Electrical characterization of CMOS transistors subject to externally applied mechanical stress

Hole and electron mobilities in CMOS structures are significantly influenced by a mechanical strain state. In the present work a new experimental device has been designed, able to apply a uniaxial in-plane strain along different crystallographic orientations. A hole mobility enhancement of +10% and an electron mobility decrease of −5% have been demonstrated with the application of a 0.05% compressive 1 1 0 strain; a hole mobility enhancement of +2% and an electron mobility decrease of −3% have been induced into the material with the application of a 0.05% compressive 1 0 0 strain.     

Grain-boundary structure of oxygen-free high-conductivity (OFHC) copper subjected to severe plastic deformation and annealing

The influence of grain-boundary structure on grain growth in copper subjected to severe plastic deformation has been studied using orientation imaging microscopy. The investigation was carried out on oxygen-free high-conductivity (OFHC) copper which was wire drawn to a true strain of about 4 and processed by equal-channel angular extrusion (ECAE) to 4 and 8 passes via “route B_c” (where the billet is rotated by 90° in the same direction between consecutive passes). The grain-boundary character distribution (GBCD) of the as-drawn wire was similar to that of ECAE-processed specimens, and both materials possessed a higher fraction of high-angle grain boundaries (HAGBs) than special coincidence-site lattice (CSL) boundaries. While the high fraction of HAGBs was retained in the annealed wires, they were transformed to CSL boundaries in the annealed ECAE-processed materials. In spite of an initially smaller grain size, when annealed at 750 °C for 1 h, the grain size of the 4-pass ECAE-processed material was larger than that of the wire drawn to a similar strain. This difference was attributed to a high density of high-mobility 35–50° 0 0 1 boundaries in the 4-pass ECAE materials. On the other hand, the presence of 50–60° 1 1 1  pinning boundaries in the annealed 8-pass material accounted for the smaller grain size after recrystallization.     

Effect of the extrusion conditions on microstructure evolution of the extruded Al–Mg–Si–Cu alloy rods

Hot extrusion experiment was conducted using an Al–Mg–Si–Cu alloy and the effect of the extrusion conditions on microstructure and texture changes through the radial direction was investigated by using SEM/EBSP analysis method. In the surface layer where severe frictional shear deformation is predominant, the recrystallized 1 1 0//ED grains surrounded by high angle grain boundaries are formed in spite of the existence of some peripheral overcoarse grains. Strong 1 0 0//ED and 1 1 1//ED fiber textures evolve in the center where axisymmetric deformation along the extrusion direction is intensive. As the extrusion ratio increases, number of 1 1 1//ED grains remarkably decreases while the number of 1 0 0//ED grains apparently increases. It is also found that the 1 0 0//ED grains surrounded by low angle grain boundaries form orientation colonies in the center of the extruded rods.     

Dependencies of grain refinement on processing route and die angle in equal channel angular extrusion of bcc materials

The efficiency of grain refinement in equal channel angular extrusion of body-centered cubic (bcc) materials is investigated based on slip activities from crystal plasticity simulations, which account for both the macroscopic and crystallographic features of deformation. It is shown that the characteristics of slip activities, especially the relative contributions of slip systems newly activated or reversed at the transitions between successive passes, vary significantly with the processing routes (A, B and C) and die angles ( = 90° and 120°). The simulations assuming {1 1 0}111 slip suggest that routes B and A lead to the most significant contributions of newly activated slip systems and hence are most efficient for grain refinement with  = 90° and 120°, respectively. Further incorporation of {1 1 2}111 slip systems leads to the highest efficiency by route B for both die angles. These predictions are in partial agreement with experimental observations in the literature. Comparison of these results with those of face-centered cubic materials reveals the relevance of crystal structure and deformation mechanism during grain refinement.     

Effect of texture and testing conditions on strain localization during cyclic deformation of copper polycrystals

Fatigue tests were performed on pure copper polycrystals with a crystallographic texture different from that produced by ‘standard’ thermomechanical treatments, which emphasize multi-slip 111–100 textures. The texture along the loading axis deviated by 10–15° from these two poles for the samples used here. The experiments were initiated by ramp loading as a mechanical pretreatment and the cyclic stress–strain curve (CSSC) was established by step tests using enough cycles at each step to insure saturation. Under these conditions, a plateau was observed in the CSSC at an appropriate stress level and in a reproducible fashion.     

Solid phase epitaxy on N-type polysilicon films formed by aluminium induced crystallization of amorphous silicon

In this work, undoped amorphous silicon layers were deposited on n-type AIC seed films and then annealed at different temperatures for epitaxial growth. The epitaxy was carried out using halogen lamps (rapid thermal process or RTP) or a tube conventional furnace (CTP). We investigated the morphology of the resulting 2 µm thick epi-layers by means of optical microscopy. An average grain size of about 40 µm is formed after 90 s annealing at 1000 °C in RTP. The stress and degree of crystallinity of the epi-layers were studied by micro-Raman Spectroscopy and UV–visible spectrometer as a function of annealing time. The presence of compressive stress is observed from the peak position which shifts from 520.0 cm^− 1 to 521.0 cm^− 1 and 522.3 cm^− 1 after CTP annealing for 10 min and 90 min, respectively. It is shown that the full width at half maximum (FWHM) varies from 9.8 cm^− 1 to 15.6 cm^− 1, and the magnitude of stress is changing from 325 MPa to 650 MPa. Finally, the highest crystallinity is achieved after annealing at 1000 °C for 90 min in a tube furnace exhibiting a crystalline fraction of 81.5%. X-ray diffraction technique was used to determine the preferential orientation of the poly-Si thin films formed by SPE technique on n⁺ type AIC layer. The preferential orientation is 100 for all annealing times at 1000 °C.     

Grain boundary plane distributions and single-step versus multiple-step grain boundary engineering

The ‘five-parameter’ (i.e. both misorientation and grain boundary plane) distribution in type 304 austenitic stainless steel has been measured and evaluated for an ‘as-received’ (AR) specimen and specimens undergoing both single-step grain boundary engineering processing (SSGBE) and multiple-step grain boundary engineering processing (MSGBE) comprising three iterations. The results showed that the fundamental requirement for twinning-related GBE is to maximise concomitantly the proportion of both Σ3 and Σ9 boundaries, which in turn supports the development of special planes in the grain boundary network. 1 1 0 and 1 1 1 tilt and twist boundaries play a key role in the formation of ‘special’ grain boundary planes. MSGBE added increased proportions of Σ3 boundaries and resulted in development of different characteristics in the planes distribution compared to SSGBE. These modifications are likely to result in improved grain boundary properties after MSGBE compared to SSGBE.     

Experiments and simulations of directionally annealed ODS MA 754

Both directional and isothermal annealing experiments have been performed on the hot-rolled ODS nickel-based superalloy MA 754. Directional annealing of MA 754 produced an elongated, coarse grain structure with a {1 1 0}1 0 0 texture for all hot-zone velocities examined, with the grain aspect ratio and twin boundary density decreasing with increasing hot-zone velocity. Isothermal annealing also produced elongated structures, but with larger grain aspect ratios and a stronger {1 1 0}1 0 0 texture. In order to elucidate the results of the experimental studies, a front-tracking computer-based model [H.J. Frost, C.V. Thompson, C.L. Howe, J.H. Whang, Scripta Metall. 22 (1988) 65–70] was modified to simulate the directional/isothermal annealing processes for materials with particles. Simulations of directional annealing with particles aligned in the direction of hot-zone movement could produce (at the appropriate hot-zone velocities) columnar grain structures with some finer grains clustered around the particles. Contrary to experimental observations, simulations of isothermal annealing in similar particle-containing material did not produce columnar grain structures, but equi-axed grains whose size was defined by the spacing between the lines of particles. Thus, the simulation results suggest that it is the texture, and not the particles, of the hot-rolled MA 754 that leads to a columnar grain structure.     

Effect of orientational order of tris(8-hydroxyquinolinato)aluminum(III) on electroabsorption

The electroabsorption (EA) spectrum was analyzed in terms of the orientational order of tris(8-hydroxyquinolinato)aluminum(III) (Alq₃) molecules, where the orientational order parameter P_n(cosθ) (θ: the tilt angle of molecule; P_n: nth Legendre polynomial; : thermodynamic average) was used to quantify the anisotropic orientational order of Alq₃. It was shown that the EA intensity is a function of S₁ and S₂ at the modulation frequency ω, whilst it is a function of S₂ at the second-harmonic frequency 2ω. The EA spectrum for the vacuum deposited Alq₃ was obtained from the optical transmittance measurement. The results suggested that the spontaneous polarization of Alq₃ is generated in the evaporated films.     

Molecular dynamics simulations on nanoindentation mechanisms of multilayered films

Molecular dynamics (MD) simulations were carried out to study the effects of indention deformation, contact, and adhesion on Al, Ni, and Al/Ni multilayered films. The results show that when the indention depth of the sample increased, the maximum load, plastic energy, and adhesion increased. Jump-contact behavior was observed at the beginning of the loading process. Force relaxation and adhesion took place at the holding depth and during the unloading process, respectively. The glide bands of the interface were on the {1 1 1} 1 1 0 slip systems and the maximum width of the glide bands was about 1 nm. The mechanical responses of the indented films are also discussed.     

Length scale effects on recrystallization and texture evolution in Cu layers of a roll-bonded Cu–Nb composite

Recrystallization textures were investigated in thin layers of both pure Cu and alloyed Cu combined with Nb in roll-bonded composites. Texture analysis using X-ray revealed that Cube orientation was the dominant texture component after recrystallization in rolled monolithic pure Cu whereas {2 1 5} 2 1 1 and B/S were the dominant components for the recrystallized alloyed Cu. In the composites, however, the rolling texture is retained during annealing in both the pure Cu and the alloyed Cu layers when the layer thickness enters the sub-micron regime. This is attributed to the nucleation and growth of recrystallizing grains being impeded via a reduction in recrystallization driving pressure and the grain boundary movement and growth being limited due to the layer thickness effect. A new term—“confined recrystallization” was also introduced to describe more accurately the morphological evolution observed within the sub-micron thick layers after annealing and highlights the contrast to either simple recovery or continuous recrystallization.     

Dynamic recrystallization during high temperature deformation of magnesium

As a consequence of the high critical stresses required for the activation of non-basal slip systems, dynamic recrystallization plays a vital role in the deformation of magnesium, particularly at a deformation temperature of 200 °C, where a transition from brittle to ductile behavior is observed. Uniaxial compression tests were performed on an extruded commercial magnesium alloy AZ31 at different temperatures and strain rates to examine the influence of deformation conditions on the dynamic recrystallization (DRX) behavior and texture evolution. Furthermore, the role of the starting texture in the development of the final DRX grain size was investigated. The recrystallized grain size, measured at large strains (  −1.4) seemed to be more dependent on the deformation conditions than on the starting texture. In contrast to pure magnesium, AZ31 does not undergo grain growth at elevated deformation temperatures, i.e. 400 °C, even at a low strain rate of 10⁻⁴ s⁻¹. Certain deformation conditions gave rise to a desired fully recrystallized microstructure with an average grain size of 18 μm and an almost random crystallographic texture. For samples deformed at 200 °C/10⁻² s⁻¹, optical microscopy revealed DRX inside of deformation twins, which was further investigated by EBSD.     

Investigation of hot ductility in Al-killed boron steels

The influence of boron to nitrogen ratio, strain rate and cooling rate on hot ductility of aluminium-killed, low carbon, boron microalloyed steel was investigated. Hot tensile testing was performed on steel samples reheated in argon to 1300 °C, cooled at rates of 0.3, 1.2 and 3.0 °C s⁻¹ to temperatures in the range 750–1050 °C, and then strained to failure at initial strain rates of 1 × 10⁻⁴ or 1 × 10⁻³ s⁻¹. It was found that the steel with a B:N ratio of 0.19 showed deep hot ductility troughs for all tested conditions; the steel with a B:N ratio of 0.47 showed a deep ductility trough for a high cooling rate of 3.0 °C s⁻¹ and the steel with a near-stoichiometric B:N ratio of 0.75 showed no ductility troughs for the tested conditions. The ductility troughs extended from 900 °C (near the Ae₃ temperature) to 1000 or 1050 °C in the single-phase austenite region. The proposed mechanism of hot ductility improvement with increase in B:N ratio in these steels is that the B removes N from solution, thus reducing the strain-induced precipitation of AlN. Additionally, BN co-precipitates with sulphides, preventing precipitation of fine MnS, CuS and FeS, and forming large, complex precipitates that have no effect on hot ductility.     

Preparation and characterization of ultrafine alumina via sol–gel polymeric route

Ultrafine alumina powder was prepared through resin formation between urea and formaldehyde. Aluminium stearate soap was introduced during resin preparation. Ethylene glycol was used to terminate the thermosetting reaction. Calcination of the product was carried out at 700, 1000, 1100, 1300 and 1400 °C to obtain aluminium oxide.IR and Raman spectroscopic analysis indicated the occupation of Al³⁺ at different sites in the polymer network (CO, NH₂, CO, NH, and CH₂OH).X-ray diffraction of powder calcined at 1000 °C revealed the presence of a mixture of α- and θ-alumina together, while a mixture of α- and β-alumina phases were obtained on calcination at 1400 °C. Transmission electron microscope (TEM) examination of the powder fired at 700 °C showed uniform grains in the form of clusters with average size between 22.02 and 30.5 nm. Clusters are multi-particles as evident from the electron diffraction pattern. Crystallite size of alumina powder calcined at 1000 °C was found to be ≈25.67 nm, while that of powder calcined at1400 °C was ≈30.52 nm. The calculated specific surface area of alumina powder calcined at 1000 °C was 59.17 m² g⁻¹, while that calcined at 1400 °C was 49.77 m² g⁻¹.     

Microstructure evolution of Mg–Al–Zn alloys during compression test at low strain and temperature

The microstructure evolutions and texture changes during the compression test were investigated using an extruded magnesium alloy with average grain sizes of 11.4 and 49.6 μm. The deformation twins were formed in all the samples; however, a comparison of the fraction of deformation twins on the effect of grain size and initial texture, i.e., the cutting position (normal or parallel to the extrusion), showed that the fine-grained alloy and/or the sample with the normal-cut to the extrusion had a lower fraction of deformation twins. On the other hand, the texture change showed different tendencies depending on the grain size and/or the initial texture. In the coarse-grained alloy, since the dominant deformation mechanism was the deformation twins, the lattice was rotated without relation to the initial texture. However, in the fine-grained alloy, even the applied strain of 0.20, the intensity peaks existed at 10-10 and the basal texture remained in the sample with the parallel- and normal-cut to the extrusion, respectively. This resulted from the difference in the fraction of deformation twins and the occurrence of partial grain boundary sliding.     

Mechanism of nucleation and growth of cubic boron nitride thin films

The mechanism and the crystallography of the nucleation and growth of cubic boron nitride (c-BN) films deposited on 100-oriented silicon substrate by RF bias sputtering have been studied by means of cross-sectional high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Both methods provide experimental information showing no sp²-bonded BN layer formation in the subsurface region of c-BN phase. This is clear evidence for layer-by-layer homoepitaxial growth of cubic boron nitride without graphitic monolayers in the near-surface region of the film. The turbostratic boron nitride (t-BN) consists of thin sub-layers, 0.5–2 nm thick, growing in such a way that a sub-layer normal is almost parallel to the growth direction. t-BN also comprises a large volume fraction of the grain boundaries with high interface energies. The present result and the finding by Shtansky et al. [Acta Mater. 48, 3745 (2000)], who showed that an individual sub-layer consists of parallel lamellae in both the hexagonal (h-BN) and rhombohedral (r-BN) configurations, demonstrate that high intrinsic stress in the films is due to the complex structure of sp²-bonded BN. The crystallography of c-BN films indicates heteroepitaxial nucleation of cubic phase on the graphitic BN structural precursor. The present results are consistent with stress-induced c-BN formation.     

Low cycle fatigue mechanism of René 80 at high temperature–high strain

The low cycle fatigue René 80, a Ni-base superalloy, was studied at temperature of 871 °C, R = (_min/_max) = 0 and strain rate of about 2 × 10⁻³ s⁻¹. The dislocation structure and failure surface observations were evaluated through TEM and SEM. TEM studies showed that at Δ_t = 0.8% during the first cycle the dislocations formed a hexagonal network in the γ-phase matrix. When the number of cycles increased, the density of dislocations increased as well. At N = N_f and Δ_t = 0.8% the cutting of γ′ precipitates took place. SEM studies at Δ_t = 0.8% and N = N_f showed that fatigue crack initiation generally occurred at the surface, where it is depleted of the γ′ phase as a result of oxidation by the high-temperature exposure. In addition to depleted zones, the grain boundary oxidation and oxide spikes were also considered as further crack initiation sites.     

Compressive and wear behaviors of bulk nanostructured Al2024 alloy

Compressive and wear properties of bulk nanostructured Al2024 alloy prepared by mechanical milling and hot pressing methods were investigated. Al2024 powders were subjected to high-energy milling for 30 h to produce nanostructured alloy. As-milled powders were compacted at 500 °C under 250 MPa in a uniaxial die. Consolidated sample had an average hardness and relative density values of 207.6 HV and 98%, respectively. Uniaxial compression tests at strain rates in the range of 1.67 × 10⁻⁴–1.67 × 10⁻² s⁻¹ were performed using an Instron-type machine. The wear behavior of nanostructured sample was investigated using a pin-on-disk technique under an applied load of 20 N. The compression and wear experiments were also executed on samples of commercial coarse-grained Al2024-O (annealed) and Al2024-T6 (artificially-aged) alloys, for comparison. The structure of consolidated Al2024 was characterized by X-ray diffraction (XRD). The yield strength and compressive strength of nanostructured Al2024 reached a value of 698 MPa and 712 MPa at strain rate of 1.67 × 10⁻⁴ s⁻¹, respectively, which was considerably higher than those for coarse-grained Al2024-O and Al2024-T6 counterparts. Worn surfaces and the wear debris were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and XRD. Nanostructured Al2024 revealed a low friction coefficient of 0.3 and a wear rate of 12 × 10⁻³ mg/m, which are significantly lower than those obtained for Al2024-O and Al2024-T6 alloys. This enhanced wear resistance was mainly caused by nanocrystalline structure with high hardness value. The dominating wear mechanism of nanostructured Al2024 appeared to be delamination mechanism.     

Superplastic behavior of a fine-grained ZK60 magnesium alloy processed by high-ratio differential speed rolling

Grain size of the ZK60 alloy was effectively reduced to 12 μm through high-ratio differential speed rolling (HRDSR) for a thickness reduction of 70% in a single pass. Due to the strengthening effects of grain boundaries and particles, the HRDSR processed ZK60 exhibited a high tensile strength of 340 MPa. Low temperature superplasticity was attained at 473–493 K at low strain rates (5 × 10⁻⁴ s⁻¹) and high strain rate superplasticity was attained at 523–553 K at high strain rates (10⁻² s⁻¹). The optimum superplastic temperature was found to be 553 K where a maximum tensile elongation of 1000% was obtained at 1 × 10⁻³ s⁻¹. The deformation behavior of the HRDSR processed ZK60 at elevated temperatures could be depicted by considering contribution of grain boundary sliding and slip creep to total plastic flow. Difference in superplastic deformation behavior between the HRDSR processed and equal channel angular press processed ZK60 alloys was examined and discussed.     

Preparation of multilayered nanocrystalline thin films with composition-modulated interfaces

The properties of multilayer thin film structures depend on the morphology and structure of interfaces. A broad interface, in which the composition is varying, can enhance, e.g., the hardness of multilayer thin films. In the present experiments multilayers of TiAlN and CrN as well as TiAlN, CrN and MoS₂ were studied by using unbalanced magnetron sputter sources. The sputter sources were arranged side by side on an arc. This arrangement permits development of a transition zone between the layers, where the composition changes continuously. The multilayer system was deposited by one-fold oscillating movement of substrates in front of sputter sources. Thicknesses of layers could be changed both by oscillation frequency and by the power applied to sputter sources. Ti/Al: 50/50 at%, pure chromium and MoS₂ targets were used in the sputter sources. The depositions were performed in an Ar–N₂ mixture at 0.22 Pa working pressure. The sputtering power of the TiAl source was feed-back adjusted in fuzzy-logic mode in order to avoid fluctuation of the TiAl target sputter rate due to poisoning of the target surface. Structure characterization of films deposited on 1 0 0 Si wafers covered by thermally grown SiO₂ was performed by cross-sectional transmission electron microscopy. At first a 100 nm thick Cr base layer was deposited on the substrate to improve adhesion, which was followed by a CrN transition layer. The CrN transition layer was followed by a 100 nm thick TiAlN/CrN multilayer system. The TiAlN/CrN/MoS₂ multilayer system was deposited on the surface of this underlayer system. The underlayer systems Cr, CrN and TiAlN/CrN were crystalline with columnar structure according to the morphology of zone T of the structure zone models. The column boundaries contained segregated phases showing up in the under-focused TEM images. The surface of the underlayer system was wavy due to dome-shaped columns. The nanometer-scaled TiAlN/CrN/MoS₂ multilayer system followed this waviness. Crystallinity of the TiAlN and CrN layers in the multilayer system decreases with increasing thickness of the MoS₂ layer.