed. Experiments were performed with proton beams available at the Nuclear Research Center for Agriculture and Medicine (NRCAM) in Karaj, Iran and at the National Cancer Center (NCC) in Seoul, Korea with protons of primary energies of about 10–30 MeV and 72–220 MeV respectively. The contribution of the secondary particle dose increases as the proton energy decreases. The origin of the secondary particles in interactions with protons having high and intermediate energies due to various nuclear reactions was calculated by the both ALICE and TALYS computer codes. The secondary microdosimetry doses were also calculated by GEANT4 code. There is large discrepancy between experimental and calculated results in low proton energies. It has been verified that there is a good correlation between the experimentally obtained results and the reaction cross sections predicted by ALICE and TALYS codes.     

Large-angle proton emission in the 9Be(p, 2p) reaction at 300 MeV

A ⁹Be(p, 2p) coincidence experiment performed to further elucidate the reaction mechanism for the production of energetic wide-angle protons in intermediate-energy proton-induced reac- tions is reported. Detectors in a coplanar geometry were used to measure coincidences between trigger protons at 90° to the beam and forward-angle protons on the opposite side of the beam. The incident proton energy was 300 MeV. We report both the inclusive spectra for the trigger protons and the differential mean multiplicities for the coincidence events.The outgoing proton energies were measured using NaI detectors. Trigger protons were grouped into 10 MeV bins covering the kinetic energy range from 55 to 155 MeV. The forward protons were measured over a kinetic energy range of 65–280 MeV and an angular range of 14–60° with respect to the beam.The present results are compared with two previous experiments which covered a more restrictive kinematical range. Calculations are performed with both phase-space and direct knockout models, and compared with experiment. Observation of angle and energy correlation effects suggested by knockout models indicate that such direct mechanisms provide a significant contribution to energetic wide-angle inclusive proton spectra.     

Calculations of particle and heavy ion interactions with space shielding materials using the SHIELD-HIT transport code

Spectra of secondary particles produced by nucleus–nucleus interactions and heavy-ion interactions in the extended targets of interest for space research were calculated using the Monte Carlo code SHIELD-HIT. This code simulates the interactions of hadrons and atomic nuclei of arbitrary charge and mass number (Z,A) with complex extended targets in a wide energy range, from 10 GeV/u down to 1 MeV/u, and to thermal energies in the case of neutrons. Inelastic nuclear reactions in SHIELD-HIT are simulated using the Russian models of nuclear reactions. The total reaction cross sections evaluated by these models are discussed for proton and carbon interactions with different nuclei in a wide energy range. Production of secondary neutrons and charged secondary particles from the thick targets of lead, water and PMMA irradiated by ⁴He, ¹²C and ²⁸Si ions of different energies was calculated and compared with the experimental data. The results obtained by SHIELD-HIT are in reasonable agreement with experiments and are promising for further applications in space research.     

LET spectra measurements on LDEF: variations with shielding and location

LET spectra measurements made with passive plastic nuclear track detectors (PNTDs) were found to depend on detector orientation, shielding and experiment location. LET spectra were measured at several locations on LDEF as part of the P0006 LETSME experiment (Benton and Parnell, 1984), the P0004 Seeds in Space experiment (Parks and Alston, 1984), the A0015 Free Flyer Biostacks and the M0004 Fiber Optics Data Link experiment (Taylor, 1984). Locations included the east, west and Earth sides of the LDEF satellite. The LET spectra measured with PNTDs deviated significantly from calculations, especially for high LET particles (LET_∞·H₂O ≥ 100 keV/μm). At high LETs, short-range inelastic secondary particles produced by trapped proton interactions with the nuclei of the detector were found to be the principal contributor to LET spectra. At lower LETs, the spectra appeared to be due to short-range, inelastic and stopping primary protons, with primary GCR particles making a smaller contribution.

The dependence of LET spectra on detector orientation and shielding was studied using the four orthogonal stacks in the P0006 experiment. Both measurements of total track density and LET spectra showed a greater number of particles arriving from the direction of space than from Earth. Measurements of LET spectra in CR-39 PNTD on the east (leading) and west (trailing) sides of LDEF showed a higher rate of production at the west side. This was caused by a larger flux of trapped protons on the west side as predicted by the east/west trapped proton anisotropy in the South Atlantic Anomaly (SAA).

Track density measured in CR-39 PNTDs increased as a function of shielding depth in the detector stack. A similar measurement made in a thick stack of CR-39 interspersed with layers of Al and exposed to 154 MeV protons at a ground-based accelerator showed a similar result, indicating that a significant fraction of the particle events counted were from secondaries and that the total cross-section for production of proton-induced secondaries increased as the energy of primary protons attenuated. Little change was seen in either total differential or integral LET spectra as a function of shielding depth, indicating that the increase in cross section with decreasing proton energy affected mostly the shorter range secondary components. Similarity in the slopes of LET spectra from ground-based proton exposures and the A0015 LET spectra showed that modeling of a monoenergetic proton beam transported through a 1-D geometry was a useful first step in modeling the production of secondary particles by trapped protons in the SAA.     

Polarization of protons from the Be(d, p)Be reaction

The polarization of protons from the ⁹Be(d, p)¹⁰Be reaction has been measured for deuteron energies between 1 and 6 MeV. Angular distributions of the polarization for the ground state proton group (Q=4.59 MeV) have been measured for laboratory angles 10° and 135° at 2.5, 4.0 and 5.5 MeV. The polarization at a laboratory angle of 30° was measured in 0.2 MeV steps between 1 and 6 MeV. In addition the polarization of protons leaving ¹⁰Be in its first excited state (Q=1.22 MeV) was measured between 10° and 90° for a deuteron bombarding energy of 5.5 MeV. Measurements were made by conventional double-scattering techniques using elastic scattering from helium at 45° as the analyser. The results show a strong energy dependence contrary to what one might expect on the basis of the lack of structure in the cross section. The maximum polarization observed at each energy is about 0.35.     

SAMPEX observations of energetic hydrogen isotopes in the inner zone

We report observations of geomagnetically-trapped hydrogen isotopes at low altitudes, near the feet of field lines in the inner zone, made with the PET instrument aboard the SAMPEX satellite. We have mapped protons from 19 to 500 MeV, and have discovered a collocated belt of deuterons, which we have mapped from 18 to 58 MeV/nucleon. We found deuterium at about 1% of the level of the proton flux at the same energy per nucleon, and no tritium at energies of tens of MeV/nucleon with an upper limit of about 0.1% of the proton flux. Protons and deuterons showed similar time dependence, with fluxes approximately tripling from July 1992 to March 1996, and similar pitch-angle dependence. The high-L limits of the proton and deuteron belts as functions of energy were organized by rigidity, as was to be expected if these limits were set for both species by inability of particles to sustain adiabatic motion and stable trapping.     

Response of a track-etch-based LET-spectrometer to high-energy protons

The spectrometer of linear energy transfer (LET) was developed. It is based on the chemically etched polyallyldiglycolcarbonate (PADC) track-etch detector. LET spectra are estimated through track parameter determination and analysed by an automatic optical image analyser LUCIA G. Three PADC materials were used: 0.5 mm thick Page, 0.5 and 1 mm thick Tastrak; they were exposed to protons with energies up to 1000 MeV. Such energetic protons are generally not directly registrable in any of PADCs mentioned; the tracks observed correspond mostly to secondary particles created through nuclear interactions of primary protons. LET spectra permit to calculate the dose absorbed in the detector due to these secondary particles and to compare it with the ionization collision dose of primary protons. It is observed that the dose due to secondary particles represents a few percent of the ionization collision dose. Their ratio varies slightly with proton energy, and some differences between the three PADCs used were also observed. The importance of results obtained for on-board spacecraft dosimetry is analysed and discussed.