Name: Hybrid Printing for the Fabrication of Smart Sensors (Video) | JoVE Journal
Uploaded: 2019-01-31T13:00:00.000+00:00
Duration: 8 min 35 s
Description: Learn hybrid printing for fabricating multilayer sensors on 3D printed substrates using inkjet technology. This method enhances sensor functionality for automated production and collaborative robotics applications.

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5 minutes

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 after any step except steps 6.3 - 6.6 and steps 9.2 - 9.5.
1. Preparation of 3D-printed Substrates
<ol>
	<li>Prepare computer-aided design (CAD) drawings, ideally using the stereolithography .stl file format. 
	NOTE: The used designs are illustrated in Supplementary Figure 2 and Supplementary Figure 3.</li>
	<li>Choose the AM process based on the material properties required by the target application (see Table 1 for the respective process limitations). 
	NOTE: In this work, we used samples made of 3D-printed copper, as well as 3D-printed ceramics.</li>
	<li>Fabricate the copper substrate by 3D-printing with wax and lost wax casting39.</li>
	<li>Fabricate the ceramic substrate by lithography-based ceramic manufacturing (LCM) technology40&#160;(see Video 1).</li>
	<li>Fabricate the acrylate substrate using a high-resolution polymer 3D-printer37 and remove the supporting wax from the printed part.
	<ol>
		<li>Put the printed part inside an oven at 65 &#176;C for 1 h to melt the supporting wax.</li>
		<li>After removing the printed part from the oven, put it inside an ultrasonic oil bath at 65 &#176;C to remove the wax from holes, small openings, etc.</li>
	</ol>
	</li>
	<li>Clean the substrates using a wiper wetted with acetone, as possible surface impurities greatly affect the later inkjet print quality. 
	NOTE: The preparation of AM substrates can be done using different equipment and processes. Depending on the fabrication strategy, the surface and bulk properties may vary as well. It is, therefore, crucial to control these properties using the inspection techniques recommended later (see, for instance, section 4 of this protocol).</li>
</ol>
2. Fabrication of Interconnects
NOTE: The fabrication of interconnects differs depending on the type (conductive/nonconductive) of substrate.
<ol>
	<li>Fabricate interconnects on nonconductive (ceramic) substrates.
	<ol>
		<li>Dispense the low temperature curable conductive adhesive with a time-pressure microdispenser mounted on a microassembly station into the appropriate vias of the printed parts.</li>
		<li>Leave the fabricated interconnects to dry for 10 min at 23 &#176;C and with ambient pressure. 
		NOTE: For the ceramic substrate, the interconnects can also be fabricated using solder paste and high-temperature curing.</li>
	</ol>
	</li>
	<li>Fabricate interconnects on conductive substrates.
	<ol>
		<li>Dispense the insulating ink all over the vias&#8217; (holes/holes in the substrate) circumference via a time-pressure microdispenser.</li>
		<li>Perform the photonic curing using intense pulsed light as suggested by the ink supplier.
		<ol>
			<li>Open the tray of the photonic curing equipment containing the substrate table.</li>
			<li>Move the copper sample to the substrate table of the photonic curing equipment and fix it using the provided magnetic fixtures.</li>
			<li>Adjust the height of the equipment&#8217;s substrate table to move the sample to the focus plane of the curing equipment.</li>
			<li>Close the tray and adjust the curing profile as recommended by the material&#8217;s supplier for the printed material in the equipment&#8217;s software interface and press the start button.</li>
		</ol>
		</li>
		<li>Fill the via with low-temperature curing conductive paste (Table of Materials). 
		NOTE: In general, it is possible to use all forms of one-component, epoxy-based conductive adhesives which are temperature activated.</li>
		<li>Dry the fabricated interconnects for 10 min at 23 &#176;C.</li>
	</ol>
	</li>
</ol>
3. Preparation of the Inkjet Printing System
<ol>
	<li>Clean/purge the print head nozzles with the purge setting in the printer software, using the appropriate chemical for the respective ink: use isopropanol for insulating inks; use triethylene glycol monomethyl ether for the conductive ink. Purge the nozzles by pressing the purge button in the printer&#8217;s software interface until the solution ejected from the respective nozzles is clear. 
	NOTE: The amount of chemical necessary depends on the printer, nozzle, and chemical. In this experiment, approximately 2 mL was used.</li>
	<li>Fill the ink containers with approximately 1.5 mL of nanoparticles silver ink with 50 wt.% metal loading and an average particle size of 110 nm using a syringe, for instance, with a 3 mL barrel, and an 18 G Luer lock dispensing needle.</li>
	<li>Use one print head to jet the ink by pressing the Start head button in the printer&#8217;s software interface.</li>
	<li>Use the pre-adjusted jetting profile of the printer for the jetting of the conductive ink.
	<ol>
		<li>Move the print head to the dropview position using the Go to dropview position option in the printer software interface and observe the jetting of the ink.</li>
		<li>Change the parameters of the voltage profile that is preinstalled for the print head and the print head temperature in order to adjust the drop velocity, shape, and volume. Adjust the ink pressure to avoid any spilling of the ink and to reduce the formation of satellite droplets. 
		NOTE: For the printing system used in this protocol, the operational maximum jetting voltage was set to 40 V and a jetting profile of 1 &#181;s rise/fall time with 10 - 14 &#181;s hold time was used. The silver ink was jetted at 45 &#176;C. The optimum ink pressure is dependent on the ink level. The voltage in the voltage profile has to be increased or reduced depending on the state (e.g., temperature, viscosity) of the ink and the current temperature of the head, as well as the state of the used print head. To achieve proper jetting, we recommend changing the voltage upward in small steps of 1 V. If there is no improvement in the drop shape, reduce the voltage in small steps of 1 V. Follow this procedure until a stable dropping is achieved.</li>
	</ol>
	</li>
	<li>Adjust the printing parameters for the insulating ink in the same manner as done for the silver ink.
	<ol>
		<li>Use another print head to jet the low-k dielectric material, which is a mixture of acrylate-type monomers. 
		NOTE: Again, an operational jetting voltage of 40 V and a 1 &#181;s rise/fall time with 8 &#181;s hold time was used in this protocol. The dielectric ink could be jetted at 50 &#176;C. The optimum ink pressure is dependent on the actual ink level. Generally, the used parameters highly depend on the properties of the ink, as well as of the substrate or layer onto which it should be printed. During the fabrication process, the printing parameters might have to be adjusted dynamically. Please refer to the user manual of the printing system on how to properly adjust printer parameters.</li>
	</ol>
	</li>
</ol>
4. Inspection of the Surface Properties of the Respective Substrates for Printability and the Adjustment of Printer Parameters for the First Layer
<ol>
	<li>Perform profilometer measurements to determine the surface roughness.
	<ol>
		<li>Put the sample on the substrate table (stage) of the profilometer.</li>
		<li>If not homed, home the stage using the home button in the software interface.</li>
		<li>Choose the respective resolution and area which is mapped in the software interface.</li>
		<li>Place the measurement head at the starting position and start the measurement using the jog option and start button in the software interface.</li>
		<li>After the measurement is finished, check the result for consistency (e.g., are the shown heights plausible for the number of printed layers) and save the data.</li>
	</ol>
	</li>
	<li>Perform SEM inspections as per the user manual to analyze the surface quality.</li>
	<li>Perform contact angle measurements as described in the user manual of the SEM station to determine the wettability properties.</li>
	<li>Fix the substrate on the substrate table using adhesive tape and mark its position appropriately.</li>
	<li>Adjust the nozzle and printing parameters in the settings of the software interface by editing the properties of the print head in the printer&#8217;s software interface.
	<ol>
		<li>Again, move the print head to the dropview position using the Go to dropview position option in the printer&#8217;s software interface and observe the jetting of the ink. If necessary, adjust the printing parameters to optimize the jetting.</li>
		<li>Choose a nozzle which ejects well-defined and homogeneous drops of ink for printing.</li>
		<li>Enter the number of the chosen nozzle in the printer&#8217;s preferences.</li>
	</ol>
	</li>
	<li>Perform the drop size tests to determine the size of one printed drop on the respective substrate.
	<ol>
		<li>Print a drop pattern, using a known printer configuration.</li>
		<li>Determine the achieved drop size using a calibrated microscope or the inbuilt camera system of the printer.</li>
		<li>Ensure that the subsequently used printing resolution is appropriate for the observed ink wetting to fabricate a homogeneous and closed surface (e.g., choose a printing resolution of 900 - 1,000 dpi for a drop size of 40 - 50 &#181;m).</li>
	</ol>
	</li>
	<li>Perform an FIB analysis (Table of Materials), as per the manufacturer&#8217;s instruction, to ensure a sufficient bulk homogeneity for conductive substrates.</li>
</ol>
5. Curing Parameter Adjustments for the First Layer
<ol>
	<li>Print multiple structures, using a layer of the ink used for the first device layer, onto a dummy substrate (i.e., a sample of the same material which can later be disposed and is used for testing purposes only).</li>
	<li>Use thermal curing in an oven at 130 &#176;C for at least 30 min at ambient pressure for the printed conductive silver patterns on a ceramic substrate. 
	NOTE: Depending on the size of the sample, use a pod to hold the sample inside the oven.</li>
	<li>Use the photonic curing for the insulating ink on the metal substrate.
	<ol>
		<li>Open the tray of the photonic curing equipment containing the substrate table.</li>
		<li>Move the sample to the substrate table of the photonic curing equipment and fix it accordingly (using, for instance, provided magnetic fixtures).</li>
		<li>Adjust the height of the equipment&#8217;s substrate table, using the table spindle to move the sample to the focus plane of the curing equipment.</li>
		<li>Close the tray and adjust the curing profile as recommended by the supplier for the printed material in the equipment&#8217;s software interface and press the start button.</li>
	</ol>
	</li>
	<li>Control the homogeneity of the surface qualitatively using a microscope and quantitatively using a profilometer.
	<ol>
		<li>Put the sample on the substrate table (stage) of the profilometer.</li>
		<li>If not homed, home the stage using the respective button in the software.</li>
		<li>Choose the respective resolution and area which should be mapped.</li>
		<li>Place the measurement head at the starting position and start the measurement.</li>
		<li>After the measurement is finished, check the result for consistency and save the data.</li>
	</ol>
	</li>
	<li>Repeat photonic or thermal curing procedures using adopted curing parameters if necessary.
	<ol>
		<li>Increase the used photonic energy in small steps of, for instance, 5 V in the software interface of the photonic curing equipment if the achieved resistance is too high. Decrease the used energy if the sample shows signs of burning.</li>
	</ol>
	</li>
	<li>Adjust the equipment parameters for the curing of the first functional device layer so that a conductivity sufficient for the application at hand is reached, but yet no burning of the printed structure occurs.</li>
</ol>
6. Inkjet Printing and Curing of the First Device Layer
<ol>
	<li>Fix the substrate on the substrate table using adhesive tape and mark its position appropriately.</li>
	<li>As the first layer is conductive, for the ceramic and acrylate type substrate, use substrate table heating of 60 &#176;C. 
	NOTE: The temperature must not exceed a temperature which might affect the respective substrate (e.g., the acrylate tolerates only up to 65 &#176;C). This adjustment can be done in the printer settings.</li>
	<li>Adjust the nozzle and printing parameters in the settings of the software interface.
	<ol>
		<li>Move the print head to the dropview position and observe the jetting of the ink.</li>
		<li>Choose a nozzle which ejects well-defined and homogeneous drops of ink for printing.</li>
		<li>Enter the number of the chosen nozzle in the printer&#8217;s preferences.</li>
	</ol>
	</li>
	<li>Adjust the used resolution of the print head to deposit a homogeneous layer of ink according to the previously determined substrate properties: for low-wettability substrates, for instance, a large contact angle and small drop size increase the printing resolution. Lower the resolution for high-wettability substrates. 
	 
	NOTE: The adjustment of the printing parameters can be done in the printer settings.</li>
	<li>Select the appropriate reference point to print the pattern and store its coordinates.</li>
	<li>Load the respective scalable vector graphic (.svg) file and select an appropriate resolution and size, dependent on the desired pattern and the dimensions of the substrate in the printer software.</li>
	<li>Perform printing. Repeat the printing of one layer of ink until the homogeneity of the print is satisfying.</li>
	<li>Control the homogeneity of the printed layer using a calibrated microscope or using the inbuilt camera system of the printer.
	<ol>
		<li>Move the camera of the printer to the print position and observe the quality of the print given in the printer&#8217;s software interface.</li>
	</ol>
	</li>
	<li>Cure the first layer using the parameters determined in section 5 of this protocol.
	<ol>
		<li>For silver ink on a polymer substrate (acrylate, foil), use a 1 ms pulse at 250 V with a reduced amount of energy (525 mJ/cm2).</li>
		<li>For silver ink on a ceramic substrate, use heat curing in an oven as recommended with the ink (e.g., 130 &#176;C for 30 min).</li>
		<li>Cure the printed dielectric ink at 200 V with 1 ms pulses and repeat the pulses 8x at the frequency of 1 Hz. 
		NOTE: The spectra of the emitted light used in photonic curing is quite broad (ultra-violet&#8211;near-infrared [UV-NIR]). Still, the amount of UV light is sufficient to initiate the photopolymerization and cure the insulating layer.</li>
	</ol>
	</li>
</ol>
7. Inspection of the Surface Properties of the Respective Substrates for Printability and the Adjustment of Printer Parameters for Subsequent Layers
NOTE: Please refer to the user manuals of the measurement equipment to perform the profilometer measurements and microscopy inspections.
<ol>
	<li>Perform profilometer measurements to determine the roughness and thickness of the printed layer.
	<ol>
		<li>Put the sample on the substrate table of the profilometer.</li>
		<li>If not homed, home the stage using the respective button in the software.</li>
		<li>Choose the respective resolution and area which needs to be mapped.</li>
		<li>Place the measurement head at the starting position and start the measurement.</li>
		<li>After the measurement is finished, check the result for consistency and save the data.</li>
	</ol>
	</li>
	<li>Perform contact angle measurements to determine the wettability properties. 
	NOTE: Refer to the user manual of the measurement equipment at hand on how to properly perform contact angle measurements.</li>
	<li>Perform drop size tests to determine the size of one printed drop on the respective substrate.
	<ol>
		<li>Print a drop pattern using a known printer configuration.</li>
		<li>Determine the achieved drop size using a calibrated microscope or the printer&#8217;s inbuilt inspection system.</li>
	</ol>
	</li>
	<li>Adjust the used resolution of the print head to achieve a homogeneous layer of ink: for low-wettability substrates, for instance, a large contact angle and small drop size increase the printing resolution. Lower the resolution for high-wettability substrates.</li>
	<li>Control the electrical properties of the first layer: for a conductive first layer, use the four-point probe to determine the achieved conductivity.
	<ol>
		<li>Put the sample on the substrate table.</li>
		<li>Lower the measurement head onto the conductive track, making sure the probe has good contact with the printed structure, to be analyzed.</li>
	</ol>
	</li>
	<li>For an insulating first layer, make sure the surface homogenously covers the conductor below. Use a microscope for confirming. Verify the insulating properties using a multimeter.</li>
</ol>
8. Curing Parameter Adjustments for Subsequent Layers
<ol>
	<li>Print multiple structures, using a layer of the ink used for the next device layer, onto a dummy substrate with an equivalent previous layer.</li>
	<li>Use only photonic curing for all substrates.</li>
	<li>After curing, control the electrical and structural properties of the printed layer: to determine if the conductivity is sufficient, use a four-point probe measurement.</li>
	<li>Control the homogeneity of the surface qualitatively using a microscope and quantitatively using the profilometer.</li>
	<li>Repeat photonic curing procedures if necessary.</li>
	<li>Adjust the equipment parameters for the curing of the subsequent functional device layer.</li>
</ol>
9. Inkjet Printing and Curing of Subsequent Device Layers
<ol>
	<li>Fix the substrate on the substrate table appropriately at the previously marked position.</li>
	<li>Adjust the nozzle and printing parameters as determined from the previous step.</li>
	<li>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.</li>
	<li>Load the respective .svg file with appropriate resolution and size.</li>
	<li>Perform printing. Repeat the printing of one layer of ink until the homogeneity of the print is satisfying.</li>
	<li>Control the homogeneity of the printed layer under a microscope (here, the inbuilt camera system of the printer is used).</li>
	<li>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.</li>
	<li>After curing, control the electrical and structural properties of the printed layer: to determine if the conductivity range of the conductive layer is acceptable, use a multimeter.</li>
</ol>

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<li>Lesch, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Large+Scale+Inkjet-Printing+of+Carbon+Nanotubes+Electrodes+for+Antioxidant+Assays+in+Blood+Bags%5BTitle%5D)+AND+%22Journal+of+Electroanalytical+Chemistry%22%5BJournal%5D)">Large Scale Inkjet-Printing of Carbon Nanotubes Electrodes for Antioxidant Assays in Blood Bags.</a> Journal of Electroanalytical Chemistry. 717, 61-68 (2014).</li>
<li>Sarfraz, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+Printed+H2S+Sensor+with+Electro-Optical+Response%5BTitle%5D)+AND+%22Sensors+and+Actuators+B%3A+Chemical%22%5BJournal%5D)">A Printed H2S Sensor with Electro-Optical Response.</a> Sensors and Actuators B: Chemical. 191, 821-827 (2014).</li>
<li>Sarfraz, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Printed+Copper+Acetate+Based+H2S+Sensor+on+Paper+Substrate%5BTitle%5D)+AND+%22Sensors+and+Actuators+B%3A+Chemical%22%5BJournal%5D)">Printed Copper Acetate Based H2S Sensor on Paper Substrate.</a> Sensors and Actuators B: Chemical. 173, 868-873 (2012).</li>
<li>Huang, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+Novel+Paper-Based+Flexible+Ammonia+Gas+Sensor+via+Silver+and+SWNT-PABS+Inkjet+Printing%5BTitle%5D)+AND+%22SWNT-PABS+Inkjet+Printing.+Sensors+and+Actuators+B%3A+Chemical%22%5BJournal%5D)">A Novel Paper-Based Flexible Ammonia Gas Sensor via Silver and SWNT-PABS Inkjet Printing.</a> SWNT-PABS Inkjet Printing. Sensors and Actuators B: Chemical. 197, 308-313 (2014).</li>
<li>Kamyshny, A., Steinke, J., Magdassi, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Metal-based+inkjet+inks+for+printed+electronics%5BTitle%5D)+AND+%22Open+Applied+Physics+Journal%22%5BJournal%5D)">Metal-based inkjet inks for printed electronics.</a> Open Applied Physics Journal. 4, 19-36 (2011).</li>
<li>Perelaer, J., de Gans, B. J., Schubert, U. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Ink-jet+Printing+and+Microwave+Sintering+of+Conductive+Silver+Tracks%5BTitle%5D)+AND+%22Advanced+Materials%22%5BJournal%5D)">Ink-jet Printing and Microwave Sintering of Conductive Silver Tracks.</a> Advanced Materials. 18, 2101-2104 (2006).</li>
<li>Hummelgard, M., Zhang, R., Nilsson, H. -E., Olin, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Electrical+sintering+of+silver+nanoparticle+ink+studied+by+in+situ+TEM+probing%5BTitle%5D)+AND+%22PLoS+One%22%5BJournal%5D)">Electrical sintering of silver nanoparticle ink studied by in situ TEM probing.</a> PLoS One. 6, (2011).</li>
<li>Kumpulainen, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Low+temperature+nanoparticle+sintering+with+continuous+wave+and+pulse+lasers%5BTitle%5D)+AND+%22Optics+and+Laser+Technology%22%5BJournal%5D)">Low temperature nanoparticle sintering with continuous wave and pulse lasers.</a> Optics and Laser Technology. 43, 570-576 (2011).</li>
<li>Schröder, K., McCool, S., Furlan, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Broadcast+Photonic+Curing+of+Metallic+Nanoparticle+Films%5BTitle%5D)+AND+%22Technical+Proceedings+of+the+2006+NSTI+Nanotechnology+Conference+and+Trade+Show%22%5BJournal%5D)">Broadcast Photonic Curing of Metallic Nanoparticle Films.</a> Technical Proceedings of the 2006 NSTI Nanotechnology Conference and Trade Show. 3, 198-201 (2006).</li>
<li>Lopes, A. J., Lee, I. H., MacDonald, E., Quintana, R., Wicker, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Laser+Curing+of+Silver-Based+Conductive+Inks+for+In-Situ+3D+Structural+Electronics+Fabrication+in+Stereolithography%5BTitle%5D)+AND+%22Journal+Materials+Processing+Technology%22%5BJournal%5D)">Laser Curing of Silver-Based Conductive Inks for In-Situ 3D Structural Electronics Fabrication in Stereolithography.</a> Journal Materials Processing Technology. 214 (9), 1935-1945 (2014).</li>
<li>Faller, L. -M., Mitterer, T., Leitzke, J. P., Zangl, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Design+and+Evaluation+of+a+Fast%2C+High-Resolution+Sensor+Evaluation+Platform+Applied+to+MEMS+Position+Sensing%5BTitle%5D)+AND+%22IEEE+Transactions+on+Instrumentation+and+Measurement%22%5BJournal%5D)">Design and Evaluation of a Fast, High-Resolution Sensor Evaluation Platform Applied to MEMS Position Sensing.</a> IEEE Transactions on Instrumentation and Measurement. 67 (5), 1014-1027 (2018).</li>
<li>Faller, L. -M., Zangl, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Feasibility+Considerations+on+an+Inkjet-Printed+Capacitive+Position+Sensor+for+Electrostatically+Actuated+Resonant+MEMS-Mirror+Systems%5BTitle%5D)+AND+%22Journal+of+Microelectromechanical+Systems%22%5BJournal%5D)">Feasibility Considerations on an Inkjet-Printed Capacitive Position Sensor for Electrostatically Actuated Resonant MEMS-Mirror Systems.</a> Journal of Microelectromechanical Systems. 26 (3), 559-568 (2017).</li>
<li>Faller, L. -M., Zangl, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Robust+design+of+an+inkjet-printed+capacitive+sensor+for+position+tracking+of+a+MOEMS-mirror+in+a+Michelson+interferometer+setup%5BTitle%5D)+AND+%22Proceedings+of+SPIE+10246%2C+Smart+Sensors%2C+Actuators%2C+and+MEMS+VIII%22%5BJournal%5D)">Robust design of an inkjet-printed capacitive sensor for position tracking of a MOEMS-mirror in a Michelson interferometer setup.</a> Proceedings of SPIE 10246, Smart Sensors, Actuators, and MEMS VIII. , Barcelona, Spain. 1024611 (2017).</li>
<li>Faller, L. -M., Zangl, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Robust+design+of+a+3D-+and+inkjet-printed+capacitive+force%2Fpressure+sensor%5BTitle%5D)+AND+%222016+17th+International+Conference+on+Thermal%2C+Mechanical+and+Multi-Physics+Simulation+and+Experiments+in+Microelectronics+and+Microsystems+%28EuroSimE%29%22%5BJournal%5D)">Robust design of a 3D- and inkjet-printed capacitive force/pressure sensor.</a> 2016 17th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE). , IEEE. Montpellier, France. (2016).</li>
<li>Mühlberger, M., et al. Digital Printing on 3D Printed Surfaces. , Available from:
 <a target="_blank" href="http://www.addmanu.at/fileadmin/shares/addmanu/docs/PROFACTOR_mmuehl_digital_printing_on_3D_printed_surfaces.pdf">http://www.addmanu.at/fileadmin/shares/addmanu/docs/PROFACTOR_mmuehl_digital_printing_on_3D_printed_surfaces.pdf</a> (2016).</li>
<li>Wang, P. -C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+inkjet+printing+of+catalyst+Pd+ink+for+selective+metallization+apply+to+product+antenna+on+PC%2FABS+substrate%5BTitle%5D)+AND+%222013+8th+International+Microsystems%2C+Packaging%2C+Assembly+and+Circuits+Technology+Conference+%28IMPACT%29%22%5BJournal%5D)">The inkjet printing of catalyst Pd ink for selective metallization apply to product antenna on PC/ABS substrate.</a> 2013 8th International Microsystems, Packaging, Assembly and Circuits Technology Conference (IMPACT). , IEEE. Taipei, Taiwan. (2013).</li>
<li>Quintero, A. V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Printing+and+encapsulation+of+electrical+conductors+on+polylactic+acid+%28PLA%29+for+sensing+applications%5BTitle%5D)+AND+%222014+IEEE+27th+International+Conference+on+Micro+Electro+Mechanical+Systems+%28MEMS%29%22%5BJournal%5D)">Printing and encapsulation of electrical conductors on polylactic acid (PLA) for sensing applications.</a> 2014 IEEE 27th International Conference on Micro Electro Mechanical Systems (MEMS). , IEEE. San Francisco, CA. (2014).</li>
<li>Unnikrishnan, D., Kaddour, D., Tedjini, S., Bihar, E., Saadaoui, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((CPW-Fed+Inkjet+Printed+UWB+Antenna+on+ABS-PC+for+Integration+in+Molded+Interconnect+Devices+Technology%5BTitle%5D)+AND+%22IEEE+Antennas+and+Wireless+Propagation+Letters%22%5BJournal%5D)">CPW-Fed Inkjet Printed UWB Antenna on ABS-PC for Integration in Molded Interconnect Devices Technology.</a> IEEE Antennas and Wireless Propagation Letters. 14, 1125-1128 (2015).</li>
<li>i.materialise. Lost Wax Printing & Casting. , 
 <a target="_blank" href="https://i.materialise.com/en/3d-printing-technologies/lost-wax-printing-casting">https://i.materialise.com/en/3d-printing-technologies/lost-wax-printing-casting</a> (2018).</li>
<li>Lithoz. Lithoz' LCM-Technology. , 
 <a target="_blank" href="http://www.lithoz.com/en/additive-manufacturing/lcm-technology">http://www.lithoz.com/en/additive-manufacturing/lcm-technology</a> (2018).</li>
<li>Faller, L. -M., Krivec, M., Abram, A., Zangl, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((AM+Metal+Substrates+for+Inkjet-Printing+of+Smart+Devices%5BTitle%5D)+AND+%22Materials+Characterization%22%5BJournal%5D)">AM Metal Substrates for Inkjet-Printing of Smart Devices.</a> Materials Characterization. , (2018).</li>
<li>Hutchings, I. M., Martin, G. D. Introduction to Inkjet Printing for Manufacturing. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aHutchings%2C+IM+%22Inkjet+Technology+for+Digital+Fabrication%22">Inkjet Technology for Digital Fabrication</a>. Hutchings, I. M., Martin, G. D. , John Wiley & Sons Ltd. West Sussex, UK. 1-20 (2013).</li>
<li>Baek, M. I., Hong, M. Equalization of Jetting Performance. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aBaek%2C+MI+%22Inkjet-Based+Micromanufacturing%22">Inkjet-Based Micromanufacturing</a>. Korvink, J. G., Smith, P. J., Shin, D. -Y. , WILEY-VCH Verlag GmbH & Co. KG. Weinheim, Germany. 159-172 (2012).</li>
<li>Zhang, T. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=%22Methods+for+Fabricating+Printed+Electronics+with+High+Conductivity+and+High+Resolution%22">Methods for Fabricating Printed Electronics with High Conductivity and High Resolution</a>. , Electronic Thesis and Dissertation Repository. London, UK. (2014).</li>
<li>Suganuma, K. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aSuganuma%2C+K+%22Introduction+to+Printed+Electronics%22">Introduction to Printed Electronics</a>. , Springer Science & Business Media. New York, NY. (2014).</li>
<li>Baxter, L. K. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aBaxter%2C+LK+%22Capacitive+Sensors%3A+Design+and+Applications%22">Capacitive Sensors: Design and Applications</a>. , John Wiley & Sons. (1997).</li>
</ol>

The authors have nothing to disclose.

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 &amp;micro;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 &amp;micro;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 &amp;micro;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

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...

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, ...

hybrid-printing-for-the-fabrication-of-smart-sensors

Research

JoVE Journal

Engineering

Planar and three-dimensional printing of conductive metallic inks is described. Our approach provides new avenues for fabricating printed electronic, optoelectronic, and biomedical devices in unusual layouts at the microscale.

Planar and Three-Dimensional Printing of Conductive Inks

A bioprinter was used to create patterned hydrogels based on a sacrificial mold.  The poloxamer mold was backfilled with a second hydrogel and then eluted, leaving voids which were filled with a third hydrogel. This method uses fast elution and good printability of poloxamer to generate complex architectures from biopolymers.

Printing Thermoresponsive Reverse Molds for the Creation of Patterned Two-component Hydrogels for 3D Cell Culture

The study demonstrates the growth of iridium oxide-reduced graphene oxide (IrO2-RGO) nanohybrid thin films on irregular and rough screen-printed carbon substrate through a green electrochemical synthesis, and their implementation as a pH sensor with a patterned paper-fluidic platform.

Iridium Oxide-reduced Graphene Oxide Nanohybrid Thin Film Modified Screen-printed Electrodes as Disposable Electrochemical Paper Microfluidic pH Sensors

Here, we present a protocol to fabricate organic thin film solar cells using a mini-slot die coater and related in-line structure characterizations using synchrotron scattering techniques.

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

This paper investigates the suitability of inkjet printing for the manufacturing of dye-sensitized solar cells. A binder-free TiO2 nanoparticle ink was formulated and printed onto a FTO glass substrate. The printed layer was fabricated into a cell with an active area of 0.25 cm2 and an efficiency of 3.5%.

Digital Printing of Titanium Dioxide for Dye Sensitized Solar Cells

In this paper, we present a protocol to selectively deposit organic materials on textiles, which allows for the direct integration of organic electronic devices with wearables. The fabricated devices can be fully integrated in textiles, respecting their mechanical appearance and enabling sensing capabilities.

A Simple and Scalable Fabrication Method for Organic Electronic Devices on Textiles

This protocol describes a solution-based fabrication strategy for high-performance, flexible, transparent electrodes with fully-embedded, thick metal mesh. Flexible transparent electrodes fabricated by this process demonstrate among the highest reported performances, including ultra-low sheet resistance, high optical transmittance, mechanical stability under bending, strong substrate adhesion, surface smoothness, and environmental stability.

Scalable Solution-processed Fabrication Strategy for High-performance, Flexible, Transparent Electrodes with Embedded Metal Mesh

We present a detailed method to fabricate a deformable lateral NIPIN phototransistor array for curved image sensors. The phototransistor array with an open mesh form, which is composed of thin silicon islands and stretchable metal interconnectors, provides flexibility and stretchability. The parameter analyzer characterizes the electrical property of the fabricated phototransistor.

Fabrication of Flexible Image Sensor Based on Lateral NIPIN Phototransistors

Two recent technologies-tattoo and textiles-have demonstrated promising results in cutaneous sensing. Here, we present the fabrication and evaluation methods of tattoo and textile electrodes for cutaneous electrophysiological sensing. These electronic interfaces made of conductive polymers outperform the existing standards in terms of comfort and sensitivity.

Conformable Wearable Electrodes: From Fabrication to Electrophysiological Assessment

This paper provides a technique for manufacturing chip-based supercapacitors using an inkjet printer. Methodologies are described in detail to synthesize inks, adjust software parameters, and analyze the electrochemical results of the manufactured supercapacitor.

Elaborate Control of Inkjet Printer for Fabrication of Chip-based Supercapacitors

Flexible electrodes have a wide range of applications in soft robotics and wearable electronics. The present protocol demonstrates a new strategy to fabricate highly stretchable electrodes with high resolution via lithographically defined microfluidic channels, which paves the way for future high-performance soft pressure sensors.

Microfluidic Channel-Based Soft Electrodes and Their Application in Capacitive Pressure Sensing

Learn hybrid printing for fabricating multilayer sensors on 3D printed substrates using inkjet technology. This method enhances sensor functionality for automated production and collaborative robotics applications.

Hybrid Printing for the Fabrication of Smart Sensors

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