Analysis of total dose-induced dark current in CMOS image sensors from interface state and trapped charge density measurements

The origin of total ionizing dose induced dark current in CMOS image sensors is investigated by comparing dark current measurements to interface state density and trapped charge density measurements. Two types of photodiode and several thick-oxide-FETs were manufactured using a 0.18-µm CMOS image sensor process and exposed to 10-keV X-ray from 3 krad to 1 Mrad. It is shown that the radiation induced trapped charge extends the space charge region at the oxide interface, leading to an enhancement of interface state SRH generation current. Isochronal annealing tests show that STI interface states anneal out at temperature lower than 100°C whereas about a third of the trapped charge remains after 30 min at 300°C

Identification of radiation induced dark current sources in pinned photodiode CMOS image sensors

This paper presents an investigation of Total Ionizing Dose induced dark current sources in Pinned PhotoDiodes (PPD) CMOS Image Sensors based on pixel design variations. The influence of several layout parameters is studied. Only one parameter is changed at a time enabling the direct evaluation of its contribution to the observed device degradation. By this approach, the origin of radiation induced dark current in PPD is localized on the pixel layout. The PPD peripheral STI does not seem to play a role in the degradation. The PPD area and an additional contribution independent on the pixel dimensions appear to be the main sources of the TID induced dark current increase

Radiation Effects in CMOS Isolation Oxides: Differences and Similarities With Thermal Oxides

Radiation effects in thick isolation oxides of modern CMOS technologies are investigated using dedicated test structures designed using two commercial foundries. Shallow Trench Isolation and Pre-Metal Dielectric are studied using electrical measurements performed after X-ray irradiations and isochronal annealing cycles. This paper shows that trapping properties of such isolation oxides can strongly differ from those of traditional thermal oxides usually used to process the gate oxide of Metal Oxide Semiconductor Field Effect Transistors. Buildup and annealing of both radiation-induced oxide-trap charge and radiation-induced interface traps are discussed as a function of the oxide type, foundry and bias condition during irradiation. Radiation-induced interface traps in such isolation oxides are shown to anneal below 100°C contrary to what is usually observed in thermal oxides. Implications for design hardening and radiation tests of CMOS Integrated Circuits are discussed

Some Reflections about the Ancient Aqueduct of Galermi (Syracuse, Italy)

Since 2012, the Centre Camille Jullian team carries out an interdisciplinary study of the aqueduct Galermi, architectural work and hydraulic engineering of about 30 km long. This aqueduct, built between the 5th century BC and the Roman Empire, first supplied drinking water to Greek and/or Roman Syracuse. In the 16th–17th centuries, partial transformations have been done and changed the function of the channel, with the installation of flour mills. In the 19th century, the new Italian state gradually expropriated immediate neighbors who exploited abusively the aqueduct. It was then devoted only to irrigate the Syracusan territory according to a system of concessions that has almost remained unchanged since the 19th century. The paper will present this program and the last results that the team obtained in the last two years, particularly about intakes of water and underground galleries, and which chronology can be proposed

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

Enhanced Radiation-Induced Narrow Channel Effects in Commercial 0.18 μm Bulk Technology

Total ionizing dose effects are investigated in input/output transistors that are fabricated by using a commercial 0.18 μm bulk process. An enhanced radiation-induced narrow channel effect is demonstrated in N-type metal-oxide semiconductor (NMOS) and P-type metal-oxide semiconductor (PMOS) transistors, leading to a significant threshold voltage shift which may compromise circuit operations. Calculations using a code dedicated to radiation-induced charge trapping in oxides show that the radiation-induced positive charge trapping in trench oxides leads to the modifications of the electrical characteristics experimentally evidenced. Radiation hardening issues are finally discussed as a function of the device geometry and design

Simulation of Single Particle Displacement Damage in Silicon – Part I: Global Approach and Primary Interaction Simulation

A comprehensive approach is developed for the simulation of Single Particle Displacement Damage in silicon, from the incident particle interaction in silicon, to the resulting electrical effect observed experimentally. The different steps of the global approach are described. The paper then focuses on the first step corresponding to Monte Carlo simulation of the primary interaction. The characteristics of the Primary Knock-On Atom (PKA) generated by neutron- or proton-silicon interactions for different energies are explored, analyzing in particular the PKA range in energies and species. This leads to the selection of 1 and 10 keV silicon atoms as good candidates to best represent the displacement cascades generated by all PKA. These PKA characteristics will be used as input in the following Molecular Dynamics simulation step, developed in a separate paper to simulate the displacement cascade generation and evolution. Monte Carlo simulations are also performed in a geometry representative of an image sensor, analyzing the distribution of non-ionizing deposited energy. The obtained distributions appear very similar for incident neutrons from 3 to 18 MeV and incident protons of 200 MeV, in agreement with similarities observed in experimentally measured dark current distributions in image sensors. The effect of geometric parameters on these distributions is finally explored

Vulnerability of CMOS image sensors in megajoule class laser harsh environment

CMOS image sensors (CIS) are promising candidates as part of optical imagers for the plasma diagnostics devoted to the study of fusion by inertial confinement. However, the harsh radiative environment of Megajoule Class Lasers threatens the performances of these optical sensors. In this paper, the vulnerability of CIS to the transient and mixed pulsed radiation environment associated with such facilities is investigated during an experiment at the OMEGA facility at the Laboratory for Laser Energetics (LLE), Rochester, NY, USA. The transient and permanent effects of the 14 MeV neutron pulse on CIS are presented. The behavior of the tested CIS shows that active pixel sensors (APS) exhibit a better hardness to this harsh environment than a CCD. A first order extrapolation of the reported results to the higher level of radiation expected for Megajoule Class Laser facilities (Laser Megajoule in France or National Ignition Facility in the USA) shows that temporarily saturated pixels due to transient neutron-induced single event effects will be the major issue for the development of radiation-tolerant plasma diagnostic instruments whereas the permanent degradation of the CIS related to displacement damage or total ionizing dose effects could be reduced by applying well known mitigation techniques

Total-Ionizing Dose Effects on Charge Transfer Efficiency and Image Lag in Pinned Photodiode CMOS Image Sensors

The total ionizing dose effects on image lag in pinned photodiode CMOS image sensors are investigated thanks to various device variants in order to isolate the major radiation induced effects on the charge transfer. It is shown that the main cause of the charge transfer degradation is the radiation induced defects generation in the pre-metal dielectric and in the transfer gate spacer vicinity which modifies the potential diagram at the photodiode/transfer gate interface by the creation of a potential pocket retaining the electrons that are not transferred. For 0.1 kGy(SiO2) 5 kGy(SiO2) the defects generated in the pre-metal dielectric influence the whole photodiode potential inducing a pinning voltage increase and degrading the charge transfer by enlarging the potential pocket effect which becomes the main image lag source. The reported results clarify the impact of ionizing radiation on the charge transfer suggesting radiation hardened by design solutions for future space or nuclear applications

Coupled experiment/simulation approach for the design of radiation-hardened rare-earth doped optical fibers and amplifiers

We developed an approach to design radiation-hardened rare earth -doped fibers and amplifiers. This methodology combines testing experiments on these devices with particle swarm optimization (PSO) calculations. The composition of Er/Yb-doped phosphosilicate fibers was improved by introducing Cerium inside their cores. Such composition strongly reduces the amplifier radiation sensitivity, limiting its degradation: we observed a gain decreasing from 19 dB to 18 dB after 50 krad whereas previous studies reported higher degradations up to 0°dB at such doses. PSO calculations, taking only into account the radiation effects on the absorption efficiency around the pump and emission wavelengths, correctly reproduce the general trends of experimental results. This calculation tool has been used to study the influence of the amplifier design on its radiation response. The fiber length used to ensure the optimal amplification before irradiation may be rather defined and adjusted to optimize the amplifier performance over the whole space mission profile rather than before integration in the harsh environments. Both forward and backward pumping schemes lead to the same kind of degradation with our active fibers. By using this promising coupled approach, radiation-hardened amplifiers nearly insensitive to radiations may be designed in the future