Electronic Materials

It is text book for 2nd year engineering undergraduates of electronics and communication engineering department of Abdul Kalam Technical University Lucknow Uttar Pradesh India. The book was co-written by eminent scientist/engineer of University Science Instrumentation Centre University of Delhi Prof. Dinesh.  The book contains chapters on semiconductor materials, crystal structure, bonding forces, charge carriers, excess carriers, junction properties, field effect transistors, bipolar junction transistor, optoelectronic devices and materials, negative conductance microwave devices and four layer power devices.

Using a combination of first principles and semiempirical calculation, we explore the structural, electronic, and optical properties of a wide range of perovskite (ABX3) nanoparticle of different size and composition. The variations of the BX3 backbone structure considered include all possible combinations of the cations B=Pb,Sn and the anions X=Cl,Br,I, while the interstitial cation A is either methylamonium (MA), or formamidinium (FA), or guanidine amine (GA), or dimethylamine (DEA). Our results indicate that the orientational disorder of the A moieties may affect the structural and electronic properties of the NPs while the optical properties exhibit a clear dependence on the NPs’ size and the types of B cations and X anions, but they are quite insensitive to the type of A cation.

The Cr 2ϩ doped CdS 0.8 Se 0.2 crystals were grown by the vertical, self-seeded, physical vapor transport (PVT) technique. Good quality, crack-and inclusionfree single crystals were grown with an average Cr 2ϩ concentration of 5 ϫ 10 18 cm Ϫ3 . Different source-to-tip distances were used to improve the segregation coefficient (Cr crystal /Cr source ) of the grown crystals. It was observed that lowering the source-to-tip distance increases the segregation coefficient dramatically. With a 2-cm source-to-tip distance, good quality crystals were grown with uniform Cr 2ϩ concentration throughout the ingot. The segregation coefficient was found to be ϳ0.85. The composition of the crystals was also found to be fairly uniform along the length and across the diameter.

Epitaxial growth of a metal (CoSi2)/insulator (CaF2) nanometer-thick layered structure on Si(lll) was demonstrated and the resistivity of CoSi2 epilayer in this structure was investigated. An epitaxial CoSi2 layer on CaF2 was obtained by the two-step growth technique, i.e. solid phase epitaxy with the epitaxial Si layer grown in the first step and Co deposited in the second step. This technique was shown to be effective to avoid the Co agglomeration on CaF2 layer observed in the co-evaporation of Si and Co. An epitaxial CaF2 layer was formed on CoSi2/CaF2 at low substrate temperature (450°C) with partially ionized and accelerated CaF2 beam, to avoid Co agglomeration in the CoSi2/CaF2 underlayer as well. Obtained results showed a single-crystalline nature in reflection high-energy electron diffraction (RHEED) and transmission electron microscopy (TEM) observations. The resistivity of a few nm-thickCoSi2 epilayers embedded by CaF2 has been investigated. We studied thickness and annealing temperature dependence of resistivity and showed that a minimum resistivity of 30~tD cm was obtained in a 2 nm-thickCoSi2 sample annealed at 860°C.

A nickel silicide process for Si1-xGex, Si1-x-yGexCy, and Si1-yCy alloy materials compatible with Si technology has been developed. Low-resistivity-phase (12–20 µΘ cm) nickel silicides have been obtained for these alloys with different low sheet-resistance temperature windows. The study shows that thin (15–18 nm) silicide layers with high crystalline quality, smooth silicide surface, and smooth interface between silicide and the underlying material are achievable. The technique could be used to combine the benefits of Ni silicide and Si1-xGex, Si1-x-yGexCy, and Si1-yCy alloys. The technique is promising for Si or Si1-xGex, Si1-x-yGexCy, and Si1-yCy alloy-based metal-oxide semiconductor, field-effect transistors (MOSFETs) or other device applications.

The doping process of Zn is widely used for fabricating InP-based optoelectronic devices. Methods generally used for Zn doping in InP are in-situ doping during the growth and postgrowth ex-situ doping, such as closed ampoule diffusion and diffusion from evaporated Zn-thin film. In-situ Zn doping by metal-organic chemical vapor deposition shows low doping efficiency due to the high-equilibrium vapor pressure of Zn. 1 Moreover, the hole concentration saturates approximately at 1-2 ϫ 10 18 /cm 3 , presumably due to a similar self-concentration mechanism.

ABSTRACT The SmartCut process was first developed to obtain silicon-on-insulator (SOI) materials. Now an industrial process, the main Unibond SOI-structure trends are reported in this paper. Many material combinations can be achieved by this process, because it appears to enable the generic development of new structures. Several of the new structures combining different materials and different bonding layers are described. These include SiGe and strained-Si films onto an oxidized Si wafer, silicon-on-insulating multilayer (SOIM) structures, and InP or 4H-SiC film transfers onto low-cost substrates via metallic or even refractory conductive-film bonding layers. More recently, an original bonding process based on mark patterning, wafer bonding, and layer transfer has been proposed to obtain structures in which the relative crystalline-axis orientations of both the film and the substrate can be controlled accurately. In this case, a SmartCut process that includes a mark-patterning step appears well suited for precise control of axis orientations. A procedure is described to obtain an ultra-thin Si film bonded onto a Si wafer. An example of a pure screw-dislocation network achieved by the mark patterning, bonding, and layer-transfer process is reported in this paper. The results have important implications for nanostructure development.

Applying the discharge crucible (DC) method, the viscosity, density, and surface tension were determined for Sn-9Zn and Sn-2.92Ag-0.4Cu-3.07Bi (SAC + Bi) alloys. For comparison, the dilatometric, maximum bubble pressure, and capillary flow methods were used for measurements of these same physicochemical properties for the Sn-2.92Ag-0.4Cu-3.07Bi (SAC + Bi) alloy. The measurements were performed for Sn-9Zn and SAC + Bi alloys in the temperature range from 513 K to 723 K and 530 K to 1180 K, respectively. The experimental data obtained show that addition of Bi to SAC increases the density and decreases the surface tension and viscosity in comparison with SAC solder. Additionally it was found that the properties studied by different methods (maximum bubble pressure, dilatometric, capillary flow, and discharge crucible) were almost identical.

Using ZnO nano-colloids, thin films of ZnO have been deposited and characterized. The nano-colloid has been synthesized using a top-down wet chemistry method starting from submicron ZnO particles. The steric stabilization technique is implemented using stearic acid as a capping agent to prevent agglomeration of the ZnO nanoparticles. A stable suspension is achieved, exhibiting strong optical absorbance and a band edge at 376 nm. The simple chemistry enables a uniform film on a variety of substrates using spin coating. Current-voltage (I–V) measurements of ZnO films deposited on quartz after annealing treatment show a resistivity of 1.89×105 Ω · cm.

By measuring the drift velocity of electrons in diamond as a function of applied electric field, we
demonstrate that ultra-pure diamond exhibits negative differential electron mobility in the [100] direction
below 140 K. Negative electron mobility is normally associated with III–V or II–VI semiconductors with
an energy difference between different conduction band valleys. The observation of negative mobility in
diamond, an elemental group IV semiconductor, is explained in terms of repopulation effects between
different equivalent conduction band valleys using a model based on the Boltzmann equation.

Electroless Ni-P layers with three different P contents (6.1 wt.%, 8.8 wt.%, and 12.3 wt.%) were deposited on copper (Cu) substrates. Multilayered samples of Sn-3.5Ag/Ni-P/Cu stack were prepared and subjected to multiple reflows at 250°C. A tensile test was performed to investigate the effect of P content on the solder joint strength. The low P samples exhibited the highest joint strength after multiple reflows, while the strength of medium and high P samples decreased more rapidly. From interfacial analysis, the Ni 3 Sn 4 intermetallic compound (IMC) formed at the interface of low P sample was found to be more stable, while the one of medium and high P samples spalled into the molten solder. The IMC spallation sped up the consumption of electroless Ni-P, leading to the large formation of Cu-Sn IMCs. Fractographic and microstructural analyses showed that the degradation in solder joint strength was due to the formation of layers of voids and growth of Cu-Sn IMCs between the solder and the Cu substrate.

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Electroless Ni-P layers with three different P contents (6.1 wt.%, 8.8 wt.%, and 12.3 wt.%) were deposited on copper (Cu) substrates. Multilayered samples of Sn-3.5Ag/Ni-P/Cu stack were prepared and subjected to multiple reflows at 250°C. A tensile test was performed to investigate the ...

Heteroepitaxial growth of Ge films on Si is necessary for the progress of integrated Si photonics technology. In this work, an in-house assembled plasma enhanced chemical vapor deposition reactor was used to grow high quality epitaxial Ge films on Si (100) substrates. Low economic and thermal budget were accomplished by the avoidance of ultra-high vacuum conditions or high temperature substrate pre-deposition bake for the process. Films were deposited with and without plasma assistance using germane (GeH4) precursor in a single step at process temperatures of 350–385 °C and chamber pressures of 1–10 Torr at various precursor flow rates. Film growth was realized at high ambient chamber pressures (>10−6 Torr) by utilizing a rigorous ex situ substrate cleaning process, closely controlling substrate loading times, chamber pumping and the dead-time prior to the initiation of film growth. Plasma allowed for higher film deposition rates at lower processing temperatures. An epitaxial gro...

We report on low-resistance and thermally stable Pd/Ru ohmic contacts to surface-treated p-GaN (3 ϫ 10 17 cm Ϫ3 ). It is shown that annealing at 500°C for 2 min in a N 2 ambient improves ohmic contact properties. Specific contact resistance is measured to be 9.2(Ϯ0.2) ϫ 10 Ϫ4 and 2.4(Ϯ0.2) ϫ 10 Ϫ5 ⍀cm 2 for the as-deposited and annealed samples, respectively. Atomic force microscopy results show that the surfaces of both the contacts are remarkably smooth with a root-mean-square (rms) roughness of about 0.6 nm. The current-voltagetemperature (I-V-T) and calculation results indicate that, for the as-deposited contact, thermionic field emission is dominant, while for the annealed contact, field emission dominates the current flow.

The aim of this study is to understand the effect of the glass frit chemistry used in thick-film Ag pastes on the electrical performance of the silicon solar cell. The study focuses on the physical behavior of the glass frit during heat treatment as well as the resulting Ag−Si contact interface structure. We observe that the glass frit transition temperature (Tg) and softening characteristics play a critical role in the contact interface structure. The glass transition temperature also significantly influences the contact ohmicity of the thick-film metal grid. A high glass frit transition temperature generally results in thinner glass regions between the Ag bulk of the grid and the Si emitter. It was found that a glass frit (with high Tg) that crystallizes fast during the firing cycle after etching the silicon nitride and Si emitter results in smaller Ag crystallite precipitation at the contact interface. This results in smaller junction leakage current density (Jo2) and higher open-circuit voltage (Voc). Using high Tg pastes (with the appropriate Ag powder size), greater than 0.78 fill factors and >17.4% efficiency were achieved on 4 cm2 untextured single crystal Si solar cells with 100 Ω/sq emitters.

We report on magneto-optical investigations of Ni-doped amorphous AlN (a-AlN) thin films. The a-AlN was grown by radiofrequency (rf) sputtering on Si (0001) substrates at low temperature and doped with Ni at fixed concentrations with different a-AlN layer thicknesses. As-grown a-AlN:Ni layers were annealed up to 900°C for 5 min and 15 min time duration in nitrogen ambient at atmospheric pressure. Each sample was characterized by the magneto-optical Kerr effect (MOKE) in both polar and longitudinal geometries. Only the 65-nm-thick a-AlN:Ni layers showed linear enhancement of magnetization after thermal treatment up to 900°C, indicating the presence of a critical a-AlN:Ni layer thickness supporting the formation of magnetic domains. No measurable MOKE signal was observed in the longitudinal geometry for any tested samples with different thicknesses. This observation confirms that the easy magnetization axis in a-AlN:Ni layers is out of plane due to the strong magnetic anisotropy observed in polar MOKE geometry. The morphology of as-grown and annealed a-AlN:Ni films was characterized by atomic force microscopy (AFM), magnetic force microscopy (MFM), and scanning electron microscopy (SEM) and revealed the existence of nanoclusters. The size distribution of nanoclusters was studied as a function of annealing time and temperature, and the results correlate well with those obtained from the MOKE measurements.

Tantalum-doped tin oxide transparent conductive thin films were deposited on glass substrates by radio frequency and direct current reactive magnetron cosputtering methods in an argon and oxygen environment. Optimization of the thin films for photovoltaic applications was performed using a dimensionless figure of merit by combining electrical and transparency properties. The optimized thin film showed a weight-averaged transmittance of 83%, a band gap value of 3.2 eV, resistivity of 5.2 9 10 À3 X cm, and bulk carrier concentration of 1.2 9 10 20 cm À3. The lowest resistivity among all films was 2.1 9 10 À3 X cm, corresponding to a weight-averaged transmittance of 62%. The optimized deposition condition was carried out by co-sputtering on heated substrates at 270°C. Thin films deposited under this optimized condition were applied for our perovskite solar cells, and demonstrated promising power conversion efficiency.

In this paper, indium tin oxide (ITO) thin films were prepared by unipolar and bipolar direct current (DC)-pulsed magnetron sputtering in a mixture of argon and oxygen onto unheated glass substrates. The target of ITO with 10 wt.% tin is used. The influences of polar modes (unipolar and bipolar); output frequencies (0 to 33 kHz); and times and off times on the optical, electrical, and structural properties of ITO films are investigated. The correlations between the deposition parameters and the film properties are discussed. It is found that the resistivity with 10−3 Θ-cm and transmittance with ≥90% of amorphous ITO films can be prepared by the reactive bipolar DC-pulsed sputtering with t on− between 45 µs and 85 µs (i.e., t on−/t on+ is 9–17), and t on+, t off− and t off+ are constant at 5 µs, 10 µs, and 5 µs, respectively. An optimal condition, based on the polar mode and frequency of reactive-pulsed sputtering, for obtaining the high transmittance and low resistivity of ITO films is suggested.

This paper is concerned with the mechanics of interfacial fracture that are active in two common testing configurations of solder joint reliability. Utilizing eutectic Pb-Sn/Cu as a reference system and assuming the presence of a predefined crack size in the intermetallic compound (IMC) layer, stress intensity factors (K I and K II) at the crack are numerically calculated for the two given configurations. The analysis of the tensile test configuration reveals that the fracture occurs by the crack-opening mode (K I mode), as anticipated, but that it is greatly assisted by the viscoplasticity of the solder. With nonuniform viscoplastic deformation across the joint, K I is found to increase much more rapidly than it would without the solder, decreasing the critical crack size to the micron scale. The same mechanism is also responsible for the development of a K II comparable to K I at the crack tip, that is, |K I /K II | $ 1. It is also found that the predominant fracture mode in the bump shear configuration is crack opening, not crack shearing. This is an unexpected result, but numerical analyses as well as experimental observations provide consistent indications that fracture occurs by crack opening. During shear testing, bump rotation due to nonzero rotational moment in the test configuration is found to be responsible for the change in the fracture mode because the rotation makes K I become dominant over K II. With rotational moment being affected by the geometry of the bump, it is further found that the fracture behavior may vary with bump size or shape.

The bump resistance of flip-chip solder joints was measured experimentally and analyzed by the finite-element method. Kelvin structures for flip-chip solder joints were designed and fabricated to measure the bump resistance. The measured value was only about 0.9 mΘ at room temperature, which was much lower than that expected. Three-dimensional (3-D) modeling was performed to examine the current and voltage distribution in the joint. The simulated value was 7.7 mΘ, which was about 9 times larger than the experimental value. The current crowding effect was found to be responsible for the difference in bump resistance. Therefore, the measured bump resistance strongly depended on the layout of the Kelvin structure. Various layouts were simulated to investigate the geometrical effect of bump resistance, and a significant geometrical effect was found. A proper layout was proposed to measure the bump resistance correctly. The Kelvin structure would play an important role in monitoring void formation and microstructure changes during the electromigration of flip-chip solder joints.

Low-cycle fatigue (LCF) tests on as-cast Sn-3.5Ag, Sn-3Ag-0.5Cu, Sn-3Ag-0.5Cu-1Bi, and Sn-3Ag-0.5Cu-3Bi solders was carried out using a noncontact strain-controlled system at 20°C with a constant frequency of 0.1 Hz. The addition of Cu does not significantly affect the fatigue life of eutectic Sn-Ag solder. However, the fatigue life was significantly reduced with the addition of Bi. The LCF behavior of all solders followed the Coffin-Manson relationship. The fatigue life of the present solders is dominated by the fracture ductility and can be described by the ductility-modified Coffin-Manson's relationship. Steps at the boundaries of dendrite phases were the initiation sites for microcracks for Sn-3.5Ag, Sn-3Ag-0.5Cu, and Sn-3Ag-0.5Cu-1Bi solders, while for Sn-3Ag-0.5Cu-3Bi solder, cracks initiated along both the dendrite boundaries and subgrain boundaries in the dendrite phases. The linking of these cracks and the propagation of cracks inside the specimen occurred both transgranularly through eutectic phases and intergranularly along dendrite boundaries or subgrain boundaries.

In this paper we show the latest achievements of HgCdTe-based infrared bispectral focal plane arrays (FPAs) at LETI infrared laboratory. We present and compare the two different pixel architectures that are studied now in our laboratory, named ''NPN'' and ''pseudo-planar''. With these two technologies, a wide range of system applications in dual-band detection can be covered. Advantages of both architectures will be pointed out. We also review performances obtained with these different architectures. The first one has been studied for several years in our laboratory, and we review results obtained on FPAs of size 256 · 256 pixels on a 25 lm pitch, in the MWIR/MWIR (3 lm/5 lm) range. Very high noise equivalent temperature difference (NETD) operability is obtained, at 99.8% for the k c = 3 lm band and 98.7% for the k c = 5 lm band. The second one has been developed more recently, to address other applications that need temporal coherence as well as spatial coherence. We show detailed performances measured on pseudo-planar type FPAs of size 256 · 256 pixels on a 30 lm pitch, in the MWIR/LWIR (5 lm/9 lm) range. The results are also very promising for these prototypes, with NETD as low as 15 mK for an integration time as short as 1 ms, and good operability. The main manufacturing issues are also presented and discussed for both pixel architectures. Challenging process steps are, firstly, molecular beam epitaxy (MBE) HgCdTe heterostructure growth, on large substrates (cadmium zinc telluride) and heterosubstrates (germanium), and, secondly, detector array fabrication on a nonplanar surface. In particular, trenches or hole etching steps, photolithography and hybridization are crucial to improve uniformity, number of defects and performances. Some results of surface, structural and electrical characterizations are shown to illustrate these issues. On the basis of these results, the short-term and longterm objectives and trends for our research and development are presented, in terms of pixel pitch reduction, wavelengths, and dual-band FPA size.

The fluorine stability of two parylenes, aliphatic-fluorinated AF-4 (␣, ␣, ␣Ј, ␣Ј poly(p-tetrafluoroxylylene) and aromatic-fluorinated VT-4 (2, 3, 5, 6 poly(p-tetrafluoroxylylene), were investigated underneath Al, Al 2 O 3 , and TaN X overlayers with and without exposure to oxygen reactive-ion etching (RIE). No fluorine diffusion was observed for Al films deposited onto the as-received parylenes. However, after oxygen RIE, x-ray photoelectron spectroscopy (XPS) depth profiling detected fluorine diffusion throughout Al and to a lesser extent Al 2 O 3 but in contrast to Ta 2.67 N. Metal-fluoride bonding was evident at the metal/parylene interface for all the overlayers after the parylene was exposed to oxygen RIE and annealed.

This paper consid,ers the influence of _composite pulse eleclToplated nickel/tin WVS"j iayering: o" lft" mitigation of Sn whiskei growttr. The performance of ih".o-porit. p"ulsed plating-method in the mitigation of Sn whisker growth is also .o*pu".d with t'wo otf,er plating procedures. The results indicate that, uit.r a period of 6 months, the compoiite pulsed ptating-technique demonstrates much better resistance to Sn whisker growth than other plating t..ftttiq"es such as pure Sn plating and Sn plating \^Tth a Ni.underlayer onto a brass substrate subjected to various envirbnmental conditions. The primalY conclusions are based on the analysis of microstructural characteristics, the u"""ugu residual stress distribution in the film over different time periods .o*p,it"a by x-ray diffraction, the formation of intermetallic compounds, and the amounf of Sn whisker growth in each case.

Lead telluride-based materials demonstrate the highest thermoelectric performance in the temperature range from 200°C to 400°C, and they are of interest for numerous waste heat recovery applications. Unfortunately, these conventionally grown materials are usually very brittle, which results in significant material loss during module manufacturing and a decrease in module reliability when subjected to continuous vibrations common for automotive applications. We present a hot extrusion process developed for the first time for PbTe which yields polycrystalline materials with strong mechanical properties combined with high thermoelectric performance. n-Type lead telluride was extruded from conventionally synthesized and powdered material at temperatures in the range of 450°C to 520°C depending on material stoichiometry. The extruded rods were of cylindrical shape with 2.54 cm diameter and lengths up to 40 cm. Young's modulus measured using mechanical spectroscopy varied from 59 GPa to 51 GPa for temperatures in the range of 20°C to 300°C. Slicing and dicing of extruded rods to obtain cubical samples with 2 mm side demonstrated no difficulties, illustrating the material homogeneity and its potential for manufacturing module legs. The microstructure of the material was studied by scanning electron microscopy. Doping with antimony iodide during the milling process controls the conduction electron concentration in the range from 1 9 10 19 cm À3 to 6 9 10 19 cm À3 . For optimized doping of 0.08 wt.% SbI 3 , the maximum thermoelectric figure of merit (ZT) reaches a value of 0.99 at 380°C, as measured by the Harman method. The combination of high thermoelectric performance and improved fracture toughness makes this novel hot-extruded polycrystalline PbTe material highly competitive for many applications.

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Velika ponuda autmatskih osigurača, žarulja, kućnih zvona, razdvojni ormari i razvojne kutije, prekidače i utičnice, sabirnice, stezaljke, motorne sklopke, zidne ventilatore, a potom i razne kvalitetne rasvjete kao što su dekorativne svjetiljke, svjetiljke panik, prijenosne svijetiljke i alata, prije svega profesionalnog alata za što kvalitetnije obavljanje poslova.

A thermodynamic description of the Al-Ca-Sr system is carried out using the modified quasichemical model. The three binary systems Al-Ca, Al-Sr, and Ca-Sr have been re-optimised based on the experimental phase equilibria and thermodynamic properties available in the literature. Good agreement was obtained for the calculated binary phase diagrams and their thermodynamic properties. The established database of this system predicted one saddle point, one peritectic, seven quasi-peritectics, and two ternary eutectics.

Piezoelectric materials are widely referred to as “smart” materials because they can transduce mechanical pressure acting on them to electrical signals and vice versa. They are extensively utilized in harvesting mechanical energy from vibrations, human motion, mechanical loads, etc., and converting them into electrical energy for low power devices. Piezoelectric transduction offers high scalability, simple device designs, and high‐power densities compared to electro‐magnetic/static and triboelectric transducers. This review aims to give a holistic overview of recent developments in piezoelectric nanostructured materials, polymers, polymer nanocomposites, and piezoelectric films for implementation in energy harvesting. The progress in fabrication techniques, morphology, piezoelectric properties, energy harvesting performance, and underpinning fundamental mechanisms for each class of materials, including polymer nanocomposites using conducting, non‐conducting, and hybrid fillers are d...

Most commercial copper nanoparticles are covered with an oxide shell and cannot be sintered into conducting lines/films by conventional thermal sintering. To address this issue, past efforts have utilized complex reduction schemes and sophisticated chambers to prevent oxidation, thereby rendering the process cost ineffective. To alleviate these problems, we demonstrate a reactive sintering process using intense pulsed light (IPL) in the present study. The IPL process successfully removed the oxide shells of copper nanoparticles, leaving a conductive, pure copper film in a short period of time (2 ms) under ambient conditions. The in situ copper oxide reduction mechanism was studied using several different experiments and analyses. We observed instant copper oxide reduction and sintering through poly(N-vinylpyrrolidone) functionalization of copper nanoparticles, followed by IPL irradiation. This phenomenon may be explained by oxide reduction either via an intermediate acid created by ultraviolet (UV) light irradiation or by hydroxyl (-OH) end groups, which act like long-chain alcohol reductants.

In this study, a systematic experimental work was performed to evaluate the reliability of the anisotropic conductive adhesive film (ACF) joint at high temperature for flip-chip-on-flex (FCOF) assemblies. A four-point probe method was developed to measure the contact resistance at high temperature. Measurement was also conducted along the length of the chip. The correlation between the increased resistance and the failure mechanism was investigated using scanning electron microscopy (SEM). Initially, the contact resistance increased linearly with rising temperature, but later, it increased abruptly. This changeover was related to the glass-transition temperature (T g ) of the ACF matrix. The coefficient of thermal expansion (CTE) is very high at temperatures above T g ; thus, the ACF swells too much, reducing the mechanical contact of the particles with the bump and/or pad. Again, as the adhesive strength becomes weaker at temperatures above the glass transition, it is unable to resist the thermal stress of the flex. The cumulative thermal stress at the edges dislodges the particles from the interconnection. Even below T g , the thermal stress at the edges is higher than the middle point. Thus, the contact resistance varied from the middle joint of the chip to that of the corner at the same high temperature. To reduce the contact resistance at the corner joint of the FCOF packages bonded by ACF, a square-shaped chip instead of a chip with a higher aspect ratio should be used. It was also suggested to use an adhesive with a higher glass-transition temperature and lower CTE.

The high-intensity, high-resolution x-ray source at the European Synchrotron Radiation Facility (ESRF) has been used in x-ray diffraction (XRD) experiments to detect intermetallic compounds (IMCs) in lead-free solder bumps. The IMCs found in 95.5Sn3.8Ag0.7Cu solder bumps on Cu pads with electroplated-nickel immersion-gold (ENIG) surface finish are consistent with results based on traditional destructive methods. Moreover, after positive identification of the IMCs from the diffraction data, spatial distribution plots over the entire bump were obtained. These spatial distributions for selected intermetallic phases display the layer thickness and confirm the locations of the IMCs. For isothermally aged solder samples, results have shown that much thicker layers of IMCs have grown from the pad interface into the bulk of the solder. Additionally, the XRD technique has also been used in a temperature-resolved mode to observe the formation of IMCs, in situ, during the solidification of the solder joint. The results demonstrate that the XRD technique is very attractive as it allows for nondestructive investigations to be performed on expensive state-of-the-art electronic components, thereby allowing new, lead-free materials to be fully characterized.

In this study, ball grid array (BGA) packages with Sn-3.0Ag-0.5Cu (SAC305) solder balls were reballed with Sn-37Pb solder balls. Three different reballing methods were used. The non-reballed lead-free BGAs were assembled with SAC305 and Sn-37Pb solder pastes to form the lead-free and mixed assemblies. The reballed Sn-Pb BGAs were assembled with Sn-37Pb solder paste to form the reballed Sn-Pb assemblies. All assemblies were subjected to a temperature cycling test with a temperature range of À55°C to 125°C. For the same component type, the reballed BGA assemblies showed similar temperature cycling reliability regardless of the reballing methods. However, the temperature cycling reliability of the reballed assemblies was worse than that of the mixed and the lead-free assemblies. The mean cycles-to-failure of the mixed assemblies was larger than or equal to that of the lead-free assemblies. Failure analysis revealed that the failure site in reballed Sn-Pb assemblies was located in the bulk solder at the component side regardless of the component type and the reballing method, indicating that the reballing method did not influence the crack propagation in reballed assemblies. The mixed assemblies had the same failure site as the lead-free assemblies, i.e., in the bulk solder at the component side. The microstructure differences between the tin-lead, lead-free, and mixed assemblies are also discussed in detail.

The solid-state annealing behavior of two high-lead solders, 95Pb5Sn and 90Pb10Sn (in wt.%), was examined. After reflow, Cu 3 Sn intermetallics formed on the Cu under bump metallurgy (UBM) for both solder alloys. However, solidstate annealing produced significantly different reaction morphologies for the two solder compositions. The Cu 3 Sn intermetallics spalled off faster at higher temperatures in the 95Pb5Sn solder. In the case of 90Pb10Sn solder, the Cu 3 Sn intermetallics continued to grow even after 1500 h at 170°C. The difference was explained by a two-step phenomenon-Sn diffusion from the bulk solder region to the solder/Cu 3 Sn interface (J Sn ), and subsequent intermetallic formation (I Cu3Sn ) by interdiffusion of Cu and Sn. For 95Pb5Sn, the relation, J Sn Ͻ I Cu3Sn was postulated because of insufficient supply of Sn. The relation, J Sn Ͼ I Cu3Sn was suggested for the continuous intermetallic growth of the 90Pb10Sn solder. Although a small difference was expected between the two quantities in both solder alloys, the difference in the solid-state annealing behavior was dramatic.

In this work, tensile creep tests for Sn-1.0Ag-0.5Cu-0.02Ni solder have been conducted at various temperatures and stress levels to determine its creep properties. The effects of stress level and temperature on creep strain rate were investigated. Creep constitutive models (such as the simple power-law model, hyperbolic sine model, double power-law model, and exponential model) have been reviewed, and the material constants of each model have been determined based on experimental results. The stress exponent and creep activation energy have been studied and compared with other researchers' results. These four creep constitutive models established in this paper were then implemented into a user-defined subroutine in the ANSYSä finite-element analysis software to investigate the creep behavior of Sn-1.0Ag-0.5Cu-0.02Ni solder joints of thin fine-pitch ball grid array (TFBGA) packages for the purpose of model comparison and application. Similar simulation results of creep strain and creep strain energy density were achieved when using the different creep constitutive models, indicating that the creep models are consistent and accurate.

A series of pure siliceous and Zn-modified MCM-41 spheres were synthesized at room temperature, atmospheric pressure and at short reaction times. Mesoporous molecular sieves were characterized by a number of techniques: XRD, N 2 adsorption, TEM, XPS and NH 3 -TPD. Pure siliceous MCM-41 exhibits the typical hexagonal array of well-defined pores with a mean pore diameter of 3.0 nm. Addition of a small percentage of Zn (Zn/Si ratio 0.02) into the synthesis gel produces a material with increased lattice parameter (a o ), pore diameter and total adsorption capacity. These results suggest the incorporation of zinc, with a larger ionic radius, into the silica framework. Unfortunately, higher zinc contents (Zn/Si ratio 0.04) produce a deterioration of the long-range order of the material, together with a decrease in the surface area and total pore volume. In this sample, the presence of small ZnO nanoparticles embedded into the silica matrix can be envisaged. From a catalytic point of view, these Zn-modified MCM-41 mesoporous molecular sieves appear as quite interesting materials to be used as a catalyst by themselves or as a support for noble metal catalysts.

The growth of cubic GaN on 3C-SiC/Si(100) by metal-organic chemical vapor deposition (MOCVD) under various growth temperatures, thicknesses of 3C-SiC, and V/III ratios was studied. The fractions of cubic and hexagonal phases in the films were estimated from the integrated x-ray diffraction intensities of the cubic (002) and hexagonal (1011) planes. A smooth SiC layer, a high growth temperature, and a moderate V/III ratio are three key factors for the nucleation of the cubic phase and its subsequent growth. Hexagonal GaN with its c-axis perpendicular to the substrate preferentially grows at the low temperature of 750°C. The inclusion of the cubic phase increases with increasing growth temperature. The optimum growth conditions for dominant cubic GaN formation were a growth temperature of 950°C, a 1.5 µm thick SiC layer, and a V/III ratio of 1500. With these growth conditions, a cubic GaN layer with the cubic component of 91% was obtained.

We have developed a system for the simultaneous measurement of the electrical conductivity and the Seebeck coefficient for thermoelectric samples in the temperature region of 300 K to 1000 K. The system features flexibility in sample dimensions and easy sample exchange. In order to verify the accuracy of the setup we have referenced our system against the NIST standard reference material 3451 and other setups and can show good agreement. The developed system has been used in the search for a possible high temperature Seebeck standard material. FeSi2 emerges as a possible candidate as this material combines properties typical for thermoelectric materials with large scale fabrication, good spatial homogeneity, and thermal stability up to 1000 K.

A novel thermosonic (TS) bonding process for gold wire bonded onto chips with copper interconnects was successfully developed by depositing a thin, titanium passivation layer on a copper pad. The copper pad oxidizes easily at elevated temperature during TS wire bonding. The bondability and bonding strength of the Au ball onto copper pads are significantly deteriorated if a copper-oxide film exists. To overcome this intrinsic drawback of the copper pad, a titanium thin film was deposited onto the copper pad to improve the bondability and bonding strength. The thickness of the titanium passivation layer is crucial to bondability and bonding strength. An appropriate, titanium film thickness of 3.7 nm is proposed in this work. One hundred percent bondability and high bonding strength was achieved. A thicker titanium film results in poor bond-ability and lower bonding strength, because the thicker titanium film cannot be removed by an appropriate range of ultrasonic power during TS bonding. The protective mechanism of the titanium passivation layer was interpreted by the results of field-emission Auger electron spectroscopy (FEAES) and electron spectroscopy for chemical analysis (ESCA). Titanium dioxide (TiO2), formed during the die-saw and die-mount processes, plays an important role in preventing the copper pad from oxidizing. Reliability of the high-temperature storage (HTS) test for a gold ball bonded on the copper pad with a 3.7-nm titanium passivation layer was verified. The bonding strength did not degrade after prolonged storage at elevated temperature. This novel process could be applied to chips with copper interconnect packaging in the TS wire-bonding process.

Interface evolution caused by thermal aging under different temperatures and durations was investigated by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that approximately 30-nm-thick and discontinuous Cu-Al intermetallic compounds (IMCs) were present in the initial bonds before aging. Cu-Al IMCs grew under thermal aging with increasing aging time. The growth kinetics of the Cu-Al IMCs was correlated to the diffusion process during aging; their combined activation energy was estimated to be 1.01 eV. Initially, Al-rich Cu-Al IMCs formed in the as-bonded state and early stage of aging treatment. Cu 9 Al 4 was identified by selected-area electron diffraction (SAD) as the only type of Cu-Al IMC present after thermal aging at 250°C for 100 h; this is attributed to the relatively short supply of aluminum to the interfacial reaction.

Recently, Au/Ni/p-type GaN ohmic contacts annealed in an air ambient have been widely investigated. However, to obtain a low specific-contact resistance, the annealing window is limited. In this study, to understand the oxidation function of metallic Ni, the Au/Ni/p-type GaN structure was annealed in an air ambient for 10 min at various temperatures. Using x-ray photoelectron spectroscopy (XPS) analysis, the metallic Ni was oxidized into NiO and NiO1.3 compositions at annealing temperatures of 500°C and 600°C, respectively. However, metallic Ni still existed on the interface of the Ni/p-type GaN annealed at 400°C. The associated barrier heights of 0.42 eV, 0.21 eV, and 0.31 eV were obtained with p-type GaN for the Ni, NiO, and NiO1.3 contacts, respectively. The hole concentrations of p-type NiO and p-type NiO1.3 were 2.6×1016 cm−3 and 2.0×1018 cm−3, respectively. The lower hole concentration of the p-type NiO would lead to reducing the valence-band bending of the p-type GaN, as well as the barrier height for holes crossing from the p-type NiO to the p-type GaN. The formation of NiO was thus an important issue for lowering the specific-contact resistance of the Au/Ni/p-type GaN ohmic contacts annealed in an air ambient.

AlxGayIn1−x−yAs/InP strained-layer multiple-quantum-well lasers emitting at 1.3 µm have been grown by solid source molecular beam epitaxy, and the performance characteristics have been studied. The lasers contain 4, 5, or 6 compressively strained quantum wells in the active region. They exhibit low transparency current densities, high gain coefficients, and high characteristic temperatures compared to conventional GaInAsP/InP quantum well lasers. The results show that desired lasing features can be achieved with relatively simple layer structures if the doping profiles and waveguide structures are properly designed and the material is grown to high structural perfection.

The worldwide transition to lead-free electronics has increased the usage of several lead-free pad finishes for electronic assembly manufacturers, including immersion silver, immersion tin, electroless nickel-immersion gold, and organic solderability preservatives. This study assesses and compares immersion silver as a circuit board finish in terms of its ease of use, wettability, solderability, shelf life, appearance, solder joint strength, intermetallic and void formation, reliability, and costs.

New metal/polymer composite filaments for fused deposition modeling (FDM) processes were developed in order to observe the thermo-mechanical properties of the new filaments. The acrylonitrile butadiene styrene (ABS) thermoplastic was mixed with copper and iron particles. The percent loading of the metal powder was varied to confirm the effects of metal particles on the thermo-mechanical properties of the filament, such as tensile strength and thermal conductivity. The printing parameters such as temperature and fill density were also varied to see the effects of the parameters on the tensile strength of the final product which was made with the FDM process. As a result of this study, it was confirmed that the tensile strength of the composites is decreased by increasing the loading of metal particles. Additionally, the thermal conductivity of the metal/polymer composite filament was improved by increasing the metal content. It is believed that the metal/polymer filament could be used to print metal and large-scale 3-dimensional (3D) structures without any distortion by the thermal expansion of thermoplastics. The material could also be used in 3D printed circuits and electromagnetic structures for shielding and other applications.