Semiconducting TiO2 displays non-volatile multi-state, hysteretic behavior in its I-V characteristics that can be exploited as a memory material in a memristive device. We exposed memristive TiO2 devices in the on and off resistance states to 45 Mrad(Si) of ~1-MeV gamma radiation and 23 Mrad(Si) of 941-MeV Bi-ions under zero bias conditions and none of the devices were degraded. These results suggest that TiO2 memristive devices are good candidates for radiation hard electronics for aerospace.

The use of annular MOSFET design, which has demonstrated total-dose radiation immunity in CMOS circuits, can improve the hot-carrier reliability of CMOS circuits by reducing the drain electric field compared to conventionally designed MOSFETs. A theoretical analysis of the annular n-MOSFET in saturation verifies the reduction of the drain electric field in properly designed MOSFETs. Hot-carrier data for an enclosed 0.25-/spl mu/m n-MOSFET demonstrate an improvement in hot-carrier lifetime by more than 3x compared to a conventional device in the same technology.

The geometric component of charge pumping current-was examined in n-channel metal-oxide-silicon field effect transistors (MOSFETs) following low-temperature irradiation. In addition to the usual dependencies on channel length and gate bias transition time, the geometric component was found to increase with radiation-induced oxide-trapped charge density and decreasing temperature. A postirradiation injection of electrons into the gate oxide reduces the geometric component along with the density of oxide-trapped charge, which clearly demonstrates that the two are correlated. A fit of the injection data to a first-order model for trapping kinetics indicates that the electron trapping occurs predominantly at a single type of Coulomb-attractive trap site. The geometric component results primarily from the bulk recombination of channel electrons that fail to transport to the source or drain during the transition from inversion to accumulation. The radiation response of these transistors suggests that Coulomb scattering by oxide-trapped charge increases the bulk recombination at low temperatures by impeding electron transport. These results imply that the geometric component must be properly accounted for when charge pumping irradiated n-channel MOSFETs at low temperatures.

We fabricated bismuth (Bi) nanowires with low energy electron beam lithography using silver (Ag) nanocrystal shadowmasks and a subsequent chlorine reactive ion etching. Submicron-size metal contacts on the single Bi nanowire were successfully prepared by in situ focused ion beam metal deposition for transport measurements. The temperature dependent resistance measurements on the 50 nm wide Bi nanowires showed that the resistance increased with decreasing temperature, which is characteristic of semiconductors and insulators.

In this paper the underlying mechanisms that produce the crossover in worst-case hot-carrier stress condition observed at room temperature in some deep submicron lightly-doped-drain (LDD) NMOS devices and at cryogenic temperatures for devices with longer channel lengths are investigated. Experiments were performed that demonstrate the generality of the cross-over. The role of stress temperature, measurement temperature and stress condition were experimentally addressed. The temperature dependence of the mobility was measured, and an analysis is presented that shows that mobility changes alone do not explain the observed changes in the transconductance. A model is proposed that allows for changes in the source-drain resistance with stress time. It is suggested that the origin of the time-dependent increasing source-drain resistance was the injection of charge, either in the form of fixed charge or as interface states, into the spacer oxide above the LDD region. This model is used to explain the qualitative dependence of the worst-case stress condition on channel length and temperature. Finally, it is suggested that the methodology used to design the LDD structure be modified to account for these new observations

Human T-lymphotropic virus type 1 (HTLV-1) infection has been discovered recently in people of Amerindian descent living in coastal areas of British Columbia, Canada. DNA sequencing combined with phylogenetic analysis and restriction fragment length polymorphism (RFLP) typing of HTLV-1 strains recovered from these British Columbia Indians (BCI) was conducted. Sequence-based phylogenetic trees distributed the BCI isolates among the Japanese subcluster (subcluster B) and the geographically widely distributed subcluster (subcluster A) of the large HTLV-1 cosmopolitan cluster. Long terminal repeat (LTR) RFLP typing revealed three distinct, equally frequent LTR cleavage patterns, two of which were of previously recognized Japanese and widely dispersed cosmopolitan types. A third, new cleavage pattern was detected which may have arisen by recombination between two other HTLV-1 genotypes. Our results suggest multiple origins for HTLV-1 in BCI, which are equally consistent with (i) a cluster of recent sporadic infections, (ii) ancient endemic vertical transmission through Amerindian lineages, or (iii) both.

We have compared the immunoglobulin isotype and IgG subclass and the titre of neutralizing antibody responses to the human T celt lymphotropic virus type I (HTLV‐I) between a group of asymptomatic HTLV‐I infected individuals and a group with the neurological disease HTLV‐I associated myelopathy/tropical spastic paraparesis (HAM/TSP). A western blot titration assay and an envelope peptide ELISA were used to determine the presence and titre of isotype and IgG subclass responses to the gag p19 and p24 proteins and to the envelope protein. Significant increases were observed in the number of individuals seropositive for a particular isotype and IgG subclass in the HAM/TSP group versus the asymptomatic group particularly for IgM and IgE and to a lesser extent, IgA. The predominant IgG subclasses to the HTLV‐I p19, p24 and envelope proteins were IgG 1 and IgG 3 . This finding was also observed in the titres of the antibody responses to these HTLV‐I proteins. The HAM/TSP group also exhibited significantly higher neutralizing antibody titres than the asymptomatic group. This evidence suggests that some form of chronic immune stimulation might be involved in the immunopathogenesis of HAM/TSP. In addition, by following the Western blot titre to the IgM and IgE isotypes in particular, it may be possible to identify asymptomatic individuals progressing to HAM/TSP.

Background: Recent epidemiology studies have demonstrated the presence of HTLV-I and its close relative, HTLV-II in several aboriginal populations in North, Central and South America but not in Canadian Indian populations. HTLV-II appears to be more prevalent than HTLV-I in aboriginal populations of the Americas. Recently several clinical cases of HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP) and a case of adult T-cell leukemia (ATL) have been identified in British Columbian Indians. This data suggests that a new endemic area of HTLV-I infection may be present within British Columbian Indian population. However, it has recently been shown that HTLV-II may also be associated with a neurological disease similar to HAM/TSP.

A method to evaluate the sensitivity of p-channel MOSFETs to hot-carrier-induced damage by using the total injected charge as the degradation monitor is presented. The advantage of the method is that lifetimes for all devices made with a particular process correlate to the same straight line with respect to the total injected charge with the slope about 1.8. It then becomes easy to compare the hot-carrier sensitivity of p-channel devices made by different process technologies.<>

The entire envelope gene of human T cell leukaemia virus type I (HTLV-I) has been successfully expressed in a baculovirus non-fusion vector system. The HTLV-I envelope protein accumulated within the insect cells as inclusion bodies which allowed efficient recovery of the recombinant protein. In an attempt to study the role of the HTLV-I envelope glycoprotein as an immunogenic target, mice were immunized with the envelope protein inclusion bodies (env-I.B.) in the presence or absence of an adjuvant. Antibodies of broad specificity were produced against the HTLV-I envelope protein in the presence or absence of an adjuvant as detected by Western blotting, radioimmunoprecipitation and peptide ELISA. Neutralizing antibody was detected when env-I.B. immunizations were carried out in the presence of high doses of a new adjuvant composed of a mycobacterial cell wall extract. In a combined immunization regimen, env-I.B. were found to enhance and broaden the antibody response to the HTLV-I envelope glycoprotein, following priming with various recombinant vaccinia virus (RVV) constructs expressing either the entire native HTLV-I envelope (gp46 and gp21) or just the surface envelope protein (gp46). Increased titres of neutralizing antibodies were observed following priming with the RVV expressing gp46 only. Results indicate that immunization regimes that involve priming with RVV expressing HTLV-I envelope followed by boosting with recombinant baculoviral HTLV-I envelope might be useful in eliciting protective immune responses in vivo.

Bonded wafer substrates have been made which are optimized for integrating high energy, particle detector arrays with their readout electronics. The detectors are processed in the handle wafer, which is a 300 mum thick, high resistivity, [111] crystal orientation silicon wafer. This wafer is bonded to a primary wafer using a low temperature process that does not affect the detector material. The support electronics are processed in the remnant of the primary wafer, which is a submicron thick [100] crystal orientation silicon film formed by a bond-and-etchback procedure. These two device materials are isolated from each other by a radiation hardened dielectric film. The integrated process is based on a low temperature, radiation hardened VLSI CMOS process which is also shown not to seriously affect the detector material.

A constant gate current stress method for characterizing the hot-carrier aging effect in p-channel MOSFETs is described. Unlike the conventional constant voltage stress method, the gate current is monitored and maintained constant during the stress by adjusting the drain voltage at short time intervals. This approach ensures a constant electron injection rate into the oxide during the stress period. It eliminates the degradation saturation effect. In order to compare hot-carrier sensitivities, it is desirable to be able to correlate the devices with different gate lengths from the same process technology into one straight line. This has been achieved by utilizing the substrate current extrapolated at lifetime, I/sub sub/(t= tau ), rather than the initial substrate current, I/sub sub/(0), as the hot-carrier generation indicator. Therefore, by combining the constant gate current stress test method with the modified lifetime extrapolation procedure, it also becomes possible to compare the hot-carrier sensitivities of different process technologies.<>

Isolates of HTLV-I have been characterized from a number of different regions of the world; however, there has not been a nucleotide sequence analysis of an HTLV-I isolate from a South American country. Reported here is an individual from Chile identified with the HTLV-I-associated neurological disease HAM/TSP. The sera and the nucleic acid sequence of the HTLV-I present in peripheral blood lymphocytes from this Chilean HAM/TSP patient over a two year period are characterized. During this time, the patient's condition grew progressively worse. While the serological profile of this patient was unremarkable in comparison with other HAM/TSP patients previously described, nucleic acid sequence analysis identified two nucleotide positions which contained nucleotides unique to this Chilean isolate. The nucleotide sequence analysis also indicates that the Chilean HTLV-I isolate is more closely related to Caribbean and Japanese isolates of HTLV-I than to the African and U.S. isolates described so far.

It is shown that the correlation model developed in previous work to determine hot-carrier device lifetime from radiation-induced interface state data can be extended to lightly-doped drain (LDD) devices by selecting different, but equivalent, failure criteria. Excellent agreement between the model and experimental data is shown for LDD devices from several different manufacturers. These results indicate that a radiation test can be used as a quick alternative to a voltage stress test for predicting hot-carrier-induced device lifetime. Charge pumping measurement results are presented that demonstrate the basis for such a correlation.< >

Gaseous haloalkyl radicals were prepared by the photolysis of iodohaloalkanes in Pyrex vessels containing mercury (I) halides. Cleavage of the carbon-iodine bond gave mercury (II) halide and a radical which was subsequently shown to react on the ground state electronic energy surface. The usefulness of this method for chemical activation rate constant studies is illustrated by measurement of unimolecular rate constants for decomposition of CH2ClCH2Cl and CF3CH3. Possible mechanisms for photodecomposition of iodoalkanes in the presence of mercury (I) halides are discussed.

The transient response modeling commonly seen in the literature of silicon devices exposed to bursts of ionizing radiation is not capable of handling many current hardness assurance issues in integrated circuits. A new model is presented and compared with the standard model. Results of validation experiments using IC test transistors and an op amp IC are provided and are shown to agree with the new model.

: The present Invention is directed to a novel gallium arsenide field effect transistor and, more particularly, to a novel gallium arsenide field effect transistor which exhibits greatly improved tolerance to the effects of pulsed ionizing radiation.