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This work was supported in part by the European Union's Horizon 2020 research and innovation programme under grant agreement No. 857558, and the Ministry of Education, Science and Technological Development of the Republic of Serbia, under the project No. 43011., The RADiation sensitive metal-oxide-semiconductor field-effect-transistors (RADFETs) were irradiated with gamma rays up to absorbed dose of 110 Gy(H2O). The results of threshold voltage, V-T , during irradiation with various positive gate biases showed the increase in V-T with gate bias. The threshold voltage shift, Delta V-T , during irradiation was fitted very well. The contributions of both the fixed traps (FTs) and switching traps (STs) during radiation on Delta V-T were analyzed. The results show the significantly higher contribution of FTs than STs. A function that describes the dependence of threshold voltage shift and its components on gate bias was proposed, which fitted the experimental values very well. The annealing at the room temperature without gate bias of irradiated RADFETs was investigated. The recovery of threshold voltage, known as fading, slightly increase with the gate bias applied during radiation. The Delta V-T shows the same changes as the threshold voltage component due to fixed states, Delta V-ft , while there is no change in the threshold voltage component due to switching traps, Delta V-st ., European Union's Horizon 2020 research and innovation programme 857558, Ministry of Education, Science & Technological Development, Serbia 43011

This work was supported in part by the European Union's Horizon 2020 research and innovation programme (Grant No. 857558) and the Ministry of Education, Science and Technology Development of the Republic of Serbia (Project No. 43011)., We investigated the influence of gamma radiation of 50 Gy(H2O) on radiation-sensitive p-channel metal-oxide-semiconductor field-effect transistors with an Al gate (RADFETs) with gate oxide thicknesses of 400 and 1000 nm and gate voltages of 0 and 5 V. The obtained results showed that the sensitivity S at a given gate voltage increases with the square of the gate oxide thickness. After irradiation (IR), spontaneous annealing (SA) was performed at room temperature without voltage at the gate. We present the behaviors of fixed traps and switching traps, determined by the midgap technique, and that of fast switching traps, determined by the charge-pumping technique, during IR and SA. A very important characteristic of dosimetric transistors is fading, which represents the recovery of the threshold voltage of the irradiated RADFETs during SA. The maximum fading is about 15% after 9100 h, except for the RADFETs with a gate oxide thickness of 1000 nm and a gate voltage of 5 V, for which it is about 30%. A fitting equation for fading was proposed, which fitted the experimental fading values very well., European Union's Horizon 2020 research and innovation programme 857558, Ministry of Education, Science & Technological Development, Serbia 43011

Measurement of absorbed dose and dose rate is a common task in radiation environments such as space. This is accomplished with the specialized instruments known as radiation dosimeters. Among the most commonly used radiation dosimeters in space missions are those based on the Radiation Sensitive Field Effect Transistors (RADFETs). In this paper, we propose a design concept for a radiation hardened readout system for the real-time measurement of absorbed dose and dose rate with RADFET. The successive switching between the absorbed dose and dose rate readout modes, as well as the subsequent data processing, are performed by the self-adaptive fault-tolerant Multiprocessing System-on-Chip (MPSoC). The integrated framework controller and the real-time monitoring of particle flux with the embedded Static Random Access Memory (SRAM) enable the autonomous selection of operating and fault-tolerant modes, thus achieving the optimal performance under variable radiation conditions.

Pre-irradiation device characteristics, gamma radiation response, and possible use in radiation dosimetry have been investigated for MOSFETs with a 100 nm thick Er2O3 gate dielectric. The performance of these novel devices has been compared with that of commercial pMOS dosimeters (RadFETs) with a standard SiO2 gate oxide of the same thickness. The radiation sensitivity of the Er2O3 is significantly higher than that of SiO2, and this is particularly pronounced at lower dose levels. Significantly larger numbers of positive charges are trapped in the Er2O3 dielectric than in SiO2 during irradiation exposure, resulting in increased threshold voltage shift. After two weeks of room temperature annealing, 11.9% and 24.0% fading have been observed in SiO2 and Er2O3 samples, respectively. Higher fading for Er2O3 may be related to higher number of shallow traps close to the dielectric/silicon interface. These initial results are promising for the possible use of Er2O3 as a new gate dielectric in pMOS dosimeters. The observed enhancement of device sensitivity can be a milestone for the introduction of the pMOS dosimeters in personal dosimetry applications.

We have studied the effects of Co-60 gamma irradiation on electrical characteristics of metal oxide semiconductor field effect transistors (MOSFETs) with radio-frequency-sputtered Hafnium Oxide (HfO2) gate dielectric, and possible interaction mechanisms between irradiation and HfO2/Si gate stack. The electrical response of the HfO2 devices has been compared with those of experimental and commercial MOSFETs with conventional Silicon Dioxide (SiO2) dielectrics of the similar thickness. We have observed only small threshold voltage shifts during irradiation of the HfO2 MOSFETs; the SiO2 MOSFETs exhibit more than 10 times larger shifts. We have found interesting radiation-induced charge trapping mechanisms by analysis of X-ray photoelectron spectroscopy (XPS) measurements of HfO2/Si gate dielectric stack. The XPS analyses before and after different irradiation doses indicate that both the passivation and charge trapping occurs under radiation exposure. The passivation of dangling bonds significantly decreases the sensitivity of the HfO2 MOSFETs to irradiation. The small threshold shift is predominantly due to the breaking oxygen bonds, especially in HfOx and SiOx core levels. The obtained results demonstrate that the HfO2 based devices are almost insensitive to the irradiation compared to the conventional SiO2 gate and passivation effects significantly decrease radiation sensitivity of HfO2- based device.

This work presents results of a total ionising dose experiment, during which p-channel RADFETs were irradiated and measured under different gate bias conditions using an in-situ technique. The measurement system allowed threshold voltage shifts and temperature sensitivity of the shift to be measured during irradiation to 60 krad(Si) and the subsequent 55 day period of annealing. The experimental results obtained allow improved insight into temperature sensitivity related problems of RADFET based dosimetry systems for space and terrestrial applications. The results show that the radiation-induced decrease in mobility, caused by the interface trap build-up, has a predominant effect on RADFET temperature coefficients.

Different low-cost commercial general-purpose MOSFETs and a RADFET are subjected to ionizing photon beams for comparison. The main characteristics of the radiation response, such as sensitivity, reproducibility, and short-term fading, have been determined using traditional measurement algorithms and others previously developed by our research group. Several vertical and lateral p-channel transistor structures have been preliminarily analysed and the most promising device, the 3N163, has been fully characterized in different configurations (single and two stacked transistors, unbiased and biased during irradiation) and compared with ad-hoc transistors to detect ionizing radiation (RADFETs). Although all the transistors are reliable for photon dosimetry, the two-stacked configurations with the 3N163 model transistor show high sensitivities to 6 MV photon beams (33 ± 2 mV/Gy for the unbiased mode and 62 ± 3 mV/Gy for the biased mode). These values are similar to the 57.1 ± 0.7 mV/Gy of the analysed RADFET in unbiased mode. The uncertainty of the two-stacked configuration is comparable to the uncertainty obtained with the RADFET, but reproducibility is even better than in the latter. In contrast, RADFETs present the lowest short-term fading among the studied MOSFETs.

The behavior of radiation-induced fixed traps (FTs) in gate oxide and radiation-induced switching traps (STs) near and at the gate oxide/substrate interface during irradiation up to high absorbed doses has been considered. The zero-bias voltage regime, the simplest and most popular solution in practice, was chosen. Indeed, it is very difficult to predict the creation of radiation defects in the case of low electric fields, because there is a compromise between the external low electric fields induced by work function differences and the internal electrical fields induced by radiation-induced charged defects in the oxide. It was shown that the density of FTs is higher than the density of STs for lower absorbed doses, though the trend is reversed for doses greater than 700 Gy. Although the number of FTs is much higher than the number of STs, many FTs are located in the bulk, far from the oxide/semiconductor interface and their influence on channel carriers is much smaller than the influence of STs that are located closer to the channel. The equation for fitting the threshold voltage components induced by FTs ( Δ V ft ) and by STs ( Δ V st ) is proposed and very good fittings are obtained. It is shown that five experimental irradiation points are sufficient to draw a good conclusion about the values of the fitting parameters, i.e., the voltage saturation values and the degree of linearity.

A comparative study of radiation-sensitive field effect transistors (RADFETs) response to photon and electron beams has been carried out in reference conditions. Both types of beams, routinely used in clinical radiotherapy, have been applied to RADFETs manufactured by Tyndall National Institute. All tests were carried out on RADFETs of several gate oxide thicknesses, sizes and technological processes. Experimental results showed very similar behaviour in terms of sensitivity, linearity and short-term post-irradiation fading with dose ranges typical of clinical radiation treatments. Influence of the temperature has been minimized by biasing RADFETs at zero temperature coefficient drain current during readout process. This novel experimental study shows that analysed RADFETs can be suitable to be used for dose verification in radiation therapies where electron beams are used in intra-operative radiotherapy (IORT).

Extraction of radiation dose information from MOSFET (RADFET) based dosimetry systems usually relies on biasing the MOSFET during readout at zero temperature coefficient drain current ( ${{\mbi {I}}_{{ZTC}}}$ ), measured before irradiation. This current can vary due to accumulated radiation doses and thermal fluctuations, which degrades dosimetric accuracy. This work presents a method to reduce thermal drift related to this ${{\mbi {I}}_{{ZTC}}}$ shift. It is based on biasing with two carefully chosen currents during readout according to a thermal model suitable for MOSFETs. An experiment including irradiation and thermal cycles has been carried out to test the proposed method, using five types of RADFETs with three different gate-oxide thicknesses. If we compare the thermal drift of the output voltage measured using our proposed method with that measured using the usual constant ${{\mbi {I}}_{{ZTC}}}$ method, the linear thermal coefficient shows reductions of 33% to 80% for ${\mbi{I}_{{ZTC}}}$ shifts between $-15\%$ and $ + 65\% $ .

Radiation-sensing Field Effect Transistors (RadFETs or MOSFET dosimeters) with SiO2 gate dielectric have found applications in space, radiotherapy clinics, and high-energy physics laboratories. More sensitive RadFETs, which require modifications in device design, including gate dielectric, are being considered for personal dosimetry applications. This paper presents results of a detailed study of the RadFET energy response simulated with PENELOPE Monte Carlo code. Alternative materials to SiO2 were investigated to develop high-efficiency new radiation sensors. Namely, in addition to SiO2, Al2O3 and HfO2 were simulated as gate material and deposited energy amounts in these layers were determined for photon irradiation with energies between 20keV and 5MeV. The simulations were performed for capped and uncapped configurations of devices irradiated by point and extended sources, the surface area of which is the same with that of the RadFETs. Energy distributions of transmitted and backscattered photons were estimated using impact detectors to provide information about particle fluxes within the geometrical structures. The absorbed energy values in the RadFETs material zones were recorded. For photons with low and medium energies, the physical processes that affect the absorbed energy values in different gate materials are discussed on the basis of modelling results. The results show that HfO2 is the most promising of the simulated gate materials.

In this study conducted numerical experiments aimed to determine the physical shielding factors (PSF) for two different MOSFET structures. The purpose of this paper was to present the new possibilities of the Monte Carlo numerical simulations for interaction of gamma irradiation of 60Co and 137Cs with semiconductor devices that are often located as dosimeters together with complex electronics power systems. The transport of incident photon particles is simulated with Monte Carlo code FOTELP-2014. When kovar is used as a lid in the gamma radiation field, the implemented calculations show that the PSF values for the ESAPMOS RADFET structure are significantly higher than the PSF values for the standard MOSFET structure.

The irradiation response of Radiation Sensing Field Effect Transistor (RadFET), also known as MOSFET/pMOS dosimeter, to high energy X-rays and electron beams was investigated. The threshold voltages before and after irradiation were measured and the trap densities in the gate oxide and oxide/silicon interface of the RadFETs are evaluated. The RadFETs were irradiated with 6 MV X-rays, and 10 and 18 MeV electron beams emitted from a Linear accelerator (LINAC). Linear and non-linear fits to experimental results showed that after an initial linear response up to several Gy, deviation from the linearity occurred due to electric field screening by the radiation induced oxide trapped charges. The radiation-induced fixed traps (FTs) and switching traps (STs) were analysed and the FT density was found to be higher than the ST density for all beam types and doses. The radiation response, fading characteristics, and variation of the trapped charges of the RadFETs showed similar behaviour in tests. Abant İzzet Baysal Üniversitesi- AIBU - BAP. 2015.03.02.954 - BAP. 2014.03.02.705 Türkiye Cumhuriyeti Kalkınma Bakanlığı - 2012 K 120360 - 2016K121110

Gamma-ray irradiation and post-irradiation response at room and elevated temperature of radiation sensitive p-channel MOS transistors have been studied. The response was observed on the basis of threshold voltage shift determined from transistors transfer characteristics. These characteristics together with charge-pumping characteristics proved to be useful in providing a detailed insight into the processes that occur during gamma-ray irradiation and subsequent annealing at room temperature and later at elevated temperature. In particular, the influence of fixed oxide traps, switching oxide traps (known as slow switching traps) and switching traps at Si/SiO 2 interface (known as fast switching traps) on threshold voltage shift has been analyzed.

The paper investigates a possibility of pMOS dosimeter re-use for the measurement of gamma-ray irradiation. The dosimeters were irradiated to the dose of 35 Gy, annealed at room and elevated temperatures, after which they were irradiated again to the same dose value. Changes in the threshold voltage shift during those processes were followed, and it was shown that their re-use depends on a gate polarization during irradiation. For the gate polarization of 5 V during irradiation the pMOS dosimeters can be re-used for measurements of the irradiation dose after annealing without prior calibration. The pMOS dosimeters with the gate polarization during irradiation of 2.5 V can also be re-used for irradiation dose measurements but they require calibration. It is shown that for their re-use it is necessary to anneal the pMOS dosimeter so that the fading is higher than 50%. [Projekat Ministarstva nauke Republike Srbije, br. 171007]

The RADFETs (pMOS dosimeters) were irradiated by ionizing radiation from Co-60 gamma-ray source to dose of 230 Gy(Si) without gate bias, and their reproducibility and sensitivity to radiation were investigated. The completely automatic system containing switching matrix have been used, enabling very reliable measurements of RADFET electrical characteristics. Two sample types from each RADFET chip, with the same gate oxide thickness, but different geometry (channel width and length), were investigated. The samples have shown good reproducibility of the threshold voltage shift during irradiation, i.e., the radiation sensitivity was similar for all samples. Using MG and CP techniques, it has been shown that the slow switching (border) trap density is negligible, but the fixed trap density saturates and the fast switching trap density is linear. (C) 2011 Elsevier B.V. All rights reserved.

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.

We investigate the energy response of RADFET to high energy photons, electrons, protons and neutrons with FLUKA Monte Carlo simulation code. We combine Monte Carlo and device simulations to describe radiation effects in the RADFET gate oxide due to photon and proton exposure. Comparisons with photon irradiation measurements show reasonable agreement.

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.

We have subjected n-channel power VDMOSFETs to a positive and negative high electric field stress (HEFS) followed by biased annealing at 150 °C. Stress-induced defects have been monitored using midgap-subthreshold and charge-pumping techniques, the use of which in tandem has enabled an insight into behaviours of fixed and switching traps in the gate oxide and oxide/silicon interface. The repetition of the stress/annealing sequence has resulted in some quantitative but no qualitative differences in response compared to the original sequence. We have observed complex kinetics of different types the stress-induced defects during post-HEFS annealing, including an intriguing latent buildup of “true” interface traps. Comparison of post-HEFS and post-irradiation annealing data has indicated differences of the nature of defects induced by Fowler-Nordheim injection and irradiation in our samples.

A complete study of the defects created in the gate oxide and at the gate oxide/substrate interface of metal–oxide–semiconductor transistors with thick gate oxide ( t ox > 10 nm) during high electric field stress, and the mechanisms responsible for these defects creation have been given. In addition, some results of positive/negative high electric field stress with constant gate voltage of commercial n-channel power metal–oxide–semiconductor transistors with thick gate oxide of 100 nm, have been explained using this study.

Response of RADFETs manufactured at Tyndall National Institute to protons with energies of up to 60 MeV has been studied. RADFET response is compared for different biasing configurations and the effect of package lids is investigated.

The results of positive/negative Fowler–Nordheim high electric field stress and thermal post-high electric field stress annealing of commercial n-channel power VDMOSFETs have been presented. They have shown that gate bias sign has an influence on the fixed trap behavior during high electric field stress, but has no influence on any defect type behavior during thermal post-high electrical field stress annealing. In addition, slow switching traps have different behavior, but fast switching traps have the same behavior during thermal post-high electrical field stress annealing and thermal post-irradiation annealing.

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.

The analysis of defect generations in SiO 2 and at SiO 2 /Si interface during positive/negative high electric field stress of commercial n-channel power VDMOSFETs has been given. Some additional experiments containing the gate bias switching have helped in these defects nature investigations. The combined application of midgap subthreshold technique and charge pumping technique have represented very useful tool for the switching trap behavior revealing. The fixed trap density (Δ N ft ) and switching trap density (Δ N st ) in two power VDMOSFET types during Fowler–Nordheim injections have shown different behaviors.

Key aspects of continuous operation of Radiation Sensitive Field Effect Transistors (RADFETs) as radiation monitors in space missions are addressed. The effect of possible temperature fluctuations and long-term fading on threshold-voltage measurement of Implanted and Unimplanted gate oxide RADFETs were studied. Evidence for temperature coefficient changes following irradiation and annealing cycles is presented. In addition, fading of unimplanted gate oxide RADFETs is shown to be significantly lower than that of Implanted ones.

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.

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.

The paper presents new experimental evidence of the latent interface-trap buildup during annealing of gamma-ray irradiated power VDMOSFETs. We try to reveal the nature of this still ill-understood phenomenon by isothermal annealing, switching temperature annealing and switching bias annealing experiments. Possible explanations of obtained experimental results are discussed in the context of several models for post-irradiation behavior of radiation-induced defects.

The paper presents results of a study of post-irradiation effects in two types of gamma-ray irradiated power VDMOSFETS, commercially available from different manufacturers. Isothermal annealing with constant and switching gate bias, as well as isochronal annealing have been performed. The application of charge-pumping measurements in commercial three-terminal VDMOSFETs is also discussed. Besides enabling insight into the post-irradiation response of investigated devices, obtained results point out some interesting post-irradiation phenomena.

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.

Postirradiation effects in γ-ray irradiated n- and p-channel MOSFETs are analysed. The effects of gate technology (Al- and Si-gate), type of thermal gate oxide (dry or wet) and gate bias have been investigated. It is shown that during the irradiation the formation of interface traps is typically larger in Al-gate samples than in Si-gate ones. During annealing at 140°C, an increase in interface-trap density is observed in all the samples. This increase is correlated with a decrease in oxide-trap charge density and is found to be increased by a positive gate bias. In Al-gate samples, the increase in interface-trap density occurs at the beginning of annealing, while in Si-gate samples interface-trap buildup is delayed, i.e. a latent interface-trap generation is observed. At later annealing times, the passivation of interface traps dominates in all the samples. Possible explanations for observed effects are offered and critically discussed.

Influence of gate bias on creation-passivation processes of interface traps in irradiated n-channel MOS transistors during thermal annealing has been investigated. The experimental results, which show the dependence of these processes on gate bias, are explained by combined hydrogen-water (H-W) model. The modelling of kinetics of creation and passivation of interface traps, based on bimolecular theory and numerical analysis, is also performed. Numerical simulation shows that H-W model predicts the maximum of interface trap density and latent interface trap buildup during thermal 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.

A study of sensitivity and fading of pMOS dosimeters, with a two-layer (thermal+CVD) gate oxide with various thicknesses, is presented. Analysed dosimetric parameters appear not to exhibit any systematic dependence on dose rate. Oxide-trap charge density is not always found to increase with the gate oxide thickness, which is explained in terms of a complex influence of the oxide electric field in the zero-bias regime on the initial e − –h + recombination process and on the spatial distribution of trapped holes. After negligible formation of interface traps during irradiation, interface traps build up significantly in all samples during annealing, and this build-up is found to be in close correlation with oxide-trap charge neutralization. The possibility for increasing the sensitivity and extending the measurable dose range by applying a positive gate bias is also explored. In general, the results support the use of the thick CVD layer for improvement of sensitivity and long-term stability of pMOS dosimetric transistors.

The processes during postirradiation thermal annealing of γ-ray irradiated n-channel MOSFETs with both wet and dry gate oxides are investigated. For both analysed technologies, a so called “latent” interface trap buildup is observed, followed at very late annealing times by the decrease in the interface-trap density. A model is proposed that successfully accounts for the experimental results. Implications of observed effects for total dose hardness assurance test methods implementation are discussed.

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.

Response of pMOS dosemeters during two successive irradiations with gamma-ray irradiation to a dose of 35 Gy and annealing at room and elevated temperature has been studied. The response was followed on the basis of threshold voltage shift, determined from transfer characteristics, as a function of absorbed dose or annealing time. It was shown that the threshold voltage shifts during first and second irradiation for the gate bias during irradiation of 5 and 2.5 V insignificantly differ although complete fading was not achieved after the first cycle of annealing. In order to analyse the defects formed in oxide and at the interface during irradiation and annealing, which are responsible for threshold voltage shift, midgap and charge-pumping techniques were used. It was shown that during first irradiation and annealing a dominant influence to threshold voltage shift is made by fixed oxide traps, while at the beginning of the second annealing cycle, threshold voltage shift is a consequence of both fixed oxide traps and slow switching traps.

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 processes in n-channel power MOSFETs during γ-ray irradiation and subsequent annealing at elevated temperature are investigated. The creation of positive oxide-trap charge dominates during irradiation, leading to a negative threshold voltage shift. The so-called ‘latent’ interface-trap buildup, observed during annealing, is identified as the main contributor to the threshold voltage rebound. At very late annealing times, a significant decrease in the number of interface traps occurs. Possible mechanisms for the observed effects, as well as their implications for hardness assurance are discussed.

In 2007, the European Space Agency (ESA) initiated the development of European Crew Personal Active Dosimeters. The hardware development objective is to produce an active personal dosimeter which shows absorbed dose and dose equivalent spectra similar to a Tissue Equivalent Proportional Counter (TEPC), but which is based on more robust silicon detector devices. Several detector/dosimeter components have been investigated – by computer simulations – for their performance in the radiation field at the ISS position.

Isothermal annealing experiments with switched gate bias have been performed to determine the properties of the latent interface-trap buildup during postirradiation annealing of metal-oxide-semiconductor transistors. It has been found that a bias-independent process occurs until the start of the latent interface-trap buildup. During the buildup itself, oxide-trap charge is not permanently neutralized, but is temporarily compensated. (C) 2000 American Institute of Physics. (DOI: 10.1063/1.1336159)

RADFETs (RADiation sensitive Field Effect Transistors) are integrating ionizing radiation dosimeters operating on the principle of conversion of radiation-induced threshold voltage shift into absorbed dose. However, one of the major drawbacks of RADFETs is the inability to provide the information on the dose rate in real-time using the conventional absorbed dose measurement technique. The real-time monitoring of dose rate and absorbed dose can be achieved with the current mode dosimeters such as PN and PIN diodes/photodiodes, but these dosimeters have some limitations as absorbed dose meters and hence they are often not a suitable replacement for RADFETs. In that sense, this paper investigates the possibility of using the RADFET as a real-time dose rate meter so that it could be applied for simultaneous online measurement of the dose rate and absorbed dose. A RADFET sample, manufactured by Tyndall National Institute, Cork, Ireland, was tested as a dose rate meter under gamma irradiation from a Co-60 source. The RADFET was configured as a PN junction, such that the drain, gate and source terminals were grounded, while the radiation-induced current was measured at the bulk terminal, whereby the bulk was successively biased with 0 , 10 , 20 and 30 V. In zero-bias mode the radiation-induced current was unstable, but in the biased mode the current response was stable for the investigated dose rates from 0.65 to 32.1 Gy h−1 and up to the total absorbed dose of 25 Gy. The current increased with the dose rate in accordance with the power law, whereas the sensitivity of the current read-out was linear with respect to the applied bias voltage. Comparison with previously analyzed PIN photodiodes has shown that the investigated RADFET is competitive with PIN photodiodes as a gamma radiation dose rate meter and therefore has the potential to be employed for the real-time monitoring of the dose rate and absorbed dose.

The paper presents recent developments in quality assurance of radiation cancer treatments involving RADFETs (MOSFET dosimeters) developed and manufactured at Tyndall National Institute. Construction of a RADFET linear array for intracavitary in-vivo dosimetry is described in detail

In order to achieve lower initial threshold voltage, a boron implantation has been done through thermally grown 400 nm gate oxide of the radiation sensitive p-channel MOSFET (RADFET). The paper presents and discusses the results of a recent study aimed to provide detailed characterisation of radiation response of this type of RADFET. Implications of the implantation for practical RADFET applications and basic mechanisms underlying device radiation behaviour are analysed.

This paper presents results of a study of post-irradiation behavior of commercial n-channel power VDMOSFETs. Gamma-ray irradiated transistors have been subjected to the series of isothermal and isochronal annealings. The response of EFL1N10 devices, manufactured by domestic vendor, Ei-Microelectronics, is compared to that of Intersil's IRF510 devices. It has been found that during isothermal annealing EFL1N10 devices exhibit the so called latent interface-trap buildup (LITB), while such phenomenon hasn't been observed in IRF510. Additional switching temperature annealing and switching bias annealing experiments performed on EFL1N10 may prove useful in revealing details of LITB.

The density of fixed traps (FTs), ΔN ft (cm−2), during isothermal annealing of irradiated radiation-sensitive field-effect transistors (RADFETs) from room temperature to 200 °C has been modelled. The modelling has shown that a simple, two-defect model (2DM), containing two defect types: one defect type for positively charged FTs (PCFTs), and another for negatively charged FTs (NCFTs), is applicable for the temperatures up to 100 °C. However, the three-defect model (3DM), which includes additional PCFT type, should be used for temperatures from 100 to 200 °C. The models describing the behaviour of NCFTs during isothermal annealing have also been analysed. The activation energies of , and , for two PCFT types and one NCFT type, respectively, have been found. In addition, isochronal unannealed curves have been well fitted using logistic function. The modelling of isochronal annealing has also shown that one PCFT type up to 100 °C, and two PCFT types for 100–200 °C, respectively, are active, and additional defect(s) should be included for the temperatures higher than 200 °C. The isochronal annealing, which is significantly less time consuming than isothermal annealing, could be very good tool for the revealing of defects created by various stress types.

The rebound effect, observed in commercial n-channel power VDMOSFETs during biased thermal annealing, following γ-radiation exposure, is analysed. Rebound is caused predominantly by ‘latent’ interface-trap generation, which occurs in transistors irradiated and annealed with positive bias applied to the gate, after initial apparent saturation of the interface-trap density. Latent, interface-trap buildup may cause difficulties in predicting device response in low dose rate environments, such as space.

Several RADFET biasing configurations have been compared in terms of radiation sensitivity, dose rate dependence and fading. Positive gate bias increases sensitivity, however the drawback is that the fading is also increased and dose rate dependence is observed. Samples irradiated with zero and negative gate bias have lower sensitivity, but don't exhibit significant fading and dose rate dependence. The mechanisms underlying the observed effects have been analysed.