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The variations in the threshold voltage shift in p-channel power VDMOSFET during the gamma ray irradiation was investigated in the dose range from 10 to 100 Gy. The investigations were performed without the gate bias and with 5 V gate bias. The devices with 5 V gate bias exhibit a linear dependence between the threshold voltage shift and the radiation dose. The densities of radiation-induced fixed and switching traps were determined from the sub-threshold I-V characteristics using the midgap technique. It was shown that the creation of fixed traps is dominant during the irradiation. The possible mechanisms responsible for the fixed and switching traps creation are also analyzed in this paper. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 171007]

In order to analyze the processes induced by electrical breakdown and discharge responsible for memory effect in krypton-filled tube at low pressure, experimental data mean value of electrical breakdown time delay $$\bar{t}_{d}$$ as a function of afterglow period τ (memory curve) was used. Analysis showed that in the 1 μs 30 s the concentration of N(4S) atoms decreases significantly so that the dominant role in initiation of breakdown is taken over by cosmic rays and natural radioactivity. The increase in discharge current leads to the decrease in $$\bar{t}_{d}$$ in the 1 μs 7 ms due to the increase in probability for breakdown. It has also been show that exposure of krypton-filled tube to low dose of gamma ray irradiation as well as UV irradiation with wavelength higher than 300 nm leads to the decrease in $$\bar{t}_{d}$$ . This decrease occurs for τ > 7 ms, when N(4S) atoms play a dominant role in breakdown initiation.

Examination of electrical breakdown time delay t d as a function of relaxation time τ and analyzing of processes in insulating gas responsible for delay response of commercial gas-filled surge arresters (GFSA) manufactured by CITEL, SIEMENS and EPCOS was performed. It was shown that positive ions remained from previous breakdown and discharge, as well as positive ions formed in post discharge have a dominant role in breakdown initiation up to τ ≈ 1.5 s . In this case delay response is determined only by formative time in insulating gas. In insulating gas of GFSA manufactured by CITEL in the 1.5 s τ 3.10 3 s interval the dominant role in breakdown initiation is due to long living electrically neutral active particles and delay response is determined by statistical time delay. The irradiation of these devices with low doses of gamma rays leads to decrease in delay response down to the values which correspond to formative time in insulating gas. Presented results show that full relaxation of processes in insulating gas after breakdown and discharge ceases for GFSAs manufactured by SIEMENS and EPCOS occur for τ ≈ 200 ms , while for GFSAs manufactured by CITEL such relaxation occurs for about 3.10 3 s .

Research presented in this paper is dealing with the determination of static breakdown voltage U s in an argon-filled tube at 0.5 mbar pressure, for different inter-electrode gaps d with the aim of separating vacuum and gas breakdown processes contribution in electrical breakdown time delay. The U s determination was performed using data on the dynamic breakdown voltage experimental data obtained for different voltage increase rates. It was shown that up to d ≈ 9 mm estimated value of U s is relatively small change corresponds to breakdown which is vacuum-like, where as for d > 9 mm, breakdown takes place as in normal gas discharge. For d ≈ 1 1 mm , U s has the minimal value, when gas ionization process induced by secondary electron emission from the cathode is maximal. The measurement of electrical breakdown time delay t d was performed for three different values of inter-electrode gap: 0.1, 4 and 11 mm. On the basis of memory curve (mean value of electrical breakdown time delay t ‾ d as a function of relaxation time) behavior and statistical analysis of td data, mechanisms which make main impact to breakdown initiation were estimated for different values τ . Also, the impact of additional electron yield originating from UV radiation with wavelengths 302, 312.5 and 313.1 nm on the memory curve were investigated.

The processes which are responsible for breakdown initiation in nitrogen-filled tube at 6.6×102 Pa (6.6 mbar) and inter electrode gap 0.1 mm have been investigated. These processes have been monitored based on experimental data of electrical breakdown time delay td as a function of relaxation time τ. It was shown that, for τ 150 s breakdown is initiated by cosmic rays. Also, it was shown that the increase in applied voltage and glow current, as well as presence of external radiation, lead to the decrease of td value.

In this paper, the results of radiation sensitive field effect transistors (Al-gate p-channel metal-oxide-semiconductor field effect transistors) sensitivity to gamma and X-ray irradiation are presented. Radiation fields were created using 60Co source for three dose ranges (0-1 Gy, 0-5 Gy, and 0-50 Gy), as well as X-ray unit of 280 kVp spectrum for a single dose range from 0 to 5 Gy. The sensitivity was characterized by the threshold voltage shift, determined from reader circuit measurements, as a function of absorbed radiation dose. It was shown that for the three dose ranges of gamma radiation, as well as for the X-ray range from 0 Gy to 5 Gy there is approximately a linear dependence between threshold voltage shift DVT and radiation dose D. The application of positive bias of +5 V at the RADFET gate during irradiation, for these ranges of gamma radiation, also for X-ray dose range, leads to the increase in DVT and also, approximately a linear dependence between DVT and D, is established. Moreover, it was shown that the sensitivity of RADFET is much higher in the case of X-ray irradiation then in the case of gamma-ray irradiation for the same dose range. [Projekat Ministarstva nauke Republike Srbije, br. 171007]

The processes responsible for initiation of electrical breakdown in xenon-filled tube with two spherical iron electrodes at 2.7-mbar pressure have been analyzed. The analysis is based on the experimental data of electrical breakdown time delay as a function of afterglow period. It is shown that positive ions remaining from previous discharge, as well as positive ions created in mutual collisions of metastable atoms in afterglow, have a dominant role in secondary emission of electrons from the cathode which lead to initiation of breakdown in early afterglow. In late afterglow, dominant role in initiation of breakdown is taken by N(4S) atoms formed during the discharge by dissociation of ground state nitrogen molecules that are present as impurities in xenon. When the concentration of N(4S) atoms decreases sufficiently, the initiation of breakdown is caused by cosmic radiation. Small doses of gamma-ray irradiation also contribute to the initiation of breakdown, but only for large values of the afterglow period.

The gamma-ray irradiation sensitivity to radiation dose range from 0.5 Gy to 5 Gy and post-irradiation annealing at room and elevated temperatures have been studied for p-channel metal-oxide-semiconductor field effect transistors (also known as radiation sensitive field effect transistors or pMOS dosimeters) with gate oxide thicknesses of 400 nm and 1 mm. The gate biases during the irradiation were 0 and 5 V and 5 V during the annealing. The radiation and the post-irradiation sensitivity were followed by measuring the threshold voltage shift, which was determined by using transfer characteristics in saturation and reader circuit characteristics. The dependence of threshold voltage shift DVT on absorbed radiation dose D and annealing time was assessed. The results show that there is a linear dependence between DVT and D during irradiation, so that the sensitivity can be defined as DVT/D for the investigated dose interval. The annealing of irradiated metal-oxide-semiconductor field effect transistors at different temperatures ranging from room temperature up to 150°C was performed to monitor the dosimetric information loss. The results indicated that the dosimeters information is saved up to 600 hours at room temperature, whereas the annealing at 150°C leads to the complete loss of dosimetric information in the same period of time. The mechanisms responsible for the threshold voltage shift during the irradiation and the later annealing have been discussed also. [Projekat Ministarstva nauke Republike Srbije, br. 17007]

This paper presents the experimental data of breakdown voltage and electrical breakdown time delay for air-filled tube at p = 0.7 mbar pressure. The breakdown voltage was measured for product p·d (d is inter-electrode gap) from 0.005 to 0.2 mbar cm, i.e. when breakdown was a consequence of gas and vacuum mechanisms combined. It was shown that the static breakdown voltage, which was determined from experimental data of the dynamic breakdown voltage, retains approximately constant value. The shape of the memory curve, which displays the mean value of electrical breakdown time delay t ¯ d vs. relaxation time τ, is very similar to that previously obtained in the case of breakdown induced by Townsend's mechanism alone. UV and gamma radiation lead to the decrease of t ¯ d values for values τ > 30 ms and this decrease is larger in the presence of UV radiation. UV and gamma radiation shorten the relaxation time needed for memory curve to reach saturation. On the basis of exponential and Gaussian distributions of experimental data, the contribution of the statistical time delay and the formative time to total electrical breakdown time delay for different values of relaxation time is considered.

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 influence of gate bias during gamma-ray irradiation on the threshold voltage shift of radiation sensitive p-channel MOSFETs determined on the basis of transfer characteristics in saturation has been investigated. It has been shown that for the gate bias during the irradiation of 5 V and 10 V the sensitivity of these transistors can be presented as the threshold voltage shift and the absorbed irradiation dose ratio. On the bases of the subthreshold characteristics and transfer characteristics in saturation using the midgap technique we have determined the densities of radiation induced oxide traps and interface traps responsible for the threshold voltage shift. In addition, the charge pumping technique was used to determine the energy density of true interface traps. It has been shown that radiation-induced oxide traps have dominant role on threshold voltage shift, especially for gate biases during the irradiation of 5 V and 10 V.

AlGaN/GaN high electron mobility transistors (HEMTs) with [email protected] gate-length and incorporated C-doped GaN buffer layers have been exposed to gamma radiation. The devices have been irradiated to cumulative doses up to 10^7 rad. The effect of gamma irradiation on the direct current (DC) and low-frequency noise properties of these devices have been investigated in reference to the unexposed device. The DC and noise characteristics show deteriorating device performance upon the gamma exposure. However, some DC parameters, such as transconductance, tended to recover after the irradiation. The gate leakage current and low-frequency noise power spectra indicate this trend even couple of months after the irradiation.

The contribution of statistical time delay and formative time to total electrical breakdown time delay in an argon-filled tube at 4mbar pressure for afterglow periods from 3msto300s has been analyzed. This contribution was analyzed on the basis of total electrical breakdown time-delay experimental data and their standard deviation. It was shown that for values of afterglow period from 3to70ms, the contribution of statistical time delay to total electrical breakdown time delay can be neglected. For afterglow periods higher then 70ms the experimental results of total electrical breakdown time delay can be described by Laue’s distribution, which was developed for statistical time delay. It shows that in this case the formative time is much smaller than the statistical time delay, so the total electrical breakdown time delay is approximately equal to the statistical time delay.

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.

The contributions of positive ions and neutral active particles, remaining from previous breakdown and discharge as well as contribution of gamma photons from and radiation sources and cosmic rays to the electrical breakdown initiation in commercial gas-filled surge arresters have been analysed. This analysis was performed on the basis of time delay mean value as a function of afterglow period ? ('memory curve') and the breakdown voltage mean value as a function of ?. The values of static breakdown voltage were estimated on the basis of the experimental breakdown voltage data as a function of voltage increase rate using a linear polynomial fit.

Results of the statistical analysis of the electrical breakdown time delay for neon-filled tube at 6.5 mbar with and without /spl gamma/ and ultraviolet (UV) irradiation are presented in this paper. Experimental distributions of the breakdown time delay are established on the basis of 1000 successive and independent measurements for different exposition dose rates of /spl gamma/-irradiation, and UV illumination with known spectrum. Obtained experimental density distributions are modeled with convolution-based model, proposing two independent random variables with exponential and Gaussian distribution, respectively. The tendency of the breakdown time delay distribution to change shape from the exponential-like to the Gaussian-like is found by increasing the exposition rate of the /spl gamma/ irradiation. In addition, the characteristic strong reduction of the time delay is identified in the tube under the UV illumination.

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.

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.

The contribution of some neutral active states formed during previous discharge to the breakdown initiation has been analysed in nitrogen and neon at 6.6?mbar pressure on the basis of the time delay mean value as a function of afterglow period ? ('memory curve') and the breakdown voltage mean value as a function of ?. The contribution of Compton's electrons induced by gamma radiation and photoelectrons induced by UV radiation to breakdown initiation has also been studied. It has been shown that in the early afterglow (up to 30?ms) positive ions formed in the collisions between metastable molecules and highly vibrationally excited molecules in nitrogen and positive ions formed in collision between metastable atoms in neon have a dominant role in breakdown initiation. Gamma and UV radiation lead to a decrease in ion concentration in the early afterglow due to recombination of ions with electrons released from the tube walls and electrodes. For ? values from 30?ms up to 7?s in nitrogen, gamma and UV radiation have a negligible influence on the breakdown initiation owing to the presence of a significant concentration of atoms in the ground state in the afterglow and no possibility of creation of positive ions. The influence of gamma radiation on breakdown initiation in neon is insignificant for ? interval from 30?ms to 0.15?s, whereas UV radiation has a significant influence on breakdown initiation for ? > 30?s. When the concentration of neutral active states decreases enough, the breakdown initiation is caused by cosmic rays in the case of non-irradiated tubes and gamma/UV photons in the case of gamma/UV irradiated tubes; this is manifested by the memory curve saturation. The memory curve saturation in the case of irradiated nitrogen and neon-filled tubes occurs at lower ? values than in the case of non-irradiated tubes, and it is a consequence of increased electron yield in the inter-electrode space.

The memory effect, due to postafterglow survival of some species which affect subsequent breakdown, was analyzed from the behavior of memory curves. In early afterglow, up to several tens of a millisecond, the memory effect in nitrogen is a consequence of the presence of positive ions formed by the collision between metastable molecules and highly vibrationally excited molecules remaining from the previous discharge. In late afterglow, the memory effect is due to N(4S) atoms created during the previous discharge and in early afterglow. When the atom density is reduced enough the breakdown is initiated by cosmic rays which always exists. In late afterglow in nitrogen the memory effect is very sensitive on cathode material.

The influence of positive ions and neutral active states on the memory effect in nitrogen-filled discharge tubes at 1.3 and 4.0 mbar pressures has been investigated. Analysing the thermal velocity of these particles as well as drift velocity of positive ions, it is shown that the positive ions have a dominant role in the breakdown initiation for afterglow periods lower than 30 ms, while the role of the neutral active states can be ignored because of their electrical neutrality. The estimated value of the positive ion recombination time in the afterglow for the pressures considered is about 30 ms. The atoms in ground states have a dominant role in breakdown initiation for afterglow periods higher than 30 ms. Our supposition is based on the earlier results that the long-lived Lewis–Rayleigh glow lasts up to several hours as a consequence of the recombination of these atoms on the wall. A detailed analysis of relaxation processes has shown that a contribution of vibrationally excited molecules as well as atomic and molecular metastable states created during the previous discharge cannot contribute to the memory effect significantly. Also, the contribution of cosmic rays to memory effect is analysed for the afterglow periods when the concentration of atoms in the ground state decreases to such a low value that their role in the secondary electron emission from the cathode is ignored.

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 results of the electrical breakdown time-delay as a function of the relaxation time τ, known as 'the memory curve', are presented. The memory curve was experimentally established for the relaxation times from 3 ms to 300 s, for the Ne-filled diode at 7 mbar pressure. Statistical analysis was used to analyse the obtained time-delay values. The results show that for the relaxation times τ ≤ 0.1 s the dominant part of the total time-delay is the breakdown formative time (tf ~ 0.1 ms). The breakdown formative time obtained in this investigation shows the same 'memory effect' as the breakdown total time-delay, because it slowly increases with τ. For τ > 0.1 s, the statistical time-delay makes up the dominant part of the total time-delay, as was reported earlier.

The recombination of positive ions and atoms during an afterglow period, created during previous electrical breakdown and gas discharge, at the molybdenum glass and copper is investigated using the time delay method. It has been shown that the recombination of the positive ions at the copper wall, while the atoms at the molybdenum wall, at room temperature, is more intensive. The temperature influence on the recombination of these particles at copper has also been monitored by the same method, showing that the positive ion recombination rate increases and atom recombination rate decreases with temperature.

The paper presents the results of investigation of the electrical breakdown in low pressure gases when the secondary electrons released from the cathode play the dominant role in the initiation of electrical breakdown. The secondary electrons are created by the charged and neutral species formed during the previous breakdown and discharge as well as by γ-rays. Electrical breakdown investigations are based on the measurements of electrical breakdown voltage and electrical breakdown time delay for gas-filled tubes with spherical electrodes with diameters much larger than an interelectrode distance. Stochastic nature of both the breakdown voltage and time delay are discussed and their distributions based on experimental data are shown. The methods for the determination of static breakdown voltage are also analysed. The influence of different parameters (overvoltage, cathode material and its surface purity, gas pressure, glow current, etc) on time delay are studied. A special attention is paid to the memory effect in various gases that depends on the positive ion recombination times, catalytic recombination times in the case of nitrogen and hydrogen, as well as metastable states deexcitation times in noble gases. The analysis of this effect is done by memory curves on the basis of which the presence of long-lived neutral active states can be followed to their very low concentrations when cosmic and environment radiation play the dominant role in electrical breakdown initiation.

The mechanisms leading to initiation of electrical breakdown in geometrically identical argon-filled tubes at different pressures were investigated by the memory curves. It was shown that the positive ions and metastable states, remaining from the previous discharge, have the dominant role in the initiation of breakdown in early and late afterglow periods, respectively. Contributions to the breakdown of gamma photons from radioactive sources (60Co) and cosmic rays were also analyzed.

Contributions of krypton ions and krypton metastables, as well as contributions of gamma-radiation and cosmic rays to the electrical breakdown in a krypton-filled tube have been analysed by use of the time delay method. The experimental results have shown that each of these contributions strictly depends on the afterglow period. The time delay method has enabled the determination of both the recombination time of positive ions and the lifetime of metastables, created in previous discharge. The obtained value of metastable lifetime is in agreement with its theoretical value. The dependence of the electrical breakdown on exposed dose rate of gamma-rays from the radiation source has also been investigated.

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 temperature dependence of the creation and the passivation of interface traps in irradiated n-channel MOSFETs during annealing has been investigated. The obtained results show that the creation process is directly related to the neutralization of the positive oxide trapped charge, and that hydrogen atoms (ions) and water molecules are directly responsible for the creation process and for the passivation process, respectively. A combined hydrogen-water (HW) model which explains the experimental results is proposed.

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.

In this paper we extend the available experimental data for breakdown delay times as a function of the afterglow time to short afterglow times for a pulsed obstructed discharge in nitrogen. Measurements were performed at 6.6 mbar in research grade nitrogen by application of a high-vacuum procedure. The delay times are separated into formative and statistical time lags and their dependence on the afterglow time is discussed. A model is developed that is able to reproduce the breakdown delay time behaviour for short afterglow times which is based on ion density decay through the diffusion. A transition from the effective diffusion coefficient of to the free diffusion of ions is observed at times of the order of 20 ms. The model was applied both in a simple approximate analytical form and in a numerical form with accurate representation of the geometry of the tube. When applied in conjunction with our earlier model of the breakdown delay appropriate for longer afterglow times the theory can predict the behaviour of the breakdown delay times between 0.5 ms and several hours.

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.

The instability of pMOS dosimetric transistors in the form of threshold voltage drift could be an important source of errors in low dose measurements. The source of the drift is, according to the recent nomenclature, switching states concerned with near-interfacial oxide traps (border traps), and we have investigated them for 10 different types of specially prepared pMOS transistors. It has been found that the density of these states depends on the received dose, the bias during irradiation, the temperature, and the thickness of the gate oxide and its hydrogen content. A tunneling model that successfully describes the threshold voltage drift and explains these experimental results is presented. The possible physical picture of border traps and two specific structural models of defects in the SiO/sub 2/ which could be concerned with these experimental results are also discussed. >

This article describes an electrical system aimed at measuring and data acquisition of breakdown voltages of vacuum and gas-filled tubes. The measurements were performed using a nitrogen-filled tube at 4 mbar pressure. Based on the measured breakdown voltage data as a function of the applied voltage increase rate, a static breakdown voltage is estimated for the applied voltage gradient ranging from 0.1 to 1 V s−1 and from 1 to 10 V s−1. The histograms of breakdown voltages versus applied voltage increase rates from 0.1 and 0.5 V s−1 are approximated by the probability density functions using a fitting procedure.

The paper describes dose response and signal fading of Al-gate p-channel (metal oxide semiconductor field effect transistors) MOSFETs in the range of gamma radiation doses used in radiation therapy. MOSFETs with thicknesses of the gate oxide layer of 1 mu m and 400 nm were used. The response was characterized by the threshold voltage shift and was studied as a function of the absorbed dose and time after irradiation. The dosimeters with the 1-mu m-thick oxide layer can be effectively used for measuring doses in the 0.1-5 Gy range. The dosimeters with 400-nm-thick oxide layer are suitable for measuring doses above 5 Gy. Both types of the dosimeters retain dosimetric information for long periods of time. (C) 2013 Elsevier Ltd. All rights reserved.

Postirradiation effect measurements on NMOS Al-gate transistors are performed. Rebound failures are demonstrated during the bias–thermal annealing. It is established that the interface traps, created during irradiation, are responsible for rebound.

The surface recombination of nitrogen atoms in afterglow is studied by the time delay method, accompanied by the macrokinetic diffusive model. The method consists of the measurement of the dependence of the mean value of the breakdown time delay on afterglow period td=f(τ) and fitting of the data by the model that was developed. Excited N2(A 3∑+u) nitrogen molecules formed in the surface‐catalyzed recombination on cathode produce secondary electrons. The electrons entering the interelectrode space determine the time delay in electrical breakdown. The time delay method is very efficient in nitrogen atom detection down to a natural radioactivity level. By fitting the calculated curve to the experimental data, we have: (1) shown that the nitrogen atom recombination on the glass container walls is second‐order in N while the recombination on the copper electrode is the first order; (2) determined the value of the surface recombination coefficient for molybdenum glass; (3) determined the combined probability o...

A long-time decay of activated nitrogen is studied by the time-delay method. The kinetics in late nitrogen afterglow is determined by nitrogen atom recombination. Surface-catalysed excitation of nitrogen atom recombination at the cathode gives a metastable induced electron yield in the inter-electrode space (the Auger de-excitation process) that determines the time delay. The probability of N2(A3 Sigma u+) metastable state formation by recombination at the electrode surface is determined, as are the contribution to electron yield from this mechanism and the contribution from the gas phase metastable species. On the basis of the above-cited mechanism, the time-delay method is found to be very efficient for detection of activated nitrogen.

This paper presents realization of a digital embedded system for measuring electrical breakdown time delay. The proposed system consists of three major parts: dc voltage supply, analog subsystem, and a digital subsystem. Any dc power source with the range from 100 to 1000 V can be used in this application. The analog subsystem should provide fast and accurate voltage switching on the testing device as well as transform the signals that represent the voltage pulse on the device and the device breakdown into the form suitable for detection by a digital subsystem. The insulated gate bipolar transistor IRG4PH40KD driven by TC429 MOSFET driver is used for high voltage switching on the device. The aim of a digital subsystem is to detect the signals from the analog subsystem and to measure the elapsed time between their occurrences. Moreover, the digital subsystem controls various parameters that influence time delay and provides fast data storage for a large number of measured data. For this propose, we used the PIC18F4550 microcontroller with a full-speed compatible universal serial bus (USB) engine. Operation of this system is verified on different commercial and custom made gas devices with different structure and breakdown mechanisms. The electrical breakdown time delay measurements have been carried out as a function of several parameters, which dominantly influence electrical breakdown time delay. The obtained results have been verified using statistical methods, and they show good agreement with the theory. The proposed system shows good repeatability, sensitivity, and stability for measuring the electrical breakdown time delay.

The positive space charge decay time in nitrogen afterglow was determined by the time delay method. Also, the influence of overvoltage on this determination was discussed through the effects of ionic drift, electron collection and acceleration. The time delay method is used for ion and metastable detection thanks to secondary electron emission from the cathode surface.

The effects of UV-radiation on electron- and X-irradiation induced damage in CMOS transitors are investigated. It is found that the threshold voltage instabilities caused by the electron- and X-irradiation can be annealed by UV-radiation. Experimental data obtained are analyzed in view of mechanisms responsible for the observed annealing effects. Russian text ignored