Diagnostics of degradation processes induced by pulsed electric signals at the aluminum-silicon interface

Thermal conditions in an aluminum metallization stripe deposited onto a single crystal silicon substrate have been studied during the passage of single rectangular electric pulse with a current density of j < 8 × 10¹⁰ A/m² and a duration of τ = 100–1000 μs. Based on the results of this analysis, a method of diagnostics of the state of metallization contact systems and determination of the conditions of their safe operation is proposed.     

Features of electrostimulated degradation of aluminum metallization on silicon surface in the presence of dielectric steps

Features of thermal degradation of the aluminum metallization layers deposited onto the silicon surface with dielectric steps have been studied during the passage of single rectangular electric pulses with a current density amplitude of j < 8 × 10¹⁰ A/m₂ and a duration of 100–1000 μs. An approach to the diagnostics of metallization in the presence of dielectric sublayers is proposed, which allows the range of safe operation parameters to be determined.     

Degradation processes induced by nonstationary electric signals in metallization systems on silicon

The temperature regimes of operation of an aluminum metallization layer on a silicon plate have been analyzed for the passage of an electric pulse with a current density buildup rate of Δj/Δt ≤ 1.5 × 10¹⁴ A/(m² s). The temperature dynamics in this system has been calculated and compared to the experimental results. Degradation processes in the metallization layer-silicon structure have been observed, which are related to the formation of a liquid phase at the metal-semiconductor interface and the contact melting of a metallization layer under the conditions of nonstationary heating.     

Phase transformations in metallization systems under conditions of nonstationary thermal action

First-order phase transitions induced in aluminum metallization layers by the passage of single rectangular current pulses with amplitude up to 8 × 10¹⁰ A/m² and durations within 100–1000 μs are considered. The formation of local fused zones and their subsequent migration during current passage have been experimentally studied. The main mechanisms of interphase boundary propagation due to heat evolution at the solid/liquid interface under conditions of nonstationary heating of the metal film are established. The velocity of liquid-phase propagation (～25 m/s) along the metallization stripe has been determined in experiment and a method of calculating the length of a fused zone upon the current pulse passage is proposed.     

Studying diffusion in multilayer thin-film structures on silicon by the contact melting technique

Features of the contact melting in thin-film structures comprising an aluminum layer with a thickness of h ₁ = 5 μm and a metal (Ti, Ni, Mo) or semiconductor (Si, Ge) sublayer (h ₂ = 0.1 μm) on a single crystal silicon plate (h ₃ = 500 μm) have been studied. The contact melting was caused by single rectangular electric pulses with a current density of j < 9 × 10¹⁰ A/m² and a duration of τ = 100–1000 μs passing through the Al layer. The duration and rate of melting in the samples were determined using voltage waveforms measured by an oscillograph. A method has been developed based on an analysis of the mechanisms of contact interaction in the Al film—sublayer system (with allowance for experimental data on the time of sublayer dissolution in the Al film) for estimating the coefficients of mutiphase diffusion of the system components during the passage of a current pulse.     

Generation of dislocation loops in silicon near local heat sources

The thermal conditions created in an aluminum metallization layer on a silicon wafer by a rectangular current pulse are analyzed at pulse heights of up to 6 × 10¹⁰ A/m² and pulse durations from 50 to 10³ μs. The thermoelastic stress developing in silicon substrates as a result of unsteady-state heating of the metallization layer is calculated. The theoretically predicted formation of linear defects near thermal shock sources in silicon is confirmed by experimental data.     

Effective electromechanical properties of ferroelectric piezoactive composites of the crystal-ceramic type based on (Pb1−x Cax)TiO3

Based on the previously proposed models, effective electromechanical properties of the ferroelectric piezoactive composites of the “single-domain crystal-ceramic” and “polydomain crystal-ceramic” types are determined for the first time. Features of the concentration dependence of the piezoelectric coefficients of four types (e _3j ^* , d _3j ^* , g _3j ^* , and h _3j ^* ) are interpreted. Advantages of the new composites in comparison with the known ferroelectric piezoceramic materials of the PbTiO₃ type are considered and explained. It is shown that the coefficients e _3j ^* are most sensitive to a change in the system parameters; some reasons for this sensitivity are established.     

Artificial Pinning Centers on MgB2 Superconducting Thin Films Coated by FeO Nanoparticles

MgB₂ thin films were fabricated on MgO (100) single crystal substrates. First, deposition of boron was performed by rf magnetron sputtering on MgO substrates and followed by a post deposition annealing at 850?°C in magnesium vapor. In order to investigate the effect of FeO nanoparticles on magnetic properties of MgB₂ thin films, the films were coated with different concentrations of FeO nanoparticles by spin coating process. The magnetic field dependence of the critical current density $J_{\mathrm{c}}$ was calculated from the M?CH loops and also magnetic field dependence of the pinning force density $f_{\mathrm{p}}(b)$ was determined for the films containing different concentrations of FeO nanoparticles. The values of the critical current density $J_{\mathrm{c}}$ in zero field at 5?K was found to be around 1×10⁶?A/cm² for pure MgB₂ film, 1.4×10⁶ for MgB₂ film coated with 25?%, 7.2×10⁵ for MgB₂ film coated with 33?%, 9.1×10⁵ for MgB₂ film coated with 50?% and 1.1×10⁶?A/cm² for MgB₂ film coated with 100?%. It?was?found that the film coated with 25?% FeO nanoparticles has slightly enhanced critical current density and it can be noted that especially the film coated with 25?% FeO became stronger in the magnetic field. The films coated with FeO were successfully produced and they indicated the presence of artificial pinning centers created by FeO nanoparticles. The superconducting transition temperature of the film coated with 25?% FeO nanoparticles was determined by moment?Ctemperature (M?CT) measurement to be 34?K which is 4?K higher than that of the pure film.     

Flexural vibrations of semiconductor wafers in the presence of a pulsed thermal excitation source

An analysis is made of the action of current pulses on a metal film lying on a semiconductor wafer. It is shown that the passage of current pulses of amplitude (1–7)×10¹⁰ A/m² and duration 50–200 μs across aluminum tracks excites sound. Experimental dependences of the energy of the flexural vibrations as a function of the duration and amplitude of the pulsed action were obtained. It was observed for the first time that the melting of a metal-semiconductor contact is accompanied by an abrupt increase in the energy of the flexural vibrations of the wafer. Pis’ma Zh. Tekh. Fiz. 25, 57–63 (March 12, 1999)     

Sublimation study of BiBr3

Steady-state sublimation vapour pressures of anhydrous bismuth tribromide have been measured by the continuous gravimetric Knudsen-effusion method from 369.3 to 478.8 K. Additional effusion measurements have also been made from 435.4 to 478.6 K by the torsion—effusion method. Based on a correlation of Δ_sub H ₂₉₈ ⁰ and Δ_sub S ₂₉₈ ⁰ , a recommended p(T) equation has been obtained for BiBr₃(s) $$\alpha - {\rm B}i{\rm B}r_3 :log{\text{ }}p = - C\alpha /T - 12.294log{\text{ }}T + 5.79112 \times 10^{ - 3} {\text{ }}T + 47.173$$ with Cα=(Δ _subH ₂₉₈ ⁰ +20.6168)/1.9146×10^-2 $$\beta - {\rm B}i{\rm B}r_3 :log{\text{ }}p = - C\beta /T - 23.251log{\text{ }}T + 1.0492 \times 10^{ - 2} {\text{ }}T + 77.116$$ with Cβ=(Δ _subH ₂₉₈ ⁰ +46.2642)/1.9146×10^-2 where p is in Pa, T in Kelvin, Δ _sub H ₂₉₈ ⁰ in kJ mol^?1. Condensation coefficients and their temperature dependence have been derived from the effusion measurements.     

Optical study of charge dynamics along thec-axis in high-T c superconductors

Comparing the optical spectra withE∥c for typical high-T _c superconducting cuprates, we discuss the charge dynamics along thec-axis. The plasma energy or the mass anisotropic factorm _* ^c //m _* ^b is one of the key parameters determining the spectrum forE∥c. In Bi₂Sr₂CaCu₂O₈ and La_2?x Sr _x CuO₄ with a largem _* ^c /m _* ^b , the plasma energy is smaller than the superconducting gap energy, and thus the supercurrent along thec-axis is a kind of Josephson current flowing through insulating layers such as the BiO layers. On the other hand, in YBa₂Cu₃O₇ with a smallm _* ^c /m _* ^a , it seems that the coherent supercurrent flows along thec-axis. Although the spectrum forE∥c strongly depends on samples, presumably due to the difference in the hole concentration, a clear anisotropy between theab- and thec-directions is observed in the characteristics energy scales such as the plasma energy as well as the reflectivity knee energy.     

Sorption of 131I− and 131IO 3 − from aqueous solution on nickel hydroxide at 20°C

Sorption of ¹³¹I^? and ¹³¹IO ₃ ^? from aqueous solution on solid Ni(OH)₂ at 20°C was studied. It was found that in sorption from aqueous solution, after 120-min contact of the liquid and solid phases at V/m = 500 ml g^?1, with an increase in the concentration of I^? and IO ₃ ^? from 10^?5 to 10^?3 M the distribution coefficients K _d decrease from 16.4 to 5.3 ml g^?1 for ¹³¹I^? and from 113.6 to 30.8 ml g^?1 for ¹³¹IO ₃ ^? . The influence of various anions (Cl^?, NO ₃ ^? , SO ₄ ^2? , and BO ₃ ^3? ) on sorption of ¹³¹I^? and ¹³¹IO ₃ ^? from aqueous solution on solid Ni(OH)₂ was studied. It was found that, with an increase in the concentration of these ions from 10^?5 to 10^?1 M, the distribution coefficients K _d of ¹³¹I^? and ¹³¹IO ₃ ^? decrease by a factor of 3–10.     

Molecular beam epitaxy of semipolar AlN(11\bar{2}2) and GaN(11\bar{2}2) on m-sapphire

We report on the plasma-assisted molecular-beam epitaxy of semipolar $\hbox{AlN}(11\bar{2}2)$ and GaN( $11\bar{2}2$ ) films on $(1\bar{1}00)$ m-plane sapphire. AlN deposited on m-sapphire settles into two main crystalline orientation domains, $\hbox{AlN}(11\bar{2}2)$ and $\hbox{AlN}(10\bar{1}0),$ whose ratio depends on the III/V ratio. Growth under moderate nitrogen-rich conditions enables to isolate the $(11\bar{2}2)$ orientation. The in-plane epitaxial relationships of $\hbox{AlN}(11\bar{2}2)$ on m-plane sapphire are $[11\bar{2}\bar{3}]_{\rm AlN} \vert \vert [0001]_{\rm sapphire}$ and $[1\bar{1}00]_{\rm AlN} \vert \vert [11\bar{2}0]_{\rm sapphire}.$ GaN deposited directly on m-sapphire results in ( $11\bar{2}2$ )-oriented layers with ( $10\bar{1}\bar{3}$ )-oriented inclusions. A ～100 nm-thick AlN( $11\bar{2}2$ ) buffer imposes the ( $11\bar{2}2$ )-orientation for the GaN layer grown on top. By studying the Ga-desorption on GaN( $11\bar{2}2$ ), we conclude that these optimal growth conditions corresponds to a Ga excess of one monolayer on the GaN( $11\bar{2}2$ ) surface.     

Topological Investigations of Excess Molar Volumes and Excess Isentropic Compressibilities of Ternary Mixtures Containing Pyrrolidin-2-one at 308.15 K

Excess molar volumes, ${V^{\rm E}_{ijk}}$ , and speeds of sound, u _ijk , of pyrrolidin-2-one (2-Py) (i)+benzene or methyl benzene (j)+propan-1-ol (k) ternary mixtures and speeds of sound, u _ij , of benzene or methyl benzene (i)+propan-1-ol (j) binary mixtures have been measured dilatometrically and interferrometrically over the complete mole fraction range at 308.15 K. Speed-of-sound data have been utilized to evaluate excess isentropic compressibilities for binary and ternary mixtures. ${V^{\rm E}_{ijk}}$ and ${\left({\kappa_S^{\rm E}}\right)_{ijk}}$ values have been fitted to a Redlich–Kister equation to predict ternary adjustable parameters and standard deviations. Topological investigations employed for predicting excess molar volumes and excess isentropic compressibilities, ${\left({\kappa _S^{\rm E}} \right)_{ij}}$ , of 2-Py + benzene or methyl benzene or propan-1-ol binary mixtures have been extended to ternary mixtures (by employing the concept of a connectivity parameter of third degree, ³ ξ, of a molecule) to obtain an expression that describes well the measured ${V^{\rm E}_{ijk}}$ and ${\left({\kappa_S^{\rm E}}\right)_{ijk}}$ values.     

Computer simulation of vortex pinning in type II superconductors. II. Random point pins

Pinning of vortices in a type II superconductor by randomly positioned identical point pins is simulated using the two-dimensional method described in a previous paper (Part I). The system is characterized by the vortex and pin numbers (N _v ,N _p ), the vortex and pin interaction ranges (R _v ,R _p ), and the amplitude of the pin potentialA _p . The computation is performed for many cases: dilute or dense, sharp or soft, attractive or repulsive, weak or strong pins, and ideal or amorphous vortex lattice. The total pinning forceF as a function of the mean vortex displacementX increases first linearly (over a distance usually much smaller than the vortex spacing and thanR _p ) and then saturates, fluctuating about its average \(\bar F\) . We interpret \(\bar F\) as the maximum pinning forcej _c B of a large specimen. For weak pins the prediction of Larkin and Ovchinnikov for two-dimensional collective pinning is confirmed: \(\bar F\) =const· \(\bar W\) /R _p c ₆₆, where \(\bar W\) is the mean square pinning force andc ₆₆ is the shear modulus of the vortex lattice. If the initial vortex lattice is chosen highly defective (“amorphous”) the constant is 1.3–3 times larger than for the ideal triangular lattice. This finding may explain the often observed “history effect”. The function \(\bar F\) (A _p ) exhibits a jump, which for dilute, sharp, attractive pins occurs close to the “threshold value” predicted for isolated pins by Labusch. This jump reflects the onset of plastic deformation of the vortex lattice, and in some cases of vortex trapping, but isnot a genuine threshold. For strong pins \(\bar F\) ～(N _p \(\bar W\) )^1/2 approaches the direct summation limit. For both weak and strong pinningj _c B is related to the mean squareactual (not maximum) force of each pin. This mean square in general is not proportional toA _p ² but, due to relaxation of the vortex lattice, may be smaller or larger than its rigid-lattice limit. Therefore, simple power lawsj _c ～n _p A _p ² orj _c ～n _p A _p in general donot hold except for very weak or unphysically strong pinning.     

Numerical simulation of burning front propagation

In the context of a numerical experiment, it is shown that the switching wave described by the reaction-diffusion equation can be delayed at a medium inhomogeneity with a thickness Δ and amplitude Δβ for a finite time τ = τ(Δβ, Δ) up to a complete stop at it (τ = ∞). Critical values Δβ _c and Δ _c corresponding to the autowave stop are found. The similarity laws \(\tau \sim (\Delta _c - \Delta )^{ - \gamma _\Delta } \) and \(\tau \sim (\Delta \beta _c - \Delta \beta )^{ - \gamma _\beta } \) are established, and the critical indices and are found. The similarity law is established for critical values of amplitude and width of the inhomogeneity corresponding to the autowave stop Δβ _c ～ Δ _c ^-δ where δ ≈ 1.     

Thermophysical Properties of Molten Yttrium Measured by Non-contact Techniques

Understanding the nature and behavior of liquid metals requires accurate values of their physical properties (e.g., density, surface tension, viscosity). However, maintaining samples of matter in their liquid phases, in particular under supercooled conditions, is a great challenge when dealing with refractory metals. This is due mainly to their high melting temperatures (e.g., 3,695 K for W), their high vapor pressure, and the risk of melt contamination with a support or crucibles. Electrostatic levitation, laser heating in vacuum, and non-contact characterization techniques circumvented these difficulties and allowed the determination of the properties of several metals in their liquid state, above their melting temperature as well as in their supercooled phase. In this work, several thermophysical properties were successfully measured with an electrostatic levitation furnace under vacuum conditions. For the first time, density and viscosity data of yttrium were reported over large temperature intervals in the liquid phase. Over the 1,560 to 2,100 K temperature span, the density can be expressed as $\rho (T)=4.15\times 10^3-0.21\, (T - T_{\rm m})$ (kg·m^???3) with T _m = 1,796 K, yielding a volume expansion coefficient of 5.1 × 10^???5 K^???1. In addition, the surface tension can be expressed as $\sigma \left( T \right)=8.04\times 10^2-0.05\,(T - T_{\rm m})$ (mN·m^???1) and the viscosity as $\eta \left( T \right)=0.00287\,\exp \left[ {{1.1\times 10^5} \mathord{\left/ {\vphantom {{1.1\times 10^5} {\left( {\mbox{RT}} \right)}}} \right. \kern-0em} {\left( {\mbox{RT}} \right)}} \right]$ mPa·s over the 1,830 to 2,070 K interval. The results, in particular those for viscosity, suggest that performing similar experiments in microgravity could improve the accuracy of the measurements.     

Effect of strain rate on interfacial fracture behaviors of Sn-58Bi/Cu solder joints

The interfacial reactions and mechanical properties of Sn-58Bi/Cu solder joints reflowed at different temperatures ranging from 180 to 220 °C for constant time of 10 min were investigated with various strain rates. Only a continuous Cu₆Sn₅ intermetallic compound (IMC) layer was formed at the interface between the Sn-58Bi solder and the Cu substrate during reflow. The equivalent thickness of the Cu₆Sn₅ layer increased with increasing reflow temperature, and the relationship between Cu₆Sn₅ layer equivalent thickness (X) and reflow temperature (T) is obtained by using method of linear regression and presented as $ X = 0.01 \times T + 0.187 $ . For the tensile property, the tensile strength of solder joint gradually decreased as the reflow temperature it increased, whereas it increased with increasing strain rate. Moreover, the fracture behavior of Sn-58Bi/Cu solder joint indicated the ductile fracture with low strain rate (5 × 10^?4 and 1 × 10^?3 s^?1), while toward brittle fracture with high strain rate (2 × 10^?3 and 1 × 10^?2 s^?1). The strain rate sensitivities of the solder joints fractured with various modes were also investigated, and it is found that the tensile strength of the solder is more sensitive to the strain rate than that of the IMC layer.     

Acoustic emission in dislocation-containing silicon exposed to current and thermal influences

An investigation was made of acoustic emission in silicon single crystals during passage of an electric current. It was observed that in the temperature range studied (T=300−450K) acoustic emission signals whose intensity increases with increasing dislocation density are excited in a static electric field. The acoustic emission of silicon single crystals with and without dislocations is compared. It is assumed that the acoustic emission in silicon is caused by the unpinning and migration of dislocations under the influence of the direct electric current and thermoelastic stresses. The activation energy of this process is estimated as E=0.53±0.05 eV during passage of a direct current of density j=2.8×10⁵ A/m². Pis’ma Zh. Tekh. Fiz. 25, 28–32 (February 12, 1999)     

Measurements of Decoherence Times in a Josephson Charge Qubit Using Fast Pulses

We study decoherence of a Josephson charge qubit using fast pulses to perform qubit rotations. The gate charge dependence of the decoherence rate indicates that the low frequency fluctuations affecting the qubit are from charges distributed with a 1/f-type spectrum. Assuming the form S_q(ω) = α/|ω|, we find $\sqrt \alpha$ = 4 × 10^?3e, which is slightly higher than the value found from very low frequency noise measurements. PACS numbers: 03.67.-a, 75.40.+r, 85.25.Cp.