Dark Current Random Telegraph Signal Research Articles

Probing Dark Current Random Telegraph Signal in a Small Pitch Vertically Pinned Photodiode CMOS Image Sensor After Proton Irradiation

The dark current degradation and dark current random telegraph signal (DC-RTS) after proton irradiation are studied in new scale silicon microvolumes by using a commercial CMOS image sensor. Results show that previously reported empirical models describing the displacement damage-induced degradations are still valid despite the 10–100 times smaller depletion volume used. In addition, no evidence of significant total ionizing dose effects is observed. Finally, the reduction of the fraction of RTS pixels detected and the fraction of multilevel RTS pixels is directly linked to the reduction in pixel volume.

Displacement Damage Effects in Backside Illuminated CMOS Image Sensors

Displacement damage effects in backside illuminated CMOS image sensors (BSI CISs) are investigated. Several BSI CISs with distinct epitaxial layer thicknesses are irradiated by several protons and neutrons to study the influence of technology parameters and radiation parameters on the radiation response of these imagers. A significant degradation in quantum efficiency (QE) is observed for thick epitaxial layer at the absorbed dose of 1230 TeV/g. Dark-current damage factor of 0.141 e⁻·s⁻¹·μ m⁻³·(TeV/g)⁻¹ is determined in BSI CIS. The influence of particle types, particle energy, and radiation fluence on dark current distributions is presented at the same displacement damage dose (DDD). Dark current random telegraph signal (DC-RTS) is reported and the variation in epitaxial layer thickness has no influence on DC-RTS behavior. This work highlights the relationship between key parameters and DDD: the limiting factors of the imager performance are single pixel [hot pixel and random telegraph signal (RTS) pixel] at a low DDD range, mean dark current and single pixel at a medium DDD range, and mean dark current in the high DDD case, respectively.

Investigation of random telegraph signal in CMOS image sensors irradiated by protons.

ABSTRACT CMOS image sensors were irradiated by protons of 50 and 70 MeV and the dark current random telegraph signal (RTS) is investigated. After exposure to the protons, the experimental results provide new evidence that confirms the existence of a correlation between radiation-induced hot pixels and RTS pixels. Moreover, the evolutions of the percentage of hot pixels showing RTS behavior at distinct conditions are presented, suggesting the different dependence of two kinds of pixels on operation conditions. The results of the isochronal annealing experiment demonstrate that the defects responsible for RTS behavior are the cluster defects able to enhance thermal generation through Shockley-Read-Hall (SRH) mechanism.

Study of dark current random telegraph signal in proton-irradiated backside illuminated CMOS image sensors

The dark current random telegraph signal (DC-RTS) has been investigated in a four-transistor pinned photodiode 0.18-μm backside illuminated CMOS image sensor (BSI CIS). The sensors were irradiated by high energy protons of 50, 60 and 70 MeV, respectively. After exposure to protons, the radiation-induced variations of the number of RTS pixels, the number of RTS levels and transition maximum amplitude are analyzed. The effect of proton energy on RTS occurrence probability is studied using two types of theoretical models. Furthermore, DC-RTS dependence on the epitaxial layer thickness of the sensors is discussed, showing that there is no significant difference for DC-RTS phenomenon in different epitaxial layers.

Wavelet Analysis of RTS Noise in CMOS Image Sensors Irradiated With High-Energy Photons

This article explores the phenomenon of dark current random telegraph signal (DC-RTS) noise in commercial off-the-shelf CMOS image sensors. Five sensors were irradiated with high-energy photons to a variety of doses and analyzed with a wavelet-based signal reconstruction algorithm. The algorithm is explained in detail and the radiation effects on individual pixels are discussed. Finally, the production rate of RTS pixels as a function of dose is explored, providing information on the underlying defect structure responsible for this noise source.

Phosphorus Versus Arsenic: Role of the Photodiode Doping Element in CMOS Image Sensor Radiation-Induced Dark Current and Random Telegraph Signal

This work investigates the role of the phosphorus doping element in the radiation-induced dark current in a CMOS image sensor (CIS) photodiode. The neutron and proton irradiations on shallow arsenic-based photodiode CISs and deep phosphorus-based photodiodes CISs have been performed. The results highlight the applicability of the same dark current increase and random telegraph signal (RTS) models. Already verified on other photodiode structures, these results further extend the universality of these analytic tools. Moreover, it emphasizes that the phosphorus element does not play a significant role either in the radiation-induced dark current increase or in the dark current RTS. The results on RTS after annealing reveal the same recovery dynamic than those already observed in irradiated image sensors, suggesting that the phosphorus element does not play a significant role after annealing. Therefore, this work is a piece of experimental evidence supporting the idea that RTS induced by displacement damage is principally due to defect clusters mainly constituted of intrinsic silicon defects such as clusters of vacancies and interstitials.

Radiation-Induced Variable Retention Time in Dynamic Random Access Memories

The effect of gamma-ray and neutron radiations on the variable retention time (VRT) phenomenon occurring in dynamic random access memory (DRAM) is studied. It is shown that both ionizing radiation and nonionizing radiation induce VRT behaviors in DRAM cells. It demonstrates that both Si/SiO2 interface states and silicon bulk defects can be a source of VRT. It is also highlighted that radiation-induced VRT in DRAMs is very similar to the radiation-induced dark current random telegraph signal in image sensors. Both phenomena probably share the same origin, but high-magnitude electric fields seem to play an important role in VRT only. Defect structural fluctuations (without change of charge state) seem to be the root cause of the observed VRT whereas processes involving trapping and emission of charge carriers are unlikely to be a source of VRT. VRT also appears to be the most probable cause of intermittent stuck bits in irradiated DRAMs.

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.

Total Ionizing Dose Radiation-Induced Dark Current Random Telegraph Signal in Pinned Photodiode CMOS Image Sensors

In this paper, several studies on total ionizing dose effects on pinned photodiode CMOS images sensors are presented. More precisely, the evolution of a parasitic signal called random telegraph signal (RTS) is analyzed through several photodiode designs. It is shown that the population of pixels exhibiting this fluctuation depends on the design variants. This population also increases in a different way with the dose: the effects are not the same considering a low or high X-rays irradiation. Moreover, a statistical analysis is realized in order to better characterize the defects responsible for RTS. It turns out that an electric-field enhancement signature can appear in some specific cases.

In-Depth Analysis on Radiation Induced Multi-Level Dark Current Random Telegraph Signal in Silicon Solid State Image Sensors

Radiation-induced phenomena constitute a big concern for image sensors dedicated to space application. Particles (such as protons or electrons) can impact the crystalline structure of the detector and create switches in the dark response. This may be a problem, especially for calibration and so on image quality. This article aims at expressing the method used for switch detection and showing some properties of these Random Telegraph Signals (RTS), concerning, among other things, their amplitudes, discrete levels, and switching times. A first analysis of these results is also given.

Statistical Analysis of Random Telegraph Signal Maximum Transition Amplitudes in an Irradiated CMOS Image Sensor

This paper aims to propose a new approach to model the Dark Current Random Telegraph Signal (DC-RTS) maximum transition distribution in irradiated CMOS Image Sensors (CIS). Based on some outcomes of the Extreme Value Theory (EVT), it can be used to predict this distribution at the end of a given space mission. An example of application of this methodology is presented in detail.

Dark Current Random Telegraph Signals in Solid-State Image Sensors

This paper focuses on the Dark Current-Random Telegraph Signal (DC-RTS) in solid-state image sensors. The DC-RTS is investigated in several bulk materials, for different surface interfaces and for different trench isolation interfaces. The main parameter used to characterize the DC-RTS is the transition maximum amplitude which seems to be the most appropriate for studying the phenomenon and identifying its origin. Proton, neutron and Co-60 Gamma-ray irradiations are used to study DC-RTS induced by both Total Ionizing Dose (TID) and Displacement damage (Dd) dose. Conclusions are drawn by analyzing the correlation between the exponential slope of the transition maximum amplitude histogram and the location of the DC-RTS-induced defects. The presented results can be extrapolated to predict DC-RTS distributions in various kinds of solid state image sensors.

Proton and &lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;$\gamma$&lt;/tex&gt; &lt;/formula&gt;-Rays Irradiation-Induced Dark Current Random Telegraph Signal in a 0.18-&lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;$\mu{\hbox{m}}$&lt;/tex&gt; &lt;/formula&gt; CMOS Image Sensor

The dark current random telegraph signal (RTS) behavior has been studied in a five-transistor-per-pixel (5T) pinned photodiode 0.18-μm COTS active pixel sensor (APS). Several devices, irradiated using protons and gamma rays, have been studied in order to assess the ionizing and displacement damage effects. The influence of the proton energy, fluence, ionizing dose and applied bias during irradiation on the number of RTS pixels, the number of discrete levels, maximum transition amplitude, and mean switching time constants is investigated.

Radiation Effects in Pinned Photodiode CMOS Image Sensors: Pixel Performance Degradation Due to Total Ionizing Dose

Several Pinned Photodiode (PPD) CMOS Image Sensors (CIS) are designed, manufactured, characterized and exposed biased to ionizing radiation up to 10 kGy(SiO2 ). In addition to the usually reported dark current increase and quantum efficiency drop at short wavelengths, several original radiation effects are shown: an increase of the pinning voltage, a decrease of the buried photodiode full well capacity, a large change in charge transfer efficiency, the creation of a large number of Total Ionizing Dose (TID) induced Dark Current Random Telegraph Signal (DC-RTS) centers active in the photodiode (even when the Transfer Gate (TG) is accumulated) and the complete depletion of the Pre-Metal Dielectric (PMD) interface at the highest TID leading to a large dark current and the loss of control of the TG on the dark current. The proposed mechanisms at the origin of these degradations are discussed. It is also demonstrated that biasing (i.e., operating) the PPD CIS during irradiation does not enhance the degradations compared to sensors grounded during irradiation.

Displacement Damage Effects in Pinned Photodiode CMOS Image Sensors

This paper investigates the effects of displacement damage in Pinned Photodiode (PPD) CMOS Image Sensors (CIS) using proton and neutron irradiations. The DDD ranges from 12 TeV/g to 1.2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> TeV/g. Particle fluence up to 5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> n.cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> is investigated to observe electro-optic degradation in harsh environments. The dark current is also investigated and it would appear that it is possible to use the dark current spectroscopy in PPD CIS. The dark current random telegraph signal is also observed and characterized using the maximum transition amplitude.

Evidence of a Novel Source of Random Telegraph Signal in CMOS Image Sensors

This letter reports a new source of dark current random telegraph signal in CMOS image sensors due to meta-stable Shockley-Read-Hall generation mechanism at oxide interfaces. The role of oxide defects is discriminated thanks to the use of ionizing radiations. A dedicated RTS detection technique and several test conditions (radiation dose, temperature, integration time, photodiode bias) reveal the particularities of this novel source of RTS.

Further measurements of random telegraph signals in proton irradiated CCDs

The probability/incident proton for creation of a defect in a charge-coupled device (CCD) which shows dark current random telegraph signal (RTS) behavior has been measured for energies of 1.5, 10 and 46 MeV. The probability was found to be proportional to the non-ionizing energy loss (NIEL) for elastic collisions. Plots of RTS probability versus mean dark current indicate a correlation with the amount of field enhanced emission. If a pixel already has a defect showing field enhanced emission, it is more likely to show RTS effects. The amplitudes themselves are not correlated with the degree of field enhanced emission. An alternative to the bulk metastable defect model is proposed, based on the reorientation of the phosphorus-vacancy center in a high electric field.