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静态随机存储器总剂量辐射效应及评估技术的研究
李茂顺
学位类型硕士
导师余学峰
2010-06-04
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业微电子学与固体电子学
关键词Sram 总剂量辐射效应 敏感参数 偏置条件 剂量率
摘要随着集成电路的发展,静态随机存储器(Static Random Access Memory,简称SRAM)逐渐成为数字处理、信息处理、自动控制设备中不可缺少的部件,并被广泛地应用到各类航天器和卫星的控制系统中。然而空间电离辐射环境会给SRAM带来辐射损伤,降低其可靠性和稳定性,严重时会导致器件功能失效,最终影响航天任务的顺利进行。因此,开展SRAM器件的电离辐射响应规律和损伤机理的研究,建立大规模SRAM 集成电路的测试方法和评估技术,对我国抗辐射电子学及航天领域的发展具有重要的意义。 本文主要以1Mbit的静态随机存储器为研究对象,对大规模SRAM集成电路的辐射效应及辐射损伤机理进行了研究,并对SRAM总剂量辐射效应评估方法进行了初步探索。主要的研究工作与结论如下: 由于对大规模SRAM集成电路的总剂量辐射效应研究不同于一般意义上的SRAM功能测试和故障检测,需要有专门的辐射效应测试系统。根据这个要求,我们自制了一套SRAM多参数测试系统,该系统除了能进行SRAM读写功能检测外,还能测试器件的输出高低电平、静态及动态功耗电流、传输延迟以及输入输出波形的比较等,为SRAM的辐射效应和损伤机理研究提供了有利的武器。 为了更加准确地对SRAM的辐射效应进行评估,需要确立SRAM总剂量辐射下的敏感参数。文中对SRAM器件的多个电特性参数和功能参数的辐照敏感度进行了分析,最终确立了功耗电流作为SRAM辐射效应的敏感参数。同时,对SRAM的电参数和功能参数的相关性进行了研究,确立了器件功能失效的预警量。 由于实际工作中的SRAM常常处于不同的偏置状态,因此有必要对不同偏置条件下SRAM的辐射效应进行研究。本文共进行了八种不同偏置条件下的SRAM总剂量辐照实验及退火实验,结果表明:偏置条件对SRAM器件的辐射损伤有较大影响,不同偏置条件下的SRAM器件的辐射损伤明显不同,其中静态加电偏置的损伤最大,其次是工作状态,浮空状态最小。不同偏置条件下的差异主要来自于内部电势和电场分布不同等因素。辐照偏置条件不同,SRAM器件参数在退火过程中的恢复程度也不同。辐照损伤越大的偏置条件下,电参数和功能参数随退火时间恢复的程度越小,通过研究初步认为该现象主要与辐射感生的陷阱能级有关联。另外,退火温度对器件参数的恢复影响很大,其中高温更有利于器件参数的退火。 为了更好地对实际空间中的SRAM辐射效应进行模拟评估,本文进行了不同剂量率下的SRAM辐照实验,结果表明:无论是电参数的退化还是功能参数的失效,都表现出低剂量率损伤明显大于高剂量率的情况。并且在辐照过程中,不同剂量率均出现功能参数在一定的总剂量辐照后的“恢复”现象,认为这种现象主要是由于大量的界面陷阱电荷产生,补偿了氧化物陷阱电荷的作用,使得器件阈值电压明显回漂造成的。
其他摘要With the development of the integrated circuits, Static Random Access Memory (SRAM) is becoming the essential components in the digital-process equipments and auto-controlling devices. Especially, it is widely used in the controlling system in kinds of spacecrafts and secondary planets in the recent years. However, the cosmic rays and high energy particles will induce damages and decrease the reliability and stability of the devices. Due to long time irradiation, the device function may be invalidated. Therefore, it is necessary to research on the radiation effects and damage mechanisms of the SRAM devices, which is important to the development of the radiation-hardened SRAM devices. The total-dose radiation effects and damage mechanisms of 1Mbit SRAM were investigated. Moreover, the evaluation methods of radiation effects were studied. The main work and conclusions are described as follows: Because the research on radiation effects of large-scale SRAM circuits is more complicated than the regular functional test or failure detection, special test system is needed. So we made a set of multi-parameter test system, which can test the read-write function, high- and low-level voltages, dissipation currents, transit delay time and output waveforms. The establishment of the sensitive parameters to radiation is important to the evaluation of SRAM radiation levels. In this paper, the sensitivities of many electrical and functional parameters were analyzed, and the static current dissipation and the dynamic current dissipation were confirmed as the sensitive parameters. Meanwhile, the relationship between the electrical parameters and the functional parameters was studied, and the degradation of static current dissipation was confirmed as warning value of the functional invalidation. In the consideration of various bias situation adopted in the space, the radiation effects under different bias conditions were studied. In this paper, eight different biases were chosen during irradiation and annealing. The results have shown that the damages were quite different with different bias conditions: the static state was the worst condition, and next was the operation state, and there were least irradiation damages in the state of floating. It is considered that the differences mainly resulted from the different potentials and fields in the devices. In addition, with different bias conditions, the recovery situations of the parameters were also different: the larger damages occurred during irradiation, the smaller recovery turned up during annealing. It is thought that this phenomenon is related to the energy level of the radiation-induced defects. Moreover, the annealing temperature can have influence on the recovery of the parameters, and high temperature would accelerate the annealing process. Finally, the dose-rate effects of SRAM were investigated. The experiment results showed that the damages under low dose rate were higher than that of high dose rate, both for the degradation of the electrical parameters and the functional parameters. There were “rebound” of the parameters after a certain dose under all dose rates. It is considered that the phenomenon is resulted from the growth of the interface-trapped charges, which can compensate the action of the oxide-trapped charges and induce the backing shift of the threshold voltages.
文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4451
专题材料物理与化学研究室
作者单位中国科学院新疆理化技术研究所
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李茂顺. 静态随机存储器总剂量辐射效应及评估技术的研究[D]. 北京. 中国科学院研究生院,2010.
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