This work has been supported by the COMET K1 ASSIC Austrian Smart Systems Integration Research Center. The COMET-Competence Centers for Excellent Technologies-Program is supported by BMVIT, BMWFW, and the federal provinces of Carinthia and Styria.

CAUTION: Before using the considered inks and adhesives, please consult the relevant Material Safety Data Sheets (MSDS). The employed nanoparticle ink and adhesives may be toxic or carcinogenic, dependent on the filler. Please use all appropriate safety practices when performing inkjet printing or the preparation of samples and make sure to wear appropriate personal protective equipment (safety glasses, gloves, lab coat, full-length pants, closed-toe shoes).
NOTE: The protocol can be paused af...

<ol>
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A way to fabricate multilayer sensor structures on 3D-printed substrates and on foil is demonstrated. AM metal, as well as ceramic and acrylate type and foil substrates are shown to be suitable for multilayer inkjet printing, as the adhesion between the substrate and the different layers is sufficient, as well as the respective conductivity or insulation capability. This could be shown by printing layers of conductive structures on insulating material. Furthermore, the printing and curing processes for all layers was suc...

Additive manufacturing (AM) is standardized as a process where materials are joined to make objects from 3D model data. This is usually done layer upon layer and, thus, contrasts with subtractive manufacturing technologies, such as semiconductor fabrication. Synonyms include 3D-printing, additive fabrication, additive process, additive techniques, additive layer manufacturing, layer manufacturing, and freeform fabrication. These synonyms are reproduced from the standardization by the American Society of Testing and Materials (ASTM)1 to provide a unique definition. In the literature, 3D-printing is referred to as the process where thickness of the printed objects is in the range of centimeters to even meters2.
More common processes, such as stereolithography3, enable the printing of polymers, but the 3D-printing of metal is also already commercially available. The AM of metals is employed in manifold areas, such as for the automotive, aerospace4, and medical5 sectors. An advantage for aerospace structures is the possibility to print lighter devices through simple structural changes (e.g., by using a honeycomb design). Consequently, materials with, for instance, greater mechanical strength, that would otherwise add a significant amount of weight (e.g.,&#160;titanium instead of aluminum)6, can be employed.
While the 3D-printing of polymers is already well established, metal 3D-printing is still a vibrant research topic, and a variety of processes have been developed for the 3D-printing of metal structures. Basically, the available methods can be combined into four groups7,8, namely 1) using a laser or electron beam for cladding in a wire-fed process, 2) sintering systems using a laser or electron beam, 3) selectively melting powder using a laser or electron beam (powder bed fusion), and 4) a binder jetting process where, commonly, an inkjet print head moves over a powder substrate and dispenses binding agent.
Depending on the process, the respective manufactured samples will exhibit different surface and structural properties7. These different properties will have to be considered in further efforts to further functionalize the printed parts (e.g., by fabricating sensors on their surfaces).
In contrast to 3D-printing, the printing processes to achieve such a functionalization (e.g., screen and inkjet printing) cover only limited object heights from less than 100 nm9 up to a few micrometers and are, thus, often also referred to as 2.5D-printing. Alternatively, laser-based solutions for high-resolution patterning have also been proposed10,11. A comprehensive review of the printing processes, the thermally dependent melt temperature of nanoparticles, and the applications is given by Ko12.
Although screen printing is well established in the literature13,14, inkjet printing provides an improved upscaling ability, together with an increased resolution for the printing of smaller feature sizes. Besides that, it is a digital, noncontact printing method enabling the flexible deposition of functional materials on three-dimensional. Consequently, our work is focused on inkjet printing.
Inkjet printing technology has already been employed in the fabrication of metal (silver, gold, platinum, etc.) sensing electrodes. Application areas include temperature measurement15,16, pressure and strain sensing17,18,19, and biosensing20,21, as well as gas or vapor analysis22,23,24. The curing of such printed structures with limited height extension can be done using various techniques, based on thermal25, microwave26, electrical27, laser28, and photonic29 principles.
Photonic curing for inkjet-printed structures allows researchers to use high-energy, curable, conductive inks on substrates with a low-temperature resistance. Exploiting this circumstance, the combination of 2.5D- and 3D-printing processes can be employed to fabricate highly flexible prototypes in the area of smart packaging30,31,32 and smart sensing.
The conductivity of 3D-printed metal substrates is of interest to the aerospace sector, as well as for the medical sector. It does not just improve the mechanical stability of certain parts but is beneficial in near-field as well as capacitive sensing. A 3D-printed metal housing provides additional shielding/guarding of the sensor&#39;s front-end since it can be electrically connected.
The aim is to fabricate devices using AM technology. These devices should provide a sufficiently high resolution in the measurement they are employed for (often at micro- or nanoscale) and, at the same time, they should fulfill high standards regarding reliability and quality.
It has been shown that AM technology presents the user with enough flexibility to fabricate optimized designs33,34 which improve the overall measurement quality that can be achieved. Additionally, the combination of polymers and single-layer inkjet printing has been presented in previous research35,36,37,38.
In this work, available studies are extended, and a review about the physical properties of AM substrates, with a focus on metals,and their compatibility with multilayer inkjet printing and photonic curing is provided. An exemplary multilayer coil design is provided in Supplementary Figure 1. The results are used for providing strategies for the inkjet printing of multilayer sensor structures on AM metal substrates.

<table>
	<tbody>
		<tr>
			<td>PiXDRO LP 50</td>
			<td>Meyer Burger AG</td>
			<td></td>
			<td>Inkjet-Printer with dual-head assembly.</td>
		</tr>
		<tr>
			<td>SM-128 Spectra S-class</td>
			<td>Fujifilm Dimatix</td>
			<td></td>
			<td>Printheads with nozzle diameter of 50 &#181;m, 50 pL calibrated dropsize and 800 dpi maximum resolution.</td>
		</tr>
		<tr>
			<td>DMC-11610/DMC-11601</td>
			<td>Fujifilm Dimatix</td>
			<td></td>
			<td>Disposable printheads with nozzle diameter 21.5 &#181;m, 1 or 10 pL calibrated dropsize</td>
		</tr>
		<tr>
			<td>Sycris I50DM-119</td>
			<td>PV Nanocell</td>
			<td></td>
			<td>Conductive silver nanoparticle ink with 50 wt.% silver loading, with an average particle size of 120 nm, in triethylene glycol monomethyl ether.</td>
		</tr>
		<tr>
			<td>Solsys EMD6200</td>
			<td>SunChemical</td>
			<td></td>
			<td>Insulating, low-k dielectric ink which is a mixture of acrylate-type monomers. Viscosity is 7-9 cps.</td>
		</tr>
		<tr>
			<td>Dycotec DM-IN-7002-I</td>
			<td>Dycotec</td>
			<td></td>
			<td>UV curable insulator, Surface Tension: 37.4 mN/m</td>
		</tr>
		<tr>
			<td>Dycotec DM-IN-7003C-I</td>
			<td>Dycotec</td>
			<td></td>
			<td>UV curable insulator, Surface Tension: 29.7 mN/m</td>
		</tr>
		<tr>
			<td>Dycotec DM-IN-7003-I</td>
			<td>Dycotec</td>
			<td></td>
			<td>UV curable insulator, Surface Tension: 31.4 mN/m</td>
		</tr>
		<tr>
			<td>Dycotec DM-IN-7004-I</td>
			<td>Dycotec</td>
			<td></td>
			<td>UV curable insulator, Surface Tension: 27.9 mN/m</td>
		</tr>
		<tr>
			<td>Pulseforge 1200</td>
			<td>Novacentrix</td>
			<td></td>
			<td>Photonic curing/sintering equipment.</td>
		</tr>
		<tr>
			<td>DektatkXT</td>
			<td>Bruker</td>
			<td></td>
			<td>Stylus Profiler with stylus tip of 12.5 &#181;m diameter and constant force of 4 mg.</td>
		</tr>
		<tr>
			<td>C4S</td>
			<td>Cascade Microtech</td>
			<td></td>
			<td>Four-point-probe measurement head.</td>
		</tr>
		<tr>
			<td>2000</td>
			<td>Keithley</td>
			<td></td>
			<td>Multimeter to evaluate the measurements using the four-point-probe.</td>
		</tr>
		<tr>
			<td>Helios NanoLab600i</td>
			<td>FEI</td>
			<td></td>
			<td>Focused Ion Beam analysis station which provides high-energy gallium ion milling.</td>
		</tr>
		<tr>
			<td>SeeSystem</td>
			<td>Advex Instruments</td>
			<td></td>
			<td>Water contact angle measurement device.</td>
		</tr>
		<tr>
			<td>Projet 3500 HDMax</td>
			<td>3D Systems</td>
			<td></td>
			<td>Professional high-resolution polymer 3D-printer. See also (accessed Sep. 2018): https://www.3dsystems.com/sites/default/files/projet_3500_plastic_0115_usen_web.pdf</td>
		</tr>
		<tr>
			<td>Polytec PU 1000</td>
			<td>Polytec PT</td>
			<td></td>
			<td>Electrically conductive adhesive based on Polyurethane, available</td>
		</tr>
		<tr>
			<td>Microdispenser</td>
			<td>Musashi</td>
			<td></td>
			<td>Needle for microdispensing.</td>
		</tr>
		<tr>
			<td>Micro-assembly station</td>
			<td>Finetech</td>
			<td></td>
			<td>Equipment for assembly of, e.g., printed circuit boards (PCBs) and placing of chemicals (e.g. solder) and SMD parts.</td>
		</tr>
	</tbody>
</table>

hybrid printing for the fabrication of smart sensors

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.

From the SEM images shown in Figure 1, conclusions on the printability on the respective substrates can be drawn. The scale bars are different due to the different ranges of the surface roughness. In Figure 1a, the surface of the copper substrate is shown, which is by far the smoothest. Figure 1c, on the other hand, shows steel, a substrate which is not usable for inkjet printing due to the high poro...

Watch this Scientific Journal Video about Hybrid Printing for the Fabrication of Smart Sensors at JoVE.com

Hybrid Printing for the Fabrication of Smart Sensors

Here we present a protocol for the fabrication of inkjet-printed multilayer sensor structures on additively manufactured substrates and foil.

A method to combine additively manufactured substrates or foils and multilayer inkjet printing for the fabrication of sensor devices is presented. First, ...

We focus on the combination of 3D printed substrates and inkjet printing which is subject to vivid research. We believe that their combination can enable a complete and normal censor system concept in automated production lines in collaborative robotics. So the main advantage of this technique is its use of use.While it's still assures a high quality of the obtained measurements. Which are gathered with the tele adoption system prototypes. When combining 3D and inkjet printing for functionalization.It is important to consider the substrate properties as well as the ink properties for individual layers. Also, the curing dose depends on a combination of both. Fabricate the ceramic substrate by the lithography-based ceramic manufacturing technology.To fabricate interconnects on on non-conductive substrates, dispense the low temperature, curable conductive adhesive, with a time pressure micro-dispenser mounted on a micro-assembly station into the appropriate vias of the printed parts. Leave the fabricated interconnects to dry for ten minutes at twenty three degrees Celsius and with ambient pressure. After preparation of the inkjet printing system and inspection of the surface properties for print ability as described in the text protocol.Fix the substrate on the substrate table using adhesive tape and mark its position appropriately. Adjust the nozzle and printing parameters in the settings of the software interface by editing the properties of the print head in the printers software interface. Move the print head to the drop view position using the go to drop view position option in the printers software interface and observe the jetting of the ink.If necessary adjust the printing parameters to optimize the jetting. Choose the nozzle which ejects well defined and homogeneous drops of ink for printing. Enter the number of the chosen nozzle in the printers preferences.Perform the drop size tests to determine the size of one printed drop on the substrate to do so print a drop pattern using a known printer configuration. Determine the achieved drop size, using a calibrated microscope or the inbuilt camera system of the printer. Ensure that the subsequently used printing resolution is appropriate for the observed ink wetting to fabricate a homogeneous and closed surface.Print multiple structures with a layer of ink used for the first device layer onto a dummy substrate. Use the photonic curing process for the insulating ink on the metal substrate. Open the tray of the photonic curing equipment containing the substrate table.Move the sample to the substrate table of the photonic curing equipment and fix it accordingly. Adjust the height of the equipment substrate table using the table spindle to move the sample to the focus plane of the curing equipment. Close the tray, adjust the curing profile as recommended by the supplier for the printed material and the equipment software interface and press the start button.Adjust the nozzle and printing parameters as described in the text protocol and then perform printing. Repeat the printing of one layer of ink until the homogeneity of the print is satisfactory. Control the homogeneity of the printed layer, using a calibrated microscope.Or using the inbuilt camera system of the printer. Move the camera of the printer to the print position and observe the quality of the print given in the printer software interface. For silver ink on a ceramic substrate, use heat curing in an oven.As recommended with the ink. To cure printed dye-electric ink use the photonic curing equipment with 200 volts bank voltage and with one millisecond pulses, and repeat the pulses eight times at a frequency of one hertz. Perform profilometer measurements to determine the roughness and thickness of the printed layer.Put the sample on the substrate table of the profilometer. If not honed, hone the measurement head using the respective button in the software. Choose the resolution and area, which needs to be mapped.Place the measurement head at the starting position and start the measurement. Upon completion of the measurement, check the result for consistency, and save the data. After adjustment of the printer and curing parameters, for subsequent layers as described in the text protocol.Fix the sustrate on the substrate table at the previously marked position. Adjust the nozzle and printing parameters as before. Select the appropriate reference point to print the pattern, and make sure the printed patterns are well aligned with each other to ensure proper functionality of the device afterward.Load the respective SVG file with appropriate resolution and size. Perform printing. Repeat the peintin of one layer of ink until the homogeneity of the print is satisfactory.Control the homogeneity of the printed layer under a microscope. Here, the inbuilt camera system of the printer is used. Use photonic curing only for the curing of this layer.Use the parameters determined beforehand, for an insulating layer or a conductive layer on the insulator. After curing, control the electircal and structural properties of the printed layer. To determine if the conductivity range of the conductive layer is acceptable, use a multimitor.To determine the surface quality of the 3D printed substrates. Scanning electron microscopy analysis are done. The surface of the copper substrate is shown, which is by far the smoothest.Conversely, steel as a substrate that is not usable for ink jet printing, due to the high porosity and unstable contact angle. Also, shown are SEM images of the bronze substrate and the titanium sample surface. The conductive tracts on the aluminum based ceramic substrate have good surface homogeneity.As visualized here as the smoothness of the blue curves. Additionally, surfaces which loss their structural integrity can be identified by the large gradients in their height profiles. These measurement results are gathered using a demonstrator, which employs a capacitative sensing principal.Here, the smoothness of the curves illustrates the high achievable quality despite the structural deficiencies that might result from the printing processes. The most crucial steps are to assure sufficient homogeneity and to control the surface properties of the printed structures. These metrics are crucial enabling factors for subsequent steps.The combination of 3D printed substrates and inkjet printing as means for functionalization are of high important starts the development of future robotic devices and automated production. These techniques enable the fabrication of adaptable sensor systems to be used for retrofitting and in conformable systems. Which are considered the future of collaborative robotics.

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8.0K Views.  Alpen-Adria-Universität Klagenfurt. We focus on the combination of 3D printed substrates and inkjet printing which is subject to vivid research. We believe that their combination can enable a complete and normal censor system concept in automated production lines in collaborative robotics. So the main advantage of this technique is its use of use.While it's still assures a high quality of the obtained measurements. Which are gathered with the tele adoption system prototypes. When combining 3D and inkjet printing for func...