Dark Current Spikes Research Articles

Thermal and electric field driven rf breakdown precursor formation on metal surfaces

The phenomenon of electric breakdown poses serious challenges to the design of devices that operate in high electric field environments. Experimental evidence points toward breakdown events that are accompanied by elevated temperatures and dark current spikes, which is attributed to high-asperity nanostructure formation that enhances the local electric field and triggers a runaway process. However, the exact mechanistic origin of such nanostructures under typical macroscopic operational conditions of electric field and magnetic-field-mediated heating remains poorly understood. In this work, we simulate the evolution of a copper surface under the combined action of the electric fields and elevated temperatures. Using a mesoscale curvature-driven surface evolution model, we show how a copper surface can undergo a type of dynamical instability that naturally leads to the formation of sharp asperities in realistic experimental conditions. Exploring the combined effect of fields and temperature rise, we identify the critical regimes that allow for the formation of breakdown precursors. The results show that thermoelastic stresses, while not essential, can significantly lower the critical electric field required for runaway surface instability, which is consistent with experimental observations that thermal effects can increase breakdown rates. Published by the American Physical Society 2024

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.

Dark current spikes as an indicator of mobile dislocation dynamics under intense dc electric fields

Breakdown of metals subject to intense electric fields is a long-standing limiting factor in high-voltage applications. The mechanism leading to breakdown nucleation is not completely understood. Previously, it was suggested that breakdown can be nucleated by a critical transition in the population of mobile dislocations near the surface of electrodes. This was formulated in terms of a mean-field mobile dislocation density fluctuation (MDDF) model. Based on this model, it was proposed that prebreakdown fluctuations of the mobile dislocation density might be observed as spikes in the dark current between the electrodes. We constructed a setup in which these fluctuations were measured. The rate of fluctuations, as a function of the electric field between the electrodes, agrees with the predictions of the MDDF model, both in functional form and in absolute numerical rates. This numerical agreement was obtained using previously derived numerical parameters of the model. In addition, for each electric field, the distribution of times between current fluctuations was examined. The results indicate that each such prebreakdown fluctuation is the result of a two-step process. This characteristic, too, is in line with the MDDF model, which predicts that a characteristic prebreakdown current event is described as two separate steps in a Markov process, occurring in quick succession.

Low Temperature Alpha Particle Irradiation of a STAR1000 CMOS APS

A STAR1000 CMOS active pixel sensor was irradiated with alpha particles at -130 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">deg</sup> C and dark current measurements were made at temperatures up to 25 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">deg</sup> C. Approximately 90% of dark current spikes were seen to anneal near room temperature. This implies that room temperature irradiations will not give a good estimate of on-orbit effects for cooled applications.

Analyses of images of neutron interactions and single particle displacement damage in CCD arrays

The purpose of this work is to understand the interaction of high energy neutrons with CCDs with the aim of deploying them in flight experiments to gather a database of atmospheric neutron interaction events in silicon cells. The new results in this paper include: 1) early-time multilevel RTS signals from dark current spikes, which have never been resolved before and 2) improved resolution of the frequency distributions of event intensity and comparison with results from a radiation transport code. This work adds to the state of the art by providing a novel perspective on the formation and evolution (annealing) of displacement damage complexes in silicon and by demonstrating that CCDs can provide an attractive combination of spatial and intensity resolution for the interaction events of neutrons and other particles within silicon cells.

Single particle dark current spikes induced in CCDs by high energy neutrons

This paper presents an analysis of dark signal nonuniformity induced in a charge coupled device (CCD) by 90 MeV neutrons. Random telegraph signal switching between multiple levels was seen for some dark current spikes. The probability distribution of the dark current spikes is shown to be pseudo-exponential and the distribution remains exponential during annealing, but with an increasing decay constant. Similar dark current spikes were also observed to be generated in an APS device exposed to high energy neutrons at the WNR facility.

Electron and neutron radiation damage effects on a two-phase CCD

Surface and bulk radiation damage effects on a two-phase charge-coupled device (CCD), operated in a multipinned phase (MPP) mode have been evaluated. Two-phase CCD's are one of the candidates for application in the vertex detector of a future linear collider. Flat-band voltage shifts, dark current, dark current spikes, and charge transfer efficiency (CTE) were studied on devices subjected to irradiation with fluences reaching 4.3/spl times/10/sup 12/ electrons/cm/sup 2/ and 8.9/spl times/10/sup 9/ neutrons/cm/sup 2/. An additional source of dark signal in electron irradiated devices was observed and explained by impact ionization by holes, released by tunneling from defect states near the Si-SiO/sub 2/ interface. A model for the CTE in a two-phase CCD as a function of temperature, background charges, and clock timing is described. Calculations based on the model are in good agreement with the experimentally determined values of CTE in electron and neutron irradiated CCD's.

Investigation of the radiation performance of CCD sensors in a vertex detector application

The radiation performance of a Hamamatsu S5466 and an EEV CCD02-06 silicon CCD sensors, working in a Multi-Pinned Phase (MPP) mode has been evaluated, in view of their possible use in the vertex detector of a future linear collider. We have examined the influence of the electron irradiation from a β-source with fluencies up to 4.3×10 12 e −/ cm 2 on the parameters of the CCD sensors such as dark current, dark current spikes, drive pulse voltages and charge transfer inefficiency (CTI). The changes of the parameters of the devices resulting from the irradiation are reported and discussed.

Proton effects in charge-coupled devices

Basic mechanisms and ground-test data for radiation effects in solid-state imagers are reviewed, with a special emphasis on proton-induced effects on silicon charge-coupled devices (CCDs). For the proton fluxes encountered in the space environment, both transient ionization and displacement damage effects arise from single-particle interactions. In the former case, individual proton tracks will be seen; in the latter, dark-current spikes (or hot pixels) and trapping states that cause degradation in charge-transfer efficiency will be observed. Proton-induced displacement damage effects on dark current and charge transfer are considered in detail, and the practical implications for shielding, device hardening, and ground testing are discussed.

Radiation Hardened P-Surface Channel CCD's

A process for total dose hardening of surface p-channel CCD's with overlapping polysilicon gates has been developed by optimizing the process steps associated with the gate oxides and polysilicon gates. 16-bit shift registers fabricated with this process can be operated up to 1×106 rads (Si) with threshold voltage shifts of ≤ 2V for the buried gates, and ≤ 1.5V for the surface gates on the best devices fabricated. The charge transfer efficiency for the devices with -10V gate bias during irradiation is unchanged after 1×106 rads (Si), but drops to 0.999 for the devices with OV gate bias during irradiation. The average dark current increases to only 1.75 times the initial value after 1×106 rads (Si) for devices with -10V gate bias during irradiation, and to 4 times the initial value for the devices with OV gate bias. No additional dark current spikes are observed up to 1×106 rads (Si). These results represent a very large improvement in hardness over typical CCD's.