Effects of stress conditions on the generation of negative bias temperature instability-associated interface traps

The exponent n of the generation of an interface trap(Nit),which contributes to the power-law negative bias temperature instability(NBTI)degradation,and the exponent’s time evolution are investigated by simulations with varying the stress voltage Vgand temperature T.It is found that the exponent n in the diffusion-limited phase of the degradation process is irrelevant to both Vgand T.The time evolution of the exponent n is affected by the stress conditions,which is reflected in the shift of the onset of the diffusion-limited phase.According to the diffusion profiles,the generation of the atomic hydrogen species,which is equal to the buildup of Nit,is strongly correlated with the stress conditions,whereas the diffusion of the hydrogen species shows Vg-unaffected but T-affected relations through the normalized results.     

Study on the drain bias effect on negative bias temperature instability degradation of an ultra-short p-channel metal-oxide-semiconductor field-effect transistor

This paper studies the effect of drain bias on ultra-short p-channel metal-oxide-semiconductor field-effect transistor (PMOSFET) degradation during negative bias temperature (NBT) stress. When a relatively large gate voltage is applied, the degradation magnitude is much more than the drain voltage which is the same as the gate voltage supplied, and the time exponent gets larger than that of the NBT instability (NBTI). With decreasing drain voltage, the degradation magnitude and the time exponent all get smaller. At some values of the drain voltage, the degradation magnitude is even smaller than that of NBTI, and when the drain voltage gets small enough, the exhibition of degradation becomes very similar to the NBTI degradation. When a relatively large drain voltage is applied, with decreasing gate voltage, the degradation magnitude gets smaller. However, the time exponent becomes larger. With the help of electric field simulation, this paper concludes that the degradation magnitude is determined by the vertical electric field of the oxide, the amount of hot holes generated by the strong channel lateral electric field at the gate/drain overlap region, and the time exponent is mainly controlled by localized damage caused by the lateral electric field of the oxide in the gate/drain overlap region where hot carriers are produced.     

Study on the degradation of NMOSFETs with ultra-thin gate oxide under channel hot electron stress at high temperature

This paper studies the degradation of device parameters and that of stress induced leakage current (SILC) of thin tunnel gate oxide under channel hot electron (CHE) stress at high temperature by using n-channel metal oxide semiconductor field effect transistors (NMOSFETs) with 1.4-nm gate oxides. The degradation of device parameters under CHE stress exhibits saturating time dependence at high temperature. The emphasis of this paper is on SILC of an ultra-thin-gate-oxide under CHE stress at high temperature. Based on the experimental results, it is found that there is a linear correlation between SILC degradation and V_h degradation in NMOSFETs during CHE stress. A model of the combined effect of oxide trapped negative charges and interface traps is developed to explain the origin of SILC during CHE stress.     

Study on the negative bias temperature instability effect under dynamic stress

This paper studies negative bias temperature instability (NBTI) under alternant and alternating current (AC) stress.Under alternant stress,the degradation smaller than that of single negative stress is obtained.The smaller degradation is resulted from the recovery of positive stress.There are two reasons for the recovery.One is the passivation of H dangling bonds,and another is the detrapping of charges trapped in the oxide.Under different frequencies of AC stress,the parameters all show regular degradation,and also smaller than that of the direct current stress.The higher the frequency is,the smaller the degradation becomes.As the negative stress time is too small under higher frequency,the deeper defects are hard to be filled in.Therefore,the detrapping of oxide charges is easy to occur under positive bias and the degradation is smaller with higher frequency.     

Flat-roof phenomenon of dynamic equilibrium phase in the negative bias temperature instability effect on a power MOSFET

The effect of the static negative bias temperature(NBT) stress on a p-channel power metal–oxide–semiconductor field-effect transistor(MOSFET) is investigated by experiment and simulation. The time evolution of the negative bias temperature instability(NBTI) degradation has the trend predicted by the reaction–diffusion(R–D) model but with an exaggerated time scale. The phenomena of the flat-roof section are observed under various stress conditions, which can be considered as the dynamic equilibrium phase in the R–D process. Based on the simulated results, the variation of the flat-roof section with the stress condition can be explained.     

Degradation mechanism of enhancement-mode AlGaN/GaN HEMTs using fluorine ion implantation under the on-state gate overdrive stress

The degradation mechanism of enhancement-mode Al Ga N/Ga N high electron mobility transistors(HEMTs)fabricated by fluorine plasma ion implantation technology is one major concern of HEMT’s reliability.It is observed that the threshold voltage shows a significant negative shift during the typical long-term on-state gate overdrive stress.The degradation does not originate from the presence of as-grown traps in the Al Ga N barrier layer or the generated traps during fluorine ion implantation process.By comparing the relationships between the shift of threshold voltage and the cumulative injected electrons under different stress conditions,a good agreement is observed.It provides direct experimental evidence to support the impact ionization physical model,in which the degradation of E-mode HEMTs under gate overdrive stress can be explained by the ionization of fluorine ions in the Al Ga N barrier layer by electrons injected from 2DEG channel.Furthermore,our results show that there are few new traps generated in the Al Ga N barrier layer during the gate overdrive stress,and the ionized fluorine ions cannot recapture the electrons.     

The role of hydrogen in negative bias temperature instability of pMOSFET

The NBTI degradation phenomenon and the role of hydrogen during NBT stress are presented in this paper. It is found that PBT stress can recover a fraction of V_th shift induced by NBTI. However, this recovery is unstable. The original degradation reappears soon after reapplication of the NBT stress condition. Hydrogen-related species play a key role during a device's NBT degradation. Experimental results show that the diffusion species are neutral, they repassivate Si dangling bond which is independent of the gate voltage polarity. In addition to the diffusion towards gate oxide, hydrogen diffusion to Si-substrate must be taken into account for it also has important influence on device degradation during NBT stress.     

Effect of substrate bias on negative bias temperature instability of ultra-deep sub-micro p-channel metal--oxide--semiconductor field-effect transistors

The effect of substrate bias on the degradation during applying a negative bias temperature (NBT) stress is studied in this paper. With a smaller gate voltage stress applied, the degradation of negative bias temperature instability (NBTI) is enhanced, and there comes forth an inflexion point. The degradation pace turns larger when the substrate bias is higher than the inflexion point. The substrate hot holes can be injected into oxide and generate additional oxide traps, inducing an inflexion phenomenon. When a constant substrate bias stress is applied, as the gate voltage stress increases, an inflexion comes into being also. The higher gate voltage causes the electrons to tunnel into the substrate from the poly, thereby generating the electron--hole pairs by impact ionization. The holes generated by impact ionization and the holes from the substrate all can be accelerated to high energies by the substrate bias. More additional oxide traps can be produced, and correspondingly, the degradation is strengthened by the substrate bias. The results of the alternate stress experiment show that the interface traps generated by the hot holes cannot be annealed, which is different from those generated by common holes.     

Effect of Channel Length and Width on NBTI in Ultra Deep Sub-Micron PMOSFETs

The effects of channel length and width on the degradation of negative bias temperature instability （NBTI） are studied. With the channel length decreasing, the NBTI degradation increases. As tile channel edges have more damage and latent damage for the process reasons, the device can be divided into three parts： the gate and source overlap region, the middle channel region, and the gate and drain overlap region. When the NBTI stress is applied, the non-uniform distribution of the generated defects in the three parts will be generated due to the inhomogeneous degradation. With tile decreasing channel length, tile channel edge regions will take up a larger ratio to the middle channel region and the degradation of NBTI is enhanced. The channel width also plays an important role in the degradation of NBTI. There is an inflection point during the decreasing channel width. There are two particular factors： the lower vertical electric field effect for the thicker gate oxide thickness of the sha/low trench isolation （STI） edge and the STI mechanical stress effecting on the NBTI degradation. The former reduces and the latter intensifies the degradation. Under the mutual compromise of the both factors, when the effect of the STI mechanical stress starts to prevail over the lower vertical electric field effect with the channel width decreasing, the inflection point comes into being.     

Hot-Carrier Stress Effects on GIDL and SILC in 90nm LDD-MOSFET with Ultra-Thin Gate Oxide

Hot-carrier degradation for 90 nm gate length lightly-doped drain （LDD） NMOSFET with ultra-thin （1.4 nm） gate oxide is investigated under the low gate voltage stress （LGVS） and peak substrate current （Isub max） stress. It is found that the degradation of device parameters exhibits saturating time dependence under the two stresses. We concentrate on the effect of these two stresses on gate-induced-drain leakage （GIDL） current and stress induced leakage current （SILC）. The characteristics of the GIDL current are used to analyse the damage generated in the gate-to-LDD region during the two stresses. However, the damage generated during the LGVS shows different characteristics from that during Isub stress. SILC is also investigated under the two stresses. It is found experimentally that there is a linear correlation between the degradation of SILC and that of threshold voltage during the two stresses. It is concluded that the mechanism of SILC is due to the combined effect of oxide charge trapping and interface traps for the ultra-short gate length and ultra-thin gate oxide LDD NMOSFETs under the two stresses.     

A note on scaled variance ratio estimation of the Hurst exponent with application to agricultural commodity prices

The measure of long-term memory is important for the study of economic and financial time series. This paper estimates the Hurst exponent from a Scaled Variance Ratio model for 17 commodity price series under the efficient market null H₀:H=0.5. The distribution about the estimates of H are obtained from 90%, 95% and 99% confidence intervals generated from 20,000 Monte Carlo replications of a geometric Brownian motion. The results show that the scaled variance ratio provides a very good and stable estimate of the Hurst exponent, but the estimates can be quite different from the measure obtained from rescaled range or R–S analysis. In general commodity prices are consistent with the underlying assumption of a geometric Brownian motion.     

On the effects of NBTI degradation in p-MOSFET devices

This paper presents the effects of interface trap concentration and threshold voltage shift on NBTI degradation in p-MOSFETs. To explore the degradation mechanisms, transistors having an EOT of 1.1 nm and 5 nm were simulated by applying various stress conditions. The NBTI degradation mechanism was studied by varying the gate voltage, temperature and substrate doping level. The simulations show NBTI degradation in terms of the threshold voltage shift, ΔV_th and number of interface traps, ΔN_it. The simulation results show an improved degradation trend in terms of ΔV_th and ΔN_it when the substrate doping level is increased.     

Evaluation of negative bias temperature instability in ultra-thin gate oxide pMOSFETs using a new on-line PDO method

A new on-line methodology is used to characterize the negative bias temperature instability (NBTI) without inherent recovery. Saturation drain voltage shift and mobility shift are extracted by I_D-V_D characterizations, which were measured before stress, and after every certain stress phase, using the proportional differential operator (PDO) method. The new on-line methodology avoids the mobility linearity assumption as compared with the previous on-the-fly method. It is found that both reaction--diffusion and charge-injection processes are important in NBTI effect under either DC or AC stress. A similar activation energy, 0.15 eV, occurred in both DC and AC NBTI processes. Also degradation rate factor is independent of temperature below 90\du\ and sharply increases above it. The frequency dependence of NBTI degradation shows that NBTI degradation is independent of frequencies. The carrier tunnelling and reaction--diffusion mechanisms exist simultaneously in NBTI degradation of sub-micron pMOSFETs, and the carrier tunnelling dominates the earlier NBTI stage and the reaction--diffusion mechanism follows when the generation rate of traps caused by carrier tunnelling reaches its maximum.     

Vibrational non-equilibrium in the hydrogen–oxygen reaction. Comparison with experiment

A theoretical model is proposed for the chemical and vibrational kinetics of hydrogen oxidation based on consistent accounting of the vibrational non-equilibrium of the HO₂ radical that forms as a result of the bimolecular recombination H+O₂ → HO₂. In the proposed model, the chain branching H+O₂ = O+OH and inhibiting H+O₂+M = HO₂+M formal reactions are treated (in the terms of elementary processes) as a single multi-channel process of forming, intramolecular energy redistribution between modes, relaxation, and unimolecular decay of the comparatively long-lived vibrationally excited HO₂ radical, which is able to react and exchange energy with the other components of the mixture. The model takes into account the vibrational non-equilibrium of the starting (primary) H₂ and O₂ molecules, as well as the most important molecular intermediates HO₂, OH, O₂(¹Δ), and the main reaction product H₂O. It is shown that the hydrogen–oxygen reaction proceeds in the absence of vibrational equilibrium, and the vibrationally excited HO₂(v) radical acts as a key intermediate in a fundamentally important chain branching process and in the generation of electronically excited species O₂(¹Δ), O(¹D), and OH(²Σ⁺). The calculated results are compared with the shock tube experimental data for strongly diluted H₂–O₂ mixtures at 1000 < T < 2500 K, 0.5 < p < 4 atm. It is demonstrated that this approach is promising from the standpoint of reconciling the predictions of the theoretical model with experimental data obtained by different authors for various compositions and conditions using different methods. For T < 1500 K, the nature of the hydrogen–oxygen reaction is especially non-equilibrium, and the vibrational non-equilibrium of the HO₂ radical is the essence of this process. The quantitative estimation of the vibrational relaxation characteristic time of the HO₂ radical in its collisions with H₂ molecules has been obtained as a result of the comparison of different experimental data on induction time measurements with the relevant calculations.     

Analysis of femtosecond laser ionization/dissociation of polyatomic molecule C6H10O from one-colour pump-probe measurement

This paper reports that a one-colour fs pump-probe measurement has been carried out for studying photoionization/photodissociation of cyclohexanone (C6H10O) in intense laser field. Two of the fragments from cyclohexanone, C2H3+ and C3H3+ , are studied under 800 nm laser pump-probe and the results obtained show similar time evolutions. It proposes a feasible model for analysing the experimental observations of the one-colour fs pump-probe measurement. The results demonstrate that as an intermediate product, the excited molecular parent ions play a very important role in photionization/photodissociation processes in intense laser field.     

The switch of the worst case on NBTI and hot-carrier reliability for 0.13 μm pMOSFETs

This investigation describes experiments on two sizes of p-channel metal-oxide-semiconductor field-effect-transistors (pMOSFETs), to study the negative bias temperature instability (NBTI) and hot-carrier (HC) induced degradation. This work demonstrates that the worst condition for pMOSFETs under HC tests occurs in CHC (channel HC, stressed at V_g = V_d) mode at high temperature. This study also shows that the worst degradation of pMOSFETs should occur in NBTI. This inference is based on a comparison of results for forward saturation current (I_ds,f) and reverse saturation current (I_ds,r) obtained in NBTI and HC tests.     

Niobates et tantalates d'europium de type “Bronze de Tungsténe Quadratique”—II: Evalution Des Niveaux D'Enerige Dans La Structure

From the magnetic and electrical properties of some TTB type niobates and tantalates of Eu¹¹ with general formula Eu_xNbO₃ (0.5$\text{}\text{?}$x$\text{}\text{?}$ 0.6), Eu_0.5TaO₃ and EuBCM₅O₁₅ (M = Ta, Nb; B = Eu¹¹, Sr, Ba; C = Na, K) we have derived a schematic energy level model of Goodenough type for tungsten bronze type structure. This was found to be qualitatively in agreement with experimental results but could not account for large amounts of Eu³⁺ calculated on the basis of Mössbauer spectra. Computed electrostatic potentials in the TTB structure allowed verification of the proposed energy level diagram for Eu_0.6NbO₃. However, for Eu_0.5NbO₃ and EuBCM₅O₁₅, agreement between theoretical potentials and experimental results is obtained by ordering the Eu³⁺ ions in perovskite cages along the c axis of the structure. With three arrangements of the ordered perovskite units, it was possible to account for the amounts of Eu³⁺ found experimentally in most of the compounds.