Dark Current Nonuniformity Research Articles

Effect of proton beam irradiation on the tracking efficiency of CMOS image sensors

A star tracker provides accurate space positioning and reference for satellites, intercontinental strategic missiles, and other spacecrafts. However, the main imaging unit of the star sensor – the image sensor – is affected by the space radiation environment and, in turn, affects the precision with which the star is located by the star tracker. In this study, the parameter degradation of a CMOS image sensor (CIS) after proton irradiation with different fluences was investigated. An outfield test platform for star map collection was built using the star sensor lens and image collection system. The influence of dark current, dark-current nonuniformity, and photo-response nonuniformity of the irradiated CIS on the star diagonal distance measurement error and star-point centroid position detection accuracy was studied. The results showed that with increasing proton fluences, the CIS noise increased, leading to an increase in the error in the measured diagonal distance of the star and a decrease in the star’s position detection accuracy. Among these parameters, the dark current plays the greatest role in influencing the measurement accuracy of the star tracker. Furthermore, when a tracker is exposed to space radiation with fluences that are same as those used in this experiment, it is beneficial to reduce the integration time. This reduction in the time will decrease the noise and improve the position measurement accuracy.

A Kinetic Monte Carlo Algorithm to Model the Annealing Process and Compute the Dark Current Nonuniformity

A simulation chain, composed of GEANT4 and a kinetic Monte Carlo (KMC) algorithm, dedicated to study the annealing process of defects produced after energetic particle irradiation is presented. Results will be used to compute dark current nonuniformity (DCNU).

Heavy Ion Irradiation Induced Single Particle Displacement Damage in 8T Global Shutter CMOS Image Sensor

The single particle displacement damage effects and mechanisms in 8T Global Shutter CMOS image sensors (CISs) are studied. We provide radiation effects due to 129Xe ion irradiations of 8T Global Shutter CIS by the analyses of dark current spikes and dark current non-uniformity (DCUN). The experimental results show that low fluence irradiation-induced dark current distributions in 8T global shutter CIS exhibit a clear exponential hot pixel tail that appears difficult to match with cumulative radiation effect physical models. The degradation mechanism is a high electric field distribution exists at the overlap region between gate and pinned-photodiode (PPD). The emission rate of a defect can be dramatically enhanced via a high electric field. Irradiation-induced defects are the sources of the dark electron generation and the electric field acts as an amplifier.

Lookup Table Approach for Radiometric Calibration of Miniaturized Multispectral Camera Mounted on an Unmanned Aerial Vehicle

Over recent years, miniaturized multispectral cameras mounted on an unmanned aerial vehicle (UAV) have been widely used in remote sensing. Most of these cameras are integrated with low-cost, image-frame complementary metal-oxide semiconductor (CMOS) sensors. Compared to the typical charged coupled device (CCD) sensors or linear array sensors, consumer-grade CMOS sensors have the disadvantages of low responsivity, higher noise, and non-uniformity of pixels, which make it difficult to accurately detect optical radiation. Therefore, comprehensive radiometric calibration is crucial for quantitative remote sensing and comparison of temporal data using such sensors. In this study, we examine three procedures of radiometric calibration: relative radiometric calibration, normalization, and absolute radiometric calibration. The complex features of dark current noise, vignetting effect, and non-uniformity of detector response are analyzed. Further, appropriate procedures are used to derive the lookup table (LUT) of correction factors for these features. Subsequently, an absolute calibration coefficient based on an empirical model is used to convert the digital number (DN) of images to radiance unit. Due to the radiometric calibration, the DNs of targets observed in the image are more consistent than before calibration. Compared to the method provided by the manufacturer of the sensor, LUTs facilitate much better radiometric calibration. The root mean square error (RMSE) of measured reflectance in each band (475, 560, 668, 717, and 840 nm) are 2.30%, 2.87%, 3.66%, 3.98%, and 4.70% respectively.

Comparison of X-Ray and Electron Radiation Effects on Dark Current Non-Uniformity and Fluctuations in CMOS Image Sensors

This article investigates the dark current as well as the dark current random telegraph signal (RTS) after 1-MeV electron, 3-MeV electron, and 10-keV X-ray irradiations in a pinned photodiode CMOS image sensor (CIS). A large range of deposited ionizing dose from 10 to 525 krad(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) is considered. The displacement damage dose deposited through electron irradiation ranges from 60 to 1200 TeV · g <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . Results on dark current distributions highlight the predominance of the ionizing damage in opposition to the displacement damage induced by the electron irradiations. Moreover, the dark current distributions also suggest that if the ionizing dose is high enough [i.e., beyond 50 krad(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )], the trapped positive charges in the silicon oxides create high magnitude electric field regions leading to an electric field enhancement (EFE) of the dark current which is neither present at lower doses nor in pristine image sensors. This EFE mechanism also seems to have a strong influence on the RTS leading to a clear discrepancy from the existing dark current nonuniformity model developed for amplitude distributions in CISs as well as from what is reported in the literature in the more studied ionizing dose range. Annealing treatments after electron irradiations have highlighted the existence of specific population of pixels sharing the same well-defined maximum transition amplitudes (i.e., maximum amplitude between two dark current levels). The results suggest the use of maximum transition amplitude spectroscopy applied to dark current RTS to push forward the investigation on radiation-induced defects creation and identification.

Radiation Effects Due to 3MeV Proton Irradiations on Back-Side Illuminated CMOS Image Sensors**Supported by the National Natural Science Foundation of China under Grant No 11675259, the National Defense Pre-research Foundation of China under Grant No 6140A2404051, and the West Light Foundation of Chinese Academy of Sciences under Grant Nos 2016-QNXZ-B-8 and 2016-QNXZ-B-2.

Benefitting from the higher quantum efficiency and sensitivity compared with the front-side illumination (FSI) CMOS image sensors (CISs), backside illumination (BSI) CMOS image sensors tend to replace CCDs and FSI CISs for space applications. However, the radiation damage effects and mechanisms of BSI CISs in the radiation environment are not well understood. We provide radiation effects due to 3 MeV proton irradiations of BSI CISs dedicated to imaging by the analyses of mean dark current increase, dark current nonuniformity and full well capacity in pixel arrays and isolated photodiodes. Additionally, the present annealing certifies the radiation-induced defects, which are responsible for the parameter degradations in BSI CISs.

Comparison of Methods to Calculate the Dark Current Nonuniformity

Analytical and Monte Carlo dark current nonuniformity (DCNU) prediction methods are compared. The difference is studied according to different assumptions used for the calculations. The analysis is performed as a function of the incident proton fluence. The convergence of the DCNU toward a Gaussian distribution predicted by the central limit theorem is also investigated.

Impact of the Border Crossing Effects on the DCNU for Pixel Arrays Irradiated With High Energy Protons

A 3D Monte Carlo model based on GEANT4, dedicated to the simulation of the Dark Current Non Uniformity (DCNU) in image sensors, is used to study the impact of the geometrical dimensions of pixels, on the shape of the DCNU. The study focuses on the inelastic nuclear interaction which is the dominant process for high degradation levels (tail of the DCNU). Simulations made on different pixel geometries demonstrate that border crossing effect impacts the shape of the DCNU only for very small pixel dimensions (depleted volume <; 8 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ).

Modeling the Dark Current Non-Uniformity of Image Sensors With GEANT4

The 3D Monte Carlo transport code GEANT 4 was used to simulate the Dark Current Non Uniformity of image sensors. The method includes three different physical processes: the Coulombic scattering, the nuclear elastic interaction and the nuclear inelastic interaction. The dark current distribution is directly deduced from the damage distribution according to the Universal Damage Factor of Srour (UDF). Comparisons have been performed with experimental measurements made on two CMOS Image Sensors (JADE from E2 V and HAS2 from ON SEMICONDUCTOR) irradiated with protons of various energies ranging from 30 MeV to 185 MeV. Despite the simplifying assumptions of the model, the calculations are demonstrated to be in quite good agreement with experimental data.

Analysis and evaluation of uniformity of SWIR InGaAs FPA—Part I: Material issues

The nonuniformity caused by fluctuations of indium composition, thickness and doping concentration of epitaxial absorption layer of InGaAs focal plane arrays (FPAs) is estimated theoretically with the incorporation of practical status. By the measurements on epitaxy wafers of 2 in. size, the fluctuation of indium composition is observed to be less than ±0.2% and ±1% for lattice matched In 0.53Ga 0.47As and wavelength extended In 0.80Ga 0.20As photodetector structures respectively, while the thickness and doping fluctuations are assumed to be the same. Results show that the response nonuniformity caused by fluctuation of indium composition is dependent on the target wavelength and can be neglected with a minor composition fluctuation if the cutoff wavelength is well set. The total response nonuniformity induced by the effects of thickness and doping fluctuations, which dominates the FPA performance for large signal applications, is estimated to be less than ±0.1% and ±0.5% for In 0.53Ga 0.47As and In 0.80Ga 0.20As FPAs smaller than 1 in. in maximum side length. Neglecting the effects of defects, the total detectivity nonuniformity caused by these fluctuations is about ±2% for In 0.53Ga 0.47As FPA and will reach up to about ±19% for In 0.80Ga 0.20As FPA, where the dark current nonuniformity due to the fluctuation of composition plays the most critical role.

Displacement Damage Effects Due to Neutron and Proton Irradiations on CMOS Image Sensors Manufactured in Deep Submicron Technology

Displacement damage effects due to proton and neutron irradiations of CMOS image sensors dedicated to imaging are presented through the analysis of the dark current behavior in pixel arrays and isolated photodiodes. The mean dark current increase and the dark current nonuniformity are investigated. Dark current histogram observations are compared to damage energy distributions based on GEANT 4 calculations. We also discuss, through annealing analysis, which defects could be responsible for the dark current in CMOS image sensors.

Ionization versus displacement damage effects in proton irradiated CMOS sensors manufactured in deep submicron process

Proton irradiation effects have been studied on CMOS image sensors manufactured in a 0.18 μ m technology dedicated to imaging. The ionizing dose and displacement damage effects were discriminated and localized thanks to 60Co irradiations and large photodiode reverse current measurements. The only degradation observed was a photodiode dark current increase. It was found that ionizing dose effects dominate this rise by inducing generation centers at the interface between shallow trench isolations and depleted silicon regions. Displacement damages are is responsible for a large degradation of dark current non-uniformity. This work suggests that designing a photodiode tolerant to ionizing radiation can mitigate an important part of proton irradiation effects.

Enhanced dark current generation in proton-irradiated CMOS active pixel sensors

The dark current increase due to proton-induced displacement damage is studied in a standard and a radiation-hardened CMOS active pixel sensor (APS). Several devices have been irradiated with protons of different energies and fluences. The influence of the proton energy and fluence on the mean dark current increase and the dark current nonuniformity is investigated. Dark current density histograms are obtained by the theory based on collision kinematics. They are determined by the number of elastic and inelastic collisions and the damage these interactions create in the pixel sensitive volume. It is shown that field enhanced emission has to be taken into account to predict accurately the distribution of the dark current density increase. We also compare the results with data found in literature for charge coupled devices (CCD) and charge injection devices (CID).

Performance analysis of a color CMOS photogate image sensor

The performance of a color CMOS photogate image sensor is reported. It is shown that by using two levels of correlated-double sampling it is possible to effectively cancel all fixed-pattern noise due to read-out circuit mismatch. Instead the fixed-pattern noise performance of the sensor is limited by dark current nonuniformity at low signal levels, and conversion gain nonuniformity at high signal levels. It is further shown that the imaging performance of the sensor is comparable to low-end CCD sensors but inferior to that reported for high-end CCD sensors due to low quantum efficiency, high dark current, and pixel cross-talk. As such the performance of CMOS sensors is limited at the device level rather than at the architectural level. If the imaging performance issues can be addressed at the fabrication process level without increasing cost or degrading transistor performance, CMOS has the potential to seriously challenge CCD as the solid-state imaging technology of choice due to low power dissipation and compatibility with camera system integration.