A. Jaksic

Radiochemistry on chip

We have developed an integrated microfluidic platform for producing 2-[(18)F]-fluoro-2-deoxy-D-glucose ((18)F-FDG) in continuous flow from a single bolus of radioactive isotope solution, with constant product yields achieved throughout the operation that were comparable to those reported for commercially available vessel-based synthesisers (40-80%). The system would allow researchers to obtain radiopharmaceuticals in a dose-on-demand setting within a few minutes. The flexible architecture of the platform, based on a modular design, can potentially be applied to the synthesis of other radiotracers that require a two-step synthetic approach, and may be adaptable to more complex synthetic routes by implementing additional modules. It can therefore be employed for standard synthesis protocols as well as for research and development of new radiopharmaceuticals.

The Technology Demonstration Module On-Board PROBA-II

As a semiconductor component radiation effects and technology demonstration experiment, the Technology Demonstration Module (TDM) integrated into the PROBA-II satellite, was launched on November 2nd 2009, into a 800 km polar orbit. This SEU/SEL experiment, in strong support to the Reference SEU Monitor database , will be described and details given about ground testing and calibrations. Since ground testing was carried out on flight lot devices and under flight operational conditions, the in-orbit SEU/SEL database will eventually become a vital reference point for improved modeling, prediction and testing. Evidence to confirm this promise is starting to emerge and will be presented at the end of the paper. As the present in-orbit number of events is still small, only the first month of flight performance will be presented with strong emphasis on validating correct operation of monitored devices.

MODELLING OF KINETICS OF CREATION AND PASSIVATION OF INTERFACE TRAPS IN METAL-OXIDE-SEMICONDUCTOR TRANSISTORS DURING POSTIRRADIATION ANNEALING

The dependencies of creation–passivation processes of interface traps in irradiated n-channel metal-oxide-semiconductor transistors on the temperature and gate bias during annealing have been investigated. The experimental results, which are explained by the hydrogen–water (H–W) model, show the influence of both the annealing temperature and gate bias on these processes. The modelling of creation–passivation kinetics of interface traps, based on bimolecular theory and numerical analysis, is also performed. Numerical modelling shows that the H–W model can include the temperature and gate bias dependencies of creation of interface traps, latent interface trap buildup and the decrease of interface trap density.

Analysis of postirradiation annealing of n-channel power vertical double-diffused metal–oxide–semiconductor transistors

The behavior of densities of the oxide trapped charge and the interface traps in gamma-ray irradiated n-channel power vertical double-diffused metal–oxide–semiconductor transistors during annealing at different temperatures and gate biases has been investigated. The experimental results have revealed the existence of a latent interface trap buildup (LITB) process. By use of numerical modeling, based on the hydrogen–water (H–W) model, the LITB process has been successfully simulated. The interface trap densities have been determined by both the midgap and the charge pumping methods, and the results have shown good qualitative agreement between these two methods. Isochronal annealing and switching bias experiments have also been performed. The experimental results are consistent with the H–W model.

Formation and passivation of interface traps in irradiated n-channel power VDMOSFETs during thermal annealing

Abstract The annealing of γ-ray irradiated commerical n-channel power VDMOSFETs at elevated temperature is investigated. Rebound effect, observed in the samples annealed with positive gate bias, is primarily the consequence of a very long-term postirradiation interface-trap buildup. At later annealing times, a significant decrease in the number of interface traps is observed. In order to explain obtained results, we propose a modification to the hydrogen ion transport model for the formation of interface traps. According to our model, H+ ions created during irradiation are responsible only for the initial fraction of the total interface-trap buildup. The other fraction is attributed to H+ ions produced when molecular hydrogen, released at the SiSiO2 interface in interface-trap creation reaction, diffuses back into the bulk of the oxide and is cracked at positive charge centres. Simultaneously with the generation of interface traps, their passivation also takes place. Passivation, probably caused by hydrogen atoms and water molecules, becomes predominant at later annealing times, leading to the decrease in interface-trap density.

Latent interface-trap generation in commercial power VDMOSFETs

Latent interface-trap generation is one of the most controversial post-irradiation effects in MOSFETs, which can have a significant impact on device performance and reliability in radiation environments. In this paper, we present new experimental evidence of latent interface-trap buildup in commercial power VDMOSFETs: its dependencies on dose, temperature and gate bias applied during irradiation and annealing. We discuss several models for latent interface-trap buildup and show that the most consistent is one which involves the diffusion of molecular hydrogen from structures adjacent to the gate oxide (CVD oxide, poly-Si gate), and its cracking on positive charge centers in the oxide. The cracking reaction liberates hydrogen ions, which drift to the Si/SiO/sub 2/ interface to form interface traps. Some hypothesis from the recently proposed H-W model for post-irradiation behavior of interface traps may help resolve the question of the source of hydrogen sufficient to cause up to 800% increase in interface-trap density, experimentally observed. The implications of latent interface-trap generation for hardness assurance test methods are also discussed.

Comparison between post-irradiation annealing and post-high electric field stress annealing of n-channel power VDMOSFETs

Abstract The behavior of the defects created in the gate oxide and at the Si/SiO 2 interface of n-channel power vertical double-diffused metal-oxide-semiconductor field-effect transistors (VDMOSFETs) by irradiation and positive high electric field stress have been investigated. Interface traps exhibit the same behavior after both types of stress, while there are significant differences in post-stress responses of the charge trapped in the oxide, consisting of fixed and switching component.

Radiation-induced statistical uncertainty in the threshold voltage measurement of MOSFET dosimeters.

The results of a recent study on the limiting uncertainties in the measurement of photon radiation dose with MOSFET dosimeters are reported. The statistical uncertainty in dose measurement from a single device has been measured before and after irradiation. The resulting increase in 1/f noise with radiation dose has been investigated via various analytical models. The limit of uncertainty in the ubiquitous linear trend of threshold voltage with dose has been measured and compared to two nonlinear models. Inter-device uncertainty has been investigated in a group of 40 devices, and preliminary evidence for kurtosis and skewness in the distributions for devices without external bias has been observed.

Heavy-Ion Induced Charge Yield in MOSFETs

The heavy-ion induced electron/hole charge yield in silicon-oxide versus electric field is presented. The heavy-ion charge yield was determined by comparing the voltage shifts of MOSFET transistors irradiated with 10-keV X-rays and several different heavy ions. The obtained charge yield for the heavy ions is in average nearly an order of magnitude lower than for the X-rays for the entire range of measured electric fields.

The role of fixed and switching traps in long-term fading of implanted and unimplanted gate oxide RADFETs

Radiation-sensing field effect transistors (RADFETs) have become widely used as radiation monitors in space missions. However, partial recovery (fading) of the dosimetric parameter (threshold voltage shift) may introduce severe complexities in measured dose analysis. The evolution of charge trap density during irradiation and postirradiation annealing of implanted and unimplanted RADFETs with different gate oxide thickness was studied in detail. It was found that a surprisingly high increase of border traps and their subsequent annealing in positively biased 400 nm implanted RADFETs were the origin of substantial fading, whereas the same devices irradiated with zero bias exhibited much lower fading. Additional differences between implanted and unimplanted RADFETs irradiated and annealed with and without bias are discussed.