Column-like Grains Research Articles

Enhanced ferromagnetism in Ni doped Aurivillius compound Bi6Fe2Ti3O18 thin films prepared by chemical solution deposition

Ni doped Aurivillius Bi6Fe2Ti3O18 (xBFNTO, x = 0, 0.3, 0.6, 0.9) thin films with greatly enhanced ferromagnetism have been successfully synthesized on fused quartz substrate using a non-toxic solution-based method. The use of earth abundant materials and convenient annealing processes imply the great potential on industrial manufacture of multiferroic information storage. It can be found that Ni ions doping not only leads to an enlarged crystal lattice but also contributes to the formation of larger and column-like grains compared with pure BFTO thin film. Besides, Raman spectroscopy makes additional remarks on the specific doping position of Ni ions. Most importantly, highly improved magnetism has been detected by M-H curves which can be resulted from the anti-DM interaction. The doping level of Ni and magnetization of xBFNTO shows non-linear relationship which is possible to be explained by multivalent Ni ions (Ni2+, Ni3+), and the optimum doped concentration has been explored at x = 0.6 (Ms at 4.806 emu/cm3). This work moves a solid step on studies of layer-structured Aurivillius compounds.

Microstructure, electric flame-off characteristics and tensile properties of silver bonding wires

Compared with gold wire, silver wire is cheaper and enjoys better electrical conductivity. These days copper wire is becoming more commonly used, but the reliability of its bonding still has problems in some pads. Since Ag wires have similar hardness and bonding properties to Au wires, they can be applied in some pads. In the present study, the annealing effect (at 225–275 °C for 30 min) on the tensile mechanical properties of silver wires with ϕ = 23 μm was investigated. In addition, the microstructural characteristics and the mechanical properties before and after an electric flame-off (EFO) process were also studied. Experimental results indicate that with annealing temperatures of more than 250 °C, the silver wires possessed a fully annealed structure, the tensile strength and the hardness decreased, and the elongation was raised significantly. Through recrystallization, the matrix structure transformed from long-thin grains to equiaxed grains. The microstructure of the free air ball (FAB) of the various annealed wires after an EFO process were column-like grains. The column-like grains grew from the heat-affected zone (HAZ) to the Ag ball. Under the thermal effect of EFO, the necks of the Ag balls underwent recrystallization and grain growth was induced, and the annealed Ag wires had a shorter zone of HAZ (220 μm). Additionally, the decreased hardness and the low strength of the HAZ resulted in the breakage sites of the EFO wires being in the HAZ near the Ag balls. The bonding strength and the neck-strength of the Ag wires were more than 7gf and possessed excellent bonding properties.

A simulation study of the effect of the diverse valence-band offset and the electronic activity at the grain boundaries on the performance of polycrystalline Cu(In,Ga)Se 2 solar cells

The paper presents a two-dimensional simulation study of a polycrystalline Cu(In,Ga)Se 2 (CIGS) solar cell with various shapes of grains inside the CIGS absorber layer. The grain boundaries (GBs) with a diverse valence-band offset ( VBO) and the density of defect states ( N tA) are considered so as to evaluate their effects on the performance of the CIGS cell. The numerical simulations show that a CIGS cell with column-like grains can achieve a high conversion efficiency ( η), while the η of a CIGS cell with diamond-like grains is low if the VBO at the GBs exceeds 0.4 eV. The VBO at which the η of the CIGS cell with diamond-like grains peaks is found at 0.20–0.27 eV. A favorable VBO mainly depends on the shape of the grains, but it also depends on the N tA. The simulations of the CIGS cells in the substrate and superstrate configurations showed that their performances change if the VBO is varied. This result also implies that the configuration of the CIGS cell is important and the substrate configuration with larger grains in the space-charge region has a considerable advantage if the VBO ranges from 0 eV to 0.2 eV.

An investigation into the crystallization and electric flame-off characteristics of 20 μm copper wires

Copper wires are used in electronic packaging, however the workability and reliability still need to be improved. This work investigates the microstructural characteristics and mechanical properties of annealed wires and un-annealed wires. In addition, the interface bonding characteristics of Al pads are also studied. Experimental results indicate that at the two annealing conditions of 610 °C/0.02 s and 510 °C/0.4 s, 20 μm copper wires possessed a fully annealed structure. Compared with the un-annealed wire, the annealed tensile strength and the annealed hardness decreased, and the annealed elongation increased. Through thermal crystallization, the matrix structure transformed from long, thin grains to equiaxed grains and a few annealed twins. The microstructure of the free air ball (FAB) after an EFO process consisted of column-like grains, and grew from the heat-affected zone (HAZ) to the Cu ball. As for bonding testing, the pull strength of the bonded samples increased with increasing the Al film thickness (from 76 nm to 800 nm).

Recrystallization, Electric Flame-Off Characteristics, and Electron Backscatter Diffraction of Copper Bonding Wires

In the present study, the neck fracture properties of annealed wire with ? = 20 ?m (0.8 mil) at 200°C ~ 300°C for 1 h and unannealed wire were compared. The microstructural characteristics, the mechanical properties and the texture transition using electron back scatter diffraction methods before and after an electric flame-off (EFO) process were also studied. Experimental results indicate that the annealing temperatures of more than 225°C, the 20 ?m copper wires possessed a fully annealed structure, the tensile strength and the hardness decreased, and the elongation was raised. Through recrystallization, the matrix structure transferred from long, thin grains to equiaxed grains and a few annealed twins. The microstructure of the free air ball (FAB) after an EFO process consisted of column-like grains, and grew from the heat-affected zone (HAZ) to the Cu ball. For the 225°C annealed and unannealed wires, their preferred orientations on the wire and the neck were ?100?//AD. Under the thermal effect of EFO, the orientation of the Cu balls were mainly ?101?//AD and ?111?//AD for annealed wires. Additionally, the hardness of the Cu balls and the strength of the neck sites of the EFO wires were able to affect the reliability of the copper wire bonding.

Electric Flame-Off Characteristics and Fracture Properties of 20 μm Thin Copper Bonding Wire

In the present study, the neck fracture properties of annealed wire with � ¼ 20 mm (0.8 mil) at 225 � C for 1 hour and un-annealed wire were compared. In addition, the microstructural characteristics, the mechanical properties and the texture transition using EBSD methods before and after an electric flame-off (EFO) process were also studied. Experimental results indicate that the recrystallization temperature of the as-drawn wire was � 225 � C, and the annealed copper wires possessed a fully annealed structure. Through recrystallization, the matrix structure transferred from long, thin grains to equiaxed grains and a few annealed twins. The microstructure of the free air ball (FAB) after an EFO process consisted of column-like grains, and grew from the heat-affected zone (HAZ) to the Cu ball. For the annealed and un-annealed wires, their preferred orientations on the wire and the neck were h100i == AD. Under the thermal effect of EFO, the orientation of the Cu balls were mainly h101i == AD and h111i == AD for annealed wires. Additionally, the hardness of the Cu balls and the strength of the neck sites of the EFO wires were able to affect the reliability of the copper wire bonding. [doi:10.2320/matertrans.MRA2008145]

Recrystallization and fracture characteristics of thin copper wire

In this study, the annealed effect (at 150 °C ∼ 250 °C for 1 h) on the tensile mechanical properties of thin copper wires with φ = 25 μm (1 mil) was investigated. The microstructural characteristics and the mechanical properties before and after an electric flame-off (EFO) were also studied. Results indicate that with annealing temperatures of more than 200 °C, the wires possessed a fully annealed structure, the tensile strength and the hardness decreased, and the elongation was raised significantly. Through recrystallization, equiaxed grains and a few annealed twins formed in the matrix structure. The microstructures of the free air ball (FAB) of the various wires after EFO contained column-like grains. The column-like grains grew from the heat-affected zone (HAZ) to the Cu ball, and the preferred orientation was . According to Weibull’s reliability analysis, the failure rates of all the specimens were the modus of wear-failure. The tensile strength and the reliability of both the 200 °C and 250 °C annealed wires in the HAZs showed the highest values of all.

Recrystallization Effect and Electric Flame-Off Characteristic of Thin Copper Wire

Compared with gold wire, copper wire is cheaper and possesses lower cost, greater strength and better electrical conductivity, and therefore is becoming more commonly used. But the lower ductility and oxidation undermine the reliability of copper wire bonding, making the wire susceptible to breaking. In the present study, the annealed effect (at 150-250°C for 1 hour) on the tensile mechanical properties of copper wires with Φ = 25μm (1 mil) was investigated. In addition, the microstructural characteristics and the mechanical properties before and after an electric flame-off (EFO) process were also studied. Experimental results indicate that with annealing temperatures of more than 200°C, the copper wires possessed a fully annealed structure, the tensile strength and the hardness decreased, and the elongation was raised significantly. Through recrystallization, the matrix structure transferred from long, thin grains to equiaxed grains and a few annealed twins. The microstructures of the free air ball (FAB) of the variation annealing wires after an EFO process were column-like grains. The column-like grains grew from the heat-affected zone (HAZ) to the Cu ball, and the preferred orientation was (100). Under the thermal effect of EFO, the necks of the Cu balls underwent recrystallization and the grain growth was induced. Additionally, the decreased hardness and the strength of the HAZ resulted in the breakage sites of the EFO wires being in the HAZ near the Cu balls.

Defect Structure of Heteroepitaxial Zn2-2xCuxInxS2 Layers Grown by Pulsed Laser Deposition on (111) Si, (001) Si and (001) GaP Substrates

Zn2-2xCuxInxS2 (ZCIS) films might be attractive for absorbers in solar cells (band gap variation from Eg(ZnS) = 3.67 eV to Eg(CuInS2) = 1.53 eV at room temperature). Therefore, we have grown ZCIS on (001)GaP, (001)Si and (111)Si substrates at 500°C by pulsed laser deposition (PLD). Epitaxial growth on (001) GaP substrates could be proved for all compositions between ZnS and CuInS2. However, there is a striking asymmetry in twin nucleation that occurs for cubic ZCIS (CuInS2 content less than 22 mol-%) preferably on the (1̄1̄1) and (111) planes of the [1̄10] zone. In addition, beside the dislocations lying in-clined to the interface, perfect 60° misfit dislocations coexist that align parallel to [110] and [1̄10] , having b=1/2<011> and {111} slip planes inclined to the interface. Additional Cu- and/or In-sulfides could not be detected in the monocrystalline films. CuAu-I type ordering was observed for CuInS2-rich compositions as Zn0.22Cu0.46In0.32S, Zn0.044Cu0.544In0.412S and pure CuInS2 only. On (001) Si the films appear to be polycrystalline for all compositions between Zn0.2Cu0.4In0.4S and Zn0.62Cu0.19In0.19S. At Zn0.7Cu0.15In0.15S there is the transition between poly- and monocrystalline growth, i.e. the range of monocrystalline growth is strongly restricted to the lattice matched position. In these layers twins have been nucleated on all four inclined {111} planes. On chemically treated (111) Si the films grew epitaxially for compositions 0.1 ≤ x ≤ 0.7. They are monocrystalline, but consist of polysynthetically twinned column-like grains which are precisely oriented to the (111) Si sub-strate. Coherent Σ=3{111} twin boundaries exist parallel to the interface and incoherent Σ=3{112} grain boundaries are for-med perpendicular to it. Perfect dislocations that lie along <110> directions and parallel to the interface envelop the colums to form a dislocation network like a honeycomb. The films become polycrystalline for compositions x > 0.7. On non-treated (111) Si substrates, similar to the deposition on molybdenum-coated glass, the ZCIS films are polycrystalline, but a distinct <111> texture exists. Extended defects have been produced inside both the GaP and chemically treated Si substrates due to the preferred Cu out-diffusion from the layer. In the GaP substrates a Cu3P phase is formed but within the Si substrates amor-phisized regions occur exclusively. With increasing ZnS content the propensity to form these defects decreases appreciably.

Structural properties of thin Zn 0.62Cu 0.19In 0.19S alloy films grown on Si(111) substrates by pulsed laser deposition

Alloys of Zn 2−2 x Cu x In x S 2 (ZCIS) have been grown on Si(111) substrates by pulsed laser deposition (PLD). The thin films grew epitaxially on chemically treated Si(111) regardless of an about 2–5 nm thick interfacial amorphous layer between the ZCIS and the Si substrate. The particular Zn 0.62Cu 0.19In 0.19S layers under investigation consist of column-like grains propagating from the interface to the layer surface. Despite of the existence of the amorphous layer in the interfacial region each ZCIS grain is precisely oriented to the structure of the underlying silicon substrate and to the neighboring ZCIS grains without any azimuthal misorientation. Each individual column-like grain contains many twin lamellae of various thickness that lie parallel to the interface and, therefore, coherent Σ3{111} twin boundaries occur. Σ3{112} grain boundaries are formed perpendicular to the interface during the intergrowth of the individual columns. Perfect dislocations with their lines parallel to the interface envelop the columns and finally, a dislocation network like a honeycomb can be observed during TEM plane-view observation. However, polycrystalline ZCIS layers exhibiting a distinct 〈111〉 texture have been formed on untreated Si(111) substrates, where the 2–2.5 nm thick intermediate native layer consists of amorphous SiO x . The individual ZCIS grains were found to be polysynthetically twinned too. Amorphisized regions have always been produced inside the chemically treated Si substrates due to the out-diffusion of copper from the layer into the Si substrate that seems to be favored against that of Zn. However, the amorphous native SiO x layer which covers the untreated silicon substrates prevents substantially the out-diffusion of metal atoms from the layer into the substrate and, therefore, no diffusion-induced defects have been generated inside the untreated Si substrate.

Two-dimensional model of impurity diffusion in polysilicon-silicon structures

A model for B-diffusion in polysilicon-silicon structures is presented which allows for grain boundary motion, segregation of impurity-to-grain boundaries, different diffusivities in grain-and-grain boundaries, and influence of interfacial oxide layer thickness on the 2-D diffusion profile. The derivation of the model equations for cubic and column-like grains is discussed.