Solid-liquid interdiffusion (SLID) bonding in the Au-In system: experimental study and 1D modelling

Au-In bonds with a nominal composition of about 60 at.% In were fabricated for use in wafer-level packaging of MEMS. The microstructure of the bonds was studied by scanning electron microscopy. The bond hermeticity was then assessed using oxidation of Cu thin discs predeposited within the sealed packages. The three intermetallic compounds AuIn2, AuIn and Au7In3 were observed. Their thickness evolution during bonding and after subsequent heat treatment was successfully modelled using a finite difference model of diffusion, thermodynamic data and diffusion coefficients calibrated from isothermal diffusion couples. 17% of the packages were hermetic and, although the origin of the leaks could not be clearly identified, it appeared that hermeticity was correlated with the unevenness of the metallisation and/or wafer and the fact that the bonds shrink due to density differences as the relative fractions of the various phases gradually evolve

Microwave plasma-assisted reactive HiPIMS of InN films: Plasma environment and material characterisation

This work focuses on the low temperature fabrication process of InN thin films via microwave plasma-assisted reactive high power impulse magnetron sputtering (MAR-HiPIMS). The influence of microwave plasma on the HiPIMS discharge process at various nitrogen flows and microwave powers was monitored and characterised through in situ diagnostics, including following HiPIMS I(V,t) curves, optical emission spectroscopy (OES), as well as performing time-resolved Langmuir probe and time-of-flight mass spectroscopy (ToF-MS) measurements. This was followed by the deposition of InN films via standard reactive HiPIMS (reference sample) and MAR-HiPIMS and their characterisation via X-ray diffraction (XRD), reflectometry (XRR), as well as scanning and transmission electron microscopy (SEM, TEM). It was found that the microwave plasma facilitates the dissociation/activation of nitrogen species and supplies seed electrons to the magnetron discharge plasma. Furthermore, the energy of the incoming ions was determined via ToF-MS, and it was possible to identify their plasma origin and temporal behaviour. The produced R-HiPIMS sample was highly metallic, with no nitride phase detected. The MAR-HiPMS film, however, was stoichiometric and exhibited (0002) direction texturing, with an optical bandgap of approx. 1.5 eV, electron concentration of 2.72 × 1020 cm−3 and electron mobility of 7.16 cm2V−1 s−1 (in the range for polycrystalline InN)

Amorphous silicon passivated contacts for diffused junction silicon solar cells

Carrier recombination at the metal contacts is a major obstacle in the development of high-performance crystalline silicon homojunction solar cells. To address this issue, we insert thin intrinsic hydrogenated amorphous silicon [a-Si:H(i)] passivating films between the dopant-diffused silicon surface and aluminum contacts. We find that with increasing a-Si:H(i) interlayer thickness (from 0 to 16 nm) the recombination loss at metal-contacted phosphorus (n +) and boron (p+) diffused surfaces decreases by factors of ∼25 and ∼10, respectively. Conversely, the contact resistivity increases in both cases before saturating to still acceptable values of ∼ 50 mΩ cm2 for n+ and ∼100 mΩ cm2 for p+ surfaces. Carrier transport towards the contacts likely occurs by a combination of carrier tunneling and aluminum spiking through the a-Si:H(i) layer, as supported by scanning transmission electron microscopy-energy dispersive x-ray maps. We explain the superior contact selectivity obtained on n+ surfaces by more favorable band offsets and capture cross section ratios of recombination centers at the c-Si/a-Si:H(i) interface

From pulsed-DCMS and HiPIMS to microwave plasma-assisted sputtering: Their influence on the properties of diamond-like carbon films

The fabrication of high-hardness non-hydrogenated diamond-like carbon (DLC) via standard magnetron sputtering (MS) is often hindered by the low sputtering yields and ionisation rates of carbon, therefore investigations into pulsed alternatives of MS, else sputtered species post-ionisation methods, are of particular interest. This work focuses on investigating the influence of pulsed-direct current MS (pDCMS), high power impulse magnetron sputtering (HiPIMS) and their microwave plasma-assisted (MA-pDCMS, MA-HiPIMS) variants on the properties of the fabricated DLC films. Two setups were used for the pDCMS- and HiPIMS-based methods, respectively. The films were characterised using Raman spectroscopy, nanoindentation, X-ray reflectometry and scanning electron microscopy, where the pDCMS-produced films were additionally characterised by film-stress measurements. Moreover, in situ time-resolved Langmuir probe plasma analysis was performed under HiPIMS and MA-HiPIMS conditions to analyse the influence of the magnetron and microwave plasmas on one another. For both DCMS- and HiPIMS-based procedures, it was found that the addition of microwave plasma did not facilitate attaining hardnesses beyond 30 GPa, however, it did enable modifying the morphology of the films. Furthermore, this study shows the potential of synchronised sputtering with substrate biasing, as well as the importance of microwave plasma source positioning in relation to the substrate

Measurements of local chemistry and structure in Ni(O)-YSZ composites during reduction using energy-filtered environmental TEM

Energy-filtered transmission electron microscopy images are acquired during the reduction of a NiO–YSZ composite in H2 up to 600 °C. Temperature-resolved quantitative information about both chemistry and structure is extracted with nm spatial resolution from the data, paving the way for the development of detailed reduction models

Hydrogen plasma treatment for improved conductivity in amorphous aluminum doped zinc tin oxide thin films

Improving the conductivity of earth-abundant transparent conductive oxides (TCOs) remains an important challenge that will facilitate the replacement of indium-based TCOs. Here, we show that a hydrogen (H-2)-plasma post-deposition treatment improves the conductivity of amorphous aluminum-doped zinc tin oxide while retaining its low optical absorption. We found that the H-2-plasma treatment performed at a substrate temperature of 50 degrees C reduces the resistivity of the films by 57% and increases the absorptance by only 2%. Additionally, the low substrate temperature delays the known formation of tin particles with the plasma and it allows the application of the process to temperature-sensitive substrates. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License

Nd-nickelate solid oxide fuel cell cathode sensitivity to Cr and Si contamination

The stability of Nd-nickelate, considered as an alternative solid oxide fuel cell (SOFC) cathode material, was evaluated in this work on its tolerance towards contaminants

High performance amorphous Zn-Sn-O: impact of composition, microstructure, and thermal treatments in the optoelectronic properties

Zinc and tin oxides are both earth-abundant materials with demonstrated applicability as electrodes in several optoelectronic devices. The presence of grain boundaries in these polycrystalline films generally limits the electron mobility. By a combinatorial study of ZnO and SnO2, a transparent conducting amorphous zinc tin oxide (ZTO) electrode, free of grain boundaries, with a dense (void-free) microstructure has been developed. We show how tuning the stoichiometry (Zn4.5Sn30.2O65.3) and film's microstructure during sputtering deposition, allows achieving electron mobilities up to 25 cm(2)/Vs and free carrier concentrations of similar to 7 x 10(19) cm(-3). The effects of post-deposition thermal treatments are furthermore studied. The ZTO films keep their dense amorphous microstructure upon annealing up to 500 degrees C, as confirmed by cross-section TEM and XRD, while presenting a clear improvement in electron mobility up to 35 cm(2)/Vs when annealed in oxygen-rich atmospheres

Passivated contacts to n+ and p+ silicon based on amorphous silicon and thin dielectrics

Carrier recombination at the metal contact regions has now become a critical obstacle to the advancement of high efficiency diffused junction silicon solar cells. The insertion of a thin dielectric interlayer - forming a metal-insulator-semiconductor (MIS) contact - is a known approach to reduce contact recombination. However, an insulator thickness less than 25 Å is usually required for current transport, making it difficult to simultaneously achieve good surface passivation. This paper compares standard MIS contacts to a newly developed contact structure, involving hydrogenated amorphous silicon (a-Si:H) over-layers. The contact structures are trialed on both n+ and p+ lightly diffused surfaces, with SiO2 and Al2O3 insulator layers, respectively. In both cases significant improvements in the carrier-selectivity of the contacts is achieved with the addition of the a-Si:H over-layers. Simulations of idealized cell structures are used to highlight the performance and technological benefits of these carrier-selective structures over standard locally diffused contacts

Cr-poisoning in (La,Sr)(Co,Fe)O-3 cathodes after 10,000 h SOFC stack testing

After 10,000 h solid oxide fuel cell (SOFC) stack operation, the Cr-poisoning situation in (La0.6Sr0.4) (Co0.2Fe0.8)O-3 (LSCF)-based cathode material is depicted in this work. Systematic Cr profiling by energy-dispersive X-ray spectroscopy (EDS), from post-operation samples taken at different locations within the air flow field, reveals Cr accumulation in electrochemically active cathode regions, although the major amount of Cr is trapped in inactive surface-proximal cathode regions; the 20 m LSCF current collector does not fully impede the Cr access to the functional cathode