|Place of Conferral||北京|
|Keyword||Cmos图像传感器 钳位光电二极管 电离总剂量效应 位移损伤效应 抗辐射加固|
宇航成像技术广泛应用于对地遥感观测、空间态势监控、航天器姿态控制等航天工程，是横跨航天器平台技术和有效载荷技术两大领域的关键性技术，其最为核心的组件是各类高性能高可靠光电探测器件，具体到可见光和近红外波段，主要是CCD和CMOS图像传感器。相对于传统的CCD，CMOS图像传感器器件感光像素阵列与读出电路、图像处理电路等可单片集成，工作电压较低，且采用随机读出方式，便于进行窗选等可配置操作，更加符合未来宇航设备轻小型、智能化、长寿命等发展趋势。由于卫星工作的绕地轨道上存在银河宇宙射线、太阳粒子和地球俘获带质子、电子等复杂的辐射环境，给CMOS图像传感器的正常工作带来威胁，导致其性能随在轨工作时间增加逐步退化，降低了空间任务的效果和卫星的有效使用寿命。高可靠性和长寿命的光学系统一直是空间探索任务的追求，因此CMOS图像传感器的空间辐射环境适应性和耐受力成为国内外辐射效应研究领域的热点。为了安全可靠的将CMOS图像传感器应用于空间辐射环境，针对器件在轨应用、抗辐射加固及评估中遇到的各种问题，国内外对CMOS图像传感器空间辐射效应开展了诸多的研究。在总结前人的研究成果时，我们发现在以下几方面缺乏深入研究。在效应机理研究方面，国内外主要针对电离总剂量辐射损伤机理开展了相关试验研究，对位移损伤效应及单粒子效应造成的损伤机制研究较少；在抗辐射加固设计方面，对CMOS 图像传感器的加固方法研究涉及工艺、版图、电路结构等方面，并且用设计实际器件验证加固原理，但综合设计加固较少，国内的相关研究大多停留在理论阶段；在试验样品选取方面，国内外大部分研究都是立足于CMOS 图像传感器的整体电路作为研究对象，由于没有对电路内部单元及元件中的辐照感生缺陷进行定量分离与测试，从而很难从本质上定量揭示辐射损伤机理。此外，随着CMOS图像传感器的制造工艺从深亚微米、超深亚微米到纳米量级的不断减小，像素数越来越高，带来了很多新的辐照损伤物理机制，辐照损伤效应仍有很多问题亟待深入研究。针对前面分析国内外研究中存在的问题，本论文选取 3T、4T不同像素类型为研究对象，以单独封装的CMOS图像传感器像素单元、以及器件整体电路为研究对象，首先建立了CMOS图像传感器的辐射效应测试系统与参数测试方法，通过CMOS图像传感器的γ射线、电子、质子、中子辐照试验，基于像素单元以及整体电路建立CMOS 图像传感器的空间辐射效应及损伤机理模拟试验研究方法，获得了器件在不同粒子辐照下的暗信号、暗信号非均匀性、饱和输出电压等电学参数及光谱响应的变化规律，分析了不同粒子辐照导致的电离总剂量效应、位移损伤效应ehehedan。通过研究像素单元的辐射损伤与电路性能参数退化的相关性，分析了辐射诱发缺陷与器件电学、光学参数退化的相关性。通过以上研究获得了辐射效应与机理的相关结果：γ射线与电子辐照主要导致电离总剂量效应，表现为暗信号、暗信号非均匀性、饱和输出电压产生退化，其机理是辐照在场氧中感生氧化物陷阱电荷与界面态，界面态占主导；质子辐照除导致电离总剂量效应，还导致位移损伤，中子辐照主要导致位移损伤。位移损伤主要表现为暗信号、光谱响应特性发生变化，此外还产生大量的热像素和随机电码信号，其机理主要是辐照感生点缺陷、缺陷簇等体损伤，形成禁带中的陷阱能级。通过不同粒子辐照试验探寻了深亚微米工艺条件下4T-CIS的弱点，提出了国产CIS的抗辐射加固优化建议，研究了辐射损伤对4T-CIS图像拖影的影响，获得图像拖影的退化规律，结合器件工艺结构和能带模型，分析了图像拖影退化的物理机理。通过项目实施建立的测试系统与测试方法为国产器件研制、工程应用评估提供了良好的支撑。试验内容设计与国产CMOS图像传感器的设计与工艺充分结合，相关研究结果对CMOS图像传感器抗辐射工艺的发展、辐射损伤评估方法和试验标准的建立具有重要的指导作用。
Space imaging techniques are widely applied to remote sensing, spatial trend monitoring, spacecraft attitude control and aerospace engineering, is across the key technologies of the platform technology of spacecraft and payload technology. The most core components are all kinds of high performance and high reliable photoelectric detection device, specific to the visible light and near infrared band, mainly of CCD and CMOS image sensors. Compared with the traditional CCD, CMOS image sensor pixel array and readout circuit, the image processing circuit can be monolithic integration, working voltage is low, and using random readout method, for window selection can be configured to operate, more in line with the future aerospace equipment light small, intelligent, long-life development trend. CMOS image sensor is the critical device in the satellite of weather forecast, astronomy, earth observation, navigation, and so on. Due to the complex radiation environment consist of Galactic cosmic rays, solar particles, and proton or electron from earth capture belts, the radiation effects induced by radiation environment will affect CMOS image sensor, rusulting in CMOS image sensor performance degradation gradually with the working hours of satellites in orbit, also the effective life of satellite. Because The optical system with high reliability and long life is always the pursuit of space missions, CMOS image sensor space radiation environment adaptability and tolerance has become a international hot research field. Due to the high sensitivity of CMOS image sensor, it is a difficult point of space radiation effects study that the sensitivity of defects caused by radiation in CMOS image sensor. On the basis of the research results acqured for CMOS image sensor radiation effects so far, the critical parameters of CMOS image sensor are high radiation effects sensitivity, such as dark signal, saturation output voltage, and so on. The cause of CMOS image sensor parameters degradation induced by radiation could be represented on the previous research on radiation effects of microelectronic devices. The effects of total ionizing dose took more thorough understanding, and the relevant technology, construction and CMOS image sensor’s operating mode for effective suppression of radiation damage were suggested. But the displacement damage parameter degradation mechanism of CMOS image sensor is still in the exploratory stage. In the test sample selection, most of the research at home and abroad are based on CMOS image sensor integrated circuit as the research object, because not to irradiation the internal circuit unit and components in the sense of birth defects were separated and quantitated by test, so it is difficult to essentially quantitative uncovering the mechanism of radiation damage. In addition, with the development of CMOS image sensor manufacturing process from the deep sub micron and super deep submicron to nanometer scale decreases, pixel number is more and more high, bringing the many new radiation damage to the physical mechanism, effects of irradiation injury still has many problems which need to be further studied.Base on the previous study results, this paper investigates the damage mechanism of CMOS image sensor induced by ionizing and displacement radiation, and analyzes the property degradation mechanism induced by proton incidence by comparing the CMOS image sensor s’ parameters degradation generated by incident 60Co-gamma ray and proton. This paper points out alse the effectiveness and limitation of the calculation method base on non-ionizing energy loss. For the first time the new method of separating displacement defects was proposed. The displacement damage was separated from the parameters degradation of CMOS image sensor exposed to proton according to the comparison between the ionization damage and displacement damage. This paper pointed out that the CMOS image sensor parameters change caused by displacement defects reflect the different influences of defects of various nature. After exposure to γ-ray, the most sensitive to radiation--dark signals and dark signal non-uniformity are discussed，the physical mechanism of the degradation with irradiation. One can see from the experimental，mean dark signals dramatically increased with total dose for both operated and static devices. Static device seems more affected by irradiation than operated device. We found that most of the total dark signal in a pixel is coming from the depletion of the photodiode edge at the surface and next is caused by the leakage of the source region of the reset transistor. Dark signal non uniformity follows the dark current evolution with total dose. These characterizations encompassed Cobalt-60 and low electron total ionizing dose, proton and neutron displacement damage tests at room temperature and annealing. This gives us the opportunity to discuss differences and similarities on this APS of degradation of saturation output induced by cobalt-60, electron, proton and neutron irradiation. The experiments show that the saturation output is degraded markedly induced by total ionizing dose, degradations of saturation output at different total dose and the recovery after annealing are compared, while no obvious degradation after neutron irradiation (neutron irradiation only induced displacement damage) . Mechanisms for these saturation output changes are discussed, saturated output degradation mainly caused by photodiode depletion layer capacitance decreases of irradiation, resulting in full-well capacity decline.In summary, this paper further enriched and improved the mechanism of CMOS image sensor radiation damage effects through the separation of the CMOS image sensor ionization damage and displacement damage. And improved emerging and impacting mechanism of displacement damage in CMOS image sensor irradiated by protons. This paper also provides the new ideas and methods for analysing the relationship between defects and parameters degradation of CMOS image sensor. In addition, the effect of radiation on CMOS image sensor output circuit and the spectral response filled the related research deficiencies of CMOS image sensor radiation effects. Last of all, the previous research resluts are summarized, and further promote the refinement, and provide ideas and guidance for further research in the next step.
|汪波. 3T和4T-CMOS图像传感器空间辐射效应及损伤机理研究[D]. 北京. 中国科学院大学,2016.|
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