Mikko Nelo

Formulation of Screen Printable Cobalt Nanoparticle Ink for High Frequency Applications

In this work, magnetic metallic cobalt nanoparticles with an average particle size of 28nm were processed as a dry powder with surface coating material and other organic additives to form a screen-printable ink to be cured at 110 - C. EFTEM and TGA-DSC- MS-analyses were used to measure the thickness of the polymer, its coverage on cobalt nanoparticles and the inorganic solid content of the ink. The resolution of the printed patterns and the print quality were evaluated by surface profller, FESEM and optical microscopy. The relative permeability of the thick fllm patterns with good printability was measured with a shorted microstrip structure over the frequency range of 0.2 to 4GHz and complex permeability values were calculated from measured scattering parameter data. The ink attained real part of complex permeability values of up to 5.13 at 200MHz with 70wt.% of magnetic flller. The developed ink can be utilized in various printed electronics applications such as antenna substrates and magnetic sensors.

Using the emulsion technique and an iron catalyst to enhance the wood protection properties of tall oil

ZusammenfassungThe aim of this study was to investigate whether the two problems relating to wood protection with tall oil can be solved with one single treatment. The results showed that it is possible to combine the use of an iron catalyst to enhance the drying properties with the emulsion technique to reduce the amount of oil needed. In addition to enhanced drying properties, the iron catalyst also considerably improved the water repellent efficiency.

Fully printed memristors for a self-sustainable recorder of mechanical energy

Memristors have attracted significant interest in recent years because of their role as a missing electronic component and unique functionality that has not previously existed. Since the first discoveries of the existence of memristive materials, various different fabrication processes for memristors have been presented. Here, a simple additive fabrication process is demonstrated where memristors were deposited on a polymer substrate by conventional inkjet printing. The memristor structure was printed on a 125 μm thick polyethylene terephthalate (PET) substrate by sandwiching a thin layer of TiO x between two silver nanoparticle ink electrodes. Current–voltage (IV) characterization measurements were performed and they showed clear memristive behavior when voltage pulse amplitude varied between −1.5 V and 1.5 V. The corresponding resistance change is approximately between 150 Ω and 75 kΩ. In order to demonstrate the switching scheme in practical application, printed memristors and a printed voltage doubler were connected with a piezoelectric element. The element was subjected to impact-type excitation thus producing an electric charge that was able to switch the memristor between high and low resistive states. These results pave the way for an exploitation of cost-efficient, self-sufficient, all-printable memory elements for wide utilization in future electronics applications.

Dielectric properties of novel polyurethane–PZT–graphite foam composites

Flexible foam composite materials offer multiple benefits to future electronic applications as the rapid development of the electronics industry requires smaller, more efficient, and lighter materials to further develop foldable and wearable applications. The aims of this work were to examine the electrical properties of three- and four-phase novel foam composites in different conditions, find the optimal mixture for four-phase foam composites, and study the combined effects of lead zirconate titanate (PZT) and graphite fillers. The flexible and highly compressible foams were prepared in a room-temperature mixing process using polyurethane, PZT, and graphite components as well as their combinations, in which air acted as one phase. In three-phase foams the amount of PZT varied between 20 and 80 wt% and the amount of graphite, between 1 and 15 wt%. The four-phase foams were formed by adding 40 wt% of PZT while the amount of graphite ranged between 1 and 15 wt%. The presented results and materials could be utilized to develop new flexible and soft sensor applications by means of material technology.

Facile synthesis of nanostructured carbon materials over RANEY® nickel catalyst films printed on Al2O3 and SiO2 substrates

A quick and convenient approach that combines a printing process and chemical vapor deposition is developed for facile construction of nanostructured metal–carbon composite structures. Films of porous RANEY® nickel catalyst particles are deposited on various substrates by stencil printing from dispersions of the catalyst and poly(methyl methacrylate) in 2-(2-butoxyethoxy)ethyl acetate. After removing the organic binders at elevated temperatures, the mesoporous Ni film is applied as a growth template for synthesizing nanostructured carbon materials on the surface. Depending on the synthesis conditions, carbon nanofibers and nanotubes, as well as graphite deposits, are found to form on the substrates, allowing a robust and scalable production of carbon based inert electrodes of high specific surface area. In addition to structural characterization of the composites by means of scanning and transmission electron microscopy, Raman spectroscopy, X-ray diffraction, thermal gravimetric and surface adsorption analyses, the produced carbon/RANEY® nickel composites are also studied as electrodes in electrochemical capacitors (specific capacitance of ∼12 F g−1) and in field emitter devices with a low turn-on field (<1.0 V μm−1). The results indicate the carbon/RANEY® nickel composites are suitable for direct integration on substrates used frequently in microelectronics.

Inkjet-Printed Memristor: Printing Process Development

In the last five years, research on memristive devices has been under ever increasing interest. Additionally, recent development in printed techniques provides new approaches to fabricate also memristive devices in inexpensive and flexible manner. Thus their research is an important effort towards fully printed electronics applications. In this work, an organometallic precursor solution for a memristive layer was synthesised and formulated for inkjet-printable form. Layers of the solution were determined with surface profilometry in order to find feasible layer thickness for memristive behaviour. Memristors were inkjet-printed on copper- and titanium-coated glass sheets, and various heat-treatments were carried out. The influence of the heat-treatments on the durability and resistance values of the memristors was evaluated. Microstructural and phase changes in the memristive layer were observed with X-ray diffraction and field emission scanning electron microscopy analysis.