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Superconducting devices with high-density integration are required for applications, such as high-performance detectors and quantum computing. Here, the direct bonding of Nb electrodes at room temperature using a surface activated bonding method was investigated. We directly bonded Nb bonding pads and then performed current–voltage measurements in a 3 He cryostat. A superconducting current of 1–5 mA was confirmed for the bonded interconnect. The transition temperature was 7.3–9.3 K. These values are affected by the quality of the bonding interface. According to cross-sectional transmission electron microscopy observations and energy-dispersive x-ray spectroscopy analysis of the bonding interface, the Nb layers were bonded with a 3-nm-thick intermediate layer made of Si and Nb between them. The Si sources were the bonding substrate and the bonding jig in the bonding apparatus. [ABSTRACT FROM AUTHOR]

Surface passivation of organic–inorganic halide perovskites (OIHPs) is a crucial step to annihilate the surface defects and to control the deteriorated ion migration phenomenon. Here, we study the role of lead sulfate (PbSO4) as an effective passivator in OIHP single crystals (SCs). Using impedance spectroscopy, we evaluate the ion migration and electrical properties of lead sulfate-passivated methylammonium lead tri-bromide (MAPbBr3) SCs. We found that the low-frequency impedance response that is assigned to the ionic motion in the MAPbBr3 SC is strongly affected by the inorganic PbSO4 surface treatment. The activation energy corresponding to the ion migration of MAPbBr3 SC is increased from 0.28 to 0.36 eV after PbSO4 surface treatment. The temperature-dependent I–V hysteresis of the MAPbBr3 SCs upon PbSO4 passivation was also measured. We found that such PbSO4 surface treatment stabilizes the crystal surface and improves the hysteresis properties of the crystals at elevated temperatures. [ABSTRACT FROM AUTHOR]

In nonvolatile resistive memory and neuromorphic computing, the formation and rupture of a conductive filament after the forming process causes a reversible resistance transition between low- and high-resistance states. We confirm herein that conductance fluctuations by sweeping the applied voltage before and after "semi-forming" appear in Pt/NiO/Pt resistive switching cells through an investigation of nonpolar resistive transitions after semi-forming and "second forming." The increase in conductance owing to conductance fluctuations originates from the modification of oxygen-vacancy densities at grain boundaries in the NiO layer. Moreover, this modification may disappear at 470 K. The influence of a significant Joule heating caused by current through a fat filament created by second forming determines whether the cell conductance after the reset takes on the value of the conductance just after second forming or that of the initial conductance. Thus, Joule heating seems to be the driving force behind the reset in Pt/NiO/Pt cells. [ABSTRACT FROM AUTHOR]

Free radicals from processing plasmas are known to cause damage to dielectric films used in semiconductor devices. Many radicals are highly reactive and can readily interact with the material exposed to the plasma. This can modify the chemical structure of the material causing deterioration of electrical and mechanical properties of the films. This work detects the transmission of oxygen radicals through single- and double-layer silicon-nitride and silicon-dioxide freestanding films. The films were exposed to oxygen plasma. A fluorophore dye was used to detect the oxygen radicals traversing through the films. By measuring the fluorescence of the dye before and after multiple timedplasma exposures, the transmission properties of oxygen radicals through the material were found. The results indicate that the absorption length of oxygen radicals increases with increasing plasma exposure times for Si3N4 films because the oxygen plasma oxidizes the top layer of the film and forms a less dense silicon oxynitride layer. For SiO2 films, the absorption length was found to decrease as a function of plasma exposure time because of oxidation of the SiO2 surface which leads to the formation of a denser oxide layer on the surface of the sample. [ABSTRACT FROM AUTHOR]

A detailed characterization of the crystal structure and electrical properties of epitaxially grown SBT thin films with (001) and (116) orientation is presented. The preparation of epitaxial grown SrBi(sub 2)Ta(sub 2)O(sub 9) (SBT) films with (001) and (116) orientations on (100) and (110) SrTiO3 substrates by using MOCVD is also described.

Atomic force microscopy was used to study rheological and tribological characteristics of polystyrene and poly (vinyl methyl ether) blends.

Sulfur diffusion into GaAlA layers with varying Al content using GaS and As as diffusion source is discussed. X-ray diffraction analysis was used to select the GaS diffusion source. Diffusion was performed in a sealed quartz ampoule at 820 degrees Centigrade and arsenic pressure of 1 atm. It is shown that the sulfur was diffused without any surface damage. Good agreement was also obtained for experimental and theoretical results.

An improved interference method is proposed to determine ordinary and extraordinary refractive index dispersions of nematic liquid crystals (LCs). In this method, an LC cell coated with a thin metal layer is used as a Fabry-Perot interferometer, which shows us a sharp transmission fringe. To ensure high reliability, the wavelength dispersion of the refractive index of the metal is taken into account in fitting calculation. In spite of measuring ordinary and extraordinary components, the LC cell, polarizers, and other equipment are not rotated during the experiment. The index evaluation from a single spectrum avoids errors depending on the measurement position owing to nonuniformities of molecular orientation and cell thickness because we can obtain the two indices at exactly the same position. This system can adapt to a wide frequency range and does not require any specific wavelength light source or laser. We demonstrate the determination of ordinary and extraordinary refractive index dispersions of a nematic liquid crystal in the visible and nearinfrared regions. Furthermore, we quantitatively reproduce the measured spectrum by calculation using the measured refractive indices. [ABSTRACT FROM AUTHOR]

Resistive switching (RS) in metal/oxide/metal stack structures plays a key role in resistive RAM. The formation and rupture of conductive filaments have been widely accepted as an origin of RS mechanism especially in binary transition metal oxides. Forming exhibits some analogies with a dielectric breakdown of SiO2 thin films. In this study, Time-Dependent Forming (TDF) characteristics of Pt/NiO/Pt stack structures have been investigated. The results revealed that the formation of conductive filaments at the forming process by applying constant voltage followed a weakest-link theory and that the weakest spots were almost randomly distributed in NiO thin films according to the Poisson statistics. Furthermore, the distribution of TDF characteristics depends on NiO crystallinity. A small variation of initial resistance tends to result in a large variation of time to forming and vice versa. [ABSTRACT FROM AUTHOR]

The strain distributions and carrier confinement potential variations in semiconductor strained dots and wires are determined by using analytical and finite-element-method calculations. The wires and dots are made of lattice-mismatched wires. The confinement potentials are modified locally by the inhomogeneous strain distribution in the dots and wires. This modification generates a localization in the carrier wave function.

Two-color photon-gated persistent spectral hole burning by electron transfer from a doped donor to an acceptor branched to a host polymer matrix was investigated. The results confirmed that the hole formation mechanism was donor-acceptor electron transfer. Thermal stability of the burnt holes increased when the acceptor was branched into the host polymer, poly(methylmethacrylate).

Memristors are receiving keen interest because of their potential varied applications and promising large-scale information storage capabilities. Tantalum oxide is a memristive material that has shown promise for high-performance nonvolatile computer memory. The microphysics has been elusive because of the small scale and subtle physical changes that accompany conductance switching. In this study, we probed the atomic composition, local chemistry, and electronic structure of functioning tantalum oxide memristors through spatially mapped O K-edge x-ray absorption. We developed a time-multiplexed spectromicroscopy technique to enhance the weak and possibly localized oxide modifications with spatial and spectral resolutions of <30 nm and 70 meV, respectively. During the initial stages of conductance switching of a micrometer sized crosspoint device, the spectral changes were uniform within the spatial resolution of our technique. When the device was further driven with millions of high voltage-pulse cycles, we observed lateral motion and separation of ~100 nm-scale agglomerates of both oxygen interstitials and vacancies. We also demonstrate a unique capability of this technique by identifying the relaxation behavior in the material during electrical stimuli by identifying electric field driven changes with varying pulse widths. In addition, we show that changes to the material can be localized to a spatial region by modifying its topography or uniformity, as against spatially uniform changes observed here during memristive switching. The goal of this report is to introduce the capability of time-multiplexed x-ray spectromicroscopy in studying weak-signal transitions in inhomogeneous media through the example of the operation and temporal evolution of a memristor. [ABSTRACT FROM AUTHOR]

By using electric-field-induced optical second-harmonic generation measurement coupled with the conventional current-voltage (I-V) measurement, we studied the carrier transport of organic double-layer diodes with a Au/pentacene/fluorine polymer (FP)/indium zinc oxide (IZO) structure. The rectifying I-V characteristics were converted into the I-E characteristics of the FP and pentacene layers. Results suggest a model in which Schottky-type electron injection from the IZO electrode to the FP layer governs the forward electrical conduction (V > 0), where the space charge electric field produced in the FP layer by accumulated holes at the pentacene/FP interface makes a significant contribution. On the other hand, Schottky-type injection by accumulated interface electrons from the pentacene layer to the FP layer governs the backward electrical conduction (V < 0). The electroluminescence generated from the pentacene layer in the region V > 0 verifies the electron transport across the FP layer, and supports the above suggested model. [ABSTRACT FROM AUTHOR]

The conduction characteristics of Pt/NiO/Pt resistive switching cells were investigated systematically through DC and AC conductance measurements in each of three resistance states: the initial state, the low resistance state (LRS), and the high resistance state (HRS). In the initial state, two different conduction processes are dominant, although this dominance is temperature-dependent. The activation energy (Ea) of the DC conductance was approximately 4.3 meV below 170 K. In addition to the low Ea, the frequency and temperature dependence of the AC conductance confirmed that the conduction originated from hopping between isolated sites. However, above 170 K, the Ea of the DC conductance was 330 meV, and this conductance was independent of frequency at low frequencies. The dominant conduction process above 170 K was found to be band conduction from analysis of the AC conductance. The resistance in the LRS varied linearly with temperature and was almost independent of frequency, thus representing the characteristics of metallic band conduction of conductive filaments. In the HRS, the DC conductance exhibited an Ea of 16 meV, which was higher than that in the initial state (4.3 meV), thus indicating that the dominant conduction mechanism in the HRS is different to the mechanism in the initial state. From discussions based on a filament model, it was concluded that filament conduction is dominant in the HRS. As a result, it is proposed that the resistive switching originates from changes in the conduction properties of the filaments themselves rather than from their rupture and formation. [ABSTRACT FROM AUTHOR]

We investigate the effects of pulse duration on the dynamics of the nascent plasma and bubble induced by laser ablation in water. To examine the relationship between the nascent plasma and the bubble without disturbed by shot-to-shot fluctuation, we observe the images of the plasma and the bubble simultaneously by using two intensified charge coupled device detectors. We successfully observe the images of the plasma and bubble during the pulsed-irradiation, when the bubble size is as small as 20 μm. The light-emitting region of the plasma during the laser irradiation seems to exceed the bubble boundary in the case of the short-pulse (30-ns pulse) irradiation, while the size of the plasma is significantly smaller than that of the bubble in the case of the long-pulse (100-ns pulse) irradiation. The results suggest that the extent of the plasma quenching in the initial stage significantly depends on the pulse duration. Also, we investigate how the plasma-bubble relationship in the very early stage affects the shape of the atomic spectral lines observed at the later delay time of 600 ns. The present work gives important information to obtain high quality spectra in the application of underwater laser-induced breakdown spectroscopy, as well as to clarify the mechanism of liquid-phase laser ablation. [ABSTRACT FROM AUTHOR]

In this article, we evidence the lower formation energy and improved stability of the conductive filament (CF) formed in TiN\Ta2O5\Ta resistive-switching memory cells treated in NH3 atmosphere at 400°C. This annealing treatment results in (i) lower forming voltage, (ii) lower CF resistance, and (iii) longer retention lifetime of the oxygen-vacancy (Vo) chain constituting the CF. Atomistic insights into these processes are provided by ab initio calculations performed for hydrogen (H) species incorporated in non-stoichiometric Ta2O5 supercells: (i) Vo formation energy is reduced by the presence of H, (ii) Vo-chain CF conductivity is increased by Vo + OH complex formation, and (iii) Vo-chain retention is strengthened by the stable Vo + OH complex. As a result, efficient CF formation and excellent state stability are obtained after 15 days at 250°C. [ABSTRACT FROM AUTHOR]

As the gate size continues to decrease in nanoscale transistors, having metal gates with amorphous or near amorphous structures can potentially reduce grain-induced work function variation. Furthermore, amorphous materials are known to have superior diffusion barrier properties, which can help prevent work function change due to the diffusion of metals in contact with the gate. In this work we show that with the addition of cobalt, thin films of polycrystalline TiN become more amorphous with a smaller grain size. Cox(TiN)1-x films, where x=60-80%, appear to consist of nanocrystals embedded in an amorphous matrix, and are thermally stable with no significant crystallization up to an annealing temperature of at least 600 °C. Reducing the nitrogen gas flow ratio during sputter deposition from 9% to 2.5% further decreases the films' crystallinity, which is apparent by more sparse and even smaller nanocrystals. In addition to being partially amorphous, these CoTiN films also exhibit good thermal stability, low resistivity, low roughness, and have the potential for atomic layer deposition compatibility. Even though these materials are not completely amorphous, their small crystal size and amorphous matrix can potentially reduce work function variation and improve their diffusion barrier property. These properties make CoTiN a good candidate as a gate material for future nanoelectronic devices and technology. [ABSTRACT FROM AUTHOR]

We investigate the effects of temporal laser profile on the emission spectra of laser ablation plasma in water. We use short-interval (76 ns) double pulses with different pulse durations of the composing two pulses for the irradiation of underwater target. Narrow atomic spectral lines in emission spectra are obtained by the irradiation, where the two pulses are wide enough to be merged into a single-pulse-like temporal profile, while deformed spectra are obtained when the two pulses are fully separated. The behavior of the atomic spectral lines for the different pulse durations is consistent with that of the temporal profiles of the optical emission intensities of the plasma. All these results suggest that continuous excitation of the plasma during the laser irradiation for ~100 ns is a key to obtain narrow emission spectral lines. [ABSTRACT FROM AUTHOR]

Detection of surface charges has various applications in medicine, electronics, biotechnology, etc. The source of surface charge induction may range from simple charge-polarized molecules like water to complicated proteins. It was recently discovered that surface charge accumulation can alter the temperature at which VO2 undergoes a Mott transition. Here, we deposited polar molecules onto the surface of two-terminal thin-film VO2 lateral devices and monitored the joule-heatingdriven Mott transition, or conductance switching. We observed that the power required to induce the conductance switching reduced upon treatment with polar molecules and, using in-situ blackbody-emission direct measurement of local temperature, we show that this reduction in power was accompanied by reduction in the Mott transition temperature. Further evidence suggested that this effect has specificity to the nature of the species used to induce surface charges. Using x-ray absorption spectroscopy, we also show that there is no detectable change in oxidation state of vanadium or structural phase in the bulk of the 40 nm VO2 thin-film even as the phase transition temperature is reduced by up to 20K by the polar molecules. The ability to alter the phase transition parameters by depositing polar molecules suggests a potential application in sensing surface charges of different origins and this set of results also highlights interesting aspects of the phase transition in VO2. [ABSTRACT FROM AUTHOR]

The effects of plasma exposure and vacuum-ultraviolet (VUV) irradiation on the mechanical properties of low-k porous organosilicate glass (SiCOH) dielectric films were investigated. Nanoindentation measurements were made on SiCOH films before and after exposure to an electron-cyclotron-resonance plasma or a monochromatic synchrotron VUV beam, to determine the changes of film hardness, elastic modulus, and crack threshold due to these exposures. This permits the effects of ion bombardment and photon bombardment to be analyzed separately. The role of energetic ions was examined with a variety of inert plasma-exposure conditions. The role of VUV photons was analyzed as a function of synchrotron photon energy. It was found that both energetic ions and VUV photons with energies larger than the bond energy of the Si-O bond cause a significant increase in film hardness along with a smaller increase in elastic modulus and crack threshold. Differential Fourier transform infrared spectra and x-ray photoemission spectroscopy results show that the energetic ions affect the SiCOH properties mainly through physical bombardment, during which the ions transfer their momentum to the Si-O-Si backbone and transform them into more energetically stable Si-O-Si network structures. This results in the Si-O-Si network structures becoming densified. VUV photons assist reaction that increase the number of bridging O3=Si-O-Si=O3 bonds and deplete nonbridging O3=Si-O and C-Si=O3 bonds. This increased degree of cross linking in porous organosilicate dielectrics can substantially enhance their hardness and elastic modulus while showing no significant film shrinkage or densification. [ABSTRACT FROM AUTHOR]

The effects of homogenous electron beam (EB) irradiation on the crystal growth and thermoelectric properties of n-type Bi-Se-Te and p-type Bi-Sb-Te thin films were investigated. Both types of thin films were prepared by flash evaporation, after which homogeneous EB irradiation was performed at an acceleration voltage of 0.17MeV. For the n-type thin films, nanodots with a diameter of less than 10nm were observed on the surface of rice-like nanostructures, and crystallization and crystal orientation were improved by EB irradiation. The resulting enhancement of mobility led to increased electrical conductivity and thermoelectric power factor for the n-type thin films. In contrast, the crystallization and crystal orientation of the p-type thin films were not influenced by EB irradiation. The carrier concentration increased and mobility decreased with increased EB irradiation dose, possibly because of the generation of defects. As a result, the thermoelectric power factor of p-type thin films was not improved by EB irradiation. The different crystallization behavior of the n-type and p-type thin films is attributed to atomic rearrangement during EB irradiation. Selenium in the n-type thin films is more likely to undergo atomic rearrangement than the other atoms present, so only the crystallinity of the n-type Bi-Se-Te thin films was enhanced. [ABSTRACT FROM AUTHOR]

In this work, experimental measurements of the electronic band gap of low-k organosilicate dielectrics will be presented and discussed. The measurement of bandgap energies of organosilicates will be made by examining the onset of inelastic energy loss in core-level atomic spectra using X-ray photoelectron spectroscopy. This energy serves as a reference point from which many other facets of the material can be understood, such as the location and presence of defect states in the bulk or at the interface. A comparison with other measurement techniques reported in the literature is presented. [ABSTRACT FROM AUTHOR]

We study the metal-GaSb alloy formation, the structural properties and the electrical characteristics of the metal-alloy/GaSb diodes by employing metal materials such as Ni, Pd, Co, Ti, Al, and Ta, in order to clarify metals suitable for GaSb p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) as metal-GaSb alloy source/drain (S/D). It is found that Ni, Pd, Co, and Ti can form alloy with GaSb by rapid thermal annealing at 250, 250, 350, and 450 °C, respectively. The Ni-GaSb and Pd-GaSb alloy formation temperature of 250 ° C is lower than the conventional dopant activation annealing for ion implantation, which enable us to lower the process temperature. The alloy layers show lower sheet resistance (RSheet) than that of p+-GaSb layer formed by ion implantation and activation annealing. We also study the electrical characteristics of the metal-alloy/GaSb junctions. The alloy/n-GaSb contact has large Schottky barrier height (øB) for electrons, ~0.6 eV, and low øB for holes, ~0.2 eV, which enable us to realize high on/off ratio in pMOSFETs. We have found that the Ni-GaSb/GaSb Schottky junction shows the best electrical characteristics with ideal factor (n) of 1.1 and on-current/off-current ratio (Ion/Ioff) of ~104 among the metal-GaSb alloy/GaSb junctions evaluated in the present study. These electrical properties are also superior to those of a p>+-n diode fabricated by Be ion implantation with activation annealing at 350 °C. As a result, the Ni-GaSb alloy can be regarded as one of the best materials to realize metal S/D in GaSb pMOSFETs. [ABSTRACT FROM AUTHOR]

The preparation and magnetic properties of the CdGeP2:Mn single crystal layer and polycrystalline powders are discussed. It was possible to reveal room temperature ferromagnetism for the first time in the magnetic semiconductor CdGeP2:Mn.

Water uptake in porous low-k dielectrics has become a significant challenge for both back-end-of-line integration and circuit reliability. The influence of absorbed water on the mechanical properties of plasma-enhanced chemical-vapor-deposited organosilicate glasses (SiCOH) was investigated with nanoindentation. The roles of physisorbed (α-bonded) and chemisorbed (β-bonded) water were examined separately through annealing at different temperatures. Nanoindentation measurements were performed on dehydrated organosilicate glass during exposure to varying humidity conditions. The elastic modulus and hardness for as-deposited SiCOH are intimately linked to the nature and concentration of the absorbed water in the dielectric. Under mild-annealing conditions, the water-related film mechanical property changes were shown to be reversible. The mechanical properties of UV-cured SiCOH were also shown to depend on absorbed water, but to a lesser extent because UV curing depopulates the hydrophilic chemical groups in SiCOH. High-load indentation tests showed that in-diffusion of water in the film/substrate interface can degrade the hardness of SiCOH/Si film stacks significantly, while not significantly changing the elastic modulus. [ABSTRACT FROM AUTHOR]

The temporary increase in the electrical surface conductivity of low-k organosilicate glass (SiCOH) during exposure to vacuum-ultraviolet radiation (VUV) is investigated. To measure the photoconductivity, patterned 'comb structures' are deposited on dielectric films and exposed to synchrotron radiation in the range of 8-25 eV, which is in the energy range of most plasma vacuum-ultraviolet radiation. The change in photo surface conductivity induced by VUV radiation may be beneficial in limiting charging damage of dielectrics by depleting the plasma-deposited charge. [ABSTRACT FROM AUTHOR]

Plasmas, known to emit high levels of vacuum ultraviolet (VUV) radiation, are used in the semiconductor industry for processing of low-k organosilicate glass (SiCOH) dielectric device structures. VUV irradiation induces photoconduction, photoemission, and photoinjection. These effects generate trapped charges within the dielectric film, which can degrade electrical properties of the dielectric. The amount of charge accumulation in low-k dielectrics depends on factors that affect photoconduction, photoemission, and photoinjection. Changes in the photo and intrinsic conductivities of SiCOH are also ascribed to the changes in the numbers of charged traps generated during VUV irradiation. The dielectric-substrate interface controls charge trapping by affecting photoinjection of charged carriers into the dielectric from the substrate. The number of trapped charges increases with increasing porosity of SiCOH because of charge trapping sites in the nanopores. Modifications to these three parameters, i.e., (1) VUV induced charge generation, (2) dielectric-substrate interface, and (3) porosity of dielectrics, can be used to reduce trapped-charge accumulation during processing of low-κ SiCOH dielectrics. Photons from the plasma are responsible for trapped-charge accumulation within the dielectric, while ions stick primarily to the surface of the dielectrics. In addition, as the dielectric constant was decreased by adding porosity, the defect concentrations increased. [ABSTRACT FROM AUTHOR]

InxGa1-xSb is an attractive candidate for high performance III-V p-metal-oxide-semiconductor field effect transistors (pMOSFETs) due to its high bulk hole mobility that can be further enhanced with the use of strain. We fabricate and study InxGa1-xSb-channel pMOSFETs with atomic layer deposition Al2O3 dielectric and self-aligned source/drain formed by ion implantation. The effects of strain and heterostructure design for enhancing transistor performance are studied systematically. Different amounts of biaxial compression are introduced during MBE growth, and the effect of uniaxial strain is studied using wafer-bending experiments. Both surface and buried channel MOSFET designs are investigated. Buried (surface) channel InxGa1-xSb pMOSFETs with peak hole mobility of 910 (620) cm2/Vs and subthreshold swing of 120 mV/decade are demonstrated. Pulsed I-V measurements and low-temperature I-V measurements are used to investigate the physics in transistor characteristics. [ABSTRACT FROM AUTHOR]

Damage induced in low-k porous organosilicate glass (SiCOH) dielectric films by exposure to an electron cyclotron resonance (ECR) plasma was investigated. The effects of charged-particle bombardment and vacuum ultraviolet radiation were separated. Flux measurements showed that the ECR plasma has a greater photon flux in the vacuum ultraviolet (VUV) range than in the UV range. Damage was measured by examining the surface potential and capacitance-voltage characteristics after exposure. It was found that during argon ECR plasma processing, 75% of the charge accumulation comes from ions at the surface, while 25% of the charge accumulation occurs from charge trapped within the bulk of the dielectric film. The charge accumulation can be modified by changing the bias voltage of the wafer chuck. UV exposure was shown to repair both sources of damage. Fourier transform infrared (FTIR) spectroscopy results showed no significant change except for Si-(CH3)x bonds. It was found that both charged-particle bombardment and radiation from the ECR plasma damage these bonds. Ellipsometric measurements showed that both the dielectric thickness and the dielectric constant changed during plasma exposure. In addition, both plasma-induced swelling and UV-exposure shrinking effects were observed. The plasma-induced swelling occurs at the surface of the dielectric without changing the porosity of the dielectric, while UV-induced shrinking changes the porosity significantly. [ABSTRACT FROM AUTHOR]

The dependence of Pt film thickness and forming gas annealing on the interface fracture properties and interface composition of Ti/Pt bilayer gate electrode films on a HfO2 gate dielectric are reported. These fracture properties and composition results are directly compared to work function tuning behavior witnessed in metal-oxide semiconductor (MOS) capacitors fabricated from the same films. The interface fracture energy of the metal bilayer/gate dielectric interface is strongly dependent on thickness after a forming gas anneal but shows no thickness dependence in the as-deposited case. The flat-band voltage increases abruptly and then remains constant as the thickness of the Pt film is increased in the as-deposited case but varies gradually with increasing Pt thickness after a forming gas anneal. Angle-resolved x-ray photoelectron spectroscopy characterization of the resulting fracture surfaces confirms that Ti diffusion to the metal bilayer/gate dielectric interface is responsible for these effects. [ABSTRACT FROM AUTHOR]

A bilayer metal structure has been demonstrated to adjust the gate work function over the Si band gap. The underlying tuning mechanism is believed to be due to metal interdiffusion based on comparison of work function behavior under different anneal conditions. In this paper, we conduct physical characterization on bilayer metal gates and successfully verify that the interdiffusion is the cause of the work function tuning. Furthermore, we find that metal interdiffusion significantly slows down after an initial anneal, resulting in a stable work function. A diffusion model involving the annealing out of fast diffusion paths is proposed to explain the work function results. [ABSTRACT FROM AUTHOR]

GeO2 was grown by a slot-plane-antenna (SPA) high density radical oxidation, and the oxidation kinetics of radical oxidation GeO2 was examined. By the SPA radical oxidation, no substrate orientation dependence of growth rate attributed to highly reactive oxygen radicals with low oxidation activation energy was demonstrated, which is highly beneficial to three-dimensional structure devices, such as multigate field-effect transistors, to form conformal gate dielectrics. The electrical properties of an aluminum oxide (Al2O3) metal-oxide-semiconductor gate stack with a GeO2 interfacial layer were investigated, showing very low interface state density (Dit), 1.4×1011 cm-2 eV-1. By synchrotron radiation photoemission spectroscopy, the conduction and the valence band offsets of GeO2 with respect to Ge were estimated to be 1.2±0.3 and 3.6±0.1 eV, which are sufficiently high to suppress gate leakage. [ABSTRACT FROM AUTHOR]

Schottky barrier height modulation in metal/Ge Schottky junction was demonstrated by inserting an ultrathin interfacial silicon nitride layer. The SiN interfacial layer suppressed strong Fermi level pinning in metal/Ge Schottky junction, which resulted in effective control of Schottky barrier height. Metal/SiN/Ge Schottky diode was systematically investigated in terms of SiN thickness dependence and metal work function dependence. At an optimal SiN thickness, Ohmic contact between metal and Ge was obtained as a result of Fermi level depinning, and almost ideal Schottky barrier height determined by the work function difference between the metal and Ge was achieved. This technology was finally applied to metal source/drain Ge metal-oxide-semiconductor field-effect-transistors with low source/drain resistance. [ABSTRACT FROM AUTHOR]

The valence band offsets and the effective work function of metals and metal bilayers on SiO2 were investigated using density functional theory within the local density approximation. Metal-oxide interface effects and the underlying metal thickness in contact with oxide were examined. As model systems both low and high work function metals had been chosen, i.e., aluminum and nickel, and their bilayers on β-quartz. It is found that the effective work function of a metal on oxide is strongly controlled by the interface atomic arrangement, the calculated valence band offset differences leading up to 0.5 eV for interfaces containing excess oxygen. It is also shown that one or two atomic layers of the underlying metal are sufficient to shift the effective work function of bilayers to that of underlying metal. [ABSTRACT FROM AUTHOR]

We developed a fully analytical ballistic theory of carbon nanotube field effect transistors enabled by the development of an analytical surface potential capturing the temperature dependence and gate and quantum capacitance electrostatics. The analytical ballistic theory is compared to the experimental results of a ballistic transistor with good agreement. The validated analytical theory enables intuitive circuit design, provides techniques for parameter extraction of the bandgap and surface potential, and elucidates on the device physics of drain optical phonon scattering and its role in reducing the linear conductance and intrinsic gain of the transistor. Furthermore, a threshold voltage definition is proposed reflecting the bandgap-diameter dependence. Projections for key analog and digital performances are discussed. [ABSTRACT FROM AUTHOR]

The electronic structure of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was studied using ultraviolet photoelectron spectroscopy of vapor and thin film and inverse photoemission spectroscopy of thin film. The threshold ionization energy of PCBM was found to be 7.17±0.04 eV in gas phase and 5.96±0.02 eV in solid phase. The threshold electron affinity was 3.9±0.1 eV in solid phase. These values are 0.4-0.6 eV smaller than C60. The density functional theory calculations gave consistent results with these trends and suggested that the electron donation from the side chain to C60 backbone raised the C60-backbone-derived π orbitals of PCBM. The polarization energy of PCBM is 1.21 eV, which is almost the same as C60 but is about 0.5 eV smaller than the value of typical aromatic hydrocarbons. [ABSTRACT FROM AUTHOR]

This study reports on the first experimental observations of electrically biased paramagnetic defects at 800 °C N2 annealed HfxSi1-xO2 (x=0.4, and 0.6)/(100)Si and HfO2/(100)Si interfaces in metal oxide silicon structures. These defects are examined by electrical-field controlled electron spin resonance (ESR) and correlated with capacitance-voltage (C-V) analysis. Distributions of ESR measured density of interface traps (ESR-Dit), Pb0 and Pb1, exhibit distinct charge humps and peaks in the Si bandgap with maximum defect density of 0.9–1.9×1012 cm-2 eV-1 in the Hf0.4Si0.6O2/Si interface. Three Pb0 and one Pb1 charged ESR-Dit peaks with density of 1.7–2.8×1012 cm-2 eV-1 are observed in the Hf0.6Si0.4O2/Si interface. Cross-sectional transmission electron microscopic images show decreasing interfacial layer (IL) thickness with increasing hafnium composition (x) at the HfxSi1-xO2/Si interface. The roughest IL observed at the HfO2/Si interface may have contributed to an ESR-Dit of Pb0 greater than 2×1013 cm-2 eV-1 and a pinned Fermi level near the midgap. It appears that the energy distributions of interface defects in HfxSi1-xO2/Si and HfO2/Si have different signatures compared to those at SiO2/Si interface, especially the charged peak near the midgap. [ABSTRACT FROM AUTHOR]

First principles calculation shows that the Nb and W atoms have a tendency to mix instead of phase separate in the Nb–W bulk within the entire composition range, and the interaction between Nb and W atoms has a nonlinear effect on the density of states of the Nb–W bulk at the Fermi level. Calculation also reveals that the surface segregation of Nb atoms is energetically favorable with an energy decrease of 0.4–0.55 eV/atom, and the segregation has important effects on the electronic structures of Nb–W surfaces. Interestingly, the work function of Nb–W phases is insensitive to the composition as well as the Nb surface segregation when W is in the range of 0–60 at. %, and over this composition range, the work function remains relatively stable. [ABSTRACT FROM AUTHOR]

The interface between hafnium oxide grown by atomic layer deposition and (100) GaAs treated with HCl cleaning and (NH4)2S passivation has been characterized. Synchrotron radiation photoemission core level spectra indicated successful removal of the native oxides and formation of passivating sulfides on the GaAs surface. Layer-by-layer removal of the hafnia film revealed a small amount of As2O3 formed at the interface during the dielectric deposition. Traces of arsenic and sulfur out diffusion into the hafnia film were observed after a 450 °C postdeposition anneal and may be the origins for the electrically active defects. Transmission electron microscopy cross section images showed thicker HfO2 films for a given precursor exposure on sulfur treated GaAs versus the nontreated sample. In addition, the valence-band and the conduction-band offsets at the HfO2/GaAs interface were deduced to be 3.18 eV and a range of 0.87–1.36 eV, respectively. It appears that HCl+(NH4)2S treatments provide a superior chemical passivation for GaAs and initial surface for atomic layer deposition. [ABSTRACT FROM AUTHOR]

Electron spin resonance measurements on 4 and 40 nm thick (HfO2)0.6(SiO2)0.4 and (HfO2)0.4(SiO2)0.6 high-κ films on (100)Si wafers detected Pb0 and Pb1 defects at the dielectric/Si interface and verified their identities with g value mapping. Annealings of a 4 nm thick (HfO2)0.6(SiO2)0.4 film in nitrogen at 800 and 1000 °C monotonically lowered total interface states. In contrast, the same annealings monotonically increased the total interface states observed in 40 nm thick films of both compositions. For the 4 nm technologically relevant thickness, the annealed (HfO2)0.6(SiO2)0.4 composition on (100)Si had lower interface states than the (HfO2)0.4(SiO2)0.6 composition on (100)Si. After nitrogen annealing at 800 °C, a third defect believed to be the EX, appears in larger quantities in the thicker 40 nm films. [ABSTRACT FROM AUTHOR]

A semiclassical double-well model of dielectric relaxation current in glasses is extended to (i) nonzero temperature, (ii) complex bias histories, and (iii) strong electric fields. At finite temperature, thermal excitation yields a contribution linear in temperature, which adds to the temperature-independent contribution from tunneling from the zero-temperature case. Both contributions vary linearly with applied field and have a time dependence of 1/tn. Experimental measurements in three different glasses are shown to agree with this prediction, and it is shown how to use such measurements to estimate the material parameters t0 and σ0. For complex bias histories, a principle of superposition is found, as observed experimentally, if the applied fields are weak compared to the material parameter E0, estimated to be on the order of 107 V/m. For an electric field pulsed periodically from 0 to E, the current can be decomposed into a fast contribution due to particles tunneling back and forth every cycle of the field, and a slow residual contribution whose time dependence is the same as that for a continuous bias, but whose magnitude is reduced by the duty cycle of the periodic bias. For a sinusoidal electric field, thermal excitation gives a contribution to the dielectric constant that varies linearly with temperature and has a real part that varies logarithmically with frequency and an imaginary part that varies as the inverse tangent of frequency. For tunneling, both parts are independent of temperature and vary approximately as the logarithm of frequency, a dependence observed experimentally and almost indistinguishable from that suggested by the 1/tn current response to a step voltage. For strong electric fields, the current that flows after the field is removed is found to be dominated by particles that fell forward when the field was on. Since particles fall forward quickly but tunnel back slowly, even strong fields applied for a short period of time can produce a large, long-lasting return current. These analyses lead to a number of testable predictions, and should be useful for understanding the phenomenon of dielectric relaxation and its impact on electronic devices. [ABSTRACT FROM AUTHOR]

Systematic studies of the heteroepitaxial growth of germanium nanowires on silicon substrates were performed. These studies included the effect of sample preparation, substrate orientation, preanneal, growth temperature, and germane partial pressure on the growth of epitaxial germanium nanowires. Scanning electron microscopy and transmission electron microscopy were used to analyze the resulting nanowire growth. Germanium nanowires grew predominantly along the <111> crystallographic direction, with a minority of wires growing along the <110> direction, irrespective of the underlying silicon substrate orientation [silicon (111), (110), and (100)]. Decreasing the partial pressure of germane increased the number of <111> nanowires normal to the silicon (111) surface, compared to the other three available <111> directions. The growth rate of nanowires increased with the partial pressure of germane and to a lesser degree with temperature. The nucleation density of nanowire growth and the degree of epitaxy both increased with temperature. However, increasing the growth temperature also increased the rate of sidewall deposition, thereby resulting in tapered nanowires. A two-step temperature process was used to initiate nanowire nucleation and epitaxy at a high temperature, followed by nontapered nanowire growth at a lower temperature. Preannealing gold films in hydrogen or argon before nanowire growth reduced the yield of nanowires grown on silicon samples, especially on silicon (111) substrates, but not on silicon oxide. Gold annealing studies performed to investigate this preanneal effect showed greater gold agglomeration on the silicon samples compared to silicon oxide. The results and conclusions obtained from these studies give a better understanding of the complex interdependencies of the parameters involved in the controlled heteroepitaxial growth of vapor-liquid-solid grown germanium nanowires. [ABSTRACT FROM AUTHOR]

We present a model that provides a description of the microwave dielectric loss in oxides. The dielectric loss (tan δ) in single crystal and polycrystalline MgO and Al[sub 2]O[sub 3] is measured over the temperature range 70–300 K. We are able to model the dielectric loss in terms of a two-phonon difference model. There are two key parameters in this model: The third derivative, [lowercase_phi_synonym][sub 3], of the lattice potential and the linewidth, γ, of the thermal phonons. In polycrystalline samples, rather than considering the different mechanisms of extrinsic loss, it is assumed that the main effect of extrinsic factors is a modification of the linewidth of the thermal phonons. By varying γ(T), it is shown that the model can describe the loss in both single crystals and polycrystallines materials. In single crystal and polycrystalline MgO, we use γ as a fitting parameter. In single crystal and polycrystalline Al[sub 2]O[sub 3], we obtain γ(T) by Raman spectroscopy. The theory gives the right order of magnitude of the measured loss. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A bilayer metal structure has adjusted the gate work function over the Si band and physical characterization is conducted on bilayer metal gates in order to verify that the interdiffusion is the cause of the work function tuning. The metal interdiffusion slowed down after an initial anneal, resulting in a stable work function, and a different model involving the annealing out of fast diffusion paths is described for explaining the work function results.

Abnormal superconducting critical current density changes against temperaturein BiPbSrCaCuO was investigated. The results showed that these abnormal changesmainly occured in the temperature range of 50 to 80 K. Good intergrain couplingconditions and excess additional flux pinning sites enhanced the critical current density at temperatures above 50 K.

An abnormal temperature change was detected in bismuth lead strontium calcium copper oxide during a study. The abnormal T(sub c) change was found betweeen the z values of .01 and .1 based on the equation Bi1.6Pb.4Sr2Ca2(Cu1-zTiz)3Ox(.01

Helium-ion etching was used to clean-polish the surface of a high-Tc YBa2Cu3O7-y superconductor. Results showed that helium-ion etching decreased surface roughness under a clean atmosphere. The polishing mechanism's effectiveness is due to the small coordination number of the convex part as compared to that of the concave part's. The etching rate of the convex part thus becomes larger than that of the concave part and in the process the surface roughness decreases. A knock-on cascade model was used to discuss the polishing mechanism.