Scooter D. Johnson

Characterization of as-deposited and sintered yttrium iron garnet thick films formed by aerosol deposition

We have employed the aerosol deposition method (ADM) to direct-write 39-µm-thick polycrystalline films of yttrium iron garnet at room temperature onto sapphire at a rate of 1–3 µm/min as a first step toward integration into microwave magnetic circuits. The resulting randomly oriented polycrystalline films are composed of fractured compact nanosized crystallites. Upon postdeposition sintering at 1280 °C the density and magnetic properties become closer to those of the bulk. These results suggest that the ADM shows promise for depositing very thick films at high deposition rates to produce structurally and magnetically uniform films that retain the structural properties of the starting powder.

ZnS/diamond composite coatings for infrared transmission applications formed by the aerosol deposition method

The deposition of nano-crystalline ZnS/diamond composite protective coatings on silicon, sapphire, and ZnS substrates, as a preliminary step to coating infrared transparent ZnS substrates from powder mixtures by the aerosol deposition method is presented. Advantages of the aerosol deposition method include the ability to form dense, nanocrystalline lms up to hundreds of microns thick at room temperature and at a high deposition rate on a variety of substrates. Deposition is achieved by creating a pressure gradient that accelerates micrometer- scale particles in an aerosol to high velocity. Upon impact with the target substrate the particles fracture and embed. Continued deposition forms the thick compacted lm. Deposition from an aerosolized mixture of ZnS and diamond powders onto all targets results in linear trend from apparent sputter erosion of the substrate at 100% diamond to formation of a lm with increasing fractions of ZnS. The crossover from abrasion to lm formation on sapphire occurs above about 50% ZnS and a mixture of 90% ZnS and 10% diamond forms a well-adhered lm of about 0.7 μm thickness at a rate of 0.14 μm/min. Resulting lms are characterized by scanning electron microscopy, pro lometry, infrared transmission spectroscopy, and x-ray photoemission spectroscopy. These initial lms mark progress toward the future goal of coating ZnS substrates for abrasion resistance.

Aerosol Deposition of Yttrium Iron Garnet for Fabrication of Ferrite-Integrated On-Chip Inductors

We have employed aerosol deposition (AD) to deposit 39 μm thick polycrystalline films of yttrium iron garnet at room temperature onto sapphire at a rate of 1-3 μm/min as an initial investigation of utilizing AD for fabricating ferrite-integrated on-chip inductors. We characterize the structural and magnetic properties of the as-received starting powder, as-deposited film, and a pressed puck formed from the starting powder. Results show that the films are comprised of randomly oriented polycrystalline grains with structural and magnetic properties that closely resemble that of the starting powder. Results from coating a gold single-turn inductor show an increase in inductance of 79% up to ~300 MHz without affecting the Q-factor. These results demonstrate AD as a promising technique for depositing thick ferrite films at high deposition rates for low-temperature fabrication of ferrite-integrated on-chip inductors.

Magnetic and structural properties of sintered bulk pucks and aerosol deposited films of Ti-doped barium hexaferrite for microwave absorption applications

We report structural, compositional, and magnetic properties for a commercially available doped barium hexaferrite material produced by Temex Ceramics. The material is designed to absorb electromagnetic radiation near the upper edge of the Ku frequency band ( ∼18 GHz) and may serve as an important component to microwave circuitry. To aid in the development of such circuits that may utilize this or similar materials, we present results of the material properties of the raw starting powder, sintered pucks, and in the form of a film deposited by aerosol deposition. We find that the structural and magnetic properties are consistent with the parent compound, barium hexaferrite. Samples sintered at 1250 °C show some degree of preferred magnetic and structural orientation. Chemical analysis indicates that a titanium dopant has been added and that the material demonstrates broad absorption above 13 GHz that improves with sintering temperature. To our knowledge, this is the first report on the properties of this c...

Real-time Growth Study of Plasma Assisted Atomic Layer Epitaxy of InN Films by Synchrotron X-ray Methods

The temporal evolution of high quality indium nitride (InN) growth by plasma-assisted atomic layer epitaxy (ALEp) on a-plane sapphire at 200 and 248 °C was probed by synchrotron x-ray methods. The growth was carried out in a thin film growth facility installed at beamline X21 of the National Synchrotron Light Source at Brookhaven National Laboratory and at beamline G3 of the Cornell High Energy Synchrotron Source, Cornell University. Measurements of grazing incidence small angle x-ray scattering (GISAXS) during the initial cycles of growth revealed a broadening and scattering near the diffuse specular rod and the development of scattering intensities due to half unit cell thick nucleation islands in the Yoneda wing with correlation length scale of 7.1 and 8.2 nm, at growth temperatures (Tg) of 200 and 248 °C, respectively. At about 1.1 nm (two unit cells) of growth thickness nucleation islands coarsen, grow, and the intensity of correlated scattering peak increased at the correlation length scale of 8.0 a...

Effect of varying plasma properties on III-nitride film growth by plasma enhanced atomic layer epitaxy

Plasma enhanced atomic layer epitaxy (PEALE) is a layer-by-layer crystalline growth technique that is based on a pair of self-terminating and self-limiting gas-surface half-reactions, in which at least one half-reaction involves species from a plasma. The inclusion of plasma generally offers the benefit of substantially reduced growth temperatures and greater flexibility in tailoring the gas-phase chemistry to produce varying film characteristics. The benefits plasmas provide come at the cost of a complex array of process variables that often challenge the ability to predict, a priori, the influence of any one input parameter. This work focuses on the use of plasma diagnostics to inform the choice of process conditions for PEALE. Optical emission spectroscopy in the plasma source and charged particle collectors at the substrate are employed to characterize a Fiji 200 (Veeco) deposition tool. In particular, the authors assess the total ion flux reaching the substrate surface and the relative fractions of atomic and molecular species generated in the plasma source under a variety of gas input flow fractions (Ar/N2 and Ar/N2/H2) used in the PEALE growth of AlN and InN films. Changes in plasma parameters are then linked with changes in film characteristics.Plasma enhanced atomic layer epitaxy (PEALE) is a layer-by-layer crystalline growth technique that is based on a pair of self-terminating and self-limiting gas-surface half-reactions, in which at least one half-reaction involves species from a plasma. The inclusion of plasma generally offers the benefit of substantially reduced growth temperatures and greater flexibility in tailoring the gas-phase chemistry to produce varying film characteristics. The benefits plasmas provide come at the cost of a complex array of process variables that often challenge the ability to predict, a priori, the influence of any one input parameter. This work focuses on the use of plasma diagnostics to inform the choice of process conditions for PEALE. Optical emission spectroscopy in the plasma source and charged particle collectors at the substrate are employed to characterize a Fiji 200 (Veeco) deposition tool. In particular, the authors assess the total ion flux reaching the substrate surface and the relative fractions of a...

Plasma-assisted atomic layer epitaxial growth of aluminum nitride studied with real time grazing angle small angle x-ray scattering

Wide bandgap semiconducting nitrides have found wide-spread application as light emitting and laser diodes and are under investigation for further application in optoelectronics, photovoltaics, and efficient power switching technologies. Alloys of the binary semiconductors allow adjustments of the band gap, an important semiconductor material characteristic, which is 6.2 eV for aluminum nitride (AlN), 3.4 eV for gallium nitride, and 0.7 eV for (InN). Currently, the highest quality III-nitride films are deposited by metalorganic chemical vapor deposition and molecular beam epitaxy. Temperatures of 900 °C and higher are required to deposit high quality AlN. Research into depositing III-nitrides with atomic layer epitaxy (ALEp) is ongoing because it is a fabrication friendly technique allowing lower growth temperatures. Because it is a relatively new technique, there is insufficient understanding of the ALEp growth mechanism which will be essential to development of the process. Here, grazing incidence small...