Finite Element Analysis on the Influence of Contact Resistivity in an Extraordinary Magnetoresistance Magnetic Field Micro Sensor

In this paper, an extraordinary magnetoresistance (EMR) device made of an InSb/Au hybrid structure was investigated. Those devices have a large potential in becoming a new generation of highly sensitive and cheap magnetic micro sensors. A crucial factor for the performance is the interface between the InSb and Au, which suffers from a certain contact resistivity. The Finite Element Method (FEM) was employed to simulate the current redistribution in the device, under an applied magnetic field. Specifically, the influence of the contact resistivity between the InSb bulk and Au shunt was studied. In a device with optimized geometry and without contact resistivity between the layers of InSb and Au, the EMR effect and the sensitivity show values of 1.89×10⁴% and 0.02%/(10^?4?T), respectively, at 1?Tesla. For values of contact resistivity up to 10^?8????cm² the EMR effect is almost constant, while for higher values the EMR effect decreases exponentially. However, the sensitivity of the device does not decrease until 5×10^?6????cm² of contact resistivity. Only beyond this value the sensitivity, which in most cases is associated with the performance of the device, will deteriorate.     

Comparative analysis of oxide phase formation and its effects on electrical properties of SiO2/InSb metal-oxide-semiconductor structures

We report on the changes in the interfacial phases between SiO₂ and InSb caused by various deposition temperatures and heat treatments. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to evaluate the relative amount of each phase present at the interface. The effect of interfacial phases on the electrical properties of SiO₂/InSb metal-oxide-semiconductor (MOS) structures was investigated by capacitance-voltage (C-V) measurements. The amount of both In and Sb oxides increased with the deposition temperature. The amount of interfacial In oxide was larger for all samples, regardless of the deposition and annealing temperatures and times. In particular, the annealed samples contained less than half the amount of Sb oxide compared with the as-deposited samples, indicating a strong interfacial reaction between Sb oxide and the InSb substrate during annealing. The interface trap density sharply increased for deposition temperatures above 240 °C. The C-V measurements and Raman spectroscopy indicated that elemental Sb accumulation due to the interfacial reaction of Sb oxide with InSb substrate was responsible for the increased interfacial trap densities in these SiO₂/InSb MOS structures.     

Directional solidification and growth characteristics of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Er<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>/ZrO<Subscript>2</Subscript> ternary eutectic ceramic by laser floating zone melting

Directionally solidified Al₂O₃/Er₃Al₅O₁₂/ZrO₂ ternary eutectic ceramic in situ composite rods with length of 110 mm have been fabricated by laser floating zone melting. The microstructural characteristics of steady growth zone, initial growth zone and solid/liquid interface are investigated under high temperature gradient. In the steady growth zone, the eutectic spacing (λ) is rapidly decreased as increasing the growth rate (V), and the corresponding relationship between growth rate and eutectic spacing is determined to be λ = 11.14 × V ^?1/2. The temperature gradient has been measured to be about 5.3 × 10³ K/cm. In the initial growth zone, the melting process and temperature distribution are recorded by infrared thermal imager, and several unstable complex microstructures are observed. In the quenched zone, the regular eutectics with minimum eutectic spacing of 200 nm are obtained. Moreover, the solid/liquid interface during solidification shows convex interface morphology and the interface height is gradually decreased as increasing the growth rate. The eutectic growth behaviors at the center and edge of the as-grown rod are compared and discussed.     

Mechanical properties of Sn-Ag3Sn alloys

The structure and properties of Sn-Ag₃Sn directionally-frozen eutectic alloys have been examined over the growth range 2×10^?4 to 2×10^?1 mm sec^?1. The structure is predominantly broken lamellar to 1.3×10^?2 mm sec^?1, but with relatively poor alignment to the growth direction at smaller growth rates. The tensile and compressive strengths were measured. These increase monotonically to the growth rate at which cellular growth ensues, after which point they fall. The hardness of the eutectic closely parallels the compressive properties as the growth rate increases. Quenching from 200° C produces a marked increase in compressive strength and hardness, attributed to the quench-hardening of the Sn-rich phase.     

Microstructural defects and their origins in Cd–CuCd3 eutectic

Abstract

In this investigation, macrostructural and microstructural imperfections, formed in the fibrous Cd–CuCd₃ eutectic during unidirectional solidification, were characterized and the factors important in their formation were studied. The effect of growth rate R, imposed thermal gradient G, and natural convection on the defect morphology were investigated, and the important physical factors that determine the manner in which microstructural defects form were considered. Convection was found to play a minimal role in defect formation. The most important variable was found to be the ratio G/R, which determined the solid/liquid interface shape during solidification. When low values of G/R were used, eutectic cells were formed. For intermediate values of G/ R, the microstructure was found to contain features analogous to nodes in single–phase materials. Only when high values of G/R were used were all microstructural defects eliminated, producing a nearly perfect structure of parallel CuCd₃ rods in a matrix of cadmium. The morphology of branching and curving rods, which were found to be the primary microstructural defects, indicates that both the solid/solid interfacial free energy and its anisotropy are important factors in rod branching, and a branching mechanism consistent with the observations made was proposed. Anisotropy in the solid/solid interfacial free energy was considered to account for the formation of blades; however, kinetic considerations were required to account for the growth dependence of the rod-to-blade transition observed in this eutectic.

MST/130     

Chill modification in AI–Si–Sb eutectic alloys

Abstract

Interface undercooling and Si interparticle spacing measurements and observations of the Si phase structure are presented for Al–12·7Si–0·2Sb (wt-%) alloys directionally solidified over the growth velocity range 20–820 μm S^?1 with a temperature gradient in the liquid of 32 K cm^?1. The undercooling measurements show that the undercooling decreases over the growth velocity range where chill modification occurs. Some cozonal twinning was observed in the fibres but the density of twinning decreased with increasing growth velocity and many fibres were observed to be twin free. The measured undercoolings and spacings are related to growth curves derived from the Jackson and Hunt analysis of eutectic growth, after allowance for a constitutional undercooling term due to Sb buildup at the growth interface during solidification. It is shown that the present measurements can be reconciled with a chill modification mechanism that assumes a faceted–non-faceted transition in the Si phase, but not with a mechanism that considers that the chill modified structure is a rapidly solidified flake structure.

MST/3164     

Effect of microstructural variables on tensile behaviour of A356 cast aluminium alloy

Abstract

The effects of microstructural variables, including secondary dendrite arm spacing (SDAS), the size of primary α phase, the aspect ratio of eutectic Si particle and the thickness of eutectic wall structure, on tensile behaviour of A356 cast aluminium alloy, were quantitatively identified using linear regression analysis method. For systematic microstructural control of A356 specimen, directional solidification method was used with different solidification rates of 5, 25, 50 and 100 μm s^?1 respectively. The linear regression analysis suggests that each microstructural variable affects tensile strength and tensile elongation of A356 cast aluminium alloy in a similar fashion. The change in tensile behaviour with varying microstructural variables in A356 cast aluminium alloy is discussed based on fractographic and micrographic observations.     

Electromigration behaviors in Sb particle-reinforced composite eutectic SnAgCu solder joints

Due to the limited capacity of solder joints in microprocessors for the higher current density (usually 10³–10⁴ A/cm²), electromigration (EM), known as the mass movement resulting from imposition of high current density, has gained extensive attention during the last decades, specifically, the EM-induced damages in the eutectic 95.5Sn–3.8Ag–0.9Cu (e-SAC) that were heavily used in the electronic packaging industry. In order to conquer the instable physical properties of e-SAC in the severe service environment, composite approach was developed. One of the promising ways was intentionally incorporated metal-particles reinforcements. In this study, the e-SAC with 1 wt% Sb particles additive was investigated under the current density of 10⁴ A/cm² and 120 °C the ambient temperature. Unlike the non-composite solders that had obvious formation of hillock and valley at the anode side and cathode side, respectively. The crack initiated at the edge of the cathode interface and propagated to the center in the Sb particle-reinforced composite solder. The Sn–Sb phase, formed near the cathode interface after the first-reflow, blocked the movement of metal atoms/ions, but then induced the current crowding. In addition, synergistic influence of the compressive and tensile stress caused the fracturing of the Sn–Sb phase in the solder matrix due to its brittleness and immobility.     

Growth of eutectic composites in the InSb–MnSb system

Eutectic composites in the InSb–MnSb system have been grown by the Bridgman method in vertical geometry using a growth charge of eutectic composition. The composites consisted of a [110]-oriented single-crystal InSb matrix and single-crystal MnSb needles aligned in the growth direction. As the solidification rate was raised from 0.5 to 6 mm/h, the length of the needles increased, whereas their diameter dropped from 20 to 4 µm. Further raising the solidification rate led to spontaneous crystallization. Characteristically, the electrical and magnetic properties of the eutectic composites in the InSb–MnSb system were found to exhibit large anisotropy. The low-temperature resistivity of the composites across the needles is four to five times that along the needles. With increasing temperature, the resistivity ratio drops by up to a factor of 2–3. This can be accounted for in terms of a geometric factor. The electrical conductivity of the composites is determined primarily by the MnSb phase, whose volume along the growth direction was considerably larger. According to magnetic measurements, the eutectic composites in the InSb–MnSb system are ferromagnets with a Curie temperature of ? 600 K.     

Investigation of the transport properties of InSb single-crystal films obtained by directional crystallization

Both n-type and p-type InSb films (with a wide range of carrier concentration) were obtained by the directional crystallization method from the melt on large areas of mica, quartz and sapphire substrates. The p-type films were doped with germanium. It is shown that, depending on the crystallization conditions, one can obtain films of different structure: dendritic films, films containing macrodefects and homogeneous single-crystal films. The optimal growth conditions of single-crystal films having transport properties close to those of bulk material are given. The investigation of some transport properties in single-crystal p-type InSb films was carried out in the temperature range 77–600 K.A hole mobility in the range from 180 cm² V^-1 s^-1 to 5×10³ cm² V^-1 s^-1 in films with a concentration p=1.2×10¹⁶?5×10¹⁸cm^-3 of uncompensated acceptors was observed.An investigation of the concentration and temperature dependence of the hole mobility was carried out. Experimental results are in good agreement with the theory if a combined impurity, acoustic and optical mode scattering is taken into account.The phonon drag effect in p-type InSb films was observed. The temperature dependence of the thermoelectric power shows fair agreement with Herring's theory.     

Copper effects in mechanical,thermal and electrical properties of rapidly solidified eutectic Sn–Ag alloy

The Sn–3.5 wt%Ag alloy considered as a good alternative to Pb–Sn alloys. This study aims to investigate the effects of Cu or Sb additions by 3 or 5 wt% to melt-spun Sn–3.5%Ag alloy. Ternary melt-spun Sn–Ag–Cu and Sn–Ag–Sb alloys investigated using X-ray diffractions (XRD), Scanning electron microscope (SEM), Dynamic resonance technique (DRT), Instron machine, Vickers hardness tester and Differential scanning calorimetry (DSC). The results revealed that the microstructures of the β-Sn phase, Ag₃Sn and Cu₃Sn intermetallic compounds (IMCs) in the solder matrices were refined due to the effect of Cu additions and melt-spun process. Moreover, increasing Cu content promotes Ag₃Sn intermetallic compound (IMC) formation. Consequently, the addition of “3 wt%” of Cu reduced the creep rate ? from (3.79?×?10^?3) to (1.65?×?10^?3) and delayed the fracture point. The tensile results showed an improvement in Young’s modulus by 47% (30.3 GPa), ultimate tensile strength (UST) by 11.6% (23.9 MPa), and in toughness by 20.5% (952.32 J/m³) compared to the eutectic Sn–Ag alloy. Vickers hardness has improved by 3.3% (136.71 MPa) and thermal activation energy by 54% (90.40 KJ/mol) when compared with that of eutectic Sn–Ag alloy. Those improvements are related to the lack of lattice strain from 7.56?×?10^?4 without “3 wt%” of Cu to 5.26?×?10^?4 with “3 wt%” of Cu. Its melting temperature (T_m) increased by 3 °C due to Ag₃Sn IMC increased and Cu₃Sn formation, but the pasty rang (mushy zone) decreased by 4 °C with “3 wt%” of Cu. The small lattice strains resulted with “3 wt%” of Cu made the electrical resistivity of this alloy more stable at elevated temperatures. The mechanical, thermal and electrical improvements of Sn_93.5–Ag_3.5–Cu₃ alloy provide good physical performance for soldering process and electronic assembly.     

Formation of AI-Cr-Si quasicrystal with high silicon concentration by rapid quenching and its thermal and electrical properties

A quasicrystal revealing five-fold symmetry has been found to be formed in a rapidly quenched Al₆₂Cr₁₉Si₁₉ alloy containing a large amount of metalloid silicon. From analysis by the TEM/EDX method, the quasicrystalline single phase was determined to have a composition of Al_62.5Cr_17.6Si_19.9. The quasicrystal is composed of randomly-oriented equiaxed grains with an average size of 0.5 μm. The quasicrystal transforms to a stable Al₁₃Cr₄Si₄ compound with a complex cubic structure in the temperature range of 710 to 800 K. The activation energy and heat for the transformation are 85 kJ mol^?1 and 2.57 kJ mol^?1, respectively. The electrical resistivities (?) at 4.2 and 250 K are 2.83 and 3.65 μ?m, respectively, and its temperature coefficient at 250 K is 9.33 × 10^?4K^?1. The formation of the quasicrystal in the vicinity of Ai₁₃Cr₄Si₄ was inferred to be due to the combination effect of a great supercooling ability caused by the low melting temperature for AI-Si and Cr-Si eutectic type alloys and the difficulty of diffusivity of the constituent atoms in the ternary compound with a large unit cell and a strong bonding nature between chromium and aluminium or silicon.     

Decrease in fatigue life of Sn - 3.8 wt-%Ag - 1.2 wt-%Cu alloy solder joints due to thermal cycling

Abstract

Copper plates joined with a thin solder layer (60 μm thick) of Sn - 3.8 wt-%Ag - 1.2 wt-% Cu alloy were subjected to heat treatments: a thermal cycling of a temperature range between 321 K and 381 K (Δ T = 60 K) and an isothermal heating at 357 K, and then subjected to a fatigue test at 6 MPa stress amplitude. Solder joints made with a thin solder layer of Sn - Pb eutectic alloy were also examined for comparison. After heat treatments, the η phase developed and dispersed at the bonding interface of the solder joints with increasing numbers of thermal cycling and with increasing time of isothermal heating. Small voids also appeared in the η phase after heat treatments. Fine cracks appeared in the η phase after thermal cycling for 2000 cycles and higher, but no cracks were observed after isothermal heating. There was no large difference in fatigue lifetime after thermal cycling between Sn - Ag - Cu alloy solder joints and Sn - Pb eutectic alloy solder joints. The fatigue lifetime of Sn - Ag - Cu alloy solder joints and Sn - Pb eutectic alloy solder joints was 2 - 3 × 105 with no thermal cycling and was greatly reduced to 0.1 - 0.6 × 10⁵ after 8000 thermal cycles. The fatigue lifetime was also decreased to 0.6 - 1.0 × 10⁵ after isothermal heating for 16 000 min, but the decrease in fatigue lifetime was gradual compared to that after thermal cycling. The decrease in fatigue lifetime after smaller numbers of thermal cycles is explained by coarsening of the η phase, and the large decrease in fatigue lifetime after a large number of thermal cycles is explained by the appearance of cracks in the η phase during thermal cycling.     

Phase composition of thin oxide films on InSb

Two methods of phase analysis for solids with complex compositions have been developed in our previous investigations.The first method is thermodynamic analysis which enables a phase diagram to be plotted and by means of this the spatial distribution of phases as a result of chemical interactions between two different solids at an interface may be predicted.The second method is cyclic voltammetry using carbon paste electrodes; with this method it is possible to analyse the phase composition of small objects, e.g. thin (about 0.01 μm) films. The limit of detection of phases by this method is about 10¹⁵ cm^-3, i.e. about two orders of magnitude lower than that of modern expensive Auger electron spectroscopy, electron spectroscopy for chemical analysis and other surface analysis methods.Both methods were applied to the InSb/native oxide system. Using the first method three alternative ternary In-Sb-O diagrams were constructed and the experimental data obtained with the second method permitted us to select the most probable diagram.Our results showed that thin (about 0.1 μm) native oxide films on InSb have multilayer structures in which each layer has a different phase composition. When the oxidation occurs under quasi-equilibrium conditions the phase compositions from the InSb surface to the top of the film are as follows: I, In₂O₃+Sb; II, In₂O₃+Sb₂O₃+Sb; III, In₂O₃+Sb₂O₄; IV, InSbO₄. However, when the In-Sb-O system is far from equilibrium during oxidation, unstable phase complexes such as Sb₆O₁₃+Sb₂O₃ or In₂O₃+Sb₂O₅ may be observed; films obtained by anodic oxidation of InSb in 0.1 M KOH are an example of this situation.     

Experimental determination of solid–liquid interfacial energy for succinonitrile solid solution in equilibrium with the succinonitrile–(D) camphor eutectic liquid

The equilibrated grain boundary groove shapes for Succinonitrile (SCN) solid solution in equilibrium with the Succinonitrile (SCN)–D Camphor (DC) eutectic liquid were directly observed. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficient and solid–liquid interface energy for SCN solid solution in equilibrium with the SCN–DC eutectic liquid has been determined to be (5.39 ± 0.27) × 10⁻⁸ K m and (7.88 ± 0.79) × 10⁻³ J m⁻² with present numerical method and Gibbs–Thomson equation, respectively. The grain boundary energy of SCN rich phase of the SCN–DC eutectic system has been determined to be (14.95 ± 1.79) × 10⁻³ J m⁻² from the observed grain boundary groove shapes. Thermal conductivity ratio of the liquid phase to the solid phase for SCN–0.16 mole % DC alloy has also been measured.     

Deformation mechanisms of a bimodal eutectic Mg72Cu5Zn23 ultrafine composite

Deformation behavior of a Mg₇₂Cu₅Zn₂₃ alloy containing bimodal eutectic structure has been systematically investigated based on microstructural changes upon different amounts of compressive strain. The microstructural evolution of the sample at the early stage of the deformation up to 3% strain reveals that a large number of twins form homogeneously in the α-Mg phase of the coarse eutectic structure. After further deformation to failure, propagation of cracks takes place along the interface between the fine and coarse eutectic structures forming a typical dimple-like morphology on the fracture surface, indicative of the effective dissipation of the stress.     

Microstructures formed by directional solidification of two ternary eutectic alloys of Bi–Cd–In system

Abstract

Microstructures of the two ternary eutectic alloys of the Bi–Cd–In system were studied using slow unidirectional solidification, followed by quenching to form a representative solid/liquid interface for subsequent observation. The eutectic reactions were found to take the form L?BiIn+BiIn₂+Cd at 77.5°C and L?BiIn₂+_?+Cd at 61.5°C. The 77.5°C eutectic was observed to be of the faceted (BiIn)–faceted (Cd)–non-faceted (BiIn₂) type, while all three phases of the 61.5°C eutectic showed faceting. The BiIn and BiIn₂ phases of the 77.5°C eutectic formed a quasiregular microstructure with the Cd phase growing relatively independently. The phases of the 61.5°C eutectic tended to form a lamellar microstructure with a BiIn₂–?–Cd–_?–BiIn₂ phase sequence. Both eutectics were observed to obey the usual phase spacing law, λ²R=constant, where λ is the phase spacing and R is the growth rate.     

InSb/InAs quantum dots grown by liquid phase epitaxy

The first original results on the growth of quantum dots (QDs) in the InSb/InAs system by liquid phase epitaxy (LPE) are reported. The density and dimensions of QDs were studied by methods of scanning probe microscopy and atomic force microscopy. The surface density, shapes, and dimensions of LPE-grown nanoislands depend on the growth conditions (temperature, cooling rate, and solution melt-substrate contact time). In the interval of temperatures T = 420–445°C, homogeneous arrays of InSb quantum dots on InAs(100) substrates were obtained with an average height of H = 3.4 ± 1nm, a radius of R = 27.2 ± 7.5 nm, and a density of up to 1.9 × 10¹⁰ cm^?2.     

Electrical and microstructural investigation of Au/Pd/ri ohmic contacts for AIGaAs/GaAs heterojunction bipolar transistors

Abstract

The microstructure and electrical properties of as deposited and annealed Au (400 nm)/Pd (75 nm)/Ti (10 nm) contact structures to p type GaAs, C doped with a concentration of 5 × 10¹⁸ and 5 × 10¹⁹ cm^?3, have been investigated using transmission electron microscopy, and current-voltage measurements as afunction of temperature in the range 198–348 K. The specific contact resistivities have also been measured using the transmission line method. It was found that increasing the epilayer doping level by an order of magnitude, from 5 × 10¹⁸ to 5 × 10¹⁹ cm^?3, caused the dominant current transport mechanism to change from thermionic field emission to field emission. For the lower level doped epilayers generationrecombination within the depletion region was found to be the dominant current transport mechanism for temperatures below 289 K. The contacts to the more highly doped epilayers (C doped, 5 × 10¹⁹ cm^?3) had specific contact resistivities of 0·08 ± 0·03 Ωmm and 0·05 ± 0·06 Ωmm, respectively. These values, together with a minimal metal penetration in the semiconductor of <15 nm, indicate that these contacts are suitable for heterojunction bipolar device applications.

MST/3325     

Tensile and fatigue behaviour of Ni–Ni3Si eutectic in situ composites

A Ni–Ni₃Si composite was fabricated via a eutectic reaction (Ni–Ni₃Si) using a rapidly cooled directional solidification technique at a solidification rate of 40?μm?s^?1. The composite consisted of approximately 62.2% Ni–Si solid solution and 37.8% Ni–Ni₃Si eutectic phase in volume. Four-point bend fatigue tests were carried out on the composite. The fatigue strength of the alloy was measured to be 520?MPa (maximum cyclic stress). It was found that the fatigue cracks were preferably initiated in the Ni–Ni₃Si eutectic phase, and that the Ni matrix was fractured in a cleavage fashion. It was probably attributed to the high level of supersaturated Si in the Ni matrix, which led to inducing the embrittlement of the Ni matrix.