|关键词||Cmos图像传感器 热像素 质子辐照 位移损伤 暗信号|
CMOS图像传感器（CMOS Image Sensor，CIS）在空间光电探测领域获得了越来越广泛的应用。空间辐射环境作用于CIS可产生辐射损伤效应：电离总剂量效应、位移损伤、单粒子效应。目前，CIS电离总剂量效应的研究开展较多,而位移损伤研究开展相对较少，特别对于位移损伤导致的CIS热像素，还缺乏深入认识。然而，哈勃望远镜、美国中段探测试验卫星及NEOssat等卫星上都出现了空间位移损伤效应导致的CCD热像素，对卫星的光电探测性能产生了严重影响。因此，有必要针对位移损伤导致CIS热像素的规律与机理开展研究，从而可通过地面试验评估和预计CIS的空间环境适应性，并采取相应的应对措施，为CIS的空间应用提供科学依据与技术支撑。本文通过CIS的质子辐照试验及退火试验，研究了CMOS图像传感器在质子辐照下产生热像素的规律与机理。首先，基于目前光电成像器件位移损伤的研究方法，建立了针对CIS热像素的测试方法：先通过辐照前后器件暗场图像的采集与处理，获得位移损伤导致热像素的总体规律，然后分析单个热像素暗的变化规律，通过统计获得整体效应规律的同时，也可深入分析局部的规律与机理。针对CIS器件进行了3MeV和10MeV质子辐照实验。在实验过程中针对每种能量质子进行了多个注量点测试。辐照实验结束后，对器件进行常温退火实验，获得热像素随着时间的变化规律，对比不同辐照条件下热像素的退火规律。在实验结束后，根据不同能量质子对器件产生的影响，结合质子在半导体内部产生缺陷的理论分析，获得了不同缺陷产生的热像素的性质，并进行了对比。然后，对辐照后的CIS器件进行了等时的变温退火实验，获得了不同温度下器件热像素的变化规律，对照不同缺陷在不同温度下的表现，获得了不同能量质子导致的缺陷的组成。不同温度的退火也可以给空间应用提供一个减轻热像素影响的指导。此外，在测试的时候采用了变温测试，用以计算器件的激活能，从而判断是否存在电场增强效应。通过辐照实验，发现3MeV质子相对于10MeV质子能产生更多的热像素，但是产生的热像素亮度不如10MeV质子。而无论何种质子，产生的热像素数量都随着注量的提升呈线性增长。经过常温退火后，发现3MeV质子产生的热像素不如10MeV质子产生的温度。经过变温退火实验和变温测试，确定器件内的主要缺陷是空缺-磷原子对和E70，这个CIS器件不存在电场增强效应。
CMOS image sensors (CIS) are the result of the continuous improvements in image-dedicated CMOS technology. These devices reach very high performance levels in power consumption, miniaturization, cost and speed thanks to scaling compared to traditional charge coupled device (CCD). Thanks to all these features, CIS are now good candidates in demanding applications such as medical imaging, particle detection, and space remote sensing. In the space radiation environment,-rays, electrons, protons and high energy particles impinge electronic devices, interact with CIS and alter their electrical properties. The radiation-induced damages can be separated into two phenomena: ionization effects and displacement damage effects. Dedicated studies on CIS behavior under irradiation have been carried out. Some of these studies propose results on devices or test vehicles with an optimized design for total dose hardness. Thanks to the last generation of CIS and to the CIS hardened against TID, ionizing effect impacts are clearly reduced. Few studies exist concerning the effects of displacement damage on CIS and displacement damage mechanism has not been well understood. In CIS, displacement damage defects located in the photodiode space charge area increase the mean dark current, which induces hot pixel and leads to the degradation of CIS performance. At present, it has been found that the displacement damage effect induces hot pixels, which has a serious impact on the Hubble Space Telescope and NEOssat satellite's photoelectric detection performance. In addition, there is no effective means to eliminate the effect of hot pixels on optoelectronic imaging devices. Therefore, it is necessary to carry out research on the problem of CIS hot pixels caused by displacement damage, and provide scientific basis and technical support for the space applications of CIS.Firstly, based on the research methods of displacement damage of photoelectric imaging devices, this paper proposes a test method for CIS hot pixels. The main concern of the test lies in the dark current parameters of the CIS. By collecting images before and after irradiation in dark condition, the hot pixels can be obtained. The analysis method for a single pixel is adopted to distinguish the hot pixels with different brightness and obtain more accurate hot pixel variation rules. Afterwards, the change law of hot pixels and related defect theory are combined to obtain the mechanism of hot pixel generation.Secondly, on the basis of the test method, proton irradiation for CIS devices has been carried out with different energies. Various fluences were used for each energy proton during the experiment. At the end of the experiment, depending on the influence of protons of different energies on the device, the differences in defect types generated by different energies are referenced, thereby obtaining the differences in the nature of the hot pixels generated by different defects. According to the change of dark current of the device under different fluence proton irradiation, the change of hot pixels caused by the fluence was obtained. After the irradiation experiment, the devices were annealed at room temperature, and the changes of thermal pixels generated by different energies during the annealing process were compared to obtain the change rule of thermal pixels over time.Finally, the isochronous temperature-variable annealing experiment was performed on CIS devices irradiated by different energy proton. The composition of defects generated by different energy displacement damages can be obtained more accurately by comparing the variation of hot pixels of devices at different temperatures and the behavior of different defects at different temperatures. In addition, annealing at different temperatures can also provide guidance to space applications to mitigate the effects of hot pixels.In summary, based on the current displacement damage theory, this paper studies the hot pixel problems caused by proton radiation in CMOS image sensors which is based on the actual needs of space applications, and provides theoretical guidance for the space application of CMOS image sensors.
|王田晖. CMOS图像传感器在质子辐照下产生热像素的规律与机理研究[D]. 北京. 中国科学院大学,2018.|
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