Daniel Söderström

This work presents a comprehensive study of dose rate effects on Ag-doped metaphosphate glass radiophotoluminescent (RPL) dosimeters for doses ranging bewteen 1 Gy and 100 MGy. Data from multiple irradiation campaigns with diverse radiation fields, such as 60Co gamma radiation, X-rays with energy spectrum up to 100 keV, monoenergetic electron beams, and mixed fields offer valuable insights for accurate dosimetry in high-radiation environments. Dose rates ranging over 8 decades, from 0.1 kGy/h to 18 MGy/h are experimentally tested. Low dose rate effects can be observed at low doses; however, for doses higher than 100 kGy, both overestimation and underestimation can occur depending on the dose rate.

Electronic systems distributed along high-energy particle accelerators need rigorous radiation hardness qualification to ensure an adequate availability of the beam. This work presents the radiation levels on a distributed system, featuring a commercial Cypress 90-nm memory, that is deployed around the Large Hadron Collider (LHC), the largest accelerator within CERN. This investigated system is a part of the LHC magnet power converter system, with 752 units distributed under the LHC beam line, and 256 units within shielded areas close to the accelerator tunnel. The radiation levels on the system were put in relation to the radiation qualifications and operational goals of the system. The embedded commercial memory has previously been tested for radiation effects, and has a characterized upset cross section. The use of these distributed devices with known cross sections as an aid in radiation level monitoring is also discussed.

Three SDRAMs from the same manufacturer with technology node sizes 110, 72, and 63 nm, were investigated under proton irradiation and using scanning electron microscopy (SEM). The radiation-induced faults were characterized and compared between the different part types. The devices under test (DUT) were irradiated with protons and experienced single event effects (SEE) in the form of stuck bits and single bit upsets (SBU). Analysis of the data retention times of bits which had SBU and were stuck during irradiation, showed similar patterns of retention time degradation, suggesting that the SBUs and stuck bits in all three part types could be induced by the same mechanism. Detailed data retention time analyses were also performed before and after irradiation to investigate the evolution of data retention times after irradiation, and after periods of annealing. The largest radiation-induced retention time losses were found to anneal, but the bits least affected directly after irradiation experienced decreasing data retention time as a function of annealing time. SEM imaging showed differences in the memory cell structure between the tested part types. The largest node size device was the most sensitive to the radiation, both for SEE and cumulative radiation effects.

The effect of 53 MeV proton irradiation on the reliability of silicon carbide power MOSFETs was investigated. Post-irradiation gate voltage stress was applied and early failures in time-dependent dielectric breakdown (TDDB) test were observed for irradiated devices. The applied drain voltage during irradiation affects the degradation probability observed by TDDB tests. Proton-induced single event burnouts (SEB) were observed for devices which were biased close to their maximum rated voltage. The secondary particle production as a result of primary proton interaction with the device material was simulated with the Geant4-based toolkit.

The effect of 20 MeV electron radiation on the lifetime of the silicon carbide power MOSFETs was investigated. Accelerated constant voltage stress (CVS) was applied on the pristine and irradiated devices and time-to-breakdown ( T _BD ) and charge-to-breakdown ( Q _BD ) of gate oxide were extracted and compared. The effect of electron radiation on the device lifetime reduction can be observed at lower stress gate-to-source voltage ( V _GS ) levels. The models of T _BD and Q _BD dependence on the initial gate current ( I _G0 ) are proposed which can be used to describe the device breakdown behaviour.

The radiation-induced emission (RIE) of Gd³⁺-doped sol–gel silica glass has been shown to have suitable properties for use in the dosimetry of beams of ionizing radiation in applications such as radiotherapy. Linear electron accelerators are commonly used as clinical radiotherapy beams, and in this paper, the RIE properties were investigated under electron irradiation. A monochromator setup was used to investigate the light properties in selected narrow wavelength regions, and a spectrometer setup was used to measure the optical emission spectra in various test configurations. The RIE output as a function of depth in acrylic was measured and compared with a reference dosimeter system for various electron energies, since the dose–depth measuring abilities of dosimeters in radiotherapy is of key interest. The intensity of the main radiation-induced luminescence (RIL) of the Gd³⁺-ions at 314 nm was found to well represent the dose as a function of depth, and was possible to separate from the Cherenkov light that was also induced in the measurement setup. After an initial suppression of the luminescence following the electron bunch, which is ascribed to a transient radiation-induced attenuation from self-trapped excitons (STEX), the 314 nm component was found to have a decay time of approximately 1.3 ms. An additional luminescence was also observed in the region 400 nm to 600 nm originating from the decay of the STEX centers, likely exhibiting an increasing luminescence with a dose history in the tested sample.

Integrated circuits (ICs) are a keystone for most critical applications operating in high-level radiation environments, spanning from high-energy nuclear applications up to space applications. The long-term reliability of these applications is essential for safe operation. However, the radiation effects for ICs are commonly investigated using fresh circuits, leaving the coupled effect of radiation and aging degradation unknown. This article investigates the impact of negative bias temperature instability (NBTI) aging degradation mechanism on the heavy-ion single event upset (SEU) radiation susceptibility of 28-nm ultra-thin body and buried oxide (UTBB) fully depleted silicon on insulator (FD-SOI) technology using a custom-designed test vehicle. NBTI aging degradation mechanism has been experimentally proven to increase the SEU sensitivity up to $2\times $ for 28-nm UTBB FD-SOI flip-flops. A comprehensive framework is presented to analyze the underlying mechanisms for the impact of NBTI, which includes NBTI aging mechanism modeling, SEU SPICE simulation, TCAD irradiation simulation, and Monte-Carlo simulation of radiation effects. The framework offered a quantitative prediction of the effect of NBTI degradation mechanism on the heavy-ion SEU radiation sensitivity.