空间辐射环境下CMOS图像传感器的暗电流幅值分布模型研究

With the development of space science and techniques, CMOS image sensors are so important as sensing equipments which are applied in scientific research and military areas such as space detection, satellites attitude determination, aerospace photography and intercontinental ballistic missile guidance. However, radiation from space do great harm to the Si-photoelectric device, which results in pixels' average dark-current increase, brings a part of the pixels with high dark-current peaks and even makes some pixels invalid. Thus, the SNR and image quality of the sensors are badly influenced. In this project, radiation mechanism of semiconductor and important technical reports will be reviewed firstly to investigate the characteristics of dark-current amplitudes of pixels exposed to various radiation sources. Then dark-current amplitudes distributions models under complicated radiation environment will be founded based on two basic models: one is the Gaussian model (corresponding to the total-ionizing-dose-like radiation) and the other is exponential law (corresponding to the displacement-damage-dose-like radiation). Compared with modeling methods based on the types of incident particles, proposed methods give advantages that the models will be more transplantable in various radiation environments. Moreover, in order to deal with the dark-current degradation and improve the dynamic range as well as SNR of CMOS image sensors, a feedback system will be designed according to the dark-current amplitudes distribution models.

随着空间科学技术的发展，CMOS图像传感器作为重要的感知设备被广泛应用到空间探测、卫星姿态定位、航天拍摄、洲际导弹制导等科研及军事领域。然而，空间存在的各种辐射会对硅光电器件造成损伤，导致图像传感器像素平均暗电流增强，部分像素还会产生较高的暗电流峰值甚至出现失效，造成图像传感器的信噪比下降，成像质量严重受损。结合半导体辐射理论及文献研究，在对各种粒子入射下暗电流幅值特征进行分析的基础上，本项目将尝试通过仿真及辐照实验手段研究基于高斯分布(对应总剂量类辐射效应)及指数分布(对应移位损伤类辐射效应)两种基础分布模型建立复杂辐射环境下像素阵列的暗电流幅值分布模型。该方法特色在于基于辐射效应而非基于某种粒子对暗电流幅值分布进行建模，大大减小了建模的工作量并提高了模型的环境适用性。本项目还将依据模型设计动态范围调节及暗电流抑制系统，用于在空间辐射环境下提高图像传感器动态范围并抑制暗电流噪声。

空间环境中存在各种高能粒子，这些粒子入射到CMOS图像传感器中会使像素器件产生缺陷，引起图像传感器暗电流均值及其不一致性增强。在长期空间任务中,像素暗电流噪声在累积辐射剂量效应下发生的严重退化已成为制约CMOS图像传感器输出高信噪比图像的首要噪声问题。针对这一问题，在自然基金委的支持下，项目组结合空间辐射环境的特点，基于半导体物理损伤机理，开展了辐射效应下CMOS图像传感器暗电流特征的分析和研究，提出了一套暗电流幅值分布的建模理论和方法。该理论和方法为空间质子、电子辐射及混合辐射环境下，CMOS图像传感器暗电流噪声的评估提供了科学的指导和可量化的分析策略。项目成果进一步与经典噪声的分析方法结合，可以为特定任务轨道,特定任务期内CMOS图像传感器的信噪比建模提供理论支撑，实现CMOS图像传感器在轨使用寿命预测；且能够为高信噪比空间图像传感器的设计提供理论依据、地面辐射验证的空间环境模拟方案及性能评估方法。