Similarities Between Proton and Neutron Induced Dark Current Distribution in CMOS Image Sensors

Several CMOS image sensors were exposed to neutron or proton beams (displacement damage dose range from 4 TeV/g to 1825 TeV/g) and their radiation-induced dark current distributions are compared. It appears that for a given displacement damage dose, the hot pixel tail distributions are very similar, if normalized properly. This behavior is observed on all the tested CIS designs (4 designs, 2 technologies) and all the tested particles (protons from 50 MeV to 500 MeV and neutrons from 14 MeV to 22 MeV). Thanks to this result, all the dark current distribution presented in this paper can be fitted by a simple model with a unique set of two factors (not varying from one experimental condition to another). The proposed normalization method of the dark current histogram can be used to compare any dark current distribution to the distributions observed in this work. This paper suggests that this model could be applied to other devices and/or irradiation conditions

Radiation damages in CMOS image sensors: testing and hardening challenges brought by deep sub-micrometer CIS processes

This paper presents a summary of the main results we observed after several years of study on irradiated custom imagers manufactured using 0,18 µm CMOS processes dedicated to imaging. These results are compared to irradiated commercial sensor test results provided by the Jet Propulsion Laboratory to enlighten the differences between standard and pinned photodiode behaviors. Several types of energetic particles have been used (gamma rays, X-rays, protons and neutrons) to irradiate the studied devices. Both total ionizing dose (TID) and displacement damage effects are reported. The most sensitive parameter is still the dark current but some quantum eficiency and MOSFET characteristics changes were also observed at higher dose than those of interest for space applications. In all these degradations, the trench isolations play an important role. The consequences on radiation testing for space applications and radiation-hardening-by-design techniques are also discussed

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

Radiation Induced Point and Cluster-Related Defects with Strong Impact to Damage Properties of Silicon Detectors

This work focuses on the investigation of radiation induced defects responsible for the degradation of silicon detectors. Comparative studies of the defects induced by irradiation with 60Co- rays, 6 and 15 MeV electrons, 23 GeV protons and 1 MeV equivalent reactor neutrons revealed the existence of point defects and cluster related centers having a strong impact on damage properties of Si diodes. The detailed relation between the microscopic reasons as based on defect analysis and their macroscopic consequences for detector performance are presented. In particular, it is shown that the changes in the Si device properties after exposure to high levels of 60Co- doses can be completely understood by the formation of two point defects, both depending strongly on the Oxygen concentration in the silicon bulk. Specific for hadron irradiation are the annealing effects which decrease resp. increase the originally observed damage effects as seen by the changes of the depletion voltage. A group of three cluster related defects, revealed as deep hole traps, proved to be responsible specifically for the reverse annealing. Their formation is not affected by the Oxygen content or Si growth procedure suggesting that they are complexes of multi-vacancies located inside extended disordered regions.Comment: 14 pages, 15 figure

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 DCRTS 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

Hardening approach to use CMOS image sensors for fusion by inertial confinement diagnostics

A hardening method is proposed to enable the use of CMOS image sensors for Fusion by Inertial Confinement Diagnostics. The mitigation technique improves their radiation tolerance using a reset mode implemented in the device. The results obtained evidence a reduction of more than 70% in the number of transient white pixels induced in the pixel array by the mixed neutron and γ-ray pulsed radiation environment

Radiation Effects on CMOS Active Pixel Image Sensors

Today, Complementary-Metal-Oxide-Semiconductor (CMOS) Image Sensors (CIS), also called Active Pixel Sensors (APS), are the most popular imager technology with several billions manufactured every year. They represent about 90% of the imager market and should exceed 95% in a couple of years. Compared to the main alternative imager technology, the Charge Coupled Device (CCD), CISs have several major benefits such as low-power consumption, high-integration, high speed and the capacity to integrate advanced CMOS functions on-chip (and even inside the pixel). Thanks to the latest technology innovations, CISs are now matching the performances of CCDs in terms of image quality and sensitivity placing them at the forefront even in high-end applications such as digital single-lens reflex, scientific instruments, and machine vision. Thanks to these advantages, CISs are also used in harsh radiation environment for applications such as: space applications, X-ray medical imaging, electron microscopy, nuclear facility monitoring and remote handling (nuclear power plants, nuclear waste repositories, nuclear physics facilities…), particle detection and imaging, military applications etc.. Designing, hardening and testing a sensor for such applications require the understanding of the CIS behavior when exposed to radiation sources. Understanding and improving further the intrinsically good radiation hardness of APS has been a topic of interest since its invention. This interest has been recently growing with the coming of new behaviors brought by the profound evolution of CIS technologies (as discussed throughout this manuscript) compared to the older generation mainstream CMOS processes used in early work. The aim of this chapter is to give an overview of the parasitic effects that can undergo a modern CIS when it is exposed to a high energy particle radiation field

Radiation Damage in CMOS Image Sensors for Space Applications

The space radiation environment is damaging to silicon devices, such as Complementary Metal Oxide Semiconductor (CMOS) image sensors, affecting their performance over time or causing total failure. The first part of this work investigates a Charge Coupled Device (CCD) style CMOS image sensor designed for TDI (Time Delay and Integration) mode imaging, a mode commonly used for Earth observation. Damage from high energy protons in the space environment decreases the Charge Transfer Efficiency (CTE) and increases the dark current of such devices. Experimental work on proton damaged devices is presented, showing the effects on CTE and dark current. The results are compared to a standard CCD by a simulation to take into account the different dimensions and operating conditions of the two devices. The second part of this work describes an experimental campaign to determine the effects of process variations (namely the introduction of deep doping wells and the variation of epitaxial silicon thickness) on the rate of Single Event Latchup (SEL) in CMOS Active Pixel Sensor (APS) devices. SEL is a potentially destructive phenomenon which occurs in CMOS technology but not in CCDs. Test devices were subjected to heavy ion bombardement and SEL rates recorded for a range of heavy ions causing varying amounts of ionisation. A simulation using Technology Computer Aided Design (TCAD) was developed to predict the SEL rates due to heavy ions and to understand the characteristic shape of the SEL cross section vs. Linear Energy Transfer (LET) curves produced by SEL experiments. The simuation was carried out for structures representative of each of the design variants