Momčilo M. Pejović

Surface recombination of atoms in a nitrogen afterglow

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...

Analysis of gamma-radiation induced instability mechanisms in CMOS transistors

Abstract Gamma-radiation induced instabilities of threshold voltage and gain factor of Al-gate and Si-gate CMOS transistors, as well as the underlying changes in positive gate oxide charge and interface trap densities are presented. The data are analyzed in terms of physico-chemical and electrophysical processes responsible for creation of the gate oxide charge and interface traps, and a generalized model which explains in detail the experimental data obtained is proposed.

Analysis of mechanisms which lead to electrical breakdown in argon using the time delay method

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.

Modelling of charged particle decay in nitrogen afterglow

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.

Creation and passivation of interface traps in irradiated MOS transistors during annealing at different temperatures

Abstract 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.

Surface recombination in breakdown time delay experiments: Effect of different cathode materials

The late afterglow in nitrogen with iron electrode is studied by the breakdown time delay method, i.e., by measuring the breakdown time delay td as a function of the afterglow time τ. It is proposed that the cause of the secondary electrons initiating the breakdown is the energy of the surface recombination of nitrogen atoms on the iron electrode. The gas-phase and macrokinetic diffusive models are used to describe the experimental breakdown time delay data. By fitting the theoretical curve to the experimental data: (1) it has been confirmed that the recombination on the molybdenum glass is of the second order and the value of the surface recombination coefficient is determined at 4 mbar; (2) it has been shown that the surface recombination on the iron electrode is of the second order, and the effective recombination coefficients are determined; (3) the analytical form of the recombination coefficient as a function of the adsorption characteristics of surfaces and the pressure of the parent gas has been derived. In addition, the orders of surface recombination on the molybdenum-, aluminum-, and gold-plated electrode were determined by the same method.

Memory effects in the afterglow: open questions on long-lived species and the role of surface processes

The memory effect, the phenomenon that some active species survive very long afterglow periods and affect subsequent breakdown, was observed more than 40 years ago. The effects have been observed even over periods of several hours. Attempts to explain the memory effect in nitrogen were mostly based on hypothetical metastables and on the A3Σ state. However, such explanations had to neglect some quenching processes which are known to be very effective under the conditions of the experiments. The explanation based on atoms remaining from the previous discharge and recombining on the cathode to produce initial electrons was shown to be fully consistent with all the experimental data for nitrogen including a wide range of pressures and the addition of oxygen impurities. The memory effect was also shown to be sensitive to the work function of the cathode material. Thus, an attempt was made to use the memory effect as a diagnostic tool to establish the data on the dominant loss of nitrogen atoms from the discharge which is recombination on the walls of the tube. However, a possible role of higher vibrational levels has not been fully addressed, mainly due to the shortage of data. On the other hand, the memory effect which was observed for rare gases cannot be explained on the basis of the standard data unless the presence of molecular impurities is invoked. Another open issue would be the role of charges accumulated on the glass surfaces and whether those may be released to the gas phase. The aim of this paper is to summarize the achievements of the model based on atom recombination and to point out how the breakdown model associated with the memory effect may be completed and how it may be applied in practical discharges.

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.

Kinetics of activated nitrogen states in late afterglow by the time-delay method

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.

pMOS dosimetric transistors with two-layer gate oxide

Abstract 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.