Analyzing the Radiation Degradation of 4-Transistor Deep Submicron Technology CMOS Image Sensors
Analyzing the Radiation Degradation of 4-Transistor Deep Submicron Technology CMOS Image Sensors
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DOI：
10.1109/jsen.2012.2186287
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发表时间：
2012-01
影响因子：
4.3
通讯作者：
J. Tan;B. Buttgen;Cynthia Yin
中科院分区：
文献类型：
--
作者：
J. Tan;B. Buttgen;Cynthia Yin
本文研究了采用标准0.18 μm工艺设计的4晶体管（4T）互补金属氧化物半导体（CMOS）图像传感器的辐射退化问题。本文的重要贡献是系统地评估了x射线辐射对图像传感器的影响，从单个器件水平到像素水平，再到整个传感器水平。分析了传感器的主要退化参数。本文还包括不同几何形状的像素内mosfet、钉住光电二极管（PPD）和转移门（TG）的测试结构。在高达109 krad的不同x射线剂量下进行表征。通过改变TG电荷转移时间和积分时间，分析了主要的衰减——暗信号的增加。PPD和TG是对传感器暗信号最敏感的元件。对传感器的辐射相关尺寸效应也进行了评估，结果与3T像素不同。转移栅长度对暗信号的影响不仅与热重通道内电场的变化有关，还与局部缺陷的产生有关。像素内mosfet用于识别辐射引起的暗信号增加的来源。浅沟隔离（STI）氧化物是传感器辐射退化的原因。在短波段辐照后，观察到量子效率略有下降。介绍了设计硬化的基本技术。辐射相关尺寸效应对传感器的影响以及STI效应的讨论结果可作为未来容辐射传感器布局设计的指导。识别像素暗电流的来源有助于确定在何处以及如何更有效地抑制像素暗电流的产生。
This paper presents a radiation degradation study on 4-Transistor (4T) complementary metal-oxide-semiconductor (CMOS) image sensors designed in standard 0.18-μm technology. The significant contribution of this paper is a systematic evaluation of the X-ray radiation effects on image sensors from the individual device level, to the pixel level and to the level of the entire sensor. The major degradation parameters of the sensor have been analyzed. This paper also includes test structures of varying geometries of in-pixel MOSFETs, pinned photodiodes (PPD), and transfer gates (TG). Characterization was performed during different X-ray doses up to 109 krad. The major degradation-an increase in the dark signal-is analyzed by modifying the TG charge transfer time and integration time. The PPD and the TG are the elements most sensitive to the dark signal of the sensor. The radiation-related dimensional effects on the sensors are also evaluated, which show different results compared to 3T pixels. The transfer-gate length influences the dark signal due to not only the electric field variation in the TG channel but also the local defect generations. In-pixel MOSFETs are used to identify the origin of increases in radiation-induced dark signal. Shallow trench isolation (STI) oxides are responsible for the radiation degradation of the sensor. A slight degradation of the quantum efficiency was observed after radiation in the short-wavelength region. Basic hardening-by-design techniques are also presented. The discussion results of the radiation-related dimensional effects on the sensors together with the STI effect can be used as a guideline for future layout designs of radiation-tolerant sensors. Identifying the pixel dark current origin can help to determine where and how to suppress the pixel dark current generation more effectively.