Stretchable conductive films were obtained by screen printing and thermal treatment of a homogenous ink comprising a thermally reducible silver formate complex, an acrylate monomer, and a radical initiator. In the curing process, both the filler nanoparticles and the polymer matrix are generated in situ, at temperatures as low as 100 degrees C. The obtained conductors, consisting of percolated silver nanoparticles embedded in a polymeric matrix, typically show a resistivity of (2-4) x 10(-5) Omega.m. When applied on an elastomeric substrate, the composite is stretchable up to 200% with very low R/R-0 values, which is unprecedented for stretchable silver composite inks. Quasi-in situ confocal laser scanning microscopy of the strained samples revealed an initial fracture strain above 40%, which is unusually high for metal-nanoparticle films. The described system was compared to some commercial stretchable screen-printing inks and proved superior with regard to both R/R-0 and resistance to cyclic tensile loading.

A method to combine additively manufactured substrates or foils and multilayer inkjet printing for the fabrication of sensor devices is presented. First, three substrates (acrylate, ceramics, and copper) are prepared. To determine the resulting material properties of these substrates, profilometer, contact angle, scanning electron microscope (SEM), and focused ion beam (FIB) measurements are done. The achievable printing resolution and suitable drop volume for each substrate are, then, found through the drop size tests. Then, layers of insulating and conductive ink are inkjet printed alternately to fabricate the target sensor structures. After each printing step, the respective layers are individually treated by photonic curing. The parameters used for the curing of each layer are adapted depending on the printed ink, as well as on the surface properties of the respective substrate. To confirm the resulting conductivity and to determine the quality of the printed surface, four-point probe and profilometer measurements are done. Finally, a measurement set-up and results achieved by such an all-printed sensor system are shown to demonstrate the achievable quality.

Resistive temperature sensors on two different commercially available uncoated paper substrates have been manufactured using inkjet printing of silver nanoparticles. Their dedication is to be integrated in lightweight materials made from natural fibre-reinforced biopolymers for condition monitoring during the manufacturing process and beyond. The printed sensors have nominal resistances of a few hundred Ohms and kOhms, depending on the roughness and porosity of the respective paper substrate. Compared to previous research in this field, the manufactured sensors were fully characterised and extensively tested as part of this work. Furthermore, the influence of the individual paper characteristics on the electrical properties was studied using white-light interferometry and SEM imaging. All sensors show a good linear temperature dependence, minimal hysteresis and low baseline drift in the temperature range of interest (20 degrees C - 80 degrees C). In an extended temperature range (-25 degrees C to 150 degrees C) and exposed to humidity (0%rH-80%rH) the accuracy and overall quality of the sensors decrease expectedly, still the temperature sensing principle can be exploited depending on the individual application and precision requirements.

A study to characterize surface and structural properties of 3D-printed metal substrates for multilayer inkjet-printing is presented. Such substrates can enable and alleviate the fabrication of smart and functional packages, implants or spare parts. For the characterization, a multilayer structure composed of an insulating layer and a superposed conductive layer is inkjet-printed onto the various 3D-printed metallic substrates. The printing is done using equivalent settings for all substrates. The characterization is based on microscopic and Focused Ion Beam (FIB) images, as well as profilometer and contact angle measurements of the substrates. Furthermore, microscopic images and four-point-probe resistance- and profilometer measurements are carried out, to gain insight into the quality of the multilayer print. We show the diversity in surface and structural properties of 3D-printed substrates, also for those fabricated using the same process. Also, the 3D-printed samples exhibit different wettability properties than metals processed using standard processes. Finally, we can also demonstrate the suitability of selected substrates for inkjet-printing.

A new fabrication technique based on the combined printing of Ag-nanoparticles and dielectric material was developed. The processing, composed of inkjet printing and intense pulsed light sintering/curing, enables a fast, controllable and highly-adaptable structuring of 3D conductor/insulator structures on various types of substrates including ones with low-temperature stability and flexible ones. With this process the classical vias of the multi-layer structure are replaced by a direct connection between the layers achieved by an absence of insulation material at designated areas providing a fast and efficient method for multilayer prototyping. For testing and demonstration a multilayer planar coil structure was fabricated with an overall thickness of 30 µm on the PET substrate. The electromagnetic properties of the structures were successfully tested and verified by comparing several experiments to finite element method simulations. The theoretical simulations show an excellent match with experimental measurements of several structures thus giving confidence in the reliability of the proposed process.

A screen printed pH sensor was developed using a PANI layer as a proton sensitive material for the in-situ measurements of matrix cross-linking. The sensor showed a linear response in a broad pH range (3–10) and had an evident cross-talk to Cl− ions. Preliminary in-situ measurements showed a substantial signal change during the cross-linking process.

A rapid advanced packaging concept, consisting of inkjet photopolymer printing and Ag nanoparticles printing, was investigated for the construction of a pressure sensor package. Acrylate-type 3D package housing with 7 through-holes was printed with a polyjet printer and the through-vias and connection pads were manufactured via Ag glue dispensing and inkjet printing of Ag nanoparticle ink. The flip-chip packaging concept was pursued for the electrical connection between the package and the pressure sensor dye.

Emerging from 2D printed electronics, 3D printed electronics promise a break-through in additive manufacturing and prototyping of electronics. However, transferring the know-how from 2D flexible electronics to 3D parts with complex structures (e.g. internal vias and external interconnects) might not be a straightforward approach. As an example, the variation of light intensity with respect to the distance and angle of incidence casts doubt on the efficiency of the intense pulsed laser (IPL) as a robust sintering method for metallic traces in 3D printed bulk structures, whereas IPL is currently by far the most prevailing sintering technique for 2D printed flexible electronics. Sintering of metallic traces in 3D printed parts can be executed either as a sequential layer-by-layer printing and processing step (LP) or as a bulk post-processing step (BP). In the current study, a survey on the most common sintering strategies for inkjet printed silver nanoparticles was conducted, while the compatibility to 3D printed structures was brought into the focal point. To discover the capabilities and limitations of six sintering methods (i.e. IPL, ohmic curing, thermal heating, laser, atmospheric plasma and microwave sintering) for 3D printed electronics, a comparative study utilizing the same materials and diagnostic methods was pursued. The results revealed that for 3D functional parts, some of the sintering techniques can be considered as complementary methods for each other, whereas a few showed readily the potential to be adapted in 3D printed electronics production.

An additive manufacturing concept, consisting of 3D photopolymer printing and Ag nanoparticle printing, was investigated for the construction of a microfluidic biosensor based on immobilized cytochrome P450 enzyme. An acylate-type microfluidic chamber composed of two parts, i.e. chamber-housing and chamber-lid was printed with a polyjet 3D printer. A 3-electrode sensor structure was inkjet-printed on the lid using a combination of Ag and graphene printing. The working electrode was covered with carbon nanotubes by drop-casting and immobilized with cytochrome P450 2D6 enzyme. The microfluidic sensor shows a significant response to a test xenobiotic, i.e. dextromethorphan; the cyclic voltammetrical measurements show a corresponding oxidation peak at 0.4 V with around 5 μM detection limit.

The increasing demand for miniaturization of electronic packages and assemblies necessitates tighter tolerances in dispensing interconnects and robotic control for placement. In fact, due to increasing requirements in regards to cycle time and accuracy of interconnects (i.e. surface mount adhesives), contactless dispensing is constantly gaining acceptance. In this study, inkjet printing of adhesives is proposed as a promising contactless methodology, in which a precise volume control of dispensed material is applicable. Exploiting the drop-on-demand (DOD) process of inkjet printing, the deposition of non-conductive adhesives (NCA) by means of inkjet printer equipped with an industrial inkjet print-head were investigated. Correspondingly, individual droplets of different kinds of NCA were jetted from small diameter vessels directly to a specified position on the substrate to create the bonding patterns for die-attachment. The resulting die-attach was subsequently characterized, in terms of uniformity, thickness and flatness.

A great deal of attention has been attracted to the additive manufacturing technique of 3D printing in rapid prototyping of electronic packages. This technique enables fast and reliable production of complex structures with arbitrary configurations and possesses several advantages over the conventional manufacturing methods, such as mechanical machining and laser cutting. In addition, 3D printed packages can be considered as a try-out for the assessment of customized design prior to mass production, which will significantly reduce the expensive machining costs and material waste. This study proposes an innovative approach to construct simple radio frequency identification (RFID) package by integrating a surface acoustic wave (SAW) transponder in a 3D printed housing. On that account, an acrylate-type plastic SAW transponder housing was 3D-printed, and the corresponding wireless antenna and contact pads were produced via ink-jet printing with a silver nanoparticle (NP) ink. The proper functionality of the silver tracks was obtained by sintering the printed NPs using a photonic curing device. A flip-chip configuration has been pursued for connecting the chip pads to the corresponding pads on the housing. The performance of the package has been tested with a wireless reading unit via antenna-bridge for SAW transponders.

A continuous-flow, coil-type photoelectrocatalytic microreactor for the degradation of caffeine was designed, assembled and characterized. Its main components are the photocatalytically active anode and the cathode coils, which are wrapped around a silica-glass rod and placed into a UV-transparent housing. The anode coil was prepared by anodic oxidation of the titanium coil, which leads to the formation of vertically aligned, titanium dioxide, nanotube arrays that exhibit a high photocatalytic activity and are rigidly attached to the titanium wire. The photocatalytic, electrocatalytic and photoelectrocatalytic activities of the assembled microreactor were measured systematically while changing the main parameters that affect the device's efficiency. The most significant change in the microreactor's design in terms of efficiency was to place the cathode coils on both sides of the anode coil, which resulted in the shortest time for complete degradation of the caffeine. When an applied anodic bias potential of 4 V was used in the most efficient microreactor design, 1 mL of the 40 mg/L caffeine was fully decomposed in 55 min. (C) 2016 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Self-ordered, vertically aligned, titanium oxide (TiO2) nanotubes were grown on an electropolished titanium foil by anodic oxidation in a viscous organic electrolyte. We chose two different anodization times to obtain nanotubes of approximately 9 and 17 pm in length. Some of the TiO2 nanotubes were post-treated with TiCl4 or hydrothermally with TiO2 P25. Their structure and morphology were investigated with field-emission scanning electron microscopy (FSEM) and transmission electron microscopy (TEM). To improve the sensitizing of the high-aspect-ratio nanotubes with dye we used a new approach in which the TiO2 arrays were immersed into the dye solution at elevated temperature in an autoclave. The current voltage characteristics of the assembled DSSCs gave an average energy-conversion efficiency of 5.7% for the untreated nanotubes. (C) 2016 Elsevier Ltd. All rights reserved.

A rapid advanced packaging concept, consisting of 3D photopolymer printing and Ag nanoparticle printing, was investigated for the construction of a simple radio frequency identification (RFID) package with integrated surface acoustic wave transponder (SAW). An acrylate-type SAW package housing was printed with a multi-jet 3D printer and the corresponding antenna for the wireless read-out was manufactured via inkjet printing of Ag nanoparticle ink. The corresponding Ag structure had a thickness of about 2μm with a sheet resistance of 250mΩsq−1 after the photonic sintering processing. The chip-on-board and flip-chip packaging concepts were pursued for connecting the antenna structure to the chip pads. The SAW package prototype in a flip-chip configuration showed a significant signal to noise ratio (SNR) of about 30dB via antenna-bridged radio frequency link at a moderate distance of 3cm.

The sensitivity of two commercial metal oxide (MOx) sensors to ethylene is tested at different relative humidities. One sensor (MiCS-5914) is based on tungsten oxide, the other (MQ-3) on tin oxide. Both sensors were found to be sensitive to ethylene concentrations down to 10 ppm. Both sensors have significant response times; however, the tungsten sensor is the faster one. Sensor models are developed that predict the concentration of ethylene given the sensor output and the relative humidity. The MQ-3 sensor model achieves an accuracy of ±9.2 ppm and the MiCS-5914 sensor model predicts concentration to ±7.0 ppm. Both sensors are more accurate for concentrations below 50 ppm, achieving ±6.7 ppm (MQ-3) and 5.7 ppm (MiCS-5914).

Two types of MOx sensor structures, SnO2 and WO3, of different thicknesses were synthesized on top of the interdigitated Au electrodes and used for the measurements of the ethylene gas. The SEM micrographs revealed inhomogeneities of the WO3 layer and the presence of cracks on the edges of Au electrodes which correlates with the lack of reproducibility of the WO3 sensors. Both sensor structures showed a significant sensitivity to ethylene gas: the sensitivities of both MOx-types were higher at higher temperatures which was more evident in the case of SnO2 structure. The SnO2 layer had approximately 5-times higher sensitivity than the WO3 sensor of the same thickness. The saturation (T10) and desaturation (T90) times were shorter for WO3 sensors at lower temperatures while SnO2 was saturated and desaturated faster at higher temperatures. Sensors with thinner active layer possessed higher sensitivities and shorter T10 and T90 times.

Photocatalytic phenol dissociation was studied in a microreactor, with a TiO 2 layer immobilized on the reactor inner walls. Experiments were conducted for various residence times, initial concentrations, pH values, and UV light irradiation intensities. The intermediates and products (catechol, hydroquinone, and resorcinol) were quantitatively investigated to determine the predominant reaction pathways for the investigated anatase catalyst. A three-dimensional mathematical model was used to simulate the heterogeneous photocatalysis reaction conditions with Langmuir–Hinshelwood mechanism, considering the adsorption/desorption thermodynamic equilibria, and for kinetic parameter estimation via regression analysis. The effectiveness factor, Thiele modulus, and the correction function were calculated to determine the pore diffusion effects. The value of pH had the dramatic effect of lowering the reaction rate due to the competitive adsorption of hydroxide ions and protons on the catalyst surface. A phenol conversion of 79.5% was achieved at the residence time of 7.22 min, but without total mineralization. © 2014 American Institute of Chemical Engineers AIChE J , 61: 572–581, 2015

A photocatalytic, TiO2-based microreactor is designed and fabricated on a metal-titanium foil. The microchannel is mechanically engraved in the substrate foil, and a double-layered TiO2 anatase film is immobilized on its inner walls with a two-step synthesis, which included anodization and a hydrothermal treatment. X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirm the presence of an approximately 10-μm-thick layer of titania nanotubes and anatase nanoparticles. The SEM and transmission electron microscopy (TEM) of the cross sections show a dense interface between the titanium substrate and the TiO2 nanotubes. An additional layer of TiO2-anatase nanoparticles on the top of the film provides a large, photocatalytic surface area. The metal-titanium substrate with a functionalized serpentine channel is sealed with UV-transparent Plexiglas, and four 0.8-mW UV LEDs combined with a power controller on a small printed-circuit board are fixed over the substrate. The photocatalytic activity and the kinetic properties for the degradation of caffeine are provided, and the longer-term stability of the TiO2 film is evaluated. The results show that after 6 months of use and 3600 working cycles the microreactor still exhibits 60% of its initial efficiency.